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<p>The long-term exposure of deep underground structures to triaxial stress states poses a significant threat to the stability of concrete structures. This study systematically reveals the confining pressure-dependent transition mechanism of steel fiber reinforcement (from fiber-dominated enhancement to matrix-dominated failure) through integrated triaxial compression, direct shear, and splitting tests combined with PFC simulations. The microfracture morphology of the specimens was observed using scanning electron microscopy (SEM), and the crack evolution behavior was analyzed via PFC numerical simulation. The results indicate that in compression tests, the peak strength, residual strength, and elastic modulus of steel fiber-reinforced UHPC (SFRC) increase with confining pressure. Particularly at low confining pressures, steel fibers significantly enhance the compressive strength. However, at high confining pressures, the reinforcing effect of steel fibers diminishes, and specimens predominantly fail in shear. Direct shear tests demonstrate that the peak and residual shear strengths of SFRC increase linearly with normal stress, significantly outperforming plain UHPC. Brazilian splitting tests reveal that steel fibers increase the tensile strength of concrete by 55.1%. SEM observations indicate ductile fracture characteristics in SFRC, with steel fibers effectively reducing microcrack development. PFC simulations confirm that steel fibers withstand tensile and shear stresses, inhibit crack propagation, and enhance concrete toughness.</p>

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Multi-Axial Mechanical Response and Crack Propagation in Steel Fiber-Reinforced Ultra-High-Performance Concrete: Synergistic Experimental and Discrete Element Approach

  • 期刊论文

  • 发表日期：

    2026年6月23日

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  • Zhe Tan,
  • Yanlin Zhao,
  • Rui Luo,
  • Shuailong Lian,
  • Minzhen Zhang,
  • Lianyang Zhang,
  • Zhao Liu

摘要

The long-term exposure of deep underground structures to triaxial stress states poses a significant threat to the stability of concrete structures. This study systematically reveals the confining pressure-dependent transition mechanism of steel fiber reinforcement (from fiber-dominated enhancement to matrix-dominated failure) through integrated triaxial compression, direct shear, and splitting tests combined with PFC simulations. The microfracture morphology of the specimens was observed using scanning electron microscopy (SEM), and the crack evolution behavior was analyzed via PFC numerical simulation. The results indicate that in compression tests, the peak strength, residual strength, and elastic modulus of steel fiber-reinforced UHPC (SFRC) increase with confining pressure. Particularly at low confining pressures, steel fibers significantly enhance the compressive strength. However, at high confining pressures, the reinforcing effect of steel fibers diminishes, and specimens predominantly fail in shear. Direct shear tests demonstrate that the peak and residual shear strengths of SFRC increase linearly with normal stress, significantly outperforming plain UHPC. Brazilian splitting tests reveal that steel fibers increase the tensile strength of concrete by 55.1%. SEM observations indicate ductile fracture characteristics in SFRC, with steel fibers effectively reducing microcrack development. PFC simulations confirm that steel fibers withstand tensile and shear stresses, inhibit crack propagation, and enhance concrete toughness.