Curved concrete bridges - Computational Analysis and Design of Bridge Structures - page 181

3. 3D finite element model. 3D FEM is considered the most sophisticated
method among the three models. Earlier, it was most used in refined
local analysis as shown in the NCHRP Report (Nutt and Valentine
2008). However, with today's advanced technology and meshing capa-
bility, it becomes a powerful tool in detailed local stress investigation
to make sure all is within the allowables. An illustrated example is
provided for the demonstration of this type of modeling.

6.2.2 Modeling of material properties
The mathematical properties of structural components are usually assumed
according to the codes issued by the responsible authority. These properties
for static loading, including stress-strain relationship, concrete-cracking
effect, yield, and ultimate strength of steel and concrete, were discussed in
Chapter 4 for RC bridges.
For nonstatic loading, which could affect bridge member stiffness, the
nonlinear properties of concrete are required in modeling, and they will be
covered in Chapter 17—Dynamic/Earthquake Analysis.

6.2.3 Modeling of live loads
When all of the girders in a span are parallel and the span is contained
entirely within the limits of a vertical and/or horizontal curve, the profile
effect is simply the sum of the vertical curve effect and the horizontal curve
effect.

∆ = ∆ + ∆ (6.15)

total vertical effect horizontal effect

When analyzing concrete curved bridges using FEA, it is crucial to model
the live load value and position along the longitudinal direction of the
bridge to yield proper live load response. Also vehicular effects, especially
centrifugal forces, should be considered. The horizontally curved bridge is
applied by a lateral load due to the centrifugal force from traffic. According
to the AASHTO LRFD bridge design specification, the centrifugal force
is defined as the product of design truck weight and a C factor, which is
defined as

2

v
Rg

C f

= (6.16)

where:
g is the gravitational acceleration
R is the bridge curvature radius
v is the design lane speed
f is equal to 4/3 (to 1.5) for all limit state other than fatigue