NONLINEAR RESPONSE OF TORSIONALLY COUPLED BASE-ISOLATED STRUCTURE

Nonlinear response of torsionally coupled base isolated system to rand om ground motion is obtained under different parametric variations usi ng 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) Correspo nding fixed base system to investigate the effectiveness of base isola tion; and (2) corresponding symmetric system to highlight the effect o f torsional coupling. The isolator consists of an array of elastomeric bearings between the foundation and the rigid base slab. The bidirect ional hysteretic restoring force provided by the isolator against hori zontal movement is modeled by a set of coupled nonlinear differential equations. The results of the parametric study help in understanding t he behavior and effective design of torsionally coupled bae isolated s tructures.