Seismic fragility analysis of NPP cabinets considering high-frequency excitations using an efficient numerical model

Electrical cabinets are critical for the reliable operation of nuclear power plants (NPPs), yet their seismic fragility under high-frequency ground motions remains insufficiently addressed. This study develops a computationally efficient three-dimensional finite element model for an anchored NPP electrical cabinet that explicitly accounts for excitation frequency relative to cabinet dynamics. The cabinet is idealized with beam and shell elements, while omitted panel masses are represented by an equivalent lumped mass whose location is optimized using Response Surface Methodology. The optimized model reproduces shaking-table-identified fundamental frequencies with a maximum error of 1.99% and accurately matches measured top-of-cabinet acceleration histories. Seismic fragility is evaluated through incremental dynamic analysis using two controlled suites of motions: a low-frequency set dominated below the fundamental mode and a high-frequency set concentrated near the first-mode frequency. High-frequency excitation produces a consistent leftward shift of fragility curves, indicating earlier exceedance of a functional acceleration limit, and reduces the HCLPF capacity by about 22% compared with low-frequency excitation. These findings demonstrate that excitation frequency relative to cabinet dynamics critically influences seismic vulnerability, and neglecting high-frequency effects can yield unconservative capacity estimates. The proposed framework provides an efficient basis for frequency-sensitive seismic fragility evaluation of NPP cabinets.