Crack Width Predictions of Hybrid Reinforced Concrete Beams with FRP and Steel Rebars

Crack analysis is one of the most significant and relevant topics in the study of reinforcedconcrete structures. The evolution of the crack state and the magnitude of the crack widthis influenced by numerous physical and mechanical parameters that make analyticalmodelling of the problem particularly complex. The interaction between reinforcementand concrete and the related stress transfer mechanisms are the key aspects to be definedfor an effective solution of the structural problem. For concrete structures reinforced withsteel rebars, the existing models, while not entirely exhaustive, are well established andoffer reliable predictions. Similarly, for concrete beams reinforced with FRP rebars, crackwidth calculation models have been developed, demonstrating good reliability, althoughfurther experimental validation is still required. On the other hand, in concrete beamswith hybrid reinforcement comprising steel and FRP rebars, models for predictingmaximum crack widths have not yet been adequately established. This is due to thechallenges associated with accounting for the different mechanics of reinforcement-to-concrete stress transfer and the variability of the mechanical and geometric parametersinvolved. The present paper is devoted to the analysis of the cracking of concrete beamsreinforced with FRP and steel rebars. The influence of the main involved parameters suchas the ratio between the amount of FRP and steel reinforcements, the mechanicalproperties of the materials and the configuration of the reinforcement is evaluated by theanalysis of a database of experimental results. The American and Italian guidelinesproposed for purely FRP-reinforced beams were calibrated for hybrid-reinforced beamsand the effectiveness was evaluated through the comparison between their prediction andexperimental data.