3D Finite Element Analysis of Seismic Behavior of Soil-Piled Raft-Structural System

Abstract

Piled raft foundations are mainly used in case of high rise buildings and important structures to control total and differential settlement and to enhance the bearing capacity. Behavior of structural system placed on piled raft foundation during earthquake is considered fairly complex due to dynamic interaction between soil, pile, raft, and structure. Traditionally, piled raft foundation and structure under seismic load are designed without considering flexible base condition, although soil flexibility may have significant effect on the response of soil–pile raft–structure system. In this connection, present study is an attempt to numerically investigate the seismic behavior of piled raft supported structural system embedded in homogenous soft clay using 3D finite element model in ABAQUS/CAE v6.8. Two representative fixed base periods of structure, such as, 0.3 and 2.0 s which represents low, and high rise structure respectively are considered to be supported on piled raft foundation. Nonlinearity of soil is modeled by Mohr–Coulomb soil plasticity model. Elastic responses are obtained for both soil-piled raft–structure system and fixed base system with recorded motion of 1995 Kobe earthquake. Present study calculated the maximum shear forces at the column (VB,col) and pile head (VB,pile) and compared with those for the same structure in the fixed base condition (VB,fixed). Results indicated that shear force considerably increases in pile head for both low and high rise structures as compared to fixed base shear. Further, increase at pile head observed to be significant when pile length asymmetry introduced considering optimum pile group design philosophy. However, increase in shear at column is marginal in long period structure.