Accounting for the influence of ground motion response spectral shape and duration in the equivalent lateral force design procedure

Abstract

A framework is proposed to explicitly account for the influence of ground motion response spectral shape and duration in the ASCE 7-16 equivalent lateral force design procedure, which currently considers only ground motion intensity, as quantified by Sa(T1). The scalar, dimensionless parameter SaRatio is used to characterise response spectral shape, while significant duration, Ds, is used to quantify duration. Design base shear adjustment factors are computed based on (i) the extended seismic hazard at a site, expressed in terms of the SaRatio and Ds values of the anticipated ground motions; and (ii) the sensitivity of the structure to the effects of response spectral shape and duration. Since these factors account for the influence of additional ground motion characteristics on structural collapse risk, their use in structural design should help achieve a more uniform distribution of collapse risk over different geographical regions and structural systems, in line with the objective of using risk-targeted seismic design maps. Sample calculations using the extended seismic hazard in Los Angeles as a benchmark indicate, for example, that a reinforced concrete moment frame building in Eugene with fundamental elastic modal period 1.0 s would need to be designed to a base shear 67 % higher than the current standard, while a similar structure in San Francisco would need to be designed to a base shear 43 % higher.