Approximate and refined analysis methods - Computational Analysis and Design of Bridge Structures - page 24

Minimum distance from wheel center to curb
= 300 mm (S3.6.1.3)

Minimum distance between wheels of two trucks = 1200 mm

Equivalent strip width

Figure 2.8 Transverse live load moments of a bridge deck.

− → = M E : 1220 0 25 + . S (2.1b)

where:
E is the equivalent strip width in mm
S is the stringer spacing
+M is the positive moment region
−M is the negative moment region

The dead load effect can be obtained by treating dead load as stationary
load acting on a continuous beam. Trucks, as the live load, have to be
moved laterally to determine the maximum positive and negative moments.
Multiple presence factor (1.2, 1.0, and 0.85 for one, two, and three trucks,
respectively, as per AASHTO LRFD) shall be considered in the analysis.
Figure 2.8 shows the lateral loading for determining transverse moments
on a bridge deck.
The dominant failure modes of a bridge deck are either flexure shear
or punching shear. The punching shear is not obtained easily by even the
refined analysis method, such as FEM, unless a very fine meshed model
is built around the critical location. Figure 2.9 adopted from laboratory
tests by Hwang et al. (2010) shows the footprint of a truck wheel and its
punching shear critical locations. As specified in the AASHTO LRFD
Specifications (2013) for punching shear, the shear strength V n , multiplied
by the strength reduction factor φ, shall be larger than the ultimate shear
produced by the wheels (Equation 2.2).

V ≤ ϕ V (2.2)

u n

Without shear reinforcement, the shear strength of concrete V n in Equation
2.3 is governed by AASHTO Equation 5.13.3.6.3-1 in metric form