Frequency Content in Earthquake Simulation

Random processes with frequency content similar to that of recorded earthquakes are generated by using linear filters to remove the very low and very high frequency components of white noise. The mean-squared responses of single-degree-of-freedom structures to these filtered processes are compared with the corresponding responses to white noise excitation. For linear structures exact analytical solutions for mean-squared displacement and velocity response are presented. Using an equivalent white noise to approximate the nonwhite noise excitation generally extends the frequency range of adequate approximation, particularly for small structural damping. For yielding structures Monte Carlo simulation is used to obtain response levels for some representative situations. The effect of a second-order filter on yielding system response is somewhat different than for a linear system; in fact, it is more like the effect of a first-order filter on linear system response.