Fatigue tests and design of thin cold-formed square hollow section-to-plate T connections under cyclic in-plane bending

Thin-walled tubular sections (t<4 mm) are increasingly being used in the road transportation industry and agricultural industry for applications such as lighting poles, traffic sign supports, truck trailers, swing-ploughs, haymakers, and linkage graders. These structures are subjected to fatigue loading and some failures have been observed. Both the International Institute of Welding and International Committee for the Development and Study of Tubular Construction fatigue guides for welded tubular joints apply only to tubes with a thickness above 4 mm. This paper deals with the fatigue design of tube-to-plate T joints under cyclic in-plane bending using the classification method. Forty-eight specimens, made up by welding a square hollow section tube (t<4 mm) to a plate, are fatigue tested. The effects of in-line galvanizing, steel grade, stress ratio, and tube wall thickness on the fatigue life of these joints are investigate. The design stress range-to-number of cycles (S-N) curves, derived from the least squares method of analysis, show that the S-N curves for the tube-to-plate joints lie above the existing S-N curves in the Australian, European, and Canadian standards.