Elimination of torsion and pounding of isolated asymmetric structures under near-fault ground motions

Abstract

This paper aims at forcing the isolated asymmetric structures to behave as symmetric structures with, theoretically, no absolute torsional responses. In addition, it attempts to provide efficient protection to such structures against severe near-fault ground motions considering limited seismic gaps with no seismic pounding. To achieve these goals, the recently proposed multi-feature roll-in-cage (RNC) isolator is used. An improved full-feature sap2000 model (Computers and Structures, Inc., Walnut Creek, CA, USA) is first developed for the RNC isolator then validated using analytical and experimental results. Next, an RNC isolation method that could eliminate the eccentricities between both structural centers of mass and rigidity is employed to theoretically remove structural torsion. It is based on using different isolator sets with unequal elastic stiffness to allow for shifting the center of rigidity at the isolation level, having dominant lateral behavior in case of isolated structures, to coincide with the structural center of mass above that level. After that, the ability of the RNC isolator to provide efficient seismic isolation considering relatively limited seismic gaps is investigated under unidirectional and bidirectional near-fault earthquakes. This could be attained through the independent source of high hysteretic damping and pre-yield elastic stiffness of the RNC isolator, in addition to its integrated self-stopping or buffer mechanism. The obtained results demonstrate the capability of the RNC isolator to, theoretically, eliminate torsional responses of isolated asymmetric structures besides providing relatively efficient seismic isolation, with no seismic pounding, considering insufficient or limited seismic gaps under severe near-fault unidirectional and simultaneous bidirectional ground motions. Copyright © 2015 John Wiley & Sons, Ltd.