10 Web Splice 3655l

Chapter 10

Web splice

Introduction The web of a plate girder consists generally of several pieces connected together, since web plate can be obtained 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 ()

s s

s

s

s

s

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 S – S, the normal stresses and shear stresses at the section must be transferred from

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 and from there by the two bolts to the web plate B.

Q

s

Q P1

Sec s-s

r'1 r'2

r'1 r'2

r'm

r'm

61 62

C

s

C1  1  p1  t 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

Horizontal force on one bolt =

C1 1  p1  t  m m

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. Q  Vertical force on one bolt = mn

The additional forces due the couple Qe are usually neglected. - Minimum number of rows of bolts in the splice plate S is two.  Maximum force on remotes +

2

 Q   1  p1  t  bolt =     m  mn   

2

-

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 = qb As n Rb = Fb  d  min t Fb =   Fub

(n = No. of shear planes)

Fb =   Fub  depends on end distance (S), (Table 6.2)

End distance in direction of force

3d



1.2



2.5d 1.0



2 d 0.8



1.5d 0.6



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 of the 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 =

 Iw M    I total

    A / 6 Aw w      M   M  A flange  A w / 6   6A flange  A w    

The bolts in splice are subjected to vertical force due to shear force and to horizontal force to bending moment.

   

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 same diameter). 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; Fmax Fi   di d max

M W  d max Fmax  I I= the moment of inertia about the neutral axis of the bolt group on one side only of the splice above and below the neutral axis =  d 2

F1 F2 d 2 d1

d2 d1

F2 F1

M w  2m  F1  d1  F2  d 2  ...........  Fmax  d max   Fmax  Fmax 2 2  2m    d1   d 2  ...........  Fmax  d max  d max  d max 

Mw



Fmax 2  2m  d1  d 22  ...........  d max d max Fmax  2m  d max

Fmax 



2 d 

M W  d max

d

2

Vertical force due to shear Qbolt =

Q applied mn

Maximum force on remotest bolt =

Fmax 

2

 Q applied    m n

   

2

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

K1 

M w  y max 2 y 

Q , and K 2  m

K12  K 22 Number of rows = . n  R 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.

3

t w hw t s hs  2x Note 12 12 hs = hw - 2- 5‫ ט‬cm

3

hs = hw - (5 →10 cm )

ts tw hw

hs