Design Examples of Steel and Steel-Concrete Composite Bridges - Finite Element Analysis and Design of Steel and Steel-Concrete Composite Bridges - page 316

F w

Figure 4.87 Design height for upper and lower wind bracings.

are transmitted to the bearings by systems of upper and lower wind bracings
as well as end portal frames. The upper and lower wind bracings carry wind
forces on the main truss as shown in Figure 4.87 . Wind bracings are quite
important to the lateral stability of the upper chord compression members
since they define the buckling outside the plane of the truss, and therefore,
wind forces applied to this bridge can be sufficiently estimated using the
design rules specified in EC1 [3.2] as follows:

1

2 rv b CA ref , x
v b ¼ c dir c season v b , 0 ¼ 1

F w ¼

: 0 1 : 0 26 ¼ 26m = s

5 60 ¼ 450m 2

A ref , x ¼ 7 :

1
2 1

25 26 2 F w ¼ : 5 : 7 450 ¼ 1,083,712 : 5N ¼ 1083 : 7kN

Considering the structural analysis for the upper wind bracing system
shown in Figure 4.88 , the critical design wind force in the diagonal bracing
members can be calculated as follows:

Distributed wind loads q WL ð Þ¼ 1083 : 7 0 : 5 = 60 ¼ 9 : 03 kN = m

R A
A

R B

60 m

B

Fsin a

a

6

6000

q WL = 15.35 kN/m

Figure 4.88 Loads on the upper wind bracing.