Experimental studies of the ultimate behavior of seismically-isolated structures

Experimental studies of the ultimate behavior of seismically-isolated structures - Printable Version

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Experimental studies of the ultimate behavior of seismically-isolated structures - arshiakh - 08-13-2014

A large-scale earthquake simulator study of a seismically isolated, three-story reinforced concrete building was performed in conjunction with a series of component tests of reduced-scale high-damping rubber isolators. The goal of the study was to experimentally verify the behavior of structures founded on elastomeric isolators under severe ground motions and to provide data for future correlative computer analyses and building code development. The reinforced concrete frame structure was constructed at 0.4 scale to represent one of two identical buildings on the campus of Tohoku University in Sendai, Japan. The Sendai buildings were built as a research environment for the performance of seismically isolated structures during actual earthquakes. The research program described in this report was intended to augment the field results by subjecting a large-scale isolated model to beyond-design-level earthquake ground motions on an earthquake simulator. A parallel investigation of the large-displacement behavior of individual high-damping rubber isolators was undertaken to quantify their fundamental mechanical properties as well as their ultimate capacities and failure mechanisms. The test results indicate that properly designed and manufactured bearings exhibit both a gradual stiffening and an increase in energy dissipation under shear loading due to strain crystallization in the rubber compound. The particular bearings studied displayed stable response with substantial energy dissipation over a wide range of shear deformations although they were subject to softening and subsequent rapid stiffness recovery after cycling to large strains. The seismically isolated reinforced concrete building model was subjected to simulated earthquakes of a range of intensities. The properties of the reduced-scale isolators were selected to match those of the first high-damping rubber bearings installed in the full-size building in the 1980s. The stiffness of the system is, therefore, greater than designs following current practice in the United States because it reflects the conservatism associated with implementing a new technology. This larger stiffness reduced the effectiveness of the isolation system under moderate shaking, which is undesirable from a design standpoint; but under the most severe ground motions, the bearings stiffened and acted as a fail-safe mechanism. The larger shear forces transmitted to the structure led to distributed yielding in the frame, but it was demonstrated that the isolators were not the weak link.

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