Applied Loads and Stability of Steel and Steel-Concrete Composite Bridges - Finite Element Analysis and Design of Steel and Steel-Concrete Composite Bridges - page 129

effect of the structural element considered, with a maximum value of
1000 kN for Q lak and 6000 kN for Q lbk . The lines carrying special traffic
and associated loading details may be specified. Traction and braking forces
shall be combined with the corresponding vertical loads. In the case of a
bridge carrying two or more tracks, the braking forces on one track shall
be considered with the traction forces on the other track. Where two or
more tracks have the same permitted direction of travel, either traction
on two tracks or braking on two tracks shall be taken into account. It should
be noted that braking and traction forces may be resisted using special sys-
tems of braking bracing added to the upper or lower wind bracing systems.
In this case, their effect on the bridge components above the bearings can be
neglected since the forces can be transmitted directly to the bearings.
3.4.2.4 Wind Forces
Wind actions on railway bridges fluctuate with time and act directly as pres-
sures on the external surfaces of the main carrying systems of the bridge and
on moving trains. Pressures act on areas of the surface resulting in forces nor-
mal to the surface of the main carrying systems of the bridge. The wind
action is represented by a simplified set of pressures or forces whose effects
are equivalent to the extreme effects of the turbulent wind. The wind actions
calculated using the rules specified in EC1 (BS EN 1991-1-4) [ 3.2 ] are char-
acteristic values determined from the basic values of wind velocity or the
velocity pressure. The response of the bridge to wind actions depends on
the size, shape, and dynamic properties of the bridge. EC1 [ 3.2 ] covers
dynamic response due to along-wind turbulence in resonance with the
along-wind vibrations of a fundamental flexural mode shape with constant
sign. The response of the bridge should be calculated from the peak velocity
pressure, q p , at the reference height in the undisturbed wind field, the force
and pressure coefficients, and the structural factor c s c d . q p depends on the
wind climate, the terrain roughness and topography, and the reference
height. q p is equal to the mean velocity pressure plus a contribution from
short-term pressure fluctuations.
According to EC1 [ 3.2 ] , wind forces are calculated for bridges of con-
stant depth and with cross sections as shown in Figure 3.11 consisting of
a single deck with one or more spans. Wind actions for other types of bridges
(e.g., arch bridges, bridges with suspension cables or cable-stayed, roofed
bridges, moving bridges, and bridges with multiple or significantly curved
decks) may be defined in the National Annex. Wind actions on bridges
produce forces in the x -, y -, and z -directions as shown in Figure 3.12 , where