Computer-Aided Assessment of Progressive Collapse of Reinforced Concrete Structures according to GSA Code Huda Helmy 1 ; Hamed Salem 2 ; and Sherif Mourad 3 Abstract: 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 struc- tures 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 con- sider 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 guide- lines met the GSA limits and were found to have a low potential for progressive collapse. DOI: 10.1061/(ASCE)CF.1943-5509.0000350. © 2013 American Society of Civil Engineers. CE Database subject headings: Structural failures; Progressive collapse; Concrete structures; Computer applications; Assessment. Author keywords: Progressive collapse; GSA; ELS; AEM; Slabs; Membrane action; Collapsed area; Rotation limits. Introduction Several structural progressive collapses have taken place in the last few decades. For example, in 1968 the collapse of the Ronan building in East London took place because of a gas explosion on the 18th floor. In 1995, the Murrah Federal Office Building in Okla- homa City collapsed because of a terrorist bomb explosion at the ground floor. In 2001, the famous World Trade Center, New York, collapsed because of planes impacting the upper levels of the tower (Shankar 2004). The status of RC structures regarding their vul- nerability to progressive collapse has become an important question. In the current study, a progressive collapse assessment of a typical ten-story RC structure was carried out according to the GSA code. The structure was designed according to ACI 318-08 [American Concrete Institute (ACI) 2008]. Fully nonlinear dynamic analysis for the structure after removal of a primary vertical element is carried out using the applied-element method (AEM) (Meguro and Tagel-Din 2000, 2001; Tagel-Din and Meguro 2000a, b). The AEM is based on the discrete crack approach and is capable of following the struc- ture’s behavior to its total collapse. Objective The objective of this study is to evaluate the resistance of RC structures, designed according to ACI 318-08, to progressive col- lapse initiated by the loss of a primary vertical support. General Services Administration Code The General Services Administration (GSA) (2003) is an inde- pendent agency of the U.S. government, established in 1949 to help manage and support the basic functioning of federal agencies. The GSA limits were set to reduce the potential for progressive collapse in new federal office buildings, assess the potential for progressive collapse in existing federal office buildings, and develop potential upgrades to facilities if required. The loading combination according to the GSA code depends on the analysis type. For a static analysis, the load combination is 2 3 ðDL 1 0:25LLÞ, where DL is the dead load and LL is the live load. For a dynamic analysis, the load combination is DL 1 0:25LL. The analysis specified by the GSA assumes a sudden removal of a primary support like columns or walls. For a framed or flat plate structure, the removed column has different locations depending on the structural system as shown in Fig. 1. For a shear or load-bearing wall structure, the removed wall has different locations depending on the structure system as shown in 1 Senior Structural Engineer, Egypt Branch, Applied Science Interna- tional, 103 Almen St., Agoza, Giza, Egypt (corresponding author). E-mail: eng_hudahelmy@hotmail.com 2 Associate Professor, Dept. of Structural Engineering, Cairo Univ., Giza, Egypt. 3 Professor, Dept. of Structural Engineering, Cairo Univ., Giza, Egypt. Note. This manuscript was submitted on September 3, 2011; approved on April 3, 2012; published online on April 10, 2012. Discussion period open until March 1, 2014; separate discussions must be submitted for individual papers. This paper is part of the Journal of Performance of Constructed Facilities, Vol. 27, No. 5, October 1, 2013. ©ASCE, ISSN 0887-3828/2013/5-529–539/$25.00. JOURNAL OF PERFORMANCE OF CONSTRUCTED FACILITIES © ASCE / SEPTEMBER/OCTOBER 2013 / 529