Plastic mechanism analysis of welded thin-walled T-joints made up of circular braces and square chords under in-plane bending

Welded thin-walled T-joints made up of circular hollow section (CHS) braces and square hollow section (SHS) chords were tested under static in-plane bending load. The hollow sections are cold-formed and have thicknesses less than 4 mm. The CHS-SHS T-joints are used in building the undercarriages and structural supports of equipment and structural systems used in the road transport and agricultural industries. Failure in the CHS-SHS T-joints was observed to occur as a result of chord-face yielding. Chord cracking was also observed after large deformations, resulting in a peak load being attained in these joints. There is no design formula in the existing CIDECT design guides, IIW static recommendation and Eurocode 3 for CHS-SHS T-joints under in-plane bending. In this paper, load versus chord flange indentation graphs, for the CHS-SHS T-joints are used to determine the deformation limit that defines the ultimate strength of the joints. The deformed shape of the chord observed from experimental tests is used to create a yield line model. The weld size and the rounded corners of the SHS chord are considered in the model. A formula is derived, for the ultimate strength of the CHS brace and SHS chord vierendeel connections based on a plastic mechanism analysis using yield line theory. There is a reasonably good agreement between the ultimate strength predicted using this formula and that determined experimentally.