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832019 Indian STANDARDS 13920-1993 Code of Practice
This Indian Standard was adopted by the Bureau of Indian Standards after the draft finalized bythe Earthquake Engineering Sectional Committee had been approved by the Civil Engineering
Division CouncilIS 4326 1976 lsquoCode of practice for earthquake resistant design and construction of buildingsrsquowhile covering certain special features for the design and construction of earthquake resistantbuildings included some details for achieving ductility in reinforced concrete buildings With a view to keep abreast of the rapid developments and extensive research that has been carried out inthe field of earthquake resistant design of reinforced concrete structures the technical committeedecided to cover provisions for the earthquake resistant design and detailing of reinforced concretestructures separately
This code incorporates a number of important provisions hitherto not covered in IS 4326 1976The major thrust in the formulation of this standard is one of the following lines
a) As a result of the experience gained from the performance in recent earthquakes of reinforced concrete structures that were designed and detailed as per IS 4326 1976 manydeficiencies thus identified have been corrected in this code
b) Provisions on detailing of beams and columns have been revised with an aim of providingthem with adequate toughness and ductility so as to make them capable of undergoingextensive inelastic deformations and dissipating seismic energy in a stable manner
c) Specifications on a seismic design and detailing of reinforced concrete shear walls have beenincluded
The other significant changes incorporated in this code are as follows
a) Material specifications are indicated for lateral force resisting elements of frames
b) Geometric constraints are imposed on the cross section for flexural members Provisions onminimum and maximum reinforcement have been revised The requirements for detailing of longitudinal reinforcement in beams at joint faces splices and anchorage requirements aremade more explicit Provision are also included for calculation of design shear force and fordetailing of transverse reinforcement in beams
c) For members subjected to axial load and flexure the dimensional constraints have been
imposed on the cross section Provisions are included for detailing of lap splices and for thecalculation of design shear force A comprehensive set of requirements is included on theprovision of special confining reinforcement in those regions of a column that are expected toundergo cyclic inelastic deformations during a severe earthquake
d) Provisions have been included for estimating the shear strength and flexural strength of shear wall sections Provisions are also given for detailing of reinforcement in the wall webboundary elements coupling beams around openings at construction joints and for thedevelopment splicing and anchorage of reinforcement
Whilst the common methods of design and construction have been covered in this code specialsystems of design and construction of any plain or reinforced concrete structure not covered by thiscode may be permitted on production of satisfactory evidence regarding their adequacy for seismicperformance by analysis or tests or both
The Sectional Committee responsible for the preparation of this standard has taken into
consideration the view of manufacturers users engineers architects builders and technologistsand has related the standard to the practices followed in the country in this field Due weightagehas also been given to the need for international co-ordination among standards prevailing indifferent seismic regions of the world
In the formulation of this standard assistance has been derived from the following publications
i) ACI 318-89318R-89 Building code requirements for reinforced concrete and commentarypublished by American Concrete Institute
ii) ATC-11 Seismic resistance of reinforced concrete shear walls and frame joints Implicationsof recent research for design engineers published by Applied Technology Council USA
iii) CAN3-A23 3-M84 1984 Design of concrete structures for buildings Canadian Standards Association
iv) SEADC 1980 Recommended lateral force requirements and commentary published byStructural Engineers Association of California USA
The composition of the technical committees responsible for formulating this standard is given in Annex A
This edition 12 incorporates Amendment No 1 (November 1995) and Amendment No 2(March 2002) Side bar indicates modification of the text as the result of incorporation of theamendments
832019 Indian STANDARDS 13920-1993 Code of Practice
CONCRETE STRUCTURES SUBJECTED TOSEISMIC FORCES mdash CODE OF PRACTICE
1 SCOPE
11 This standard covers the requirements fordesigning and detailing of monolithic reinforcedconcrete buildings so as to give them adequatetoughness and ductility to resist severeearthquake shocks without collapse
111 Provisions of this code shall be adopted inall reinforced concrete structures which arelocated in seismic zone III IV or V
112 The provisions for reinforced concreteconstruction given herein apply specifically tomonolithic reinforced concrete constructionPrecast andor prestressed concrete membersmay be used only if they can provide the samelevel of ductility as that of a monolithicreinforced concrete construction during or afteran earthquake
2 REFERENCES
21 The Indian Standards listed below are
necessary adjunct to this standard
3 TERMINOLOGY
30 For the purpose of this standard thefollowing definitions shall apply
31 Boundary Elements
Portions along the edges of a shear wall thatare strengthened by longitudinal andtransverse reinforcement They may have thesame thickness as that of the wall web
32 Crosstie
Is a continuous bar having a 135deg hook with a
10-diameter extension (but not lt 75 mm) at
each end The hooks shall engage peripherallongitudinal bars
33 Curvature Ductility
Is the ratio of curvature at the ultimatestrength of the section to the curvature at firstyield of tension steel in the section
34 HoopIs a closed stirrup having a 135deg hook with a10-diameter extension (but not lt 75 mm) ateach end that is embedded in the confined coreof the section It may also be made of two piecesof reinforcement a U-stirrup with a 135deg hookand a 10-diameter extension (but not lt 75 mm)at each end embedded in the confined core anda crosstie
35 Lateral Force Resisting System
Is that part of the structural system whichresists the forces induced by earthquake
36 Shear Wall
A wall that is primarily designed to resistlateral forces in its own plane
37 Shell Concrete
Concrete that is not confined by transversereinforcement is also called concrete cover
38 Space Frame
A three dimensional structural system
composed of interconnected members withoutshear or bearing walls so as to function as acomplete self-contained unit with or withoutthe aid of horizontal diaphragms or floorbracing systems
381 Vertical Load Carrying Space Frame
A space frame designed to carry all verticalloads
382 Moment Resisting Space Frame
A vertical load carrying space frame in whichthe members and joints are capable of resisting
forces primarily by flexure
IS No Title
456 1978 Code of practice for plain andreinforced concrete ( thirdrevision)
1786 1985 Specification for high strengthdeformed steel bars and wiresfor concrete reinforcement( third revision )
For the purpose of this standard the followingletter symbols shall have the meaningindicated against each where other symbolsare used they are explained at the appropriate
place All dimensions are in mm loads inNewton and stresses in MPa (Nsq mm) unlessotherwise specified
5 GENERAL SPECIFICATION
51 The design and construction of reinforcedconcrete buildings shall be governed by theprovisions of IS 456 1978 except as modified
by the provisions of this code
52 For all buildings which are more than3 storeys in height the minimum grade of concrete shall be M20 ( f ck = 20 MPa )
53 Steel reinforcements of grade Fe 415 ( seeIS 1786 1985 ) or less only shall be used
However high strength deformed steel barsproduced by the thermo-mechanical treatmentprocess of grades Fe 500 and Fe 550 havingelongation more than 145 percent andconforming to other requirements of IS 1786 1985 may also be used for thereinforcement
Ag mdash gross cross sectional area of column wall
Ah mdash horizontal reinforcement areawithin spacing S v
Ak mdash area of concrete core of column
Asd mdash reinforcement along each diagonalof coupling beam
Ash mdash area of cross section of bar formingspiral or hoop
Ast mdash area of uniformly distributed vertical reinforcement
A v mdash vertical reinforcement at a joint
Cw mdash centre to centre distance betweenboundary elements
D mdash overall depth of beam
Dk mdash diameter of column core measuredto the outside of spiral or hoop
d mdash effective depth of member
dw mdash effective depth of wall section
Es mdash elastic modulus of steel
f ck mdash characteristic compressive strengthof concrete cube
f y mdash yield stress of steel
h mdash longer dimension of rectangularconfining hoop measured to itsouter face
hst mdash storey height
L AB mdash clear span of beam
lo mdash length of member over whichspecial confining reinforcement isto be provided
lw mdash horizontal length of wall
ls mdash clear span of coupling beam M u mdash factored design moment on entire
wall section
mdash hogging moment of resistance of beam at end A
mdash sagging moment of resistance of beam at end A
mdash hogging moment of resistance of beam at end B
mdash sagging moment of resistance of beam at end B
mdash moment of resistance of beam
framing into column from the left
M u lim
Ah
M u lim
As
M u lim
Bh
M u lim
Bs
M u lim
bL
mdash moment of resistance of beamframing into column from the right
M uv mdash flexural strength of wall web
Pu mdash factored axial load
S mdash pitch of spiral or spacing hoops S v mdash vertical spacing of horizontal
reinforcement in web
tw mdash thickness of wall web
mdash shear at end A of beam due to deadand live loads with a partial factorof safety of 12 on loads
mdash shear at end B of beam due to deadand live loads with a partial factorof safety of 12 on loads
V j mdash shear resistance at a joint
V u mdash factored shear force
V us mdash shear force to be resisted byreinforcement
mdash depth of neutral axis from extremecompression fibre
α mdash inclination of diagonalreinforcement in coupling beam
ρ mdash vertical reinforcement ratio
ρc mdash compression reinforcement ratio ina beam
ρmax mdash maximum tension reinforcementratio for a beam
ρmin mdash minimum tension reinforcementratio for a beam
τ c mdash shear strength of concrete
mdash maximum permissible shear stressin section
τ v mdash nominal shear stress
M u lim
bR
V D L+
a
V D L+
b
xu xu
τcmax
832019 Indian STANDARDS 13920-1993 Code of Practice
These requirements apply to frame membersresisting earthquake induced forces and
designed to resist flexure These members shallsatisfy the following requirements
611 The factored axial stress on the memberunder earthquake loading shall not exceed01 f ck
612 The member shall preferably have awidth-to-depth ratio of more than 03
613 The width of the member shall not be lessthan 200 mm
614 The depth D of the member shall
preferably be not more than 14 of the clearspan
62 Longitudinal Reinforcement
622 The maximum steel ratio on any face atany section shall not exceed ρmax = 0025
623 The positive steel at a joint face must beat least equal to half the negative steel at thatface
624 The steel provided at each of the top andbottom face of the member at any section alongits length shall be at least equal to one-fourth of the maximum negative moment steel providedat the face of either joint It may be clarifiedthat redistribution of moments permitted inIS 456 1978 (clause 361) will be used only for vertical load moments and not for lateral loadmoments
625 In an external joint both the top and thebottom bars of the beam shall be provided withanchorage length beyond the inner face of thecolumn equal to the development length intension plus 10 times the bar diameter minusthe allowance for 90 degree bend(s) ( seeFig 1 ) In an internal joint both face bars of the beam shall be taken continuously through
the column
626 The longitudinal bars shall be splicedonly if hoops are provided over the entire splicelength at a spacing not exceeding 150 mm ( seeFig 2 ) The lap length shall not be less thanthe bar development length in tension Lapsplices shall not be provided (a) within a joint(b) within a distance of 2d from joint face and(c) within a quarter lengh of the member whereflexural yielding may generally occur under theeffect of earthquake forces Not more than50 percent of the bars shall be spliced at onesection
627 Use of welded splices and mechanicalconnections may also be made as per 25252of IS 456 1978 However not more than half the reinforcement shall be spliced at a sectionwhere flexural yielding may take place Thelocation of splices shall be governed by 626
63 Web Reinforcement
631 Web reinforcement shall consist of vertical hoops A vertical hoop is a closedstirrup having a 135deg hook with a 10 diameter
extension (but not lt 75 mm) at each end that is
621 a) The top as well as bottomreinforcement shall consist of at leasttwo bars throughout the memberlength
b) The tension steel ratio on any face atany section shall not be less than
ρmin = 024 where f ck and f y
are in MPa
f ck f y frasl
FIG 1 ANCHORAGE OF BEAM B ARS IN AN
E XTERNAL JOINT
FIG 2 L AP SPLICE IN BEAM
832019 Indian STANDARDS 13920-1993 Code of Practice
embedded in the confined core ( see Fig 3a ) Incompelling circumstances it may also be madeup of two pieces of reinforcement a U-stirrupwith a 135deg hook and a 10 diameter extension(but not lt 75 mm) at each end embedded in the
confined core and a crosstie ( see Fig 3b ) Acrosstie is a bar having a 135deg hook with a 10diameter extension (but not lt 75 mm) at eachend The hooks shall engage peripherallongitudinal bars
632 The minimum diameter of the barforming a hoop shall be 6 mm However in
beams with clear span exceeding 5 m theminimum bar diameter shall be 8 mm
633 The shear force to be resisted by the vertical hoops shall be the maximum of
a) calculated factored shear force as peranalysis and
b) shear force due to formation of plastichinges at both ends of the beam plus thefactored gravity load on the span This isgiven by ( see Fig 4 )
where and are the sagging and hogging moments of resistance of
the beam section at ends A and B respectively These are to be calculated as per IS 456 1978
L AB is clear span of beam and are the shears at ends A and B respectively due to vertical loads with a partial safety factor of 12 on loads The design shear at end A shall be thelarger of the two values of V ua computed above Similarly the design shear at end B shall be the
larger of the two values of V ub computed above
i) for sway to right
and and
ii) for sway to left
and
FIG 3 BEAM WEB REINFORCEMENT
M u lim As
M u lim Ah
M u limBs
M u limBh
VD L+a V
D L+b
832019 Indian STANDARDS 13920-1993 Code of Practice
634 The contribution of bent up bars andinclined hoops to shear resistance of the sectionshall not be considered
635 The spacing of hoops over a length of 2d ateither end of a beam shall not exceed (a) d4and (b) 8 times the diameter of the smallestlongitudinal bar however it need not be lessthan 100 mm ( see Fig 5 ) The first hoop shallbe at a distance not exceeding 50 mm from the joint face Vertical hoops at the same spacing asabove shall also be provided over a lengthequal to 2d on either side of a section where
flexural yielding may occur under the effect of earthquake forces Elsewhere the beam shallhave vertical hoops at a spacing not exceedingd2
7 COLUMNS AND FRAME MEMBERSSUBJECTED TO BENDING AND AXIALLOAD
71 General
711 These requirements apply to framemembers which have a factored axial stress inexcess of 01 f ck under the effect of earthquakeforces
712 The minimum dimension of the membershall not be less than 200 mm However inframes which have beams with centre to centrespan exceeding 5 m or columns of unsupportedlength exceeding 4 m the shortest dimension of the column shall not be less than 300 mm
713 The ratio of the shortest cross sectionaldimension to the perpendicular dimension shallpreferably not be less than 04
72 Longitudinal Reinforcement
721 Lap splices shall be provided only in the
central half of the member length It should beproportioned as a tension splice Hoops shall beprovided over the entire splice length atspacing not exceeding 150 mm centre to centreNot more than 50 percent of the bars shall bespliced at one section
722 Any area of a column that extends morethan 100 mm beyond the confined core due toarchitectural requirements shall be detailed inthe following manner In case the contributionof this area to strength has been consideredthen it will have the minimum longitudinal andtransverse reinforcement as per this code
FIG 4 C ALCULATION OF DESIGN SHEAR FORCE FOR BEAM
832019 Indian STANDARDS 13920-1993 Code of Practice
However if this area has been treated asnon-structural the minimum reinforcementrequirements shall be governed byIS 456 1978 provisions minimum longitudinaland transverse reinforcement as perIS 456 1978 ( see Fig 6 )
73 Transverse Reinforcement
731 Transverse reinforcement for circularcolumns shall consist of spiral or circular hoopsIn rectangular columns rectangular hoops maybe used A rectangular hoop is a closed stirruphaving a 135deg hook with a 10 diameterextension (but not lt 75 mm) at each end that isembedded in the confined core ( see Fig 7A )
732 The parallel legs of rectangular hoop shallbe spaced not more than 300 mm centre tocentre If the length of any side of the hoopexceeds 300 mm a crosstie shall be provided(Fig 7B) Alternatively a pair of overlappinghoops may be provided within the columm ( seeFig 7C) The hooks shall engage peripheral
longitudinal bars733 The spacing of hoops shall not exceed half the least lateral dimension of the columnexcept where special confining reinforcement isprovided as per 74
734 The design shear force for columns shallbe the maximum of
a) calculated factored shear force as peranalysis and
b) a factored shear force given by
V u = 14
where and are moment of
resistance of opposite sign of beams framinginto the column from opposite faces ( seeFig 8 ) and hst is the storey height The beam
moment capacity is to be calculated as perIS 456 1978
74 Special Confining Reinforcement
This requirement shall be met with unless alarger amount of transverse reinforcement isrequired from shear strength considerations
FIG 5 BEAM REINFORCEMENT
FIG 6 REINFORCEMENT REQUIREMENT FOR COLUMN WITH MORE THAN 100 mm
PROJECTION BEYOND CORE
M bLu lim M
bRu lim+
hst
----------------------------------------------
M bLu lim M
bRu lim
832019 Indian STANDARDS 13920-1993 Code of Practice
741 Special confining reinforcement shall beprovided over a length lo from each joint facetowards midspan and on either side of anysection where flexural yielding may occurunder the effect of earthquake forces ( see
Fig 9 ) The length lsquolorsquo shall not be less than(a) larger lateral dimension of the member atthe section where yielding occurs (b) 16 of clear span of the member and (c) 450 mm
742 When a column terminates into a footingor mat special confining reinforcement shallextend at least 300 mm into the footing or mat( see Fig 10 )
743 When the calculated point of contra-flexure under the effect of gravity andearthquake loads is not within the middle half of the member clear height special confiningreinforcement shall be provided over the full
height of the column744 Columns supporting reactions fromdiscontinued stiff members such as walls shallbe provided with special confiningreinforcement over their full height ( seeFig 11 ) This reinforcement shall also beplaced above the discontinuity for at least thedevelopment length of the largest longitudinalbar in the column Where the column issupported on a wall this reinforcement shall beprovided over the full height of the column itshall also be provided below the discontinuityfor the same development length
745 Special confining reinforcement shall beprovided over the full height of a column whichhas significant variation in stiffness alongits height This variation in stiffness may result
FIG 8 C ALCULATION OF DESIGN SHEAR
FORCE FOR COLUMN
832019 Indian STANDARDS 13920-1993 Code of Practice
due to the presence of bracing a mezzaninefloor or a RCC wall on either side of the
column that extends only over a part of thecolumn height ( see Fig 12 )
746 The spacing of hoops used as specialconfining reinforcement shall not exceed 14 of minimum member dimension but need not beless than 75 mm nor more than 100 mm
747 The area of cross section Ash of the barforming circular hoops or spiral to be used asspecial confining reinforcement shall not beless than
where
Example Consider a column of diameter 300mm Let the grade of concrete be M20 and thatof steel Fe 415 for longitudinal and confiningreinforcement The spacing of circular hoops Sshall not exceed the smaller of (a) 14 of minimum member dimension = 14 times 300 =75 mm and (b) 100 mm Therefore S = 75 mm Assuming 40 mm clear cover to thelongitudinal reinforcement and circular hoopsof diameter 8 mm Dk = 300 ndash 2 times 40 + 2 times 8 =236 mm Thus the area of cross section of thebar forming circular hoop works out to be4728 mm2 This is less than the cross sectionalarea of 8 mm bar (5027 mm2) Thus circularhoops of diameter 8 mm at a spacing of 75 mmcentre to centre will be adequate
748 The area of cross section Ash of the barforming rectangular hoop to be used as specialconfining reinforcement shall not be less than
where
FIG 11 SPECIAL CONFINING REINFORCEMENT REQUIREMENT FOR COLUMNS UNDER DISCONTINUED W ALLS
Ash = area of the bar cross section
S = pitch of spiral or spacing of hoops
Dk = diameter of core measured to theoutside of the spiral or hoop
f ck = characteristic compressive strength of concrete cube
f y = yield stress of steel (of circular hoop orspiral)
Ag = gross area of the column cross sectionand
Ash 009 SDk
f ck
f y-------
Ag
Ak
------- 10ndash=
Ak = area of the concrete core =
h = longer dimension of the rectangularconfining hoop measured to its outer
π4--- D
2
k
Ash 018 Sh
f ck
f y-------
Ag
Ak
------- 10ndash=
832019 Indian STANDARDS 13920-1993 Code of Practice
NOTE The dimension lsquohrsquo of the hoop could be reducedby introducing crossties as shown in Fig 7B In thiscase Ak shall be measured as the overall core arearegardless of the hoop arrangement The hooks of crossties shall engage peripheral longitudinal bars
Example Consider a column of 650 mm times500 mm Let the grade of concrete be M20 andthat of steel Fe 415 for the longitudinal andconfining reinforcement Assuming clear coverof 40 mm to the longitudinal reinforcement andrectangular hoops of diameter 10 mm the sizeof the core is 590 mm times 440 mm As both thesedimensions are greater than 300 mm either a
pair of overlapping hoops or a single hoop withcrossties in both directions will have to beprovided Thus the dimension lsquohrsquo will be thelarger of (i) 5902 = 295 mm and (ii) 4402 =220 mm The spacing of hoops S shall notexceed the smaller of (a) 14 of minimum
member dimensions = 14 times 500 = 125 mm and(b) 100 mm Thus S = 100 mm The area of cross section of the bar forming rectangularhoop works out to be 6447 mm2 This is lessthan the area of cross section of 10 mm bar(7854 mm2) Thus 10 mm diameterrectangular hoops at 100 mm cc will beadequate Similar calculations indicate that asan alternative one could also provide 8 mmdiameter rectangular hoops at 70 mm cc
8 JOINTS OF FRAMES
81 The special confining reinforcement asrequired at the end of column shall be provided
FIG 12 COLUMNS WITH V ARYING STIFFNESS
face It shall not exceed 300 mm ( seeFig 7 ) and
Ak = area of confined concrete core in therectangular hoop measured to itsoutside dimensions
832019 Indian STANDARDS 13920-1993 Code of Practice
through the joint as well unless the joint isconfined as specified by 82
82 A joint which has beams framing into all vertical faces of it and where each beam widthis at least 34 of the column width may be
provided with half the special confiningreinforcement required at the end of thecolumn The spacing of hoops shall not exceed150 mm
9 SHEAR WALLS
91 General Requirements
911 The requirements of this section apply tothe shear walls which are part of the lateralforce resisting system of the structure
912 The thickness of any part of the wall shallpreferably not be less than 150 mm
913 The effective flange width to be used inthe design of flanged wall sections shall beassumed to extend beyond the face of the webfor a distance which shall be the smaller of (a)half the distance to an adjacent shear wall weband (b) 110 th of the total wall height
914 Shear walls shall be provided withreinforcement in the longitudinal andtransverse directions in the plane of the wallThe minimum reinforcement ratio shall be0002 5 of the gross area in each direction Thisreinforcement shall be distributed uniformlyacross the cross section of the wall
915 If the factored shear stress in the wallexceeds 025 or if the wall thicknessexceeds 200 mm reinforcement shall beprovided in two curtains each having barsrunning in the longitudinal and transversedirections in the plane of the wall
916 The diameter of the bars to be used in anypart of the wall shall not exceed 110th of thethickness of that part
917 The maximum spacing of reinforcementin either direction shall not exceed the smallerof lw 5 3tw and 450 mm where lw is thehorizontal length of the wall and tw is the
thickness of the wall web92 Shear Strength
921 The nominal shear stress τ v shall becalculated as
where
922 The design shear strength of concrete τcshall be calculated as per Table 13 of IS 456 1978
923 The nominal shear stress in the wall τ vshall not exceed τc max as per Table 14 of
IS 456 1978924 When τ v is less than τc shearreinforcement shall be provided in accordancewith 914 915 and 917
925 When τ v is greater than τc the area of horizontal shear reinforcement Ah to beprovided within a vertical spacing S v is givenby
where V us = ( V u ndash τc tw dw ) is the shear force
to be resisted by the horizontal reinforcementHowever the amount of horizontalreinforcement provided shall not be less thanthe minimum as per 914
926 The vertical reinforcement that isuniformly distributed in the wall shall not beless than the horizontal reinforcementcalculated as per 925
93 Flexural Strength
931 The moment of resistance M uv of thewall section may be calculated as for columnssubjected to combined bending and axial load
as per IS 456 1978 The moment of resistanceof slender rectangular shear wall section withuniformly distributed vertical reinforcement isgiven in Annex A
932 The cracked flexural strength of the wallsection should be greater than its uncrackedflexural strength
933 In walls that do not have boundaryelements vertical reieforcement shall beconcentrated at the ends of the wall Eachconcentration shall consist of a minimum of 4 bars of 12 mm diameter arranged in at least
2 layers94 Boundary Elements
Boundary elements are portions along the walledges that are strengthened by longitudinaland transverse reinforcement Though theymay have the same thickness as that of thewall web it is advantageous to provide themwith greater thickness
941 Where the extreme fibre compressivestress in the wall due to factored gravity loadsplus factored earthquake force exceeds 02 f ckboundaty elements shall be provided along the
vertical boundaries of walls The boundary
V u = factored shear force
tw = thickness of the web and
dw = effective depth of wall section Thismay by taken as 08 lw for rectangular
sections
f ck
V us
087 f y Ah dw
S v
------------------------------------=
832019 Indian STANDARDS 13920-1993 Code of Practice
elements may be discontinued where thecalculated compressive stress becomes lessthan 015 f ck The compressive stress shall becalculated using a linearly elastic model andgross section properties
942 A boundary element shall have adequateaxial load carrying capacity assuming shortcolumn action so as to enable it to carry anaxial compression equal to the sum of factoredgravity load on it and the additionalcompressive load induced by the seismic forceThe latter may be calculated as
where
943 If the gravity load adds to the strength of the wall its load factor shall be taken as 08
944 The percentage of vertical reinforcementin the boundary elements shall not be less than08 percent nor greater than 6 percent Inorder to avoid congestion the practical upper
limit would be 4 percent945 Boundary elements where required asper 941 shall be provided throughout theirheight with special confining reinforcement asper 74
946 Boundary elements need not be providedif the entire wall section is provided withspecial confining reinforcement as per 74
95 Coupled Shear Walls
951 Coupled shear walls shall be connected byductile coupling beams If the earthquakeinduced shear stress in the coupling beam
exceeds
where ls is the clear span of the coupling beamand D is its overall depth the entireearthquake induced shear and flexure shallpreferably be resisted by diagonalreinforcement
952 The area of reinforcement to be providedalong each diagonal in a diagonally reinforcedcoupling beam shall be
where V u is the factored shear force and α isthe angle made by the diagonal reinforcementwith the horizontal At least 4 bars of 8 mmdiameter shall be provided along each diagonalThe reinforcement along each diagonal shall be
enclosed by special confining reinforcement asper 74 The pitch of spiral or spacing of tiesshall not exceed 100 mm
953 The diagonal or horizontal bars of acoupling beam shall be anchored in theadjacent walls with an anchorage length of 15times the development length in tension
96 Openings in Walls
961 The shear strength of a wall withopenings should be checked along criticalplanes that pass through openings
962 Reinforcement shall be provided along the
edges of openings in walls The area of the vertical and horizontal bars should be such asto equal that of the respective interrupted barsThe vertical bars should extend for the fullstorey height The horizontal bars should beprovided with development length in tensionbeyond the sides of the opening
97 Discontinuous Walls
Columns supporting discontinuous walls shallbe provided with special confiningreinforcement as per 744
98 Construction Joints
The vertical reinforcement ratio across ahorizontal construction joint shall not be lessthan
where τ v is the factored shear stress at the joint Pu is the factored axial force (positive forcompression) and Ag is the gross crosssectional area of the joint
99 Development Splice and AnchorageRequirement
991 Horizontal reinforcement shall beanchored near the edges of the wall or in theconfined core of the boundary elements
992 Splicing of vertical flexural reinforcementshould be avoided as far as possible in regionswhere yielding may take place This zone of flexural yielding may be considered to extendfor a distance of lw above the base of the wall orone sixth of the wall height whichever is moreHowever this distance need not be greaterthan 2 lw Not more than one third of this vertical reinforcement shall be spliced at such asection Splices in adjacent bars should be
staggered by a minimum of 600 mm
M u = factored design moment on the entirewall section
M uv = moment of resistance provided bydistributed vertical reinforcementacross the wall section and
Cw = center to center distance between theboundary elements along the two vertical edges of the wall
M u M uvndash
Cw
--------------------------
832019 Indian STANDARDS 13920-1993 Code of Practice
993 Lateral ties shall be provided aroundlapped spliced bars that are larger than 16 mmin diameter The diameter of the tie shall not beless than one fourth that of the spliced bar norless than 6 mm The spacing of ties shall not
exceed 150 mm center to center
994 Welded splices and mechanicalconnections shall confirm to 25252 of IS 456 1978 However not more than half thereinforcement shall be spliced at a sectionwhere flexural yielding may take place
ANNEX A
( Clause 931 )
MOMENT OF RESISTANCE OF RECTANGULAR SHEAR WALL SECTION
A-1 The moment of resistance of a slender rectangular shear wall section with uniformlydistributed vertical reinforcement may be estimated as follows
These equations were derived assuming a rectangular wall section of depth lw and thickness twthat is subjected to combined uni-axial bending and axial compression The vertical reinforcementis represented by an equivalent steel plate along the length of the section The stress-strain curveassumed for concrete is as per IS 456 1978 whereas that for steel is assumed to be bi-linear Twoequations are given for calculating the flexural strength of the section Their use depends on
whether the section fails in flexural tension or in flexural compression
(a) For
where
ρ = vertical reinforcement ratio = Ast ( tw lw )
Ast = area of uniformly distributed vertical reinforcement
β = 087 f y (0003 5 Es)
Es = elastic modulus of steel and
Pu = axial compression on wall
(b) For
where
The value of xu lw to be used in this equation should be calculated from the quadratic equation
where
xu lwlt xu lw
xu lw lt xu lwlt 10
832019 Indian STANDARDS 13920-1993 Code of Practice
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Copyright
BIS has the copyright of all its publications No part of these publications may be reproduced in any formwithout the prior permission in writing of BIS This does not preclude the free use in the course of implementing the standard of necessary details such as symbols and sizes type or grade designationsEnquiries relating to copyright be addressed to the Director (Publications) BIS
Review of Indian Standards
Amendments are issued to standards as the need arises on the basis of comments Standards are alsoreviewed periodically a standard along with amendments is reaffirmed when such review indicates that nochanges are needed if the review indicates that changes are needed it is taken up for revision Users of Indian Standards should ascertain that they are in possession of the latest amendments or edition byreferring to the latest issue of lsquoBIS Cataloguersquo and lsquoStandards Monthly Additionsrsquo
This Indian Standard has been developed from Doc No CED 39 (5263)
Amendments Issued Since Publication
Amend No Date of Issue
Amd No 1 November 1995
Amd No 2 March 2002
BUREAU OF INDIAN STANDARDS
Headquarters
Manak Bhavan 9 Bahadur Shah Zafar Marg New Delhi 110002Telephones 323 01 31 323 33 75 323 94 02
Telegrams Manaksanstha(Common to all offices)
Regional Offices Telephone
Central Manak Bhavan 9 Bahadur Shah Zafar MargNEW DELHI 110002
323 76 17323 38 41
Eastern 114 C I T Scheme VII M V I P Road KankurgachiKOLKATA 700054
This Indian Standard was adopted by the Bureau of Indian Standards after the draft finalized bythe Earthquake Engineering Sectional Committee had been approved by the Civil Engineering
Division CouncilIS 4326 1976 lsquoCode of practice for earthquake resistant design and construction of buildingsrsquowhile covering certain special features for the design and construction of earthquake resistantbuildings included some details for achieving ductility in reinforced concrete buildings With a view to keep abreast of the rapid developments and extensive research that has been carried out inthe field of earthquake resistant design of reinforced concrete structures the technical committeedecided to cover provisions for the earthquake resistant design and detailing of reinforced concretestructures separately
This code incorporates a number of important provisions hitherto not covered in IS 4326 1976The major thrust in the formulation of this standard is one of the following lines
a) As a result of the experience gained from the performance in recent earthquakes of reinforced concrete structures that were designed and detailed as per IS 4326 1976 manydeficiencies thus identified have been corrected in this code
b) Provisions on detailing of beams and columns have been revised with an aim of providingthem with adequate toughness and ductility so as to make them capable of undergoingextensive inelastic deformations and dissipating seismic energy in a stable manner
c) Specifications on a seismic design and detailing of reinforced concrete shear walls have beenincluded
The other significant changes incorporated in this code are as follows
a) Material specifications are indicated for lateral force resisting elements of frames
b) Geometric constraints are imposed on the cross section for flexural members Provisions onminimum and maximum reinforcement have been revised The requirements for detailing of longitudinal reinforcement in beams at joint faces splices and anchorage requirements aremade more explicit Provision are also included for calculation of design shear force and fordetailing of transverse reinforcement in beams
c) For members subjected to axial load and flexure the dimensional constraints have been
imposed on the cross section Provisions are included for detailing of lap splices and for thecalculation of design shear force A comprehensive set of requirements is included on theprovision of special confining reinforcement in those regions of a column that are expected toundergo cyclic inelastic deformations during a severe earthquake
d) Provisions have been included for estimating the shear strength and flexural strength of shear wall sections Provisions are also given for detailing of reinforcement in the wall webboundary elements coupling beams around openings at construction joints and for thedevelopment splicing and anchorage of reinforcement
Whilst the common methods of design and construction have been covered in this code specialsystems of design and construction of any plain or reinforced concrete structure not covered by thiscode may be permitted on production of satisfactory evidence regarding their adequacy for seismicperformance by analysis or tests or both
The Sectional Committee responsible for the preparation of this standard has taken into
consideration the view of manufacturers users engineers architects builders and technologistsand has related the standard to the practices followed in the country in this field Due weightagehas also been given to the need for international co-ordination among standards prevailing indifferent seismic regions of the world
In the formulation of this standard assistance has been derived from the following publications
i) ACI 318-89318R-89 Building code requirements for reinforced concrete and commentarypublished by American Concrete Institute
ii) ATC-11 Seismic resistance of reinforced concrete shear walls and frame joints Implicationsof recent research for design engineers published by Applied Technology Council USA
iii) CAN3-A23 3-M84 1984 Design of concrete structures for buildings Canadian Standards Association
iv) SEADC 1980 Recommended lateral force requirements and commentary published byStructural Engineers Association of California USA
