LAUSR

In this study, in order to investigate the effect of the nonlinearity of superstructure supported by group-pile foundation and liquefiable ground on the piles and surrounding ground soils, three-dimensional (3D) dynamic finite element analysis is conducted, in which the strong nonlinear behavior of both soil and structure is considered during earthquake loading process. In the calculation, RC pile is modeled by AFD model proposed by Zhang and Kimura (Soils Found 42(3):77–92, 2002), which can describe the axial-force dependent nonlinear behavior of RC piles properly and a sophisticate elastoplastic constitutive model proposed by Zhang et al. (Soils Found 47(4):635–648, 2007, Front Archit Civ Eng China 5(2):121–150, 2011) is adopted, which can properly describe density (overconsolidation), structured and stress-induced anisotropy of soft soil in a unified way under drained/undrained condition subjected to monotonic/cyclic loading. For superstructure, its mechanical behavior is described by three different 3D models, (1) a beam element theory proposed by Goto et al. (J Struct Eng 41A:411–420, 1995) that can take into consideration both the material and geometric nonlinearity; (2) trilinear beam that can roughly consider the material nonlinearity; (3) linear elastic beam. The main purpose of the research is to find out, the influence of not only the material nonlinearity, but also the geometric nonlinearity of the superstructure, with a unified calculating model in which the superstructure, the foundation and the soft are included. The calculated results show that the nonlinear behavior of superstructure has less influence on soft ground, but the large deformation of the superstructure may give rise to large extra moment of pier, which, as the results, will increase the external forces acting on the piles. Therefore, both the geometric and material nonlinear behavior of superstructure should be properly taken into consideration in seismic design, especially when it is built on a liquefiable ground.