Effect of two horizontal components of earthquake on nonlinear response of torsionally coupled base isolated structures

摘要

Torsion in base-isolated structures using bilinear rubber isolators effected by two horizontal componentsnof earthquake simultaneously is investigated under various principal parameters including number ofnstoreys; ratio of uncoupled torsional frequency to lateral frequency in the superstructure; ratio of uncoupledntorsional frequency to lateral frequency in the isolation system; mass eccentricity in the superstructure andnisolation system; and, in addition, the direction of eccentricity. Structure was supposed a shear structurenand it was modeled by using concentrated mass and springs. Isolators are modelled by using nonlinearnsprings considering the interaction of isolator behaviour in two directions. The effect of variation in considerednparameters on the behaviour of the superstructure and isolation system is investigated under sevennground motions. It is demonstrated that the parameters affect asymmetric structure behaviour with respectnto symmetric one. The results of our investigations help us to understand the asymmetric structure behaviournunder bidirectional earthquake by comparing it with a symmetric one. These results demonstrate thatnasymmetry in the superstructure or isolation system could have a signifi cant effect on the torsional behaviournof isolated structures. In addition, the results show that the use of rigid superstructures and calculationnof dynamic torsion by multiplying eccentricity by the dynamic base shear are unacceptable assumptions.nTorsional effect on the isolated structural behaviour is amplifi ed by considering two horizontal componentsnof earthquake and comparing them with just one horizontal component. Copyright © 2010 John Wiley &nSons, Ltd.