Assessment of Building Robustness against Disproportionate Collapse

This paper presents a methodology to assess the robustness of moment-resisting RC frame buildings under multiple-column-loss scenarios. In the proposed approach, kinetic and strain energy are employed as objective measures of the dynamic effects and the plastic deformations induced in buildings by the sudden loss of a bearing element, whereas a unique chord rotation is used as an explicit indicator of the global system deformation. These quantities are utilized to define a critical path index $I_{\mathrm{CP}}$ that allows identifying the areas most impacted by column loss and determining the location of the next critical column in the building. The proposed index is integrated into a systematic methodology that identifies the minimum number of columns that need to be removed to induce structural collapse. An extensive numerical investigation was conducted on three-dimensional RC buildings of varying height. Comparisons between the demand induced on the buildings by the identified critical path and random column removals confirm that the sequence identified by the proposed methodology is the one that induces the most severe demands on the structure. Correlation between the variation of the system strain energy and the activation of secondary resisting mechanisms that develop as more columns are removed also confirms the ability of taller buildings to engage larger portions of the structure in resisting progressive collapse. The proposed methodology provides an objective approach for comparing the relative robustness of buildings subjected to column losses and help advance the understanding and mitigation of disproportionate collapse.