Robustness: Theoretical Framework

More frequent use of advanced types of structures with limited redundancy and serious consequences in case of failure combined with increased requirements to efficiency in design and execution followed by increased risk of human errors has made the need of requirements to robustness of structures essential. Further, the collapse of the World Trade Centre towers and a number of collapses of structural systems during the last 10 years has increased the interest in robustness. Typically modern structural design codes require that 'the consequence of damages to structures should not be disproportional to the causes of the damages'. However, despite the importance of robustness for structural design such requirements are not substantiated in more detail, nor has the engineering profession been able to agree on an interpretation of robustness which facilitates for its quantification. In this paper a theoretical and risk based framework is presented which facilitates the quantification of robustness and thus supports the formulation of pre-normative guidelines.