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Chapter 10

Web splice

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Introduction

The web of a plate girder consists generally of several

pieces connected together, since web plate can beobtained according to the depth in the lengths from 5 to

10 m only. In welded construction, shop web splice shall

be made with penetration butt welds next Fig ()

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s s ss

ss

Field splices in the web shall be designed to resist the

shear and moments at the splice section. In bolted

construction, splice plate shall be provided on each side as

shown in last Fig. ().

If a web is cut at section SS, the normal stresses and

shear stresses at the section must be transferred from

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plate A to plate B by splice plates and bolts. One of the best

methods to make a web splice is to put splice plates on the

web

1-Calculation of splice plate

The compression force C1 in the part of the web (height p1)

is transmitted by the two bolts r1 to the splice plates andfrom there by the two bolts to the web plate B.

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Sec s-s

mr' mr'

r'12r' r'2

1r'

s

QQs

C

P1

6 1

6 2

tpC 111

let m= No. of bolts in one row depending on diameter of

bolts and pitch.

n = number of rows on one side of the splice

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Horizontal force on one bolt =m

tp

m

C 111

The shearing force Q is transmitted from the web plate A

by all the bolts in this side to the splice plate S and from

their by all the bolts in the other side to the web plate B.

Vertical force on one bolt =

nm

Q

- The additional forces due the couple Qe are usually

neglected.

- Minimum number of rows of bolts in the splice plate Sis two.

Maximum force on remotes + bolt =m

tp

nm

Q2

112

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- This maximum force (Rsh and Rb).

- Rsh = the shear strength of bolts (clause 6.4.1,p100).

- Rb = the bearing strength of bolts (clause 6.4.2,

p100).

qb = 0.25 Fub For bolts of grade (4.6, 5.6, 8.8)

qb = 0.20 Fub For bolts of grade (4.8, 5.8, 6.8, 10.9)

Rsh = qbAsn (n = No. of shear planes)

Rb = Fb d min t

Fb

= Fub

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Fb = Fub

depends on end distance (S), (Table 6.2)

End distance in direction of force

1.2 1.0 0.8 0.6

3d 2.5d 2 d 1.5d

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2-Second Method for web splice

The number of bolts connecting the splice plate to the web is

determined from the condition that the resisting moment ofthe web should equal the resisting moment of the bolts.

Let M and Q be the maximum resistance bending moment

and the actual shear force respectively at the splice section.

Mw bending moment takes by the web

=

wflange

wwflange

wtotalw

AA6

AM6/AA

6/AMI

IM

The bolts in splice are subjected to vertical force due to

shear force and to horizontal force to bending moment.

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Due to moment there will be horizontal force in each bolt

which will be proportional to the distance of the bolt

from the C.G of the bolt group (all bolts are of the samediameter). Due to shear, the bolts are subjected to vertical

force and it is assumed that this force is the same in all

bolts.

The pitch of bolts provided should be uniform. This can

be proved as shown below:-

Let Fmax be the force in the bolt situated as maximum

distance dmax from the C.G of the bolt group. The force Fi

in any bolt at di distance from C.G of the bolts will be

given by;i

max

maxi d

d

FF

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I

dMF maxWmax

2dd d1

d2 d1

F1

F2

2F1F

I= the moment ofinertia about the

neutral axis of the

bolt group on one

side only of thesplice above and

below the neutral

axis = 2d

maxmax22

max

max21

max

max

maxmax2211w

dF...........d

d

Fd

d

Fm2

dF...........dFdFm2M

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2

max

max

max22

21

max

maxw

dd

Fm2

d...........ddd

Fm2M

2maxW

max

d

dMF

Vertical force due to shear Qbolt =nm

Qapplied

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Maximum force on remotest bolt =

= least strength of one bolt (shear or bearing) = R

2

applied2max

nm

QF

Putting .

Number of rows = .

m

QKand,

y

yMK 22

maxw1

R

KKn

22

21

3-Thickness of splice plate

Two splice plates, one on each side, are provided the

moment of inertia of the two splice plates must be less

than the moment of inertia of the web.

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Note

hs = hw - 2- 5 cmhs = hw - (510 cm )

122

12

33

sswwht

xht

hstw

ts

hw