Experimental investigation of minimum shear reinforcement in post-tensioned SCC I-girders

Minimum shear reinforcement in prestressed concrete members is provided to prevent brittle failure after diagonal cracking of the members. Current code provisions for minimum shear reinforcement, including ACI 318–25, AASHTO 2024, and IS 1343:2012, rely on empirical equations, resulting in significant variation in requirements. These provisions were developed primarily for conventionally vibrated, normal-strength concrete, where aggregate interlock contributes substantially to post-cracking shear transfer, and their applicability to self-compacting concrete (SCC) remains largely unverified. The present study evaluates these provisions for post-tensioned self-compacting concrete I-girders through the testing of eight specimens designed with minimal shear reinforcement. All tested specimens have failed in web shear but retained adequate reserve shear strength. However, the shear load at initial cracking of specimens has been found to be lower than the shear strength contribution of concrete as per IS 1343:2012 guidelines in six of the eight tested specimens. The shear reinforcement has also yielded at or before web cracking in six specimens, to indicate that the minimum shear reinforcement requirement in the IS 1343:2012 code provisions is insufficient to accommodate the diagonal tension force transferred at cracking. Shear reinforcement strains have been strongly localised at the critical crack, with ultimate strains in gauges outside the crack region generally remaining below yield strain to indicate ultimate shear strength is significantly influenced by number of shear reinforcement bars intersecting the inclined shear cracks.