The composition of the technical committees responsible for formulating this standard is given in Annex A
This edition 12 incorporates Amendment No 1 (November 1995) and Amendment No 2(March 2002) Side bar indicates modification of the text as the result of incorporation of theamendments
832019 Indian STANDARDS 13920-1993 Code of Practice
CONCRETE STRUCTURES SUBJECTED TOSEISMIC FORCES mdash CODE OF PRACTICE
1 SCOPE
11 This standard covers the requirements fordesigning and detailing of monolithic reinforcedconcrete buildings so as to give them adequatetoughness and ductility to resist severeearthquake shocks without collapse
111 Provisions of this code shall be adopted inall reinforced concrete structures which arelocated in seismic zone III IV or V
112 The provisions for reinforced concreteconstruction given herein apply specifically tomonolithic reinforced concrete constructionPrecast andor prestressed concrete membersmay be used only if they can provide the samelevel of ductility as that of a monolithicreinforced concrete construction during or afteran earthquake
2 REFERENCES
21 The Indian Standards listed below are
necessary adjunct to this standard
3 TERMINOLOGY
30 For the purpose of this standard thefollowing definitions shall apply
31 Boundary Elements
Portions along the edges of a shear wall thatare strengthened by longitudinal andtransverse reinforcement They may have thesame thickness as that of the wall web
32 Crosstie
Is a continuous bar having a 135deg hook with a
10-diameter extension (but not lt 75 mm) at
each end The hooks shall engage peripherallongitudinal bars
33 Curvature Ductility
Is the ratio of curvature at the ultimatestrength of the section to the curvature at firstyield of tension steel in the section
34 HoopIs a closed stirrup having a 135deg hook with a10-diameter extension (but not lt 75 mm) ateach end that is embedded in the confined coreof the section It may also be made of two piecesof reinforcement a U-stirrup with a 135deg hookand a 10-diameter extension (but not lt 75 mm)at each end embedded in the confined core anda crosstie
35 Lateral Force Resisting System
Is that part of the structural system whichresists the forces induced by earthquake
36 Shear Wall
A wall that is primarily designed to resistlateral forces in its own plane
37 Shell Concrete
Concrete that is not confined by transversereinforcement is also called concrete cover
38 Space Frame
A three dimensional structural system
composed of interconnected members withoutshear or bearing walls so as to function as acomplete self-contained unit with or withoutthe aid of horizontal diaphragms or floorbracing systems
381 Vertical Load Carrying Space Frame
A space frame designed to carry all verticalloads
382 Moment Resisting Space Frame
A vertical load carrying space frame in whichthe members and joints are capable of resisting
forces primarily by flexure
IS No Title
456 1978 Code of practice for plain andreinforced concrete ( thirdrevision)
1786 1985 Specification for high strengthdeformed steel bars and wiresfor concrete reinforcement( third revision )
For the purpose of this standard the followingletter symbols shall have the meaningindicated against each where other symbolsare used they are explained at the appropriate
place All dimensions are in mm loads inNewton and stresses in MPa (Nsq mm) unlessotherwise specified
5 GENERAL SPECIFICATION
51 The design and construction of reinforcedconcrete buildings shall be governed by theprovisions of IS 456 1978 except as modified
by the provisions of this code
52 For all buildings which are more than3 storeys in height the minimum grade of concrete shall be M20 ( f ck = 20 MPa )
53 Steel reinforcements of grade Fe 415 ( seeIS 1786 1985 ) or less only shall be used
However high strength deformed steel barsproduced by the thermo-mechanical treatmentprocess of grades Fe 500 and Fe 550 havingelongation more than 145 percent andconforming to other requirements of IS 1786 1985 may also be used for thereinforcement
Ag mdash gross cross sectional area of column wall
Ah mdash horizontal reinforcement areawithin spacing S v
Ak mdash area of concrete core of column
Asd mdash reinforcement along each diagonalof coupling beam
Ash mdash area of cross section of bar formingspiral or hoop
Ast mdash area of uniformly distributed vertical reinforcement
A v mdash vertical reinforcement at a joint
Cw mdash centre to centre distance betweenboundary elements
D mdash overall depth of beam
Dk mdash diameter of column core measuredto the outside of spiral or hoop
d mdash effective depth of member
dw mdash effective depth of wall section
Es mdash elastic modulus of steel
f ck mdash characteristic compressive strengthof concrete cube
f y mdash yield stress of steel
h mdash longer dimension of rectangularconfining hoop measured to itsouter face
hst mdash storey height
L AB mdash clear span of beam
lo mdash length of member over whichspecial confining reinforcement isto be provided
lw mdash horizontal length of wall
ls mdash clear span of coupling beam M u mdash factored design moment on entire
wall section
mdash hogging moment of resistance of beam at end A
mdash sagging moment of resistance of beam at end A
mdash hogging moment of resistance of beam at end B
mdash sagging moment of resistance of beam at end B
mdash moment of resistance of beam
framing into column from the left
M u lim
Ah
M u lim
As
M u lim
Bh
M u lim
Bs
M u lim
bL
mdash moment of resistance of beamframing into column from the right
M uv mdash flexural strength of wall web
Pu mdash factored axial load
S mdash pitch of spiral or spacing hoops S v mdash vertical spacing of horizontal
reinforcement in web
tw mdash thickness of wall web
mdash shear at end A of beam due to deadand live loads with a partial factorof safety of 12 on loads
mdash shear at end B of beam due to deadand live loads with a partial factorof safety of 12 on loads
V j mdash shear resistance at a joint
V u mdash factored shear force
V us mdash shear force to be resisted byreinforcement
mdash depth of neutral axis from extremecompression fibre
α mdash inclination of diagonalreinforcement in coupling beam
ρ mdash vertical reinforcement ratio
ρc mdash compression reinforcement ratio ina beam
ρmax mdash maximum tension reinforcementratio for a beam
ρmin mdash minimum tension reinforcementratio for a beam
τ c mdash shear strength of concrete
mdash maximum permissible shear stressin section
τ v mdash nominal shear stress
M u lim
bR
V D L+
a
V D L+
b
xu xu
τcmax
832019 Indian STANDARDS 13920-1993 Code of Practice
These requirements apply to frame membersresisting earthquake induced forces and
designed to resist flexure These members shallsatisfy the following requirements
611 The factored axial stress on the memberunder earthquake loading shall not exceed01 f ck
612 The member shall preferably have awidth-to-depth ratio of more than 03
613 The width of the member shall not be lessthan 200 mm
614 The depth D of the member shall
preferably be not more than 14 of the clearspan
62 Longitudinal Reinforcement
622 The maximum steel ratio on any face atany section shall not exceed ρmax = 0025
623 The positive steel at a joint face must beat least equal to half the negative steel at thatface
624 The steel provided at each of the top andbottom face of the member at any section alongits length shall be at least equal to one-fourth of the maximum negative moment steel providedat the face of either joint It may be clarifiedthat redistribution of moments permitted inIS 456 1978 (clause 361) will be used only for vertical load moments and not for lateral loadmoments
625 In an external joint both the top and thebottom bars of the beam shall be provided withanchorage length beyond the inner face of thecolumn equal to the development length intension plus 10 times the bar diameter minusthe allowance for 90 degree bend(s) ( seeFig 1 ) In an internal joint both face bars of the beam shall be taken continuously through
the column
626 The longitudinal bars shall be splicedonly if hoops are provided over the entire splicelength at a spacing not exceeding 150 mm ( seeFig 2 ) The lap length shall not be less thanthe bar development length in tension Lapsplices shall not be provided (a) within a joint(b) within a distance of 2d from joint face and(c) within a quarter lengh of the member whereflexural yielding may generally occur under theeffect of earthquake forces Not more than50 percent of the bars shall be spliced at onesection
627 Use of welded splices and mechanicalconnections may also be made as per 25252of IS 456 1978 However not more than half the reinforcement shall be spliced at a sectionwhere flexural yielding may take place Thelocation of splices shall be governed by 626
63 Web Reinforcement
631 Web reinforcement shall consist of vertical hoops A vertical hoop is a closedstirrup having a 135deg hook with a 10 diameter
extension (but not lt 75 mm) at each end that is
621 a) The top as well as bottomreinforcement shall consist of at leasttwo bars throughout the memberlength
b) The tension steel ratio on any face atany section shall not be less than
ρmin = 024 where f ck and f y
are in MPa
f ck f y frasl
FIG 1 ANCHORAGE OF BEAM B ARS IN AN
E XTERNAL JOINT
FIG 2 L AP SPLICE IN BEAM
832019 Indian STANDARDS 13920-1993 Code of Practice
embedded in the confined core ( see Fig 3a ) Incompelling circumstances it may also be madeup of two pieces of reinforcement a U-stirrupwith a 135deg hook and a 10 diameter extension(but not lt 75 mm) at each end embedded in the
confined core and a crosstie ( see Fig 3b ) Acrosstie is a bar having a 135deg hook with a 10diameter extension (but not lt 75 mm) at eachend The hooks shall engage peripherallongitudinal bars
632 The minimum diameter of the barforming a hoop shall be 6 mm However in
beams with clear span exceeding 5 m theminimum bar diameter shall be 8 mm
633 The shear force to be resisted by the vertical hoops shall be the maximum of
a) calculated factored shear force as peranalysis and
b) shear force due to formation of plastichinges at both ends of the beam plus thefactored gravity load on the span This isgiven by ( see Fig 4 )
where and are the sagging and hogging moments of resistance of
the beam section at ends A and B respectively These are to be calculated as per IS 456 1978
L AB is clear span of beam and are the shears at ends A and B respectively due to vertical loads with a partial safety factor of 12 on loads The design shear at end A shall be thelarger of the two values of V ua computed above Similarly the design shear at end B shall be the
larger of the two values of V ub computed above
i) for sway to right
and and
ii) for sway to left
and
FIG 3 BEAM WEB REINFORCEMENT
M u lim As
M u lim Ah
M u limBs
M u limBh
VD L+a V
D L+b
832019 Indian STANDARDS 13920-1993 Code of Practice
634 The contribution of bent up bars andinclined hoops to shear resistance of the sectionshall not be considered
635 The spacing of hoops over a length of 2d ateither end of a beam shall not exceed (a) d4and (b) 8 times the diameter of the smallestlongitudinal bar however it need not be lessthan 100 mm ( see Fig 5 ) The first hoop shallbe at a distance not exceeding 50 mm from the joint face Vertical hoops at the same spacing asabove shall also be provided over a lengthequal to 2d on either side of a section where
flexural yielding may occur under the effect of earthquake forces Elsewhere the beam shallhave vertical hoops at a spacing not exceedingd2
7 COLUMNS AND FRAME MEMBERSSUBJECTED TO BENDING AND AXIALLOAD
71 General
711 These requirements apply to framemembers which have a factored axial stress inexcess of 01 f ck under the effect of earthquakeforces
712 The minimum dimension of the membershall not be less than 200 mm However inframes which have beams with centre to centrespan exceeding 5 m or columns of unsupportedlength exceeding 4 m the shortest dimension of the column shall not be less than 300 mm
713 The ratio of the shortest cross sectionaldimension to the perpendicular dimension shallpreferably not be less than 04
72 Longitudinal Reinforcement
721 Lap splices shall be provided only in the
central half of the member length It should beproportioned as a tension splice Hoops shall beprovided over the entire splice length atspacing not exceeding 150 mm centre to centreNot more than 50 percent of the bars shall bespliced at one section
722 Any area of a column that extends morethan 100 mm beyond the confined core due toarchitectural requirements shall be detailed inthe following manner In case the contributionof this area to strength has been consideredthen it will have the minimum longitudinal andtransverse reinforcement as per this code
FIG 4 C ALCULATION OF DESIGN SHEAR FORCE FOR BEAM
832019 Indian STANDARDS 13920-1993 Code of Practice
However if this area has been treated asnon-structural the minimum reinforcementrequirements shall be governed byIS 456 1978 provisions minimum longitudinaland transverse reinforcement as perIS 456 1978 ( see Fig 6 )
73 Transverse Reinforcement
731 Transverse reinforcement for circularcolumns shall consist of spiral or circular hoopsIn rectangular columns rectangular hoops maybe used A rectangular hoop is a closed stirruphaving a 135deg hook with a 10 diameterextension (but not lt 75 mm) at each end that isembedded in the confined core ( see Fig 7A )
732 The parallel legs of rectangular hoop shallbe spaced not more than 300 mm centre tocentre If the length of any side of the hoopexceeds 300 mm a crosstie shall be provided(Fig 7B) Alternatively a pair of overlappinghoops may be provided within the columm ( seeFig 7C) The hooks shall engage peripheral
longitudinal bars733 The spacing of hoops shall not exceed half the least lateral dimension of the columnexcept where special confining reinforcement isprovided as per 74
734 The design shear force for columns shallbe the maximum of
a) calculated factored shear force as peranalysis and
b) a factored shear force given by
V u = 14
where and are moment of
resistance of opposite sign of beams framinginto the column from opposite faces ( seeFig 8 ) and hst is the storey height The beam
moment capacity is to be calculated as perIS 456 1978
74 Special Confining Reinforcement
This requirement shall be met with unless alarger amount of transverse reinforcement isrequired from shear strength considerations
FIG 5 BEAM REINFORCEMENT
FIG 6 REINFORCEMENT REQUIREMENT FOR COLUMN WITH MORE THAN 100 mm
PROJECTION BEYOND CORE
M bLu lim M
bRu lim+
hst
----------------------------------------------
M bLu lim M
bRu lim
832019 Indian STANDARDS 13920-1993 Code of Practice
741 Special confining reinforcement shall beprovided over a length lo from each joint facetowards midspan and on either side of anysection where flexural yielding may occurunder the effect of earthquake forces ( see
Fig 9 ) The length lsquolorsquo shall not be less than(a) larger lateral dimension of the member atthe section where yielding occurs (b) 16 of clear span of the member and (c) 450 mm
742 When a column terminates into a footingor mat special confining reinforcement shallextend at least 300 mm into the footing or mat( see Fig 10 )
743 When the calculated point of contra-flexure under the effect of gravity andearthquake loads is not within the middle half of the member clear height special confiningreinforcement shall be provided over the full
height of the column744 Columns supporting reactions fromdiscontinued stiff members such as walls shallbe provided with special confiningreinforcement over their full height ( seeFig 11 ) This reinforcement shall also beplaced above the discontinuity for at least thedevelopment length of the largest longitudinalbar in the column Where the column issupported on a wall this reinforcement shall beprovided over the full height of the column itshall also be provided below the discontinuityfor the same development length
745 Special confining reinforcement shall beprovided over the full height of a column whichhas significant variation in stiffness alongits height This variation in stiffness may result
FIG 8 C ALCULATION OF DESIGN SHEAR
FORCE FOR COLUMN
832019 Indian STANDARDS 13920-1993 Code of Practice
due to the presence of bracing a mezzaninefloor or a RCC wall on either side of the
column that extends only over a part of thecolumn height ( see Fig 12 )
746 The spacing of hoops used as specialconfining reinforcement shall not exceed 14 of minimum member dimension but need not beless than 75 mm nor more than 100 mm
747 The area of cross section Ash of the barforming circular hoops or spiral to be used asspecial confining reinforcement shall not beless than
where
Example Consider a column of diameter 300mm Let the grade of concrete be M20 and thatof steel Fe 415 for longitudinal and confiningreinforcement The spacing of circular hoops Sshall not exceed the smaller of (a) 14 of minimum member dimension = 14 times 300 =75 mm and (b) 100 mm Therefore S = 75 mm Assuming 40 mm clear cover to thelongitudinal reinforcement and circular hoopsof diameter 8 mm Dk = 300 ndash 2 times 40 + 2 times 8 =236 mm Thus the area of cross section of thebar forming circular hoop works out to be4728 mm2 This is less than the cross sectionalarea of 8 mm bar (5027 mm2) Thus circularhoops of diameter 8 mm at a spacing of 75 mmcentre to centre will be adequate
748 The area of cross section Ash of the barforming rectangular hoop to be used as specialconfining reinforcement shall not be less than
where
FIG 11 SPECIAL CONFINING REINFORCEMENT REQUIREMENT FOR COLUMNS UNDER DISCONTINUED W ALLS
Ash = area of the bar cross section
S = pitch of spiral or spacing of hoops
Dk = diameter of core measured to theoutside of the spiral or hoop
f ck = characteristic compressive strength of concrete cube
f y = yield stress of steel (of circular hoop orspiral)
Ag = gross area of the column cross sectionand
Ash 009 SDk
f ck
f y-------
Ag
Ak
------- 10ndash=
Ak = area of the concrete core =
h = longer dimension of the rectangularconfining hoop measured to its outer
π4--- D
2
k
Ash 018 Sh
f ck
f y-------
Ag
Ak
------- 10ndash=
832019 Indian STANDARDS 13920-1993 Code of Practice
NOTE The dimension lsquohrsquo of the hoop could be reducedby introducing crossties as shown in Fig 7B In thiscase Ak shall be measured as the overall core arearegardless of the hoop arrangement The hooks of crossties shall engage peripheral longitudinal bars
Example Consider a column of 650 mm times500 mm Let the grade of concrete be M20 andthat of steel Fe 415 for the longitudinal andconfining reinforcement Assuming clear coverof 40 mm to the longitudinal reinforcement andrectangular hoops of diameter 10 mm the sizeof the core is 590 mm times 440 mm As both thesedimensions are greater than 300 mm either a
pair of overlapping hoops or a single hoop withcrossties in both directions will have to beprovided Thus the dimension lsquohrsquo will be thelarger of (i) 5902 = 295 mm and (ii) 4402 =220 mm The spacing of hoops S shall notexceed the smaller of (a) 14 of minimum
member dimensions = 14 times 500 = 125 mm and(b) 100 mm Thus S = 100 mm The area of cross section of the bar forming rectangularhoop works out to be 6447 mm2 This is lessthan the area of cross section of 10 mm bar(7854 mm2) Thus 10 mm diameterrectangular hoops at 100 mm cc will beadequate Similar calculations indicate that asan alternative one could also provide 8 mmdiameter rectangular hoops at 70 mm cc
8 JOINTS OF FRAMES
81 The special confining reinforcement asrequired at the end of column shall be provided
FIG 12 COLUMNS WITH V ARYING STIFFNESS
face It shall not exceed 300 mm ( seeFig 7 ) and
Ak = area of confined concrete core in therectangular hoop measured to itsoutside dimensions
832019 Indian STANDARDS 13920-1993 Code of Practice
through the joint as well unless the joint isconfined as specified by 82
82 A joint which has beams framing into all vertical faces of it and where each beam widthis at least 34 of the column width may be
provided with half the special confiningreinforcement required at the end of thecolumn The spacing of hoops shall not exceed150 mm
9 SHEAR WALLS
91 General Requirements
911 The requirements of this section apply tothe shear walls which are part of the lateralforce resisting system of the structure
912 The thickness of any part of the wall shallpreferably not be less than 150 mm
913 The effective flange width to be used inthe design of flanged wall sections shall beassumed to extend beyond the face of the webfor a distance which shall be the smaller of (a)half the distance to an adjacent shear wall weband (b) 110 th of the total wall height
914 Shear walls shall be provided withreinforcement in the longitudinal andtransverse directions in the plane of the wallThe minimum reinforcement ratio shall be0002 5 of the gross area in each direction Thisreinforcement shall be distributed uniformlyacross the cross section of the wall
915 If the factored shear stress in the wallexceeds 025 or if the wall thicknessexceeds 200 mm reinforcement shall beprovided in two curtains each having barsrunning in the longitudinal and transversedirections in the plane of the wall
916 The diameter of the bars to be used in anypart of the wall shall not exceed 110th of thethickness of that part
917 The maximum spacing of reinforcementin either direction shall not exceed the smallerof lw 5 3tw and 450 mm where lw is thehorizontal length of the wall and tw is the
thickness of the wall web92 Shear Strength
921 The nominal shear stress τ v shall becalculated as
where
922 The design shear strength of concrete τcshall be calculated as per Table 13 of IS 456 1978
923 The nominal shear stress in the wall τ vshall not exceed τc max as per Table 14 of
IS 456 1978924 When τ v is less than τc shearreinforcement shall be provided in accordancewith 914 915 and 917
925 When τ v is greater than τc the area of horizontal shear reinforcement Ah to beprovided within a vertical spacing S v is givenby
where V us = ( V u ndash τc tw dw ) is the shear force
to be resisted by the horizontal reinforcementHowever the amount of horizontalreinforcement provided shall not be less thanthe minimum as per 914
926 The vertical reinforcement that isuniformly distributed in the wall shall not beless than the horizontal reinforcementcalculated as per 925
93 Flexural Strength
931 The moment of resistance M uv of thewall section may be calculated as for columnssubjected to combined bending and axial load
as per IS 456 1978 The moment of resistanceof slender rectangular shear wall section withuniformly distributed vertical reinforcement isgiven in Annex A
932 The cracked flexural strength of the wallsection should be greater than its uncrackedflexural strength
933 In walls that do not have boundaryelements vertical reieforcement shall beconcentrated at the ends of the wall Eachconcentration shall consist of a minimum of 4 bars of 12 mm diameter arranged in at least
2 layers94 Boundary Elements
Boundary elements are portions along the walledges that are strengthened by longitudinaland transverse reinforcement Though theymay have the same thickness as that of thewall web it is advantageous to provide themwith greater thickness
941 Where the extreme fibre compressivestress in the wall due to factored gravity loadsplus factored earthquake force exceeds 02 f ckboundaty elements shall be provided along the
vertical boundaries of walls The boundary
V u = factored shear force
tw = thickness of the web and
dw = effective depth of wall section Thismay by taken as 08 lw for rectangular
sections
f ck
V us
087 f y Ah dw
S v
------------------------------------=
832019 Indian STANDARDS 13920-1993 Code of Practice
elements may be discontinued where thecalculated compressive stress becomes lessthan 015 f ck The compressive stress shall becalculated using a linearly elastic model andgross section properties
942 A boundary element shall have adequateaxial load carrying capacity assuming shortcolumn action so as to enable it to carry anaxial compression equal to the sum of factoredgravity load on it and the additionalcompressive load induced by the seismic forceThe latter may be calculated as
where
943 If the gravity load adds to the strength of the wall its load factor shall be taken as 08
944 The percentage of vertical reinforcementin the boundary elements shall not be less than08 percent nor greater than 6 percent Inorder to avoid congestion the practical upper
limit would be 4 percent945 Boundary elements where required asper 941 shall be provided throughout theirheight with special confining reinforcement asper 74
946 Boundary elements need not be providedif the entire wall section is provided withspecial confining reinforcement as per 74
95 Coupled Shear Walls
951 Coupled shear walls shall be connected byductile coupling beams If the earthquakeinduced shear stress in the coupling beam
exceeds
where ls is the clear span of the coupling beamand D is its overall depth the entireearthquake induced shear and flexure shallpreferably be resisted by diagonalreinforcement
952 The area of reinforcement to be providedalong each diagonal in a diagonally reinforcedcoupling beam shall be
where V u is the factored shear force and α isthe angle made by the diagonal reinforcementwith the horizontal At least 4 bars of 8 mmdiameter shall be provided along each diagonalThe reinforcement along each diagonal shall be
enclosed by special confining reinforcement asper 74 The pitch of spiral or spacing of tiesshall not exceed 100 mm
953 The diagonal or horizontal bars of acoupling beam shall be anchored in theadjacent walls with an anchorage length of 15times the development length in tension
96 Openings in Walls
961 The shear strength of a wall withopenings should be checked along criticalplanes that pass through openings
962 Reinforcement shall be provided along the
edges of openings in walls The area of the vertical and horizontal bars should be such asto equal that of the respective interrupted barsThe vertical bars should extend for the fullstorey height The horizontal bars should beprovided with development length in tensionbeyond the sides of the opening
97 Discontinuous Walls
Columns supporting discontinuous walls shallbe provided with special confiningreinforcement as per 744
98 Construction Joints
The vertical reinforcement ratio across ahorizontal construction joint shall not be lessthan
where τ v is the factored shear stress at the joint Pu is the factored axial force (positive forcompression) and Ag is the gross crosssectional area of the joint
99 Development Splice and AnchorageRequirement
991 Horizontal reinforcement shall beanchored near the edges of the wall or in theconfined core of the boundary elements
992 Splicing of vertical flexural reinforcementshould be avoided as far as possible in regionswhere yielding may take place This zone of flexural yielding may be considered to extendfor a distance of lw above the base of the wall orone sixth of the wall height whichever is moreHowever this distance need not be greaterthan 2 lw Not more than one third of this vertical reinforcement shall be spliced at such asection Splices in adjacent bars should be
staggered by a minimum of 600 mm
M u = factored design moment on the entirewall section
M uv = moment of resistance provided bydistributed vertical reinforcementacross the wall section and
Cw = center to center distance between theboundary elements along the two vertical edges of the wall
M u M uvndash
Cw
--------------------------
832019 Indian STANDARDS 13920-1993 Code of Practice
993 Lateral ties shall be provided aroundlapped spliced bars that are larger than 16 mmin diameter The diameter of the tie shall not beless than one fourth that of the spliced bar norless than 6 mm The spacing of ties shall not
exceed 150 mm center to center
994 Welded splices and mechanicalconnections shall confirm to 25252 of IS 456 1978 However not more than half thereinforcement shall be spliced at a sectionwhere flexural yielding may take place
ANNEX A
( Clause 931 )
MOMENT OF RESISTANCE OF RECTANGULAR SHEAR WALL SECTION
A-1 The moment of resistance of a slender rectangular shear wall section with uniformlydistributed vertical reinforcement may be estimated as follows
These equations were derived assuming a rectangular wall section of depth lw and thickness twthat is subjected to combined uni-axial bending and axial compression The vertical reinforcementis represented by an equivalent steel plate along the length of the section The stress-strain curveassumed for concrete is as per IS 456 1978 whereas that for steel is assumed to be bi-linear Twoequations are given for calculating the flexural strength of the section Their use depends on
whether the section fails in flexural tension or in flexural compression
(a) For
where
ρ = vertical reinforcement ratio = Ast ( tw lw )
Ast = area of uniformly distributed vertical reinforcement
β = 087 f y (0003 5 Es)
Es = elastic modulus of steel and
Pu = axial compression on wall
(b) For
where
The value of xu lw to be used in this equation should be calculated from the quadratic equation
where
xu lwlt xu lw
xu lw lt xu lwlt 10
832019 Indian STANDARDS 13920-1993 Code of Practice
BIS is a statutory institution established under the Bureau of Indian Standards Act 1986 to promoteharmonious development of the activities of standardization marking and quality certification of goods andattending to connected matters in the country
Copyright
BIS has the copyright of all its publications No part of these publications may be reproduced in any formwithout the prior permission in writing of BIS This does not preclude the free use in the course of implementing the standard of necessary details such as symbols and sizes type or grade designationsEnquiries relating to copyright be addressed to the Director (Publications) BIS
Review of Indian Standards
Amendments are issued to standards as the need arises on the basis of comments Standards are alsoreviewed periodically a standard along with amendments is reaffirmed when such review indicates that nochanges are needed if the review indicates that changes are needed it is taken up for revision Users of Indian Standards should ascertain that they are in possession of the latest amendments or edition byreferring to the latest issue of lsquoBIS Cataloguersquo and lsquoStandards Monthly Additionsrsquo
This Indian Standard has been developed from Doc No CED 39 (5263)
Amendments Issued Since Publication
Amend No Date of Issue
Amd No 1 November 1995
Amd No 2 March 2002
BUREAU OF INDIAN STANDARDS
Headquarters
Manak Bhavan 9 Bahadur Shah Zafar Marg New Delhi 110002Telephones 323 01 31 323 33 75 323 94 02
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Regional Offices Telephone
Central Manak Bhavan 9 Bahadur Shah Zafar MargNEW DELHI 110002
323 76 17323 38 41
Eastern 114 C I T Scheme VII M V I P Road KankurgachiKOLKATA 700054
CONCRETE STRUCTURES SUBJECTED TOSEISMIC FORCES mdash CODE OF PRACTICE
1 SCOPE
11 This standard covers the requirements fordesigning and detailing of monolithic reinforcedconcrete buildings so as to give them adequatetoughness and ductility to resist severeearthquake shocks without collapse
111 Provisions of this code shall be adopted inall reinforced concrete structures which arelocated in seismic zone III IV or V
112 The provisions for reinforced concreteconstruction given herein apply specifically tomonolithic reinforced concrete constructionPrecast andor prestressed concrete membersmay be used only if they can provide the samelevel of ductility as that of a monolithicreinforced concrete construction during or afteran earthquake
2 REFERENCES
21 The Indian Standards listed below are
necessary adjunct to this standard
3 TERMINOLOGY
30 For the purpose of this standard thefollowing definitions shall apply
31 Boundary Elements
Portions along the edges of a shear wall thatare strengthened by longitudinal andtransverse reinforcement They may have thesame thickness as that of the wall web
32 Crosstie
Is a continuous bar having a 135deg hook with a
10-diameter extension (but not lt 75 mm) at
each end The hooks shall engage peripherallongitudinal bars
33 Curvature Ductility
Is the ratio of curvature at the ultimatestrength of the section to the curvature at firstyield of tension steel in the section
34 HoopIs a closed stirrup having a 135deg hook with a10-diameter extension (but not lt 75 mm) ateach end that is embedded in the confined coreof the section It may also be made of two piecesof reinforcement a U-stirrup with a 135deg hookand a 10-diameter extension (but not lt 75 mm)at each end embedded in the confined core anda crosstie
35 Lateral Force Resisting System
Is that part of the structural system whichresists the forces induced by earthquake
36 Shear Wall
A wall that is primarily designed to resistlateral forces in its own plane
37 Shell Concrete
Concrete that is not confined by transversereinforcement is also called concrete cover
38 Space Frame
A three dimensional structural system
composed of interconnected members withoutshear or bearing walls so as to function as acomplete self-contained unit with or withoutthe aid of horizontal diaphragms or floorbracing systems
381 Vertical Load Carrying Space Frame
A space frame designed to carry all verticalloads
382 Moment Resisting Space Frame
A vertical load carrying space frame in whichthe members and joints are capable of resisting
forces primarily by flexure
IS No Title
456 1978 Code of practice for plain andreinforced concrete ( thirdrevision)
1786 1985 Specification for high strengthdeformed steel bars and wiresfor concrete reinforcement( third revision )
For the purpose of this standard the followingletter symbols shall have the meaningindicated against each where other symbolsare used they are explained at the appropriate
place All dimensions are in mm loads inNewton and stresses in MPa (Nsq mm) unlessotherwise specified
5 GENERAL SPECIFICATION
51 The design and construction of reinforcedconcrete buildings shall be governed by theprovisions of IS 456 1978 except as modified
by the provisions of this code
52 For all buildings which are more than3 storeys in height the minimum grade of concrete shall be M20 ( f ck = 20 MPa )
53 Steel reinforcements of grade Fe 415 ( seeIS 1786 1985 ) or less only shall be used
However high strength deformed steel barsproduced by the thermo-mechanical treatmentprocess of grades Fe 500 and Fe 550 havingelongation more than 145 percent andconforming to other requirements of IS 1786 1985 may also be used for thereinforcement
Ag mdash gross cross sectional area of column wall
Ah mdash horizontal reinforcement areawithin spacing S v
Ak mdash area of concrete core of column
Asd mdash reinforcement along each diagonalof coupling beam
Ash mdash area of cross section of bar formingspiral or hoop
Ast mdash area of uniformly distributed vertical reinforcement
A v mdash vertical reinforcement at a joint
Cw mdash centre to centre distance betweenboundary elements
D mdash overall depth of beam
Dk mdash diameter of column core measuredto the outside of spiral or hoop
d mdash effective depth of member
dw mdash effective depth of wall section
Es mdash elastic modulus of steel
f ck mdash characteristic compressive strengthof concrete cube
f y mdash yield stress of steel
h mdash longer dimension of rectangularconfining hoop measured to itsouter face
hst mdash storey height
L AB mdash clear span of beam
lo mdash length of member over whichspecial confining reinforcement isto be provided
lw mdash horizontal length of wall
ls mdash clear span of coupling beam M u mdash factored design moment on entire
wall section
mdash hogging moment of resistance of beam at end A
mdash sagging moment of resistance of beam at end A
mdash hogging moment of resistance of beam at end B
mdash sagging moment of resistance of beam at end B
mdash moment of resistance of beam
framing into column from the left
M u lim
Ah
M u lim
As
M u lim
Bh
M u lim
Bs
M u lim
bL
mdash moment of resistance of beamframing into column from the right
M uv mdash flexural strength of wall web
Pu mdash factored axial load
S mdash pitch of spiral or spacing hoops S v mdash vertical spacing of horizontal
reinforcement in web
tw mdash thickness of wall web
mdash shear at end A of beam due to deadand live loads with a partial factorof safety of 12 on loads
mdash shear at end B of beam due to deadand live loads with a partial factorof safety of 12 on loads
V j mdash shear resistance at a joint
V u mdash factored shear force
V us mdash shear force to be resisted byreinforcement
mdash depth of neutral axis from extremecompression fibre
α mdash inclination of diagonalreinforcement in coupling beam
ρ mdash vertical reinforcement ratio
ρc mdash compression reinforcement ratio ina beam
ρmax mdash maximum tension reinforcementratio for a beam
ρmin mdash minimum tension reinforcementratio for a beam
τ c mdash shear strength of concrete
mdash maximum permissible shear stressin section
τ v mdash nominal shear stress
M u lim
bR
V D L+
a
V D L+
b
xu xu
τcmax
832019 Indian STANDARDS 13920-1993 Code of Practice
These requirements apply to frame membersresisting earthquake induced forces and
designed to resist flexure These members shallsatisfy the following requirements
611 The factored axial stress on the memberunder earthquake loading shall not exceed01 f ck
612 The member shall preferably have awidth-to-depth ratio of more than 03
613 The width of the member shall not be lessthan 200 mm
614 The depth D of the member shall
preferably be not more than 14 of the clearspan
62 Longitudinal Reinforcement
622 The maximum steel ratio on any face atany section shall not exceed ρmax = 0025
623 The positive steel at a joint face must beat least equal to half the negative steel at thatface
624 The steel provided at each of the top andbottom face of the member at any section alongits length shall be at least equal to one-fourth of the maximum negative moment steel providedat the face of either joint It may be clarifiedthat redistribution of moments permitted inIS 456 1978 (clause 361) will be used only for vertical load moments and not for lateral loadmoments
625 In an external joint both the top and thebottom bars of the beam shall be provided withanchorage length beyond the inner face of thecolumn equal to the development length intension plus 10 times the bar diameter minusthe allowance for 90 degree bend(s) ( seeFig 1 ) In an internal joint both face bars of the beam shall be taken continuously through
the column
626 The longitudinal bars shall be splicedonly if hoops are provided over the entire splicelength at a spacing not exceeding 150 mm ( seeFig 2 ) The lap length shall not be less thanthe bar development length in tension Lapsplices shall not be provided (a) within a joint(b) within a distance of 2d from joint face and(c) within a quarter lengh of the member whereflexural yielding may generally occur under theeffect of earthquake forces Not more than50 percent of the bars shall be spliced at onesection
627 Use of welded splices and mechanicalconnections may also be made as per 25252of IS 456 1978 However not more than half the reinforcement shall be spliced at a sectionwhere flexural yielding may take place Thelocation of splices shall be governed by 626
