Design shear strength formula for high strength concrete beams

After a brief review on the concrete shear strength mechanisms, two very reliable expressions for predicting the shear strength of beams without transverse reinforcement are reported: the one proposed by Bažant and Kim, which is valid for Normal Strength Concrete (NSC) beams, and the other recently proposed by the authors, which is valid for High Strength Concrete (HSC) beams. Hence a summary of a shear strength model for beams with stirrups is provided, which was derived on the basis of the Bažant and Kim expression and therefore is adequate only for NSC beams. On the basis of the expression obtained for HSC without stirrups and of the model already proposed for NSC with stirrups, a shear strength expression for HSC beams with stirrups is derived. The obtained expression is applied to an experimental program of 116 HSC beams with stirrups, and is found to predict the test results better than ACI Code, Eurocode and CEB/FIP Model Code. A design formula is hence proposed, which is adequately conservative and accurate. A design example of a HSC beam with stirrups is carried out, and the various design expressions previously considered are compared.