Report No.: CCEER-13-4
Title: Longitudinal Seismic Performance of Precast Bridge Girders Integrally Connected to a Cast-in-Place Bentcap
Authors: Almer, K. and Sanders, D.
Date: April 2013
Department of Civil Engineering/258
University of Nevada, Reno
Reno, NV 89557
Precast bridge girders are popular throughout the United States primarily because they allow for better construction tolerances, quicker construction methods at the job site, and elimination of falsework over traffic lanes. In high seismic regions, continuity between the superstructure and substructure are necessary in order to resist the large lateral force demands resulting from an earthquake. However, lack of design guidance and experimental data have raised questions about the ability of the girder-to-bentcap connections to provide the necessary continuity under seismic loading. This study examines the performance of precast u-girders integrally connected to a cast-in-place bentcap subjected to longitudinal seismic loading. The objective was to develop design guidelines for the girder-to-bentcap connection and the joint that are consistent with current construction methods and typical reinforcement details used by the Nevada Department of Transportation. To accomplish this objective, four 40% scale bridge models were experimentally tested at the University of Nevada, Reno Large Scale Structures Laboratory. The experimental program focused on the influence of post-tensioning on the connection behavior. In addition to experimental testing, analytical modeling was used to compare against measured behavior from the experimental program.
Experimental testing confirmed that the girder-to-bentcap connection details used in this study were sufficient in providing the necessary continuity with or without girder post-tensioning; however post-tensioning improved joint performance. Additionally, the lateral load carrying capacity of each specimen was limited by a large horizontal crack that developed at the top of the joint. Analytical models were developed that closely predicted the measured response up to development of this joint crack. Strut-and-tie models were developed based on experimental measurements in order to account for the beneficial effects of post-tensioning observed in the experimental tests. The strut-and-tie models also indicated design provisions for out-of-plane joint reinforcement and additional vertical reinforcement at the top of the joint need to be included in current joint design methods. Results from the experimental and analytical studies were used to develop design recommendations for providing adequate girder-to-bentcap connection details and adequate joint reinforcement for precast bridge girders in high seismic regions.