Seismic Response of Columns in Curved Bridges

There are many components of a curved bridge system that influence behavior during seismic loading. The substructure, superstructure, and bearing types have a dramatic impact on system behavior. To study this impact, a 2/5ths scale, curved bridge was designed and tested on the multiple shake table array in the University of Nevada Reno, Large-Scale Structures Laboratory. In addition, extensive analytical modeling has been undertaken. This paper focuses on the design and performance of the single-column, dropped-bent cap, substructure for the bridge. A parametric study was conducted to determine the optimal column size based on conventional details typically used in practice. After completing this study, the column was designed according to the AASHTO LRFD Bridge Design Specifications and AASHTO Seismic Guide Specifications for LRFD Seismic Bridge Design. Specific elements of the substructure response were found to be determined by the global response of the system. These include the torsional stiffness of the system, abutment-column interaction, and column plastic hinging. In particular it was found that column behavior was a combination of single and double curvature despite being pinned to the superstructure. This was due to the constraints at the top and bottom of the column in the radial and tangential directions. This paper discusses the performance of the columns during the experiment and presents initial comparisons with analytical results. It was concluded that the curvature of the bridge directly impacts the torsional loading and rotations at columns and bearings when shear keys are still intact. Once the shear keys fail, torsional loading and rotations change as system torsional modes are excited. Along with these discoveries, reverse bending of the columns is also expected and should be considered when designing single column bents in curved bridges. Experimental column investigation in curved bridge systems has provided information that could not be determined from component testing.