Shear Behavior of Grouped Long Studs in Novel Noncellular Steel–UHPC Joints of Hybrid Girder Continuous Rigid-Frame Bridge

Abstract

To address the structural complexity and construction difficulties associated with conventional cellular steel–concrete joints (SCJs), this study proposes an innovative noncellular steel–ultrahigh-performance concrete (UHPC) joint (SUJ) for hybrid continuous girder bridges, in which headed studs are solely used to connect the steel box girder with monolithic UHPC grout. The proposed SUJ has been successfully implemented in the Yuanshui Bridge of the Yiyang–Changde Expressway ( G 55 17 ) in China, demonstrating its practical feasibility. Based on this joint configuration, push-out tests were conducted to investigate the shear behavior of long stud groups ( D 22 × 180    mm at 200-mm spacing), and the effects of stud diameter, aspect ratio, spacing, and configuration were systematically evaluated. Test results showed that all specimens failed by stud shank failure, and the grouped-stud arrangement resulted in an average 6.8% reduction in shear capacity per stud compared with single studs; meanwhile, increasing the aspect ratio from 3.6 to 8.2 led to a 6.6% decrease in shear capacity. Although denser arrangements using smaller diameter studs achieved comparable total shear resistance at similar shear areas, the elastic shear stiffness per stud of grouped studs was significantly reduced, and the interfacial slip between steel beams and UHPC blocks failed to satisfy the ductility requirement of current standards. Parametric analysis further confirmed that stud diameter plays a dominant role in shear capacity, whereas reduced stud spacing and increased stud row number adversely affect both shear capacity and ductility. Accordingly, an empirical formula incorporating a reduction factor related to stud row number is proposed to predict the ultimate shear resistance of grouped long studs, showing good agreement with experimental results.