Design of Earthquake Resistant Server Computer Structures

This paper presents the design features of an electrical equipment frame structure that can withstand a severe earthquake test profile. Original designs of these structures were optimized to survive shock and shipping vibrations only, since the majority of products experience shock and vibrations during transportation. Shock and vibration found in the shipping environment are oriented in the vertical direction only. Increased concerns for equipment survivability and safety during seismic events have driven new requirements for consideration when designing equipment’s frame structure and incorporation of tests having earthquake profiles into testing regimes. This adds horizontal components of vibration into design considerations and demands design compromises that will optimize performance for both horizontal and vertical vibrations. Frame and assembly mounting design for both orientations will be discussed and test criteria specifically for vertical vibration will be described in order to compare to tests geared toward combinations of vertical and horizontal vibrations. Structures created under these new requirements are rigid in all three axes, especially in the horizontal direction where low frequency seismic vibrations can induce large displacement of the frame members and subassemblies installed in the frame. Both the subassembly components and the frame assembly must be modified to reach the optimum design for multi-directional vibration. The development of the frame structure and related hardware involves extensive uniaxial and triaxial earthquake simulation testing in both raised floor and non-raised floor environments. The dynamic responses of the system under different earthquake test profiles are recorded and analyzed in both the time and frequency domains. The computer frame and anchorage system must have adequate strength and stiffness for earthquake induced forces to prevent human injury and potential system damage. However, this same frame and anchorage system must also meet the potentially conflicting requirement of ensuring continued system operation by limiting transmitted accelerations to acceptable levels at critical system components such as hard drives.