Seismic Performance of Skewed Bridges with Sliding Rubber Bearings

Design concept of plastic hinge has been utilized in the design specification for decades. However, investigations from 1999 Chi-Chi earthquake showed construction practice of unbolted elastomeric rubber bearings, providing a sliding function as a semi-fixed bearing, is one of the reasons in controlling the failure mechanism of the bridge. Though the bridge column was protected by only dissipating friction force from bearings, large displacement on the superstructure can also be observed; if this resistance is small the bridge is skew. Therefore, a parametric study of one bridge with 20 degrees skew angle was performed. Variables include bearing type, friction coefficient, and input intensity of ground motions. It is found for the case with ideal hinge and roller support, compared to those in straight bridge; the moment and torsion in the column of skewed bridge are rapidly increasing due to skew-induced bilateral effect. Moreover, for the case with sliding rubber bearing and low friction coefficient, not only the displacement of girder should be considered in the longitudinal direction, but the one along the transversal direction should considered so that the design of displacement-restrained device can be optimized to prevent the superstructure from unseating and mitigate the unexpected impact force.