Examples of Finite Element Models of Steel Bridges - Finite Element Analysis and Design of Steel and Steel-Concrete Composite Bridges - page 560

model was presented for a comprehensive simulation of a girder bridge
including the orthotropic top/bottom/web plates and their ribs. The
authors concluded that the finite element analysis can be an effective method
to predict properties of this class of bridges. In order to reflect the actual
behaviors of the bridge decks accurately, an advanced parametric design lan-
guage (APDL), in the commercially available software ANSYS [ 6.10 ] , was
used to perform a 3D analysis of the orthotropic steel box girder. The FE
model for the steel box girder was built using shell elements (Shell 63). In
the 3D bridge model, the total number of shells is 22,496 with a total of
22,574 joints. The authors mentioned that if modeling a larger and more
complex bridge is required, it would be difficult to set up and compute
an entire shell model; the recommended method would be a combination
of a simple entire model with high-fidelity finite elements in the specific
local section. Different mesh densities resulted in different computational
accuracies to some extent.
Graciano et al. [ 6.14 ] studied the influence of initial geometric imperfec-
tions on the postbuckling behavior of longitudinally stiffened plate girder
webs subjected to patch loading. The authors mentioned that upon recog-
nizing the significance of geometric imperfections, a large amount of
research has been conducted to develop models of characteristic imperfec-
tions for specific structures and then using these models to gain a better esti-
mate of the ultimate load [ 6.15 , 6.16 ] . Graciano et al. [ 6.14 ] performed a
sensitivity analysis using two approaches (deterministic and probabilistic)
in order to investigate the effect of varying imperfections in shape and ampli-
tude on both, the postbuckling response, and ultimate strength of plate
girders under patch loading. The sensitivity analysis was performed by means
of nonlinear finite element analysis. At first, the initial shape imperfections
are modeled using the buckling mode shapes resulting from an eigenvalue
buckling analysis. Following the eigenvalue buckling analysis, the amplitude
of the buckling shapes for the various modes was factored and then intro-
duced in the nonlinear analysis. The results showed the influence of these
modes and amplitudes on the resistance to patch loading. The finite element
software ANSYS [ 6.10 ] was used. Shell elements (Shell 181) having 4 nodes
and 6 degrees of freedom at each node were used to model the web, flanges
(top and bottom), and the longitudinal stiffener. Due to symmetry in geom-
etry, loads, and boundary conditions, only one-half of the plate girder was
modeled. Transverse stiffeners at the end of the plate girder were taken
into account by means of a rigid body kinematical constraint of the degrees
of freedom located in the corresponding side. The material herein was