A building is subjected to progressive collapse when a primary vertical structural element fails, resulting in the failure of adjoining structural elements, which cause further structural failure, leading eventually to partial or total collapse of the structure. The failure of a primary vertical support might occur because of extreme loadings such as a bomb explosion in a terrorist attack, a car colliding with supports in a parking garage, an accidental explosion of explosive materials, or a severe earthquake.
Different design codes address the progressive collapse of structures attributable to the sudden loss of a main vertical support such as the General Services Administration (GSA) code and the Unified Facilities Criteria (UFC). The alternative path method (APM) is the main analysis method for evaluating the hazard of progressive collapse in the two codes. The APM requires that the structure be capable of bridging over a missing structural element, with the resulting extent of damage being localized. In the current study, a progressive collapse assessment according to the GSA code is carried out for a typical ten-story RC-framed structure. The structure is designed according to the building code requirements for structural concrete. Fully nonlinear dynamic analysis for the structure is carried out using the applied-element method (AEM). According to the GSA code, a primary vertical structural element is removed, and the collapse area is investigated.
The investigated cases include the removal of a corner column, an edge column, an edge shear wall, internal columns, an internal shear wall, and a corner shear wall. The numerical analysis showed that, for an economic design, the analysis should consider slabs and cannot be simplified into a two- or three-dimensional frame analysis. Neglecting the slabs in the progressive collapse analysis is a very conservative approach that may lead to uneconomic design. The RC structures designed according to American Concrete Institute guidelines met the GSA limits and were found to have a low potential for progressive collapse.
Helmy, H., Salem, H., and Mourad, S.. J. Perform. Constr. Facil., Volume 27, Issue 5, 529–539, October 2013. American Society of Civil Engineers, ISSN (print): 0887-3828, ISSN (online): 1943-5509