COLUMNS FOR THE INDUSTRIAL BUILDINGS C.Teleman_S.S.III_Lecture 5 1 STEEL INDUSTRIAL BUILDINGS
Lecture 5 s.s.iii Design of Steel Structures - Faculty of Civil Engineering Iaşi
May 25, 2015
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
COLUMNS FOR THE INDUSTRIAL BUILDINGS
C.T
ele
man_
S.S
.III
_Lectu
re 5
1
STEEL INDUSTRIAL BUILDINGS
• SPECIFIC FEATURES
The cross section of the columns
• - constant or variable; • - build-up or compound from different elements interconnected (battened or laced); • - with constant section on the height of the column or variable on the height of the
column (tappered) or in steps of variation (stepped columns).
Steel elements (profiles)
• - build-up cross sections: thick plate welded (web and flanges) or hot-rolled profiles or build-up sections welded together to increase the stiffness of the cross section;
• -laced cross sections: hot-rolled profiles or build-up cross sections and the lace system is obtained from angles welded or bolted at the joints;
- battened cross sections.
Stiffening elements - ribs and stiffening diaphragms: longitudinal and transversal stiffening ribs and
diaphragms welded to the hot-rolled sections
COLUMNS FOR THE INDUSTRIAL BUILDINGS
C.T
ele
man_
S.S
.III
_Lectu
re 5
2
Fig. 1. Columns for industrial buildings with constant cross sections on the height: 1), 2)-build up or compound from hot-rolled sections for marginal and central columns; 3)- compound section from hot-rolled shapes, laced; 4)-compound section, battened, axially loaded; 5)- compound section, laced, axially loaded
Fig. 2. Columns for industrial buildings with variable sections on the height: 6)…9)-variation in two steps; 10)…13) continuous variation on the height
TYPES OF SECTIONS USED FOR COLUMNS WITH HEAVY LOADS
C.T
ele
man_
S.S
.III
_Lectu
re 5
3
• capital of the column; lateral cross-pieces are welded to the profiles and supplementary cross-piece should also be welded as intermediate web.
• brackets and the supports: the crane girder is connected to the column transferring the forces in all exploitation conditions.
02111 M
yf
tbtL
N
a)- girder is continuous the corrugated steel sheet of the platform must be welded to the diaphragms of the column, important negative bending moments and sometimes uneven negative reactions being expected. b)- girder is simply supported the corrugated steel sheet is not welded to the column because at the top flange level the translations due to the rotation of the girder on the support must be allowed.
Capital of the columns: transfer of loads through thick plates, welded to the capital and the bearing surface
C.T
ele
man_
S.S
.III
_Lectu
re 5
4
SOLUTIONS FOR THE SUPPORTS OF CRANE GIRDER ON STEPPED COLUMN
•Details of supports for the continuous crane girders
Details of simply supported crane girders 5
C.T
ele
man_
S.S
.III
_Lectu
re 5
ELEMENTS FOR THE DESIGN OF COLUMNS
Brackets on columns a) The stress is transferred to the cross section of the rib from the flanges of the bracket. b) M =Re - moment induced by the eccentricity of application of the reaction from the crane girder c) Fatigue checking is necessary for the joint considering that a single crane acts on the girder. d) horizontal diaphragm needs strengthening with vertical stiffeners
W
MAH
AA
t
tt
)2(1
21;
h
eR
h
heRRNNN
h
eRR
h
heRRNNN
MR
MR
22
22
2
1
2
01
34
Mwu
Myt
wwf
fAla
6
C.T
ele
man_
S.S
.III
_Lectu
re 5
THE JOINTS BETWEEN THE TOP AND THE BOTTOM PART OF THE COLUMN
MN M
ha T
N M
htr
I
tr ( ) ;2 2
0
00
22 3
;3
;
M
y
ech
M
y
trtr
tr
M
y
tr
tr
f
f
ht
Tf
W
M
NN M
hRtr
2
trtr lh 6,0...5,0min,
M R c T Rtr
II II
tr
II II ;
7
C.T
ele
man_
S.S
.III
_Lectu
re 5
• THE TOP PART IS PERFORATED IN THE WEB
MT h
NM
h
N0 0
02 2 2 ;
0032
;0
00
M
y
iiM
y f
th
Tf
A
N
W
M
0
22 3M
y
ech
f
,
C.T
ele
man_
S.S
.III
_Lectu
re 5
8
STIFFENING ELEMENTS IN THE CROSS SECTION AND IN THE CAPITAL AREA
Ribs and diaphragms for stiffening the columns sections and prevent from torsion effects
