Seismic response of torsionally coupled base isolated structures

摘要: An analytical study of the seismic response typical base isolated structures mounted on rubber bearings is presented. Isolated buildings are liable to have closely spaced lower modes vibration with small eccentricity between centres mass and rigidity. The structure modelled as a rigid deck lumped masses supported axially inextensible elastomeric bearings. This simplified system has three degrees freedom (dof), two translations one rotation in horizontal plane. The Green's functions for displacement 3 dof derived both undamped damped cases large eccentricities. case taken from specific building, while arises 5 per cent accidental which required by various codes. An interaction equation normalized displacements established an idealized flat velocity spectrum or hyperbolic acceleration spectrum. building would its fundamental period fall into this range design spectrum. Numerical results subjected El Centro earthquake 1940 Both time history modal superposition analysis were performed. In analysis, Complete Quadratic Combination (CQC) showed superiority over Square Root Sum Squares (SRSS) estimating maximum responses. It concluded that effect torsional coupling transient insignificant, due combined lag translational responses influence damping isolation can be high 8 10 cent.