IS800-2007 Plate Girder.ppt

IS 800 2007 plate girder

1. Mr.Naveen Choudhary,GEC,Ajmer
1
PLATE GIRDERS
Built-up sections with deep thin webs
susceptible to buckling in shear

2. 2
Types of Plate Girders
•Unstiffened Plate Girder
•Transversely Stiffened Plate Girder
•Transversely and Longitudinally Stiffened Plate Girder
web plate
flange plates
ITS
BS
LS
Mr.Naveen Choudhary,GEC,Ajmer

3. 3
SHEAR RESISTANCE OF
STIFFENED GIRDER
Shearresistanceofaweb
•Pre-bucklingbehaviour(Stage1)
–Requirementsofequilibriuminanelementinsidea
squarewebplatesubjecttoashearstressresultin
generationofcomplementaryshearstresses
–Thisresultsinelementbeingsubjectedtoprincipal
compressionalongonediagonalandtensionalong
theother
Mr.Naveen Choudhary,GEC,Ajmer

4. 4
Shear resistance of a web -1
A
q
q
45
o
B
D
C
q
E
q
Unbuckled Shear panel
Mr.Naveen Choudhary,GEC,Ajmer

5. Mr.Naveen Choudhary,GEC,Ajmer 5
Shear buckling of a plate
BUCKLING OF WEB PLATES IN SHEAR

cr

6. Mr.Naveen Choudhary,GEC,Ajmer 6
Shear resistance of a web -2
–Astheappliedloadingisincrementallyenhanced,
platewillbucklealongdirectionofcompressive
diagonal-correspondingshearstressinplate
is“criticalshearstress”
–Criticalshearstressinsuchacaseisgivenby
–Boundaryconditionsassumedtobesimply
supported2
d
t
2
112
E
2
s
k
cr
q 
















7. Mr.Naveen Choudhary,GEC,Ajmer 7
Shear resistance of a web -3
•shearbucklingcoefficient(k
s
)givenbypanelswideforei
d
c
where
c
d
k
s ..,1435.5
2






 stiffenerstransversespaced
closelywithwebsforei
d
c
where
c
d
k
s ..,1435.5
2







c
d

8. Mr.Naveen Choudhary,GEC,Ajmer 8
•Postbuckledbehaviour(Stage2)
–Compressiondiagonalisunabletoresistany
moreloadingbeyondelasticcriticalstress
–Anyfurtherincreaseinshearloadissupported
byatensilemembranefield,anchoredtotop
andbottomflangesandadjacentstiffener
membersoneithersideofweb
–Totalstateofstressinwebplatemaybe
obtainedbysuperimposingpost-buckled
membranetensilestressesuponcriticalshear
stress

9. Mr.Naveen Choudhary,GEC,Ajmer 9
Postbuckledbehaviour-1
Anchoring of Tension Field

10. Mr.Naveen Choudhary,GEC,Ajmer 10
Tension field action

11. Mr.Naveen Choudhary,GEC,Ajmer 11
•Collapsebehaviour(Stage3)
–Whenloadisfurtherincreased,tensile
membrane stresscontinuestoexertan
increasingpullonflanges
–Eventuallyresultantstressobtainedby
combiningthebucklingstressandmembrane
stressreachesyieldvalueforweb-canbe
determinedbyVon-Misesyieldcriterion

12. Mr.Naveen Choudhary,GEC,Ajmer 12
Collapsebehaviour-1
Collapse of the panel
Tensile membrane stress at yield

13. Mr.Naveen Choudhary,GEC,Ajmer 13
Three phases of tension field action
Pre-buckling post-buckling collapse

14. Mr.Naveen Choudhary,GEC,Ajmer 1414
ULTIMATE BEHAVIOUR OF TRANSVERSE WEB STIFFENERS
Transversestiffenersplayimportantrole
byincreasingwebbucklingstress
bysupportingtensionfieldafterwebbuckling
bypreventingtendencyofflangestogetpulled
towardseachother
Stiffenersshouldpossesssufficientrigidity
toensurethattheyremainstraight,while
restrictingbucklingtoindividualwebpanels

