Shear resistance of UHPC girders: Experimental database evaluation of the FHWA-HRT-23-077

The research presents a detailed evaluation of the shear model adopted by the FHWA-HRT-23-077 for Ultra-High Performance Concrete bridge girders. The evaluation is based on a statistical analysis of a surveyed experimental database that includes 198 UHPC girders tested and failed in shear. As the FHWA method requires the localization strength ftloc of the UHPC as an input, an equation to predict the ftloc was developed based on the concrete compressive strength and the fiber's characteristic ratio. The results showed that increasing the localization strain epsilon t,loc results in less conservative estimates. At epsilon t,loc of 0.004, the statistical analysis showed an average value of Vexp/Vpred is equal to 1.18, and the CoV is 24.2 %, with 144 out of 198 tests showing ratios Vexp/Vpred >= 1.0. In addition, the paper presents a reliability evaluation using Monte-Carlo simulation to assess the strength reduction factor for UHPC girders based on AASHTO LRFD Bridge Design Specifications with a targeting a reliability index equal to 3.5. It was shown that to achieve a target reliability of 3.5, a strength reduction factor of 0.85 would be more appropriate than 0.9.