Enhancing cyclic strength of welded tubular structures

Thin-walled structures are prone to fatigue failure due to cyclic loading. In order to enhance the strength of thin-walled tubular structures and improve the fatigue life of a structure, the method of concrete filling the hollow section main chord can be adopted. This method is used in long span arch bridges and tower structures. Concrete-filled steel tubular (CFST) structures are still being heavily researched. Therefore, there is no fatigue design guide for tubular joints with concrete-filled chords due to a lack of sufficient database of results relating to the size range of hollow structural steel sections, concrete grades as well as joint types. This paper investigates a thin-walled T-joint specimen subjected to axial tension and in-plane cyclic loading applied to the specimen’s brace member to determine the hot spot stresses at the weld’s toe. The aim of this paper is to build upon the current research on concrete-filled steel hollow sections joints and to determine the fatigue behaviour of a thin-walled square hollow section (SHS) T-joint under axial tension and in-plane fatigue cyclic loading. Experimental research on a T-joint with a concrete-filled square hollow section (CFSHS) chord under various loading systems was carried out to determine the hot spot stresses and to evaluate the stress concentration factors (SCFs). Stresses were measured through the use of strain gauges which assist in determining the stress distribution around the welded joint of the specimen. Once the SCFs are determined for the CFSHS T-joint, the results will be compared to that of the equivalent empty SHS T-joint. This comparison will show the improvement of the T-joint due to the concrete filling which prevents in-wards chord face deformation and reduces SCFs. Future research is working towards enabling engineers to calculate hot spot stresses without the need of performing experimental research