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systems can be predicted by the analytic models. The study also investigated
changes in dynamic behavior as the system was subjected to flexural yield
and failure. Point loads were applied and removed in increments, and
dynamic testing was conducted at each load level. It was found that signif-
icant damage is somewhat noticeable by monitoring the changes in natural
frequencies. The finite element modeling of the bridge specimens was con-
structed and analyzed using ANSYS. To obtain a comprehensive represen-
tation of the bridge specimens and their multiple failure modes, four finite
element models were constructed. Each model contained various elements
to accurately simulate experimental behavior. The mathematical represen-
tation of physical elements was prescribed by four criteria comprising ele-
ment type, real constants, material association, and key options. The
element type designated the element shape, degrees of freedom, and model-
ing capabilities. The primary elements used in the study were shell elements
(SHELL181) and solid elements (SOLID65). In all cases, the girder webs and
flanges were modeled with shell elements and the concrete deck was mod-
eled with solid elements. Three connecting elements were used in the study
comprising (TARGE170), (CONTA173), and (LINK8) elements available
in ANSYS [6.10]. The contact and target elements were used to model the
bond at the concrete/steel and concrete/grout interfaces. The SHELL181
element was a quadrilateral planar element with six degrees of freedom at
each node (three translational and three rotational). The SOLID65 element
was an eight-node solid element with three translational degrees of freedom
at each node. Special features of this element include rebar reinforcement
and support of a brittle concrete material model, which is capable of com-
pression crushing and tension cracking. Real constants for SOLID65 specify
the reinforcement properties by designating a reinforcement material, vol-
umetric ratio of reinforcement to base material, and two angles that describe
the orientation of reinforcement. A nonlinear steel material was defined
with a multilinear isotropic hardening plasticity model using experimental
results. Concrete was modeled using a bilinear stress-strain curve.
concrete composite straight bridges, which was previously detailed in Refs.
I-girders through the use of equivalent trusses. The concrete slab was repre-
sented by a set of bar elements. Diaphragms and stiffeners could be also taken
into account. In contrast to the grillage model, which was used for the anal-
ysis of bridges, the recommended 3-D model allowed for a more reliable
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