Integral bridges - Computational Analysis and Design of Bridge Structures - page 505

16.3.3 soil continuum finite element model
In this approach a 2D or 3D finite element model of the superstructure and
substructure, including surrounding soil, is built. Both pile and soil can be
modeled into a 3D finite element model using eight-node solid continuum
elements with a nonlinear response (Khodair and Hassiotis 2013). While
an elastic-plastic response was adopted for the pile elements, the Mohr-
Coulomb model with strain hardening idealized the nonlinear soil response.
A surface-to-surface contact algorithm was employed to model the sand-
pile interaction. To model the tangential contact, the friction coefficient for
the interaction between pile and soil materials was calculated.
In the 3D finite element model shown in Khodair and Hassiotis (2013),
the pile and soil were modeled using 3D eight-node solid continuum ele-
ments. Three boundary conditions were imposed in the finite element
model: (1) the pile is fixed at the bottom to model the embedment of the
piles, (2) all degrees of freedom associated with the exterior surface of
the sand surrounding the piles are restrained to model the confinement
of the galvanized steel sleeves by crushed stone backfill (which may not
be the case for others), and (3) guided fixation at the top of the pile is
modeled by tying the nodes at the top surface of the pile to a defined ref-
erence point located in the centroid of the cross section of the pile at its
top to simulate the embedment of the piles into the abutments. The steel
piles were modeled using an elastic-perfectly plastic model. The soil was
modeled using a strain hardening model implementing Mohr-Coulomb
failure criterion. The soil-pile interaction was simulated by adopting tan-
gential and normal contact behavior in the model. Master and slave sur-
faces were defined in the model such that the exterior surface of the pile
was used to model the master surface and the interior surface of the sand
was used for the slave surface.
For a predrilled hole case, such as a drilled shaft, special treatment has
to be made where interface elements allow relative movement between
the structural elements and the contact soil. More detailed descrip-
tion of the modeling technique is covered by an illustrated example in
Section 16.5.
16.4 Illustrated exaMPle of a steel gIrder
BrIdge In soIl sPrIng fInIte eleMent Model
An IAB described in a PhD dissertation at the University of Maryland
(Thanasattayawibul 2006) is used as a case study in this chapter. The cross
section of the bridge is shown in Figure 16.12. The bridge consists of a
178-mm (7″)-thick concrete slab that is supported by six girders. There is a
0.6-m (2′) overhang on each side of the bridge. There are 11 piles supporting