Nonstationary seismic response of a tank on a bilinear hysteretic soil using wavelet transform

A wavelet based nonlinear random vibration theory has been proposed in the present study to obtain responses of liquid storage tanks in form of instantaneous root mean square displacements of impulsive modes of the tank-liquid system supported on bilinear hysteretic (elasto-perfectly plastic) soil medium. The superstructure has been modeled by a combination of mass-spring-damper system. In order to evaluate the instantaneous root mean square values of the displacement responses of the tanks, zeroth moments of instantaneous power spectral density function (PSDF) have been evaluated. The hysteretic displacement is assumed to follow a truncated mixed Gaussian distribution. The evaluation of this zeroth moment depends on the post-yield or the pre-yield state of the hysteretic spring. The instantaneous root-mean-square (r.m.s) impulsive displacement response of the tank has been validated by simulation. A parametric study has been carried out to see the effects of the soil nonlinearity, the shear wave velocity in the soil and the height of the tank on tank responses.