Structures Congress 2020 432 © ASCE The Effect of Soil Modeling on the Nonlinear Response of SDOF Structures Aidin Tamhidi 1 and Mohammad Ali Ghannad, Ph.D. 2 1 Dept. of Civil and Environmental Engineering, Univ. of California, Los Angeles, Los Angeles, CA. E-mail: aidintamhidi@ucla.edu 2 Dept. of Civil Engineering, Sharif Univ. of Technology, Tehran, Iran. E-mail: ghannad@sharif.edu ABSTRACT Considering soil-structure interaction (SSI) effect in the design of structures would affect their seismic demands. Design codes, such as ASCE 7-10, usually allow engineers to reduce the design base shear accounting for SSI effect. ASCE 7-10 methodology is based on modeling the underlying soil using a set of dashpots and springs that approximate the actual nonlinear behavior of the soil through an equivalent linear model. In this study, we aimed to study the effect of different approaches for modeling of soil nonlinear behavior on the response of the superstructure. We employed two types of soil-structure systems using 1) an equivalent linear model suggested by most of the design codes, and 2) a beam on nonlinear Winkler foundation (BNWF) model for the beneath soil. The results show that the difference between the structure’s response in the two models might be negligible for structures located on soil type C. However, for structures built on soil type D, this difference could be quite considerable. The results clearly show the structure experiences less inelastic deformations when the soil undergoes more inelastic deformation; in addition, the soil experiences less plastic displacement for more ductile structures. INTRODUCTION For structures located in moderate- to high-seismicity zones, the earthquake-induced demands in many occasions govern the design procedure. Among the simplifying assumptions made during the seismic design and analysis of a structure, a fixed base condition for flexible structures located on stiff soils is usually a reasonable assumption. However, a fixed-base assumption for stiff structures located on soft soils can lead to non-negligible errors in the estimates of seismic demands. In the latter case, the underlying soil would have a more significant impact on the seismic response of the superstructure in comparison with a flexible structure located on stiff soil. Moreover, in turn, the demand imposed by the structure on the underlying soil would affect the response of the underlying soil in comparison with the free-field soil response. This effect, known as soil-structure interaction (SSI), has been the subject of many studies for more than four decades. Beginning in the 1970’s, a number of codes and researchers started to consider the SSI effect. The provision ATC3-06 (Applied Technology Council 1978) allowed engineers to reduce the design base shear through considering the stiffness and damping of the beneath soil having two sway and rocking DOFs. Novak also studied the effect of soil and foundation embedment on the response of structures to external lateral excitations such as wind and earthquake loads (Novak 1974). In the majority of these studies, the structures were modeled as linear and elastic. Most of the engineers design the structures such that they are able to undergo significant inelastic deformations when subjected to a seismic excitation. Bielak (1978) showed that the superstructure, as a component of the soil-structure system, having inelastic behavior, would Structures Congress 2020 Downloaded from ascelibrary.org by 54.162.69.248 on 07/24/20. Copyright ASCE. For personal use only; all rights reserved.