Experimental study on the behaviour and strength of high strength steel CHS T- and X-joints

This paper presents an experimental investigation on high strength steel circular hollow section (CHS) T- and X-joints. In total, seven T-joints and six X-joints were tested under axial compression in the braces and failed by chord plastification. The brace to chord diameter ratio (β) ranged from 0.60 to 0.93 and chord diameter to wall thickness ratio (2γ) varied from 42.8 to 54.3. The test specimens were composed of CHS tubes which were cold-formed from one parental steel plate with a nominal yield stress of 960 MPa. The steel plate was manufactured by the quenching and tempering (QT) technique. A robotic welding machine was employed to perform the gas metal arc welding for the fabrication of the test specimens in order to achieve consistent welding quality and a low heat input of approximately 0.38 kJ/mm. The material strength reduction of the heat affected zones (HAZ) in the CHS tube was investigated. The deformation capacity, ductility and strength of the test specimens were examined. The current CIDECT and Eurocode design rules for normal strength steel tubular joints were assessed against the obtained test results. It is shown that the material strength reduction of the HAZ was minor, and the deformation capacity and ductility of the test specimens could be considered as reasonably sufficient. The CIDECT and Eurocode mean strength predictions are unduly unconservative for the T- and X-joint specimens.