Seismic Fragility Analysis of a Nuclear Primary Containment Structure

Abstract eng:
A seismic fragility curve is an important tool in the probabilistic performance assessment of a structure when subjected to earthquake loads. The seismic fragility of a structure can be defined as the probability of exceeding certain limit state(s) of performance, given a specific level of seismic hazard. The current study deals with the seismic fragility estimation of a nuclear primary containment structure of a typical PHWR in India. The focus of this work is to estimate the seismic fragility of this structure considering a failure defined in terms of tensile cracking of the damaged concrete which leads to leakage. The structure is modelled using 3D layered shell elements with detailed damaged plasticity model for concrete. Seismic responses in terms of equivalent plastic tensile strain are studied for a set of earthquake records at different intensity levels through a series of nonlinear response-history analyses. Using regression, the ground acceleration capacity of the structure are obtained for each record. The seismic fragility curve of the structure is derived using a lognormal model using the sample capacity data. This seismic fragility curve is compared to the conventional fragility curve based on an interstorey drift ratio based failure. The results show that tensile cracking based fragilities are more severe to the drift based fragilities.

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