Progressive collapse resistance of a building collapsed during structural retrofitting

Progressive collapse is a special type of structural collapse that is caused by the propagation of a localized damage throughout several components of the structure. This collapse phenomenon is of particular interest when there is a disproportion in size between the initial and final states of structural damage. In that case, the failure of the structural system is more exactly referred to as disproportionate collapse, whereas the capability of preventing this type of collapse is termed structural robustness. Eurocodes together with other advanced codes and guidelines provide design rules to mitigate the risk of disproportionate collapse under extreme loads, including human actions. The latter frequently consist of wrong operations during construction, use or retrofitting. In this study, the progressive collapse resistance of a reinforced concrete building designed only to gravity loads and collapsed during structural retrofitting is evaluated. Retrofitting works included the concrete cover removal from a number of columns at the ground floor. The reduction in gravity load capacity caused by that type of structural retrofitting is assessed through pushdown analysis with displacement control. Two alternative capacity models of the building are considered to investigate their computational efficiency in progressive collapse analysis.