EXPERIMENTAL RESEARCH ON THE STRENGTH OF BOLTED CONNECTIONS OF HIGH STRENGTH STEEL WITH GRADE OVER 500 Mpa

In bearing-type bolted connections, the load-bearing capacity is established by the contact between the plate and the bolts. The load-bearing capacity develops with growing bolt hole elongation. Due to the existence of bolt holes, stress concentration exists near the bolt holes. For normal-strength steel, the large ductility can ease the adverse effect of such stress concentration, which ensures the full development of strength. High-strength steel has reduced ductility with lower elongation at bolt holes. The effect of stress concentration may be conspicuous. Therefore, the strength of bolted connections made of high-strength steel should be studied. This paper uses three types of high-strength steel, Q550D, Q690D and Q890D, to produce 24 groups of single-bolt double-shear connections, 16 groups of single-shear connections, 6 groups of connections with changing bolt holes and another 4 groups of connections made of normal-strength steel. The results show that the ductility of high strength steel can also ease the effect of stress concentration. No significant difference is found compared with normal-strength steel. It is also found that bolt shear failure occurs more easily in single-shear connections with increasing steel grade, which reduces the ductility of the whole connection. Based on the existing experimental results, increased design strength in the current Chinese Code for the Design of Steel Structures is suggested, which will make better use of the material strength of high-strength steel and reduce the number of bolts.