Effects of the constitutive relationship on seismic response of soils. Part II. The site amplification study

Abstract

This paper is the second part of the general paper dealing with effects of constitutive modeling on site amplification. The paper presents a parametric study of a boundary value problem of one-dimensional shear wave propagation in soil strata during seismic loading. The logarithmic function evaluated in the companion paper is utilized as a constitutive relationship and its performance is compared to that of the Ramberg–Osgood (R–O) relationship. The study is focused on prediction of amplifications in soil profile for excitations causing strains of small to medium magnitude. Construction of three-dimensional (3D) amplification functions allowed for comprehensive study of the effects of the amplitude of excitation on amplification prediction. An emphasis has been made on effects of inaccurate simulation of the soil behavior at small and medium strains. The resulting errors in amplification function are of practical significance and have a clear physical meaning as is seen from the analysis of a simpler visco-elastic “test” problem. These response patterns are confirmed by constructing the 3D response spectra for the same soil profile using factored accelerogram record of an earthquake. Comparison of the pseudo-accelerations predicted using the logarithmic and R–O constitutive relationships show that inaccuracies in constitutive modeling of soil behavior at small to medium strains may have profound effect on seismic design.