Effective Capacity of Diagonal Strut for Shear Strength of Reinforced Concrete Beams without Shear Reinforcement

The appropriate evaluation of the effective capacity of a concrete strut is an important factor in the analysis and design of concrete members using the strut-and-tie model. Current design codes for the strut-and-tie model introduce this factor using the effective compressive strength of concrete in a strut or nodal zone. This study considers that the mechanism of diagonal cracking reduces the width of a concrete strut and hence causes a reduction in the capacity of the concrete strut. Based on this approach, models for predicting the diagonal cracking strength and ultimate shear strength of simply supported beams without shear reinforcement are proposed, with the concrete strength, shear span-depth ratio (a/h), and longitudinal reinforcement ratio as the primary parameters. The predicted values are compared with proven test data from various published experiments and codes of practice to show the validity of the proposed models.