Structural safety in case of extreme actions

The behaviour of buildings and other constructions under critical events is widely recognised to be an important part of structural design. Still, the problem is often addressed in a qualitative way by many current codes and regulations and designers cannot refer to specific methodologies for the assessment or the achievement of the structural integrity of constructions. The term structural integrity is intended here as the ability of the structure to sustain extreme actions that directly affects its system without developing a major collapse. In this paper two main methods are outlined for the achievement of structural integrity: a bottom up approach, where the effects of failures of elements are investigated, disregarding the modelling of the specific action that could have triggered them; and a top-down approach, where the response of the structure to a particular accidental action is sought. The use of the first approach is proposed for assessing, by means of a set of nonlinear static analyses, the robustness of structural systems, intended as the ability of a structure to sustain local failure (Starossek, 2009) without developing a major collapse.