Effect of torsional ground motion on the seismic response of highway bridges

Abstract

Seismological aspects of rotational ground motions can be found in published research, however, studies on implications for the seismic response of structural systems are rare. This preliminary study investigates the effects of torsional component of the ground motions (TGM) on the overall seismic response of bridges and interactions among their components. For this purpose, a series of computational models of bridges were developed. The models assume linear-elastic substructure with continuous rigid deck, sliding supports and rigid abutments, and vary key parameters including skew angle (β), normalized stiffness eccentricity between the center of mass and rigidity (ex/r), gap size between deck and abutments, dominant frequency ratios. However, inelastic impact between the superstructure and abutments is modeled explicitly to ensure that consequential in-plane deck rotations are accounted for. It was shown that larger deck rotations due to TGM lead to larger impact forces, which further amplifies deck rotations. The adverse effects may be more pronounced in symmetric bridges and in bridges with significant skew. All response quantities; deformations and substructure forces, are amplified significantly due to TGMs which suggests that current design codes may underestimate seismic deformation and force demand.