Shape Optimization of UHPC Shear Keys for Precast, Prestressed, Adjacent Box-Girder Bridges

Abstract

Adjacent box-girder bridges are a popular choice for short- to intermediate-span bridges in several states because they are easy, quick to build, and cost-effective. Although longitudinal shear keys filled with grout between the girders and transverse posttensioning (TPT) ties ensure a monolithic behavior for the bridge, the durability of longitudinal shear keys still concerns researchers and engineers. Ultrahigh-performance concrete (UHPC) has been adopted as a new grout material for connections between bridge components. However, there is not yet any guidance or specification on the design of UHPC shear key configuration for adjacent box-girder bridge connections. The aim of this study was to use experimental results and finite-element (FE) modeling of direct shear, flexural, and direct tension tests to optimize a UHPC shear key configuration. These models were calibrated and validated with laboratory experimental results previously published by the authors. The models, along with different shear key configurations, were used to investigate the load transfer through previously proposed connections. After comparing the simulated shear keys in terms of the maximum load capacity, the optimized shear key shape (Type OPT) was designed to obtain a desired balance between economy and strength effects. The results demonstrated the contribution of the shear key configuration to the joint strength, and suggest that Type OPT shear key significantly increased load transfer, resulting in an enhanced serviceability. Therefore, use of Type OPT shear keys in a bridge may reduce the number of transverse shear reinforcement bars required, which in turn would improve the constructability of the bridge and reduce material and construction costs.