Estimation of strength-reduction factors for elastoplastic systems : A new approach

SUMMARY A new rule is presented to estimate strength-reduction factors in single-degree-of-freedom elastoplastic oscillators, inwhich reduction factors depend only on displacement elastic spectra, so they are not an explicit function of structuralperiod. It is found that the proposed rule yields good results when applied to accelerograms recorded in Þrm and softsoils, and for damping ratios of 2, 5 and 10 per cent of the critical. It is shown that the proposed reduction rule is moregeneral than others previously published, and at least as accurate. ( 1998 John Wiley & Sons, Ltd. KEY WORDS : strength-reduction factors; elastoplastic systems INTRODUCTIONContemporary seismic design of buildings requires, among many other things, the estimation of variousstructuralresponse parameters in the inelastic range. For instance, since enough strength must be furnishedto limit ductility demand, k, to a speciÞed value, and thus prevent collapse, estimation of k for a givenstrength is essential in the design process.Estimation of required strengths, ductility demands or inelastic displacements is usually done using