Recent events such as natural catastrophes or terrorism attacks have highlighted the necessity to ensure the structural integrity of buildings under exceptional events. According to Eurocodes and some different other national design codes, the structural integrity of civil engineering structures should be ensured through appropriate measures. Design requirements are proposed in some codes but are nowadays seen generally as not satisfactory. In particular, it is not demonstrated that, even if these requirements are respected, the risk of a progressive collapse of the structure subjected to an exceptional event will really be mitigated.A European RFCS project entitled "Robust structures by joint ductility" has been set up in 2004, for three years, with the aim to provide requirements and practical guidelines allowing to ensure the structural integrity of steel and composite structures under exceptional events through an appropriate robustness. In particular, one substructure test simulating the loss of a column in a composite building was performed at Liège University. The present paper describes in details this substructure test. In particular, the development of membrane forces is illustrated and their effects on the behaviour of the beam-to-column joints are discussed.

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The paper addresses the instability of large angle columns in high-strength steel subjected to compression loads. It presents a number of compression tests on such columns with different eccentricities and slenderness and the resulting different buckling failure modes observed. The experimental campaign is intended to widen our understanding of the behaviour of highstrength steel columns with large angle sections in compression and bending and so to complement previous experimental studies. The tests were accompanied by numerical analyses and calculations of the load carrying capacities based on current Eurocode 3 design recommendations. The numerical simulations were conducted using the FEM software FINELG, which takes into account the influence of geometrical and material non-linearities. The numerical and analytical results are compared with the corresponding experimental ones. The experimental campaign and the numerical simulations were conducted as part of the ANGELHY project funded by the European Commission's Research Fund for Coal and Steel (RFCS).

In this section, the work methodology adopted to reach the research objectives previously presented is detailed.