Frequency-Compatible Intensity Measures for Seismic Qualification of Nuclear Power Plant Cabinets Based on a High-Fidelity Numerical Model

This study develops a high-fidelity nonlinear shell-based finite element model of a full-scale Class 1E electrical cabinet for nuclear power plants (NPPs) and evaluates frequency-compatible intensity measures (IMs) for acceleration-sensitive functional failure. The model explicitly represents realistic cabinet geometry, internal mounting structures, bolted base connections, and mechanically representative contact interfaces and is validated against shaking table test results through modal and transient response comparisons. Five candidate IMs, i.e., peak ground acceleration (PGA), Sā(4–16), Sā(10–20), Sā(20–30), and Sā(10–30), are assessed in terms of sufficiency and fragility-based efficiency. PGA exhibits the strongest residual dependence on frequency content and secondary ground motion parameters, indicating its limited suitability for stiff cabinet response. The conventional spectrum-based IM, Sā(4–16), improves the prediction relative to PGA but does not fully represent the cabinet-relevant high-frequency range. In contrast, the newly examined frequency-compatible IMs reduce both residual dependence and fragility dispersion. Among them, Sā(10–30) provides the weakest dependence on predominant frequency, reducing the fitted slope from −0.067 for PGA to −0.019, and produces the lowest fragility dispersion for the validated cabinet, decreasing the logarithmic standard deviation from approximately 0.50 to 0.21. Sā(10–30) also remains the most efficient of the five candidate IMs for two modified cabinet models with different dynamic characteristics. These findings identify Sā(10–30) as a practical and robust IM for fragility assessment of stiff, acceleration-sensitive NPP electrical cabinets.