Development of a Precast Bent Cap System

Improved speed of construction and economy can be achieved through the use of precast bridge substructures. As a step in the advancement of precast bridge substructures, a precast bent cap system is developed for nonseismic regions, including a design methodology, construction guidelines, and example details for connecting a precast bent cap to cast-in-place columns or precast trestle piles. Three categories of connection details are developed: grout pockets, grouted vertical ducts, and bolted connections.

Three phases of construction and testing of the three connection types are reported. The first phase examines behavior and failure modes for grout pocket and grouted vertical duct connections through thirty-two large-scale pullout tests. Results of four full-scale bent cap-to-column connection assemblages are presented for the second phase. In addition, results of construction and testing for two full-scale bents at the construction yard of a highway contractor are provided.

Based on test results, equations for anchorage of straight or headed connectors in grout pocket or grouted vertical duct connections are established. Also, a design methodology for a precast bent cap system is developed that includes the following eight steps: 1) selection of a trial bent configuration, 2) analysis of bent cap and columns, 3) determination of connection actions, 4) selection of connection type and embedment, 5) selection of trial connector configuration, 6) analysis of connector configuration, 7) determination of connector type and embedment, and 8) determination of confining reinforcement and auxiliary reinforcement. Construction guidelines are established based on construction experiences during the three phases of research.

Lastly, design recommendations are presented in code format, and construction guidelines are presented in the form of a precast connection specification. Example connection details that conform to the design requirements and the precast connection specification are shown for each connection type.