Design Examples of Steel and Steel-Concrete Composite Bridges - Finite Element Analysis and Design of Steel and Steel-Concrete Composite Bridges - page 420

F Ed L ð maximum ¼F D : L : g g + F L : L : g q

F Ed L ð maximum ¼ 3855 1 : 3 + 4465 1 : 35

¼ 11,039 : 3 kN Tension force ð Þ

F Ed L ð minimum ¼ 3855 1 : 3 158 : 9 1 : 35 ¼ 4797 kN Tension force ð Þ

It should be noted that, from the equilibrium of joint J 10 (see
Figure 4.181 ), the force in lower chord truss member L 4 is equal to that of L 5 .

4.6.3.3 Calculation of Force in the Lower Chord Member L 3
To determine the force in the lower chord truss member L 3 (see Figure 4.182 )
using the influence line method, we can follow the same procedures adopting
for member L 4 . Hence, the forces due to the dead and live loads can be
calculated as follows:

F D : L : L ðÞ¼ 0 : 5 40 1 : 875 77 : 1 ¼ 2891 : 3kN

F L : L : L ð positive ¼ 450 1 ð : 875 + 1 : 8 Þ +0 : 5 40 1 : 875 45 : 65

¼ 3365 :

6kN

F L : L : L ð negative ¼ 7 : 5 1 ð : 875 + 1 : 8 Þ 0 : 5 40 1 : 875 2 : 45

¼ 119 :

4kN
F Ed L ð maximum ¼F D : L : g g + F L : L : g q

s

a

4 m

B

J 8

A L 2 L 3

s

10 m 30 m

g vk = 77.1 kN/m

450 kN450 kN

q vk = 45.65 kN/m

1.2 m

+

1.8

10 × 30/(40 × 4) = 1.875

Figure 4.182 Determination of the tensile force in lower chord member L 3 using the
influence line method.