Probabilistic Site-Dependent Response Spectra

A method is developed for obtaining probabilistic soil-dependent pseudo-absolute acceleration response spectra. The resulting spectra are consistent with the acceptable design risk level from future earthquakes at a specific site. Structural exposure to future earthquakes is obtained in terms of probabilities of peak ground acceleration values that can occur at firm grounds, intermediate soils, and soft soil sites. These are combined with gamma-distributed response spectral shapes (or dynamic amplification factors) and for firm grounds, intermediate soils, and soft soils. Strong earthquake ground-motion data from past seismic events are used as basis for the development of the response spectral shapes. The convolution of the probability distribution of peak ground acceleration with the corresponding probability distributions on response spectral shapes yield the probability distribution of pseudo-absolute acceleration response spectra as functions of structural period and damping. From them, response spectra for 10%, 20%, and 50% risk levels are developed at sites with firm, intermediate, and soft ground conditions.