Integral bridges - Computational Analysis and Design of Bridge Structures - page 507

Figure 16.13 Superstructure node distribution of the IAB example.
16.4.2 soil
Soil is modeled using spring elements, COMBIN39, a spring between a
node and ground. The spring is a unidirectional element with nonlinear
generalized force-deflection capability. The element has three degrees of
freedom at each node: translations in the nodal x -, y -, and z -directions,
with their properties as described in Section 16.3.2. There are three types
of springs used in the model. The first type represents the displacement in
lateral and longitudinal directions and consists of two springs. Both springs
are at the center of the web. They are modeled at each layer of the nodes
along the pile starting at one layer below the bottom of the abutment and
continuing all the way to one layer above the tip of the pile. The second
type of spring represents friction along the pile. It consists of a single spring
at each node along the web of each pile starting one layer below the bottom
of the abutment and ending one layer above the tip of the pile. The third
and final type of spring is the tip spring that represents the settlement in
the pile and consists of seven springs at each node at the tip of the pile. This
spring representation of the tip of each pile allows for uniform resistance to
pile settlement and is used in the analysis of friction piles. These pile tip-
settlement springs are replaced with fixed end conditions when analyzing
bridge models with end-bearing piles. Figure 16.11 depicts the spring model
of a steel pile used in this example.
16.5 Illustrated exaMPle of a steel
gIrder BrIdge In 3d soIl contInuuM
fInIte eleMent Model
The same example used in Section 16.4 built with soil springs is also used
here to demonstrate the soil continuum finite element model. A 3D nonlin-
ear finite element model using ANSYS was built and listed in another PhD
dissertation at the University of Maryland (Rasmi 2012). The nonlinearity
is considered for the nonlinear effect of the material plasticity of steel piles.
Due to symmetry and the complicity of the continuum modeling, only a
quarter of the bridge was modeled.
The entire model was meshed using plane and hexahedral elements.
The concrete slabs, piles, and girders were meshed using the 2D shell element