Abstract
<title>Abstract</title> <p>Previous studies have experimentally established that the deflection of the headed stud shear connection in a hybrid steel-prestressed concrete girder (steel-PC girder) increases over time under sustained external load primarily due to creep deformation of concrete induced by localized stress near the headed studs. However, the shear force acting on individual headed stud connectors and its time-dependent variation under sustained loading cannot be measured directly through experiments. To address this limitation, the present study investigates the shear deformation mechanism of the headed stud shear connection under sustained loading through both experimental and numerical approaches. Push-out tests were conducted on specimens with geometry, stud configuration, and loading conditions consistent with those of the previously tested girders, subjected to sustained shear force levels of 15% and 30% of the stud capacity for 30 and 60 days. Complementarily, three-dimensional nonlinear finite element analyses, incorporating time-dependent material constitutive models for concrete, were conducted to reproduce slip displacement, quantify the evolution of stud-level shear force, and simulate the long-term behavior of the connection under varying sustained load conditions. The analytical results clarified the mechanism by which time-dependent redistribution of shear force promotes long-term slip development, leading to an increase in joint deflection. The findings further indicate that limiting the sustained shear force level in headed stud connectors is effective in mitigating creep-induced joint deflection. Although no design equation is proposed within the scope of this study, the experimental and numerical results provide a rational basis for future design methods and serviceability assessment of headed stud shear connections in hybrid steel-PC girders.</p>