Strength of Butt Welded Connections between Equal-width Rectangular Hollow Sections (No. R817)

The report describes a series of experimental tests on tensile coupons cut from the butt welded brace-to-chord connections (T-joints) between rectangular hollow sections of equal width. The aims of the tests are to investigate whether there are any serious difficulties in producing satisfactory butt welds in the large root gaps resulting from the rounded corners of chord sections, and to establish the welding procedures that enable such connections to be pre-qualified. Rectangular hollow sections of various thicknesses and corner radii are used, resulting in root gaps ranging from 0.8 mm to 9.4 mm. Four different types of joint preparations involving the use of backing strips, fill bars, purging gas or no preparations at all are experimented with. The connections are fabricated using the Gas Metal Arc Welding (GMAW) and the Manual Metal Arc Welding (MMAW) processes. In general the GMAW process results in better quality butt welds, whether the root gap is narrow or large. A narrow root gap may present a problem if the MMAW electrode is not small enough and the brace edge is not bevelled. It is concluded that SP (Structural Purpose) butt welded connections between equal width cold-formed rectangular hollow sections which are fabricated using the GMAW and MMAW processes may be pre-qualified provided the root gap is at least 3 mm and 4 mm respectively. The prequalification applies to the horizontal and flat positions for the following weld preparations: no specific preparation, the use of backing strip and the use of purging gas on the inside of the tube. The pre-qualification does not apply to joints welded using fill bars