Database evaluation and reliability calibration for flexural strength of hybrid FRP/steel-RC Beams

Concrete beams reinforced with hybrid fiber-reinforced polymer (FRP) and steel bars combine the advantages of both FRP and steel. The corrosion resistance and service-life are improved by placing the FRP bars, while steel bars will provide better serviceability through the higher elastic modulus and better ductility through yielding. However, there are no design provisions for hybrid FRP/steel-RC members, and the design models were evaluated over limited experimental data. This study presents a statistical and reliability evaluation for designing hybrid FRP/steel-RC beams under flexure over a worldwide experimental database. The database comprises 136 hybrid FRP/steel-RC beams tested under flexure. Theoretical balanced failure states have shown the ability to correctly predict the failure mode of the specimens. Two specimens were classified inaccurately in terms of failure mode, which is attributed to the variability in the materials' properties. Statistical evaluation for moment predictions for specimens with failure mode 2 (steel yield-concrete crushing) showed a mean, standard deviation, and coefficient of variation of 1.143, 0.169, and 14.7 %, respectively. Additionally, a reliability analysis is conducted to calibrate and recommend the strength reduction factor for the ACI 440 provisions. Targeting a reliability index of 3.5, a strength reduction factor of phi = 0.80 is selected as the appropriate.