Strength of arc-welded T-joints between equal width cold-formed RHS

The paper describes laboratory tests of arc-welded T-joints between equal width rectangular hollow sections (called “matched box connections” in ANSI/AWS D1.1-2000 Structural Welding Code). The brace and chord members were cold-formed with a nominal yield stress of 350 MPa. The welds were laid using MMAW and GMAW processes without profiling the brace ends. The brace of each specimen was loaded in tension to failure with the chord supported continuously so as not to induce significant bending effects. The test results showed that the joint strength can be improved by using backing strips for the butt (or groove) welds, while backing rods (or filler rods) should not be used as they led to larger variation in joint strengths, and often, inferior strengths. The test strengths are compared with the design strengths obtained using the IIW Recommendations and Eurocode 3, Part 1.8. It is shown that for cold-formed tubes with a nominal yield stress of 350 MPa (or above), a design check on the strength of the butt (or groove) weld is required in addition to the checks on the strengths of the chord and brace members specified in the current design guidelines. An equation is proposed for calculating the strength of the weld.