Robustness of building frames further to a column loss - Substructure approach with account of dynamic effects

Nowadays, it is a concern to mitigate the risk of progressive collapse of a whole structure further to exceptional events such as explosions, impacts, fire... Different general approaches are proposed in the Eurocodes and some other national design codes to ensure the robustness of structures, although very few practical guidelines are provided. In the present study, the so-called “alternative load path method” is followed and the conventional scenario “loss of a column” is considered.
Investigations were conducted at the University of Liège in the last few years regarding the static behaviour of two-dimensional building frames suffering the loss of a column further to an unspecified accidental event. They resulted in the development of simplified analytical methods for the prediction of the structural response assuming a static behaviour. In particular, it was shown that a substructure composed of the double-beam overhanging directly the lost column and its beam-to-column joints is able to reproduce the response of a 2D frame when membrane forces develop in the beams after the formation of the global beam plastic mechanism induced by the column loss.
The dynamic behaviour of such a substructure was more recently investigated. As a result, a simplified approach was developed for the prediction of the maximal displacement of the system and subsequently the internal forces developing in the substructure, permitting the definition of ductility and resistance requirements for robustness.
In the present paper, the whole analytical procedure is applied to a particular substructure. First, the static response is determined. Then the proposed model is used to predict the dynamic behaviour of the substructure as a function of the load initially supported by the failing column and the duration of its removal. In this paper, analytical approaches developed at the University of Liège are applied to predict the response of the considered substructure and the results are compared to numerical simulations; but the development of these methods and the observed phenomena are not detailed.