Applied Loads and Stability of Steel and Steel-Concrete Composite Bridges - Finite Element Analysis and Design of Steel and Steel-Concrete Composite Bridges - page 115

own weight of cross girder depends on its length and the type of steel used.
The own weight of cross girder can be reasonably assumed to be 2-3 kN/m
of the length of cross girder, which is the pacing between the main girders.
By knowing the assumed concentrated dead loads acting on the cross girder
and its assumed own weight, the straining actions resulting from dead loads
comprising bending moment and shear force can be calculated. Finally, the
dead loads acting on the main girders (see Figure 1.20) are the weight of steel
structural parts plus the weight of tracks. The weight of steel structural parts
can be estimated from similar existing bridges or from some empirical for-
mulas, which are obtained from the data available from previously designed
railway steel bridges. The assumed weight of steel structural parts depends on
many factors including the length of main girder, type of steel used, and type
of bridge. A reasonable assumption of the weight of structural parts ( w s ) for
single-track open-timber floor bridges can be given by the following empir-
ical equations:

w s ¼ 4+0

ð Þ
for deck bridges without stringers and cross girders

: 5 L kN =

ð 3 : 1 Þ

ð Þ

w s ¼ 9+0 ð Þ

for deck bridges with stringers and cross girders

: 5 L kN =

ð 3 : 2 Þ

ð Þ

3 Þ
where L is the length of main girder in meters and the weight of structural
parts ( w s ) is divided into two main girders. For double-track bridges, the pre-
viously mentioned loads can be increased by 80-90%. By knowing the
assumed total dead load acting on the main girder, the straining actions
resulting from dead loads comprising bending moment and shear force
can be calculated. For ballasted floor railway steel bridges, the weight of
structural parts can be increased by 20-40%.

w s ¼ 11 + 0 : 5 L kN ð = m Þ ð for pony bridges Þ ð 3 :

3.2.2 Dead Loads of Highway Steel and Steel-Concrete
Composite Bridges
As an example, let us estimate the dead loads acting on different components
of the traditional through-truss highway steel bridge as shown in
Figure 1.21. Starting with the dead loads acting on a stringer, the dead loads
include the weight of flooring (1.5-2 kN/m 2 ), the weight of reinforced con-
crete slabs having a thickness of around 200 mm (5 kN/m 2 ), the weight of
reinforced concrete haunch (0.3 kN/m 2 ), and the own weight of stringer