Behavior of Stud Shear Connectors with Increasing Concrete Strength

To investigate the mechanism for the enhanced load-bearing capacity of stud connectors owing to an increase in concrete strength, the push-out test is analyzed using nonlinear finite-element (FE) models. A distinct failure mode is observed, and proofs are collected to explain the mechanism of studs with higher strength concrete. The results show that a stud with ultrahigh-performance concrete (UHPC) yields to the plastic failure initiating on the bottom surface of the stud shank and propagating through the cross section near the weld collar. The failure mode is different from that of normal-strength concrete (NSC). The local reinforcing effects, like the confinement effects on concrete strength, improved tensile strength, and constraint of the weld collar, provide a stronger constraint around the foot of the stud shank and account for the distinct failure mode. As a result, the local reinforcing effects should be included to improve the FE prediction accuracy. Underestimating the strength of studs with UHPC, the simplified method neglecting local effects may lead to a conservative design since the local reinforcing effects are neglected.