Shear Behavior and Interface Damage Mechanism of Basalt FRP Bars: Experiment and Statistical Damage Constitutive Modeling

The shear behavior of basalt fiber-reinforced polymer (BFRP) bars is crucial for their applications in geotechnical reinforcement and composite structures. In this study, double-side direct shear tests were conducted to investigate the progressive failure mechanism of BFRP bars. The results reveal a three-stage process: initial matrix-dominated vertical shear, followed by fiber-bridging dominated oblique tension-shear, and finally formation of a “brush-like” fracture surface with significant residual strength. The average peak shear strength of the ten specimens was 204.04 MPa with a coefficient of variation of 7.25%, while the initial shear modulus averaged 3.37 GPa with a coefficient of variation of 11.82%. Based on statistical damage theory, a shear constitutive model incorporating fiber bridging and residual strength is established. Parameter analysis indicates that the shape parameter m governs the post-peak softening rate, while the residual strength τres essentially determines the height of the residual plateau. The model achieves a goodness-of-fit (R2) exceeding 0.98 for most specimens, accurately describing the mechanical behavior from linear elasticity, damage-induced hardening, peak softening, to the residual stage. This study provides theoretical and experimental support for the engineering application of BFRP bars under complex stress states.