Modeling the Dynamic Behavior of Electrical Cabinets and Control Panels: Experimental and Analytical Results

Ritz vector approach for evaluating the dynamic properties of electrical cabinets is based on the premise that a single significant cabinet mode is sufficient to calculate accurate incabinet spectra needed in the seismic qualification of electrical instruments mounted inside the cabinet. It uses mathematical functions to characterize the significant mode shapes that can be either a local mode shape of the structural member or a superposition of the global cabinet and the local mode shapes. The significant modes for typical cabinets have been identified from fixed-base finite element analyses. In this paper, modal data from in situ and shake table tests for two different cabinets is used to evaluate not only the validity of finite element analysis results but also the premise for developing Ritz vector approach. A key difference observed in the test data is related to the existence of a global rocking in cabinets that are anchored at the base. A rigid body rocking due to base plate uplift cannot be evaluated from fixed-base finite element models that were used in the development of the Ritz vector approach. Finite element analyses after modifications for incorporating cabinet rocking due to base plate uplifting give results that are close to the test data. Even though the test data and the new analyses show that the significant cabinet mode is different from what has been considered in the past, the basic premise for Ritz vector approach remains unchanged. Minor modifications needed in the Ritz vector approach for incorporating cabinet rocking superimposed with local mode shapes are also presented.