Mechanics of Low Shape Factor Elastomeric Seismic Isolation Bearings

摘要

The test isolation bearings were of a design to provide horizontal and vertical isolation. This dual requirement led to a design with a shape factor smaller than usual for bearings designed to provide horizontal isolation only. The bearings were all of one basic design, but varied in the elastomer from which they were manufactured and the details of the end-plate connections. Connections used were of the doweled-type and the bolted type. Bearings were manufactured from both a filled, high-damping, natural rubber compound and an ordinary unfilled, natural rubber compound. One particular objective of the test program was to evaluate the merit of the standard cyclic shear test (with constant axial load) as a representative test for more generalized loading conditions. The behavior of the LSF bearings subjected to cyclic vertical loading was studied. Buckling tests and shear and tension failure tests were also conducted. Comparisons were made of the different bearings, of the bolted and doweled connections, and the filled and unfilled elastomers. The influences of axial load and shear strain on the shear stiffness, vertical stiffness, and damping behavior were investigated, with particular emphasis on evaluating the consequences of a low shape factor. An analytical model for the prediction of bearing behavior was reviewed and extended for application to LSF bearings.