REINFORCED CEMENT CONCRETE Lab Manual · Web viewREINFORCED CEMENT CONCRETE Lab Manual2018. REINFORCED CEMENT CONCRETE Lab Manual. 2018. Aquib AnsariPage 1

Roll No:____Name:__________________Year:____ Semester:___

REINFORCED CEMENT CONCRETE Lab Manual

CERTIFICATECertified that this file is submitted by

Shri/Ku.___________________________________________________________

Roll No.________a student of ________ year of the course __________________

______________________________________ as a part of PRACTICAL/ORAL as

prescribed by the Rashtrasant Tukadoji Maharaj Nagpur University for the

subject_____________________________________ in the laboratory of

___________________________________during the academic year

_________________________ and that I have instructed him/her for the said work,

from time to time and I found him/her to be satisfactory progressive.

And that I have accessed the said work and I am satisfied that the same is up to that

standard envisaged for the course.

Date:- Signature & Name Signature & Name of Subject Teacher of HOD

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Anjuman College of Engineering and Technology

Vision To be a centre of excellence for developing quality technocrats with

moral and social ethics, to face the global challenges for the sustainable development of society.

Mission To create conducive academic culture for learning and identifying

career goals. To provide quality technical education, research opportunities and

imbibe entrepreneurship skills contributing to the socio-economic growth of the Nation.

To inculcate values and skills, that will empower our students towards development through technology.

Vision and Mission of the DepartmentVision:

To be the centre of excellence for developing quality Civil Engineers with moral and social ethics to face global challenges for the sustainable development of society.

Mission: To create conductive academic culture for learning and identifying

career goals. To impart quality technical education along with research

opportunities. To impart knowledge and generate entrepreneurship skills

contributing to socio-economic growth of the nation. To inculcate values and skills, that will empower our students,

towards National development through technology, to preserve nature and its resources.

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Program Educational Objectives (PEOs) Apply technical knowledge to find solution to the challenges in

various areas and to develop independent thinking in the field of Civil Engineering.

Have analyze, design, technical and soft skills, for solving problem Civil Engineering.

Inculcate morality professionals and ethical sense and self confidence.

Take higher education or lifelong learning and contribute in research and development throughout life.

Program Specific Outcomes (PSOs) An ability to plan, analyze, design and execute low cost housing and construction

works.

An ability to provide the basic facilities with optimal utilization of resources to meet

the societal needs.

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PROGRAM: CE DEGREE: B.E

COURSE: Reinforced Cement Concrete SEMESTER: V CREDITS:

COURSE CODE: BECVE502P COURSE TYPE: REGULAR

COURSE AREA/DOMAIN: CONTACT HOURS: 2 hours/Week.

CORRESPONDING LAB COURSE CODE : LAB COURSE NAME : Reinforced Cement

Concrete

COURSE PRE-REQUISITES:

C.CODE COURSE NAME DESCRIPTION SEM

BECVE402P Reinforced Cement Concrete V

LAB COURSE OBJECTIVES: Student shall able to

Design of beams, columns, slab and foundation as per relevant IS Code

Understanding the professional RCC drawing.

Visit at least one site visit pertaining to above design

COURSE OUTCOMES: Design Patterns

After completion of this course the students will be able -

SNO DESCRIPTION BLOOM’S TAXONOMY

LEVEL

CO.1 Apply the knowledge in actual structural design for various buildings. 3

CO.2 Make use of structural design knowledge in reading and understanding the professional RCC drawing and draw an appropriate conclusion.

6

CO.3 Explain the implementation of working drawing and write a report during the visit to any construction site.

5

CO.4 Apply the concepts of design to find the various solution 3

CO.5 Use the knowledge of structural design to deal with complex problems 3

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Lab Instructions: Students should come to the lab/class on time unless prior permission is obtained from the

supervisor. As per department policy, a grace period of 10 minutes will be given to late

students. Student arriving after 10 minutes of the starting time will be considered absent.

Hence, he/she will automatically receive “zero” mark for the lab report.

Students will be divided into groups (preferably 5/6 students in a group). Each group

will be given a handout. This will serve as a guide for them throughout the practical.

All students must have to submit the practical report just after the entrance and before the

class start.

Practical reports have to be submitted serially.

Students have to complete the sample calculations in class and take sign from

the course teacher. (In some practical which require more times, should be completed

as possible in class time.)

