A study of net-section resistance of high strength steel bolted connections

This article presents an experimental and numerical investigation on the net section resistance of high strength steel (HSS) bolted connections subject to double shear. A total of 22 HSS and 11 mild steel (MS) bolted connection specimens were tested to net section fracture. HSS grades of Q690 and Q960, and MS grade of Q345 were studied. Although the HSS material has relatively lower ductility and a lower ratio of tensile strength to yield strength (f_u/f_y) than those of the MS material, in general, the HSS connection specimens were able to reach the connection efficiency (i.e. the ratio of the ultimate load of the connection specimens to the calculated net section resistance) of above 1.0. Subsequently, the structural behaviour of the connections was studied by finite element (FE) analysis. The effects of material ductility and f_u/f_y ratio on the stress development across the net section of the specimens were examined. It was found that HSS materials possess sufficient ductility to allow an efficient stress redistribution across the net section. Besides, the beneficial influence of the ‘reinforcement’ or the biaxial stress effect due to the presence of holes in the connection increases the ultimate capacity of the perforated main plate, and hence the HSS specimens were able to reach the net section resistance. However, the overall deformation capability of the HSS specimens was significantly lower than that of the MS specimens. A reliability analysis was carried out to re-examine the partial factor used in the current design equation for predicting the net section resistance in Eurocode 3.