Seismic Response Assessment and Recommendations for the Design of Skewed Post-Tensioned Concrete Box-Girder Highway Bridges

Report No. CCEER-08-03Seismic vulnerability of highway bridges remains an important problem and has received increased attention as a consequence of unprecedented damage observed during several major earthquakes. A significant number of research studies have examined the performance of skewed bridges under service and seismic loads. It is noted that results of these studies are particularly sensitive to modeling assumptions in view of the interacting parameters which may include: 1. Skew angle 2. Superstructure flexibility 3. Boundary conditions 4. In-span hinges (if any 5. Width-to-span ratios 6. Mass and stiffness eccentricity In this study, three dimensional improved beam stick models of two-span highway bridges with skew angles varying from 0 to 60 degree are developed to investigate seismic response characteristics of skewed reinforced concrete box-girder bridges. Relative accuracy of simplified beam-stick models are verified against counterpart finite element models. Both SAP2000 and DRAIN3DX programs were evaluated and the latter was used for the nonlinear time history analyses of the bridges. A total of six ground motions were selected such that the average acceleration response spectra (ARS) for the different intensities matched the corresponding CALTRANS target design ARS. Effect of various parameters on the overall seismic response was examined such as: effect of skew angle, support (foundation) conditions, end conditions with and without abutment-soil interaction and with and without transverse shear-keys, soil conditions, various ground motion intensities, and various aspect ratios