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Continuous Assessment Practical

Exp

NoNAME OF EXPERIMENT Date Sign Remark

1 Design of Beams

2Design of Slabs

3Design of Columns

4 Design of Footing

5 Site Visit

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CONTENTS

Exp

NoNAME OF EXPERIMENT Date Sign Remark

1 Design of Beams

2Design of Slabs

3Design of Columns

4 Design of Footing

5 Site Visit

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PRACTICAL NO – 1

DESIGN OF BEAMS

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Design of Beams

In this practical, it is intended to learn the method of designing the beams using the principles

developed in previous chapters. Design consists of selecting proper materials, shape and size of the structural

member keeping in view the economy, stability and aesthetics. The design of beams are done for the limit state

of collapse and checked for the other limit states. Normally the beam is designed for flexure and checked for

shear, deflection, cracking and bond.

Design procedureThe procedure for the design of beam may be summarized as follows:

1. Estimation of loads2. Analysis3. Design

1. Estimation of loads

The loads that get realized on the beams consist of the following:

a. Self-weight of the beam.

b. Weight of the wall constructed on the beam

c. The portion of the slab loads which gets transferred to the beams. These slab loads are due to live loads that

are acting on the slab dead loads such as self-weight of the slab, floor finishes, partitions, false ceiling and

some special fixed loads.

The economy and safety of the beams achieved depends on the accuracy with which the loads are estimated.

The dead loads are calculated based on the density whereas the live loads are taken from IS: 875 depending

on the functional use of the building.

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2. Analysis

For the loads that are acting on the beams, the analysis is done by any standard method to obtain the shear

forces and bending moments.

3. Design

a. Selection of width and depth of the beam.

The width of the beam selected shall satisfy the slenderness limits specified in IS 456: 2000 clause 23.3 to

ensure the lateral stability.

b. Calculation of effective span (le) (Refer clause 22.2, IS 456:2000)

c. Calculation of loads (w)

d. Calculation of critical moments and shears.

The moment and shear that exists at the critical sections are considered for the design. Critical sections are the

sections where the values are maximum. Critical section for the moment in a simply supported beam is at the

point where the shear force is zero. For continuous beams the critical section for the +ve bending moment is in

the span and –ve bending moment is at the support. The critical section for the shear is at the support.

e. Find the factored shear (Vu) and factored moment (Mu)

f. Check for the depth based on maximum bending moment.

Considering the section to be nearly balanced section and using the equation Annexure G, IS 456-2000

obtaining the value of the required depth d required. If the assumed depth “d” is greater than the “d required”, it

satisfies the depth criteria based on flexure. If the assumed section is less than the” d required”, revise the

section.

g. Calculation of steel.

As the section is under reinforced, use the equation G.1.1.(b) to obtain the steel.

h. Check for shear.

i. Check for developmental length.

j. Check for deflection.

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k. Check for Ast min, Ast max and distance between the two bars.

Anchorage of bars or check for development length

In accordance with clause 26.2 IS 456: 2000, the bars shall be extended (or anchored) for a certain

distance on either side of the point of maximum bending moment where there is maximum stress (Tension or

Compression). This distance is known as the development length and is required in order to prevent the bar

from pulling out under tension or pushing in under compression. The development length (Ld) is given by

where, ∅ = Nominal diameter of the bar

= Stress in bar at the section considered at design load

Zbd= Design bond stress given in table 26.2.1.1 (IS 456: 2000)

Table 26.2.1.1: Design bond stress in limit state method for plain bars in tension shall be as below:Grade of concrete M 20 M 25 M 30 M 35 M 40 and above

Design bond stress 1.2 1.4 1.5 1.7 1.9

IMPORTANT NOTES1. Due to the above requirement it can be concluded that no bar can be bent up or curtailed up to a

distance of development length from the point of maximum moment.

2. Due to practical difficulties if it is not possible to provide the required embedment or development

length, bends hooks and mechanical anchorages are used.

3. Flexural reinforcement shall not be terminated in a tension zone unless any one of the

following condition is satisfied:

a. The shear at the cut-off points does not exceed two-thirds that permitted, including the shear strength

of web reinforcement provided.

b. Stirrup area in excess of that required for shear and torsion is provided along each terminated bar over

a distance from the cut-off point equal to three-fourths the effective depth of the member. The excess


stirrup area shall be not less than 0.4bs/fy, where b is the breadth of the beam, s is the spacing and fy

is the characteristic strength of reinforcement in N/mm2. The resulting spacing shall not exceed d/8_

where _ is the ratio of the area of bars cut-off to the total area of bars at the section, and d is the

effective depth.

c. For 36 mm and smaller bars, the continuing bars provide double the area required for flexure at the cut-

off point and the shear does not exceed three-fourths that permitted.

