Modeling the Shear Connection in Adjacent Box-Beam Bridges with Ultrahigh-Performance Concrete Joints. II: Load Transfer Mechanism

Ultrahigh-performance concrete (UHPC), with its enhanced strength and durability, has been proposed as the joint material in adjacent box-beam bridges to address the issue of longitudinal cracking. Recently, the Federal Highway Administration (FHWA) performed laboratory testing of two adjacent box beams connected by a UHPC shear key containing transverse shear reinforcement bars (SRBs), and the results suggest that an improvement in the overall performance of adjacent box-beam bridges may be achieved by using the new shear key design. However, there is no information about the load transfer mechanism within the new connection. The aim of this research is to perform finite-element (FE) analysis of the two adjacent box-beam models to investigate the load transfer mechanism in, and ultimate load capacity of, the new FHWA shear key design. The three-dimensional FE model used in the study was validated based on the FHWA laboratory test results. The model is used to identify the roles of the UHPC material, the transverse SRBs, and the shear key surface roughness on the load transfer mechanism between adjacent box beams at different load levels, and to investigate the suitability of widely accepted criteria for shear key condition/performance for the new shear key design. The results of the analysis show that a shear key with a smooth surface and minimum transverse SRBs is sufficient for load transfer between adjacent box beams for the load level used in the FHWA testing and that a shear key with a sandblasted surface and minimumtransverse SRBs is capable of transferring load up to failure of the box-beam system. The results of the analysis provide valuable useful insight into the shear key behavior, which can be used to optimize the design of future UHPC shear keys. (C) 2017 American Society of Civil Engineers.