Structural optimisation for mechanical connection of very high strength (VHS) circular steel tubes

The very high strength steel was developed in Australia in the 1990s. It has a yield stress of 1350 MPa and an ultimate tensile strength of 1500MPa. Studies showed that a reduction in strength was inevitable when the steel was connected using fusion welding methods. A reduction of nearly 50% in the connection strength was reported for butt-welded and fillet welded samples. In order to recover the strength loss due to welding, different strengthening techniques were attempted, including bonding CFRP sheets around a connection. Recently, a feasibility study was reported on using a mechanical jointing method. Results showed that full strength of the VHS steel tube was achieved with failure happened in the parent metal rather than in the joint. The mechanical joint consisted of a wedge-shape gripper, a sleeve and a plug. The aim of this study was to optimise this mechanical joint through finite element modelling so that the overall weight of the mechanical joint could be minimised while retaining its integrity and strength.