Pull-out behavior and design of headed studs in steel-UHPC composite structures

This paper experimentally investigates the pull-out behavior of single studs and stud groups embedded in ultrahigh-performance concrete (UHPC). A total of 33 pull-out tests are conducted. The effects of the fiber content (rho), effective embedded depth of stud (hef), ratio of embedded depth to diameter of stud shank (hef /d), diameter of stud head (dh) are considered for single studs; the effects of the arrangement, number, and spacing of studs are considered for stud groups. Results indicate that when concrete failure governs, for single studs in UHPC with fibers: (i) the pull-out strength and ductility increase with increasing rho, hef, or dh, (ii) the pull-out strength and ductility are higher than those in normal concrete (NC), and (iii) the radius of failure cone is greater than that in NC, increasing from 1.5hef to 2.5hef. Stud groups in UHPC with fibers also have higher pull-out strength and ductility, but the group effect is more significant due to the increased overlap of the failure surface. The group effect reduces with the increasing spacing of studs, but is not obviously influenced by the fiber content. New design equations are proposed to estimate the pull-out strength of single studs and stud groups in steel-UHPC composite structures.