63 Web Reinforcement
631 Web reinforcement shall consist of vertical hoops A vertical hoop is a closedstirrup having a 135deg hook with a 10 diameter
extension (but not lt 75 mm) at each end that is
621 a) The top as well as bottomreinforcement shall consist of at leasttwo bars throughout the memberlength
b) The tension steel ratio on any face atany section shall not be less than
ρmin = 024 where f ck and f y
are in MPa
f ck f y frasl
FIG 1 ANCHORAGE OF BEAM B ARS IN AN
E XTERNAL JOINT
FIG 2 L AP SPLICE IN BEAM
832019 Indian STANDARDS 13920-1993 Code of Practice
embedded in the confined core ( see Fig 3a ) Incompelling circumstances it may also be madeup of two pieces of reinforcement a U-stirrupwith a 135deg hook and a 10 diameter extension(but not lt 75 mm) at each end embedded in the
confined core and a crosstie ( see Fig 3b ) Acrosstie is a bar having a 135deg hook with a 10diameter extension (but not lt 75 mm) at eachend The hooks shall engage peripherallongitudinal bars
632 The minimum diameter of the barforming a hoop shall be 6 mm However in
beams with clear span exceeding 5 m theminimum bar diameter shall be 8 mm
633 The shear force to be resisted by the vertical hoops shall be the maximum of
a) calculated factored shear force as peranalysis and
b) shear force due to formation of plastichinges at both ends of the beam plus thefactored gravity load on the span This isgiven by ( see Fig 4 )
where and are the sagging and hogging moments of resistance of
the beam section at ends A and B respectively These are to be calculated as per IS 456 1978
L AB is clear span of beam and are the shears at ends A and B respectively due to vertical loads with a partial safety factor of 12 on loads The design shear at end A shall be thelarger of the two values of V ua computed above Similarly the design shear at end B shall be the
larger of the two values of V ub computed above
i) for sway to right
and and
ii) for sway to left
and
FIG 3 BEAM WEB REINFORCEMENT
M u lim As
M u lim Ah
M u limBs
M u limBh
VD L+a V
D L+b
832019 Indian STANDARDS 13920-1993 Code of Practice
634 The contribution of bent up bars andinclined hoops to shear resistance of the sectionshall not be considered
635 The spacing of hoops over a length of 2d ateither end of a beam shall not exceed (a) d4and (b) 8 times the diameter of the smallestlongitudinal bar however it need not be lessthan 100 mm ( see Fig 5 ) The first hoop shallbe at a distance not exceeding 50 mm from the joint face Vertical hoops at the same spacing asabove shall also be provided over a lengthequal to 2d on either side of a section where
flexural yielding may occur under the effect of earthquake forces Elsewhere the beam shallhave vertical hoops at a spacing not exceedingd2
7 COLUMNS AND FRAME MEMBERSSUBJECTED TO BENDING AND AXIALLOAD
71 General
711 These requirements apply to framemembers which have a factored axial stress inexcess of 01 f ck under the effect of earthquakeforces
712 The minimum dimension of the membershall not be less than 200 mm However inframes which have beams with centre to centrespan exceeding 5 m or columns of unsupportedlength exceeding 4 m the shortest dimension of the column shall not be less than 300 mm
713 The ratio of the shortest cross sectionaldimension to the perpendicular dimension shallpreferably not be less than 04
72 Longitudinal Reinforcement
721 Lap splices shall be provided only in the
central half of the member length It should beproportioned as a tension splice Hoops shall beprovided over the entire splice length atspacing not exceeding 150 mm centre to centreNot more than 50 percent of the bars shall bespliced at one section
722 Any area of a column that extends morethan 100 mm beyond the confined core due toarchitectural requirements shall be detailed inthe following manner In case the contributionof this area to strength has been consideredthen it will have the minimum longitudinal andtransverse reinforcement as per this code
FIG 4 C ALCULATION OF DESIGN SHEAR FORCE FOR BEAM
832019 Indian STANDARDS 13920-1993 Code of Practice
However if this area has been treated asnon-structural the minimum reinforcementrequirements shall be governed byIS 456 1978 provisions minimum longitudinaland transverse reinforcement as perIS 456 1978 ( see Fig 6 )
73 Transverse Reinforcement
731 Transverse reinforcement for circularcolumns shall consist of spiral or circular hoopsIn rectangular columns rectangular hoops maybe used A rectangular hoop is a closed stirruphaving a 135deg hook with a 10 diameterextension (but not lt 75 mm) at each end that isembedded in the confined core ( see Fig 7A )
732 The parallel legs of rectangular hoop shallbe spaced not more than 300 mm centre tocentre If the length of any side of the hoopexceeds 300 mm a crosstie shall be provided(Fig 7B) Alternatively a pair of overlappinghoops may be provided within the columm ( seeFig 7C) The hooks shall engage peripheral
longitudinal bars733 The spacing of hoops shall not exceed half the least lateral dimension of the columnexcept where special confining reinforcement isprovided as per 74
734 The design shear force for columns shallbe the maximum of
a) calculated factored shear force as peranalysis and
b) a factored shear force given by
V u = 14
where and are moment of
resistance of opposite sign of beams framinginto the column from opposite faces ( seeFig 8 ) and hst is the storey height The beam
moment capacity is to be calculated as perIS 456 1978
74 Special Confining Reinforcement
This requirement shall be met with unless alarger amount of transverse reinforcement isrequired from shear strength considerations
FIG 5 BEAM REINFORCEMENT
FIG 6 REINFORCEMENT REQUIREMENT FOR COLUMN WITH MORE THAN 100 mm
PROJECTION BEYOND CORE
M bLu lim M
bRu lim+
hst
----------------------------------------------
M bLu lim M
bRu lim
832019 Indian STANDARDS 13920-1993 Code of Practice
741 Special confining reinforcement shall beprovided over a length lo from each joint facetowards midspan and on either side of anysection where flexural yielding may occurunder the effect of earthquake forces ( see
Fig 9 ) The length lsquolorsquo shall not be less than(a) larger lateral dimension of the member atthe section where yielding occurs (b) 16 of clear span of the member and (c) 450 mm
742 When a column terminates into a footingor mat special confining reinforcement shallextend at least 300 mm into the footing or mat( see Fig 10 )
743 When the calculated point of contra-flexure under the effect of gravity andearthquake loads is not within the middle half of the member clear height special confiningreinforcement shall be provided over the full
height of the column744 Columns supporting reactions fromdiscontinued stiff members such as walls shallbe provided with special confiningreinforcement over their full height ( seeFig 11 ) This reinforcement shall also beplaced above the discontinuity for at least thedevelopment length of the largest longitudinalbar in the column Where the column issupported on a wall this reinforcement shall beprovided over the full height of the column itshall also be provided below the discontinuityfor the same development length
745 Special confining reinforcement shall beprovided over the full height of a column whichhas significant variation in stiffness alongits height This variation in stiffness may result
FIG 8 C ALCULATION OF DESIGN SHEAR
FORCE FOR COLUMN
832019 Indian STANDARDS 13920-1993 Code of Practice
due to the presence of bracing a mezzaninefloor or a RCC wall on either side of the
column that extends only over a part of thecolumn height ( see Fig 12 )
746 The spacing of hoops used as specialconfining reinforcement shall not exceed 14 of minimum member dimension but need not beless than 75 mm nor more than 100 mm
747 The area of cross section Ash of the barforming circular hoops or spiral to be used asspecial confining reinforcement shall not beless than
where
Example Consider a column of diameter 300mm Let the grade of concrete be M20 and thatof steel Fe 415 for longitudinal and confiningreinforcement The spacing of circular hoops Sshall not exceed the smaller of (a) 14 of minimum member dimension = 14 times 300 =75 mm and (b) 100 mm Therefore S = 75 mm Assuming 40 mm clear cover to thelongitudinal reinforcement and circular hoopsof diameter 8 mm Dk = 300 ndash 2 times 40 + 2 times 8 =236 mm Thus the area of cross section of thebar forming circular hoop works out to be4728 mm2 This is less than the cross sectionalarea of 8 mm bar (5027 mm2) Thus circularhoops of diameter 8 mm at a spacing of 75 mmcentre to centre will be adequate
748 The area of cross section Ash of the barforming rectangular hoop to be used as specialconfining reinforcement shall not be less than
where
FIG 11 SPECIAL CONFINING REINFORCEMENT REQUIREMENT FOR COLUMNS UNDER DISCONTINUED W ALLS
Ash = area of the bar cross section
S = pitch of spiral or spacing of hoops
Dk = diameter of core measured to theoutside of the spiral or hoop
f ck = characteristic compressive strength of concrete cube
f y = yield stress of steel (of circular hoop orspiral)
Ag = gross area of the column cross sectionand
Ash 009 SDk
f ck
f y-------
Ag
Ak
------- 10ndash=
Ak = area of the concrete core =
h = longer dimension of the rectangularconfining hoop measured to its outer
π4--- D
2
k
Ash 018 Sh
f ck
f y-------
Ag
Ak
------- 10ndash=
832019 Indian STANDARDS 13920-1993 Code of Practice
NOTE The dimension lsquohrsquo of the hoop could be reducedby introducing crossties as shown in Fig 7B In thiscase Ak shall be measured as the overall core arearegardless of the hoop arrangement The hooks of crossties shall engage peripheral longitudinal bars
Example Consider a column of 650 mm times500 mm Let the grade of concrete be M20 andthat of steel Fe 415 for the longitudinal andconfining reinforcement Assuming clear coverof 40 mm to the longitudinal reinforcement andrectangular hoops of diameter 10 mm the sizeof the core is 590 mm times 440 mm As both thesedimensions are greater than 300 mm either a
pair of overlapping hoops or a single hoop withcrossties in both directions will have to beprovided Thus the dimension lsquohrsquo will be thelarger of (i) 5902 = 295 mm and (ii) 4402 =220 mm The spacing of hoops S shall notexceed the smaller of (a) 14 of minimum
member dimensions = 14 times 500 = 125 mm and(b) 100 mm Thus S = 100 mm The area of cross section of the bar forming rectangularhoop works out to be 6447 mm2 This is lessthan the area of cross section of 10 mm bar(7854 mm2) Thus 10 mm diameterrectangular hoops at 100 mm cc will beadequate Similar calculations indicate that asan alternative one could also provide 8 mmdiameter rectangular hoops at 70 mm cc
8 JOINTS OF FRAMES
81 The special confining reinforcement asrequired at the end of column shall be provided
FIG 12 COLUMNS WITH V ARYING STIFFNESS
face It shall not exceed 300 mm ( seeFig 7 ) and
Ak = area of confined concrete core in therectangular hoop measured to itsoutside dimensions
832019 Indian STANDARDS 13920-1993 Code of Practice
through the joint as well unless the joint isconfined as specified by 82
82 A joint which has beams framing into all vertical faces of it and where each beam widthis at least 34 of the column width may be
provided with half the special confiningreinforcement required at the end of thecolumn The spacing of hoops shall not exceed150 mm
9 SHEAR WALLS
91 General Requirements
911 The requirements of this section apply tothe shear walls which are part of the lateralforce resisting system of the structure
912 The thickness of any part of the wall shallpreferably not be less than 150 mm
913 The effective flange width to be used inthe design of flanged wall sections shall beassumed to extend beyond the face of the webfor a distance which shall be the smaller of (a)half the distance to an adjacent shear wall weband (b) 110 th of the total wall height
914 Shear walls shall be provided withreinforcement in the longitudinal andtransverse directions in the plane of the wallThe minimum reinforcement ratio shall be0002 5 of the gross area in each direction Thisreinforcement shall be distributed uniformlyacross the cross section of the wall
915 If the factored shear stress in the wallexceeds 025 or if the wall thicknessexceeds 200 mm reinforcement shall beprovided in two curtains each having barsrunning in the longitudinal and transversedirections in the plane of the wall
916 The diameter of the bars to be used in anypart of the wall shall not exceed 110th of thethickness of that part
917 The maximum spacing of reinforcementin either direction shall not exceed the smallerof lw 5 3tw and 450 mm where lw is thehorizontal length of the wall and tw is the
thickness of the wall web92 Shear Strength
921 The nominal shear stress τ v shall becalculated as
where
922 The design shear strength of concrete τcshall be calculated as per Table 13 of IS 456 1978
923 The nominal shear stress in the wall τ vshall not exceed τc max as per Table 14 of
IS 456 1978924 When τ v is less than τc shearreinforcement shall be provided in accordancewith 914 915 and 917
925 When τ v is greater than τc the area of horizontal shear reinforcement Ah to beprovided within a vertical spacing S v is givenby
where V us = ( V u ndash τc tw dw ) is the shear force
to be resisted by the horizontal reinforcementHowever the amount of horizontalreinforcement provided shall not be less thanthe minimum as per 914
926 The vertical reinforcement that isuniformly distributed in the wall shall not beless than the horizontal reinforcementcalculated as per 925
93 Flexural Strength
931 The moment of resistance M uv of thewall section may be calculated as for columnssubjected to combined bending and axial load
as per IS 456 1978 The moment of resistanceof slender rectangular shear wall section withuniformly distributed vertical reinforcement isgiven in Annex A
932 The cracked flexural strength of the wallsection should be greater than its uncrackedflexural strength
933 In walls that do not have boundaryelements vertical reieforcement shall beconcentrated at the ends of the wall Eachconcentration shall consist of a minimum of 4 bars of 12 mm diameter arranged in at least
2 layers94 Boundary Elements
Boundary elements are portions along the walledges that are strengthened by longitudinaland transverse reinforcement Though theymay have the same thickness as that of thewall web it is advantageous to provide themwith greater thickness
941 Where the extreme fibre compressivestress in the wall due to factored gravity loadsplus factored earthquake force exceeds 02 f ckboundaty elements shall be provided along the
vertical boundaries of walls The boundary
V u = factored shear force
tw = thickness of the web and
dw = effective depth of wall section Thismay by taken as 08 lw for rectangular
sections
f ck
V us
087 f y Ah dw
S v
------------------------------------=
832019 Indian STANDARDS 13920-1993 Code of Practice
elements may be discontinued where thecalculated compressive stress becomes lessthan 015 f ck The compressive stress shall becalculated using a linearly elastic model andgross section properties
942 A boundary element shall have adequateaxial load carrying capacity assuming shortcolumn action so as to enable it to carry anaxial compression equal to the sum of factoredgravity load on it and the additionalcompressive load induced by the seismic forceThe latter may be calculated as
where
943 If the gravity load adds to the strength of the wall its load factor shall be taken as 08
944 The percentage of vertical reinforcementin the boundary elements shall not be less than08 percent nor greater than 6 percent Inorder to avoid congestion the practical upper
limit would be 4 percent945 Boundary elements where required asper 941 shall be provided throughout theirheight with special confining reinforcement asper 74
946 Boundary elements need not be providedif the entire wall section is provided withspecial confining reinforcement as per 74
95 Coupled Shear Walls
951 Coupled shear walls shall be connected byductile coupling beams If the earthquakeinduced shear stress in the coupling beam
exceeds
where ls is the clear span of the coupling beamand D is its overall depth the entireearthquake induced shear and flexure shallpreferably be resisted by diagonalreinforcement
952 The area of reinforcement to be providedalong each diagonal in a diagonally reinforcedcoupling beam shall be
where V u is the factored shear force and α isthe angle made by the diagonal reinforcementwith the horizontal At least 4 bars of 8 mmdiameter shall be provided along each diagonalThe reinforcement along each diagonal shall be
enclosed by special confining reinforcement asper 74 The pitch of spiral or spacing of tiesshall not exceed 100 mm
953 The diagonal or horizontal bars of acoupling beam shall be anchored in theadjacent walls with an anchorage length of 15times the development length in tension
96 Openings in Walls
961 The shear strength of a wall withopenings should be checked along criticalplanes that pass through openings
962 Reinforcement shall be provided along the
edges of openings in walls The area of the vertical and horizontal bars should be such asto equal that of the respective interrupted barsThe vertical bars should extend for the fullstorey height The horizontal bars should beprovided with development length in tensionbeyond the sides of the opening
97 Discontinuous Walls
Columns supporting discontinuous walls shallbe provided with special confiningreinforcement as per 744
98 Construction Joints
The vertical reinforcement ratio across ahorizontal construction joint shall not be lessthan
where τ v is the factored shear stress at the joint Pu is the factored axial force (positive forcompression) and Ag is the gross crosssectional area of the joint
99 Development Splice and AnchorageRequirement
991 Horizontal reinforcement shall beanchored near the edges of the wall or in theconfined core of the boundary elements
992 Splicing of vertical flexural reinforcementshould be avoided as far as possible in regionswhere yielding may take place This zone of flexural yielding may be considered to extendfor a distance of lw above the base of the wall orone sixth of the wall height whichever is moreHowever this distance need not be greaterthan 2 lw Not more than one third of this vertical reinforcement shall be spliced at such asection Splices in adjacent bars should be
staggered by a minimum of 600 mm
M u = factored design moment on the entirewall section
M uv = moment of resistance provided bydistributed vertical reinforcementacross the wall section and
Cw = center to center distance between theboundary elements along the two vertical edges of the wall
M u M uvndash
Cw
--------------------------
832019 Indian STANDARDS 13920-1993 Code of Practice
993 Lateral ties shall be provided aroundlapped spliced bars that are larger than 16 mmin diameter The diameter of the tie shall not beless than one fourth that of the spliced bar norless than 6 mm The spacing of ties shall not
exceed 150 mm center to center
994 Welded splices and mechanicalconnections shall confirm to 25252 of IS 456 1978 However not more than half thereinforcement shall be spliced at a sectionwhere flexural yielding may take place
ANNEX A
( Clause 931 )
MOMENT OF RESISTANCE OF RECTANGULAR SHEAR WALL SECTION
A-1 The moment of resistance of a slender rectangular shear wall section with uniformlydistributed vertical reinforcement may be estimated as follows
These equations were derived assuming a rectangular wall section of depth lw and thickness twthat is subjected to combined uni-axial bending and axial compression The vertical reinforcementis represented by an equivalent steel plate along the length of the section The stress-strain curveassumed for concrete is as per IS 456 1978 whereas that for steel is assumed to be bi-linear Twoequations are given for calculating the flexural strength of the section Their use depends on
whether the section fails in flexural tension or in flexural compression
(a) For
where
ρ = vertical reinforcement ratio = Ast ( tw lw )
Ast = area of uniformly distributed vertical reinforcement
β = 087 f y (0003 5 Es)
Es = elastic modulus of steel and
Pu = axial compression on wall
(b) For
where
The value of xu lw to be used in this equation should be calculated from the quadratic equation
where
xu lwlt xu lw
xu lw lt xu lwlt 10
832019 Indian STANDARDS 13920-1993 Code of Practice
BIS is a statutory institution established under the Bureau of Indian Standards Act 1986 to promoteharmonious development of the activities of standardization marking and quality certification of goods andattending to connected matters in the country
Copyright
BIS has the copyright of all its publications No part of these publications may be reproduced in any formwithout the prior permission in writing of BIS This does not preclude the free use in the course of implementing the standard of necessary details such as symbols and sizes type or grade designationsEnquiries relating to copyright be addressed to the Director (Publications) BIS
Review of Indian Standards
Amendments are issued to standards as the need arises on the basis of comments Standards are alsoreviewed periodically a standard along with amendments is reaffirmed when such review indicates that nochanges are needed if the review indicates that changes are needed it is taken up for revision Users of Indian Standards should ascertain that they are in possession of the latest amendments or edition byreferring to the latest issue of lsquoBIS Cataloguersquo and lsquoStandards Monthly Additionsrsquo
This Indian Standard has been developed from Doc No CED 39 (5263)
Amendments Issued Since Publication
Amend No Date of Issue
Amd No 1 November 1995
Amd No 2 March 2002
BUREAU OF INDIAN STANDARDS
Headquarters
Manak Bhavan 9 Bahadur Shah Zafar Marg New Delhi 110002Telephones 323 01 31 323 33 75 323 94 02
Telegrams Manaksanstha(Common to all offices)
Regional Offices Telephone
Central Manak Bhavan 9 Bahadur Shah Zafar MargNEW DELHI 110002
323 76 17323 38 41
Eastern 114 C I T Scheme VII M V I P Road KankurgachiKOLKATA 700054
For the purpose of this standard the followingletter symbols shall have the meaningindicated against each where other symbolsare used they are explained at the appropriate
place All dimensions are in mm loads inNewton and stresses in MPa (Nsq mm) unlessotherwise specified
5 GENERAL SPECIFICATION
51 The design and construction of reinforcedconcrete buildings shall be governed by theprovisions of IS 456 1978 except as modified
by the provisions of this code
52 For all buildings which are more than3 storeys in height the minimum grade of concrete shall be M20 ( f ck = 20 MPa )
53 Steel reinforcements of grade Fe 415 ( seeIS 1786 1985 ) or less only shall be used
However high strength deformed steel barsproduced by the thermo-mechanical treatmentprocess of grades Fe 500 and Fe 550 havingelongation more than 145 percent andconforming to other requirements of IS 1786 1985 may also be used for thereinforcement
Ag mdash gross cross sectional area of column wall
Ah mdash horizontal reinforcement areawithin spacing S v
Ak mdash area of concrete core of column
Asd mdash reinforcement along each diagonalof coupling beam
Ash mdash area of cross section of bar formingspiral or hoop
Ast mdash area of uniformly distributed vertical reinforcement
A v mdash vertical reinforcement at a joint
Cw mdash centre to centre distance betweenboundary elements
D mdash overall depth of beam
Dk mdash diameter of column core measuredto the outside of spiral or hoop
d mdash effective depth of member
dw mdash effective depth of wall section
Es mdash elastic modulus of steel
f ck mdash characteristic compressive strengthof concrete cube
f y mdash yield stress of steel
h mdash longer dimension of rectangularconfining hoop measured to itsouter face
hst mdash storey height
L AB mdash clear span of beam
lo mdash length of member over whichspecial confining reinforcement isto be provided
lw mdash horizontal length of wall
ls mdash clear span of coupling beam M u mdash factored design moment on entire
wall section
mdash hogging moment of resistance of beam at end A
mdash sagging moment of resistance of beam at end A
mdash hogging moment of resistance of beam at end B
mdash sagging moment of resistance of beam at end B
mdash moment of resistance of beam
framing into column from the left
M u lim
Ah
M u lim
As
M u lim
Bh
M u lim
Bs
M u lim
bL
mdash moment of resistance of beamframing into column from the right
M uv mdash flexural strength of wall web
Pu mdash factored axial load
S mdash pitch of spiral or spacing hoops S v mdash vertical spacing of horizontal
reinforcement in web
tw mdash thickness of wall web
mdash shear at end A of beam due to deadand live loads with a partial factorof safety of 12 on loads
mdash shear at end B of beam due to deadand live loads with a partial factorof safety of 12 on loads
V j mdash shear resistance at a joint
V u mdash factored shear force
V us mdash shear force to be resisted byreinforcement
mdash depth of neutral axis from extremecompression fibre
α mdash inclination of diagonalreinforcement in coupling beam
ρ mdash vertical reinforcement ratio
ρc mdash compression reinforcement ratio ina beam
ρmax mdash maximum tension reinforcementratio for a beam
ρmin mdash minimum tension reinforcementratio for a beam
τ c mdash shear strength of concrete
mdash maximum permissible shear stressin section
τ v mdash nominal shear stress
M u lim
bR
V D L+
a
V D L+
b
xu xu
τcmax
832019 Indian STANDARDS 13920-1993 Code of Practice
These requirements apply to frame membersresisting earthquake induced forces and
designed to resist flexure These members shallsatisfy the following requirements
611 The factored axial stress on the memberunder earthquake loading shall not exceed01 f ck
612 The member shall preferably have awidth-to-depth ratio of more than 03
613 The width of the member shall not be lessthan 200 mm
614 The depth D of the member shall
preferably be not more than 14 of the clearspan
62 Longitudinal Reinforcement
622 The maximum steel ratio on any face atany section shall not exceed ρmax = 0025
623 The positive steel at a joint face must beat least equal to half the negative steel at thatface
624 The steel provided at each of the top andbottom face of the member at any section alongits length shall be at least equal to one-fourth of the maximum negative moment steel providedat the face of either joint It may be clarifiedthat redistribution of moments permitted inIS 456 1978 (clause 361) will be used only for vertical load moments and not for lateral loadmoments
625 In an external joint both the top and thebottom bars of the beam shall be provided withanchorage length beyond the inner face of thecolumn equal to the development length intension plus 10 times the bar diameter minusthe allowance for 90 degree bend(s) ( seeFig 1 ) In an internal joint both face bars of the beam shall be taken continuously through
the column
626 The longitudinal bars shall be splicedonly if hoops are provided over the entire splicelength at a spacing not exceeding 150 mm ( seeFig 2 ) The lap length shall not be less thanthe bar development length in tension Lapsplices shall not be provided (a) within a joint(b) within a distance of 2d from joint face and(c) within a quarter lengh of the member whereflexural yielding may generally occur under theeffect of earthquake forces Not more than50 percent of the bars shall be spliced at onesection
627 Use of welded splices and mechanicalconnections may also be made as per 25252of IS 456 1978 However not more than half the reinforcement shall be spliced at a sectionwhere flexural yielding may take place Thelocation of splices shall be governed by 626
63 Web Reinforcement
631 Web reinforcement shall consist of vertical hoops A vertical hoop is a closedstirrup having a 135deg hook with a 10 diameter
extension (but not lt 75 mm) at each end that is
621 a) The top as well as bottomreinforcement shall consist of at leasttwo bars throughout the memberlength
b) The tension steel ratio on any face atany section shall not be less than
ρmin = 024 where f ck and f y
are in MPa
f ck f y frasl
FIG 1 ANCHORAGE OF BEAM B ARS IN AN
E XTERNAL JOINT
FIG 2 L AP SPLICE IN BEAM
832019 Indian STANDARDS 13920-1993 Code of Practice
embedded in the confined core ( see Fig 3a ) Incompelling circumstances it may also be madeup of two pieces of reinforcement a U-stirrupwith a 135deg hook and a 10 diameter extension(but not lt 75 mm) at each end embedded in the
confined core and a crosstie ( see Fig 3b ) Acrosstie is a bar having a 135deg hook with a 10diameter extension (but not lt 75 mm) at eachend The hooks shall engage peripherallongitudinal bars
632 The minimum diameter of the barforming a hoop shall be 6 mm However in
beams with clear span exceeding 5 m theminimum bar diameter shall be 8 mm
633 The shear force to be resisted by the vertical hoops shall be the maximum of
a) calculated factored shear force as peranalysis and
b) shear force due to formation of plastichinges at both ends of the beam plus thefactored gravity load on the span This isgiven by ( see Fig 4 )
where and are the sagging and hogging moments of resistance of
the beam section at ends A and B respectively These are to be calculated as per IS 456 1978
L AB is clear span of beam and are the shears at ends A and B respectively due to vertical loads with a partial safety factor of 12 on loads The design shear at end A shall be thelarger of the two values of V ua computed above Similarly the design shear at end B shall be the
larger of the two values of V ub computed above
i) for sway to right
and and
ii) for sway to left
and
FIG 3 BEAM WEB REINFORCEMENT
M u lim As
M u lim Ah
M u limBs
M u limBh
VD L+a V
D L+b
832019 Indian STANDARDS 13920-1993 Code of Practice
634 The contribution of bent up bars andinclined hoops to shear resistance of the sectionshall not be considered
635 The spacing of hoops over a length of 2d ateither end of a beam shall not exceed (a) d4and (b) 8 times the diameter of the smallestlongitudinal bar however it need not be lessthan 100 mm ( see Fig 5 ) The first hoop shallbe at a distance not exceeding 50 mm from the joint face Vertical hoops at the same spacing asabove shall also be provided over a lengthequal to 2d on either side of a section where
flexural yielding may occur under the effect of earthquake forces Elsewhere the beam shallhave vertical hoops at a spacing not exceedingd2
7 COLUMNS AND FRAME MEMBERSSUBJECTED TO BENDING AND AXIALLOAD
71 General
711 These requirements apply to framemembers which have a factored axial stress inexcess of 01 f ck under the effect of earthquakeforces
712 The minimum dimension of the membershall not be less than 200 mm However inframes which have beams with centre to centrespan exceeding 5 m or columns of unsupportedlength exceeding 4 m the shortest dimension of the column shall not be less than 300 mm
713 The ratio of the shortest cross sectionaldimension to the perpendicular dimension shallpreferably not be less than 04
72 Longitudinal Reinforcement
721 Lap splices shall be provided only in the
central half of the member length It should beproportioned as a tension splice Hoops shall beprovided over the entire splice length atspacing not exceeding 150 mm centre to centreNot more than 50 percent of the bars shall bespliced at one section
722 Any area of a column that extends morethan 100 mm beyond the confined core due toarchitectural requirements shall be detailed inthe following manner In case the contributionof this area to strength has been consideredthen it will have the minimum longitudinal andtransverse reinforcement as per this code
FIG 4 C ALCULATION OF DESIGN SHEAR FORCE FOR BEAM
832019 Indian STANDARDS 13920-1993 Code of Practice
However if this area has been treated asnon-structural the minimum reinforcementrequirements shall be governed byIS 456 1978 provisions minimum longitudinaland transverse reinforcement as perIS 456 1978 ( see Fig 6 )
73 Transverse Reinforcement
731 Transverse reinforcement for circularcolumns shall consist of spiral or circular hoopsIn rectangular columns rectangular hoops maybe used A rectangular hoop is a closed stirruphaving a 135deg hook with a 10 diameterextension (but not lt 75 mm) at each end that isembedded in the confined core ( see Fig 7A )
732 The parallel legs of rectangular hoop shallbe spaced not more than 300 mm centre tocentre If the length of any side of the hoopexceeds 300 mm a crosstie shall be provided(Fig 7B) Alternatively a pair of overlappinghoops may be provided within the columm ( seeFig 7C) The hooks shall engage peripheral
longitudinal bars733 The spacing of hoops shall not exceed half the least lateral dimension of the columnexcept where special confining reinforcement isprovided as per 74
734 The design shear force for columns shallbe the maximum of
a) calculated factored shear force as peranalysis and
b) a factored shear force given by
V u = 14
where and are moment of
resistance of opposite sign of beams framinginto the column from opposite faces ( seeFig 8 ) and hst is the storey height The beam
moment capacity is to be calculated as perIS 456 1978
74 Special Confining Reinforcement
This requirement shall be met with unless alarger amount of transverse reinforcement isrequired from shear strength considerations
FIG 5 BEAM REINFORCEMENT
FIG 6 REINFORCEMENT REQUIREMENT FOR COLUMN WITH MORE THAN 100 mm
PROJECTION BEYOND CORE
M bLu lim M
bRu lim+
hst
----------------------------------------------
M bLu lim M
bRu lim
832019 Indian STANDARDS 13920-1993 Code of Practice
741 Special confining reinforcement shall beprovided over a length lo from each joint facetowards midspan and on either side of anysection where flexural yielding may occurunder the effect of earthquake forces ( see
Fig 9 ) The length lsquolorsquo shall not be less than(a) larger lateral dimension of the member atthe section where yielding occurs (b) 16 of clear span of the member and (c) 450 mm
742 When a column terminates into a footingor mat special confining reinforcement shallextend at least 300 mm into the footing or mat( see Fig 10 )
743 When the calculated point of contra-flexure under the effect of gravity andearthquake loads is not within the middle half of the member clear height special confiningreinforcement shall be provided over the full
height of the column744 Columns supporting reactions fromdiscontinued stiff members such as walls shallbe provided with special confiningreinforcement over their full height ( seeFig 11 ) This reinforcement shall also beplaced above the discontinuity for at least thedevelopment length of the largest longitudinalbar in the column Where the column issupported on a wall this reinforcement shall beprovided over the full height of the column itshall also be provided below the discontinuityfor the same development length
745 Special confining reinforcement shall beprovided over the full height of a column whichhas significant variation in stiffness alongits height This variation in stiffness may result
FIG 8 C ALCULATION OF DESIGN SHEAR
FORCE FOR COLUMN
832019 Indian STANDARDS 13920-1993 Code of Practice
due to the presence of bracing a mezzaninefloor or a RCC wall on either side of the
column that extends only over a part of thecolumn height ( see Fig 12 )
746 The spacing of hoops used as specialconfining reinforcement shall not exceed 14 of minimum member dimension but need not beless than 75 mm nor more than 100 mm
747 The area of cross section Ash of the barforming circular hoops or spiral to be used asspecial confining reinforcement shall not beless than
where
Example Consider a column of diameter 300mm Let the grade of concrete be M20 and thatof steel Fe 415 for longitudinal and confiningreinforcement The spacing of circular hoops Sshall not exceed the smaller of (a) 14 of minimum member dimension = 14 times 300 =75 mm and (b) 100 mm Therefore S = 75 mm Assuming 40 mm clear cover to thelongitudinal reinforcement and circular hoopsof diameter 8 mm Dk = 300 ndash 2 times 40 + 2 times 8 =236 mm Thus the area of cross section of thebar forming circular hoop works out to be4728 mm2 This is less than the cross sectionalarea of 8 mm bar (5027 mm2) Thus circularhoops of diameter 8 mm at a spacing of 75 mmcentre to centre will be adequate
748 The area of cross section Ash of the barforming rectangular hoop to be used as specialconfining reinforcement shall not be less than
where
FIG 11 SPECIAL CONFINING REINFORCEMENT REQUIREMENT FOR COLUMNS UNDER DISCONTINUED W ALLS
Ash = area of the bar cross section
S = pitch of spiral or spacing of hoops
Dk = diameter of core measured to theoutside of the spiral or hoop
f ck = characteristic compressive strength of concrete cube
f y = yield stress of steel (of circular hoop orspiral)
Ag = gross area of the column cross sectionand
Ash 009 SDk
f ck
f y-------
Ag
Ak
------- 10ndash=
Ak = area of the concrete core =
h = longer dimension of the rectangularconfining hoop measured to its outer
π4--- D
2
k
Ash 018 Sh
f ck
f y-------
Ag
Ak
------- 10ndash=
832019 Indian STANDARDS 13920-1993 Code of Practice
NOTE The dimension lsquohrsquo of the hoop could be reducedby introducing crossties as shown in Fig 7B In thiscase Ak shall be measured as the overall core arearegardless of the hoop arrangement The hooks of crossties shall engage peripheral longitudinal bars
Example Consider a column of 650 mm times500 mm Let the grade of concrete be M20 andthat of steel Fe 415 for the longitudinal andconfining reinforcement Assuming clear coverof 40 mm to the longitudinal reinforcement andrectangular hoops of diameter 10 mm the sizeof the core is 590 mm times 440 mm As both thesedimensions are greater than 300 mm either a
pair of overlapping hoops or a single hoop withcrossties in both directions will have to beprovided Thus the dimension lsquohrsquo will be thelarger of (i) 5902 = 295 mm and (ii) 4402 =220 mm The spacing of hoops S shall notexceed the smaller of (a) 14 of minimum
member dimensions = 14 times 500 = 125 mm and(b) 100 mm Thus S = 100 mm The area of cross section of the bar forming rectangularhoop works out to be 6447 mm2 This is lessthan the area of cross section of 10 mm bar(7854 mm2) Thus 10 mm diameterrectangular hoops at 100 mm cc will beadequate Similar calculations indicate that asan alternative one could also provide 8 mmdiameter rectangular hoops at 70 mm cc
8 JOINTS OF FRAMES
81 The special confining reinforcement asrequired at the end of column shall be provided
FIG 12 COLUMNS WITH V ARYING STIFFNESS
face It shall not exceed 300 mm ( seeFig 7 ) and
Ak = area of confined concrete core in therectangular hoop measured to itsoutside dimensions
832019 Indian STANDARDS 13920-1993 Code of Practice
through the joint as well unless the joint isconfined as specified by 82
82 A joint which has beams framing into all vertical faces of it and where each beam widthis at least 34 of the column width may be
provided with half the special confiningreinforcement required at the end of thecolumn The spacing of hoops shall not exceed150 mm
9 SHEAR WALLS
