Design-Oriented Ductility Bound of a Plane Frame Under Seismic Loading

Abstract

The purpose of this paper is to propose an approximate upper bound of member ductility factors of a plane building frame under a set of spectrum-compatible earthquakes. The acceleration response spectrum is assumed to be a nonincreasing function of period for a constant damping ratio and a nonincreasing function of damping ratio for a constant period. Most of the previously proposed design acceleration response spectra appear to satisfy these assumptions except in a narrow range of quite small periods. The present study shows that the upper bound (design-oriented upper bound) of member ductility factors can be drawn only when combined with a design method for almost uniform ductility, which is recognized in general to be desirable for avoiding damage concentration. It is shown that the second assumption on the acceleration response spectrum and neglect of additional damping in the equivalent linear model enable one to derive a narrower upper bound on member ductility factors. Inelastic time-history response analyses are performed to investigate the accuracy of the upper bounds and to examine the validity of an equivalent linearization technique.