Improving Rotation Capacities of Stiffened Welded Knee Joints between DuraGal C450 RHS (No. R832)

Abstract

This report describes a new welding-based solution that significantly increases the rotation capacity of a stiffened welded knee joint between DuraGal C450 RHS under opening moment. The proposed solution is more economical than the use of internal sleeves, and can be applied to new as well as existing structures. The solution involves the use of extra layers of weld on the inner (tension) flange of a stiffened welded knee joint. Laboratory test results are presented to demonstrate that the solution enables such a joint between DuraGal C450 150x50x4 or 150x50x5 RHS to satisfy the rotation capacity requirement specified for plastic design of steel frames. A number of factors that may contribute to the lack of rotation capacity of a normally welded stiffened knee joint are discussed. The reasons why the new solution results in increased rotation capacities are explained in terms of strain redistribution and strain reduction in the tensile regions around the knee joints. It is shown through experimental tests and finite element analyses that the most important parameter of the proposed solution is the width of the extra layers of weld. Although the presence of the seam weld in the inner flange results in a significantly reduced rotation capacity, the proposed solution still ensures an adequate rotation capacity for a stiffened welded knee joint between DuraGal 150x50x5RHS. This report also discusses an appropriate definition for the rotation capacity of a knee joint under opening moment, including the plastic moment to be used in measuring the rotation capacity.