91 General Requirements
911 The requirements of this section apply tothe shear walls which are part of the lateralforce resisting system of the structure
912 The thickness of any part of the wall shallpreferably not be less than 150 mm
913 The effective flange width to be used inthe design of flanged wall sections shall beassumed to extend beyond the face of the webfor a distance which shall be the smaller of (a)half the distance to an adjacent shear wall weband (b) 110 th of the total wall height
914 Shear walls shall be provided withreinforcement in the longitudinal andtransverse directions in the plane of the wallThe minimum reinforcement ratio shall be0002 5 of the gross area in each direction Thisreinforcement shall be distributed uniformlyacross the cross section of the wall
915 If the factored shear stress in the wallexceeds 025 or if the wall thicknessexceeds 200 mm reinforcement shall beprovided in two curtains each having barsrunning in the longitudinal and transversedirections in the plane of the wall
916 The diameter of the bars to be used in anypart of the wall shall not exceed 110th of thethickness of that part
917 The maximum spacing of reinforcementin either direction shall not exceed the smallerof lw 5 3tw and 450 mm where lw is thehorizontal length of the wall and tw is the
thickness of the wall web92 Shear Strength
921 The nominal shear stress τ v shall becalculated as
where
922 The design shear strength of concrete τcshall be calculated as per Table 13 of IS 456 1978
923 The nominal shear stress in the wall τ vshall not exceed τc max as per Table 14 of
IS 456 1978924 When τ v is less than τc shearreinforcement shall be provided in accordancewith 914 915 and 917
925 When τ v is greater than τc the area of horizontal shear reinforcement Ah to beprovided within a vertical spacing S v is givenby
where V us = ( V u ndash τc tw dw ) is the shear force
to be resisted by the horizontal reinforcementHowever the amount of horizontalreinforcement provided shall not be less thanthe minimum as per 914
926 The vertical reinforcement that isuniformly distributed in the wall shall not beless than the horizontal reinforcementcalculated as per 925
93 Flexural Strength
931 The moment of resistance M uv of thewall section may be calculated as for columnssubjected to combined bending and axial load
as per IS 456 1978 The moment of resistanceof slender rectangular shear wall section withuniformly distributed vertical reinforcement isgiven in Annex A
932 The cracked flexural strength of the wallsection should be greater than its uncrackedflexural strength
933 In walls that do not have boundaryelements vertical reieforcement shall beconcentrated at the ends of the wall Eachconcentration shall consist of a minimum of 4 bars of 12 mm diameter arranged in at least
2 layers94 Boundary Elements
Boundary elements are portions along the walledges that are strengthened by longitudinaland transverse reinforcement Though theymay have the same thickness as that of thewall web it is advantageous to provide themwith greater thickness
941 Where the extreme fibre compressivestress in the wall due to factored gravity loadsplus factored earthquake force exceeds 02 f ckboundaty elements shall be provided along the
vertical boundaries of walls The boundary
V u = factored shear force
tw = thickness of the web and
dw = effective depth of wall section Thismay by taken as 08 lw for rectangular
sections
f ck
V us
087 f y Ah dw
S v
------------------------------------=
832019 Indian STANDARDS 13920-1993 Code of Practice
elements may be discontinued where thecalculated compressive stress becomes lessthan 015 f ck The compressive stress shall becalculated using a linearly elastic model andgross section properties
942 A boundary element shall have adequateaxial load carrying capacity assuming shortcolumn action so as to enable it to carry anaxial compression equal to the sum of factoredgravity load on it and the additionalcompressive load induced by the seismic forceThe latter may be calculated as
where
943 If the gravity load adds to the strength of the wall its load factor shall be taken as 08
944 The percentage of vertical reinforcementin the boundary elements shall not be less than08 percent nor greater than 6 percent Inorder to avoid congestion the practical upper
limit would be 4 percent945 Boundary elements where required asper 941 shall be provided throughout theirheight with special confining reinforcement asper 74
946 Boundary elements need not be providedif the entire wall section is provided withspecial confining reinforcement as per 74
95 Coupled Shear Walls
951 Coupled shear walls shall be connected byductile coupling beams If the earthquakeinduced shear stress in the coupling beam
exceeds
where ls is the clear span of the coupling beamand D is its overall depth the entireearthquake induced shear and flexure shallpreferably be resisted by diagonalreinforcement
952 The area of reinforcement to be providedalong each diagonal in a diagonally reinforcedcoupling beam shall be
where V u is the factored shear force and α isthe angle made by the diagonal reinforcementwith the horizontal At least 4 bars of 8 mmdiameter shall be provided along each diagonalThe reinforcement along each diagonal shall be
enclosed by special confining reinforcement asper 74 The pitch of spiral or spacing of tiesshall not exceed 100 mm
953 The diagonal or horizontal bars of acoupling beam shall be anchored in theadjacent walls with an anchorage length of 15times the development length in tension
96 Openings in Walls
961 The shear strength of a wall withopenings should be checked along criticalplanes that pass through openings
962 Reinforcement shall be provided along the
edges of openings in walls The area of the vertical and horizontal bars should be such asto equal that of the respective interrupted barsThe vertical bars should extend for the fullstorey height The horizontal bars should beprovided with development length in tensionbeyond the sides of the opening
97 Discontinuous Walls
Columns supporting discontinuous walls shallbe provided with special confiningreinforcement as per 744
98 Construction Joints
The vertical reinforcement ratio across ahorizontal construction joint shall not be lessthan
where τ v is the factored shear stress at the joint Pu is the factored axial force (positive forcompression) and Ag is the gross crosssectional area of the joint
99 Development Splice and AnchorageRequirement
991 Horizontal reinforcement shall beanchored near the edges of the wall or in theconfined core of the boundary elements
992 Splicing of vertical flexural reinforcementshould be avoided as far as possible in regionswhere yielding may take place This zone of flexural yielding may be considered to extendfor a distance of lw above the base of the wall orone sixth of the wall height whichever is moreHowever this distance need not be greaterthan 2 lw Not more than one third of this vertical reinforcement shall be spliced at such asection Splices in adjacent bars should be
staggered by a minimum of 600 mm
M u = factored design moment on the entirewall section
M uv = moment of resistance provided bydistributed vertical reinforcementacross the wall section and
Cw = center to center distance between theboundary elements along the two vertical edges of the wall
M u M uvndash
Cw
--------------------------
832019 Indian STANDARDS 13920-1993 Code of Practice
993 Lateral ties shall be provided aroundlapped spliced bars that are larger than 16 mmin diameter The diameter of the tie shall not beless than one fourth that of the spliced bar norless than 6 mm The spacing of ties shall not
exceed 150 mm center to center
994 Welded splices and mechanicalconnections shall confirm to 25252 of IS 456 1978 However not more than half thereinforcement shall be spliced at a sectionwhere flexural yielding may take place
ANNEX A
( Clause 931 )
MOMENT OF RESISTANCE OF RECTANGULAR SHEAR WALL SECTION
A-1 The moment of resistance of a slender rectangular shear wall section with uniformlydistributed vertical reinforcement may be estimated as follows
These equations were derived assuming a rectangular wall section of depth lw and thickness twthat is subjected to combined uni-axial bending and axial compression The vertical reinforcementis represented by an equivalent steel plate along the length of the section The stress-strain curveassumed for concrete is as per IS 456 1978 whereas that for steel is assumed to be bi-linear Twoequations are given for calculating the flexural strength of the section Their use depends on
whether the section fails in flexural tension or in flexural compression
(a) For
where
ρ = vertical reinforcement ratio = Ast ( tw lw )
Ast = area of uniformly distributed vertical reinforcement
β = 087 f y (0003 5 Es)
Es = elastic modulus of steel and
Pu = axial compression on wall
(b) For
where
The value of xu lw to be used in this equation should be calculated from the quadratic equation
where
xu lwlt xu lw
xu lw lt xu lwlt 10
832019 Indian STANDARDS 13920-1993 Code of Practice
BIS is a statutory institution established under the Bureau of Indian Standards Act 1986 to promoteharmonious development of the activities of standardization marking and quality certification of goods andattending to connected matters in the country
Copyright
BIS has the copyright of all its publications No part of these publications may be reproduced in any formwithout the prior permission in writing of BIS This does not preclude the free use in the course of implementing the standard of necessary details such as symbols and sizes type or grade designationsEnquiries relating to copyright be addressed to the Director (Publications) BIS
Review of Indian Standards
Amendments are issued to standards as the need arises on the basis of comments Standards are alsoreviewed periodically a standard along with amendments is reaffirmed when such review indicates that nochanges are needed if the review indicates that changes are needed it is taken up for revision Users of Indian Standards should ascertain that they are in possession of the latest amendments or edition byreferring to the latest issue of lsquoBIS Cataloguersquo and lsquoStandards Monthly Additionsrsquo
This Indian Standard has been developed from Doc No CED 39 (5263)
Amendments Issued Since Publication
Amend No Date of Issue
Amd No 1 November 1995
Amd No 2 March 2002
BUREAU OF INDIAN STANDARDS
Headquarters
Manak Bhavan 9 Bahadur Shah Zafar Marg New Delhi 110002Telephones 323 01 31 323 33 75 323 94 02
Telegrams Manaksanstha(Common to all offices)
Regional Offices Telephone
Central Manak Bhavan 9 Bahadur Shah Zafar MargNEW DELHI 110002
323 76 17323 38 41
Eastern 114 C I T Scheme VII M V I P Road KankurgachiKOLKATA 700054
These requirements apply to frame membersresisting earthquake induced forces and
designed to resist flexure These members shallsatisfy the following requirements
611 The factored axial stress on the memberunder earthquake loading shall not exceed01 f ck
612 The member shall preferably have awidth-to-depth ratio of more than 03
613 The width of the member shall not be lessthan 200 mm
614 The depth D of the member shall
preferably be not more than 14 of the clearspan
62 Longitudinal Reinforcement
622 The maximum steel ratio on any face atany section shall not exceed ρmax = 0025
623 The positive steel at a joint face must beat least equal to half the negative steel at thatface
624 The steel provided at each of the top andbottom face of the member at any section alongits length shall be at least equal to one-fourth of the maximum negative moment steel providedat the face of either joint It may be clarifiedthat redistribution of moments permitted inIS 456 1978 (clause 361) will be used only for vertical load moments and not for lateral loadmoments
625 In an external joint both the top and thebottom bars of the beam shall be provided withanchorage length beyond the inner face of thecolumn equal to the development length intension plus 10 times the bar diameter minusthe allowance for 90 degree bend(s) ( seeFig 1 ) In an internal joint both face bars of the beam shall be taken continuously through
the column
626 The longitudinal bars shall be splicedonly if hoops are provided over the entire splicelength at a spacing not exceeding 150 mm ( seeFig 2 ) The lap length shall not be less thanthe bar development length in tension Lapsplices shall not be provided (a) within a joint(b) within a distance of 2d from joint face and(c) within a quarter lengh of the member whereflexural yielding may generally occur under theeffect of earthquake forces Not more than50 percent of the bars shall be spliced at onesection
627 Use of welded splices and mechanicalconnections may also be made as per 25252of IS 456 1978 However not more than half the reinforcement shall be spliced at a sectionwhere flexural yielding may take place Thelocation of splices shall be governed by 626
63 Web Reinforcement
631 Web reinforcement shall consist of vertical hoops A vertical hoop is a closedstirrup having a 135deg hook with a 10 diameter
extension (but not lt 75 mm) at each end that is
621 a) The top as well as bottomreinforcement shall consist of at leasttwo bars throughout the memberlength
b) The tension steel ratio on any face atany section shall not be less than
ρmin = 024 where f ck and f y
are in MPa
f ck f y frasl
FIG 1 ANCHORAGE OF BEAM B ARS IN AN
E XTERNAL JOINT
FIG 2 L AP SPLICE IN BEAM
832019 Indian STANDARDS 13920-1993 Code of Practice
embedded in the confined core ( see Fig 3a ) Incompelling circumstances it may also be madeup of two pieces of reinforcement a U-stirrupwith a 135deg hook and a 10 diameter extension(but not lt 75 mm) at each end embedded in the
confined core and a crosstie ( see Fig 3b ) Acrosstie is a bar having a 135deg hook with a 10diameter extension (but not lt 75 mm) at eachend The hooks shall engage peripherallongitudinal bars
632 The minimum diameter of the barforming a hoop shall be 6 mm However in
beams with clear span exceeding 5 m theminimum bar diameter shall be 8 mm
633 The shear force to be resisted by the vertical hoops shall be the maximum of
a) calculated factored shear force as peranalysis and
b) shear force due to formation of plastichinges at both ends of the beam plus thefactored gravity load on the span This isgiven by ( see Fig 4 )
where and are the sagging and hogging moments of resistance of
the beam section at ends A and B respectively These are to be calculated as per IS 456 1978
L AB is clear span of beam and are the shears at ends A and B respectively due to vertical loads with a partial safety factor of 12 on loads The design shear at end A shall be thelarger of the two values of V ua computed above Similarly the design shear at end B shall be the
larger of the two values of V ub computed above
i) for sway to right
and and
ii) for sway to left
and
FIG 3 BEAM WEB REINFORCEMENT
M u lim As
M u lim Ah
M u limBs
M u limBh
VD L+a V
D L+b
832019 Indian STANDARDS 13920-1993 Code of Practice
634 The contribution of bent up bars andinclined hoops to shear resistance of the sectionshall not be considered
635 The spacing of hoops over a length of 2d ateither end of a beam shall not exceed (a) d4and (b) 8 times the diameter of the smallestlongitudinal bar however it need not be lessthan 100 mm ( see Fig 5 ) The first hoop shallbe at a distance not exceeding 50 mm from the joint face Vertical hoops at the same spacing asabove shall also be provided over a lengthequal to 2d on either side of a section where
flexural yielding may occur under the effect of earthquake forces Elsewhere the beam shallhave vertical hoops at a spacing not exceedingd2
7 COLUMNS AND FRAME MEMBERSSUBJECTED TO BENDING AND AXIALLOAD
71 General
711 These requirements apply to framemembers which have a factored axial stress inexcess of 01 f ck under the effect of earthquakeforces
712 The minimum dimension of the membershall not be less than 200 mm However inframes which have beams with centre to centrespan exceeding 5 m or columns of unsupportedlength exceeding 4 m the shortest dimension of the column shall not be less than 300 mm
713 The ratio of the shortest cross sectionaldimension to the perpendicular dimension shallpreferably not be less than 04
72 Longitudinal Reinforcement
721 Lap splices shall be provided only in the
central half of the member length It should beproportioned as a tension splice Hoops shall beprovided over the entire splice length atspacing not exceeding 150 mm centre to centreNot more than 50 percent of the bars shall bespliced at one section
722 Any area of a column that extends morethan 100 mm beyond the confined core due toarchitectural requirements shall be detailed inthe following manner In case the contributionof this area to strength has been consideredthen it will have the minimum longitudinal andtransverse reinforcement as per this code
FIG 4 C ALCULATION OF DESIGN SHEAR FORCE FOR BEAM
832019 Indian STANDARDS 13920-1993 Code of Practice
However if this area has been treated asnon-structural the minimum reinforcementrequirements shall be governed byIS 456 1978 provisions minimum longitudinaland transverse reinforcement as perIS 456 1978 ( see Fig 6 )
73 Transverse Reinforcement
731 Transverse reinforcement for circularcolumns shall consist of spiral or circular hoopsIn rectangular columns rectangular hoops maybe used A rectangular hoop is a closed stirruphaving a 135deg hook with a 10 diameterextension (but not lt 75 mm) at each end that isembedded in the confined core ( see Fig 7A )
732 The parallel legs of rectangular hoop shallbe spaced not more than 300 mm centre tocentre If the length of any side of the hoopexceeds 300 mm a crosstie shall be provided(Fig 7B) Alternatively a pair of overlappinghoops may be provided within the columm ( seeFig 7C) The hooks shall engage peripheral
longitudinal bars733 The spacing of hoops shall not exceed half the least lateral dimension of the columnexcept where special confining reinforcement isprovided as per 74
734 The design shear force for columns shallbe the maximum of
a) calculated factored shear force as peranalysis and
b) a factored shear force given by
V u = 14
where and are moment of
resistance of opposite sign of beams framinginto the column from opposite faces ( seeFig 8 ) and hst is the storey height The beam
moment capacity is to be calculated as perIS 456 1978
74 Special Confining Reinforcement
This requirement shall be met with unless alarger amount of transverse reinforcement isrequired from shear strength considerations
FIG 5 BEAM REINFORCEMENT
FIG 6 REINFORCEMENT REQUIREMENT FOR COLUMN WITH MORE THAN 100 mm
PROJECTION BEYOND CORE
M bLu lim M
bRu lim+
hst
----------------------------------------------
M bLu lim M
bRu lim
832019 Indian STANDARDS 13920-1993 Code of Practice
741 Special confining reinforcement shall beprovided over a length lo from each joint facetowards midspan and on either side of anysection where flexural yielding may occurunder the effect of earthquake forces ( see
Fig 9 ) The length lsquolorsquo shall not be less than(a) larger lateral dimension of the member atthe section where yielding occurs (b) 16 of clear span of the member and (c) 450 mm
742 When a column terminates into a footingor mat special confining reinforcement shallextend at least 300 mm into the footing or mat( see Fig 10 )
743 When the calculated point of contra-flexure under the effect of gravity andearthquake loads is not within the middle half of the member clear height special confiningreinforcement shall be provided over the full
height of the column744 Columns supporting reactions fromdiscontinued stiff members such as walls shallbe provided with special confiningreinforcement over their full height ( seeFig 11 ) This reinforcement shall also beplaced above the discontinuity for at least thedevelopment length of the largest longitudinalbar in the column Where the column issupported on a wall this reinforcement shall beprovided over the full height of the column itshall also be provided below the discontinuityfor the same development length
745 Special confining reinforcement shall beprovided over the full height of a column whichhas significant variation in stiffness alongits height This variation in stiffness may result
FIG 8 C ALCULATION OF DESIGN SHEAR
FORCE FOR COLUMN
832019 Indian STANDARDS 13920-1993 Code of Practice
due to the presence of bracing a mezzaninefloor or a RCC wall on either side of the
column that extends only over a part of thecolumn height ( see Fig 12 )
746 The spacing of hoops used as specialconfining reinforcement shall not exceed 14 of minimum member dimension but need not beless than 75 mm nor more than 100 mm
747 The area of cross section Ash of the barforming circular hoops or spiral to be used asspecial confining reinforcement shall not beless than
where
Example Consider a column of diameter 300mm Let the grade of concrete be M20 and thatof steel Fe 415 for longitudinal and confiningreinforcement The spacing of circular hoops Sshall not exceed the smaller of (a) 14 of minimum member dimension = 14 times 300 =75 mm and (b) 100 mm Therefore S = 75 mm Assuming 40 mm clear cover to thelongitudinal reinforcement and circular hoopsof diameter 8 mm Dk = 300 ndash 2 times 40 + 2 times 8 =236 mm Thus the area of cross section of thebar forming circular hoop works out to be4728 mm2 This is less than the cross sectionalarea of 8 mm bar (5027 mm2) Thus circularhoops of diameter 8 mm at a spacing of 75 mmcentre to centre will be adequate
748 The area of cross section Ash of the barforming rectangular hoop to be used as specialconfining reinforcement shall not be less than
where
FIG 11 SPECIAL CONFINING REINFORCEMENT REQUIREMENT FOR COLUMNS UNDER DISCONTINUED W ALLS
Ash = area of the bar cross section
S = pitch of spiral or spacing of hoops
Dk = diameter of core measured to theoutside of the spiral or hoop
f ck = characteristic compressive strength of concrete cube
f y = yield stress of steel (of circular hoop orspiral)
Ag = gross area of the column cross sectionand
Ash 009 SDk
f ck
f y-------
Ag
Ak
------- 10ndash=
Ak = area of the concrete core =
h = longer dimension of the rectangularconfining hoop measured to its outer
π4--- D
2
k
Ash 018 Sh
f ck
f y-------
Ag
Ak
------- 10ndash=
832019 Indian STANDARDS 13920-1993 Code of Practice
NOTE The dimension lsquohrsquo of the hoop could be reducedby introducing crossties as shown in Fig 7B In thiscase Ak shall be measured as the overall core arearegardless of the hoop arrangement The hooks of crossties shall engage peripheral longitudinal bars
Example Consider a column of 650 mm times500 mm Let the grade of concrete be M20 andthat of steel Fe 415 for the longitudinal andconfining reinforcement Assuming clear coverof 40 mm to the longitudinal reinforcement andrectangular hoops of diameter 10 mm the sizeof the core is 590 mm times 440 mm As both thesedimensions are greater than 300 mm either a
pair of overlapping hoops or a single hoop withcrossties in both directions will have to beprovided Thus the dimension lsquohrsquo will be thelarger of (i) 5902 = 295 mm and (ii) 4402 =220 mm The spacing of hoops S shall notexceed the smaller of (a) 14 of minimum
member dimensions = 14 times 500 = 125 mm and(b) 100 mm Thus S = 100 mm The area of cross section of the bar forming rectangularhoop works out to be 6447 mm2 This is lessthan the area of cross section of 10 mm bar(7854 mm2) Thus 10 mm diameterrectangular hoops at 100 mm cc will beadequate Similar calculations indicate that asan alternative one could also provide 8 mmdiameter rectangular hoops at 70 mm cc
8 JOINTS OF FRAMES
81 The special confining reinforcement asrequired at the end of column shall be provided
FIG 12 COLUMNS WITH V ARYING STIFFNESS
face It shall not exceed 300 mm ( seeFig 7 ) and
Ak = area of confined concrete core in therectangular hoop measured to itsoutside dimensions
832019 Indian STANDARDS 13920-1993 Code of Practice
through the joint as well unless the joint isconfined as specified by 82
82 A joint which has beams framing into all vertical faces of it and where each beam widthis at least 34 of the column width may be
provided with half the special confiningreinforcement required at the end of thecolumn The spacing of hoops shall not exceed150 mm
9 SHEAR WALLS
91 General Requirements
911 The requirements of this section apply tothe shear walls which are part of the lateralforce resisting system of the structure
912 The thickness of any part of the wall shallpreferably not be less than 150 mm
913 The effective flange width to be used inthe design of flanged wall sections shall beassumed to extend beyond the face of the webfor a distance which shall be the smaller of (a)half the distance to an adjacent shear wall weband (b) 110 th of the total wall height
914 Shear walls shall be provided withreinforcement in the longitudinal andtransverse directions in the plane of the wallThe minimum reinforcement ratio shall be0002 5 of the gross area in each direction Thisreinforcement shall be distributed uniformlyacross the cross section of the wall
915 If the factored shear stress in the wallexceeds 025 or if the wall thicknessexceeds 200 mm reinforcement shall beprovided in two curtains each having barsrunning in the longitudinal and transversedirections in the plane of the wall
916 The diameter of the bars to be used in anypart of the wall shall not exceed 110th of thethickness of that part
917 The maximum spacing of reinforcementin either direction shall not exceed the smallerof lw 5 3tw and 450 mm where lw is thehorizontal length of the wall and tw is the
thickness of the wall web92 Shear Strength
921 The nominal shear stress τ v shall becalculated as
where
922 The design shear strength of concrete τcshall be calculated as per Table 13 of IS 456 1978
923 The nominal shear stress in the wall τ vshall not exceed τc max as per Table 14 of
IS 456 1978924 When τ v is less than τc shearreinforcement shall be provided in accordancewith 914 915 and 917
925 When τ v is greater than τc the area of horizontal shear reinforcement Ah to beprovided within a vertical spacing S v is givenby
where V us = ( V u ndash τc tw dw ) is the shear force
to be resisted by the horizontal reinforcementHowever the amount of horizontalreinforcement provided shall not be less thanthe minimum as per 914
926 The vertical reinforcement that isuniformly distributed in the wall shall not beless than the horizontal reinforcementcalculated as per 925
93 Flexural Strength
931 The moment of resistance M uv of thewall section may be calculated as for columnssubjected to combined bending and axial load
as per IS 456 1978 The moment of resistanceof slender rectangular shear wall section withuniformly distributed vertical reinforcement isgiven in Annex A
932 The cracked flexural strength of the wallsection should be greater than its uncrackedflexural strength
933 In walls that do not have boundaryelements vertical reieforcement shall beconcentrated at the ends of the wall Eachconcentration shall consist of a minimum of 4 bars of 12 mm diameter arranged in at least
2 layers94 Boundary Elements
Boundary elements are portions along the walledges that are strengthened by longitudinaland transverse reinforcement Though theymay have the same thickness as that of thewall web it is advantageous to provide themwith greater thickness
941 Where the extreme fibre compressivestress in the wall due to factored gravity loadsplus factored earthquake force exceeds 02 f ckboundaty elements shall be provided along the
vertical boundaries of walls The boundary
V u = factored shear force
tw = thickness of the web and
dw = effective depth of wall section Thismay by taken as 08 lw for rectangular
sections
f ck
V us
087 f y Ah dw
S v
------------------------------------=
832019 Indian STANDARDS 13920-1993 Code of Practice
elements may be discontinued where thecalculated compressive stress becomes lessthan 015 f ck The compressive stress shall becalculated using a linearly elastic model andgross section properties
942 A boundary element shall have adequateaxial load carrying capacity assuming shortcolumn action so as to enable it to carry anaxial compression equal to the sum of factoredgravity load on it and the additionalcompressive load induced by the seismic forceThe latter may be calculated as
where
943 If the gravity load adds to the strength of the wall its load factor shall be taken as 08
944 The percentage of vertical reinforcementin the boundary elements shall not be less than08 percent nor greater than 6 percent Inorder to avoid congestion the practical upper
limit would be 4 percent945 Boundary elements where required asper 941 shall be provided throughout theirheight with special confining reinforcement asper 74
946 Boundary elements need not be providedif the entire wall section is provided withspecial confining reinforcement as per 74
95 Coupled Shear Walls
951 Coupled shear walls shall be connected byductile coupling beams If the earthquakeinduced shear stress in the coupling beam
exceeds
where ls is the clear span of the coupling beamand D is its overall depth the entireearthquake induced shear and flexure shallpreferably be resisted by diagonalreinforcement
952 The area of reinforcement to be providedalong each diagonal in a diagonally reinforcedcoupling beam shall be
where V u is the factored shear force and α isthe angle made by the diagonal reinforcementwith the horizontal At least 4 bars of 8 mmdiameter shall be provided along each diagonalThe reinforcement along each diagonal shall be
enclosed by special confining reinforcement asper 74 The pitch of spiral or spacing of tiesshall not exceed 100 mm
953 The diagonal or horizontal bars of acoupling beam shall be anchored in theadjacent walls with an anchorage length of 15times the development length in tension
96 Openings in Walls
961 The shear strength of a wall withopenings should be checked along criticalplanes that pass through openings
962 Reinforcement shall be provided along the
edges of openings in walls The area of the vertical and horizontal bars should be such asto equal that of the respective interrupted barsThe vertical bars should extend for the fullstorey height The horizontal bars should beprovided with development length in tensionbeyond the sides of the opening
97 Discontinuous Walls
Columns supporting discontinuous walls shallbe provided with special confiningreinforcement as per 744
98 Construction Joints
The vertical reinforcement ratio across ahorizontal construction joint shall not be lessthan
where τ v is the factored shear stress at the joint Pu is the factored axial force (positive forcompression) and Ag is the gross crosssectional area of the joint
99 Development Splice and AnchorageRequirement
991 Horizontal reinforcement shall beanchored near the edges of the wall or in theconfined core of the boundary elements
992 Splicing of vertical flexural reinforcementshould be avoided as far as possible in regionswhere yielding may take place This zone of flexural yielding may be considered to extendfor a distance of lw above the base of the wall orone sixth of the wall height whichever is moreHowever this distance need not be greaterthan 2 lw Not more than one third of this vertical reinforcement shall be spliced at such asection Splices in adjacent bars should be
staggered by a minimum of 600 mm
M u = factored design moment on the entirewall section
M uv = moment of resistance provided bydistributed vertical reinforcementacross the wall section and
Cw = center to center distance between theboundary elements along the two vertical edges of the wall
M u M uvndash
Cw
--------------------------
832019 Indian STANDARDS 13920-1993 Code of Practice
993 Lateral ties shall be provided aroundlapped spliced bars that are larger than 16 mmin diameter The diameter of the tie shall not beless than one fourth that of the spliced bar norless than 6 mm The spacing of ties shall not
exceed 150 mm center to center
994 Welded splices and mechanicalconnections shall confirm to 25252 of IS 456 1978 However not more than half thereinforcement shall be spliced at a sectionwhere flexural yielding may take place
ANNEX A
( Clause 931 )
MOMENT OF RESISTANCE OF RECTANGULAR SHEAR WALL SECTION
A-1 The moment of resistance of a slender rectangular shear wall section with uniformlydistributed vertical reinforcement may be estimated as follows
These equations were derived assuming a rectangular wall section of depth lw and thickness twthat is subjected to combined uni-axial bending and axial compression The vertical reinforcementis represented by an equivalent steel plate along the length of the section The stress-strain curveassumed for concrete is as per IS 456 1978 whereas that for steel is assumed to be bi-linear Twoequations are given for calculating the flexural strength of the section Their use depends on
whether the section fails in flexural tension or in flexural compression
(a) For
where
ρ = vertical reinforcement ratio = Ast ( tw lw )
Ast = area of uniformly distributed vertical reinforcement
β = 087 f y (0003 5 Es)
Es = elastic modulus of steel and
Pu = axial compression on wall
(b) For
where
The value of xu lw to be used in this equation should be calculated from the quadratic equation
where
xu lwlt xu lw
xu lw lt xu lwlt 10
832019 Indian STANDARDS 13920-1993 Code of Practice
BIS is a statutory institution established under the Bureau of Indian Standards Act 1986 to promoteharmonious development of the activities of standardization marking and quality certification of goods andattending to connected matters in the country
Copyright
BIS has the copyright of all its publications No part of these publications may be reproduced in any formwithout the prior permission in writing of BIS This does not preclude the free use in the course of implementing the standard of necessary details such as symbols and sizes type or grade designationsEnquiries relating to copyright be addressed to the Director (Publications) BIS
Review of Indian Standards
Amendments are issued to standards as the need arises on the basis of comments Standards are alsoreviewed periodically a standard along with amendments is reaffirmed when such review indicates that nochanges are needed if the review indicates that changes are needed it is taken up for revision Users of Indian Standards should ascertain that they are in possession of the latest amendments or edition byreferring to the latest issue of lsquoBIS Cataloguersquo and lsquoStandards Monthly Additionsrsquo
This Indian Standard has been developed from Doc No CED 39 (5263)
Amendments Issued Since Publication
Amend No Date of Issue
Amd No 1 November 1995
Amd No 2 March 2002
BUREAU OF INDIAN STANDARDS
Headquarters
Manak Bhavan 9 Bahadur Shah Zafar Marg New Delhi 110002Telephones 323 01 31 323 33 75 323 94 02
Telegrams Manaksanstha(Common to all offices)
Regional Offices Telephone
Central Manak Bhavan 9 Bahadur Shah Zafar MargNEW DELHI 110002
323 76 17323 38 41
Eastern 114 C I T Scheme VII M V I P Road KankurgachiKOLKATA 700054
embedded in the confined core ( see Fig 3a ) Incompelling circumstances it may also be madeup of two pieces of reinforcement a U-stirrupwith a 135deg hook and a 10 diameter extension(but not lt 75 mm) at each end embedded in the
confined core and a crosstie ( see Fig 3b ) Acrosstie is a bar having a 135deg hook with a 10diameter extension (but not lt 75 mm) at eachend The hooks shall engage peripherallongitudinal bars
632 The minimum diameter of the barforming a hoop shall be 6 mm However in
beams with clear span exceeding 5 m theminimum bar diameter shall be 8 mm
633 The shear force to be resisted by the vertical hoops shall be the maximum of
a) calculated factored shear force as peranalysis and
b) shear force due to formation of plastichinges at both ends of the beam plus thefactored gravity load on the span This isgiven by ( see Fig 4 )
where and are the sagging and hogging moments of resistance of
the beam section at ends A and B respectively These are to be calculated as per IS 456 1978
L AB is clear span of beam and are the shears at ends A and B respectively due to vertical loads with a partial safety factor of 12 on loads The design shear at end A shall be thelarger of the two values of V ua computed above Similarly the design shear at end B shall be the
larger of the two values of V ub computed above
i) for sway to right
and and
ii) for sway to left
and
FIG 3 BEAM WEB REINFORCEMENT
M u lim As
M u lim Ah
M u limBs
M u limBh
VD L+a V
D L+b
832019 Indian STANDARDS 13920-1993 Code of Practice
634 The contribution of bent up bars andinclined hoops to shear resistance of the sectionshall not be considered
635 The spacing of hoops over a length of 2d ateither end of a beam shall not exceed (a) d4and (b) 8 times the diameter of the smallestlongitudinal bar however it need not be lessthan 100 mm ( see Fig 5 ) The first hoop shallbe at a distance not exceeding 50 mm from the joint face Vertical hoops at the same spacing asabove shall also be provided over a lengthequal to 2d on either side of a section where
flexural yielding may occur under the effect of earthquake forces Elsewhere the beam shallhave vertical hoops at a spacing not exceedingd2
7 COLUMNS AND FRAME MEMBERSSUBJECTED TO BENDING AND AXIALLOAD
71 General
711 These requirements apply to framemembers which have a factored axial stress inexcess of 01 f ck under the effect of earthquakeforces
712 The minimum dimension of the membershall not be less than 200 mm However inframes which have beams with centre to centrespan exceeding 5 m or columns of unsupportedlength exceeding 4 m the shortest dimension of the column shall not be less than 300 mm
713 The ratio of the shortest cross sectionaldimension to the perpendicular dimension shallpreferably not be less than 04
72 Longitudinal Reinforcement
721 Lap splices shall be provided only in the
central half of the member length It should beproportioned as a tension splice Hoops shall beprovided over the entire splice length atspacing not exceeding 150 mm centre to centreNot more than 50 percent of the bars shall bespliced at one section
722 Any area of a column that extends morethan 100 mm beyond the confined core due toarchitectural requirements shall be detailed inthe following manner In case the contributionof this area to strength has been consideredthen it will have the minimum longitudinal andtransverse reinforcement as per this code
FIG 4 C ALCULATION OF DESIGN SHEAR FORCE FOR BEAM
832019 Indian STANDARDS 13920-1993 Code of Practice
However if this area has been treated asnon-structural the minimum reinforcementrequirements shall be governed byIS 456 1978 provisions minimum longitudinaland transverse reinforcement as perIS 456 1978 ( see Fig 6 )
73 Transverse Reinforcement
731 Transverse reinforcement for circularcolumns shall consist of spiral or circular hoopsIn rectangular columns rectangular hoops maybe used A rectangular hoop is a closed stirruphaving a 135deg hook with a 10 diameterextension (but not lt 75 mm) at each end that isembedded in the confined core ( see Fig 7A )
