Prevention of disproportionate collapse of tubular construction by performance based specification of connections

摘要

This paper presents a method to calculate the required tying force requirement for connections in steel framed structures, by considering catenary action in steel beams after removal of a column. The requirement for sufficient tying force resistance is to safeguard the structure against disproportionate collapse. To enable this calculation, it is necessary to have information on the strength and stiffness of the beam-column connections when subjected to an axial tensile load in the beam. For fin plate connections to rectangular/square tubular columns, this paper will present a simple method to obtain these parameters based on results of robustness tests on fin plate connections carried out by the Building Research Establishment in the UK. This paper suggests that the tying force approach can be made to work if an internal column is removed. In this case, the calculated tying force may be considerably higher than the nominal tying force requirement specified in the current British Standards. Fortunately, this paper demonstrates that owing to a number of favourable design conditions (over-design, unused bending moment resistance of partial strength connections, reduced accidental loading, higher connection fracture resistance than the nominal tying force requirement), the connections studied in this paper would still have sufficient tying force resistance to control disproportionate collapse, perhaps explaining why it is rare to observe disproportionate collapse in steel framed buildings. Nevertheless, this paper suggests that a combination of unfavourable design conditions may increase the risk of disproportionate collapse and that connection performance plays an important part in resisting disproportionate collapse of steel framed structures. For these buildings, this paper makes a contribution to developing a sensible calculation method for checking connection tying force resistance.