Shear Capacity-Curvature Ductility Relationship of High-Strength Concrete Cantilever Beam of Different Failure Modes

This research investigated the shear capacity and curvature ductility relation of high-strength reinforced concrete cantilever beams subjected to monotonic loading. Twelve cantilever beams with section dimensions of 200×300 mm were tested. The study determined the impact of factors, such as span-to-effective depth ratios "a/d", stirrup spacing, compressive strength, and longitudinal reinforcement, on the behavior of the beam at the plastic hinge with various failure modes, i.e., flexural, shear, and combined. The specimens were divided into 4 groups, each containing 3 beams and 3 values for each variable. Strain gauges (SG) and Linear Variable Differential transformers (LVDTs) were used to measure the strains and deflections. In the first test group, as the a/d ratio increased from 750 to 850 and then to 1150 mm, shear capacity rose by 23% and 28%, while curvature ductility improved by 88% and 112%, with failure modes including shear, combined, and flexural, showing a direct and semi-linear relationship between curvature ductility and shear capacity. Increasing stirrup spacing from 100 to 150 and then to 300 led to a 59.7% and 73.5% drop in shear capacity, respectively, and a 15.3% and 62.5% reduction in curvature ductility, respectively, indicating a direct nonlinear relationship, with a change in failure mode from flexural, combined, and shear. The third group, with compressive strength values of 50.3, 55, and 65 MPa, exhibited a decrease in shear capacity of 8.17% and 9.13%, accompanied by an increase in curvature ductility of 20.17% and 153%. However, the relationship between these parameters was unclear. Moreover, the specimens showed different failure modes. The fourth group investigated longitudinal steel with ratios of 0.234, 0.6578, and 0.5555. As the ratios increased, shear capacity decreased from 34.8% to 53.2%, and the curvature ductility declined from 55.5% to 82.13%. The results revealed a direct linear relationship as the failure modes transitioned among flexural, combined, and shear.