Shear Failure of Concrete Deep I-Beams

Abstract

Relatively few studies have explored the shear behavior of concrete deep I-beams. This study presents a series of 12 shear tests on concrete deep I-beams with shear span-to-height ratios (av/h) of 1.0 and 1.5. The effects of horizontal and transverse web reinforcement on structural deformation and shear strength are compared. The findings indicate that a minimum horizontal and transverse reinforcement ratio (ρv=ρh=0.28%) significantly enhances the shear capacity. Additionally, an increase in vertical reinforcement (ρv=1.26%) shifts the failure mode from shear tension to web crushing. Increasing horizontal web reinforcement has little influence on shear capacity at av/h=1.5, while it significantly enhances strength at av/h=1.0. The upper limit of shear strength for deep I-beams, as specified by ACI 318-19, appears conservative; a limit of 0.225fc′bwd is recommended. The Strut-and-Tie Model (STM) used in ACI 318-19 is conservative, demonstrating an average experimental-to-predicted shear strength value, Vexp/Vpred=3.24, with a standard deviation of 0.63. Conversely, VecTor2 exhibits an average Vexp/Vpred of 1.07, with a standard deviation of 0.10. The panel element-based model, such as Mau’s model, is proven suitable for the analysis of deep I-beams.