Capital for the columns of industrial buildings (central columns), details of supporting the
rafter (girder or truss)
9
C.T
ele
man_
S.S
.III
_Lectu
re 5
BASE OF THE COLUMNS WITH COMPOUND SECTIONS
223
;3
21
Mw
ustr
Mw
ustr
fAH
fAH
203
;2
4
4 Mw
us
M
y fAZ
f
A
Z
003
;M
y
trM
y
x
f
th
Zf
W
eZ
23
2
2
2
1max
Mw
uf
2
2
32
;3
2
,
1
Mw
u
trs
Mw
u
sx
f
ha
Z
f
W
eZ
00 132
;;M
ytr
M
ytr
tr
tr
f
A
Hf
AA
H
h
eZH
10
C.T
ele
man_
S.S
.III
_Lectu
re 5
Gusseted base plates
11
COLUMN BASES
Hinged bases The base plate is fixed to the foundation with two hold down bolts. Both shear and axial tension forces (when present) are transferred to the bolts . Compression is transferred to the base plate.
Fixed bases The moment resistant bases have hold down bolts also and the base plate may be stiffened with outstanding gussets. The surface of the base plate is imposed by the necessity of limiting the pressure on the foundation to the resistance of the concrete. Generally, the hold down bolts take no horizontal forces, but only axial tension
C.T
ele
man_
S.S
.III
_Lectu
re 5
12
Columns with gusseted base plates
Brittle fracture is avoided by using frames mounted on base plate in which holes are drilled for the anchor bolts. The bolts have a long shank of minimum 15dia for a free deformation being appropriate column bases subjected to seismic action.
COLUMN BASES
C.Teleman_S.S.III_Lecture 5 13
HOLD DOWN BOLTS
Tension in the shank is taken entirely by bond between the bolt and the concrete. When there is not enough depth to insure the bonding, the shank is shortened and processed in different shapes to enlarge friction forces or different steel profiles or plates are welded at the bottom of the shank
Normal length of the shank Shorten shank with welded plate for distribution of friction forces
Threaded part
Threaded part
Foundation level
Foundation level
C.T
ele
man_
S.S
.III
_Lectu
re 5
14
DESIGN RESISTANCE OF THE HOLD DOWN BOLT IN BENDING MOMENT RESISTANCE FOUNDATIONS
Bond capacity of the hold down bolt
- anchor length of the bolt from the inferior face of the base plate
- diameter of the bolt
- bond resistance of the concrete for profiled round bars
For round bars with diameter under 33 mm
For round bars with diameters of more than 33 mm
2.25 – coefficient that takes into account the fact that the bolt is not profiled
Design tension resistance of the hold down bolt
C.T
ele
man_
S.S
.III
_Lectu
re 5
15
For minimum two bolts that take tension the force transmitted is:
and must comply with the condition of resistance of the bolts in tension:
2
N
th
MF Ed
fcc
Ed
Ed,T
)Fmax(F2 Ed,TRd,ancor,t
2M
subRd,ancor,t
Af9.0F
For one single row of bolts (2, externally to the column flange) :
8.1
)Fmax(F
Ed,T
Rd,anc,t
ub
Ed,T
f
Fmax1.1d
For two rows of bolts (2, externally and internally to the column flange) :
6.3
)Fmax(F
Ed,T
Rd,anc,t
ub
Ed,T
f
Fmax8.0d
Length of the bolt in the shank: bd
Edb
fd
Fl
C.T
ele
man_
S.S
.III
_Lectu
re 5
16
RESISTANCE OF THE WHOLE CONNECTION IN FOUNDATION TO SHEAR
1. Transmission of the shear force through friction between the base plate and the grout or the in-filling concrete
cf,d - friction coefficient between the base plate and the grout (=0.20 for sand and cement grout); Nc,Ed – design value of compression in the column
2. Transmission of the shear force through shear in the shank of anchor bolts and friction between the base plate and the grout Bolts shear situation is provided in the design by SR EN 1993-1-8, considering a limited lateral translation of the connection under horizontal forces. As the holes for bolts in the base plate have big diameters, bearing of the whole row of bolts does not govern. The verification addresses to small loading and cases when compression only is under the base plate. For post installed anchors the holes in the base plate are large; washers placed under nuts are welded providing the adequate shear resistance of the bolts. Cast-in place anchor bolts need normal sized holes in the base plate and the shank must in this case be designed to shear.
