Effectiveness of Unseating Prevention Cable Restrainers for Isolated Curved Bridges under Near-Fault Earthquakes

Abstract eng:
This paper examines the efficiency of cable restrainers to prevent unseating of curved bridges located at sites near active faults. Forward rupture-directivity effects associated to near-fault seismic ground motions have been responsible of catastrophic deck unseating and severe pounding damage at bridge expansion joints. Since destructive near-fault pulses are generally oriented perpendicular to the fault strike, a remarkable variability in damage level was observed depending on the orientation of bridge structures respect to the fault direction. Therefore, keeping in mind the above considerations, the as-recorded orthogonal horizontal components of two strong near-fault earthquakes have been rotated for each 15-degrees interval on the horizontal plane in order to simulate different orientations of the bridge respect to the fault. Following, a large number of three-dimensional nonlinear dynamic analyses have been performed to compare the effectiveness of various size cable restrainers to protect the bridge against seismic damage. Restrainers are bi-directionally modeled explicitly considering the possibility of yielding and failure of the cables under the high demands generated by near-fault motions. The investigation results provide sufficient evidences to conclude that, in accordance with considerable directivity of near-fault ground motions, bridge orientation with respect to the fault direction influence seismic damages and determine the protection efficiency exhibited by cable restrainers. Therefore, when it is not viable to revise road alignments to avoid a fault zone, acquisition of vital knowledge regarding to design of unseating restrainers becomes necessary for developing effective protection strategies applied to bridges located in the proximity of active faults.

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