Positive moment reinforcementa. At least one-third the positive moment reinforcement in simple members and one fourth the positive

moment reinforcement in continuous members shall extend along the same face of the member into the

support, to a length equal to Ld/3.

b. When a flexural member is part of the primary lateral load resisting system, the positive reinforcement

required to be extended into the support as described in (a) shall be anchored to develop its design

stress in tension at the face of the support.

c. At simple supports and at points of inflection, positive moment tension reinforcement shall be limited to

a diameter such that Ld computed for fd by 26.2.1 IS 456:2000 does not exceed.

Where, M1 = moment of resistance of the section assuming all reinforcement at the section to be

stressed to fd

fd = 0.87fy in the case of limit state design and the permissible stress in the case of working stress

design;

V = shear force at the section due to the design loads;

L0 = sum of the anchorage beyond the centre of the support and the equivalent anchorage value of any

hook or mechanical anchorage at simple support; and at a point of inflection, L0 is limited to the

effective depth of the members or 12∅ , whichever is greater; and∅ = Diameter of bar

The value of M1/V in the above expression may be increased by 30 percent when the ends of the reinforcement

are confined by a compressive reaction.

Negative moment reinforcement


At least one third of the total reinforcement provided for negative moment at the support shall extend beyond

the point of inflection for a distance not less than the effective depth of the member of 12∅ or one-sixteenth of

the clear span whichever is greater.

Anchorage of barsAnchoring of bars is done to provide the development length and maintain the integrity of the structure.

Anchoring bars in tensiona. Deformed bars may be used without end anchorages provided development length requirement is

satisfied. Hooks should normally be provided for plain bars in tension.

b. Bends and hooks – shall conform to IS 2502

1. Bends – The anchorage value of bend shall be taken as 4 times the diameter of the bar for each 450

bend subject to a maximum of 16 times the diameter of the bar.

2. Hooks – The anchorage value of a standard U-type hook shall be equal to 16 times

the diameter of the bar.

Anchoring bars in compressionThe anchorage length of straight bar in compression shall be equal to the development length of bars in

compression as specified in clause 26.2.1 of IS 456:2000. The projected length of hooks, bends and straight

lengths beyond bends if provided for a bar in compression, shall only be considered for development length.

Anchoring shear reinforcementa. Inclined bars – The development length shall be as for bars in tension; this length shall be measured as

under:

1. In tension zone, from the end of the sloping or inclined portion of the bar, and

2. In the compression zone, from the mid depth of the beam.

b. Stirrups – Not withstanding any of the provisions of this standard, in case of secondary reinforcement, such

as stirrups and transverse ties, complete development lengths and anchorages shall be deemed to have been

provided when the bar is bent through an angle of at least 900 round a bar of at least its own diameter and is

continued beyond the end of the curve for a length of at least eight diameters, or when

the bar is bent through an angle of 1350 and is continued beyond the end of the curve for a length of at least six

bar diameters or when the bar is bent through an angle of 1800 and is continued beyond the end of the curve

for a length of at least four bar diameters.

Reinforcement requirements1. Minimum reinforcementThe minimum area of tension reinforcement shall be not less than that given by the following


Where, As = minimum area of tension reinforcement.

b = breadth of beam or the breadth of the web of T-beam,

d = effective depth, and

fy = characteristic strength of reinforcement in N/mm2

2. Maximum reinforcementThe maximum area of tension reinforcement shall not exceed 0.04bD

Compression reinforcementThe maximum area of compression reinforcement shall not exceed 0.04bD. Compression reinforcement in

beams shall be enclosed by stirrups for effective lateral restraint.

Slenderness limits of beams to ensure lateral stabilityA beam is usually a vertical load carrying member. However, if the length of the beam is very large it may bend

laterally. To ensure lateral stability of a beam the following specifications have been given in the code.

A simply supported or continuous beam shall be so proportioned that the clear distance between the lateral

restraints does not exceed 60b or 250 b2/d whichever is less,

Where d is the effective depth of the beam

b the breadth of the compression face midway between the lateral restraints.

