A response spectra based intensity measure for seismic system reliability

Abstract

This work studies a newly proposed seismic intensity measure (IM) and evaluates its efficiency and sufficiency with respect to ground motion records and structural response, with the end goal of computing structural system reliability under seismic loads for design application. An intensity measure's efficiency is the variance of engineering demand parameters (EDPs) across different ground motions at a particular value of IM. Sufficiency corresponds to the statistical independence of EDP at a given IM from ground motion parameters such as magnitude, site to rupture distance and soil type. The proposed intensity measure (IRS)is based on spectral acceleration at the natural time period Sa(T1) and the geometric mean of spectral acceleration over a fixed range of periods RSavg. Unlike previously proposed IM's, RSavg is measured over a predetermined range of time periods (independent of natural time period) to capture higher mode effects and strength degradation. Proposed IM is verified with a single degree of freedom (DOF) lumped mass system, 5 DOF lumped mass system, archetype steel frames, and single storey reinforced concrete (RC) shear wall building by statistical studies on non-linear time history analysis results. Twenty-two far field ground motion acceleration records (forty-four individual directional components) specified by the Federal Emergency Management Agency's P695 document are used. It is found that IRSis highly efficient and sufficient for structures with time period more than 1sec and moderately efficient for shorter period structures compared to ten other intensity measures from the literature.