Shear performance and residual behavior of ultra-high performance concrete rubber-coated stud connectors subjected to various cyclic loading conditions

The innovative steel-ultra-high performance concrete (UHPC) composite structures have been adopted as the key force component in modern construction due to their exceptional mechanical properties and enhanced lifespan. To enhance composite action, the flexible rubber-coated stud connector (FRSC) has been proposed as a replacement for the ordinary stud connector (OSC), aiming to improve the ductility and energy dissipation capacity of steel-UHPC composite structures. This study conducted cyclic loading tests to investigate the shear performance of FRSCs under various cyclic loading conditions and assess the post-cyclic behavior. The test results indicated that the FRSC and OSC under monotonic and various cyclic loading were failed mainly by the stud fracture and localized UHPC damage. Unidirectional cyclic loading had little impact on the shear capacity and ductility but produced noticeable plastic deformation. The shear strength and ductility of the OSC and FRSC showed a significant reduction under fully reversed cyclic loading. Increasing hysteresis slip amplitudes increased energy dissipation but also led to greater plastic slip and stiffness degradation. After high-amplitude displacement cycle loading, the FRSC maintained sufficient shear capacity, but the OSC almost lost its load-bearing ability. Finally, a modified strength expression, incorporating the strength reduction factor, could precisely estimate the shear strength of the OSC and FRSC subjected to various loading conditions.