732 The parallel legs of rectangular hoop shallbe spaced not more than 300 mm centre tocentre If the length of any side of the hoopexceeds 300 mm a crosstie shall be provided(Fig 7B) Alternatively a pair of overlappinghoops may be provided within the columm ( seeFig 7C) The hooks shall engage peripheral
longitudinal bars733 The spacing of hoops shall not exceed half the least lateral dimension of the columnexcept where special confining reinforcement isprovided as per 74
734 The design shear force for columns shallbe the maximum of
a) calculated factored shear force as peranalysis and
b) a factored shear force given by
V u = 14
where and are moment of
resistance of opposite sign of beams framinginto the column from opposite faces ( seeFig 8 ) and hst is the storey height The beam
moment capacity is to be calculated as perIS 456 1978
74 Special Confining Reinforcement
This requirement shall be met with unless alarger amount of transverse reinforcement isrequired from shear strength considerations
FIG 5 BEAM REINFORCEMENT
FIG 6 REINFORCEMENT REQUIREMENT FOR COLUMN WITH MORE THAN 100 mm
PROJECTION BEYOND CORE
M bLu lim M
bRu lim+
hst
----------------------------------------------
M bLu lim M
bRu lim
832019 Indian STANDARDS 13920-1993 Code of Practice
741 Special confining reinforcement shall beprovided over a length lo from each joint facetowards midspan and on either side of anysection where flexural yielding may occurunder the effect of earthquake forces ( see
Fig 9 ) The length lsquolorsquo shall not be less than(a) larger lateral dimension of the member atthe section where yielding occurs (b) 16 of clear span of the member and (c) 450 mm
742 When a column terminates into a footingor mat special confining reinforcement shallextend at least 300 mm into the footing or mat( see Fig 10 )
743 When the calculated point of contra-flexure under the effect of gravity andearthquake loads is not within the middle half of the member clear height special confiningreinforcement shall be provided over the full
height of the column744 Columns supporting reactions fromdiscontinued stiff members such as walls shallbe provided with special confiningreinforcement over their full height ( seeFig 11 ) This reinforcement shall also beplaced above the discontinuity for at least thedevelopment length of the largest longitudinalbar in the column Where the column issupported on a wall this reinforcement shall beprovided over the full height of the column itshall also be provided below the discontinuityfor the same development length
745 Special confining reinforcement shall beprovided over the full height of a column whichhas significant variation in stiffness alongits height This variation in stiffness may result
FIG 8 C ALCULATION OF DESIGN SHEAR
FORCE FOR COLUMN
832019 Indian STANDARDS 13920-1993 Code of Practice
due to the presence of bracing a mezzaninefloor or a RCC wall on either side of the
column that extends only over a part of thecolumn height ( see Fig 12 )
746 The spacing of hoops used as specialconfining reinforcement shall not exceed 14 of minimum member dimension but need not beless than 75 mm nor more than 100 mm
747 The area of cross section Ash of the barforming circular hoops or spiral to be used asspecial confining reinforcement shall not beless than
where
Example Consider a column of diameter 300mm Let the grade of concrete be M20 and thatof steel Fe 415 for longitudinal and confiningreinforcement The spacing of circular hoops Sshall not exceed the smaller of (a) 14 of minimum member dimension = 14 times 300 =75 mm and (b) 100 mm Therefore S = 75 mm Assuming 40 mm clear cover to thelongitudinal reinforcement and circular hoopsof diameter 8 mm Dk = 300 ndash 2 times 40 + 2 times 8 =236 mm Thus the area of cross section of thebar forming circular hoop works out to be4728 mm2 This is less than the cross sectionalarea of 8 mm bar (5027 mm2) Thus circularhoops of diameter 8 mm at a spacing of 75 mmcentre to centre will be adequate
748 The area of cross section Ash of the barforming rectangular hoop to be used as specialconfining reinforcement shall not be less than
where
FIG 11 SPECIAL CONFINING REINFORCEMENT REQUIREMENT FOR COLUMNS UNDER DISCONTINUED W ALLS
Ash = area of the bar cross section
S = pitch of spiral or spacing of hoops
Dk = diameter of core measured to theoutside of the spiral or hoop
f ck = characteristic compressive strength of concrete cube
f y = yield stress of steel (of circular hoop orspiral)
Ag = gross area of the column cross sectionand
Ash 009 SDk
f ck
f y-------
Ag
Ak
------- 10ndash=
Ak = area of the concrete core =
h = longer dimension of the rectangularconfining hoop measured to its outer
π4--- D
2
k
Ash 018 Sh
f ck
f y-------
Ag
Ak
------- 10ndash=
832019 Indian STANDARDS 13920-1993 Code of Practice
NOTE The dimension lsquohrsquo of the hoop could be reducedby introducing crossties as shown in Fig 7B In thiscase Ak shall be measured as the overall core arearegardless of the hoop arrangement The hooks of crossties shall engage peripheral longitudinal bars
Example Consider a column of 650 mm times500 mm Let the grade of concrete be M20 andthat of steel Fe 415 for the longitudinal andconfining reinforcement Assuming clear coverof 40 mm to the longitudinal reinforcement andrectangular hoops of diameter 10 mm the sizeof the core is 590 mm times 440 mm As both thesedimensions are greater than 300 mm either a
pair of overlapping hoops or a single hoop withcrossties in both directions will have to beprovided Thus the dimension lsquohrsquo will be thelarger of (i) 5902 = 295 mm and (ii) 4402 =220 mm The spacing of hoops S shall notexceed the smaller of (a) 14 of minimum
member dimensions = 14 times 500 = 125 mm and(b) 100 mm Thus S = 100 mm The area of cross section of the bar forming rectangularhoop works out to be 6447 mm2 This is lessthan the area of cross section of 10 mm bar(7854 mm2) Thus 10 mm diameterrectangular hoops at 100 mm cc will beadequate Similar calculations indicate that asan alternative one could also provide 8 mmdiameter rectangular hoops at 70 mm cc
8 JOINTS OF FRAMES
81 The special confining reinforcement asrequired at the end of column shall be provided
FIG 12 COLUMNS WITH V ARYING STIFFNESS
face It shall not exceed 300 mm ( seeFig 7 ) and
Ak = area of confined concrete core in therectangular hoop measured to itsoutside dimensions
832019 Indian STANDARDS 13920-1993 Code of Practice
through the joint as well unless the joint isconfined as specified by 82
82 A joint which has beams framing into all vertical faces of it and where each beam widthis at least 34 of the column width may be
provided with half the special confiningreinforcement required at the end of thecolumn The spacing of hoops shall not exceed150 mm
9 SHEAR WALLS
91 General Requirements
911 The requirements of this section apply tothe shear walls which are part of the lateralforce resisting system of the structure
912 The thickness of any part of the wall shallpreferably not be less than 150 mm
913 The effective flange width to be used inthe design of flanged wall sections shall beassumed to extend beyond the face of the webfor a distance which shall be the smaller of (a)half the distance to an adjacent shear wall weband (b) 110 th of the total wall height
914 Shear walls shall be provided withreinforcement in the longitudinal andtransverse directions in the plane of the wallThe minimum reinforcement ratio shall be0002 5 of the gross area in each direction Thisreinforcement shall be distributed uniformlyacross the cross section of the wall
915 If the factored shear stress in the wallexceeds 025 or if the wall thicknessexceeds 200 mm reinforcement shall beprovided in two curtains each having barsrunning in the longitudinal and transversedirections in the plane of the wall
916 The diameter of the bars to be used in anypart of the wall shall not exceed 110th of thethickness of that part
917 The maximum spacing of reinforcementin either direction shall not exceed the smallerof lw 5 3tw and 450 mm where lw is thehorizontal length of the wall and tw is the
thickness of the wall web92 Shear Strength
921 The nominal shear stress τ v shall becalculated as
where
922 The design shear strength of concrete τcshall be calculated as per Table 13 of IS 456 1978
923 The nominal shear stress in the wall τ vshall not exceed τc max as per Table 14 of
IS 456 1978924 When τ v is less than τc shearreinforcement shall be provided in accordancewith 914 915 and 917
925 When τ v is greater than τc the area of horizontal shear reinforcement Ah to beprovided within a vertical spacing S v is givenby
where V us = ( V u ndash τc tw dw ) is the shear force
to be resisted by the horizontal reinforcementHowever the amount of horizontalreinforcement provided shall not be less thanthe minimum as per 914
926 The vertical reinforcement that isuniformly distributed in the wall shall not beless than the horizontal reinforcementcalculated as per 925
93 Flexural Strength
931 The moment of resistance M uv of thewall section may be calculated as for columnssubjected to combined bending and axial load
as per IS 456 1978 The moment of resistanceof slender rectangular shear wall section withuniformly distributed vertical reinforcement isgiven in Annex A
932 The cracked flexural strength of the wallsection should be greater than its uncrackedflexural strength
933 In walls that do not have boundaryelements vertical reieforcement shall beconcentrated at the ends of the wall Eachconcentration shall consist of a minimum of 4 bars of 12 mm diameter arranged in at least
2 layers94 Boundary Elements
Boundary elements are portions along the walledges that are strengthened by longitudinaland transverse reinforcement Though theymay have the same thickness as that of thewall web it is advantageous to provide themwith greater thickness
941 Where the extreme fibre compressivestress in the wall due to factored gravity loadsplus factored earthquake force exceeds 02 f ckboundaty elements shall be provided along the
vertical boundaries of walls The boundary
V u = factored shear force
tw = thickness of the web and
dw = effective depth of wall section Thismay by taken as 08 lw for rectangular
sections
f ck
V us
087 f y Ah dw
S v
------------------------------------=
832019 Indian STANDARDS 13920-1993 Code of Practice
elements may be discontinued where thecalculated compressive stress becomes lessthan 015 f ck The compressive stress shall becalculated using a linearly elastic model andgross section properties
942 A boundary element shall have adequateaxial load carrying capacity assuming shortcolumn action so as to enable it to carry anaxial compression equal to the sum of factoredgravity load on it and the additionalcompressive load induced by the seismic forceThe latter may be calculated as
where
943 If the gravity load adds to the strength of the wall its load factor shall be taken as 08
944 The percentage of vertical reinforcementin the boundary elements shall not be less than08 percent nor greater than 6 percent Inorder to avoid congestion the practical upper
limit would be 4 percent945 Boundary elements where required asper 941 shall be provided throughout theirheight with special confining reinforcement asper 74
946 Boundary elements need not be providedif the entire wall section is provided withspecial confining reinforcement as per 74
95 Coupled Shear Walls
951 Coupled shear walls shall be connected byductile coupling beams If the earthquakeinduced shear stress in the coupling beam
exceeds
where ls is the clear span of the coupling beamand D is its overall depth the entireearthquake induced shear and flexure shallpreferably be resisted by diagonalreinforcement
952 The area of reinforcement to be providedalong each diagonal in a diagonally reinforcedcoupling beam shall be
where V u is the factored shear force and α isthe angle made by the diagonal reinforcementwith the horizontal At least 4 bars of 8 mmdiameter shall be provided along each diagonalThe reinforcement along each diagonal shall be
enclosed by special confining reinforcement asper 74 The pitch of spiral or spacing of tiesshall not exceed 100 mm
953 The diagonal or horizontal bars of acoupling beam shall be anchored in theadjacent walls with an anchorage length of 15times the development length in tension
96 Openings in Walls
961 The shear strength of a wall withopenings should be checked along criticalplanes that pass through openings
962 Reinforcement shall be provided along the
edges of openings in walls The area of the vertical and horizontal bars should be such asto equal that of the respective interrupted barsThe vertical bars should extend for the fullstorey height The horizontal bars should beprovided with development length in tensionbeyond the sides of the opening
97 Discontinuous Walls
Columns supporting discontinuous walls shallbe provided with special confiningreinforcement as per 744
98 Construction Joints
The vertical reinforcement ratio across ahorizontal construction joint shall not be lessthan
where τ v is the factored shear stress at the joint Pu is the factored axial force (positive forcompression) and Ag is the gross crosssectional area of the joint
99 Development Splice and AnchorageRequirement
991 Horizontal reinforcement shall beanchored near the edges of the wall or in theconfined core of the boundary elements
992 Splicing of vertical flexural reinforcementshould be avoided as far as possible in regionswhere yielding may take place This zone of flexural yielding may be considered to extendfor a distance of lw above the base of the wall orone sixth of the wall height whichever is moreHowever this distance need not be greaterthan 2 lw Not more than one third of this vertical reinforcement shall be spliced at such asection Splices in adjacent bars should be
staggered by a minimum of 600 mm
M u = factored design moment on the entirewall section
M uv = moment of resistance provided bydistributed vertical reinforcementacross the wall section and
Cw = center to center distance between theboundary elements along the two vertical edges of the wall
M u M uvndash
Cw
--------------------------
832019 Indian STANDARDS 13920-1993 Code of Practice
993 Lateral ties shall be provided aroundlapped spliced bars that are larger than 16 mmin diameter The diameter of the tie shall not beless than one fourth that of the spliced bar norless than 6 mm The spacing of ties shall not
exceed 150 mm center to center
994 Welded splices and mechanicalconnections shall confirm to 25252 of IS 456 1978 However not more than half thereinforcement shall be spliced at a sectionwhere flexural yielding may take place
ANNEX A
( Clause 931 )
MOMENT OF RESISTANCE OF RECTANGULAR SHEAR WALL SECTION
A-1 The moment of resistance of a slender rectangular shear wall section with uniformlydistributed vertical reinforcement may be estimated as follows
These equations were derived assuming a rectangular wall section of depth lw and thickness twthat is subjected to combined uni-axial bending and axial compression The vertical reinforcementis represented by an equivalent steel plate along the length of the section The stress-strain curveassumed for concrete is as per IS 456 1978 whereas that for steel is assumed to be bi-linear Twoequations are given for calculating the flexural strength of the section Their use depends on
whether the section fails in flexural tension or in flexural compression
(a) For
where
ρ = vertical reinforcement ratio = Ast ( tw lw )
Ast = area of uniformly distributed vertical reinforcement
β = 087 f y (0003 5 Es)
Es = elastic modulus of steel and
Pu = axial compression on wall
(b) For
where
The value of xu lw to be used in this equation should be calculated from the quadratic equation
where
xu lwlt xu lw
xu lw lt xu lwlt 10
832019 Indian STANDARDS 13920-1993 Code of Practice
BIS is a statutory institution established under the Bureau of Indian Standards Act 1986 to promoteharmonious development of the activities of standardization marking and quality certification of goods andattending to connected matters in the country
Copyright
BIS has the copyright of all its publications No part of these publications may be reproduced in any formwithout the prior permission in writing of BIS This does not preclude the free use in the course of implementing the standard of necessary details such as symbols and sizes type or grade designationsEnquiries relating to copyright be addressed to the Director (Publications) BIS
Review of Indian Standards
Amendments are issued to standards as the need arises on the basis of comments Standards are alsoreviewed periodically a standard along with amendments is reaffirmed when such review indicates that nochanges are needed if the review indicates that changes are needed it is taken up for revision Users of Indian Standards should ascertain that they are in possession of the latest amendments or edition byreferring to the latest issue of lsquoBIS Cataloguersquo and lsquoStandards Monthly Additionsrsquo
This Indian Standard has been developed from Doc No CED 39 (5263)
Amendments Issued Since Publication
Amend No Date of Issue
Amd No 1 November 1995
Amd No 2 March 2002
BUREAU OF INDIAN STANDARDS
Headquarters
Manak Bhavan 9 Bahadur Shah Zafar Marg New Delhi 110002Telephones 323 01 31 323 33 75 323 94 02
Telegrams Manaksanstha(Common to all offices)
Regional Offices Telephone
Central Manak Bhavan 9 Bahadur Shah Zafar MargNEW DELHI 110002
323 76 17323 38 41
Eastern 114 C I T Scheme VII M V I P Road KankurgachiKOLKATA 700054
634 The contribution of bent up bars andinclined hoops to shear resistance of the sectionshall not be considered
635 The spacing of hoops over a length of 2d ateither end of a beam shall not exceed (a) d4and (b) 8 times the diameter of the smallestlongitudinal bar however it need not be lessthan 100 mm ( see Fig 5 ) The first hoop shallbe at a distance not exceeding 50 mm from the joint face Vertical hoops at the same spacing asabove shall also be provided over a lengthequal to 2d on either side of a section where
flexural yielding may occur under the effect of earthquake forces Elsewhere the beam shallhave vertical hoops at a spacing not exceedingd2
7 COLUMNS AND FRAME MEMBERSSUBJECTED TO BENDING AND AXIALLOAD
71 General
711 These requirements apply to framemembers which have a factored axial stress inexcess of 01 f ck under the effect of earthquakeforces
712 The minimum dimension of the membershall not be less than 200 mm However inframes which have beams with centre to centrespan exceeding 5 m or columns of unsupportedlength exceeding 4 m the shortest dimension of the column shall not be less than 300 mm
713 The ratio of the shortest cross sectionaldimension to the perpendicular dimension shallpreferably not be less than 04
72 Longitudinal Reinforcement
721 Lap splices shall be provided only in the
central half of the member length It should beproportioned as a tension splice Hoops shall beprovided over the entire splice length atspacing not exceeding 150 mm centre to centreNot more than 50 percent of the bars shall bespliced at one section
722 Any area of a column that extends morethan 100 mm beyond the confined core due toarchitectural requirements shall be detailed inthe following manner In case the contributionof this area to strength has been consideredthen it will have the minimum longitudinal andtransverse reinforcement as per this code
FIG 4 C ALCULATION OF DESIGN SHEAR FORCE FOR BEAM
832019 Indian STANDARDS 13920-1993 Code of Practice
However if this area has been treated asnon-structural the minimum reinforcementrequirements shall be governed byIS 456 1978 provisions minimum longitudinaland transverse reinforcement as perIS 456 1978 ( see Fig 6 )
73 Transverse Reinforcement
731 Transverse reinforcement for circularcolumns shall consist of spiral or circular hoopsIn rectangular columns rectangular hoops maybe used A rectangular hoop is a closed stirruphaving a 135deg hook with a 10 diameterextension (but not lt 75 mm) at each end that isembedded in the confined core ( see Fig 7A )
732 The parallel legs of rectangular hoop shallbe spaced not more than 300 mm centre tocentre If the length of any side of the hoopexceeds 300 mm a crosstie shall be provided(Fig 7B) Alternatively a pair of overlappinghoops may be provided within the columm ( seeFig 7C) The hooks shall engage peripheral
longitudinal bars733 The spacing of hoops shall not exceed half the least lateral dimension of the columnexcept where special confining reinforcement isprovided as per 74
734 The design shear force for columns shallbe the maximum of
a) calculated factored shear force as peranalysis and
b) a factored shear force given by
V u = 14
where and are moment of
resistance of opposite sign of beams framinginto the column from opposite faces ( seeFig 8 ) and hst is the storey height The beam
moment capacity is to be calculated as perIS 456 1978
74 Special Confining Reinforcement
This requirement shall be met with unless alarger amount of transverse reinforcement isrequired from shear strength considerations
FIG 5 BEAM REINFORCEMENT
FIG 6 REINFORCEMENT REQUIREMENT FOR COLUMN WITH MORE THAN 100 mm
PROJECTION BEYOND CORE
M bLu lim M
bRu lim+
hst
----------------------------------------------
M bLu lim M
bRu lim
832019 Indian STANDARDS 13920-1993 Code of Practice
741 Special confining reinforcement shall beprovided over a length lo from each joint facetowards midspan and on either side of anysection where flexural yielding may occurunder the effect of earthquake forces ( see
Fig 9 ) The length lsquolorsquo shall not be less than(a) larger lateral dimension of the member atthe section where yielding occurs (b) 16 of clear span of the member and (c) 450 mm
742 When a column terminates into a footingor mat special confining reinforcement shallextend at least 300 mm into the footing or mat( see Fig 10 )
743 When the calculated point of contra-flexure under the effect of gravity andearthquake loads is not within the middle half of the member clear height special confiningreinforcement shall be provided over the full
height of the column744 Columns supporting reactions fromdiscontinued stiff members such as walls shallbe provided with special confiningreinforcement over their full height ( seeFig 11 ) This reinforcement shall also beplaced above the discontinuity for at least thedevelopment length of the largest longitudinalbar in the column Where the column issupported on a wall this reinforcement shall beprovided over the full height of the column itshall also be provided below the discontinuityfor the same development length
745 Special confining reinforcement shall beprovided over the full height of a column whichhas significant variation in stiffness alongits height This variation in stiffness may result
FIG 8 C ALCULATION OF DESIGN SHEAR
FORCE FOR COLUMN
832019 Indian STANDARDS 13920-1993 Code of Practice
due to the presence of bracing a mezzaninefloor or a RCC wall on either side of the
column that extends only over a part of thecolumn height ( see Fig 12 )
746 The spacing of hoops used as specialconfining reinforcement shall not exceed 14 of minimum member dimension but need not beless than 75 mm nor more than 100 mm
747 The area of cross section Ash of the barforming circular hoops or spiral to be used asspecial confining reinforcement shall not beless than
where
Example Consider a column of diameter 300mm Let the grade of concrete be M20 and thatof steel Fe 415 for longitudinal and confiningreinforcement The spacing of circular hoops Sshall not exceed the smaller of (a) 14 of minimum member dimension = 14 times 300 =75 mm and (b) 100 mm Therefore S = 75 mm Assuming 40 mm clear cover to thelongitudinal reinforcement and circular hoopsof diameter 8 mm Dk = 300 ndash 2 times 40 + 2 times 8 =236 mm Thus the area of cross section of thebar forming circular hoop works out to be4728 mm2 This is less than the cross sectionalarea of 8 mm bar (5027 mm2) Thus circularhoops of diameter 8 mm at a spacing of 75 mmcentre to centre will be adequate
748 The area of cross section Ash of the barforming rectangular hoop to be used as specialconfining reinforcement shall not be less than
where
FIG 11 SPECIAL CONFINING REINFORCEMENT REQUIREMENT FOR COLUMNS UNDER DISCONTINUED W ALLS
Ash = area of the bar cross section
S = pitch of spiral or spacing of hoops
Dk = diameter of core measured to theoutside of the spiral or hoop
f ck = characteristic compressive strength of concrete cube
f y = yield stress of steel (of circular hoop orspiral)
Ag = gross area of the column cross sectionand
Ash 009 SDk
f ck
f y-------
Ag
Ak
------- 10ndash=
Ak = area of the concrete core =
h = longer dimension of the rectangularconfining hoop measured to its outer
π4--- D
2
k
Ash 018 Sh
f ck
f y-------
Ag
Ak
------- 10ndash=
832019 Indian STANDARDS 13920-1993 Code of Practice
NOTE The dimension lsquohrsquo of the hoop could be reducedby introducing crossties as shown in Fig 7B In thiscase Ak shall be measured as the overall core arearegardless of the hoop arrangement The hooks of crossties shall engage peripheral longitudinal bars
Example Consider a column of 650 mm times500 mm Let the grade of concrete be M20 andthat of steel Fe 415 for the longitudinal andconfining reinforcement Assuming clear coverof 40 mm to the longitudinal reinforcement andrectangular hoops of diameter 10 mm the sizeof the core is 590 mm times 440 mm As both thesedimensions are greater than 300 mm either a
pair of overlapping hoops or a single hoop withcrossties in both directions will have to beprovided Thus the dimension lsquohrsquo will be thelarger of (i) 5902 = 295 mm and (ii) 4402 =220 mm The spacing of hoops S shall notexceed the smaller of (a) 14 of minimum
member dimensions = 14 times 500 = 125 mm and(b) 100 mm Thus S = 100 mm The area of cross section of the bar forming rectangularhoop works out to be 6447 mm2 This is lessthan the area of cross section of 10 mm bar(7854 mm2) Thus 10 mm diameterrectangular hoops at 100 mm cc will beadequate Similar calculations indicate that asan alternative one could also provide 8 mmdiameter rectangular hoops at 70 mm cc
8 JOINTS OF FRAMES
81 The special confining reinforcement asrequired at the end of column shall be provided
FIG 12 COLUMNS WITH V ARYING STIFFNESS
face It shall not exceed 300 mm ( seeFig 7 ) and
Ak = area of confined concrete core in therectangular hoop measured to itsoutside dimensions
832019 Indian STANDARDS 13920-1993 Code of Practice
through the joint as well unless the joint isconfined as specified by 82
82 A joint which has beams framing into all vertical faces of it and where each beam widthis at least 34 of the column width may be
provided with half the special confiningreinforcement required at the end of thecolumn The spacing of hoops shall not exceed150 mm
9 SHEAR WALLS
91 General Requirements
911 The requirements of this section apply tothe shear walls which are part of the lateralforce resisting system of the structure
912 The thickness of any part of the wall shallpreferably not be less than 150 mm
913 The effective flange width to be used inthe design of flanged wall sections shall beassumed to extend beyond the face of the webfor a distance which shall be the smaller of (a)half the distance to an adjacent shear wall weband (b) 110 th of the total wall height
914 Shear walls shall be provided withreinforcement in the longitudinal andtransverse directions in the plane of the wallThe minimum reinforcement ratio shall be0002 5 of the gross area in each direction Thisreinforcement shall be distributed uniformlyacross the cross section of the wall
915 If the factored shear stress in the wallexceeds 025 or if the wall thicknessexceeds 200 mm reinforcement shall beprovided in two curtains each having barsrunning in the longitudinal and transversedirections in the plane of the wall
916 The diameter of the bars to be used in anypart of the wall shall not exceed 110th of thethickness of that part
917 The maximum spacing of reinforcementin either direction shall not exceed the smallerof lw 5 3tw and 450 mm where lw is thehorizontal length of the wall and tw is the
thickness of the wall web92 Shear Strength
921 The nominal shear stress τ v shall becalculated as
where
922 The design shear strength of concrete τcshall be calculated as per Table 13 of IS 456 1978
923 The nominal shear stress in the wall τ vshall not exceed τc max as per Table 14 of
IS 456 1978924 When τ v is less than τc shearreinforcement shall be provided in accordancewith 914 915 and 917
925 When τ v is greater than τc the area of horizontal shear reinforcement Ah to beprovided within a vertical spacing S v is givenby
where V us = ( V u ndash τc tw dw ) is the shear force
to be resisted by the horizontal reinforcementHowever the amount of horizontalreinforcement provided shall not be less thanthe minimum as per 914
926 The vertical reinforcement that isuniformly distributed in the wall shall not beless than the horizontal reinforcementcalculated as per 925
93 Flexural Strength
931 The moment of resistance M uv of thewall section may be calculated as for columnssubjected to combined bending and axial load
as per IS 456 1978 The moment of resistanceof slender rectangular shear wall section withuniformly distributed vertical reinforcement isgiven in Annex A
932 The cracked flexural strength of the wallsection should be greater than its uncrackedflexural strength
933 In walls that do not have boundaryelements vertical reieforcement shall beconcentrated at the ends of the wall Eachconcentration shall consist of a minimum of 4 bars of 12 mm diameter arranged in at least
2 layers94 Boundary Elements
Boundary elements are portions along the walledges that are strengthened by longitudinaland transverse reinforcement Though theymay have the same thickness as that of thewall web it is advantageous to provide themwith greater thickness
941 Where the extreme fibre compressivestress in the wall due to factored gravity loadsplus factored earthquake force exceeds 02 f ckboundaty elements shall be provided along the
vertical boundaries of walls The boundary
V u = factored shear force
tw = thickness of the web and
dw = effective depth of wall section Thismay by taken as 08 lw for rectangular
sections
f ck
V us
087 f y Ah dw
S v
------------------------------------=
832019 Indian STANDARDS 13920-1993 Code of Practice
elements may be discontinued where thecalculated compressive stress becomes lessthan 015 f ck The compressive stress shall becalculated using a linearly elastic model andgross section properties
942 A boundary element shall have adequateaxial load carrying capacity assuming shortcolumn action so as to enable it to carry anaxial compression equal to the sum of factoredgravity load on it and the additionalcompressive load induced by the seismic forceThe latter may be calculated as
where
943 If the gravity load adds to the strength of the wall its load factor shall be taken as 08
944 The percentage of vertical reinforcementin the boundary elements shall not be less than08 percent nor greater than 6 percent Inorder to avoid congestion the practical upper
limit would be 4 percent945 Boundary elements where required asper 941 shall be provided throughout theirheight with special confining reinforcement asper 74
946 Boundary elements need not be providedif the entire wall section is provided withspecial confining reinforcement as per 74
95 Coupled Shear Walls
951 Coupled shear walls shall be connected byductile coupling beams If the earthquakeinduced shear stress in the coupling beam
exceeds
where ls is the clear span of the coupling beamand D is its overall depth the entireearthquake induced shear and flexure shallpreferably be resisted by diagonalreinforcement
952 The area of reinforcement to be providedalong each diagonal in a diagonally reinforcedcoupling beam shall be
where V u is the factored shear force and α isthe angle made by the diagonal reinforcementwith the horizontal At least 4 bars of 8 mmdiameter shall be provided along each diagonalThe reinforcement along each diagonal shall be
enclosed by special confining reinforcement asper 74 The pitch of spiral or spacing of tiesshall not exceed 100 mm
953 The diagonal or horizontal bars of acoupling beam shall be anchored in theadjacent walls with an anchorage length of 15times the development length in tension
96 Openings in Walls
961 The shear strength of a wall withopenings should be checked along criticalplanes that pass through openings
962 Reinforcement shall be provided along the
edges of openings in walls The area of the vertical and horizontal bars should be such asto equal that of the respective interrupted barsThe vertical bars should extend for the fullstorey height The horizontal bars should beprovided with development length in tensionbeyond the sides of the opening
97 Discontinuous Walls
Columns supporting discontinuous walls shallbe provided with special confiningreinforcement as per 744
98 Construction Joints
The vertical reinforcement ratio across ahorizontal construction joint shall not be lessthan
where τ v is the factored shear stress at the joint Pu is the factored axial force (positive forcompression) and Ag is the gross crosssectional area of the joint
99 Development Splice and AnchorageRequirement
991 Horizontal reinforcement shall beanchored near the edges of the wall or in theconfined core of the boundary elements
992 Splicing of vertical flexural reinforcementshould be avoided as far as possible in regionswhere yielding may take place This zone of flexural yielding may be considered to extendfor a distance of lw above the base of the wall orone sixth of the wall height whichever is moreHowever this distance need not be greaterthan 2 lw Not more than one third of this vertical reinforcement shall be spliced at such asection Splices in adjacent bars should be
staggered by a minimum of 600 mm
M u = factored design moment on the entirewall section
M uv = moment of resistance provided bydistributed vertical reinforcementacross the wall section and
Cw = center to center distance between theboundary elements along the two vertical edges of the wall
M u M uvndash
Cw
--------------------------
832019 Indian STANDARDS 13920-1993 Code of Practice
993 Lateral ties shall be provided aroundlapped spliced bars that are larger than 16 mmin diameter The diameter of the tie shall not beless than one fourth that of the spliced bar norless than 6 mm The spacing of ties shall not
exceed 150 mm center to center
994 Welded splices and mechanicalconnections shall confirm to 25252 of IS 456 1978 However not more than half thereinforcement shall be spliced at a sectionwhere flexural yielding may take place
ANNEX A
( Clause 931 )
MOMENT OF RESISTANCE OF RECTANGULAR SHEAR WALL SECTION
A-1 The moment of resistance of a slender rectangular shear wall section with uniformlydistributed vertical reinforcement may be estimated as follows
These equations were derived assuming a rectangular wall section of depth lw and thickness twthat is subjected to combined uni-axial bending and axial compression The vertical reinforcementis represented by an equivalent steel plate along the length of the section The stress-strain curveassumed for concrete is as per IS 456 1978 whereas that for steel is assumed to be bi-linear Twoequations are given for calculating the flexural strength of the section Their use depends on
whether the section fails in flexural tension or in flexural compression
(a) For
where
ρ = vertical reinforcement ratio = Ast ( tw lw )
Ast = area of uniformly distributed vertical reinforcement
β = 087 f y (0003 5 Es)
Es = elastic modulus of steel and
Pu = axial compression on wall
(b) For
where
The value of xu lw to be used in this equation should be calculated from the quadratic equation
where
xu lwlt xu lw
xu lw lt xu lwlt 10
832019 Indian STANDARDS 13920-1993 Code of Practice
BIS is a statutory institution established under the Bureau of Indian Standards Act 1986 to promoteharmonious development of the activities of standardization marking and quality certification of goods andattending to connected matters in the country
Copyright
BIS has the copyright of all its publications No part of these publications may be reproduced in any formwithout the prior permission in writing of BIS This does not preclude the free use in the course of implementing the standard of necessary details such as symbols and sizes type or grade designationsEnquiries relating to copyright be addressed to the Director (Publications) BIS
Review of Indian Standards
Amendments are issued to standards as the need arises on the basis of comments Standards are alsoreviewed periodically a standard along with amendments is reaffirmed when such review indicates that nochanges are needed if the review indicates that changes are needed it is taken up for revision Users of Indian Standards should ascertain that they are in possession of the latest amendments or edition byreferring to the latest issue of lsquoBIS Cataloguersquo and lsquoStandards Monthly Additionsrsquo
This Indian Standard has been developed from Doc No CED 39 (5263)
Amendments Issued Since Publication
Amend No Date of Issue
Amd No 1 November 1995
Amd No 2 March 2002
BUREAU OF INDIAN STANDARDS
Headquarters
Manak Bhavan 9 Bahadur Shah Zafar Marg New Delhi 110002Telephones 323 01 31 323 33 75 323 94 02
Telegrams Manaksanstha(Common to all offices)
Regional Offices Telephone
Central Manak Bhavan 9 Bahadur Shah Zafar MargNEW DELHI 110002
323 76 17323 38 41
Eastern 114 C I T Scheme VII M V I P Road KankurgachiKOLKATA 700054
However if this area has been treated asnon-structural the minimum reinforcementrequirements shall be governed byIS 456 1978 provisions minimum longitudinaland transverse reinforcement as perIS 456 1978 ( see Fig 6 )
73 Transverse Reinforcement
731 Transverse reinforcement for circularcolumns shall consist of spiral or circular hoopsIn rectangular columns rectangular hoops maybe used A rectangular hoop is a closed stirruphaving a 135deg hook with a 10 diameterextension (but not lt 75 mm) at each end that isembedded in the confined core ( see Fig 7A )
732 The parallel legs of rectangular hoop shallbe spaced not more than 300 mm centre tocentre If the length of any side of the hoopexceeds 300 mm a crosstie shall be provided(Fig 7B) Alternatively a pair of overlappinghoops may be provided within the columm ( seeFig 7C) The hooks shall engage peripheral
longitudinal bars733 The spacing of hoops shall not exceed half the least lateral dimension of the columnexcept where special confining reinforcement isprovided as per 74
734 The design shear force for columns shallbe the maximum of
a) calculated factored shear force as peranalysis and
b) a factored shear force given by
V u = 14
where and are moment of
resistance of opposite sign of beams framinginto the column from opposite faces ( seeFig 8 ) and hst is the storey height The beam
moment capacity is to be calculated as perIS 456 1978
74 Special Confining Reinforcement
This requirement shall be met with unless alarger amount of transverse reinforcement isrequired from shear strength considerations
FIG 5 BEAM REINFORCEMENT
FIG 6 REINFORCEMENT REQUIREMENT FOR COLUMN WITH MORE THAN 100 mm
PROJECTION BEYOND CORE
M bLu lim M
bRu lim+
hst
----------------------------------------------
M bLu lim M
