Effect of Boundary Conditions on Seismic Response of Electrical Equipment subjected to High-Frequency Ground Motions

Abstract

The updated ground motion hazard in Central and Eastern United States contains high frequency motions. Such motions do not cause structural damage. However, safety-related electrical equipment are sensitive to high-frequency accelerations. Seismic qualification of electrical equipment requires an in-cabinet response spectrum (ICRS) which depends on the dynamic response of electrical cabinets and buildings. A linear analysis to generate ICRS can give excessively high spectral accelerations. Cabinet models with geometric nonlinearities such as a gap in the connection with building floor show that high-frequency accelerations may not propagate to the electrical equipment. Unlike linear analysis, results from nonlinear analysis of a building-cabinet model with a gap show a periodic pattern of secondary peaks and valleys at higher frequencies. In this research, the unique observation of secondary peaks is explained through fundamental principles by considering the sliding response of a cabinet representation with gap subjected to harmonic excitation. It is observed that a periodic pattern of peaks and valleys exist due to a significantly large contribution from transient response, due to localized impacts at the gap in cabinet base, and its interaction with the steady-state response.