Modeling of restoring force characteristics of rubber bearings under multi-axial loading

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Base-isolation is the recently developed technology to reduce seismic load to civil structures and currently widely used after the experience of 1995 Kobe Earthquake. High Damping Rubber (HDR), which has the damping property in addition to the flexibility, is a new material and has mainly been applied in base-isolated bearings in Japan. In this research, the phenomenological model of HDR is constructed, and this model is verified through the experiment of the base-isolated bearing under multi-axial loading conditions. High damping rubber material has not modeled yet and, thus, its main application, high damping rubber bearings (HDR), need experimental test prior to its installation to actual civil structures. In this research, the constitutive law of high damping rubber material is studied and this constitutive law is verified experimentally. At first, based on the results of the material tests, we proposed the constitutive law of high damping rubber which combines clasto-plastic body and hyper-elastic body. Here, special attention is paid systematically organize various material testing of rubber materials because current standards for mechanical testing of rubber materials are not sufficient for use to civil structures where extremely severe large deformation condition is expected in case of extreme seismic events. Then, (1) strain-field to surface of HDR was measured spatially through the image processing and (2) by applying the proposed constitutive law to the measured strain filed, we could get restoring force or the HDR. (3) Comparing the calculated restoring force with the experiment, we could verify the proposed constitutive law. Using this model, performance evaluation of HDR can be made numerically with high accuracy, which reduces the uncertainty involved in seismic design considerably.