For a cantilever, the clear distance from the free end of the cantilever to the lateral

restraint shall not exceed 25b or 100 b2/d whichever is less.

Reinforcement detailing For RCC detailing refer SP 34


PRACTICAL NO – 2

DESIGN OF SLABS

A slab is a flat two dimensional planar structural element having thickness small compared to its other

two dimensions. It provides a working flat surface or a covering shelter in buildings. It primarily transfer the load

by bending in one or two directions. Reinforced concrete slabs are used in floors, roofs and walls of buildings

and as the decks of bridges. The floor system of a structure can take many forms such as in situ solid slab,

ribbed slab or pre-cast units. Slabs may be supported on monolithic concrete beam, steel beams, walls or

directly over the columns. Concrete slab behave primarily as flexural members and the design is similar to that

of beams.

CLASSIFICATION OF SLABS1) Based of shape: Square, rectangular, circular and polygonal in shape.


2) Based on type of support: Slab supported on walls, Slab supported on beams, Slab supported on columns

(Flat slabs).

3) Based on support or boundary condition: Simply supported, Cantilever slab, Overhanging slab, Fixed or

Continues slab.

4) Based on use: Roof slab, Floor slab, Foundation slab, Water tank slab.

5) Basis of cross section or sectional configuration: Ribbed slab /Grid slab, Solid slab, Filler slab, folded

plate

6) Basis of spanning directions:One way slab – Spanning in one direction

Two way slab _ Spanning in two direction

DESIGN GUIDELINES FOR ONEWAY SLAB1 Load on slab:The load on slab comprises of Dead load, floor finish and live load. The loads are calculated per unit area

(load/m2).

a. Dead load = D x 25 kN/m2 ( Where D is thickness of slab in m)

b. Floor finish (Assumed as)= 1 to 2 kN/m2

c. Live load (Assumed as) = 3 to 5 kN/m2 (depending on the occupancy of the building)

2 Effective span of slabEffective span of slab shall be lesser of the two

a. l = clear span + d (effective depth )

b. l = Center to center distance between the support

3 Calculation of maximum Banding moment and Maximum Shear forceMax B.M = W x leff

2 / 8 Treated slab as design as simply supported

Max S.F = W x leff / 2

4 Depth of slabThe depth of slab depends on bending moment and deflection criterion. the trail depth can be obtained using


Effective depth d= Span / (l/d) Basic x modification factor)For obtaining modification factor, the percentage of steel for slab can be assumed from 0.2 to 0.5%

The effective depth d of two way slabs can also be assumed using cl.24.1,IS 456 provided short span is 3.5m

and loading class is < 3.5KN/m2

5 Checks for Bending and depth of slabUsing deflection criteria

Equate Mu = Mu limit

Mu = 0.146 x fck x b x d2 For Fe 250 Grade of steel



6 Calculation of Area of steel Ast = 0.5 fck ( ( 1 – (1- Mu / fck b d2 )1/2) b d

fy

7 Check for shear as per IS 456-20008 Check for deflection as per IS 456-2000

9 Check for Development length as per IS 456-200010 Check for cracks as per IS 456-2000

11 DETAILING REQUIREMENTS AS PER IS 456 -2000a. Nominal Cover For Mild exposure – 20 mm

For Moderate exposure – 30 mm

However, if the diameter of bar do not exceed 12 mm, or cover may be reduced by 5 mm.

Thus for main reinforcement up to 12 mm diameter bar and for mild exposure, the nominal

cover is 15 mm


b. Minimum reinforcement The reinforcement in either direction in slab shall not be less than

1. 0.15% of the total cross sectional area for Fe-250 steel

2. 0.12% of the total cross sectional area for Fe-415 & Fe-500 steel.

c. Spacing of bars The maximum spacing of bars shall not exceed

1. Main Steel – 3d or 300 mm whichever is smaller

2. Distribution steel –5d or 450 mm whichever is smaller

Where, ‘d’ is the effective depth of slab.

Note: The minimum clear spacing of bars is not kept less than 75 mm (Preferably 100 mm) though code do not

recommend any value.

d. Maximum diameter of bar: The maximum diameter of bar in slab, shall not exceed D/8,

where D is the total thickness of slab.

