Modified EC2 Model for the Shear Strength of RC Beams with Stirrups

A modification of the variable strut inclination method of the Eurocode 2 (EC2) for the shear strength calculation of reinforced concrete (RC) beams with stirrups is presented. This model incorporates two (rather than one) variable-inclination compression struts. The upper compression strut may have lower inclination than the lower compression strut, which is indicated by the trend of the principal compressive stress direction. Following the theoretical framework of the EC2 approach, the two inclination angles are determined through the lower-bound theorem of plasticity, by solving an optimization problem. The proposed truss model leads to compact closed-form expressions that can be expediently used for practical design purposes. Based on comparison with experimental results, the proposed model proves to be more accurate than the Eurocode approach to predict the actual shear strength of RC beams with stirrups, especially in the range of low amounts of transverse reinforcement where the EC2 model turns out to be very conservative.