Experimental validation of optimized ultra-high-performance concrete shear key shape for precast pre-stressed adjacent box girder bridges

Recently, ultra-high-performance concrete (UHPC) material has been adopted as a grout material to fill connections between adjacent girders. Research to date has showed that using UHPC in the shear key connections of bridges improves the bridge superstructure performance. However, shear key configuration used in the most bridges are custom-designed and do not follow any specific design code. In a previous study by the authors, an optimized shape of the UHPC shear key (OPT-UHPC) was introduced in attempt to enhance load transfer and increase ultimate strength capacity. The optimization was conducted using three 3D finite element models simulating direct shear, flexural, and direct tension tests. The objective of the present study is to experimentally measure the performance and ultimate load capacity of the OPT-UHPC shear key by placing it between two high strength concrete (HSC) components and subjecting to direct shear, direct tension, and flexural tests. These results are then compared to the modeling predictions from the previous study. Two 45°-rectangular rosette strain gauges were placed on the surface of UHPC shear key and HSC components under direct shear load to obtain the strain in the shear key and the adjacent HSC components. The test results showed the OPT-UHPC design has an ultimate load capacity 32% larger than the FHWA-UHPC shear key, even though the cross-sectional areas are approximately equal, 19677 mm2 for FHWA-UHPC and 20161 mm2 for OPT-UHPC, a difference of about 2.5%. Also, the experimental results indicate the OPT-UHPC shear key enhanced the strain distribution between the concrete components and as result improved the load transfer. Thus, the load transfer mechanism is substantially influenced by the shear key configuration.