DESIGN GUIDELINES FOR TWO WAY SLABTypes of Two Way SlabTwo way slabs are classified into two types based on the support conditions:

a) Simply supported slab

b) Restrained slabs

Two way simply supported slabsThe bending moments Mx and My for a rectangular slabs simply supported on all four edges with corners free

to lift or the slabs do not having adequate provisions to prevent lifting of corners are obtained using

Where, αx and αY are coefficients given in Table 1 (Table 27, IS 456-2000)

W- Total load /unit area

lx & ly – lengths of shorter and longer span.

Table 1 Bending Moment Coefficients for Slabs Spanning in Two Directions atRight Angles, Simply Supported on Four Sides (Table 27:IS 456-2000)


Note: 50% of the tension steel provided at mid span can be curtailed at 0.1lx or 0.1ly from support.

Two way restrained slabsWhen the two way slabs are supported on beam or when the corners of the slabs are prevented from lifting the bending moment coefficients are obtained from Table 2 (Table 26, IS456-2000) depending on the type of panel shown in Fig.These coefficients are obtained using yield line theory. Since, the slabs are restrained; negative moment arises near the supports. The bending moments are obtained using



Detailing requirements as per IS 456-20001. Slabs are considered as divided in each direction into middle and end strips as shown below

2. The maximum moments obtained using equations are apply only to middle strip.

3. 50% of the tension reinforcement provided at midspan in the middle strip shall extend in the lower part

of the slab to within 0.25l of a continuous edge or 0.15l of a discontinuous edge and the remaining 50%

shall extend into support.

4. 50% of tension reinforcement at top of a continuous edge shall be extended for a distance of 0.15l on

each side from the support and at least 50% shall be provided for a distance of 0.3l on each face from

the support.


5. At discontinuous edge, negative moment may arise, in general 50% of mid span steel shall be

extended into the span for a distance of 0.1l at top.

6. Minimum steel can be provided in the edge strip

7. Tension steel shall be provided at corner in the form of grid (in two directions) at top and bottom of slab

where the slab is discontinuous at both the edges . This area of steel in each layer in each direction

shall be equal to ¾ the area required (Ast) for maximum mid span moment. This steel

shall extend from the edges for a distance of lx/5. The area of steel shall be reduced to half (3/8 Astx)

at corners containing edges over only one edge is continuous and other is discontinuous. Fig.

DESIGN GUIDELINES FOR ONEWAY CONTINEOUS SLAB


The slabs spanning in one direction and continuous over supports are called one way continuous slabs.

These are idealized as continuous beam of unit width. For slabs of uniform section which support substantially

UDL over three or more spans which do not differ by more than 15% of the longest, the B.M and S.F are

obtained using the coefficients available in Table 12 and Table 13 of IS 456-2000. For moments at supports

where two unequal spans meet or in case where the slabs are not equally loaded, the average of the two values

for the negative moments at supports may be taken. Alternatively, the moments may be obtained by moment

distribution or any other methods.

Bending moment and Shear force coefficients for continuous slabs( Table 12, Table 13, IS 456-2000)

In case of one-way continuous slab all steps are common as that of one-way slab only bending moment

and shear force calculation are based on above coefficient and the reinforcement detailing are done as per SP

34


PRACTICAL NO – 3

DESIGN OF COLUMNS

Design of Columns LIMIT STATE OF COLLAPSE: COMPRESSION

Longitudinal or main reinforcement IS: 456 stipulate that the main reinforcement shall satisfy the

following


1. The longitudinal reinforcement in a column shall be between 0.8 to 6.0 per cent of the gross

cross-sectional area. However, in practice, the maximum amount of steel is restricted to 4 per

cent of the gross cross-sectional area provided. In any column that has a larger cross-sectional

area than that required supporting the load, the minimum percentage of steel shall be based

upon the area of concrete required to resist the direct stress and not upon the actual area.

2. In a square or rectangular column minimum of 4 bars to be provided as a longitudinal

compression reinforcement.

3. In circular or spirally reinforced columns minimum of six bars to be provided.

4. For column of five or more side, one bar at each side to be provided

5. Size of each bars should not be less than 12 mm diameters

6. Spacing of longitudinal bars along the periptery should not exceed 300 mm to ensure the

proper confinement of concrete.

Transverse reinforcementThe diameter of the polygonal links (with internal angles < 135°) or lateral ties should not be less than one-

fourth of the diameter of the largest Longitudinal] bar and in no case less than 6 mm. The diameter of the tie bar

should not be more than 20 min.

