Factors affecting site response analysis

Abstract

The objective of a site response analysis is to estimate free-field ground shaking characteristics during an earthquake for a specific hazard level and set of site conditions. The mandatory components for a site response analysis are: one or more design earthquake records with representative acceleration time histories, an idealization of the soil-rock system at the site of interest, and a scheme to generate response solutions to simplified assumed wave fields in other words appropriate modeling of the soil behavior. Normally, the free-field ground response is presented in terms of either response spectra or the variation of acceleration or velocity with time. The study aims to review and improve different components of site response analyses in order to achieve a robust methodology for more comprehensive and realistic assessment. The effects of input acceleration time histories, the applied numerical methodology, stress and frequency dependence and nonlinear site response analysis were reviewed and methodologies were suggested based on case studies. Site response of layered soil deposits was analyzed using equivalent linear and modified equivalent linear schemes. The developed methodology would be utilized to estimate earthquake characteristics on the ground for site specific investigations based on probabilistic earthquake hazard assessment. Within this perspective, site response analysis was studied with respect to (a) the determination of different scaling parameters including derivation of attenuation relationships for these parameters, (b) the evaluation of scaling parameters with respect to magnitude and distance ranges, (c) the methodology of selection and scaling of input acceleration time histories for site response analyses, (d) the methodology for selection of ground motion parameters from site response analysis as design or damage parameters for various earthquake engineering analysis such as liquefaction susceptibility, microzonation, vulnerability assessments for buildings and pipeline networks, (e) the methodology for confining stress and frequency dependence of modulus reduction and damping in equivalent linear site response analysis, (f) the review concerning the available equivalent linear site response analysis models and software, (g) formulation of modified version of Shake91 to account for stress and frequency dependency, (h) comparison of results with modified Shake91 based on selected borings, and (i) the review concerning nonlinear models for site response analysis.