Static and fatigue performance of headed stud connectors embedded in ultra-high performance concrete

The fatigue performance of headed stud connectors in steel–ultra-high performance concrete (UHPC) composite structures has not been sufficiently investigated, although their behavior under monotonic loading has been widely studied. In this study, push-out tests under monotonic and cyclic loading were carried out on 22 mm diameter headed studs. The results demonstrated that the primary failure mode for stud connectors in UHPC under both static and fatigue loading was fracture of the stud itself, with no significant cracking observed in the UHPC slab. The use of UHPC leads to a notable increase in both shear strength and fatigue strength of the connectors. Current design codes were found to be overly conservative in predicting the shear strength and fatigue strength of stud connectors. Based on the fatigue test results, a fatigue life prediction formula with 95% survival probability and a stiffness degradation model were proposed to evaluate the fatigue performance of headed stud connectors in UHPC.