Experimental Seismic Performance Evaluation of Isolation/Restraint Systems for Mechanical Equipment; Part 2: Light Equipment Study

Keywords: Isolation/restraint (I/R) systems.  Seismic performance.  Light mechanical equipment.  Displacement.  Dynamic forces.  Amplification.  Gap size.  Rubber snubbers.  Acceleration response.

Abstract: The experimental study described in this report is aimed at evaluating the seismic-performance of Isolation/Restraint (I/R) systems for light mechanical equipment. Earthquake-simulator experiments were conducted on an air-handling unit in two different conditions: supported by six I/R systems and rigidly-mounted. The test plan included seismic and system-identification tests, and incorporated different input-motion amplitudes and different I/R system properties. The test results showed that limiting the displacement of the equipment by the restraint components of the I/R systems resulted in amplification of the equipment acceleration-responses. Dynamic forces induced into the I/R systems were considerably larger than the forces predicted by the static approach. Based on the test results, reducing the gap size is the first recommendation to improve the seismic-performance of I/R systems in areas of high seismicity. Increasing the thickness of rubber snubbers is a solution to reduce the dynamic forces induced into the I/R systems, however it might result in higher acceleration and displacement responses of the equipment. Reducing hardness of rubber snubbers is not recommended as it can degrade the overall seismic performance of the I/R systems. The test results showed that higher amplification of acceleration responses should be expected for light and flexible equipment than for rugged and heavy equipment.