Effect of displacement-dependent stiffness on performance of seismically-isolated bridges: an investigation using design optimization

Varsamis, Christos
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Symans, Michael, D.
Letchford, Chris, W.
Alnaggar, Mohammed
Warn, Gordon, P.
Symans, Michael, D.
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Civil engineering
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This electronic version is a licensed copy owned by Rensselaer Polytechnic Institute (RPI), Troy, NY. Copyright of original work retained by author.
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Seismic isolation systems have been employed in bridge structures to increase their lateral flexibility, and consequently their natural period, and thereby improve their seismic performance by reflecting seismic energy away from the structure. In recent years, stiffness devices that could passively-generate both positive and negative tangential stiffness that continuously varies with displacement were introduced within bridge isolation systems in an attempt to further improve seismic performance by reducing their lateral stiffness to near-zero values and thus increasing the natural period to near infinity. Previous investigations on such displacement-dependent stiffness devices have focused on their effect on the seismic response of existing bridges, where design parameters that characterize the behavior of stiffness devices often had nominal values from preliminary designs or, at best, values obtained from sensitivity studies. A potentially different level of performance could be realized in new bridge designs if isolation system components (bearings, supplemental dampers and displacement-dependent stiffness devices) were designed simultaneously through optimization. This study concentrates on an evaluation of the effectiveness of displacement-dependent stiffness devices in improving the response of a highway bridge structure with a well-designed (optimized) seismic isolation system. A holistic design framework is developed that optimizes configurations of the isolation system with respect to multiple objectives. The identified optimized performance of the bridge structure using various combinations of the isolation system components is evaluated against criteria that quantify their relative performance and which determine how the performance is affected by the inclusion of the displacement-dependent stiffness devices within the isolation system.
School of Engineering
Dept. of Civil and Environmental Engineering
Rensselaer Polytechnic Institute, Troy, NY
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