The response reliability is dependent on the variability of the excitation, ground motion. The effect of the variability in earthquake variables on the response is sufficiently important to require careful consideration in design. The formulation of the response in the frequency domain is very efficient in the computation and evaluation of the stochastic response of structures. These results provide an important basis for the understanding of the sensitivity of earthquake variables and reveal how the effect of these variables on the response of structure to choose a few sets of parameters in a design earthquake. The results reveal that the coefficients of variation of the response in irregular structures are larger than regular structures.