bRu lim
832019 Indian STANDARDS 13920-1993 Code of Practice
741 Special confining reinforcement shall beprovided over a length lo from each joint facetowards midspan and on either side of anysection where flexural yielding may occurunder the effect of earthquake forces ( see
Fig 9 ) The length lsquolorsquo shall not be less than(a) larger lateral dimension of the member atthe section where yielding occurs (b) 16 of clear span of the member and (c) 450 mm
742 When a column terminates into a footingor mat special confining reinforcement shallextend at least 300 mm into the footing or mat( see Fig 10 )
743 When the calculated point of contra-flexure under the effect of gravity andearthquake loads is not within the middle half of the member clear height special confiningreinforcement shall be provided over the full
height of the column744 Columns supporting reactions fromdiscontinued stiff members such as walls shallbe provided with special confiningreinforcement over their full height ( seeFig 11 ) This reinforcement shall also beplaced above the discontinuity for at least thedevelopment length of the largest longitudinalbar in the column Where the column issupported on a wall this reinforcement shall beprovided over the full height of the column itshall also be provided below the discontinuityfor the same development length
745 Special confining reinforcement shall beprovided over the full height of a column whichhas significant variation in stiffness alongits height This variation in stiffness may result
FIG 8 C ALCULATION OF DESIGN SHEAR
FORCE FOR COLUMN
832019 Indian STANDARDS 13920-1993 Code of Practice
due to the presence of bracing a mezzaninefloor or a RCC wall on either side of the
column that extends only over a part of thecolumn height ( see Fig 12 )
746 The spacing of hoops used as specialconfining reinforcement shall not exceed 14 of minimum member dimension but need not beless than 75 mm nor more than 100 mm
747 The area of cross section Ash of the barforming circular hoops or spiral to be used asspecial confining reinforcement shall not beless than
where
Example Consider a column of diameter 300mm Let the grade of concrete be M20 and thatof steel Fe 415 for longitudinal and confiningreinforcement The spacing of circular hoops Sshall not exceed the smaller of (a) 14 of minimum member dimension = 14 times 300 =75 mm and (b) 100 mm Therefore S = 75 mm Assuming 40 mm clear cover to thelongitudinal reinforcement and circular hoopsof diameter 8 mm Dk = 300 ndash 2 times 40 + 2 times 8 =236 mm Thus the area of cross section of thebar forming circular hoop works out to be4728 mm2 This is less than the cross sectionalarea of 8 mm bar (5027 mm2) Thus circularhoops of diameter 8 mm at a spacing of 75 mmcentre to centre will be adequate
748 The area of cross section Ash of the barforming rectangular hoop to be used as specialconfining reinforcement shall not be less than
where
FIG 11 SPECIAL CONFINING REINFORCEMENT REQUIREMENT FOR COLUMNS UNDER DISCONTINUED W ALLS
Ash = area of the bar cross section
S = pitch of spiral or spacing of hoops
Dk = diameter of core measured to theoutside of the spiral or hoop
f ck = characteristic compressive strength of concrete cube
f y = yield stress of steel (of circular hoop orspiral)
Ag = gross area of the column cross sectionand
Ash 009 SDk
f ck
f y-------
Ag
Ak
------- 10ndash=
Ak = area of the concrete core =
h = longer dimension of the rectangularconfining hoop measured to its outer
π4--- D
2
k
Ash 018 Sh
f ck
f y-------
Ag
Ak
------- 10ndash=
832019 Indian STANDARDS 13920-1993 Code of Practice
NOTE The dimension lsquohrsquo of the hoop could be reducedby introducing crossties as shown in Fig 7B In thiscase Ak shall be measured as the overall core arearegardless of the hoop arrangement The hooks of crossties shall engage peripheral longitudinal bars
Example Consider a column of 650 mm times500 mm Let the grade of concrete be M20 andthat of steel Fe 415 for the longitudinal andconfining reinforcement Assuming clear coverof 40 mm to the longitudinal reinforcement andrectangular hoops of diameter 10 mm the sizeof the core is 590 mm times 440 mm As both thesedimensions are greater than 300 mm either a
pair of overlapping hoops or a single hoop withcrossties in both directions will have to beprovided Thus the dimension lsquohrsquo will be thelarger of (i) 5902 = 295 mm and (ii) 4402 =220 mm The spacing of hoops S shall notexceed the smaller of (a) 14 of minimum
member dimensions = 14 times 500 = 125 mm and(b) 100 mm Thus S = 100 mm The area of cross section of the bar forming rectangularhoop works out to be 6447 mm2 This is lessthan the area of cross section of 10 mm bar(7854 mm2) Thus 10 mm diameterrectangular hoops at 100 mm cc will beadequate Similar calculations indicate that asan alternative one could also provide 8 mmdiameter rectangular hoops at 70 mm cc
8 JOINTS OF FRAMES
81 The special confining reinforcement asrequired at the end of column shall be provided
FIG 12 COLUMNS WITH V ARYING STIFFNESS
face It shall not exceed 300 mm ( seeFig 7 ) and
Ak = area of confined concrete core in therectangular hoop measured to itsoutside dimensions
832019 Indian STANDARDS 13920-1993 Code of Practice
through the joint as well unless the joint isconfined as specified by 82
82 A joint which has beams framing into all vertical faces of it and where each beam widthis at least 34 of the column width may be
provided with half the special confiningreinforcement required at the end of thecolumn The spacing of hoops shall not exceed150 mm
9 SHEAR WALLS
91 General Requirements
911 The requirements of this section apply tothe shear walls which are part of the lateralforce resisting system of the structure
912 The thickness of any part of the wall shallpreferably not be less than 150 mm
913 The effective flange width to be used inthe design of flanged wall sections shall beassumed to extend beyond the face of the webfor a distance which shall be the smaller of (a)half the distance to an adjacent shear wall weband (b) 110 th of the total wall height
914 Shear walls shall be provided withreinforcement in the longitudinal andtransverse directions in the plane of the wallThe minimum reinforcement ratio shall be0002 5 of the gross area in each direction Thisreinforcement shall be distributed uniformlyacross the cross section of the wall
915 If the factored shear stress in the wallexceeds 025 or if the wall thicknessexceeds 200 mm reinforcement shall beprovided in two curtains each having barsrunning in the longitudinal and transversedirections in the plane of the wall
916 The diameter of the bars to be used in anypart of the wall shall not exceed 110th of thethickness of that part
917 The maximum spacing of reinforcementin either direction shall not exceed the smallerof lw 5 3tw and 450 mm where lw is thehorizontal length of the wall and tw is the
thickness of the wall web92 Shear Strength
921 The nominal shear stress τ v shall becalculated as
where
922 The design shear strength of concrete τcshall be calculated as per Table 13 of IS 456 1978
923 The nominal shear stress in the wall τ vshall not exceed τc max as per Table 14 of
IS 456 1978924 When τ v is less than τc shearreinforcement shall be provided in accordancewith 914 915 and 917
925 When τ v is greater than τc the area of horizontal shear reinforcement Ah to beprovided within a vertical spacing S v is givenby
where V us = ( V u ndash τc tw dw ) is the shear force
to be resisted by the horizontal reinforcementHowever the amount of horizontalreinforcement provided shall not be less thanthe minimum as per 914
926 The vertical reinforcement that isuniformly distributed in the wall shall not beless than the horizontal reinforcementcalculated as per 925
93 Flexural Strength
931 The moment of resistance M uv of thewall section may be calculated as for columnssubjected to combined bending and axial load
as per IS 456 1978 The moment of resistanceof slender rectangular shear wall section withuniformly distributed vertical reinforcement isgiven in Annex A
932 The cracked flexural strength of the wallsection should be greater than its uncrackedflexural strength
933 In walls that do not have boundaryelements vertical reieforcement shall beconcentrated at the ends of the wall Eachconcentration shall consist of a minimum of 4 bars of 12 mm diameter arranged in at least
2 layers94 Boundary Elements
Boundary elements are portions along the walledges that are strengthened by longitudinaland transverse reinforcement Though theymay have the same thickness as that of thewall web it is advantageous to provide themwith greater thickness
941 Where the extreme fibre compressivestress in the wall due to factored gravity loadsplus factored earthquake force exceeds 02 f ckboundaty elements shall be provided along the
vertical boundaries of walls The boundary
V u = factored shear force
tw = thickness of the web and
dw = effective depth of wall section Thismay by taken as 08 lw for rectangular
sections
f ck
V us
087 f y Ah dw
S v
------------------------------------=
832019 Indian STANDARDS 13920-1993 Code of Practice
elements may be discontinued where thecalculated compressive stress becomes lessthan 015 f ck The compressive stress shall becalculated using a linearly elastic model andgross section properties
942 A boundary element shall have adequateaxial load carrying capacity assuming shortcolumn action so as to enable it to carry anaxial compression equal to the sum of factoredgravity load on it and the additionalcompressive load induced by the seismic forceThe latter may be calculated as
where
943 If the gravity load adds to the strength of the wall its load factor shall be taken as 08
944 The percentage of vertical reinforcementin the boundary elements shall not be less than08 percent nor greater than 6 percent Inorder to avoid congestion the practical upper
limit would be 4 percent945 Boundary elements where required asper 941 shall be provided throughout theirheight with special confining reinforcement asper 74
946 Boundary elements need not be providedif the entire wall section is provided withspecial confining reinforcement as per 74
95 Coupled Shear Walls
951 Coupled shear walls shall be connected byductile coupling beams If the earthquakeinduced shear stress in the coupling beam
exceeds
where ls is the clear span of the coupling beamand D is its overall depth the entireearthquake induced shear and flexure shallpreferably be resisted by diagonalreinforcement
952 The area of reinforcement to be providedalong each diagonal in a diagonally reinforcedcoupling beam shall be
where V u is the factored shear force and α isthe angle made by the diagonal reinforcementwith the horizontal At least 4 bars of 8 mmdiameter shall be provided along each diagonalThe reinforcement along each diagonal shall be
enclosed by special confining reinforcement asper 74 The pitch of spiral or spacing of tiesshall not exceed 100 mm
953 The diagonal or horizontal bars of acoupling beam shall be anchored in theadjacent walls with an anchorage length of 15times the development length in tension
96 Openings in Walls
961 The shear strength of a wall withopenings should be checked along criticalplanes that pass through openings
962 Reinforcement shall be provided along the
edges of openings in walls The area of the vertical and horizontal bars should be such asto equal that of the respective interrupted barsThe vertical bars should extend for the fullstorey height The horizontal bars should beprovided with development length in tensionbeyond the sides of the opening
97 Discontinuous Walls
Columns supporting discontinuous walls shallbe provided with special confiningreinforcement as per 744
98 Construction Joints
The vertical reinforcement ratio across ahorizontal construction joint shall not be lessthan
where τ v is the factored shear stress at the joint Pu is the factored axial force (positive forcompression) and Ag is the gross crosssectional area of the joint
99 Development Splice and AnchorageRequirement
991 Horizontal reinforcement shall beanchored near the edges of the wall or in theconfined core of the boundary elements
992 Splicing of vertical flexural reinforcementshould be avoided as far as possible in regionswhere yielding may take place This zone of flexural yielding may be considered to extendfor a distance of lw above the base of the wall orone sixth of the wall height whichever is moreHowever this distance need not be greaterthan 2 lw Not more than one third of this vertical reinforcement shall be spliced at such asection Splices in adjacent bars should be
staggered by a minimum of 600 mm
M u = factored design moment on the entirewall section
M uv = moment of resistance provided bydistributed vertical reinforcementacross the wall section and
Cw = center to center distance between theboundary elements along the two vertical edges of the wall
M u M uvndash
Cw
--------------------------
832019 Indian STANDARDS 13920-1993 Code of Practice
993 Lateral ties shall be provided aroundlapped spliced bars that are larger than 16 mmin diameter The diameter of the tie shall not beless than one fourth that of the spliced bar norless than 6 mm The spacing of ties shall not
exceed 150 mm center to center
994 Welded splices and mechanicalconnections shall confirm to 25252 of IS 456 1978 However not more than half thereinforcement shall be spliced at a sectionwhere flexural yielding may take place
ANNEX A
( Clause 931 )
MOMENT OF RESISTANCE OF RECTANGULAR SHEAR WALL SECTION
A-1 The moment of resistance of a slender rectangular shear wall section with uniformlydistributed vertical reinforcement may be estimated as follows
These equations were derived assuming a rectangular wall section of depth lw and thickness twthat is subjected to combined uni-axial bending and axial compression The vertical reinforcementis represented by an equivalent steel plate along the length of the section The stress-strain curveassumed for concrete is as per IS 456 1978 whereas that for steel is assumed to be bi-linear Twoequations are given for calculating the flexural strength of the section Their use depends on
whether the section fails in flexural tension or in flexural compression
(a) For
where
ρ = vertical reinforcement ratio = Ast ( tw lw )
Ast = area of uniformly distributed vertical reinforcement
β = 087 f y (0003 5 Es)
Es = elastic modulus of steel and
Pu = axial compression on wall
(b) For
where
The value of xu lw to be used in this equation should be calculated from the quadratic equation
where
xu lwlt xu lw
xu lw lt xu lwlt 10
832019 Indian STANDARDS 13920-1993 Code of Practice
BIS is a statutory institution established under the Bureau of Indian Standards Act 1986 to promoteharmonious development of the activities of standardization marking and quality certification of goods andattending to connected matters in the country
Copyright
BIS has the copyright of all its publications No part of these publications may be reproduced in any formwithout the prior permission in writing of BIS This does not preclude the free use in the course of implementing the standard of necessary details such as symbols and sizes type or grade designationsEnquiries relating to copyright be addressed to the Director (Publications) BIS
Review of Indian Standards
Amendments are issued to standards as the need arises on the basis of comments Standards are alsoreviewed periodically a standard along with amendments is reaffirmed when such review indicates that nochanges are needed if the review indicates that changes are needed it is taken up for revision Users of Indian Standards should ascertain that they are in possession of the latest amendments or edition byreferring to the latest issue of lsquoBIS Cataloguersquo and lsquoStandards Monthly Additionsrsquo
This Indian Standard has been developed from Doc No CED 39 (5263)
Amendments Issued Since Publication
Amend No Date of Issue
Amd No 1 November 1995
Amd No 2 March 2002
BUREAU OF INDIAN STANDARDS
Headquarters
Manak Bhavan 9 Bahadur Shah Zafar Marg New Delhi 110002Telephones 323 01 31 323 33 75 323 94 02
Telegrams Manaksanstha(Common to all offices)
Regional Offices Telephone
Central Manak Bhavan 9 Bahadur Shah Zafar MargNEW DELHI 110002
323 76 17323 38 41
Eastern 114 C I T Scheme VII M V I P Road KankurgachiKOLKATA 700054
741 Special confining reinforcement shall beprovided over a length lo from each joint facetowards midspan and on either side of anysection where flexural yielding may occurunder the effect of earthquake forces ( see
Fig 9 ) The length lsquolorsquo shall not be less than(a) larger lateral dimension of the member atthe section where yielding occurs (b) 16 of clear span of the member and (c) 450 mm
742 When a column terminates into a footingor mat special confining reinforcement shallextend at least 300 mm into the footing or mat( see Fig 10 )
743 When the calculated point of contra-flexure under the effect of gravity andearthquake loads is not within the middle half of the member clear height special confiningreinforcement shall be provided over the full
height of the column744 Columns supporting reactions fromdiscontinued stiff members such as walls shallbe provided with special confiningreinforcement over their full height ( seeFig 11 ) This reinforcement shall also beplaced above the discontinuity for at least thedevelopment length of the largest longitudinalbar in the column Where the column issupported on a wall this reinforcement shall beprovided over the full height of the column itshall also be provided below the discontinuityfor the same development length
745 Special confining reinforcement shall beprovided over the full height of a column whichhas significant variation in stiffness alongits height This variation in stiffness may result
FIG 8 C ALCULATION OF DESIGN SHEAR
FORCE FOR COLUMN
832019 Indian STANDARDS 13920-1993 Code of Practice
due to the presence of bracing a mezzaninefloor or a RCC wall on either side of the
column that extends only over a part of thecolumn height ( see Fig 12 )
746 The spacing of hoops used as specialconfining reinforcement shall not exceed 14 of minimum member dimension but need not beless than 75 mm nor more than 100 mm
747 The area of cross section Ash of the barforming circular hoops or spiral to be used asspecial confining reinforcement shall not beless than
where
Example Consider a column of diameter 300mm Let the grade of concrete be M20 and thatof steel Fe 415 for longitudinal and confiningreinforcement The spacing of circular hoops Sshall not exceed the smaller of (a) 14 of minimum member dimension = 14 times 300 =75 mm and (b) 100 mm Therefore S = 75 mm Assuming 40 mm clear cover to thelongitudinal reinforcement and circular hoopsof diameter 8 mm Dk = 300 ndash 2 times 40 + 2 times 8 =236 mm Thus the area of cross section of thebar forming circular hoop works out to be4728 mm2 This is less than the cross sectionalarea of 8 mm bar (5027 mm2) Thus circularhoops of diameter 8 mm at a spacing of 75 mmcentre to centre will be adequate
748 The area of cross section Ash of the barforming rectangular hoop to be used as specialconfining reinforcement shall not be less than
where
FIG 11 SPECIAL CONFINING REINFORCEMENT REQUIREMENT FOR COLUMNS UNDER DISCONTINUED W ALLS
Ash = area of the bar cross section
S = pitch of spiral or spacing of hoops
Dk = diameter of core measured to theoutside of the spiral or hoop
f ck = characteristic compressive strength of concrete cube
f y = yield stress of steel (of circular hoop orspiral)
Ag = gross area of the column cross sectionand
Ash 009 SDk
f ck
f y-------
Ag
Ak
------- 10ndash=
Ak = area of the concrete core =
h = longer dimension of the rectangularconfining hoop measured to its outer
π4--- D
2
k
Ash 018 Sh
f ck
f y-------
Ag
Ak
------- 10ndash=
832019 Indian STANDARDS 13920-1993 Code of Practice
NOTE The dimension lsquohrsquo of the hoop could be reducedby introducing crossties as shown in Fig 7B In thiscase Ak shall be measured as the overall core arearegardless of the hoop arrangement The hooks of crossties shall engage peripheral longitudinal bars
Example Consider a column of 650 mm times500 mm Let the grade of concrete be M20 andthat of steel Fe 415 for the longitudinal andconfining reinforcement Assuming clear coverof 40 mm to the longitudinal reinforcement andrectangular hoops of diameter 10 mm the sizeof the core is 590 mm times 440 mm As both thesedimensions are greater than 300 mm either a
pair of overlapping hoops or a single hoop withcrossties in both directions will have to beprovided Thus the dimension lsquohrsquo will be thelarger of (i) 5902 = 295 mm and (ii) 4402 =220 mm The spacing of hoops S shall notexceed the smaller of (a) 14 of minimum
member dimensions = 14 times 500 = 125 mm and(b) 100 mm Thus S = 100 mm The area of cross section of the bar forming rectangularhoop works out to be 6447 mm2 This is lessthan the area of cross section of 10 mm bar(7854 mm2) Thus 10 mm diameterrectangular hoops at 100 mm cc will beadequate Similar calculations indicate that asan alternative one could also provide 8 mmdiameter rectangular hoops at 70 mm cc
8 JOINTS OF FRAMES
81 The special confining reinforcement asrequired at the end of column shall be provided
FIG 12 COLUMNS WITH V ARYING STIFFNESS
face It shall not exceed 300 mm ( seeFig 7 ) and
Ak = area of confined concrete core in therectangular hoop measured to itsoutside dimensions
832019 Indian STANDARDS 13920-1993 Code of Practice
through the joint as well unless the joint isconfined as specified by 82
82 A joint which has beams framing into all vertical faces of it and where each beam widthis at least 34 of the column width may be
provided with half the special confiningreinforcement required at the end of thecolumn The spacing of hoops shall not exceed150 mm
9 SHEAR WALLS
91 General Requirements
911 The requirements of this section apply tothe shear walls which are part of the lateralforce resisting system of the structure
912 The thickness of any part of the wall shallpreferably not be less than 150 mm
913 The effective flange width to be used inthe design of flanged wall sections shall beassumed to extend beyond the face of the webfor a distance which shall be the smaller of (a)half the distance to an adjacent shear wall weband (b) 110 th of the total wall height
914 Shear walls shall be provided withreinforcement in the longitudinal andtransverse directions in the plane of the wallThe minimum reinforcement ratio shall be0002 5 of the gross area in each direction Thisreinforcement shall be distributed uniformlyacross the cross section of the wall
915 If the factored shear stress in the wallexceeds 025 or if the wall thicknessexceeds 200 mm reinforcement shall beprovided in two curtains each having barsrunning in the longitudinal and transversedirections in the plane of the wall
916 The diameter of the bars to be used in anypart of the wall shall not exceed 110th of thethickness of that part
917 The maximum spacing of reinforcementin either direction shall not exceed the smallerof lw 5 3tw and 450 mm where lw is thehorizontal length of the wall and tw is the
thickness of the wall web92 Shear Strength
921 The nominal shear stress τ v shall becalculated as
where
922 The design shear strength of concrete τcshall be calculated as per Table 13 of IS 456 1978
923 The nominal shear stress in the wall τ vshall not exceed τc max as per Table 14 of
IS 456 1978924 When τ v is less than τc shearreinforcement shall be provided in accordancewith 914 915 and 917
925 When τ v is greater than τc the area of horizontal shear reinforcement Ah to beprovided within a vertical spacing S v is givenby
where V us = ( V u ndash τc tw dw ) is the shear force
to be resisted by the horizontal reinforcementHowever the amount of horizontalreinforcement provided shall not be less thanthe minimum as per 914
926 The vertical reinforcement that isuniformly distributed in the wall shall not beless than the horizontal reinforcementcalculated as per 925
93 Flexural Strength
931 The moment of resistance M uv of thewall section may be calculated as for columnssubjected to combined bending and axial load
as per IS 456 1978 The moment of resistanceof slender rectangular shear wall section withuniformly distributed vertical reinforcement isgiven in Annex A
932 The cracked flexural strength of the wallsection should be greater than its uncrackedflexural strength
933 In walls that do not have boundaryelements vertical reieforcement shall beconcentrated at the ends of the wall Eachconcentration shall consist of a minimum of 4 bars of 12 mm diameter arranged in at least
2 layers94 Boundary Elements
Boundary elements are portions along the walledges that are strengthened by longitudinaland transverse reinforcement Though theymay have the same thickness as that of thewall web it is advantageous to provide themwith greater thickness
941 Where the extreme fibre compressivestress in the wall due to factored gravity loadsplus factored earthquake force exceeds 02 f ckboundaty elements shall be provided along the
vertical boundaries of walls The boundary
V u = factored shear force
tw = thickness of the web and
dw = effective depth of wall section Thismay by taken as 08 lw for rectangular
sections
f ck
V us
087 f y Ah dw
S v
------------------------------------=
832019 Indian STANDARDS 13920-1993 Code of Practice
elements may be discontinued where thecalculated compressive stress becomes lessthan 015 f ck The compressive stress shall becalculated using a linearly elastic model andgross section properties
942 A boundary element shall have adequateaxial load carrying capacity assuming shortcolumn action so as to enable it to carry anaxial compression equal to the sum of factoredgravity load on it and the additionalcompressive load induced by the seismic forceThe latter may be calculated as
where
943 If the gravity load adds to the strength of the wall its load factor shall be taken as 08
944 The percentage of vertical reinforcementin the boundary elements shall not be less than08 percent nor greater than 6 percent Inorder to avoid congestion the practical upper
limit would be 4 percent945 Boundary elements where required asper 941 shall be provided throughout theirheight with special confining reinforcement asper 74
946 Boundary elements need not be providedif the entire wall section is provided withspecial confining reinforcement as per 74
95 Coupled Shear Walls
951 Coupled shear walls shall be connected byductile coupling beams If the earthquakeinduced shear stress in the coupling beam
exceeds
where ls is the clear span of the coupling beamand D is its overall depth the entireearthquake induced shear and flexure shallpreferably be resisted by diagonalreinforcement
952 The area of reinforcement to be providedalong each diagonal in a diagonally reinforcedcoupling beam shall be
where V u is the factored shear force and α isthe angle made by the diagonal reinforcementwith the horizontal At least 4 bars of 8 mmdiameter shall be provided along each diagonalThe reinforcement along each diagonal shall be
enclosed by special confining reinforcement asper 74 The pitch of spiral or spacing of tiesshall not exceed 100 mm
953 The diagonal or horizontal bars of acoupling beam shall be anchored in theadjacent walls with an anchorage length of 15times the development length in tension
96 Openings in Walls
961 The shear strength of a wall withopenings should be checked along criticalplanes that pass through openings
962 Reinforcement shall be provided along the
edges of openings in walls The area of the vertical and horizontal bars should be such asto equal that of the respective interrupted barsThe vertical bars should extend for the fullstorey height The horizontal bars should beprovided with development length in tensionbeyond the sides of the opening
97 Discontinuous Walls
Columns supporting discontinuous walls shallbe provided with special confiningreinforcement as per 744
98 Construction Joints
The vertical reinforcement ratio across ahorizontal construction joint shall not be lessthan
where τ v is the factored shear stress at the joint Pu is the factored axial force (positive forcompression) and Ag is the gross crosssectional area of the joint
99 Development Splice and AnchorageRequirement
991 Horizontal reinforcement shall beanchored near the edges of the wall or in theconfined core of the boundary elements
992 Splicing of vertical flexural reinforcementshould be avoided as far as possible in regionswhere yielding may take place This zone of flexural yielding may be considered to extendfor a distance of lw above the base of the wall orone sixth of the wall height whichever is moreHowever this distance need not be greaterthan 2 lw Not more than one third of this vertical reinforcement shall be spliced at such asection Splices in adjacent bars should be
staggered by a minimum of 600 mm
M u = factored design moment on the entirewall section
M uv = moment of resistance provided bydistributed vertical reinforcementacross the wall section and
Cw = center to center distance between theboundary elements along the two vertical edges of the wall
M u M uvndash
Cw
--------------------------
832019 Indian STANDARDS 13920-1993 Code of Practice
993 Lateral ties shall be provided aroundlapped spliced bars that are larger than 16 mmin diameter The diameter of the tie shall not beless than one fourth that of the spliced bar norless than 6 mm The spacing of ties shall not
exceed 150 mm center to center
994 Welded splices and mechanicalconnections shall confirm to 25252 of IS 456 1978 However not more than half thereinforcement shall be spliced at a sectionwhere flexural yielding may take place
ANNEX A
( Clause 931 )
MOMENT OF RESISTANCE OF RECTANGULAR SHEAR WALL SECTION
A-1 The moment of resistance of a slender rectangular shear wall section with uniformlydistributed vertical reinforcement may be estimated as follows
These equations were derived assuming a rectangular wall section of depth lw and thickness twthat is subjected to combined uni-axial bending and axial compression The vertical reinforcementis represented by an equivalent steel plate along the length of the section The stress-strain curveassumed for concrete is as per IS 456 1978 whereas that for steel is assumed to be bi-linear Twoequations are given for calculating the flexural strength of the section Their use depends on
whether the section fails in flexural tension or in flexural compression
(a) For
where
ρ = vertical reinforcement ratio = Ast ( tw lw )
Ast = area of uniformly distributed vertical reinforcement
β = 087 f y (0003 5 Es)
Es = elastic modulus of steel and
Pu = axial compression on wall
(b) For
where
The value of xu lw to be used in this equation should be calculated from the quadratic equation
where
xu lwlt xu lw
xu lw lt xu lwlt 10
832019 Indian STANDARDS 13920-1993 Code of Practice
BIS is a statutory institution established under the Bureau of Indian Standards Act 1986 to promoteharmonious development of the activities of standardization marking and quality certification of goods andattending to connected matters in the country
Copyright
BIS has the copyright of all its publications No part of these publications may be reproduced in any formwithout the prior permission in writing of BIS This does not preclude the free use in the course of implementing the standard of necessary details such as symbols and sizes type or grade designationsEnquiries relating to copyright be addressed to the Director (Publications) BIS
Review of Indian Standards
Amendments are issued to standards as the need arises on the basis of comments Standards are alsoreviewed periodically a standard along with amendments is reaffirmed when such review indicates that nochanges are needed if the review indicates that changes are needed it is taken up for revision Users of Indian Standards should ascertain that they are in possession of the latest amendments or edition byreferring to the latest issue of lsquoBIS Cataloguersquo and lsquoStandards Monthly Additionsrsquo
This Indian Standard has been developed from Doc No CED 39 (5263)
Amendments Issued Since Publication
Amend No Date of Issue
Amd No 1 November 1995
Amd No 2 March 2002
BUREAU OF INDIAN STANDARDS
Headquarters
Manak Bhavan 9 Bahadur Shah Zafar Marg New Delhi 110002Telephones 323 01 31 323 33 75 323 94 02
Telegrams Manaksanstha(Common to all offices)
Regional Offices Telephone
Central Manak Bhavan 9 Bahadur Shah Zafar MargNEW DELHI 110002
323 76 17323 38 41
Eastern 114 C I T Scheme VII M V I P Road KankurgachiKOLKATA 700054
741 Special confining reinforcement shall beprovided over a length lo from each joint facetowards midspan and on either side of anysection where flexural yielding may occurunder the effect of earthquake forces ( see
Fig 9 ) The length lsquolorsquo shall not be less than(a) larger lateral dimension of the member atthe section where yielding occurs (b) 16 of clear span of the member and (c) 450 mm
742 When a column terminates into a footingor mat special confining reinforcement shallextend at least 300 mm into the footing or mat( see Fig 10 )
743 When the calculated point of contra-flexure under the effect of gravity andearthquake loads is not within the middle half of the member clear height special confiningreinforcement shall be provided over the full
height of the column744 Columns supporting reactions fromdiscontinued stiff members such as walls shallbe provided with special confiningreinforcement over their full height ( seeFig 11 ) This reinforcement shall also beplaced above the discontinuity for at least thedevelopment length of the largest longitudinalbar in the column Where the column issupported on a wall this reinforcement shall beprovided over the full height of the column itshall also be provided below the discontinuityfor the same development length
745 Special confining reinforcement shall beprovided over the full height of a column whichhas significant variation in stiffness alongits height This variation in stiffness may result
FIG 8 C ALCULATION OF DESIGN SHEAR
FORCE FOR COLUMN
832019 Indian STANDARDS 13920-1993 Code of Practice
due to the presence of bracing a mezzaninefloor or a RCC wall on either side of the
column that extends only over a part of thecolumn height ( see Fig 12 )
746 The spacing of hoops used as specialconfining reinforcement shall not exceed 14 of minimum member dimension but need not beless than 75 mm nor more than 100 mm
747 The area of cross section Ash of the barforming circular hoops or spiral to be used asspecial confining reinforcement shall not beless than
where
Example Consider a column of diameter 300mm Let the grade of concrete be M20 and thatof steel Fe 415 for longitudinal and confiningreinforcement The spacing of circular hoops Sshall not exceed the smaller of (a) 14 of minimum member dimension = 14 times 300 =75 mm and (b) 100 mm Therefore S = 75 mm Assuming 40 mm clear cover to thelongitudinal reinforcement and circular hoopsof diameter 8 mm Dk = 300 ndash 2 times 40 + 2 times 8 =236 mm Thus the area of cross section of thebar forming circular hoop works out to be4728 mm2 This is less than the cross sectionalarea of 8 mm bar (5027 mm2) Thus circularhoops of diameter 8 mm at a spacing of 75 mmcentre to centre will be adequate
748 The area of cross section Ash of the barforming rectangular hoop to be used as specialconfining reinforcement shall not be less than
where
FIG 11 SPECIAL CONFINING REINFORCEMENT REQUIREMENT FOR COLUMNS UNDER DISCONTINUED W ALLS
Ash = area of the bar cross section
S = pitch of spiral or spacing of hoops
Dk = diameter of core measured to theoutside of the spiral or hoop
f ck = characteristic compressive strength of concrete cube
f y = yield stress of steel (of circular hoop orspiral)
Ag = gross area of the column cross sectionand
Ash 009 SDk
f ck
f y-------
Ag
Ak
------- 10ndash=
Ak = area of the concrete core =
h = longer dimension of the rectangularconfining hoop measured to its outer
π4--- D
2
k
Ash 018 Sh
f ck
f y-------
Ag
Ak
------- 10ndash=
832019 Indian STANDARDS 13920-1993 Code of Practice
NOTE The dimension lsquohrsquo of the hoop could be reducedby introducing crossties as shown in Fig 7B In thiscase Ak shall be measured as the overall core arearegardless of the hoop arrangement The hooks of crossties shall engage peripheral longitudinal bars
Example Consider a column of 650 mm times500 mm Let the grade of concrete be M20 andthat of steel Fe 415 for the longitudinal andconfining reinforcement Assuming clear coverof 40 mm to the longitudinal reinforcement andrectangular hoops of diameter 10 mm the sizeof the core is 590 mm times 440 mm As both thesedimensions are greater than 300 mm either a
pair of overlapping hoops or a single hoop withcrossties in both directions will have to beprovided Thus the dimension lsquohrsquo will be thelarger of (i) 5902 = 295 mm and (ii) 4402 =220 mm The spacing of hoops S shall notexceed the smaller of (a) 14 of minimum
member dimensions = 14 times 500 = 125 mm and(b) 100 mm Thus S = 100 mm The area of cross section of the bar forming rectangularhoop works out to be 6447 mm2 This is lessthan the area of cross section of 10 mm bar(7854 mm2) Thus 10 mm diameterrectangular hoops at 100 mm cc will beadequate Similar calculations indicate that asan alternative one could also provide 8 mmdiameter rectangular hoops at 70 mm cc
8 JOINTS OF FRAMES
81 The special confining reinforcement asrequired at the end of column shall be provided
FIG 12 COLUMNS WITH V ARYING STIFFNESS
face It shall not exceed 300 mm ( seeFig 7 ) and
Ak = area of confined concrete core in therectangular hoop measured to itsoutside dimensions
832019 Indian STANDARDS 13920-1993 Code of Practice
through the joint as well unless the joint isconfined as specified by 82
82 A joint which has beams framing into all vertical faces of it and where each beam widthis at least 34 of the column width may be
provided with half the special confiningreinforcement required at the end of thecolumn The spacing of hoops shall not exceed150 mm
9 SHEAR WALLS
91 General Requirements
911 The requirements of this section apply tothe shear walls which are part of the lateralforce resisting system of the structure
912 The thickness of any part of the wall shallpreferably not be less than 150 mm
913 The effective flange width to be used inthe design of flanged wall sections shall beassumed to extend beyond the face of the webfor a distance which shall be the smaller of (a)half the distance to an adjacent shear wall weband (b) 110 th of the total wall height
914 Shear walls shall be provided withreinforcement in the longitudinal andtransverse directions in the plane of the wallThe minimum reinforcement ratio shall be0002 5 of the gross area in each direction Thisreinforcement shall be distributed uniformlyacross the cross section of the wall
915 If the factored shear stress in the wallexceeds 025 or if the wall thicknessexceeds 200 mm reinforcement shall beprovided in two curtains each having barsrunning in the longitudinal and transversedirections in the plane of the wall
916 The diameter of the bars to be used in anypart of the wall shall not exceed 110th of thethickness of that part
