Design Examples of Steel and Steel-Concrete Composite Bridges - Finite Element Analysis and Design of Steel and Steel-Concrete Composite Bridges - page 278

F L : L : U ðÞ¼ 375 2+1 ð : 92 Þ 0 : 5 60 2 43 : 8 ¼ 4098 kN

F Ed U ðÞ¼F D : L : g g + F L : L : g q

F Ed U ðÞ¼ 4686 1 : 3 4098 1 : 35

¼ 11624 : 1 kN Compression force ð Þ

It should be noted that, from the equilibrium of joint J 6 (see Figure 4.55 ) , the
force in upper chord truss member U 5 is equal to that of U 6 . It should also be
noted that the negative distributed loads are not used since they will produce
a small tensile force, which reduces the calculated compressive force.

4.3.3.3 Calculation of Force in the Lower Chord Member L 5
To determine the force in the lower chord truss member L 5 (see Figure 4.56 )
using the influence line method, we put the unit concentrated load at point
a, and using the sectioning method, we take a section s - s , as shown in
Figure 4.56 , and then take the moment at point a. After that, we can put
the previously calculated dead and live loads acting on a main truss in the
longitudinal direction. The forces due to the dead and live loads can be
calculated as follows:
F D : L : L ðÞ¼ 0

: 5 60 1 : 92 78 : 1 ¼ 4498 : 6kN

F L : L : L ðÞ¼ 375 1 ð : 92 + 1 : 856 Þ +0 : 5 60 1 : 92 43 : 8 ¼ 3938 : 9kN

s

U 4

a

B

L 5 s

A

24 m 36 m

g vk = 78.1 kN/m

375 kN

375 kN

q vk = 43.8 kN/m

1.2 m

+

24 × 36/(60 × 7.5) = 1.92 1.856

Figure 4.56 Determination of the tensile force in lower chord member L 5 using the
influence line method.