Lewei Tong

Fatigue design of welded very thin-walled SHS-to-plate joints under in-plane bending

The existing fatigue design S-N curve for SHS-to-plate T-joints under in-plane bending is given in the Canadian Standard, CAN/CSA-S16.1-M89, in terms of the classification method. That S-N curve is however based on the class of longitudinally loaded plates with welded non-load carrying attachments, which are different from the SHS-to-plate T-joints. The increased use of welded thin-walled (t<4 mm) tubular joints in the road transport and agricultural industry for applications such as lighting poles, traffic sign supports, truck trailers, swing ploughs, haymakers and linkage graders, means that there is a need to develop fatigue design curves for tubular joints where the tube wall thickness is less than 4 mm. This paper aims to determine fatigue design curves for SHS-to-plate T-joints where the thin-walled tubes have a thickness of less than 4 mm. Tube-to-plate T-joints, made up by welding a square hollow section tube to a plate, are tested under fatigue loading. Constant stress-amplitude cyclic loading is applied to these connections as in-plane bending load. Stress concentration factors (SCFs) have been determined from strain distributions obtained using strain gauge measurements. Analysis of the fatigue test data using least squares method is carried out to determine the design curves of the tube-to-plate T-joints under in-plane bending, for both the classification method and the hot spot stress method. A class of 44 is recommended for the classification method. An S rhs -N curve is proposed, with a recommended SCF of 2.0 for the hot spot stress method.

High-Cycle Fatigue Behaviour of Welded Thin SHS-CHS T-Joints under In-Plane Bending

Static tests of welded thin walled square hollow sections (SHS) and circular hollow sections (CHS) T-joints, under in-plane bending, have been used to produce load-deformation curves from which the maximum linear response moment of connection has been determined. The loads corresponding to the maximum linear response moment and below have been applied during cyclic loading and found to produce a high-cycle fatigue response in the SHS-CHS joints. A formula has been derived for predicting the ratio between maximum linear response moment and static strength as a function of the nondimensionaL parameters. The fatigue data of the welded thin-walled SHS-CHS T-joints was found to lie within the same scatter band as the S-N data of thin-walled SHS-CHS T-joints. An analysis of the S-N data of the thin-walled SHS-CHS T-joints shows that there is a minimal difference in the design curve obtained when the inherent scatter in fatigue data is taken into account.

ULTIMATE STRENGTH OF WELDED THIN-WALLED SHS-CHS T-JOINTS UNDER IN-PLANE BENDING

Publisher Summary Welded thin-walled T-joints made up of square hollow section (SHS) chords and circular hollow (CHS) section braces are tested under static in-plane bending load. The hollow sections are cold formed and have thicknesses less than 4 mm. The SHS–CHS 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 SHS–CHS T-joints is observed to occur as a result of chordface yielding. Chord cracking is also observed after large deformations, resulting in a peak load being attained in these joints. In this chapter, load versus chord flange indentation graphs for the SHSCHS T-joints are used to determine the deformation limit that can be used in defining the ultimate strength of the joints. The deformed shape of the chord observed from experimental tests is used to create a yield line model. A formula is derived for the ultimate strength of the SHS chord and CHS brace vierendeel connections based on a plastic mechanism analysis using yield line theory. The ultimate strength determined through the use of the deformation limit criteria is compared to the ultimate strength calculated using the formula obtained from yield line theory.