Ultimate Strength, Ductility, and Failure Mode of High-Strength Frictional Bolted Joints Made of High-Strength Steel

Abstract

Further structural rationalization of steel bridges such as weight reduction of members can be realized by using high-strength steel. However, owing to the high yield-to-tensile strength ratio, failure of connected members occurs before the members in the gross area are plastic-deformed sufficiently. In this study, tensile tests of frictional bolted joints with various geometrical configurations and grades of plates and bolts were conducted to compare the failure modes of high-strength and mild steel joints and to investigate the relationship among ultimate strength, ductility, and failure mode. The results indicate that the failure modes of high-strength steel joints were the same as those of mild steel joints and can be almost classified with the respective ratios of net cross-section failure resistance and plate shear failure resistance to bolt shear failure resistance. Ultimate resistance and ductility were maximum in the case of split failure mode where these ratios were approximately 1.0; they increased as the ratios decreased. Therefore, it can be concluded that these ratios should be less than 1.0 to induce the split failure mode to enable the breaking of a high-strength steel joint after the member is plastic-deformed sufficiently.