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

Keywords: Seismic performance.  Isolation/Restraint systems.  Mechanical equipment.  Shaking table tests.  Coil springs.  Rubber snubbers.  Horizontal displacement.  Vertical displacement.  Response amplification.  Restraint components.  HVAC.  Centrifugal liquid chiller.

Abstract: This report describes experimental research aimed at evaluating the seismic performance of an isolation/restraint system, typical of the systems designed by the ASHRAE members, supporting heavy mechanical equipment. The ASHRAE-type isolation/restraint system consisted of coil springs and rubber snubbers constraining the displacement in the horizontal and vertical direction. The heavy HVAC-type mechanical equipment used as test specimen was a centrifugal liquid chiller. System-identification and seismic shake table tests were conducted on the test specimen mounted on four of the isolation/restraint systems. The test plan included variation of design parameters of the restraint component of the systems namely the gap size, rubber pad thickness and hardness, and the static capacity. The tri-axial acceleration response at the center of mass and corners of the chiller, displacement response of the chiller, and the dynamic forces induced into the isolation/restraint systems were recorded in each test. The experimental results were analyzed to determine the response amplification due to the engagement of the restraint components, to investigate the sensitivity of seismic performance of the isolation/restraint systems to the variations of their restraint component design parameters, and to compare the static design capacity of the restraint components to their dynamic (actual) capacity.