Fragility Analysis of Flexible Base Buildings

A simplified seismic risk analysis of flexible base building frames was presented which can be used for preliminary estimate of their probabilities of failure. The risk analysis procedure used the format of Probabilistic Risk Analysis (PRA) and considered band-limited white noise at the bedrock as the seismic input. The uncertainties considered in the study included those arising from the variation of ground motion, material properties and modeling and analysis procedure of the structure. In order to evolve the simplified procedure, these uncertainties were included in the analysis by a number of multiplying factors, which were considered as log normally distributed random variables, and the response of the building frame was obtained by the response spectrum method of analysis. The response analysis duly considered the base flexibility of the structure and the effect of soil condition. The proposed method of analysis was applied to a twelve-storeyed steel building frame for obtaining its probability of failure with the help of fragility curves. A parametric study was conducted to investigate the effect of a number of important parameters on the probability of failure. The parameters include mechanism of failure, soil condition, coefficient of variations of the uncertainty factors and the ductility factor used. The results of the study indicated that the base flexibility of structure, soil properties and failure mechanism have significant influence on the probability of failure and should be duly considered in the seismic risk analysis of building frames.