Design Provisions for Flexural Strength of Hybrid Reinforced Concrete Beams with Fiber-Reinforced Polymer and Steel Bars

This paper develops reliability-based design provisions for flexural strength of reinforced concrete (RC) beams with hybrid arrangements of fiber-reinforced polymer (FRP) and steel reinforcements. Firstly, three flexural failure modes of the hybrid RC beams were distinguished through balanced reinforcement ratios, and closed-form solutions for the flexural strength were proposed. Based on the Monte Carlo simulation technique, probabilistic analyses of flexural failure modes were conducted to determine the minimum and maximum flexural reinforcement ratios for the hybrid beams. The first-order second-moment method was then applied to calibrate strength reduction factors to meet uniform target reliability level, beta(T) = 3.5. Sensitivity analyses were performed to identify the most important parameters that influence the reliability indexes, indicating that the reliability of the hybrid FRP-steel RC beam decreased with the increase of the reinforcing index chi. As a result, this study recommended flexural strength reduction factors of (0.9 to 0.15 chi) for the hybrid reinforced beam to achieve the target reliability index of 3.5.