Seismic Testing and Analysis of Main Frame Computer Structure

Designing a mainframe computer structure that can withstand seismic events requires significant testing and analysis. The computer frame and anchorage system must have adequate strength and stiffness to counteract earthquake-induced forces, thereby preventing human injury and potential system damage. However, this same frame and anchorage system must also meet the requirement of ensuring continued system operation by limiting overall displacement of the structure to accepted levels. Therefore, the test and analysis scope need to include the mainframe structure and its anchorage attachment to the building's concrete floor via a raised floor structure. This paper discusses the numerical modeling and its verification to quantify the robustness of a high end computer server structure subjected to a severe seismic event. The frame of the computer is the structure where components are installed (e.g., the central processing unit, the input-output drawer, the power supply component, etc.). The dynamic response of this structure is highly related to the weight of the components, the assembly's inherent natural frequency, and the location of the structure's center of gravity. The natural frequency of various mainframe configurations were analyzed and measured by either changing the weights (i.e., adding or eliminating components) or by changing the structural stiffness (e.g., adding reinforcement brackets). The main objective of the modeling was to ensure structural integrity following a seismic test of a functional server system. Finite element analysis (FEA) was employed as part of the overall frame's structural robustness design verification, whereby the simulated modal analysis results were compared to both the experimental modal data of the frame structure as well as measured swept sine data. This design study builds toward the objective of constructing a verified model of the server frame and components, which lead to a guideline for implementing optimized reinforcement. As part of the verification, the mainframe structures were subjected to horizontal table vibration tests simulating the loads and environmental conditions endured during seismic events. During experimental verification, the dynamic responses were recorded and analyzed in both the time and frequency domains.