Flexural Performance of Steel–UHPC Composite Beams with Innovative Steel Wedge Block–Crossed Inclined Stud Connections

This paper presents an experimental study on steel–ultrahigh performance concrete (UHPC) composite beams using the steel wedge block–crossed inclined stud (SWBCIS) connections. The effects of stud inclination angles, shear connector spacings, and stud aspect ratios (stud height-to-stud diameter ratio) were tested in positive flexure by seven specimens. The failure modes, crack patterns, load-midspan deflection curves, cross-section strain distributions, and relative slip/uplift at the steel–UHPC interface were studied and presented in detail. Test results showed that the composite beam using SWBCIS had higher elastic stiffness and bearing resistance as well as postcracking deformation capacity than vertical stud connections. Increasing the stud spacing slightly improved the failure loads but significantly enhanced the ductility because of the decreased composite action caused by the accumulated splitting/uplift cracks and local crushing of the concrete. In addition, increasing the stud aspect ratio increased the failure loads smaller than a rigid composite section due to insufficient slip ductility, which could be relieved as stud spacing increased. Relative to the vertical stud connections, the SWBCIS connection was found to enable better antislip and antiuplift capacities, thereby reducing the maximum slip by 60%. Finally, based on the published nonlinear load-slip models, the nonlinear analysis of the interfacial slip distribution and load-midspan deflection relationships was performed and discussed in detail. It predicted a larger slip than test results due to higher interfacial friction activated by the SWBCIS connections and multiaxial compression of UHPC.