Validation of a CHS connection used in X-bracing diagonals

The present paper investigates the behaviour of a connection widely used at the co-planar intersection of circular hollow sections (CI-IS), a case ver y common in X-bracings. The performance of this type of connection is valid ated by means of finite element modelling. Our connection is made up of two separate gusset plates, welded externally along the generatrices of the cy lindrical surface of a CHS tin an ear-like manner), so as to accommodate th e terminal gusset plates of the interrupted CHS: in this way the two bars i ntersect and remain on the same plane. Shell elements are used to model the CHS bar connection along several diame ters on either side of the gusset plates tears). The stiffness of the cylin drical shell that is called upon to undertake the axial force of the interr upted bar, drew our attention as it affects the structural behaviour of the X-brace well before local strength phenomena assume any importance. The ac tual result of this paper is that the stiffness of the interrupted length o f the CHS bar is significantly less than that of the continuous bar: the in terrupted bar of the X-bracing cannot develop any stresses whenever this ty pe of connection is used, as any strain applied to its end will be cumulate d in the connection zone. This effectively causes our X-brace to function w ith only one of its diagonals, i.e, the continuous one. Ending-up with a si ngle-diagonal bracing can be dangerous even in the absence of material non- linearities or large displacement effects, not to mention an earthquake sit uation. These results are also compared with a formula derived by plane str ess considerations and are found in good agreement. A total of 117 variants of this connection are examined for the purpose of this analysis and the s tiffness reduction results are presented in a schematic form. (C) 2000 Else vier Science Ltd. All rights reserved.