Fatigue tests and design of welded thin-walled RHS-RHS and RHS-angle cross-beam connections under cyclic bending

Galvanized sections are suitable for use in the road transportation industry, the agricultural industry and for recreational structures. The structural systems in which galvanized sections can be used include chassis boxes, roof frames, base frames and drawbars among others. These structural systems are subjected to cyclic loading in service. The structural systems are therefore prone to fatigue failure. In Australia, galvanized sections, commonly known as DuraGal, are thin-walled with wall thicknesses less than 4 mm. There are currently no fatigue design rules for sections of thicknesses less than 4 mm. The connections under investigation namely cross-beam connections, are not covered in current fatigue design guidelines. This paper reports on fatigue tests of cross-beam connections made up of galvanized rectangular hollow sections (RHS) and angle sections. Two types of connections have been investigated, namely RHS-RHS and RHS-angle cross beams. Cross beams are manufactured by welding one member on top of another. In this investigation, welding procedure qualification was carried out by determining hardness values in the parent metal, weld metal and heat-affected zone with particular emphasis to checking the possibility of heat-affected zone cracking. Stress concentration factors were determined in typical connections to determine hot spot locations and to verify observed crack growth patterns in these connections. The fatigue test data obtained from high cycle fatigue tests are compared to existing fatigue design curves. Design curves for cross-beam connections are recommended based on deterministic methods and statistical analysis.