Curved concrete bridges - Computational Analysis and Design of Bridge Structures - page 172

(a) Single-cell box girder

(b) Multicell box girder

Spread box beams
Figure 6.1 (a-c) Types of curved concrete bridge cross sections.

(c)

analogy method, the multicellular structure is idealized as a grillage of
beams. Special attention should be paid to the modeling of shear lag and
the torsional stiffness of closed cells. If properly done, the grillage model
by this method yields results that compare well with finite element tech-
niques. The folded plate method uses plates to represent the deck, webs,
and soffit of box girders. Diaphragms are not modeled. The plates are con-
nected along their longitudinal edges, and loads are applied as harmonic
load functions. The finite strip method is essentially a special case of the
FEM but requires considerably less computational effort because a limited
number of finite strips connected along their length are used. Its drawback
is that it is limited to simply support bridges with line supports and thus not
applicable as a general analysis tool for production design.
With the advent of powerful personal computers and computer programs,
the FEM has become the method of choice for complex structural problems.
Many curved box girder bridges were analyzed by this technique. The versa-
tility of this method has allowed users to investigate several aspects of bridge
behavior, including dynamics, creep, shrinkage, and temperature changes.

6.1.2 stresses of curved concrete box under torsion
Curved bridges behave quite different from straight bridges. The curva-
ture results in off-center placement of loads and, subsequently, induces tor-
sion into the superstructure. The torsion, in turn, causes the shear stresses
to increase and plays an important role in a curved structure's behavior.
Also, the curved geometry of the bridge will result in the development of
transverse moments, which can increase the normal stresses on the outside
edges of the bridge and can result in higher tension and/or compression
stresses (Fu and Yang 1996). Post-tensioned bridges also have an additional