Shear behavior of bolted connectors with double embedded nuts in composite beams with steel-fiber reinforced concrete SFRC slabs

The behavior of bolted connectors with double embedded nuts (BCDENs) in steel-fiber reinforced concrete (SFRC) remains uncertain, restricting their application in steel-SFRC composite beams. This study explored the shear performance of four push-off test specimens, varying bolt diameters, bolt grades, and concrete strength. The analysis covered failure modes, load-slip response, load-strain behavior, shear resistance, initial slip load, stiffness, peak slip, and ductility of BCDENs. Bolt shearing off was the prevalent failure mode observed in all specimens, occasionally accompanied by concrete crushing beneath the nuts. The incorporation of steel fibers in normal-weight concrete (NC) effectively mitigated the formation and propagation concrete cracks. The horizontal slip of the concrete slab ranged between 10.8% and 26.0% of the vertical steel-concrete slip. Shear resistance and post-slip stiffness escalated with increased concrete strength, bolt diameter, and bolt grade. Validated FE models were employed for parametric studies involving concrete strength, bolt pretension, diameter, and tensile strength. Based on experimental and FE findings, practical design recommendations were proposed for predicting shear resistance and force-displacement response of BCDENs in steel-SFRC composite beams.