Seismic Fragility Analysis of a Primary Containment Structure Using IDA

Abstract

The seismic fragility of a structure is the probability of exceeding certain limit state of performance given a specific level of hazard. This fragility is typically estimated for multiple hazard levels considering monotonically increasing intensity measures, such as peak ground acceleration (PGA). The seismic safety of the primary/inner containment structure, which is the most important civil engineering structure in a nuclear power plant (NPP) housing the reactor and other major safety related components, is of utmost concern for both old and new NPP. This chapter presents a novel approach of obtaining the seismic fragility curves for a primary containment structure using incremental dynamic analysis (IDA). The limit state of performance selected for these fragility estimations is based on the collapse of the structure. In order to reduce the computation involved, a simple ‘stick model’ of the containment structure is used for the nonlinear response-history analyses in the multi-earthquake IDA. The seismic fragility curves obtained using the proposed approaches are compared with those obtained using the conventional approach considering an elastic response spectrum and a linear elastic seismic analysis of the structure. The IDA-based fragilities are found to be more realistic than those obtained using conventional methods.