Friction affected fatigue behavior of steel-UHPC composite structures and the fatigue crack growth in studs

Friction affected fatigue behavior of stud connected steel-UHPC composite structures and fatigue crack growth in studs are experimentally studied. Push-out specimens with greased interface are tested firstly to clarify the friction effects on fatigue behavior. Then, a new visualized testing is designed for visual observation of the interface response and the fatigue crack growth in studs. Finally, a new shear-friction mechanism is proposed to clarify the improved shear behavior and a new concept for fatigue life prediction is developed for stud-UHPC composite connection. Results show that the interface friction can resist a portion of shear force between steel-UHPC interface, increasing the shear stiffness and fatigue life. In the present test, the greased interface decreases the fatigue life from 1.571 and 3.414 million to 0.308 and 2.197 million for stud with the fatigue stress range of 125 MPa and 105 MPa, respectively. Interface friction force is a sub-force and affected by shear force resisted by stud, which concentrates locally in front of stud root rather than the whole interface. S -N curves for stud-normal concrete composite connection recommended by Eurocode 4 are proposed and verified for fatigue life prediction of stud-UHPC composite connection with the fatigue stress discount of 13%.