Modified Ritz vector approach for dynamic properties of electrical cabinets and control panels

Abstract

Often, the simple methods used for evaluating incabinet spectra needed in the seismic qualification of safety related electrical instruments ignore the dynamic characteristics of the electrical control panels and cabinets. Gupta et al. (Nucl. Eng. Des. 190 (1999a) 255) developed a Ritz vector approach for evaluating the dynamic properties of the cabinets and the incabinet spectra. This approach is based on the conclusions drawn from detailed finite element analyses of several cabinets. In the present paper, we illustrate the limitations of the originally proposed Ritz vector approach that were encountered during subsequent applications to actual cabinets. Modifications to the originally proposed formulations are presented and their accuracy evaluated by comparison of results for actual cabinets with the corresponding results obtained from finite element analyses. The modified Ritz vector approach can account for actual rotational constraints imparted by supporting structural members such as stiffeners. It can also be applied to bench board type cabinets in which instruments are mounted on plates or frames that are inclined to the global axes as well as to frames in which parallel frame members can vibrate in different vibration shapes due to differences in boundary conditions and non-uniform mass distribution.