Flexibility of foundation increases the base shear and horizontal strains during an out–of–plane response to an SH pulse in linear and nonlinear soil

Abstract

A two-dimensional model of a building supported by a rectangular, flexible foundation embedded in the soil is analysed for excitation by an incident SH-wave pulse. The building and foundation are assumed to be linear while the soil can experience nonlinear deformations. Work expanded on the development of nonlinear strains in the soil can consume a considerable part of the input wave energy, thus leaving less energy for excitation of the building. The soil and foundation are assumed to be isotropic, but the building is taken as anisotropic—it is stiffer in the horizontal direction than in the vertical. The system response with a small nonlinearity in the soil does not differ significantly from the linear response. However, significant differences appear in the responses of the models when a large nonlinearity occurs in the soil. Traditional methods for calculation of the base shear in the design of buildings underestimate the amplitudes and shears that accompany the response of buildings on flexible foundations. Most significant are the large, horizontal strains in the buildings’ foundations and base that result from flexible foundations and from non-vertical incidence of seismic waves.