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Seismic Performance of Bridge Restrainers At In-Span Hinges
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Since the 1971 San Fernando Earthquake, cable restrainers have been used at the hinges as retrofit schemes to prevent the unseating of bridge spans. Different approaches have been developed to design cable restrainers, but currently there is no a satisfactory method. An extensive study is being developed at the University of Nevada, Reno. In the initial phase, a set of tests was developed to establish the experimental approach of the dynamic behavior of the cable restrainers. The main objective of the current project is to investigate analytical and experimentally the response of intermediate hinges subjected to longitudinal ground motions and to develop a set of charts as a design tool. The variables considered in this study are the period ratio between adjacent frames, the restrainer slack and the type of ground motion. The analytical work is a non-linear time history analysis using artificial motions, developed based on current design spectra (ATC-32) for firm, medium and soft soil. The analytical study has been concluded. Results show cable restrainers yielding without failure and relative displacements between adjacent frames lesser than the minimum seat width for cases where the period ratios are higher than 0,7. An unscaled model, representing a concrete box girder, was built and it has been tested on a shake table at the Large-Scale Structural Laboratory of the University of Nevada, Reno. The experimental results will be used to compare and validate the analytical results. As a conclusion of this study, a set of charts that involved the nonlinearities of this problem will be developed to be used as a guide for retrofit of multiple frames with inadequate seat width.
Report No. CCEER-04-4