Effect of chloride-induced deterioration of exterior RC walls on floor response and equipment fragility in nuclear auxiliary buildings

This study evaluates the effects of chloride-induced deterioration of exterior reinforced concrete (RC) walls of a nuclear power plant. A multi-scale analytical framework was proposed, linking wall-level stiffness degradation, building-level elastic time-history analysis, and simplified equipment fragility evaluation. Wall-level finite element analyses were conducted to quantify stiffness reduction associated with corrosion-related damage mechanisms, such as bond degradation and delamination. Building-level elastic time-history analyses were then performed using a three-dimensional finite element model subjected to spectrally compatible ground motions. Floor response spectra (FRS) were generated using both envelope-based spectra derived from corner points and location-specific spectra obtained directly from acceleration tigkrtnme histories. A simplified single-degree-of-freedom equipment model was used to assess changes in seismic fragility, including median capacity and high confidence of low probability of failure (HCLPF). The results show that structural deterioration shifts the fundamental natural frequency of the building toward lower frequencies and redistributes seismic response across frequency ranges. While envelope-based FRS generally indicate reduced fragility over most frequencies, location-specific FRS reveal increased fragility near the shifted fundamental frequency and reduced fragility at lower frequencies. These findings demonstrate that deterioration effects on equipment fragility are highly frequency- and location-dependent and may be underestimated using conventional envelope-based approaches.