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Coupled Systems Mechanics Volume 4, Number 4, December 2015 , pages 297-316 DOI: https://doi.org/10.12989/csm.2015.4.4.297 |
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Seismic fragility analysis of bridge response due to spatially varying ground motions |
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C. Kun, B. Li and N. Chouw
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| Abstract | ||
| The use of fragility curves in the design of bridges is becoming common these days. In this study, experimental data have been used to develop fragility curves for the potential of girder unseating of a three-segment bridge and a bridge-abutment system including the influence of spatially varying ground motions, pounding, and abutment movement. The ground excitations were simulated based on the design spectra for different soil conditions. The Newmarket Viaduct replacement bridge in Auckland was used as the prototype bridge. These fragility curves were also applied to the 2010 Darfield and 2011 Christchurch earthquakes. The study showed that for bridges with similar characteristics as the chosen prototype and with similar fundamental frequencies, pounding could increase the probability of girder unseating by up to 35% and 30% based on the AASHTO and NZTA seating length requirements, respectively. The assumption of uniform ground excitations in many design practices, such as the NZTA requirements, could potentially be disastrous as girders might have a very good chance of unseating (as much as 53% higher chances when considering spatial variation of ground motions) even when they are designed not to. In the case of superstructures with dissimilar frequencies, the assumption of fixed abutments could significantly overestimate the girder unseating potential when pounding was ignored and underestimate the chances when pounding was considered. Bridges subjected to spatially varying ground excitations simulated based on the New Zealand design spectra for soft soil conditions with weak correlation shows the highest chances of girders falling off, of up to 65% greater than for shallow soil excitations. | ||
| Key Words | ||
| girder unseating; pounding; spatially varying ground motions; fragility curve; shake table testing | ||
| Address | ||
| C. Kun, B. Li and N. Chouw: The Department of Civil and Environmental Engineering, Faculty of Engineering, the University of Auckland, New Zealand | ||
