Inelastic seismic response of box-girder bridges due to torsional ground motions

Abstract

The torsional components of strong ground motions (TGMs) may result in unanticipated displacement and force demand particularly in highway bridges due to their complex dynamic characteristics. For this purpose, the present study investigates the effects of TGMs on the inelastic seismic response of continuous concrete box-girder highway bridges with seat type abutments. Three-dimensional finite element (3D FE) models of bridges with varying skew angles, number of bent columns, and column height-to-diameter ratios were developed using OpenSees, and a series of nonlinear response history analyses were conducted. Comparison of seismic response of bridges subjected to only translational and both translational and TGMs revealed that TGMs may result in uneven and asymmetric failure of the shear keys. Therefore, deck rotations are significantly amplified due to induced instantaneous eccentricity when deck comes in contact with shear key(s). The amplified impact forces due to TGMs further amplify the deck rotations, which in return result in higher inelastic displacement and force demand. Last but not the least, the induced torsion due to TGM combined with axial-flexure-shear interactions may result in complex failure modes, higher shear stresses, and reduction in lateral deformation and flexural capacity of the bridge columns.