The generation of uniform hazard Floor Response Spectra

Abstract

In the generation of Floor Response Spectra (FRS), there are significant uncertainties in the earthquake excitations and site conditions, which lead to uncertainty in the resultant FRS. A fully probabilistic method is developed to account for the uncertainties and to generate FRS with a desired return period (RP). The uncertainties in seismic inputs and geotechnical models from nuclear industry are considered in this research. A set of seismic inputs at the bedrock with different loading levels are used to represent the uncertainty in earthquake excitations. A large number of site profiles are developed by Monte Carlo simulation to account for the uncertainty in soil properties. Following site response analysis and soil-structure interaction (SSI) analysis, amplification factors are determined for each site under the excitations of different ground motions to address the effects of seismic wave propagation and SSI. The uncertainties are propagated from site response analysis to SSI analysis consistently. Based on these analyses and seismic hazard curves at the bedrock, uniform hazard FRS are obtained with a complete probabilistic description. In the numerical examples based on the uncertainty model in nuclear industry, the uniform hazard FRS generated by the proposed method can reduce the seismic demands significantly (up to 46% as compared to results obtained by the current practice when the RP is set to 10,000 years) to provide an economical solution for seismic design. Furthermore, it overcomes the underestimation of FRS in some frequency ranges by the current practice. Sensitivity study is performed to study the influence of the logarithmic standard deviation and the correlation coefficient between adjacent soil layers of shear-wave velocity.