Push-out tests on studs with UHPC cover embedded in UHPC-NSC composite slab

Abstract

To cope with the volumetric cost of the ultra-high-performance concrete (UHPC) and enhance performance of studs in steel–concrete composite bridges, a novel bridge slab system has been developed. In this system, the slab was made of UHPC and normal strength concrete (NSC), and the studs were covered with UHPC. Since the static behavior of studs with UHPC cover embedded in UHPC-NSC composite slab is different from in the NSC or UHPC slab, an experimental study is needed to investigate the ultimate strength of studs, as well as the relative slip and failure patterns. The mainly parameters considered include stud diameter, stud height, and stud root with or without UHPC cover. The experimental results reveal that the mechanical behavior of studs in the proposed composite slab system was successfully improved. The ultimate strengths of the studs with a diameter of 19 mm and 22 mm covered with UHPC embedded in UHPC-NSC composite slab are only 3.8 % and 2 % less than that in UHPC slab, respectively. The relative slips of stud with UHPC cover in the UHPC-NSC composite slab are larger than 6 mm, which satisfy the ductility demand in EC4. The results also show that the current design codes underestimate the actual shear strength of the stud with UHPC cover in the UHPC-NSC composite slab. Finally, an equation is proposed to predict the shear stiffness of a stud with UHPC cover embedded in the UHPC-NSC composite slab based on the energy equivalent model, and verified by the experimental results. The calculation value agrees well with the experimental result for a stud diameter≥16 mm.