Two-Dimensional Nonlinear Seismic Analysis of Soil-Well-Pier System Considering Soil Nonlinearity

Abstract

Nonlinear seismic analysis of soil-well-pier (SWP) system of a typical bridge supported on well foundation is carried out considering soil nonlinearity while the well and the pier are assumed to behave linearly. Nonlinear behaviour of soil is captured in two different ways: (a) a rigorous analysis considering nonlinear constitutive model of soil, and (b) an approximate analysis by equivalent-linear method. In the first method, multiple yield surface plasticity model available in OpenSees is used to rigorously model nonlinear hysteretic behaviour of soil. In equivalent-linear method, analysis has been carried out in two steps. In the first step, free-field analysis of soil column is performed in SHAKE2000 for a given acceleration time-history using shear-strain-dependent shear modulus and damping properties of soil to obtain effective shear modulus and damping values at each layer of soil. In the next step, these effective properties of soil are used in finite element model of soil-well pier system and linear seismic analysis is performed in OpenSees. Results of equivalent-linear analysis are compared with those from nonlinear analysis, with the objective to assess suitability of approximate analysis in the design offices.