Flexural behavior of steel fiber-reinforced geopolymer lightweight aggregate concrete beams

Eight hooked-end steel fiber-reinforced geopolymer lightweight aggregate concrete (SFGLAC) beams were tested to investigate failure modes, cracking behavior, and moment-deflection response. The fractal theory was employed to quantitatively analyze the variation in crack patterns and propagation behavior, thereby establishing the relationship between crack fractal dimension and flexural properties. To further capture the nonlinear stress–strain behavior of concrete, a novel dynamic gradient-optimized layered (DGOL) method was developed, enabling detailed cross-sectional stress analysis. Experimental results demonstrated that SFGLAC beams exhibited favorable crack distribution, characterized by narrow and densely spaced cracks that formed interconnected networks with multiple branching patterns. Quantitative fractal analysis demonstrated that the surface crack patterns exhibited distinct fractal characteristics, with the crack fractal dimension showing strong statistical correlations with both residual flexural capacity and flexural stiffness degradation. Additionally, Comparative assessments with existing design standards further indicated that both Chinese and American codes provide conservative predictions of the ultimate moment capacity of hooked-end fiber-reinforced GLAC beams. The proposed DGOL-based ultimate moment model demonstrated superior predictive accuracy with minimal dispersion, as evidenced by a coefficient of variation below 2 %.