Study on the fracture behavior of hybrid fiber-reinforced high-strength concrete single-edge notched beams: Theoretical analysis and experimental verification

To investigate hybrid fiber effects on the fracture behavior of high-strength concrete (HSC), three-point bending tests were performed on single-edge notched beams (SENB). These tests evaluated the influence of hybrid fiber types and volume fractions on load-crack mouth opening displacement (CMOD) curves, fracture energy, characteristic length, and fracture toughness. A stress-crack width ($\sigma -w$) curve for hybrid fiber-reinforced HSC (HFRHSC) was also established using the double-K fracture model and inverse analysis. Results demonstrated that fiber incorporation significantly enhanced concrete fracture behavior and had a significant strengthening and toughening effect. For single-doped wave steel fiber (WSF) reinforcement, increased WSF volume fraction improved fracture behavior. Compared to single-doped WSF, optimal hybridization of fiber types and ratios further enhanced fracture behavior while maintaining high post-cracking load-bearing capacity. A notable discrepancy emerged between the bilinear $\sigma -w$ curve derived from the double-K model and inverse analysis results. The double-K model inadequately captured nonlinear fiber-bridging stress distribution, whereas inverse analysis accurately reconstructed crack evolution control equations, revealing the gradient distribution of fiber-bridging forces in the fracture process zone. This inverse analysis approach more precisely characterized HFRHSC’s post-cracking pseudo-hardening behavior and multi-stage load-transfer mechanisms.