New Connections for Precast Girders To Cap Beams in Concrete Bridges

Abstract eng:
The use of precast girders has helped to establish Accelerated Bridge Construction (ABC) methods in the United States. However, this practice has not been extended to seismic regions due to lack of reliable connections between precast girders and cap beam. This paper characterizes the basic challenges associated with current design practice and introduces several options to establish reliable connections between precast girders and cap beams. Two mechanisms are used to establish positive moment continuity in these connections, namely shear friction and direct tension transfer. The first mechanism utilizes dowel bars running through girders while the second mechanism uses unstressed prestressed strands extended from girders into the cap beam. All connection details have been found to provide significant improvements to an existing detail for precast girder and cap beam connections that has been used by the California Department of Transportation (Caltrans). Each new connections relies on deck reinforcement for tension continuity when subjected to negative moments. For positive moment tension transfer, all but one connection utilize both mechanisms to provide tension continuity for the connection when subjected to positive moments. In one connection, large diameter dowel bars are used and all tension force corresponding to the positive moments is resisted by a shear friction mechanism. Using a large-scale experimental study, seismic performance of six different connection details between precast concrete Ishaped or bulb-tee girders and concrete cap beams was examined. The ability of the girder-to-cap connections to successfully resist positive and negative moments and the corresponding shear forces under combined gravity and seismic effects were the primary focus of this study. Additionally, the effect of vertical seismic acceleration on the connection behavior was also investigated. All connections exhibited excellent seismic performance, remaining elastic up to load levels well in excess of what would be required to develop a plastic hinge at the top of the column, including due consideration to vertical acceleration effects. All connections were subjected to large girder displacements beyond that required by seismic loading to fully quantify their performance. Experimental results from all connections and their comparisons with the asbuilt connection performance will be presented in this paper.

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