Laboratory Evaluation of Ultrahigh-Performance Concrete Shear Key for Prestressed Adjacent Precast Concrete Box Girder Bridges

Abstract

Precast adjacent box girder bridges have become a preferred solution in several states due to their simple structure, economy, and ease of construction. However, longitudinal cracks often appear along the shear keys between adjacent box girders. With its superior strength and durability, ultrahigh-performance concrete (UHPC) has been used as an alternative grout material to reduce shear key cracking and enhance load transfer. The objective of the present research was to evaluate the performance of UHPC in shear keys using direct shear, direct tension, and flexural tests. Also, this study determined the effectiveness and functionality of shear reinforcement bars by applying direct shear load on specimens with shear reinforcement. In the direct shear test, a steel frame was placed around the specimens to allow the shear key to experience pure shear force. The direct shear test established the cracking threshold and ultimate shear strength of each shear key with and without shear reinforcement bars. The test results show that the average maximum shear capacity for the UHPC shear key without shear reinforcement bars exceeded that determined from past research for any grout material and any shear key configuration. Furthermore, the average maximum shear capacity increased by a factor of 1.81 with shear reinforcement bars. The enhanced shear strength of the UHPC shear key may have an impact on the analysis and design of UHPC connections in bridges.