Abstract: The combination of high-strength concrete and steel fibers with different sizes can improve the performance of concrete deep beam, such as bearing capacity and toughness. In this paper, shear tests were carried out on one reinforced high-strength concrete deep beam and four hybrid steel fiber reinforced high-strength concrete deep beams. Through changing the volume of hybrid steel fiber and the distribution of web reinforcement, the failure mode, bearing capacity, deformation capacity, and reinforcement strain of specimens were studied. The enhancement mechanism of hybrid steel fiber for specimens was analyzed. The study results show that because of the hybrid steel fiber, the bearing capacity and deformation capacity of specimens are significantly improved, and the stiffness and bearing capacity decrease slowly in the later stage. The bearing capacity of specimens increases with the increase of the volume of hybrid steel fiber and web reinforcement ratio. The deformation capacity of specimens increased with the increase in the volume of hybrid steel fiber, but it increases first and then slightly decreases with the increase of the web reinforcement ratio. The short steel fibers function is to reinforce the concrete base-body and inhibit the forming of cracks. The long steel fibers role is to delay the development of cracks, transmit and bear the shear force at the cracks, and relieved the tensile stress of steel bars. Two kinds of steel fibers work together in the loading process of specimens. In addition, the calculation method to predict the shear capacity of hybrid steel fiber reinforced high-strength concrete deep beams was revised, with the consideration of synergistic effect of the two types of steel fibers. The calculated results were in good agreement with the test results.

Key words: steel fiber, high-strength reinforced concrete, deep beam, shear behavior, bearing capacity