Design Examples of Steel and Steel-Concrete Composite Bridges - Finite Element Analysis and Design of Steel and Steel-Concrete Composite Bridges - page 385

3

s s

y

y

270 cm

1.6

3

54

Figure 4.146 Calculation of flange fillet weld size at supports.

4.5.6 Check of Lateral Torsional Buckling of the Plate Girder
Compression Flange
To check the safety of the upper compression flange against lateral torsional
buckling,wehavetocalculatetheelasticcritical moment for lateral torsional
buckling ( M cr ). However, to calculate M cr ,wehavetoevaluatetheeffec-
tive buckling length (unsupported length) of the compression flange of this
investigated pony bridge ( l e ), which can be calculated as follows:
l e ¼

p

1 = 4 ,where I c is the inertial of the compression flange (see

p

½ EI c ad

Figure 4.147 )about z - z axis, a is the spacing between cross girders, and d is the
flexibility of the U-frame reasonably assumed ¼ 0.00006 mm/N for pony
bridges.
I c ¼ 3 50 3 12 + 3 54 3 6 3 4cm 4 = = 12 + 45 1 : = 12 ¼ 70,631 :

1 = 4 (should be not

p

4 10 4

p

l e ¼ 210,000 70,631 : 4500 0 : 00006

less than a¼ 450 cm)
Considering the cross section at midspan shown in Figure 4.147 , we can
calculate M cr as follows:
M cr ¼C b p
kl b

s

pE y
kl b

2

C w I z + E z I z GJ