The Influence of Flexural Reinforcement Yielding on the Shear Strength of Reinforced Concrete Beams with and without Shear Reinforcement

Statically indeterminate structures such as continuous beams allow redistribution of internal forces. For increasing loads after yielding of the flexural reinforcement, shear forces may increase, making it possible to reach shear failures after the full flexural capacity of the structure is developed. An extensive experimental programme consisting of 30 shear tests (15 cantilever tests and 15 continuous beam tests) was carried out to assess the shear strength of reinforced concrete beams with and without shear reinforcement. Some of the tests were designed to fail in shear after yielding of the flexural reinforcement. The main objective of this experimental study was analysing the influence of large flexural strains on shear strength. The tests were instrumented by means of surface measurements using Digital Image Correlation (DIC). These measurements allowed controlling the evolution of strains at concrete surface to obtain the rotation of the plastic hinges and tracking the development and kinematics of the critical shear crack to obtain, by accounting for suitable constitutive models, the contribution of the various shear-transfer actions. The analysis of the test results confirmed the reduction of shear strength provided by concrete with increasing flexural rotation both in tests with and without shear reinforcement. Moreover, this shear strength component weakened for increasing shear reinforcement ratios. The test results were compared with the shear strength values predicted by different design codes, showing that these formulations did not properly capture the loss of shear strength caused by plastic deformation. The proposed simplified method to calculate the shear strength of the plastic hinges accounting for the plastic rotation demand shows consistent agreement for the experimental results.