NONLINEAR RESPONSE OF TORSIONALLY COUPLED BASE-ISOLATED STRUCTURE

Nonlinear response of torsionally coupled base isolated system to random ground motion is obtained under different parametric variations using a simulation procedure. Parameters include those which characterize mass, stiffness, and damping properties of the superstructure (i.e., fixed base torsionally coupled system) and the base isolator. The mean peak responses from simulation analysis are compared to: (1) Corresponding fixed base system to investigate the effectiveness of base isolation; and (2) corresponding symmetric system to highlight the effect of torsional coupling. The isolator consists of an array of elastomeric bearings between the foundation and the rigid base slab. The bidirectional hysteretic restoring force provided by the isolator against horizontal movement is modeled by a set of coupled nonlinear differential equations. The results of the parametric study help in understanding the behavior and effective design of torsionally coupled bae isolated structures.