High-strain tests on lead-rubber bearings for earthquake loadings

R G Tyler,W H Robinson

doi:10.5459/bnzsee.17.2.90-105

Abstract

Dynamic tests on two lead-rubber bearings, 280 x 230 x 113 mm, are described in which a dynamic actuator was used to apply shear displacements of ±10 to ±140 mm at frequencies of 0.1 to 3 Hz, giving shear strains in the rubber of up to ±200%. The weight of the structure on the bearing was applied by a vertical jacking system and ranged from 35 to 455 kN. Sequences of cycles were performed to simulate earthquake conditions and force-displacement hysteresis loops were obtained. It was concluded that at strains approaching 200% in the rubber, the force-displacement hysteresis loop could be represented by the linear elastic slope of the rubber component plus a rectangle appropriate to the plastic shear of the lead, with some rounding of the corners of the hysteresis loop. There was a decrease in the area of the hysteresis loop of 20% after six cycles at 1 Hz with a maximum shear strain of 125% in the rubber; but recovery followed within minutes. In one bearing an attempt was made to locally confine the lead by screwing external plates to the first internal plate within the bearing at the top and the bottom, but no difference in performance between the two bearings was noted. The scope of the tests indicated that, with peak strains in excess of 100% in the rubber, the bearings would continue to perform satisfactorily for a sequence of very large earthquakes.

Highlights

The use of laminated rubber bearings, with damping provided by lead plugs, is an accepted technology throughout the world for the base isolation of buildings and bridge decks following the pioneering work XT
New Zealand culminating in the construction of the William Clayton Building in Wellington(1-8K Previous tests on leadrubber bearings at PEL(1~3)w e r e carried out using a converted bulldozer for producing shear displacements at ^1 Hz, but this technique was inconvenient from the point of view of varying the stroke and frequency of loading
The tests described in this paper were carried out using the Dartec dynamic test equipment in the new test hall

Summary

Introduction

The use of laminated rubber bearings, with damping provided by lead plugs, is an accepted technology throughout the world for the base isolation of buildings and bridge decks following the pioneering work XT-. The large number of individual hysteresis loops obtained from the two-cycle tests were, for each vertical load, combined together (Figure 4 ) .

Results

Conclusion