Robustness and the Eurocodes

The topic of robustness is essentially covered by two Eurocodes, EN 1990: Eurocode: Basis of Structural Design [5] which provides the high level principles for achieving robustness and EN 1991-1-7 Eurocode 1: Part 1-7 Accidental Actions [6] which provides strategies and methods to obtain robustness and the actions to consider. The EN 1991-1-7 [6] has been completed in 2004 and recently received a positive vote by the member states. The code describes the principles and application rules for the assessment of accidental actions on buildings and bridges. The leading design principle is that local damage is acceptable, provided that it will not endanger the structure and that the overall load-bearing capacity is maintained during an appropriate length of time to allow necessary emergency measures to be taken. As measures to mitigate the risk, various strategies are proposed like prevention of actions, evacuation of persons, physical protection of the structure and sufficient structural redundancy and ductility. The code makes a clear distinction between identified and unidentified accidental actions. For the identified accidental actions (impact, explosions) a structural analysis is proposed, the level of which may depend on the envisaged consequences of failure. It may vary from an analysis on the basis of static equivalent forces to a quantitative risk analysis including nonlinear dynamic structural analysis. Also for unidentified accidental actions, the measures depend on the consequence class. In these cases, more measures that are general are proposed to ensure a sufficient robustness of the structure. Enhanced redundancy, design of special key elements and three-dimensional tying for additional integrity are recommended by EN 1991-1-7 [6]. This paper summarizes the requirements of EN 1990 and discusses the choice of events to be considered for a particular situation. The paper describes EN 1991-1-7 and provides some background information as well as design examples.