Shear Strength and Crack Width Control of Concrete Beams with High-Strength Shear Reinforcement

There is a potential to reduce steel tonnage for construction through the use of high-strength steel reinforcement. However, the current version of the ACI 318 code limits the yield strength of reinforcement that could be used for shear design under gravity load conditions to 420 MPa to control diagonal crack widths. This limit is increased to 550 MPa for resisting seismic shear in special moment frames. In the current study, 12 full-scale RC beam specimens were tested to investigate the shear behavior of RC beams with high-strength SD790 (fys=790 MPa) shear reinforcement. The test variables considered in the experimental study were shear-span-to-depth ratio, stirrup spacing, stirrup yield strength, concrete compressive strength, and longitudinal reinforcement ratio. The test results of this research and those collected from the literature showed that the stress limit of the ACI 318 shear strength equations could be increased to 600 MPa for shear strength calculation. The stress limit of 790 MPa produced conservative predictions for most of the test data and for all the data if the strength reduction factor for shear design was considered. However, the degree of conservatism was significantly reduced. Also, an equation to estimate the maximum shear crack width was proposed. The proposed crack-width equation was able to predict the crack widths observed in the current and other reference studies with reasonable accuracy.