917 The maximum spacing of reinforcementin either direction shall not exceed the smallerof lw 5 3tw and 450 mm where lw is thehorizontal length of the wall and tw is the
thickness of the wall web92 Shear Strength
921 The nominal shear stress τ v shall becalculated as
where
922 The design shear strength of concrete τcshall be calculated as per Table 13 of IS 456 1978
923 The nominal shear stress in the wall τ vshall not exceed τc max as per Table 14 of
IS 456 1978924 When τ v is less than τc shearreinforcement shall be provided in accordancewith 914 915 and 917
925 When τ v is greater than τc the area of horizontal shear reinforcement Ah to beprovided within a vertical spacing S v is givenby
where V us = ( V u ndash τc tw dw ) is the shear force
to be resisted by the horizontal reinforcementHowever the amount of horizontalreinforcement provided shall not be less thanthe minimum as per 914
926 The vertical reinforcement that isuniformly distributed in the wall shall not beless than the horizontal reinforcementcalculated as per 925
93 Flexural Strength
931 The moment of resistance M uv of thewall section may be calculated as for columnssubjected to combined bending and axial load
as per IS 456 1978 The moment of resistanceof slender rectangular shear wall section withuniformly distributed vertical reinforcement isgiven in Annex A
932 The cracked flexural strength of the wallsection should be greater than its uncrackedflexural strength
933 In walls that do not have boundaryelements vertical reieforcement shall beconcentrated at the ends of the wall Eachconcentration shall consist of a minimum of 4 bars of 12 mm diameter arranged in at least
2 layers94 Boundary Elements
Boundary elements are portions along the walledges that are strengthened by longitudinaland transverse reinforcement Though theymay have the same thickness as that of thewall web it is advantageous to provide themwith greater thickness
941 Where the extreme fibre compressivestress in the wall due to factored gravity loadsplus factored earthquake force exceeds 02 f ckboundaty elements shall be provided along the
vertical boundaries of walls The boundary
V u = factored shear force
tw = thickness of the web and
dw = effective depth of wall section Thismay by taken as 08 lw for rectangular
sections
f ck
V us
087 f y Ah dw
S v
------------------------------------=
832019 Indian STANDARDS 13920-1993 Code of Practice
elements may be discontinued where thecalculated compressive stress becomes lessthan 015 f ck The compressive stress shall becalculated using a linearly elastic model andgross section properties
942 A boundary element shall have adequateaxial load carrying capacity assuming shortcolumn action so as to enable it to carry anaxial compression equal to the sum of factoredgravity load on it and the additionalcompressive load induced by the seismic forceThe latter may be calculated as
where
943 If the gravity load adds to the strength of the wall its load factor shall be taken as 08
944 The percentage of vertical reinforcementin the boundary elements shall not be less than08 percent nor greater than 6 percent Inorder to avoid congestion the practical upper
limit would be 4 percent945 Boundary elements where required asper 941 shall be provided throughout theirheight with special confining reinforcement asper 74
946 Boundary elements need not be providedif the entire wall section is provided withspecial confining reinforcement as per 74
95 Coupled Shear Walls
951 Coupled shear walls shall be connected byductile coupling beams If the earthquakeinduced shear stress in the coupling beam
exceeds
where ls is the clear span of the coupling beamand D is its overall depth the entireearthquake induced shear and flexure shallpreferably be resisted by diagonalreinforcement
952 The area of reinforcement to be providedalong each diagonal in a diagonally reinforcedcoupling beam shall be
where V u is the factored shear force and α isthe angle made by the diagonal reinforcementwith the horizontal At least 4 bars of 8 mmdiameter shall be provided along each diagonalThe reinforcement along each diagonal shall be
enclosed by special confining reinforcement asper 74 The pitch of spiral or spacing of tiesshall not exceed 100 mm
953 The diagonal or horizontal bars of acoupling beam shall be anchored in theadjacent walls with an anchorage length of 15times the development length in tension
96 Openings in Walls
961 The shear strength of a wall withopenings should be checked along criticalplanes that pass through openings
962 Reinforcement shall be provided along the
edges of openings in walls The area of the vertical and horizontal bars should be such asto equal that of the respective interrupted barsThe vertical bars should extend for the fullstorey height The horizontal bars should beprovided with development length in tensionbeyond the sides of the opening
97 Discontinuous Walls
Columns supporting discontinuous walls shallbe provided with special confiningreinforcement as per 744
98 Construction Joints
The vertical reinforcement ratio across ahorizontal construction joint shall not be lessthan
where τ v is the factored shear stress at the joint Pu is the factored axial force (positive forcompression) and Ag is the gross crosssectional area of the joint
99 Development Splice and AnchorageRequirement
991 Horizontal reinforcement shall beanchored near the edges of the wall or in theconfined core of the boundary elements
992 Splicing of vertical flexural reinforcementshould be avoided as far as possible in regionswhere yielding may take place This zone of flexural yielding may be considered to extendfor a distance of lw above the base of the wall orone sixth of the wall height whichever is moreHowever this distance need not be greaterthan 2 lw Not more than one third of this vertical reinforcement shall be spliced at such asection Splices in adjacent bars should be
staggered by a minimum of 600 mm
M u = factored design moment on the entirewall section
M uv = moment of resistance provided bydistributed vertical reinforcementacross the wall section and
Cw = center to center distance between theboundary elements along the two vertical edges of the wall
M u M uvndash
Cw
--------------------------
832019 Indian STANDARDS 13920-1993 Code of Practice
993 Lateral ties shall be provided aroundlapped spliced bars that are larger than 16 mmin diameter The diameter of the tie shall not beless than one fourth that of the spliced bar norless than 6 mm The spacing of ties shall not
exceed 150 mm center to center
994 Welded splices and mechanicalconnections shall confirm to 25252 of IS 456 1978 However not more than half thereinforcement shall be spliced at a sectionwhere flexural yielding may take place
ANNEX A
( Clause 931 )
MOMENT OF RESISTANCE OF RECTANGULAR SHEAR WALL SECTION
A-1 The moment of resistance of a slender rectangular shear wall section with uniformlydistributed vertical reinforcement may be estimated as follows
These equations were derived assuming a rectangular wall section of depth lw and thickness twthat is subjected to combined uni-axial bending and axial compression The vertical reinforcementis represented by an equivalent steel plate along the length of the section The stress-strain curveassumed for concrete is as per IS 456 1978 whereas that for steel is assumed to be bi-linear Twoequations are given for calculating the flexural strength of the section Their use depends on
whether the section fails in flexural tension or in flexural compression
(a) For
where
ρ = vertical reinforcement ratio = Ast ( tw lw )
Ast = area of uniformly distributed vertical reinforcement
β = 087 f y (0003 5 Es)
Es = elastic modulus of steel and
Pu = axial compression on wall
(b) For
where
The value of xu lw to be used in this equation should be calculated from the quadratic equation
where
xu lwlt xu lw
xu lw lt xu lwlt 10
832019 Indian STANDARDS 13920-1993 Code of Practice
BIS is a statutory institution established under the Bureau of Indian Standards Act 1986 to promoteharmonious development of the activities of standardization marking and quality certification of goods andattending to connected matters in the country
Copyright
BIS has the copyright of all its publications No part of these publications may be reproduced in any formwithout the prior permission in writing of BIS This does not preclude the free use in the course of implementing the standard of necessary details such as symbols and sizes type or grade designationsEnquiries relating to copyright be addressed to the Director (Publications) BIS
Review of Indian Standards
Amendments are issued to standards as the need arises on the basis of comments Standards are alsoreviewed periodically a standard along with amendments is reaffirmed when such review indicates that nochanges are needed if the review indicates that changes are needed it is taken up for revision Users of Indian Standards should ascertain that they are in possession of the latest amendments or edition byreferring to the latest issue of lsquoBIS Cataloguersquo and lsquoStandards Monthly Additionsrsquo
This Indian Standard has been developed from Doc No CED 39 (5263)
Amendments Issued Since Publication
Amend No Date of Issue
Amd No 1 November 1995
Amd No 2 March 2002
BUREAU OF INDIAN STANDARDS
Headquarters
Manak Bhavan 9 Bahadur Shah Zafar Marg New Delhi 110002Telephones 323 01 31 323 33 75 323 94 02
Telegrams Manaksanstha(Common to all offices)
Regional Offices Telephone
Central Manak Bhavan 9 Bahadur Shah Zafar MargNEW DELHI 110002
323 76 17323 38 41
Eastern 114 C I T Scheme VII M V I P Road KankurgachiKOLKATA 700054
due to the presence of bracing a mezzaninefloor or a RCC wall on either side of the
column that extends only over a part of thecolumn height ( see Fig 12 )
746 The spacing of hoops used as specialconfining reinforcement shall not exceed 14 of minimum member dimension but need not beless than 75 mm nor more than 100 mm
747 The area of cross section Ash of the barforming circular hoops or spiral to be used asspecial confining reinforcement shall not beless than
where
Example Consider a column of diameter 300mm Let the grade of concrete be M20 and thatof steel Fe 415 for longitudinal and confiningreinforcement The spacing of circular hoops Sshall not exceed the smaller of (a) 14 of minimum member dimension = 14 times 300 =75 mm and (b) 100 mm Therefore S = 75 mm Assuming 40 mm clear cover to thelongitudinal reinforcement and circular hoopsof diameter 8 mm Dk = 300 ndash 2 times 40 + 2 times 8 =236 mm Thus the area of cross section of thebar forming circular hoop works out to be4728 mm2 This is less than the cross sectionalarea of 8 mm bar (5027 mm2) Thus circularhoops of diameter 8 mm at a spacing of 75 mmcentre to centre will be adequate
748 The area of cross section Ash of the barforming rectangular hoop to be used as specialconfining reinforcement shall not be less than
where
FIG 11 SPECIAL CONFINING REINFORCEMENT REQUIREMENT FOR COLUMNS UNDER DISCONTINUED W ALLS
Ash = area of the bar cross section
S = pitch of spiral or spacing of hoops
Dk = diameter of core measured to theoutside of the spiral or hoop
f ck = characteristic compressive strength of concrete cube
f y = yield stress of steel (of circular hoop orspiral)
Ag = gross area of the column cross sectionand
Ash 009 SDk
f ck
f y-------
Ag
Ak
------- 10ndash=
Ak = area of the concrete core =
h = longer dimension of the rectangularconfining hoop measured to its outer
π4--- D
2
k
Ash 018 Sh
f ck
f y-------
Ag
Ak
------- 10ndash=
832019 Indian STANDARDS 13920-1993 Code of Practice
NOTE The dimension lsquohrsquo of the hoop could be reducedby introducing crossties as shown in Fig 7B In thiscase Ak shall be measured as the overall core arearegardless of the hoop arrangement The hooks of crossties shall engage peripheral longitudinal bars
Example Consider a column of 650 mm times500 mm Let the grade of concrete be M20 andthat of steel Fe 415 for the longitudinal andconfining reinforcement Assuming clear coverof 40 mm to the longitudinal reinforcement andrectangular hoops of diameter 10 mm the sizeof the core is 590 mm times 440 mm As both thesedimensions are greater than 300 mm either a
pair of overlapping hoops or a single hoop withcrossties in both directions will have to beprovided Thus the dimension lsquohrsquo will be thelarger of (i) 5902 = 295 mm and (ii) 4402 =220 mm The spacing of hoops S shall notexceed the smaller of (a) 14 of minimum
member dimensions = 14 times 500 = 125 mm and(b) 100 mm Thus S = 100 mm The area of cross section of the bar forming rectangularhoop works out to be 6447 mm2 This is lessthan the area of cross section of 10 mm bar(7854 mm2) Thus 10 mm diameterrectangular hoops at 100 mm cc will beadequate Similar calculations indicate that asan alternative one could also provide 8 mmdiameter rectangular hoops at 70 mm cc
8 JOINTS OF FRAMES
81 The special confining reinforcement asrequired at the end of column shall be provided
FIG 12 COLUMNS WITH V ARYING STIFFNESS
face It shall not exceed 300 mm ( seeFig 7 ) and
Ak = area of confined concrete core in therectangular hoop measured to itsoutside dimensions
832019 Indian STANDARDS 13920-1993 Code of Practice
through the joint as well unless the joint isconfined as specified by 82
82 A joint which has beams framing into all vertical faces of it and where each beam widthis at least 34 of the column width may be
provided with half the special confiningreinforcement required at the end of thecolumn The spacing of hoops shall not exceed150 mm
9 SHEAR WALLS
91 General Requirements
911 The requirements of this section apply tothe shear walls which are part of the lateralforce resisting system of the structure
912 The thickness of any part of the wall shallpreferably not be less than 150 mm
913 The effective flange width to be used inthe design of flanged wall sections shall beassumed to extend beyond the face of the webfor a distance which shall be the smaller of (a)half the distance to an adjacent shear wall weband (b) 110 th of the total wall height
914 Shear walls shall be provided withreinforcement in the longitudinal andtransverse directions in the plane of the wallThe minimum reinforcement ratio shall be0002 5 of the gross area in each direction Thisreinforcement shall be distributed uniformlyacross the cross section of the wall
915 If the factored shear stress in the wallexceeds 025 or if the wall thicknessexceeds 200 mm reinforcement shall beprovided in two curtains each having barsrunning in the longitudinal and transversedirections in the plane of the wall
916 The diameter of the bars to be used in anypart of the wall shall not exceed 110th of thethickness of that part
917 The maximum spacing of reinforcementin either direction shall not exceed the smallerof lw 5 3tw and 450 mm where lw is thehorizontal length of the wall and tw is the
thickness of the wall web92 Shear Strength
921 The nominal shear stress τ v shall becalculated as
where
922 The design shear strength of concrete τcshall be calculated as per Table 13 of IS 456 1978
923 The nominal shear stress in the wall τ vshall not exceed τc max as per Table 14 of
IS 456 1978924 When τ v is less than τc shearreinforcement shall be provided in accordancewith 914 915 and 917
925 When τ v is greater than τc the area of horizontal shear reinforcement Ah to beprovided within a vertical spacing S v is givenby
where V us = ( V u ndash τc tw dw ) is the shear force
to be resisted by the horizontal reinforcementHowever the amount of horizontalreinforcement provided shall not be less thanthe minimum as per 914
926 The vertical reinforcement that isuniformly distributed in the wall shall not beless than the horizontal reinforcementcalculated as per 925
93 Flexural Strength
931 The moment of resistance M uv of thewall section may be calculated as for columnssubjected to combined bending and axial load
as per IS 456 1978 The moment of resistanceof slender rectangular shear wall section withuniformly distributed vertical reinforcement isgiven in Annex A
932 The cracked flexural strength of the wallsection should be greater than its uncrackedflexural strength
933 In walls that do not have boundaryelements vertical reieforcement shall beconcentrated at the ends of the wall Eachconcentration shall consist of a minimum of 4 bars of 12 mm diameter arranged in at least
2 layers94 Boundary Elements
Boundary elements are portions along the walledges that are strengthened by longitudinaland transverse reinforcement Though theymay have the same thickness as that of thewall web it is advantageous to provide themwith greater thickness
941 Where the extreme fibre compressivestress in the wall due to factored gravity loadsplus factored earthquake force exceeds 02 f ckboundaty elements shall be provided along the
vertical boundaries of walls The boundary
V u = factored shear force
tw = thickness of the web and
dw = effective depth of wall section Thismay by taken as 08 lw for rectangular
sections
f ck
V us
087 f y Ah dw
S v
------------------------------------=
832019 Indian STANDARDS 13920-1993 Code of Practice
elements may be discontinued where thecalculated compressive stress becomes lessthan 015 f ck The compressive stress shall becalculated using a linearly elastic model andgross section properties
942 A boundary element shall have adequateaxial load carrying capacity assuming shortcolumn action so as to enable it to carry anaxial compression equal to the sum of factoredgravity load on it and the additionalcompressive load induced by the seismic forceThe latter may be calculated as
where
943 If the gravity load adds to the strength of the wall its load factor shall be taken as 08
944 The percentage of vertical reinforcementin the boundary elements shall not be less than08 percent nor greater than 6 percent Inorder to avoid congestion the practical upper
limit would be 4 percent945 Boundary elements where required asper 941 shall be provided throughout theirheight with special confining reinforcement asper 74
946 Boundary elements need not be providedif the entire wall section is provided withspecial confining reinforcement as per 74
95 Coupled Shear Walls
951 Coupled shear walls shall be connected byductile coupling beams If the earthquakeinduced shear stress in the coupling beam
exceeds
where ls is the clear span of the coupling beamand D is its overall depth the entireearthquake induced shear and flexure shallpreferably be resisted by diagonalreinforcement
952 The area of reinforcement to be providedalong each diagonal in a diagonally reinforcedcoupling beam shall be
where V u is the factored shear force and α isthe angle made by the diagonal reinforcementwith the horizontal At least 4 bars of 8 mmdiameter shall be provided along each diagonalThe reinforcement along each diagonal shall be
enclosed by special confining reinforcement asper 74 The pitch of spiral or spacing of tiesshall not exceed 100 mm
953 The diagonal or horizontal bars of acoupling beam shall be anchored in theadjacent walls with an anchorage length of 15times the development length in tension
96 Openings in Walls
961 The shear strength of a wall withopenings should be checked along criticalplanes that pass through openings
962 Reinforcement shall be provided along the
edges of openings in walls The area of the vertical and horizontal bars should be such asto equal that of the respective interrupted barsThe vertical bars should extend for the fullstorey height The horizontal bars should beprovided with development length in tensionbeyond the sides of the opening
97 Discontinuous Walls
Columns supporting discontinuous walls shallbe provided with special confiningreinforcement as per 744
98 Construction Joints
The vertical reinforcement ratio across ahorizontal construction joint shall not be lessthan
where τ v is the factored shear stress at the joint Pu is the factored axial force (positive forcompression) and Ag is the gross crosssectional area of the joint
99 Development Splice and AnchorageRequirement
991 Horizontal reinforcement shall beanchored near the edges of the wall or in theconfined core of the boundary elements
992 Splicing of vertical flexural reinforcementshould be avoided as far as possible in regionswhere yielding may take place This zone of flexural yielding may be considered to extendfor a distance of lw above the base of the wall orone sixth of the wall height whichever is moreHowever this distance need not be greaterthan 2 lw Not more than one third of this vertical reinforcement shall be spliced at such asection Splices in adjacent bars should be
staggered by a minimum of 600 mm
M u = factored design moment on the entirewall section
M uv = moment of resistance provided bydistributed vertical reinforcementacross the wall section and
Cw = center to center distance between theboundary elements along the two vertical edges of the wall
M u M uvndash
Cw
--------------------------
832019 Indian STANDARDS 13920-1993 Code of Practice
993 Lateral ties shall be provided aroundlapped spliced bars that are larger than 16 mmin diameter The diameter of the tie shall not beless than one fourth that of the spliced bar norless than 6 mm The spacing of ties shall not
exceed 150 mm center to center
994 Welded splices and mechanicalconnections shall confirm to 25252 of IS 456 1978 However not more than half thereinforcement shall be spliced at a sectionwhere flexural yielding may take place
ANNEX A
( Clause 931 )
MOMENT OF RESISTANCE OF RECTANGULAR SHEAR WALL SECTION
A-1 The moment of resistance of a slender rectangular shear wall section with uniformlydistributed vertical reinforcement may be estimated as follows
These equations were derived assuming a rectangular wall section of depth lw and thickness twthat is subjected to combined uni-axial bending and axial compression The vertical reinforcementis represented by an equivalent steel plate along the length of the section The stress-strain curveassumed for concrete is as per IS 456 1978 whereas that for steel is assumed to be bi-linear Twoequations are given for calculating the flexural strength of the section Their use depends on
whether the section fails in flexural tension or in flexural compression
(a) For
where
ρ = vertical reinforcement ratio = Ast ( tw lw )
Ast = area of uniformly distributed vertical reinforcement
β = 087 f y (0003 5 Es)
Es = elastic modulus of steel and
Pu = axial compression on wall
(b) For
where
The value of xu lw to be used in this equation should be calculated from the quadratic equation
where
xu lwlt xu lw
xu lw lt xu lwlt 10
832019 Indian STANDARDS 13920-1993 Code of Practice
BIS is a statutory institution established under the Bureau of Indian Standards Act 1986 to promoteharmonious development of the activities of standardization marking and quality certification of goods andattending to connected matters in the country
Copyright
BIS has the copyright of all its publications No part of these publications may be reproduced in any formwithout the prior permission in writing of BIS This does not preclude the free use in the course of implementing the standard of necessary details such as symbols and sizes type or grade designationsEnquiries relating to copyright be addressed to the Director (Publications) BIS
Review of Indian Standards
Amendments are issued to standards as the need arises on the basis of comments Standards are alsoreviewed periodically a standard along with amendments is reaffirmed when such review indicates that nochanges are needed if the review indicates that changes are needed it is taken up for revision Users of Indian Standards should ascertain that they are in possession of the latest amendments or edition byreferring to the latest issue of lsquoBIS Cataloguersquo and lsquoStandards Monthly Additionsrsquo
This Indian Standard has been developed from Doc No CED 39 (5263)
Amendments Issued Since Publication
Amend No Date of Issue
Amd No 1 November 1995
Amd No 2 March 2002
BUREAU OF INDIAN STANDARDS
Headquarters
Manak Bhavan 9 Bahadur Shah Zafar Marg New Delhi 110002Telephones 323 01 31 323 33 75 323 94 02
Telegrams Manaksanstha(Common to all offices)
Regional Offices Telephone
Central Manak Bhavan 9 Bahadur Shah Zafar MargNEW DELHI 110002
323 76 17323 38 41
Eastern 114 C I T Scheme VII M V I P Road KankurgachiKOLKATA 700054
due to the presence of bracing a mezzaninefloor or a RCC wall on either side of the
column that extends only over a part of thecolumn height ( see Fig 12 )
746 The spacing of hoops used as specialconfining reinforcement shall not exceed 14 of minimum member dimension but need not beless than 75 mm nor more than 100 mm
747 The area of cross section Ash of the barforming circular hoops or spiral to be used asspecial confining reinforcement shall not beless than
where
Example Consider a column of diameter 300mm Let the grade of concrete be M20 and thatof steel Fe 415 for longitudinal and confiningreinforcement The spacing of circular hoops Sshall not exceed the smaller of (a) 14 of minimum member dimension = 14 times 300 =75 mm and (b) 100 mm Therefore S = 75 mm Assuming 40 mm clear cover to thelongitudinal reinforcement and circular hoopsof diameter 8 mm Dk = 300 ndash 2 times 40 + 2 times 8 =236 mm Thus the area of cross section of thebar forming circular hoop works out to be4728 mm2 This is less than the cross sectionalarea of 8 mm bar (5027 mm2) Thus circularhoops of diameter 8 mm at a spacing of 75 mmcentre to centre will be adequate
748 The area of cross section Ash of the barforming rectangular hoop to be used as specialconfining reinforcement shall not be less than
where
FIG 11 SPECIAL CONFINING REINFORCEMENT REQUIREMENT FOR COLUMNS UNDER DISCONTINUED W ALLS
Ash = area of the bar cross section
S = pitch of spiral or spacing of hoops
Dk = diameter of core measured to theoutside of the spiral or hoop
f ck = characteristic compressive strength of concrete cube
f y = yield stress of steel (of circular hoop orspiral)
Ag = gross area of the column cross sectionand
Ash 009 SDk
f ck
f y-------
Ag
Ak
------- 10ndash=
Ak = area of the concrete core =
h = longer dimension of the rectangularconfining hoop measured to its outer
π4--- D
2
k
Ash 018 Sh
f ck
f y-------
Ag
Ak
------- 10ndash=
832019 Indian STANDARDS 13920-1993 Code of Practice
NOTE The dimension lsquohrsquo of the hoop could be reducedby introducing crossties as shown in Fig 7B In thiscase Ak shall be measured as the overall core arearegardless of the hoop arrangement The hooks of crossties shall engage peripheral longitudinal bars
Example Consider a column of 650 mm times500 mm Let the grade of concrete be M20 andthat of steel Fe 415 for the longitudinal andconfining reinforcement Assuming clear coverof 40 mm to the longitudinal reinforcement andrectangular hoops of diameter 10 mm the sizeof the core is 590 mm times 440 mm As both thesedimensions are greater than 300 mm either a
pair of overlapping hoops or a single hoop withcrossties in both directions will have to beprovided Thus the dimension lsquohrsquo will be thelarger of (i) 5902 = 295 mm and (ii) 4402 =220 mm The spacing of hoops S shall notexceed the smaller of (a) 14 of minimum
member dimensions = 14 times 500 = 125 mm and(b) 100 mm Thus S = 100 mm The area of cross section of the bar forming rectangularhoop works out to be 6447 mm2 This is lessthan the area of cross section of 10 mm bar(7854 mm2) Thus 10 mm diameterrectangular hoops at 100 mm cc will beadequate Similar calculations indicate that asan alternative one could also provide 8 mmdiameter rectangular hoops at 70 mm cc
8 JOINTS OF FRAMES
81 The special confining reinforcement asrequired at the end of column shall be provided
FIG 12 COLUMNS WITH V ARYING STIFFNESS
face It shall not exceed 300 mm ( seeFig 7 ) and
Ak = area of confined concrete core in therectangular hoop measured to itsoutside dimensions
832019 Indian STANDARDS 13920-1993 Code of Practice
through the joint as well unless the joint isconfined as specified by 82
82 A joint which has beams framing into all vertical faces of it and where each beam widthis at least 34 of the column width may be
provided with half the special confiningreinforcement required at the end of thecolumn The spacing of hoops shall not exceed150 mm
9 SHEAR WALLS
91 General Requirements
911 The requirements of this section apply tothe shear walls which are part of the lateralforce resisting system of the structure
912 The thickness of any part of the wall shallpreferably not be less than 150 mm
913 The effective flange width to be used inthe design of flanged wall sections shall beassumed to extend beyond the face of the webfor a distance which shall be the smaller of (a)half the distance to an adjacent shear wall weband (b) 110 th of the total wall height
914 Shear walls shall be provided withreinforcement in the longitudinal andtransverse directions in the plane of the wallThe minimum reinforcement ratio shall be0002 5 of the gross area in each direction Thisreinforcement shall be distributed uniformlyacross the cross section of the wall
915 If the factored shear stress in the wallexceeds 025 or if the wall thicknessexceeds 200 mm reinforcement shall beprovided in two curtains each having barsrunning in the longitudinal and transversedirections in the plane of the wall
916 The diameter of the bars to be used in anypart of the wall shall not exceed 110th of thethickness of that part
917 The maximum spacing of reinforcementin either direction shall not exceed the smallerof lw 5 3tw and 450 mm where lw is thehorizontal length of the wall and tw is the
thickness of the wall web92 Shear Strength
921 The nominal shear stress τ v shall becalculated as
where
922 The design shear strength of concrete τcshall be calculated as per Table 13 of IS 456 1978
923 The nominal shear stress in the wall τ vshall not exceed τc max as per Table 14 of
IS 456 1978924 When τ v is less than τc shearreinforcement shall be provided in accordancewith 914 915 and 917
925 When τ v is greater than τc the area of horizontal shear reinforcement Ah to beprovided within a vertical spacing S v is givenby
where V us = ( V u ndash τc tw dw ) is the shear force
to be resisted by the horizontal reinforcementHowever the amount of horizontalreinforcement provided shall not be less thanthe minimum as per 914
926 The vertical reinforcement that isuniformly distributed in the wall shall not beless than the horizontal reinforcementcalculated as per 925
93 Flexural Strength
931 The moment of resistance M uv of thewall section may be calculated as for columnssubjected to combined bending and axial load
as per IS 456 1978 The moment of resistanceof slender rectangular shear wall section withuniformly distributed vertical reinforcement isgiven in Annex A
932 The cracked flexural strength of the wallsection should be greater than its uncrackedflexural strength
933 In walls that do not have boundaryelements vertical reieforcement shall beconcentrated at the ends of the wall Eachconcentration shall consist of a minimum of 4 bars of 12 mm diameter arranged in at least
2 layers94 Boundary Elements
Boundary elements are portions along the walledges that are strengthened by longitudinaland transverse reinforcement Though theymay have the same thickness as that of thewall web it is advantageous to provide themwith greater thickness
941 Where the extreme fibre compressivestress in the wall due to factored gravity loadsplus factored earthquake force exceeds 02 f ckboundaty elements shall be provided along the
vertical boundaries of walls The boundary
V u = factored shear force
tw = thickness of the web and
dw = effective depth of wall section Thismay by taken as 08 lw for rectangular
sections
f ck
V us
087 f y Ah dw
S v
------------------------------------=
832019 Indian STANDARDS 13920-1993 Code of Practice
elements may be discontinued where thecalculated compressive stress becomes lessthan 015 f ck The compressive stress shall becalculated using a linearly elastic model andgross section properties
942 A boundary element shall have adequateaxial load carrying capacity assuming shortcolumn action so as to enable it to carry anaxial compression equal to the sum of factoredgravity load on it and the additionalcompressive load induced by the seismic forceThe latter may be calculated as
where
943 If the gravity load adds to the strength of the wall its load factor shall be taken as 08
944 The percentage of vertical reinforcementin the boundary elements shall not be less than08 percent nor greater than 6 percent Inorder to avoid congestion the practical upper
limit would be 4 percent945 Boundary elements where required asper 941 shall be provided throughout theirheight with special confining reinforcement asper 74
946 Boundary elements need not be providedif the entire wall section is provided withspecial confining reinforcement as per 74
95 Coupled Shear Walls
951 Coupled shear walls shall be connected byductile coupling beams If the earthquakeinduced shear stress in the coupling beam
exceeds
where ls is the clear span of the coupling beamand D is its overall depth the entireearthquake induced shear and flexure shallpreferably be resisted by diagonalreinforcement
952 The area of reinforcement to be providedalong each diagonal in a diagonally reinforcedcoupling beam shall be
where V u is the factored shear force and α isthe angle made by the diagonal reinforcementwith the horizontal At least 4 bars of 8 mmdiameter shall be provided along each diagonalThe reinforcement along each diagonal shall be
enclosed by special confining reinforcement asper 74 The pitch of spiral or spacing of tiesshall not exceed 100 mm
953 The diagonal or horizontal bars of acoupling beam shall be anchored in theadjacent walls with an anchorage length of 15times the development length in tension
96 Openings in Walls
961 The shear strength of a wall withopenings should be checked along criticalplanes that pass through openings
962 Reinforcement shall be provided along the
edges of openings in walls The area of the vertical and horizontal bars should be such asto equal that of the respective interrupted barsThe vertical bars should extend for the fullstorey height The horizontal bars should beprovided with development length in tensionbeyond the sides of the opening
97 Discontinuous Walls
Columns supporting discontinuous walls shallbe provided with special confiningreinforcement as per 744
98 Construction Joints
The vertical reinforcement ratio across ahorizontal construction joint shall not be lessthan
where τ v is the factored shear stress at the joint Pu is the factored axial force (positive forcompression) and Ag is the gross crosssectional area of the joint
99 Development Splice and AnchorageRequirement
991 Horizontal reinforcement shall beanchored near the edges of the wall or in theconfined core of the boundary elements
992 Splicing of vertical flexural reinforcementshould be avoided as far as possible in regionswhere yielding may take place This zone of flexural yielding may be considered to extendfor a distance of lw above the base of the wall orone sixth of the wall height whichever is moreHowever this distance need not be greaterthan 2 lw Not more than one third of this vertical reinforcement shall be spliced at such asection Splices in adjacent bars should be
staggered by a minimum of 600 mm
M u = factored design moment on the entirewall section
M uv = moment of resistance provided bydistributed vertical reinforcementacross the wall section and
Cw = center to center distance between theboundary elements along the two vertical edges of the wall
M u M uvndash
Cw
--------------------------
832019 Indian STANDARDS 13920-1993 Code of Practice
993 Lateral ties shall be provided aroundlapped spliced bars that are larger than 16 mmin diameter The diameter of the tie shall not beless than one fourth that of the spliced bar norless than 6 mm The spacing of ties shall not
exceed 150 mm center to center
994 Welded splices and mechanicalconnections shall confirm to 25252 of IS 456 1978 However not more than half thereinforcement shall be spliced at a sectionwhere flexural yielding may take place
ANNEX A
( Clause 931 )
MOMENT OF RESISTANCE OF RECTANGULAR SHEAR WALL SECTION
A-1 The moment of resistance of a slender rectangular shear wall section with uniformlydistributed vertical reinforcement may be estimated as follows
These equations were derived assuming a rectangular wall section of depth lw and thickness twthat is subjected to combined uni-axial bending and axial compression The vertical reinforcementis represented by an equivalent steel plate along the length of the section The stress-strain curveassumed for concrete is as per IS 456 1978 whereas that for steel is assumed to be bi-linear Twoequations are given for calculating the flexural strength of the section Their use depends on
whether the section fails in flexural tension or in flexural compression
(a) For
where
ρ = vertical reinforcement ratio = Ast ( tw lw )
Ast = area of uniformly distributed vertical reinforcement
β = 087 f y (0003 5 Es)
Es = elastic modulus of steel and
Pu = axial compression on wall
(b) For
where
The value of xu lw to be used in this equation should be calculated from the quadratic equation
where
xu lwlt xu lw
xu lw lt xu lwlt 10
832019 Indian STANDARDS 13920-1993 Code of Practice
BIS is a statutory institution established under the Bureau of Indian Standards Act 1986 to promoteharmonious development of the activities of standardization marking and quality certification of goods andattending to connected matters in the country
Copyright
BIS has the copyright of all its publications No part of these publications may be reproduced in any formwithout the prior permission in writing of BIS This does not preclude the free use in the course of implementing the standard of necessary details such as symbols and sizes type or grade designationsEnquiries relating to copyright be addressed to the Director (Publications) BIS
Review of Indian Standards
Amendments are issued to standards as the need arises on the basis of comments Standards are alsoreviewed periodically a standard along with amendments is reaffirmed when such review indicates that nochanges are needed if the review indicates that changes are needed it is taken up for revision Users of Indian Standards should ascertain that they are in possession of the latest amendments or edition byreferring to the latest issue of lsquoBIS Cataloguersquo and lsquoStandards Monthly Additionsrsquo
This Indian Standard has been developed from Doc No CED 39 (5263)
Amendments Issued Since Publication
Amend No Date of Issue
Amd No 1 November 1995
Amd No 2 March 2002
BUREAU OF INDIAN STANDARDS
Headquarters
Manak Bhavan 9 Bahadur Shah Zafar Marg New Delhi 110002Telephones 323 01 31 323 33 75 323 94 02
Telegrams Manaksanstha(Common to all offices)
Regional Offices Telephone
Central Manak Bhavan 9 Bahadur Shah Zafar MargNEW DELHI 110002
323 76 17323 38 41
Eastern 114 C I T Scheme VII M V I P Road KankurgachiKOLKATA 700054
NOTE The dimension lsquohrsquo of the hoop could be reducedby introducing crossties as shown in Fig 7B In thiscase Ak shall be measured as the overall core arearegardless of the hoop arrangement The hooks of crossties shall engage peripheral longitudinal bars
