Group effect and bearing capacity of multi-bolted connection for pultruded GFRP laminate

To further understand mechanical performance of the bolted connection for GFRP laminates under static tension load, axial tensile tests with parameters of number of bolts (n), end distance (S_e), pitch spacing (S_p), pre-tightening torque (M), edge distance (S_w), gauge spacing (S_g) and fiber layup were conducted on double lap bolted joints (DLBJs) composed of three pultruded GFRP laminates. The orthogonal design method was employed to determine the axial tensile test scheme. The failure mode and bearing capacity of DLBJ were obtained during the axial tensile test. The effects of aforementioned test parameters on failure mode and bearing capacity of DLBJs were uncovered and quantified. The group effect was further investigated and quantified to determine the effective number of bolts in multi-bolted connections. Finally, the prediction formulas for bearing capacity of multi-bolted connection for pultruded GFRP laminates were developed by accurately incorporating group effect. The results demonstrated that effects of end distance, pitch spacing and fiber layup on the failure mode and ultimate bearing capacity of DLBJ specimen are significant. S_e, S_w, S_p and M are important parameters affecting the effective number of bolts of multi-bolted connections. The dominant failure mode of DLBJ specimens with [+45°/90°/−45°/0°/+45°/90°/−45°/0°/−45°/90°/+45°] GFRP laminates are bearing failure in bolt hole when end distance S_e = 6d₀ and pitch spacing S_p ≥ 4d₀. For other cases of DLBJ specimens, the dominate failure is shear-out failure in GFRP laminates. The ultimate bearing capacity predicted by practical formulas developed in the present study is more accurate than that determined by existing formulas.