C.T
ele
man_
S.S
.III
_Lectu
re 5
17
RESISTANCE OF THE WHOLE CONNECTION IN FOUNDATION TO SHEAR
Resistance to shear of the connection is then designed as the sum between the friction resistance of the base plate and shear of the anchor bolts:
Ff,Rd – friction resistance of the base plate to the grout surface; Fvb,Rd – shear resistance of the anchor bolt; nb – number of bolts in shear
Resistance to shear of the bolt is:
- bearing resistance;
- shear resistance
Final verification to external loading
C.T
ele
man_
S.S
.III
_Lectu
re 5
18
3. Transmission of the shear force through shear lug
RESISTANCE OF THE WHOLE CONNECTION IN FOUNDATION TO SHEAR
Hot rolled I or H sections are used, also angles, in case of lower level of shear force. Certain design conditions are imposed for the shear lug preventing it from pulling of from foundation: - height of the shear lug: hn0.4hc - length of the shear lug: 60 mm deff,n 1.5hn
Flanges of the I section are subjected to a small local bending and the slenderness is thus limited for the flange: bfn/tfn 20. (Exceptions from verification: HEA 260, 280, 300.
C.T
ele
man_
S.S
.III
_Lectu
re 5
19
RESISTANCE OF THE WHOLE CONNECTION IN FOUNDATION TO COMBINED AXIAL FORCE AND MOMENT
Design according to EN 1993-1-8 release the concept of method of verification to failure of the individual components of the connection. Strength verifications address to possible risk areas in exploitation due to the development of the failure mechanisms of yield: cross section in the bottom part of the column, base plate and anchor bolts.
Failure mechanism: a- plastic hinge in the column; b- plastic hinge in the base plate; c- plastic hinge in the anchor bolt under the base plate; d- plastic hinge in the anchor bolt above the base plate
a b Yield length in
the bolt
Yiel
d le
ngt
h in
th
e b
olt
C.T
ele
man_
S.S
.III
_Lectu
re 5
20
RESISTANCE OF THE WHOLE CONNECTION IN FOUNDATION TO COMBINED AXIAL FORCE AND MOMENT
STAGES FOR DESIGN
I. Identify the components of the connection II. Evaluate the resistance and stiffness characteristics for every component III. Determine the global characteristics of strength and stiffness
I Components The T stub in tension – bolts in tension, part of the base plate in bending and tensioned flange of the column The T stub in compression – grout and concrete in compression ,a part of the base plate in compression and the compressed flange of the column
Note: If bending moment is dominant at the base plate, the contribution of the web in compression and the afferent base plate is not relevant. This may become important when the compression is dominant
Components of the foundations of columns:
hinged and fixed
C.T
ele
man_
S.S
.III
_Lectu
re 5
21
C.T
ele
man_
S.S
.III
_Lectu
re 5
22
DESIGN RESISTANCE OF THE CONNECTION TO AXIAL FORCES AND BENDING MOMENTS
The capacity to resist to tension of the area in left side of the connection FT,l,Rd is determined considering the following individual resistances of the components :
The capacity to resist to tension of the area in right side of the connection FT,r,Rd is determined considering the following individual resistances of the components :
The capacity to resist to compression of the area in left side of the connection FC,l,Rd is determined considering the following individual resistances of the components:
The capacity to resist to compression of the area in right side of the connection FC,r,Rd is determined considering the following individual resistances of the components:
where:
resistance of the column web in tension under the left/right flange of the column
resistance of the base plate in bending under the left/right flange of the column
resistance of the left/right flange of the column, web in compression
resistance of the concrete in foundation under the left/right flange of the column
C.T
ele
man_
S.S
.III
_Lectu
re 5
23
T STUB SUBJECTED TO TENSION
The effective length of a T-stub subjected to tension is determined on the basis of the value of the resistance of the flange of this T- stub which must be at least equal with the resistance of the basic components which are substituted by it.
