Connection of flange plate with web

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Chapter 8
Connection of flange plate with
web
1
7.1 Introduction
The web is machined and is in close contact with flange;
therefore, the vertical loads are directly transmitted to the
web direct bearing. The bearing stress on the web should
not exceed 0.75 Fy (Clause 2.6.6, p. 22). The connection of
flange plate to web is done by intermittent welding.
If we have a very short piece of a girder length (a) having
two moments M1&M2 and nearly the same shearing force
Q, taking the moment about point m;
2
M1- M2 + Qa = 0
M2- M1 = Qa
M1= F1 h
M2= F2 h
 F2 h - F1 h = Qa
F2 - F1 Q


a
h
F1
s
M1
F2
Q
Q
F2
a
a
a
M2
F1
a = 50 cm
3
Since F2 is higher than F1, there is tendency for flange
plate to slide along the web and this tendency must be
resisted by weld between web and flange plate.
 F2 h - F1 h = change in flange stress
F2 - F1
Q
 rate of change in flange stress 

a
h
If the thickness of the weld = S, the weld is
continuous and the allowable weld stress Fw,
Q
 2  S  Fw
h
4
Fw = 0.2 Fu (Clause 5.6.3.2, p. 84)
s
s
For one side weld,
Q
 S  Fw
h
(a)
s
(b)
5
For one side intermediate weld
L2
L
L2
 L 
Q

 S  Fw 
h
 L  L2 
L
L2
L
L2
L
L2
Lo
(c)
For two sides intermediate weld,
L2
L
L2
L
L2
Lo
 L 
Q

 2  S  Fw 
h
 L  L2 
(d)
6
5.6.3.3 Maximum effective length of fillet weld
(Not for plate girder)
l eff = 70 Size
For l > l eff use reduction factor 
 = 1.2 – (0.2 L) / (70 S)
5.6.3.3 One side fillet weld for any plate
thickness is allowed
7
L2
L
L2
L
L2
b
Lo
b
L2
t1
b1
L
L2
L
L2
t
t/2
Lo
b
t
s
8
-Intermittent fillet weld
L  0.75 b or
0.75 b1
Tension
L1 or L2  16 t
or
16 t1
or
200 mm
or
12 t1
or
200 mm
Compression
L1 or L2  12 t
9
The minimum size of fillet welds is 4 mm for building
and 6 mm for bridges.
The maximum size of fillet weld should not exceed
the thickness of the thinner plate to be welded.
The minimum size of fillet weld depend on the thickness of
the thicker plate:thickness t 10 mm 10-20
(mm)
Size of weld S  4 mm  5 mm
(mm)
20-30
30-50
50-100
 6 mm  8 mm  10 mm
10
- - There are no limitations for the length of fillet weld
for flange to web in weld built up plate girder.
- Single side fillet welds may be utilized only for static
loads
11
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