Fatigue tests and design of thin CHS-plate T-joints under cyclic in-plane bending

A review of existing fatigue design guidelines has been undertaken and shows that there are no fatigue design recommendations for circular hollow section-to-plate T-joints subjected to in-plane bending. This paper therefore reports on the high cycle fatigue behaviour of welded thin-walled circular hollow section (CHS) tubes of thicknesses less than 4 mm that are fillet-welded onto a plate to form a base plate moment connection. The resultant thin CHS-Plate T-joints are subjected to cyclic in-plane bending load to determine their fatigue strength at different stress ranges. The S-N data from the failed thin CHS-Plate T-joints is analysed using the least-squares method of statistical analysis to obtain a design S-N curve. The derived design S-N curve for the thin CHS-Plate T-joints is compared to existing design S-N curves and also that of square hollow section (SHS)-to-plate T-joints under in-plane bending in current fatigue design guidelines. The thin CHS-Plate T-joints are found to have a better fatigue strength compared to the existing S-N curve for SHS-Plate T-joints under in-plane bending. An appropriate design S-N curve from the group of existing design S-N curves is adopted for the design of thin CHS-Plate T-joints.