Reinforcement Anchorage in Grouted Connections for Precast Bridge Bent Cap Systems

As urban bridge construction in Texas becomes more prevalent, the need to employ progressive construction practices that minimize the impact of a project on the commuting public grows. One method identified by the Texas Department of Transportation (TxDOT) to facilitate rapid bridge erection is through the use of precast bent caps rather than traditional cast-in-place substructures.

Through work with TxDOT engineers and an Industry Review Committee (IRC), details were developed to connect precast bent caps with cast-in-place columns and precast piles. These connection details emphasized economy, ease of erection, and durability. Four primary connection systems were identified: grout pocket connections, grouted vertical duct connections, bolted connections, and grouted sleeve connections. These systems utilize both straight and upset-headed connection reinforcement.

To address concerns of adequate anchorage capacity in grout pocket and grouted vertical duct connections, pullout tests of upset-headed and straight bars simulating typical grouted connections were conducted. Variables studied included embedment depth, grout type and strength, bar size, loading type, and pocket confinement.

Twenty-four grout pocket pullout tests were conducted. Depending on the embedment depth, the anchorage strength was controlled either by the concrete breakout capacity or the steel strength. The wedging action of the grout pocket produced a favorable confining effect in the grout, but also produced significant cracks at the pocket corners which separated the tensile stress fields, resulting in reduced capacity for upset-headed bars. Anchorage design procedures were developed for straight and upset-headed bars through simple modifications to existing methods.

Eight grouted vertical duct tests were conducted. Bar development lengths were found to be much shorter than what is required in plain concrete due to the confining effects of the duct. Duct anchorages failed when the concrete and duct could no longer restrain the splitting forces in the grout. Because existing methods could not be applied to grouted duct anchorages, a design procedure was developed that limits bond stress to levels that may be easily restrained by the duct and concrete.