The pitch or spacing of lateral ties is Limited to the least of:

(I) the least lateral dimension of the compression member,

(ii) sixteen times the smallest diameter of longitudinal reinforcement to be tied, and

(iii) 300 mm

Helical reinforcementThe diameter of the helix bar shall be based on the criterion used for the ties The pitch of the spiral in the

spirally reinforced column shall neither be more than the smaller of the distances: (1) 75 mm and (ii) one-sixth

of the core diameter of the column nor be less than the larger of the: (a) 25 mm and (b) three times the diameter

of the steel bar forming the helix.

To assure that the spiral effect exceeds the shell capacity.


CoverThe IS: 456 code requirements are

1 For a longitudinal reinforcing bar in a column the nominal or clear cover should be more than the larger of the

following

a 40 mm

b Diameter of the longitudinal bar

2 For a column of minimum dimension less than 200 mm. where the diameter of the reinforcing bar does not

exceed 12 mm. a cover of 25 mm may be provided.

3 For the hoops and ties the nominal or clear cover shall not be less than the diameter of the bar used in

making the hoops or ties, nor less than 20 mm for mild exposure.

PART 1Slender Columns


PART 2Axially Loaded Short Column (with e = 0 to emin)

A compression member shall be considered as a short column when slenderness ratios (l/D) and (4/ b) are less than or equal to 12. Where l and l. are effective lengths in respect of major and minor axes, respectively; D is the depth in respect of the major axis and b is the width of the member. The members carrying bending moments which are quite small as compared to the direct compressive load are termed as axially loaded columns. When the code specified minimum eccentricity emin = (JJ500) + (D/30) or 20 mm (greater of the two) does not exceed 0.05 times the lateral dimension of the column in the direction under consideration, the axial load-carrying capacity. Pu is given by

PART 3Column Subjected to Combined Axial Load and Uniaxial Bending


Note: - Reinforcement detailing of column are done as per SP 34


PRACTICAL NO – 4

DESIGN OF FOOTING

DESIGN OF FOOTINGDesign of Isolated Column Footing

The objective of design is to determine

a. Area of footing

b. Thickness of footing


c. Reinforcement details of footing (satisfying moment and shear considerations)

d. Check for bearing stresses and development length

This is carried out considering the loads of footing, SBC of soil, Grade of concrete and Grade of steel. The

method of design is similar to the design of beams and slabs. Since footings are buried,

deflection control is not important. However, crack widths should be less than 0.3 mm.The steps followed in the

design of footings are generally iterative. The important steps in the design

of footings are;

Find the area of footing (due to service loads)

1. Assume a suitable thickness of footing

2. Identify critical sections for flexure and shear

3. Find the bending moment and shear forces at these critical sections (due to factored loads)

4. Check the adequacy of the assumed thickness

5. Find the reinforcement details

6. Check for development length

7. Check for bearing stresses

Limit state of collapse is adopted in the design pf isolated column footings. The various design steps

considered are

1. Design for flexure

2. Design for shear (one way shear and two way shear)

3. Design for bearing

4. Design for development length

5.

The materials used in RC footings are concrete and steel. The minimum grade of concrete to be used

for footings is M20, which can be increased when the footings are placed in aggressive environment,

or to resist higher stresses.

CoverThe minimum thickness of cover to main reinforcement shall not be less than 50 mm for surfaces in contact with

earth face and not less than 40 mm for external exposed face. However, where the concrete is in direct contact

with the soil the cover should be 75 mm. In case of raft foundation the cover for reinforcement shall not be less

than 75 mm.

Minimum reinforcement and bar diameter


The minimum reinforcement according to slab and beam elements as appropriate should be followed, unless

otherwise specified. The diameter of main reinforcing bars shall not be less 10 mm. The grade of steel used is

either Fe 415 or Fe 500.

Specifications for Design of footings as per IS 456 : 2000The important guidelines given in IS 456 : 2000 for the design of isolated footings are as follows:

GeneralFootings shall be designed to sustain the applied loads, moments and forces and the induced reactions and to

ensure that any settlement which may occur shall be as nearly uniform as possible, and the safe bearing

capacity of the soil is not exceeded (see IS 1904).

In sloped or stepped footings the effective cross-section in compression shall be limited by the area above

the neutral plane, and the angle of slope or depth and location of steps shall be such that the design

requirements are satisfied at every section. Sloped and stepped footings that are designed as a unit shall be

constructed to assure action as a unit.

