FRAGILITY ANALYSIS OF FLEXIBLE BASE BUILDINGS

A simplified seismic risk analysis of flexible base building frames is presented which can be used for preliminary estimate of their probabilities of failure. The risk analysis procedure uses the format of probabilistic risk analysis (PRA) and considers band limited white noise at the bedrockas the seismic input. The uncertainties considered in the study include 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 are included in the analysis by a number of multiplying factors, which are considered as log normally distributed random variables and the response of the building frame is obtained by the response spectrum method of analysis. The response analysis duly considers the base flexibility of the structure and the effect of soil condition. The proposed method of analysis is applied to a twelve storey steel building frame for obtaining its probability of failure with the help of fragility curves. A parametric study is 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. Results of the study indicate 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.

Keywords:

PRA procedure , seismic risk of structures , seismic hazard , flexible base building , fragility curve , reliability analysis