Investigations on influences of Engineered Cementitious Composites (ECC) on pull-out properties of studs in steel-concrete composite bridge

Stud plays an important role in the connection of steel-concrete composite bridge (SCCB). The stud is under pull-out load in the negative moment zone of SCCB. Engineered Cementitious Composites (ECC) are a new type of materials with tensile strain hardening and multiple cracking behavior to strengthen SCCBs. In this study, the cyclic pull-out effect on the ECC-stud connection was studied through pull-out tests. The stud diameter (d=13/16 mm) and the embedment depth (hef=40/60/80 mm) are included as design parameters, resulting in a total of 18 specimens of six scenarios. The failure mode, load-bearing capacity, and ductility factor of the specimens under cyclic loading are compared with those under monotonic loading, and the stiffness, energy dissipation capacity, and residual displacement of the specimens under cyclic loading are analyzed. Based on the experimental results, under cyclic loading, the concrete cone failure and splitting failure occur, and the threshold of hef/d between the two failure modes is 3.75–4.62, which is smaller than the threshold of the monotonic scenarios. Both concrete and splitting failure modes show ductile failure characteristics because of the bridging effect of fibers in ECC. The load-bearing capacity and ductility factor under cyclic loading are lower than those under monotonic load. This is because, under cyclic loading, the specimens show cumulative damage, which, however, is weakened due to the strengthening effect of ECC. As d and hef increase, the load-bearing capacity, ductility factor, stiffness, and energy dissipation capacity increase correspondingly, and the residual displacement decreases. The stud with a larger d shows a more obvious ductility holding stage.