Optimum characteristics of isolated structures

The effect of frequency content of the ground excitation on the optimum design of a base isolation system and a first-story damping system is investigated. The ground excitation is modeled as a filtered white noise with Kanai-Tajimi power spectral density. The stationary response, including peak response, is derived in closed form. Small “ground frequencies” result in considerable differences of the optimum design as compared with the one based on a white noise model of the excitation. Examples show the manner of applying the results to an ordinary two-story structure. Time-history analyses of the optimized structures confirm the results of the stochastic analysis.