Ultra-High Performance Concrete for Connections of Precast, Prestressed Girders Made Continuous for Live Load

Abstract

Continuity joints have often been employed in bridges with precast, prestressed girders to increase the overall ability of bridges to distribute live loads by making two simple spans continuous. However, if the continuity connection cracks due to time-dependent effects in the girders, continuity can be lost, resulting in simply supported conditions for the girders and subjecting the joint reinforcement to potential corrosion damage. A potential solution to prevent cracking in the continuity joint is using Ultra-High Performance Concrete (UHPC). UHPC has been studied to determine how effective the material is in a number of bridge applications, but not for continuity joints. Six specimens consisting of two precast girders made continuous with a UHPC joint were constructed and tested. Three of the six specimens focused on continuity joint detailing for new bridge construction and followed the AASHTO LRFD 2014 Specifications for design. The three remaining specimens focused on retrofit continuity joint detailing for existing bridges. Both designs consisted of the same reinforcement ratio determined for newly constructed continuity joints. Each specimen was tested using a static point load at mid-span of each girder in order to produce the maximum negative moment in the continuity joint. In addition, a positive moment test was conducted on the joint for the third specimen of each joint type. The results from the tests to failure showed an increase in girder capacity compared to the design values, similar crack development for both joint types, and limited flexural cracking in the joint compared to the girders. Though the joints did not fail, this indicates that the failure would likely be pushed out of the joint and into the girders for both types of connections. Overall, the retrofit specimens exhibited better performance than the newly constructed specimens, with higher ultimate capacity, less deflection under the load points, and the reinforcing bars yielding within the joint. The retrofit connection is a potential option for strengthening existing simple span bridges in service by making the girders continuous for live load.