Seismic fragility analysis for non-seismically qualified steel structure

Abstract

The cooling water (C/W) pumphouse of CANDU nuclear power plants is non-safety related and is only designed to meet the seismic requirements of the National Building Code of Canada (NBCC) for normal industrial plants and public buildings. Based on a feasibility study for CANDU seismic Probabilistic Safety Assessment (PSA), it was decided to include non-seismically qualified systems in the PSA models. Thus, it was necessary to evaluate the seismic fragility of the C/W pumphouse which houses the raw service water system. The design basis seismic ground motion at CANDU site in Korea was evaluated by AECL in 1977, based on a probabilistic approach, which resulted in Design Basis Earthquake with a peak horizontal ground acceleration of 0.2g. The peak ground acceleration considered for the design of the C/W pumphouse is 0.1g. The seismic fragility evaluation accounted for conservatism in the design, both in the seismic response and in the member capacity. The median-centered seismic capacity and the high confidence and low probability of failure (HCLPF) capacity of the pumphouse steel superstructure are 0.89g and 0.33g, respectively. The ratio of the HCLPF capacity to the design peak ground acceleration is 3.3.