Seismic Performance of Precast Girder-to-Cap Beam Connections Designed for ABC

The behavior of critical connections between prefabricated elements in bridges utilizing accelerated bridge construction (ABC) methods continues to be of utmost interest. Some of these connections will experience excessively high demand in regions that are susceptible to high seismic load. This paper presents a large-scale experimental study that investigated seismic performance of the connection between precast concrete I-shaped girders and a concrete inverted-tee cap beam using two different details. The ability of the girder-to-cap connection to successfully resist positive moment and the corresponding shear under combined gravity and seismic effects was of particular interest. The effect of vertical seismic acceleration on the connection behavior was also considered. This study utilized a half-scale test unit and replicated a portion of a typical inverted-tee cap beam, along with two 35-ft long girders with unique connection details and split bridge decks so each detail could be tested individually. Both connection details were improvements to an existing detail for precast dapped-end girders and inverted-tee cap beams that has been used by the California Department of Transportation (Caltrans). Both connections relied on deck reinforcement as the primary tension-transfer mechanism for negative moment. For positive moment tension transfer, one connection utilized unstressed grouted strands to provide continuity between the girder bottom flange and the cap beam. The other connection implemented a group of large-diameter transverse dowel bars located in the lower portion of the girder that were placed inside looped strands cast in the cap beam and subsequently encased in a cast-in-place diaphragm. Both connections exhibited excellent seismic performance, remaining elastic up to load levels well in excess of what would be required to develop a column plastic hinge, including due consideration to vertical acceleration effects. Both connections were subjected to large girder displacements in order to fully quantify their performance. Experimental results from both connection details and comparisons with the as-built detail will be presented in this paper