| Abstract | This report presents the results of an experimental and analytical study of low shape factor (LSF) elastomeric seismic isolation bearings. The test bearings were of a design developed for a seismic isolation application to provide horizontal and vertical isolation. This dual requirement led to a bearing design with a shape factor smaller than usual for bearings designed to provide horizontal isolation only. The experimental phase of the project involved the dynamic testing of a range of LSF bearings, subjected to a variety of test conditions. The bearings were all of the 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, currently the preferred shear connection for seismic isolation bearings and the bolted type, which has yet to see common use in the United States. Bearings were manufactured from both a filled, high-damping, natural rubber compound and an ordinary unfilled, natural rubber compound. An extensive series of tests was undertaken to investigate the performance characteristics of the different types of bearings. 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. A large number of tests was performed to study the behavior of the LSF bearings when subjected to cyclic vertical loading. Buckling tests and shear and tension failure tests were also conducted. On the basis of the test results a number of comparisons were made on the different bearings. The influences of axial load and shear strain on the bearing characteristics of shear stiffness, vertical stiffness, and damping behavior were investigated, with particular emphasis on evaluating the consequences of a low shape factor. Comparisons of the bolted and the doweled connections, and the filled and unfilled elastomers were also made. Design... |