15. Mr.Naveen Choudhary,GEC,Ajmer 1515
ULTIMATE BEHAVIOUR OF TRANSVERSE WEB STIFFENERS -1
Force imposed on transverse stiffeners by tension field

16. Mr.Naveen Choudhary,GEC,Ajmer 1616
GENERAL BEHAVIOUR OF LONGITUDINALLY STIFFENED GIRDERS
Generallylocatedincompressionzonesofgirder
Mainfunction-toincreasebucklingresistanceof
web
Whenitissubjectpredominantlytoshearwould
developacollapsemechanism, provided
stiffenersremainedrigiduptofailure
Onceoneofsubpanelshasbuckled,post
bucklingtensionfielddevelopsoverwholedepth
ofwebpanelandinfluenceofstiffenersmaybe
neglected

17. Mr.Naveen Choudhary,GEC,Ajmer 17
GENERAL BEHAVIOUR OF
LONGITUDINALLY STIFFENED GIRDERS –1
Longitudinal and Transverse stiffeners

18. Mr.Naveen Choudhary,GEC,Ajmer 18
8.4 Shear
Thefactoreddesignshearforce,V,inabeamdueto
externalactionsshallsatisfy
V V
d
V
d= design strength calculated as , V
d= V
n/γ
m0
8.4.1Thenominalplasticshearresistanceunderpure
shearisgivenby: V
n=V
p
A
v= shear area
Cont…3
ywv
p
fA
V

19. Mr.Naveen Choudhary,GEC,Ajmer 19
8.4.2 Resistance to Shear Buckling
for an unstiffened web
for a stiffened web
a)Simple Post-Critical Method
The nominal shear strength is
V
n = V
crV
cr= d t
w
b

b= shear stress corresponding to buckling,
b) Tension Field Method
The nominal shear strength is
V n = V tf67
wt
d yf/250 vk

20. Mr.Naveen Choudhary,GEC,Ajmer 20
8.4.2.2 Shear Buckling Design Methods
a)Simple Post-Critical Method -The nominal shear strength is
V
n = V
crV
cr= d t
w
b

b= shear stress corresponding to buckling, determined as follows:
a) When 
w< 0.8
b) When 0.8 < 
w< 1.25
c) When 
w1.25

b=0.9f
yw/(3
w
2
)
Cont…3/
ywbf    3/8.0625.01
ywwb f 
0.81.25 
w

b

21. Mr.Naveen Choudhary,GEC,Ajmer 21
λ
w = non -dimensional web slenderness ratio for shear buckling stress,
given by
The elastic critical shear stress of the web, 
cris given by:
k
v=5.35whentransversestiffenersareprovidedonlyatsupports
=4.0+5.35/(c/d)
2
forc/d<1.0
= 5.35+4.0/(c/d)
2
forc/d 1.0
Cont…)3(
,ecryww
f   
22
2
/112
w
v
cr
td
Ek






22. Mr.Naveen Choudhary,GEC,Ajmer 22
b) Tension Field Method -the nominal shear resistance, V
n, should be
V
n=V
tf
V
np
f
v= yield strength of the tension field obtained from
=1.5
bsin 2
= inclination of the tension field
The width of the tension field, w
tf, is given by:
w
tf = d cos–(c-s
c-s
t) sin   
5.0
222
3
bywvff 







c
d
1
tan c
tf
M
s
wy
fr










5.0
sin
2
    
2
0
2
//125.0
myffffyffffr ftbNftbM    sin9.0
vwtfbwtf
ftwtdV 
s
c
s
tc
w
tf

23. Mr.Naveen Choudhary,GEC,Ajmer 23
8.6 Design of Beams and Plate Girders with Solid Webs
8.6.1 Minimum Web Thickness
8.6.1.1 Serviceability Requirement
a) when transverse stiffeners are not provided
(web connection by flanges along both longitudinal edges)
(web connection by flanges along one longitudinal edge only)
b) when transverse stiffeners only are provided;
i)when c d
ii) when 0.74 d<c < d
iii) when c < 0.74 d
Cont…180
wt
d 90
wt
d w
wt
d
200 w
wt
c
200 w
wt
d
270

