Grouted Connection Tests in Development of Precast Bent Cap System

Tests were conducted as part of the first two phases of a research project that developed a design methodology, construction guidelines, and design details for connecting precast concrete bent caps to cast-in-place columns or precast concrete trestle piles in nonseismic regions. Three types of precast connections were addressed: grout pockets, grouted ducts, and bolted connections. The first phase of testing included 32 pullout tests of epoxycoated straight and headed bars embedded in a grout pocket or grouted duct. The yield strength of the bars was developed in grouted connections at an embedment depth of 13 bar diameters or less. Pullout capacity of single- and multiple-headed bars in grout pockets was predicted closely by the concrete capacity design method equations modified by a cracking factor of 0.75 to account for grout-pocket cracking. A development length equation based on a uniform bond stress model was derived for anchorage of straight bars in grouted ducts. The second phase of testing included a full-scale bent cap-to-column connection test for each connection type. Specimens in these proof tests exhibited minor levels of cracking and connector strain in the connection region at factored levels. Failure tests demonstrated adequate connector anchorage, large connector ductility, and negligible influence of shims and the grout bedding layer on response. Results from Phase 1 and Phase 2 tests were used to develop anchorage design provisions that are incorporated in the complete design methodology.