Abstract:
Deformation of soil due to seismic load imposed by the structures above can
result in the change in stresses and deformation of the structures. Considering
the interaction between soil and structure is important especially for the design of
large structures with embodiment such as nuclear power plant containment and
foundations of bridges. Engineering experience has shown that under dynamic
loading and particularly during earthquakes the bridge-soil systems undergo
significant alterations. These alternations cannot be taken into account using the
classical methods of design. Consequently, to prevent major disasters and
material loss it is imperative to perform adequate soil structure interaction
analysis. Furthermore, as some interaction phenomena have favorable effect on
the structural resistance, their consideration enables design and construction
with economy and elegance.
Three multiple span simply supported bridges, representative of typical bridges in
Bangladesh, has been analyzed. Soil supports are explicitly modeled with
equivalent springs. Radiation damping associated with wave propagation
between the masses of the superstructure and foundation-soil is one form of
energy dissipation due to soil-structure interaction(SSI). In this study, damping
due to material nonlinearly in the foundation-soil is explicitly modeled, while the
radiation damping is implicitly accounted for through equivalent viscous damping.
Beam column elements are used to model the columns and simple connection
elements are employed in modeling bearings and soil-structure springs.
Extensive parametric studies are also performed to show the influence of soil
shear modulus (400 psi, 4000 psi and 40000 psi), backwall condition (intact and
broken), bearing performances (intact and failed with two different coefficient of
friction equal to 0.2 and 0.6). Results are presented in terms of time histories of
shear force at pier columns, top displacement of pier, gap width of abutment,
plastic rotation at base of pier column and deck displacements due to variation of
bearing performances, SSI models, boundary conditions of the pier column
footings and soil conditions.
Time history analysis of bridges has considered both the fixity and flexibility of
the supports using 5% damping. Push over analysis and nonlinear time history
analyses of bridges have also been performed using both 2-D and 3-D computer
models by DRAIN-2DX and DRAIN-3DX. Raleigh's damping proportional to both
stiffness and mass matrices is used. Under peak ground acceleration (PGA) of
0.18g and O.4g bridges were analyzed under three different earthquake records
(Parkfield, EI-Centro and Nahanni).
