Experimental verification of the static method for seismic design of vibration-isolated hvac equipment

Motivated by the repeated damage to vibration-isolated equipment in almost all strong earthquakes that occurred in the past four decades, an experimental study was conducted to verify the adequacy of the current static method used for the seismic design of this type of nonstructural components. The study included earthquake-simulator tests of two HVAC equipment items supported by restrained vibration-isolators. The test results confirmed that seismic protection of vibration-isolated equipment by snubbers comes at the expense of amplified acceleration responses and dynamic loads, which are often much larger than those predicted by the static method. The differences between the predictions of the static method and actual dynamic responses of the equipment were attributed to four aspects not considered in the static method: Rotational responses of the equipment, nonlinear relationship between the gap size and seismic demands, effect of thickness and hardness of the snubbers, and effect of flexibility of the equipment.