Experimental Study of Laminated Rubber Bearings for Earthquake Isolation of Buildings : 1st Report, Static Tests for Rubber Bearings of 490 kN Rated Load

Abstract

Static tests were carried out for rubber bearings of 490 kN rated load which comprised 30 natural rubber sheets of 5 mm thickness 440 mm diameter bonded to steel plates. The tests showed that the bearings had stiffinesses to provide a 50000 kg rated mass with a horizontal natural frequency of about 0.5 Hz and a vertical one of about 17 Hz and that they could accept a displacement of about 300 mm under even a vertical load of 4 times the rated load. The tests also revealed characteristics of the horizontal restoring forces under various constant vertical loads and the vertical restoring forces under various fixed horizontal displacements. The horizontal stiffness of the bearing decreased with increased vertical load ; under a fixed vertical load, it was roughly linear for displacement. The vertical stiffness considerable decreased with horizontal displacement. These characteristics of the horizontal and the vertical stiffnesses were analyzed using simple models and fairly good results were obtained.