Applied Loads and Stability of Steel and Steel-Concrete Composite Bridges - Finite Element Analysis and Design of Steel and Steel-Concrete Composite Bridges - page 134

may be considered to be applied only along the carriageway axis and uni-
formly distributed over the loaded length. Acceleration forces should be
taken into account with the same magnitude as braking forces, but in the
opposite direction.
In the United States, AASHTO [1.23,1.24] specifies that the braking
force on highway bridges shall be taken as the greater than 25% of the axle
weights of the design truck or design tandem or 5% of the design truck plus
lane load or 5% of the design tandem plus lane load. The braking force shall
be placed in all design lanes carrying traffic heading in the same direction.
The forces shall act horizontally at a distance of 1.8 m above the roadway
surface in either longitudinal direction to cause extreme force effects.

3.4.3.2 Centrifugal Forces
The centrifugal force Q tk , specified in EC1, acting on highway bridges
should be taken as a transverse force acting at the finished carriageway level
and radially to the axis of the carriageway. The characteristic value of Q tk ,in
which dynamic effects are included, should be taken from Table 3.5 , where r
is the horizontal radius of the carriageway centerline in meters and Q v is the
total maximum weight of vertical concentrated loads of the tandem systems

of LM1, that is, P i a Qi (2 Q ik ) (see Table 3.2 ). Q tk should be assumed to act as
a point load at any deck cross section. Where relevant, lateral forces from
skew braking or skidding should be taken into account. A transverse braking
force, Q trk , equal to 25% of the longitudinal braking or acceleration force,
Q 1k , should be considered to act simultaneously with Q 1k at the finished car-
riageway level.
In the United States, AASHTO [1.23,1.24] recommends that for the
purpose of computing the radial force or overturning effect on wheel loads,
the centrifugal effect on live load shall be taken as the product of the axle
weights of the design truck or tandem and the factor C , taken as

v 2
gR

C ¼ f ð 3 : 17 Þ

where v is the highway design speed in m/s, f is equal to 4/3 for load com-
binations other than fatigue and 1.0 for fatigue, g is gravitational acceleration

Table 3.5 Characteristic Values of Centrifugal Forces Recommended by EC1 [ 3.1 ]
Q tk ¼ 0.2 Q v (kN) If r < 200 m

Q tk ¼ 40 Q v / r (kN) If 200 r 1500 m

Q tk ¼ 0 If r > 1500 m