REDUCTION FACTORS FOR BASE-ISOLATED STRUCTURES

A rational methodology to evaluate behaviour factors for base isolated structures (BIS) code design is presented. The method used in this st udy is to directly derive q-factors by the nonlinear response analysis of 2 d.f. isolated models subject to strong seismic excitations artif icially generated according to EC8 design spectra. The influence of se veral parameters on the ultimate behaviour of BIS has been analysed an d collapse spectra have been derived for base isolated structures. Hav ing defined theoretical collapse conditions for a 2 d.f. system subjec t to a set of artificial excitations; the minimum strength spectra nee ded for the structural survival have been evaluated. By dividing the e lastic design spectra by the inelastic response ones, reduction factor s for base isolated structures can be determined. A comparison with th e UBC-91 new requirements for isolated structures shows a good agreeme nt between the recommended behaviour factors and the ones calculated i n the present paper. Copyright (C) 1996, Elsevier Science Ltd