Do seismic intensity measures (IMs) measure up?

Abstract

The assumption that demand parameters D for realistic structures, i.e., complex, nonlinear dynamic systems, subjected to seismic acceleration processes A(t) correlate satisfactorily with maxima Sa(T) of responses of single degree of freedom (SDOF) linear systems to A(t) is the cornerstone of current definitions of seismic intensity measures (IMs).We show that, generally, Sa(T) and D are weakly dependent and conclude that fragilities defined as functions of Sa(T) have large uncertainties. The analysis considers linear/nonliear systems and single/multiple ordinates of Sa(T). Tools of random vibration, copula models, and multivariate extreme value theory are employed to quantify the dependence between Sa(T) and D.