Example Consider a column of 650 mm times500 mm Let the grade of concrete be M20 andthat of steel Fe 415 for the longitudinal andconfining reinforcement Assuming clear coverof 40 mm to the longitudinal reinforcement andrectangular hoops of diameter 10 mm the sizeof the core is 590 mm times 440 mm As both thesedimensions are greater than 300 mm either a
pair of overlapping hoops or a single hoop withcrossties in both directions will have to beprovided Thus the dimension lsquohrsquo will be thelarger of (i) 5902 = 295 mm and (ii) 4402 =220 mm The spacing of hoops S shall notexceed the smaller of (a) 14 of minimum
member dimensions = 14 times 500 = 125 mm and(b) 100 mm Thus S = 100 mm The area of cross section of the bar forming rectangularhoop works out to be 6447 mm2 This is lessthan the area of cross section of 10 mm bar(7854 mm2) Thus 10 mm diameterrectangular hoops at 100 mm cc will beadequate Similar calculations indicate that asan alternative one could also provide 8 mmdiameter rectangular hoops at 70 mm cc
8 JOINTS OF FRAMES
81 The special confining reinforcement asrequired at the end of column shall be provided
FIG 12 COLUMNS WITH V ARYING STIFFNESS
face It shall not exceed 300 mm ( seeFig 7 ) and
Ak = area of confined concrete core in therectangular hoop measured to itsoutside dimensions
832019 Indian STANDARDS 13920-1993 Code of Practice
through the joint as well unless the joint isconfined as specified by 82
82 A joint which has beams framing into all vertical faces of it and where each beam widthis at least 34 of the column width may be
provided with half the special confiningreinforcement required at the end of thecolumn The spacing of hoops shall not exceed150 mm
9 SHEAR WALLS
91 General Requirements
911 The requirements of this section apply tothe shear walls which are part of the lateralforce resisting system of the structure
912 The thickness of any part of the wall shallpreferably not be less than 150 mm
913 The effective flange width to be used inthe design of flanged wall sections shall beassumed to extend beyond the face of the webfor a distance which shall be the smaller of (a)half the distance to an adjacent shear wall weband (b) 110 th of the total wall height
914 Shear walls shall be provided withreinforcement in the longitudinal andtransverse directions in the plane of the wallThe minimum reinforcement ratio shall be0002 5 of the gross area in each direction Thisreinforcement shall be distributed uniformlyacross the cross section of the wall
915 If the factored shear stress in the wallexceeds 025 or if the wall thicknessexceeds 200 mm reinforcement shall beprovided in two curtains each having barsrunning in the longitudinal and transversedirections in the plane of the wall
916 The diameter of the bars to be used in anypart of the wall shall not exceed 110th of thethickness of that part
917 The maximum spacing of reinforcementin either direction shall not exceed the smallerof lw 5 3tw and 450 mm where lw is thehorizontal length of the wall and tw is the
thickness of the wall web92 Shear Strength
921 The nominal shear stress τ v shall becalculated as
where
922 The design shear strength of concrete τcshall be calculated as per Table 13 of IS 456 1978
923 The nominal shear stress in the wall τ vshall not exceed τc max as per Table 14 of
IS 456 1978924 When τ v is less than τc shearreinforcement shall be provided in accordancewith 914 915 and 917
925 When τ v is greater than τc the area of horizontal shear reinforcement Ah to beprovided within a vertical spacing S v is givenby
where V us = ( V u ndash τc tw dw ) is the shear force
to be resisted by the horizontal reinforcementHowever the amount of horizontalreinforcement provided shall not be less thanthe minimum as per 914
926 The vertical reinforcement that isuniformly distributed in the wall shall not beless than the horizontal reinforcementcalculated as per 925
93 Flexural Strength
931 The moment of resistance M uv of thewall section may be calculated as for columnssubjected to combined bending and axial load
as per IS 456 1978 The moment of resistanceof slender rectangular shear wall section withuniformly distributed vertical reinforcement isgiven in Annex A
932 The cracked flexural strength of the wallsection should be greater than its uncrackedflexural strength
933 In walls that do not have boundaryelements vertical reieforcement shall beconcentrated at the ends of the wall Eachconcentration shall consist of a minimum of 4 bars of 12 mm diameter arranged in at least
2 layers94 Boundary Elements
Boundary elements are portions along the walledges that are strengthened by longitudinaland transverse reinforcement Though theymay have the same thickness as that of thewall web it is advantageous to provide themwith greater thickness
941 Where the extreme fibre compressivestress in the wall due to factored gravity loadsplus factored earthquake force exceeds 02 f ckboundaty elements shall be provided along the
vertical boundaries of walls The boundary
V u = factored shear force
tw = thickness of the web and
dw = effective depth of wall section Thismay by taken as 08 lw for rectangular
sections
f ck
V us
087 f y Ah dw
S v
------------------------------------=
832019 Indian STANDARDS 13920-1993 Code of Practice
elements may be discontinued where thecalculated compressive stress becomes lessthan 015 f ck The compressive stress shall becalculated using a linearly elastic model andgross section properties
942 A boundary element shall have adequateaxial load carrying capacity assuming shortcolumn action so as to enable it to carry anaxial compression equal to the sum of factoredgravity load on it and the additionalcompressive load induced by the seismic forceThe latter may be calculated as
where
943 If the gravity load adds to the strength of the wall its load factor shall be taken as 08
944 The percentage of vertical reinforcementin the boundary elements shall not be less than08 percent nor greater than 6 percent Inorder to avoid congestion the practical upper
limit would be 4 percent945 Boundary elements where required asper 941 shall be provided throughout theirheight with special confining reinforcement asper 74
946 Boundary elements need not be providedif the entire wall section is provided withspecial confining reinforcement as per 74
95 Coupled Shear Walls
951 Coupled shear walls shall be connected byductile coupling beams If the earthquakeinduced shear stress in the coupling beam
exceeds
where ls is the clear span of the coupling beamand D is its overall depth the entireearthquake induced shear and flexure shallpreferably be resisted by diagonalreinforcement
952 The area of reinforcement to be providedalong each diagonal in a diagonally reinforcedcoupling beam shall be
where V u is the factored shear force and α isthe angle made by the diagonal reinforcementwith the horizontal At least 4 bars of 8 mmdiameter shall be provided along each diagonalThe reinforcement along each diagonal shall be
enclosed by special confining reinforcement asper 74 The pitch of spiral or spacing of tiesshall not exceed 100 mm
953 The diagonal or horizontal bars of acoupling beam shall be anchored in theadjacent walls with an anchorage length of 15times the development length in tension
96 Openings in Walls
961 The shear strength of a wall withopenings should be checked along criticalplanes that pass through openings
962 Reinforcement shall be provided along the
edges of openings in walls The area of the vertical and horizontal bars should be such asto equal that of the respective interrupted barsThe vertical bars should extend for the fullstorey height The horizontal bars should beprovided with development length in tensionbeyond the sides of the opening
97 Discontinuous Walls
Columns supporting discontinuous walls shallbe provided with special confiningreinforcement as per 744
98 Construction Joints
The vertical reinforcement ratio across ahorizontal construction joint shall not be lessthan
where τ v is the factored shear stress at the joint Pu is the factored axial force (positive forcompression) and Ag is the gross crosssectional area of the joint
99 Development Splice and AnchorageRequirement
991 Horizontal reinforcement shall beanchored near the edges of the wall or in theconfined core of the boundary elements
992 Splicing of vertical flexural reinforcementshould be avoided as far as possible in regionswhere yielding may take place This zone of flexural yielding may be considered to extendfor a distance of lw above the base of the wall orone sixth of the wall height whichever is moreHowever this distance need not be greaterthan 2 lw Not more than one third of this vertical reinforcement shall be spliced at such asection Splices in adjacent bars should be
staggered by a minimum of 600 mm
M u = factored design moment on the entirewall section
M uv = moment of resistance provided bydistributed vertical reinforcementacross the wall section and
Cw = center to center distance between theboundary elements along the two vertical edges of the wall
M u M uvndash
Cw
--------------------------
832019 Indian STANDARDS 13920-1993 Code of Practice
993 Lateral ties shall be provided aroundlapped spliced bars that are larger than 16 mmin diameter The diameter of the tie shall not beless than one fourth that of the spliced bar norless than 6 mm The spacing of ties shall not
exceed 150 mm center to center
994 Welded splices and mechanicalconnections shall confirm to 25252 of IS 456 1978 However not more than half thereinforcement shall be spliced at a sectionwhere flexural yielding may take place
ANNEX A
( Clause 931 )
MOMENT OF RESISTANCE OF RECTANGULAR SHEAR WALL SECTION
A-1 The moment of resistance of a slender rectangular shear wall section with uniformlydistributed vertical reinforcement may be estimated as follows
These equations were derived assuming a rectangular wall section of depth lw and thickness twthat is subjected to combined uni-axial bending and axial compression The vertical reinforcementis represented by an equivalent steel plate along the length of the section The stress-strain curveassumed for concrete is as per IS 456 1978 whereas that for steel is assumed to be bi-linear Twoequations are given for calculating the flexural strength of the section Their use depends on
whether the section fails in flexural tension or in flexural compression
(a) For
where
ρ = vertical reinforcement ratio = Ast ( tw lw )
Ast = area of uniformly distributed vertical reinforcement
β = 087 f y (0003 5 Es)
Es = elastic modulus of steel and
Pu = axial compression on wall
(b) For
where
The value of xu lw to be used in this equation should be calculated from the quadratic equation
where
xu lwlt xu lw
xu lw lt xu lwlt 10
832019 Indian STANDARDS 13920-1993 Code of Practice
BIS is a statutory institution established under the Bureau of Indian Standards Act 1986 to promoteharmonious development of the activities of standardization marking and quality certification of goods andattending to connected matters in the country
Copyright
BIS has the copyright of all its publications No part of these publications may be reproduced in any formwithout the prior permission in writing of BIS This does not preclude the free use in the course of implementing the standard of necessary details such as symbols and sizes type or grade designationsEnquiries relating to copyright be addressed to the Director (Publications) BIS
Review of Indian Standards
Amendments are issued to standards as the need arises on the basis of comments Standards are alsoreviewed periodically a standard along with amendments is reaffirmed when such review indicates that nochanges are needed if the review indicates that changes are needed it is taken up for revision Users of Indian Standards should ascertain that they are in possession of the latest amendments or edition byreferring to the latest issue of lsquoBIS Cataloguersquo and lsquoStandards Monthly Additionsrsquo
This Indian Standard has been developed from Doc No CED 39 (5263)
Amendments Issued Since Publication
Amend No Date of Issue
Amd No 1 November 1995
Amd No 2 March 2002
BUREAU OF INDIAN STANDARDS
Headquarters
Manak Bhavan 9 Bahadur Shah Zafar Marg New Delhi 110002Telephones 323 01 31 323 33 75 323 94 02
Telegrams Manaksanstha(Common to all offices)
Regional Offices Telephone
Central Manak Bhavan 9 Bahadur Shah Zafar MargNEW DELHI 110002
323 76 17323 38 41
Eastern 114 C I T Scheme VII M V I P Road KankurgachiKOLKATA 700054
through the joint as well unless the joint isconfined as specified by 82
82 A joint which has beams framing into all vertical faces of it and where each beam widthis at least 34 of the column width may be
provided with half the special confiningreinforcement required at the end of thecolumn The spacing of hoops shall not exceed150 mm
9 SHEAR WALLS
91 General Requirements
911 The requirements of this section apply tothe shear walls which are part of the lateralforce resisting system of the structure
912 The thickness of any part of the wall shallpreferably not be less than 150 mm
913 The effective flange width to be used inthe design of flanged wall sections shall beassumed to extend beyond the face of the webfor a distance which shall be the smaller of (a)half the distance to an adjacent shear wall weband (b) 110 th of the total wall height
914 Shear walls shall be provided withreinforcement in the longitudinal andtransverse directions in the plane of the wallThe minimum reinforcement ratio shall be0002 5 of the gross area in each direction Thisreinforcement shall be distributed uniformlyacross the cross section of the wall
915 If the factored shear stress in the wallexceeds 025 or if the wall thicknessexceeds 200 mm reinforcement shall beprovided in two curtains each having barsrunning in the longitudinal and transversedirections in the plane of the wall
916 The diameter of the bars to be used in anypart of the wall shall not exceed 110th of thethickness of that part
917 The maximum spacing of reinforcementin either direction shall not exceed the smallerof lw 5 3tw and 450 mm where lw is thehorizontal length of the wall and tw is the
thickness of the wall web92 Shear Strength
921 The nominal shear stress τ v shall becalculated as
where
922 The design shear strength of concrete τcshall be calculated as per Table 13 of IS 456 1978
923 The nominal shear stress in the wall τ vshall not exceed τc max as per Table 14 of
IS 456 1978924 When τ v is less than τc shearreinforcement shall be provided in accordancewith 914 915 and 917
925 When τ v is greater than τc the area of horizontal shear reinforcement Ah to beprovided within a vertical spacing S v is givenby
where V us = ( V u ndash τc tw dw ) is the shear force
to be resisted by the horizontal reinforcementHowever the amount of horizontalreinforcement provided shall not be less thanthe minimum as per 914
926 The vertical reinforcement that isuniformly distributed in the wall shall not beless than the horizontal reinforcementcalculated as per 925
93 Flexural Strength
931 The moment of resistance M uv of thewall section may be calculated as for columnssubjected to combined bending and axial load
as per IS 456 1978 The moment of resistanceof slender rectangular shear wall section withuniformly distributed vertical reinforcement isgiven in Annex A
932 The cracked flexural strength of the wallsection should be greater than its uncrackedflexural strength
933 In walls that do not have boundaryelements vertical reieforcement shall beconcentrated at the ends of the wall Eachconcentration shall consist of a minimum of 4 bars of 12 mm diameter arranged in at least
2 layers94 Boundary Elements
Boundary elements are portions along the walledges that are strengthened by longitudinaland transverse reinforcement Though theymay have the same thickness as that of thewall web it is advantageous to provide themwith greater thickness
941 Where the extreme fibre compressivestress in the wall due to factored gravity loadsplus factored earthquake force exceeds 02 f ckboundaty elements shall be provided along the
vertical boundaries of walls The boundary
V u = factored shear force
tw = thickness of the web and
dw = effective depth of wall section Thismay by taken as 08 lw for rectangular
sections
f ck
V us
087 f y Ah dw
S v
------------------------------------=
832019 Indian STANDARDS 13920-1993 Code of Practice
elements may be discontinued where thecalculated compressive stress becomes lessthan 015 f ck The compressive stress shall becalculated using a linearly elastic model andgross section properties
942 A boundary element shall have adequateaxial load carrying capacity assuming shortcolumn action so as to enable it to carry anaxial compression equal to the sum of factoredgravity load on it and the additionalcompressive load induced by the seismic forceThe latter may be calculated as
where
943 If the gravity load adds to the strength of the wall its load factor shall be taken as 08
944 The percentage of vertical reinforcementin the boundary elements shall not be less than08 percent nor greater than 6 percent Inorder to avoid congestion the practical upper
limit would be 4 percent945 Boundary elements where required asper 941 shall be provided throughout theirheight with special confining reinforcement asper 74
946 Boundary elements need not be providedif the entire wall section is provided withspecial confining reinforcement as per 74
95 Coupled Shear Walls
951 Coupled shear walls shall be connected byductile coupling beams If the earthquakeinduced shear stress in the coupling beam
exceeds
where ls is the clear span of the coupling beamand D is its overall depth the entireearthquake induced shear and flexure shallpreferably be resisted by diagonalreinforcement
952 The area of reinforcement to be providedalong each diagonal in a diagonally reinforcedcoupling beam shall be
where V u is the factored shear force and α isthe angle made by the diagonal reinforcementwith the horizontal At least 4 bars of 8 mmdiameter shall be provided along each diagonalThe reinforcement along each diagonal shall be
enclosed by special confining reinforcement asper 74 The pitch of spiral or spacing of tiesshall not exceed 100 mm
953 The diagonal or horizontal bars of acoupling beam shall be anchored in theadjacent walls with an anchorage length of 15times the development length in tension
96 Openings in Walls
961 The shear strength of a wall withopenings should be checked along criticalplanes that pass through openings
962 Reinforcement shall be provided along the
edges of openings in walls The area of the vertical and horizontal bars should be such asto equal that of the respective interrupted barsThe vertical bars should extend for the fullstorey height The horizontal bars should beprovided with development length in tensionbeyond the sides of the opening
97 Discontinuous Walls
Columns supporting discontinuous walls shallbe provided with special confiningreinforcement as per 744
98 Construction Joints
The vertical reinforcement ratio across ahorizontal construction joint shall not be lessthan
where τ v is the factored shear stress at the joint Pu is the factored axial force (positive forcompression) and Ag is the gross crosssectional area of the joint
99 Development Splice and AnchorageRequirement
991 Horizontal reinforcement shall beanchored near the edges of the wall or in theconfined core of the boundary elements
992 Splicing of vertical flexural reinforcementshould be avoided as far as possible in regionswhere yielding may take place This zone of flexural yielding may be considered to extendfor a distance of lw above the base of the wall orone sixth of the wall height whichever is moreHowever this distance need not be greaterthan 2 lw Not more than one third of this vertical reinforcement shall be spliced at such asection Splices in adjacent bars should be
staggered by a minimum of 600 mm
M u = factored design moment on the entirewall section
M uv = moment of resistance provided bydistributed vertical reinforcementacross the wall section and
Cw = center to center distance between theboundary elements along the two vertical edges of the wall
M u M uvndash
Cw
--------------------------
832019 Indian STANDARDS 13920-1993 Code of Practice
993 Lateral ties shall be provided aroundlapped spliced bars that are larger than 16 mmin diameter The diameter of the tie shall not beless than one fourth that of the spliced bar norless than 6 mm The spacing of ties shall not
exceed 150 mm center to center
994 Welded splices and mechanicalconnections shall confirm to 25252 of IS 456 1978 However not more than half thereinforcement shall be spliced at a sectionwhere flexural yielding may take place
ANNEX A
( Clause 931 )
MOMENT OF RESISTANCE OF RECTANGULAR SHEAR WALL SECTION
A-1 The moment of resistance of a slender rectangular shear wall section with uniformlydistributed vertical reinforcement may be estimated as follows
These equations were derived assuming a rectangular wall section of depth lw and thickness twthat is subjected to combined uni-axial bending and axial compression The vertical reinforcementis represented by an equivalent steel plate along the length of the section The stress-strain curveassumed for concrete is as per IS 456 1978 whereas that for steel is assumed to be bi-linear Twoequations are given for calculating the flexural strength of the section Their use depends on
whether the section fails in flexural tension or in flexural compression
(a) For
where
ρ = vertical reinforcement ratio = Ast ( tw lw )
Ast = area of uniformly distributed vertical reinforcement
β = 087 f y (0003 5 Es)
Es = elastic modulus of steel and
Pu = axial compression on wall
(b) For
where
The value of xu lw to be used in this equation should be calculated from the quadratic equation
where
xu lwlt xu lw
xu lw lt xu lwlt 10
832019 Indian STANDARDS 13920-1993 Code of Practice
BIS is a statutory institution established under the Bureau of Indian Standards Act 1986 to promoteharmonious development of the activities of standardization marking and quality certification of goods andattending to connected matters in the country
Copyright
BIS has the copyright of all its publications No part of these publications may be reproduced in any formwithout the prior permission in writing of BIS This does not preclude the free use in the course of implementing the standard of necessary details such as symbols and sizes type or grade designationsEnquiries relating to copyright be addressed to the Director (Publications) BIS
Review of Indian Standards
Amendments are issued to standards as the need arises on the basis of comments Standards are alsoreviewed periodically a standard along with amendments is reaffirmed when such review indicates that nochanges are needed if the review indicates that changes are needed it is taken up for revision Users of Indian Standards should ascertain that they are in possession of the latest amendments or edition byreferring to the latest issue of lsquoBIS Cataloguersquo and lsquoStandards Monthly Additionsrsquo
This Indian Standard has been developed from Doc No CED 39 (5263)
Amendments Issued Since Publication
Amend No Date of Issue
Amd No 1 November 1995
Amd No 2 March 2002
BUREAU OF INDIAN STANDARDS
Headquarters
Manak Bhavan 9 Bahadur Shah Zafar Marg New Delhi 110002Telephones 323 01 31 323 33 75 323 94 02
Telegrams Manaksanstha(Common to all offices)
Regional Offices Telephone
Central Manak Bhavan 9 Bahadur Shah Zafar MargNEW DELHI 110002
323 76 17323 38 41
Eastern 114 C I T Scheme VII M V I P Road KankurgachiKOLKATA 700054
elements may be discontinued where thecalculated compressive stress becomes lessthan 015 f ck The compressive stress shall becalculated using a linearly elastic model andgross section properties
942 A boundary element shall have adequateaxial load carrying capacity assuming shortcolumn action so as to enable it to carry anaxial compression equal to the sum of factoredgravity load on it and the additionalcompressive load induced by the seismic forceThe latter may be calculated as
where
943 If the gravity load adds to the strength of the wall its load factor shall be taken as 08
944 The percentage of vertical reinforcementin the boundary elements shall not be less than08 percent nor greater than 6 percent Inorder to avoid congestion the practical upper
limit would be 4 percent945 Boundary elements where required asper 941 shall be provided throughout theirheight with special confining reinforcement asper 74
946 Boundary elements need not be providedif the entire wall section is provided withspecial confining reinforcement as per 74
95 Coupled Shear Walls
951 Coupled shear walls shall be connected byductile coupling beams If the earthquakeinduced shear stress in the coupling beam
exceeds
where ls is the clear span of the coupling beamand D is its overall depth the entireearthquake induced shear and flexure shallpreferably be resisted by diagonalreinforcement
952 The area of reinforcement to be providedalong each diagonal in a diagonally reinforcedcoupling beam shall be
where V u is the factored shear force and α isthe angle made by the diagonal reinforcementwith the horizontal At least 4 bars of 8 mmdiameter shall be provided along each diagonalThe reinforcement along each diagonal shall be
enclosed by special confining reinforcement asper 74 The pitch of spiral or spacing of tiesshall not exceed 100 mm
953 The diagonal or horizontal bars of acoupling beam shall be anchored in theadjacent walls with an anchorage length of 15times the development length in tension
96 Openings in Walls
961 The shear strength of a wall withopenings should be checked along criticalplanes that pass through openings
962 Reinforcement shall be provided along the
edges of openings in walls The area of the vertical and horizontal bars should be such asto equal that of the respective interrupted barsThe vertical bars should extend for the fullstorey height The horizontal bars should beprovided with development length in tensionbeyond the sides of the opening
97 Discontinuous Walls
Columns supporting discontinuous walls shallbe provided with special confiningreinforcement as per 744
98 Construction Joints
The vertical reinforcement ratio across ahorizontal construction joint shall not be lessthan
where τ v is the factored shear stress at the joint Pu is the factored axial force (positive forcompression) and Ag is the gross crosssectional area of the joint
99 Development Splice and AnchorageRequirement
991 Horizontal reinforcement shall beanchored near the edges of the wall or in theconfined core of the boundary elements
992 Splicing of vertical flexural reinforcementshould be avoided as far as possible in regionswhere yielding may take place This zone of flexural yielding may be considered to extendfor a distance of lw above the base of the wall orone sixth of the wall height whichever is moreHowever this distance need not be greaterthan 2 lw Not more than one third of this vertical reinforcement shall be spliced at such asection Splices in adjacent bars should be
staggered by a minimum of 600 mm
M u = factored design moment on the entirewall section
M uv = moment of resistance provided bydistributed vertical reinforcementacross the wall section and
Cw = center to center distance between theboundary elements along the two vertical edges of the wall
M u M uvndash
Cw
--------------------------
832019 Indian STANDARDS 13920-1993 Code of Practice
993 Lateral ties shall be provided aroundlapped spliced bars that are larger than 16 mmin diameter The diameter of the tie shall not beless than one fourth that of the spliced bar norless than 6 mm The spacing of ties shall not
exceed 150 mm center to center
994 Welded splices and mechanicalconnections shall confirm to 25252 of IS 456 1978 However not more than half thereinforcement shall be spliced at a sectionwhere flexural yielding may take place
ANNEX A
( Clause 931 )
MOMENT OF RESISTANCE OF RECTANGULAR SHEAR WALL SECTION
A-1 The moment of resistance of a slender rectangular shear wall section with uniformlydistributed vertical reinforcement may be estimated as follows
These equations were derived assuming a rectangular wall section of depth lw and thickness twthat is subjected to combined uni-axial bending and axial compression The vertical reinforcementis represented by an equivalent steel plate along the length of the section The stress-strain curveassumed for concrete is as per IS 456 1978 whereas that for steel is assumed to be bi-linear Twoequations are given for calculating the flexural strength of the section Their use depends on
whether the section fails in flexural tension or in flexural compression
(a) For
where
ρ = vertical reinforcement ratio = Ast ( tw lw )
Ast = area of uniformly distributed vertical reinforcement
β = 087 f y (0003 5 Es)
Es = elastic modulus of steel and
Pu = axial compression on wall
(b) For
where
The value of xu lw to be used in this equation should be calculated from the quadratic equation
where
xu lwlt xu lw
xu lw lt xu lwlt 10
832019 Indian STANDARDS 13920-1993 Code of Practice
BIS is a statutory institution established under the Bureau of Indian Standards Act 1986 to promoteharmonious development of the activities of standardization marking and quality certification of goods andattending to connected matters in the country
Copyright
BIS has the copyright of all its publications No part of these publications may be reproduced in any formwithout the prior permission in writing of BIS This does not preclude the free use in the course of implementing the standard of necessary details such as symbols and sizes type or grade designationsEnquiries relating to copyright be addressed to the Director (Publications) BIS
Review of Indian Standards
Amendments are issued to standards as the need arises on the basis of comments Standards are alsoreviewed periodically a standard along with amendments is reaffirmed when such review indicates that nochanges are needed if the review indicates that changes are needed it is taken up for revision Users of Indian Standards should ascertain that they are in possession of the latest amendments or edition byreferring to the latest issue of lsquoBIS Cataloguersquo and lsquoStandards Monthly Additionsrsquo
This Indian Standard has been developed from Doc No CED 39 (5263)
Amendments Issued Since Publication
Amend No Date of Issue
Amd No 1 November 1995
Amd No 2 March 2002
BUREAU OF INDIAN STANDARDS
Headquarters
Manak Bhavan 9 Bahadur Shah Zafar Marg New Delhi 110002Telephones 323 01 31 323 33 75 323 94 02
Telegrams Manaksanstha(Common to all offices)
Regional Offices Telephone
Central Manak Bhavan 9 Bahadur Shah Zafar MargNEW DELHI 110002
323 76 17323 38 41
Eastern 114 C I T Scheme VII M V I P Road KankurgachiKOLKATA 700054
993 Lateral ties shall be provided aroundlapped spliced bars that are larger than 16 mmin diameter The diameter of the tie shall not beless than one fourth that of the spliced bar norless than 6 mm The spacing of ties shall not
exceed 150 mm center to center
994 Welded splices and mechanicalconnections shall confirm to 25252 of IS 456 1978 However not more than half thereinforcement shall be spliced at a sectionwhere flexural yielding may take place
ANNEX A
( Clause 931 )
MOMENT OF RESISTANCE OF RECTANGULAR SHEAR WALL SECTION
A-1 The moment of resistance of a slender rectangular shear wall section with uniformlydistributed vertical reinforcement may be estimated as follows
These equations were derived assuming a rectangular wall section of depth lw and thickness twthat is subjected to combined uni-axial bending and axial compression The vertical reinforcementis represented by an equivalent steel plate along the length of the section The stress-strain curveassumed for concrete is as per IS 456 1978 whereas that for steel is assumed to be bi-linear Twoequations are given for calculating the flexural strength of the section Their use depends on
whether the section fails in flexural tension or in flexural compression
(a) For
where
ρ = vertical reinforcement ratio = Ast ( tw lw )
Ast = area of uniformly distributed vertical reinforcement
β = 087 f y (0003 5 Es)
Es = elastic modulus of steel and
Pu = axial compression on wall
(b) For
where
The value of xu lw to be used in this equation should be calculated from the quadratic equation
where
xu lwlt xu lw
xu lw lt xu lwlt 10
832019 Indian STANDARDS 13920-1993 Code of Practice
BIS is a statutory institution established under the Bureau of Indian Standards Act 1986 to promoteharmonious development of the activities of standardization marking and quality certification of goods andattending to connected matters in the country
Copyright
BIS has the copyright of all its publications No part of these publications may be reproduced in any formwithout the prior permission in writing of BIS This does not preclude the free use in the course of implementing the standard of necessary details such as symbols and sizes type or grade designationsEnquiries relating to copyright be addressed to the Director (Publications) BIS
Review of Indian Standards
Amendments are issued to standards as the need arises on the basis of comments Standards are alsoreviewed periodically a standard along with amendments is reaffirmed when such review indicates that nochanges are needed if the review indicates that changes are needed it is taken up for revision Users of Indian Standards should ascertain that they are in possession of the latest amendments or edition byreferring to the latest issue of lsquoBIS Cataloguersquo and lsquoStandards Monthly Additionsrsquo
This Indian Standard has been developed from Doc No CED 39 (5263)
Amendments Issued Since Publication
Amend No Date of Issue
Amd No 1 November 1995
Amd No 2 March 2002
BUREAU OF INDIAN STANDARDS
Headquarters
Manak Bhavan 9 Bahadur Shah Zafar Marg New Delhi 110002Telephones 323 01 31 323 33 75 323 94 02
Telegrams Manaksanstha(Common to all offices)
Regional Offices Telephone
Central Manak Bhavan 9 Bahadur Shah Zafar MargNEW DELHI 110002
323 76 17323 38 41
Eastern 114 C I T Scheme VII M V I P Road KankurgachiKOLKATA 700054
BIS is a statutory institution established under the Bureau of Indian Standards Act 1986 to promoteharmonious development of the activities of standardization marking and quality certification of goods andattending to connected matters in the country
Copyright
BIS has the copyright of all its publications No part of these publications may be reproduced in any formwithout the prior permission in writing of BIS This does not preclude the free use in the course of implementing the standard of necessary details such as symbols and sizes type or grade designationsEnquiries relating to copyright be addressed to the Director (Publications) BIS
Review of Indian Standards
Amendments are issued to standards as the need arises on the basis of comments Standards are alsoreviewed periodically a standard along with amendments is reaffirmed when such review indicates that nochanges are needed if the review indicates that changes are needed it is taken up for revision Users of Indian Standards should ascertain that they are in possession of the latest amendments or edition byreferring to the latest issue of lsquoBIS Cataloguersquo and lsquoStandards Monthly Additionsrsquo
This Indian Standard has been developed from Doc No CED 39 (5263)
Amendments Issued Since Publication
Amend No Date of Issue
Amd No 1 November 1995
Amd No 2 March 2002
BUREAU OF INDIAN STANDARDS
Headquarters
Manak Bhavan 9 Bahadur Shah Zafar Marg New Delhi 110002Telephones 323 01 31 323 33 75 323 94 02
Telegrams Manaksanstha(Common to all offices)
Regional Offices Telephone
Central Manak Bhavan 9 Bahadur Shah Zafar MargNEW DELHI 110002
323 76 17323 38 41
Eastern 114 C I T Scheme VII M V I P Road KankurgachiKOLKATA 700054
BIS is a statutory institution established under the Bureau of Indian Standards Act 1986 to promoteharmonious development of the activities of standardization marking and quality certification of goods andattending to connected matters in the country
Copyright
BIS has the copyright of all its publications No part of these publications may be reproduced in any formwithout the prior permission in writing of BIS This does not preclude the free use in the course of implementing the standard of necessary details such as symbols and sizes type or grade designationsEnquiries relating to copyright be addressed to the Director (Publications) BIS
Review of Indian Standards
Amendments are issued to standards as the need arises on the basis of comments Standards are alsoreviewed periodically a standard along with amendments is reaffirmed when such review indicates that nochanges are needed if the review indicates that changes are needed it is taken up for revision Users of Indian Standards should ascertain that they are in possession of the latest amendments or edition byreferring to the latest issue of lsquoBIS Cataloguersquo and lsquoStandards Monthly Additionsrsquo
This Indian Standard has been developed from Doc No CED 39 (5263)
Amendments Issued Since Publication
Amend No Date of Issue
Amd No 1 November 1995
Amd No 2 March 2002
BUREAU OF INDIAN STANDARDS
Headquarters
Manak Bhavan 9 Bahadur Shah Zafar Marg New Delhi 110002Telephones 323 01 31 323 33 75 323 94 02
Telegrams Manaksanstha(Common to all offices)
Regional Offices Telephone
Central Manak Bhavan 9 Bahadur Shah Zafar MargNEW DELHI 110002
323 76 17323 38 41
Eastern 114 C I T Scheme VII M V I P Road KankurgachiKOLKATA 700054
BIS is a statutory institution established under the Bureau of Indian Standards Act 1986 to promoteharmonious development of the activities of standardization marking and quality certification of goods andattending to connected matters in the country
Copyright
BIS has the copyright of all its publications No part of these publications may be reproduced in any formwithout the prior permission in writing of BIS This does not preclude the free use in the course of implementing the standard of necessary details such as symbols and sizes type or grade designationsEnquiries relating to copyright be addressed to the Director (Publications) BIS
Review of Indian Standards
Amendments are issued to standards as the need arises on the basis of comments Standards are alsoreviewed periodically a standard along with amendments is reaffirmed when such review indicates that nochanges are needed if the review indicates that changes are needed it is taken up for revision Users of Indian Standards should ascertain that they are in possession of the latest amendments or edition byreferring to the latest issue of lsquoBIS Cataloguersquo and lsquoStandards Monthly Additionsrsquo
This Indian Standard has been developed from Doc No CED 39 (5263)
Amendments Issued Since Publication
Amend No Date of Issue
Amd No 1 November 1995
Amd No 2 March 2002
BUREAU OF INDIAN STANDARDS
Headquarters
Manak Bhavan 9 Bahadur Shah Zafar Marg New Delhi 110002Telephones 323 01 31 323 33 75 323 94 02
Telegrams Manaksanstha(Common to all offices)
Regional Offices Telephone
Central Manak Bhavan 9 Bahadur Shah Zafar MargNEW DELHI 110002
323 76 17323 38 41
Eastern 114 C I T Scheme VII M V I P Road KankurgachiKOLKATA 700054