Finite Element-Based Fatigue and Damage Assessment of Group Stud Shear Connectors in UHPC-Steel Composite Beams

This study investigates the static and fatigue performance of stud shear connectors embedded in Ultra-High-Performance Concrete (UHPC) for composite structures. Three stud arrangements, Type-I, Type-II, and Type-III are evaluated using nonlinear Finite Element Analysis (FEA), focusing on the stress distribution, damage evolution, and fatigue life prediction. The von Mises stress distribution revealed critical stress concentrations at the stud roots and UHPC-steel interface, with Type-III arrangement demonstrating the most uniform stress spread and effective load transfer. Progressive damage modeling revealed that failure initiated at the stud roots and propagated as the applied load increased. The fatigue analysis demonstrated a substantial enhancement in the fatigue life with increased stud embedment length and optimized stud arrangements. Among the configurations studied, the Type-III arrangement exhibited the most favorable stress distribution, characterized by a more uniform load transfer and minimal stress concentration per stud. The specimens with this configuration achieved fatigue lives of up to 323,594 cycles without any visible damage, underscoring its superior fatigue resistance and structural reliability. The findings confirm that the strategic optimization of the stud geometry and the use of group stud arrangements can improve the stress distribution and significantly enhance the durability and performance of the steel–UHPC composite connections under cyclic loading.