Impact of Surface Roughness on the Bending Behavior of GFRP Pultruded Profiles—Concrete Composite Structure

To investigate the coupled effects of interface treatment and casting thickness on the flexural behavior and load‐transfer mechanism of T‐rib GFRP‐mortar composite beams, three‐point bending tests integrating digital image correlation (DIC) and strain measurements were conducted. The results show that interface treatment mainly affects interfacial stress transfer and failure‐mode evolution, whereas casting thickness primarily determines global stiffness and load‐carrying capacity. Increasing the casting thickness increased the peak load by 67% and reduced the corresponding deflection by 86%, while improving interface roughness increased the peak load by 127% and reduced deflection by 56%. Further sectional analysis revealed that increasing casting thickness reduces interfacial shear demand through an increased moment of inertia, whereas enhanced interface roughness improves interfacial shear resistance through stronger mechanical interlocking. Based on this mechanism, a dimensionless coupling criterion Ω was proposed to characterize the balance between interfacial shear resistance and sectional geometric effects, providing a quantitative interpretation of the transition from interface‐dominated to mortar‐dominated failure.