The Design of Modern Steel Bridges - TEDI

56 The Design of Modern Steel Bridges
The loading on the principal lane is multiplied by an impact factor k varying
from 1.0 to 1.4 and given by k ¼ 1.4 0.008L, but not less than 1, where L is
the span length of the member in metres.
In France[7], bridges are classified according to the carriageway widths:
class I – bridge with carriageway width equal to or greater than 7 m
class II – bridge with carriageway width between 5.5 and 7 m
class III – bridge with carriageway width equal to or less than 5.5 m.
The carriageway width is divided into an integer number of traffic lanes of
width not less than 3 m, except that carriageways with widths between 5 and
6 m are considered to have two lanes. Two different and independent types of
loading are considered – a uniformly distributed load A and a vehicle or axle
load B. A is given by
A ¼ 2:3 þ 360
L þ 12 kN=m2
where L is the loaded length in metres. A is multiplied by coefficient a 1, which
depends on the bridge class and number of lanes to be loaded, as shown in
Table 3.4.
There is another multiplying factor a 2 ¼ V o/V, where V is the width of the
lane being considered and Vo ¼ 3.5 m for class I, 3.0 m for class II and 2.75 m
for class III. The load (a 1 a 2 A) is placed uniformly over the total widths of the
traffic lanes considered.
The vehicle or axle load B for each bridge member consists of three independent
loading systems:
(1) B c consists of two vehicles of 300 kN on each lane, with axle spacings
as shown in Fig. 3.2. The value of the vehicle load is multiplied by
Table 3.4 Coefficients a1
Bridge class Number of loaded lanes
1 2 3 4 5
I 1 1 0.9 0.75 0.7
II 1 0.9 – – –
III 0.9 0.8 – – –
Figure 3.2 Axle loading for French loading.