Design and Construction of Precast Bent Caps with Pocket Connections for High Seismic Regions

Abstract

In conventional cast-in-place reinforced concrete bridge construction, cap beams and their connection to columns are designed to be capacity protected under strong earthquakes. This is because cap beams and their connections maintain structural integrity and are difficult to repair. The same design philosophy is mandatory for precast cap beams that are used in accelerated bridge construction (ABC), particularly in moderate and high seismic zones. One of the key components of ABC is prefabricated reinforced concrete members. The NCHRP report 698 provided a synthesis of different promising ABC connections. Pocket connections were identified as practical means of joining prefabricated columns and pier caps. The AASHTO Scan 11-02 revealed more recent studies about seismic performance of pocket connections. Nevertheless, research was needed to develop practical and reliable cap beam pocket connections ensuring capacity protected behavior. A comprehensive literature search was carried out in the present study to compile and interpret data on seismic performance of cap beams with pocket connections. It was shown through extensive analyses that effects of pocket on the seismic performance of cap beams are negligible for a well-designed cap even under the worst-case scenario in which the concrete within the pocket was excluded from the cap beam section. The reason why precast cap beams with pocket connections yielded in some of the test models was identified as inadequate design rather than the pocket effect. Five practical details for precast pocket bent caps were proposed based on the lessons learned from the aforementioned tasks. Subsequently, constructability of these details was assessed. It was found that the alternative in which fully precast columns are inserted into cap pockets will result in 75% reduction in onsite work. The time saving for other details was 42%. Finally, a design guideline as well as examples were developed to facilitate field deployment of precast bent caps incorporating pocket connections.