Thickness at the Edge of FootingIn reinforced and plain concrete footings, the thickness at the edge shall be not less than 150 mm for

footings on soils, nor less than 300 mm above the tops of piles for footings on piles.

In the case of plain concrete pedestals, the angle between the plane passing through the bottom edge of the

pedestal and the corresponding junction edge of the column with pedestal and the horizontal plane (see Fig. 20)

shall be governed by the expression

Where

= calculated maximum bearing pressure at the base of the pedestal in N/mm2

= characteristic strength of concrete at 28 days in N/mm2.

Moments and ForcesIn the case of footings on piles, computation for moments and shears may be based on the assumption that the

reaction from any pile is concentrated at the centre of the pile.

For the purpose of computing stresses in footings which support a round or octagonal concrete column or

pedestal, the face of the column or pedestal shall be taken as the side of a square inscribed within the

perimeter of the round or octagonal column or pedestal.

Bending Moment


The bending moment at any section shall be determined by passing through the section a vertical plane which

extends completely across the footing, and computing the moment of the forces acting over the entire area of

the footing on one side of the said plane.

The greatest bending moment to be used in the design of an isolated concrete footing

which supports a column, pedestal or wall, shall be the moment computed in the manner at sections located as

follows

a. At the face of the column, pedestal or wall, for footings supporting a concrete column, pedestal or wall

b. Halfway between the centre-line and the edge of the wall, for footings under masonry walls; and

c. Halfway between the face of the column or pedestal and the edge of the gusseted base, for footings

under gusseted bases.

Tensile ReinforcementThe total tensile reinforcement at any section shall provide a moment of resistance at least equal to the bending

moment on the section

Total tensile reinforcement shall be distributed across the corresponding resisting section as given below:

1. In one-way reinforced footing, the-reinforcement extending in each direction shall be distributed

uniformly across the full width of the footing;

2. In two-way reinforced square footing, the reinforcement extending in each direction shall be distributed

uniformly across the full width of the footing

3. In two-way reinforced rectangular footing, the reinforcement in the long direction shall be distributed

uniformly across the full width of the footing. For reinforcement in the short direction, a central band

equal to the width of the footing shall be marked along the length of the footing and portion of the

reinforcement determined in accordance with the equation given below shall be uniformly distributed

across the central band:

where β is the ratio of the long side to the short side of the footing. The remainder of the reinforcement shall be

uniformly distributed in the outer portions of the footing.

Transfer of Load at the Base of ColumnThe compressive stress in concrete at the base of a column or pedestal shell is considered as being transferred

by bearing to the top of the supporting Pedestal or footing. The bearing pressure on the loaded area shall not

exceed the permissible bearing stress in direct compression multiplied by a value equal to


but not greater than 2, where A1 = supporting area for bearing of footing, which in sloped or stepped footing

may be taken as the area of the lower base of the largest frustum of a pyramid or cone contained wholly within

the footing and having for its upper base, the area actually loaded and having side slope of one vertical to two

horizontal; and A2 = loaded area at the column base.

a. Where the permissible bearing stress on the concrete in the supporting or supported member would be

exceeded, reinforcement shall be provided for developing the excess force, either by extending the

longitudinal bars into the supporting member, or by dowels (see 34.4.3).

b. Where transfer of force is accomplished by, reinforcement, the development length of the reinforcement

shall be sufficient to transfer the compression or tension to the supporting member

c. Extended longitudinal reinforcement or dowels of at least 0.5 percent of the cross-sectional area of the

supported column or pedestal and a minimum of four bars shall be provided. Where dowels are used,

their diameter shall no exceed the diameter of the column bars by more than 3 mm.

d. Column bars of diameters larger than 36 mm, in compression only can be dowelled at the footings with

bars of smaller size of the necessary area. The dowel shall extend into the column, a distance equal to

the development length of the column bar and into the footing, a distance equal to the development

length of the dowel.

Nominal Reinforcement1. Minimum reinforcement and spacing shall be as per the requirements of solid slab.

2. The nominal reinforcement for concrete sections of thickness greater than 1 m shall be 360 mm 2 per

metre length in each direction on each face. This provision does not supersede the requirement of

minimum tensile reinforcement based on the depth of the section.

Note :- RCC detailing are done as per SP 34


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