An Experimental and Statistical Study of Normal Strength Concrete (NSC) to Ultra High Performance Concrete (UHPC) Interface Shear Behavior

: With number of existing bridges in U.S, classified as structurally deficient and many bridges nearing end of their design service life, there is a need for a durable and accelerated construction solution. Recently, several state DOTs developed innovative solutions using Ultra-High Performance Concrete (UHPC) as infill material between prefabricated bridge components or as an overlay over existing structural elements. The normal strength concrete (NSC) to UHPC interface behavior is critical for overall performance of such structures. Experimental investigation consisting of 10 push-off specimens was performed to investigate shear transfer behavior at NSC-UHPC interface. In general, the results showed that increasing roughness depth and reinforcement area has positive effect in interface shear capacity. The experimental results were compared with current AASHTO LRFD, ACI and PCI design guidelines. Though the design guidelines were conservative; they were not accurate in predicting the interface shear strength. Additionally, a database including results from past push-off tests on NSC-UHPC interface was developed and a reliability analysis was carried out with respect to AASHTO LRFD design guidelines. The reliability index was found to be lower than the target reliability index in standard design practices.