Post‐cracking shear behavior of high‐strength‐steel π‐shaped <scp>UHPC</scp> beams without stirrups

Abstract Ultra‐high performance concrete (UHPC) is a composite material of steel fibers and concrete, where the steel fibers significantly enhance tensile strength, crack resistance, and provide shear resistance similar to stirrups. To fully utilize these properties for lightweight, high‐strength bridge structures, a high‐strength‐steel π‐shaped UHPC beam without stirrups was designed. However, existing research mainly focuses on ultimate shear strength, with limited attention to post‐cracking behavior and few shear strength formulas for π‐shaped beams. Shear tests were conducted on five π‐shaped beams with varying shear span‐to‐depth ratios and fiber contents. A new shear failure mode has been identified, characterized by alternating growth in the principal stresses and crack widths on the two side webs, as well as distinct variations in failure modes, structural response, and crack morphology. The average nominal shear strength reached 25.9 MPa, about 70% higher than traditional rectangular, T‐, and I‐sections. The post‐cracking load‐bearing capacity index of the π‐shaped UHPC beams was consistently greater than 2.5, with a post‐cracking load‐bearing capacity maintained above 60% of the ultimate load‐bearing capacity. A new energy ductility evaluation index has been proposed, defined as the ratio of failure energy to cracking energy, ranging from 13.0 to 55.0, indicating a 20% improvement over conventional sections. A modified FHWA‐based shear strength formula for π‐shaped UHPC beams is proposed, effectively accounting for shear span‐to‐depth ratio and cross‐sectional shape.