Experimental Study of Sliding Hydromagnetic Isolators for Seismic Protection

Abstract

Sliding isolation, as one of the modalities of base isolation, has demonstrated its value in seismic hazard mitigation. Conventional sliding isolation systems, however, may exhibit unacceptable large sliding displacements under severe earthquakes and may suffer a risk of unpredictable impact effect due to the insufficient isolation gap. A novel base isolation system that uses sliding hydromagnetic bearings has been proposed recently to overcome these shortcomings. These bearings comprise steel tubes with a pressurized internal fluid and attached permanent magnets, and slide over aluminum base plates also with attached permanent magnets. They minimize the friction between bearings and base plates, generate a damping force that reduces the bearings displacements to practical levels, and introduce a restoring force and a displacement constraint. In the present study, a sliding hydromagnetic isolator is designed, fabricated, and tested experimentally to assess its performance as a seismic protection system. Additionally, numerical simulations are carried out for quantifying the repulsive, damping, and friction forces involved. It is found from these studies that the applied loads on the hydromagnetic bearing does not produce fluid leakages, O-ring damage, or scratch marks on the base plates; the bearing’s friction coefficient does not exhibit a conventional friction-vertical load correlation and is therefore lower and more stable than in existing sliding isolators due to the effect of oil-solid interface; and the pressurized fluid significantly reduces the frictional force between bearing and base plate and facilitate thus the bearing’s sliding; the repulsive force increases dramatically with the bearing displacement and may effectively prevent bearings from sliding off their base plates.