Study on the deformation of hybrid BFRP-steel reinforced concrete beams considering crack development

Abstract

Hybrid fiber-reinforced polymer (FRP)-steel reinforced concrete (RC) beams exhibit various flexural failure modes depending on different equal-stiffness reinforcement ratios, the post-yield stiffness ratio, and the bond-slip behavior. This study first develops a model for the tensile behavior of hybrid Basalt FRP (BFRP) -steel reinforced concrete chords, considering the modified Bertero-Popov-Eligehausen (mBPE) bond-slip model. The rationality of the tensile stiffening model was validated through comparisons with existing experimental tests on the axial tension of chords. Subsequently, a beam deformation correction calculation method considering ‘rigid-rotation’ was proposed. The corrected theoretical calculation of the beam’s peak load shows an error of 5.0% compared to the experimental value, while modified ultimate deformation exhibits an error of 4.7%. As the bond weakens, the theory proposed in this paper is more suitable for predicting the deformation capacity of hybrid reinforced beams. ACI 440.1R-15 underestimate deformations by approximately 77.8%, limiting the normative evaluation of deformation calculations for hybrid reinforced concrete beams considering bond slip. Finally, the influence of bond-slip parameters (τ_m, s_m and $\alpha$ ) and reinforcement configurations (equal stiffness reinforcement ratio, steel/BFRP reinforcement ratio, and post-yield stiffness ratio) on beam deformation and crack width was investigated. The results indicate that the peak bond strength is a key parameter affecting crack width and deformation of the beam. The exponential rise segment parameter α and the slip s_m corresponding to peak bond strength mainly influence the load level corresponding to cracking.