Calibration of Strength Reduction Factor for Reinforced Ultra-High-Performance Concrete Bridge Girders in Flexure

Ultra-high-performance concrete (UHPC) has been widely used in bridges and other structures throughout the world. However, very limited studies have been carried out to address the strength reduction factor for reinforced UHPC girders in flexure. This paper, therefore, attempts to develop reliability-based design provisions for the flexural strength of reinforced UHPC bridge girders with steel bars. First, an extensive design scope, which included various common design scenarios, was considered to conduct stochastic simulations. Subsequently, the resistance parameters were evaluated based on the available experimental data and Monte Carlo simulation (MCS). Then, the first-order second-moment method (FOSM) was applied to calibrate strength reduction factors to meet a uniform target reliability level, beta(T) = 3.5, specified in AASHTO LRFD Bridge Design Specifications. To verify the results obtained, a comparison between strength reduction factors calibrated from MCS and those from the FOSM was conducted. Stochastic simulations indicated that the design of reinforced UHPC bridge girders was commonly controlled by the tension limit state. As a result, this study recommended a constant strength reduction factor of 0.90 for reinforced UHPC bridge girders in flexure.