24. Mr.Naveen Choudhary,GEC,Ajmer 24
c) when transverse and longitudinal stiffeners are providedat one
level only
(0.1 dfrom compression flange)
i) when c > d
ii) when 0.74 d<c <d
iii) when c < 0.74 d
d) when a second longitudinal stiffener (located at neutral axis is
provided )
Cont…w
wt
d
250 w
wt
c
250 w
wt
d
340 w
wt
d
400

25. Mr.Naveen Choudhary,GEC,Ajmer 25
Design Procedure
Initial Sizing
1)Taking L/d as 15, calculate min. d and provide suitably
2)A
freqrd.= BM/ (fy/
mo)d ; using b
f= 0.3d select flange plate
Also calculate N
f= axial force in the flange
3)Check that flange criteria gives a plastic section
b = (b
f–t
w)/2 and b/ t
f< 7.9
4)Web thickness for serviceability 67<d/ t
w< 200
choose such that t
w> d/200
5)Check for flange buckling into web
Assuming c >1.5d , d/ t
w< 345
2

26. Mr.Naveen Choudhary,GEC,Ajmer 26
Design Procedure
6)Check for shear capacity of web
V < Vd = Vn/ 
mo;Vn = A (fy
w /3) or Vcr
7)Check for calculating resistance to shear buckling
d/ t
w> 67(k
v/5.35) use kv for c/d > 1
8)Simple post-critical method
Vcr = d t
w
bwhere 
b= (
w) and 
w= (
cr)
9)If V < Vcr/ 
mothen safe else tension field calculation
reqrd.
10)Vn = V
tf = (f
v and ); also calculate M
fv= (N
f)
If V < Vn/ 
mo safe ! else revise design

27. Mr.Naveen Choudhary,GEC,Ajmer 27
Design Procedure
•8.7 Stiffener design
–a) Intermediate Transverse Web Stiffener To improve
the buckling strength of slender web due to shear.
–b) Load Carrying Stiffener To prevent local buckling
of the web due to concentrated loading.
–c) Bearing Stiffener To prevent local crushing of the
web due to concentrated loading .
–d) Torsion Stiffener To provide torsional restraint to
beams and girders at supports.
–e) Diagonal Stiffener To provide local reinforcement to
a web under shear and bearing.
–f)Tension StiffenerTo transmit tensile forces applied
to a web through a flange.

28. Mr.Naveen Choudhary,GEC,Ajmer 28
Design Procedure
11) End panel design –check as a beam between flanges
Rtf = Hq/2
A
v= c t and Vtf = A
v(fy/3) > Rtf
12) M
tf= H
qd/10
MR = tc
3
/12*fyd / (c/2) > M
tf
13) Intermediate Transverse Stiffener Design
i) decide to provide stiffener on one side or both sides
ii) choose tq > tw ; outstand bs < 14t
qalso < b
14) check for minimum stiffness Cl.8.7.2.4 p91
for c = 1.5d, c > 2 d giving
I prov. = (bs-t
w/2)
3
tq/12 > 0.75dt
w
3)/1(.25.1
dpcrdpq VVVH 
R
tf
c
bs
tq

29. Mr.Naveen Choudhary,GEC,Ajmer 29
Design Procedure
15) Check for Buckling Cl.8.7.2.5 p91
Stiffener force, Fq = V -Vcr/mo Fqd
Buckling Resist. Pq with 20tw on either side Cl.8.7.1.5 p90
Calculate Ixx and A, rxx = (Ixx/A)
Leff = 0.7d, = Leff/rxx, Find fc
Pq = fc A > Fq
16) Connection to web Cl.8.7.2.6 p92
shear = tw
2
/ 8bs kN/mm choose appropriate weld size
19) Check for Intermediate Stiffener under LoadCl.8.7.2.5 p911

ys
s
xd
x
qd
xq
M
M
F
F
F
FF
bs
tq