Strength reduction factor based on probabilistic analysis for hybrid reinforced concrete beams

The American Concrete Institute (ACI) developed ACI-318 and ACI-440 codes, providing design guidelines for concrete beams subject to flexure and reinforced with steel or Fiber-Reinforced Polymer (FRP) bars, respectively. Although using a hybrid reinforcing system that combines steel bars and FRP bars has gained significant attention, ACI codes have no design guidelines for this concept. The main objective of this study is to determine the appropriate strength reduction factor for hybrid steel/FRP RC beams (i.e., concrete beams reinforced with a hybrid system of FRP and steel bars) by conducting a comprehensive probabilistic analysis over a wide range of hybrid steel/FRP RC beams dataset. This factor is a crucial component of the design standards outlined by the American Concrete Institute (ACI). The reliability index of the beams dataset under consideration is determined within the framework of reliability analysis using the First Order Reliability Method (FORM). Furthermore, a sectional analysis is employed as a mechanical model initially verified using an experimental dataset of 95 specimens. This model is utilized to forecast the flexural capacity of beams. The study's findings indicate a substantial correlation between the strength reduction factor and the reinforcement and live-to-dead load ratios. For the objective of conservative design, a strength reduction factor of 0.65 is suggested.