C.T
ele
man_
S.S
.III
_Lectu
re 5
24
Length of an equivalent T-stub in tension with one row of bolts on the interior side and one on the exterior
The following must be analyzed: - Failure mode of the T-stub; - Failure mode of the base plate that is part of the tensioned T –stub connection; - Distances between the anchor bolts axes.
Failure modes of an equivalent T-stub are: a. mode 1: whole plastic mechanism - plastic bending of the base plate along the anchor
bolts line; b. mode 2: partial plastic mechanism because of premature failure of a bolt which stops
the development of plastic stresses in the connection; c. mode 3: braking of the bolts in tension , the connected plates acting rigid; d. mode 4: plastic failure of the web of the T-stub in tension; e. mode 1-2: plastic failure of the flange of the tensioned T-stub and important
deformation of the bolts that cancels the prying forces effects
C.T
ele
man_
S.S
.III
_Lectu
re 5
25
T STUB SUBJECTED TO COMPRESSION
The components modeled by the T-stub in compression are: -base plate in bending due to the pressure from the reaction in the foundation; -concrete and/or grout; The verification of the compressed part of the column (flange and web) is covered by the verifications of the column in the cross section at the base part.
Simplifications in the verification stages of the compressed part of the column and foundation
The dimensions of the T-stub in compression depend on: - Resistance to local crush; - In plan dimensions of the column; - Base plate dimensions; - Resistance to bending of the base plate
C.T
ele
man_
S.S
.III
_Lectu
re 5
26
Equivalent T-stub in compression: area in case of short projection; b- area in case of long projection
T STUB SUBJECTED TO COMPRESSION
T-stub in compression: 1-one row of anchor bolts; 2- surface in compression of the equivalent T-stub
C.T
ele
man_
S.S
.III
_Lectu
re 5
27
Resistance to compression of a T stub FC,Rd is determined with:
-bef and lef are the effective width and effective length of the T stub; - fjd – design resistance of the joint to pressure
-jd - coefficient of the material in the joint, equal with 2/3 if the characteristic resistance is not exceeding 1/5 of the resistance of the concrete in the foundation and the thickness of the layer is not exceeding 1/5 from the minimum width of the base plate. If the thickness of the grout is not exceeding 50 mm, the characteristic resistance of the concrete must be at least equal to the resistance of the concrete in the foundation; -FRdu - design resistance of the concrete to point load (EN 1992)
and:
C.T
ele
man_
S.S
.III
_Lectu
re 5
28
The thickness of the base plate is determined with the help of the I mode of failure of a T stub (total plastic mechanism). If one single row of anchor bolts are placed outside the flange of the column with H section then:
If there are four bolts placed in two rows inside and outside the H section of the column, then:
Resistance of the base plate Nj,Rd subjected to centric compression may be determined by summarizing the individual resistance FC,Rd of the three T stubs, which are not overlapping
The three T sub elements obtained from sizing the base plate to axial compression
C.T
ele
man_
S.S
.III
_Lectu
re 5
29
a.- hinged connection; b,c – moment resistant connection
The anchor bolts may be placed in rigid framework of steel plate with a hole greater than the diameter of the bolt. In this case the bolt and the framework must be placed inside the reinforcement of the concrete
C.T
ele
man_
S.S
.III
_Lectu
re 5
30
Cast in place anchor bolts: 1-nut; 2- washer or drilled steel
plate; 3-leveling nuts
Detail of base of column provided with shear lug according to NP-
112-2004 (rev 20011): 1- column, 2-shear lug, 3- anchor
bolt, 4-washer, leveling nut, 6-concrete filling about 50 mm thick,
7- plastic pipe
C.T
ele
man_
S.S
.III
_Lectu
re 5
31
Related Documents
