Mechanism study on the low cycle fatigue behavior of group studs shear connectors in steel-concrete composite bridges

Clustering the stud shear connectors with a narrow spacing to form group studs is useful for the concrete slab prefabrication in steel-concrete composite bridges. But the existing test and analysis results have shown that arranging studs in group tends to be unfavorable to the stud static and fatigue performance. The current fatigue design of the group studs may still experience an overestimation or an underestimation problem since the fatigue mechanism study on group studs is rare. Therefore, a parametric push-out analysis was carried out for explaining the fatigue behavior of group studs, particularly the low cycle fatigue aspect with the fatigue life lower than 2 million cycles. There were 12 static and cyclic push-out models in the analysis. Meanwhile, a series of static push-out tests were also introduced to verify the analysis works. According to the static analysis results, the unequal stud shear forces in the group studs, which were indicated by the analyzed static failure mode, resulted in the reductions of stud shear stiffness and strength. According to the low cycle cyclic analysis results, the fatigue damage initiated at the bottom point of the stud root section in the push load direction, which can be called the fatigue critical point. The low cycle fatigue life reduction of group studs, which was evaluated by the analysis results and the introduced multi-axial fatigue damage criterion, can be explained by the uneven cyclic tensile strain and stress distributions on every individual fatigue critical point in the group studs.