Numerical Investigation of the Shear Performance of Large-Diameter Hinged-Bolt Connectors in Steel–UHPC Composite Beams

Large-diameter hinged-bolt connectors markedly reduce the early slip caused by bolt-to-hole clearance in conventional bolted connectors while avoiding welding-related problems associated with large-diameter headed studs in steel–ultra-high-performance concrete (UHPC) composite beams. However, their internal load-transfer mechanism cannot be directly quantified through push-out tests. A three-dimensional nonlinear finite element model was developed and validated against twelve push-out specimens. For the UHPC specimens, the model provided quantitatively reliable predictions of peak shear resistance and ultimate slip, and accurately captured the governing bolt shear fracture failure mode. The validated model was used to quantify the distributions of shear force, axial force, and bending moment along the hinged bolt. After excluding the specimens strongly affected by concrete crushing or severe steel-flange deformation, the remaining specimens exhibited maximum bolt shear forces of approximately 68–83% of the corresponding pure-shear resistance and maximum axial forces of approximately 10–20% of the pure-tension resistance. For the investigated specimens, the effective concrete-reaction length averaged 1.53 times the smooth-shank diameter. Parametric analyses showed that increasing the bolt grade from 4.6 to 12.9 raised the peak shear resistance by approximately 131%, while progressively shifting the governing response from bolt shear fracture toward UHPC crushing. Bolt aspect ratios of 2.6–4.0 produced similar bolt-fracture-controlled responses, whereas an aspect ratio of 1.0 caused UHPC pry-out. Increasing the steel grade from Q355 to Q690 and the longitudinal bolt spacing from four to seven nominal bolt diameters raised the peak resistance by only 7.3% and 4.0%, respectively. These findings provide a mechanical basis for the rational design of large-diameter hinged-bolt connectors.