Connections of CHS concrete-filled diagonals of X-bracings

The scope of the present paper is the numerical investigation of the behaviour of concrete-filled CHS bars used as X-bracings diagonals'. The weak point for an X-brace is the point where the two diagonals intersect where, in order that the two bars remain co-planar, one of them is usually interrupted. In this case, a usual practice is to connect the interrupted bar to the continuous one by means of two gusset plates each one welded along a generatrix of the continuous bar. The result is, that the axial load is transferred as an inside-the-cross-section loading situation of the continuous bar thus causing a prohibitively excessive ovalisation of the cylindrical shell of the CHS. The in-plane transfer mechanism of the forces causes an increase of, the axial flexibility of the interrupted bar by a factor of 50-300 thus making this type of connection too flexible and therefore unsuitable for use in X-braces. Filling the tubular braces with concrete is already known as a promising technique against local buckling: the subject of the present work is the assessment the effect of this technique to the axial flexibility of the interrupted bar. From the numerical simulation point-of-view, the problem is formulated as a unilateral contact problem between the concrete in-fill and the steel shell and a parametric analysis is made to elucidate flexibility and strength aspects of this connection for the most frequently used CHS profiles. (C) 2003 Elsevier Science Ltd. All rights reserved.