Modeling of a Mainframe Server Frame Subjected to Seismic Loadings

This paper describes the finite element modeling of a mainframe server frame. The frame consists of a server rack or frame with its add-on stiffening brackets. The frame is anchored directly to the floor with bolts at each of the four corners. The Telcordia Zone 4 earthquake test profile represents a severe dynamic load input and will be used herein to analyze the mainframe server frame. The main objective of this modeling is to validate the frame design prior to actual seismic testing, which ultimately ensures the structural integrity of a functional mainframe system during a seismic event. The server frame finite element (FE) model is derived from a three dimensional CAD model of a standard sheet metal frame weldment assembly which is then simplified and meshed with finite elements. This FE model represents the server frame, welded connections, and stiffening brackets, which are specifically designed to withstand seismic test profiles. To represent the components that populate the server frame, point masses are tied to the frame at the same attachment points that exist in the real assembly. The validation of the FE model involves the use of a horizontal shaker test to assess the server frame’s stiffness. The goal of this paper is to show a good correlation between FE model and test results using two separate FE solver technologies: implicit and explicit. For an implicit solver, linear material properties were used to obtain modal behavior that approximates the actual server frame’s behavior. Once these outputs were achieved, further response refinement was attempted by porting the model to an explicit dynamic solver. An explicit solver allowed non-linear material properties and body to body contact behavior to be included in the FE model while applying the seismic test profile to the server frame using a time domain input. The explicit dynamic model outputs used to correlate to actual test results were the modal dynamics, the displacement of the top of the server frame, and the maximum reaction force at the anchored corners. Finally, a functional system was subjected to the Telcordia Zone 4 seismic test profile. The system was functional during and after the seismic test with no significant structural damage having occurred.