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PREVENTING PROGRESSIVE COLLAPSE OF MULTI-STORY BUILDINGS Yahia Tokal Civil Engineering Seminar, Lawrence Technological University, Southfield, Michigan Analysis Methods Abstract The progressive collapse of the World Trade Center towers has generated a worldwide concern of the risks of progressive collapse in multi-story buildings. The prevention of progressive collapse lies primary in the proper and effective analysis of the structures having high potential to progressivity. Different analysis methods are presented herein such as linear elastic static, non-linear static, linear elastic dynamic, and non-linear dynamic analysis. To minimize the progressive collapse risks, The structural system of the building should be able to tolerate the removal of one or more structural members and redistribute their load on the surrounding members, so that disproportionate collapse would not take place. Linear Elastic Static Analysis . • Analysis is done based on the static removal of a major structural element. • This method is approximate, and hence, design loads are conservative. • The main advantages of this method lie in its simplicity. Non-Linear Static Analysis • The main advantages of this method is that it accounts for the non-linear behavior of the members. • The ductility of the structure can be evaluated using this non-linear approach. Non-Linear Dynamic Analysis • This is the most accurate method to express the behavior of the structure following the removal of one or more structural elements. • This method is more realistic as it accounts for the ductility, yielding, cracking, and damping • It is very complicated and time consuming. Progressive Failure of Multi-story Building Proper Design against Progressive Collapse (Rittenhouse, and Smilowitz, , 2004) Progressive Collapse Chain Reaction Phenomenon (9-11 Review, 2003) Introduction Prevention of Progressive Collapse • Progressive collapse occurs when local failure of primary structural element leads to a chain reaction of structural element failures, and resulting in the collapse of all or disproportionately large part of the structure. • The total prevention of progressive collapse may not be feasible as it is uneconomic. Yet, proper designing and detailing can significantly reduce its possibility. • The interest in progressive collapse can be tracked back to the collapse of the 22-story Ronan Point apartment building in England 1968, when a gas explosion in the 18th floor caused the floors above to collapse. • The alternate load path method focuses on providing a redundant load path following the loss of an individual structural member, so that a disproportionate collapse will not take place. • Integrity, continuity, and energy-dissipating capacity in the structural members are essential to transfer the loads from the locally damaged region to adjacent regions capable of sustaining these additional loads without collapse. (a) Ordinary Design (b) Alternate Load Path Design Behavior of Beam after removal of the Middle Column: Alternate Load Path Design (Baldridge and Humay, 2003) The weight and impact of the collapsed upper floors caused a series of progressive failures of the corner bay of the building, which collapsed from top to bottom all the way to the ground. Conclusion • The analysis of multi-story buildings subjected to progressive collapse can be preliminary started using a simple method such as the linear elastic static method. If further analysis is necessary, more advanced analysis approaches can be used such as the non-linear elastic static and the non-linear dynamic analyses (Marjanishvili, 2004). • The size, shape, and importance of the building are the major factors used to determine the most suitable analysis approach for each building • To prevent progressive collapse, the structural system of the building should be able to tolerate the removal of one or more structural members and redistribute their load on the surrounding members, so that disproportionate collapse would not take place Progressive Collapse of the Ronan Point apartment building in England 1968 (Shankar, 2004) References • Rittenhouse, T. and Smilowitz, R., (2004). “Building Protection on Main Street, USA”, Design-Build Dateline • Burns, J., Abruzzo, J., Tamaro, M. (2003). “Structural System for Progressive Collapse Prevention” • GSA (2003), “Progressive Collapse Analysis and Design Guideline for New Federal Office Buildings and Major Modernization Projects” General Service Administration, Washington, D.C. • Marjanishvili, S. M., (2004). “Progressive Analysis Procedure for Progressive Collapse”, Journal of Performance of Constructed Facilities-ASCE, May, pp. 79-85. • Shankar, R., (2004). “Progressive Collapse Basics”, Modern Steel Construction, pp. 37-41. • Baldridge and Humay (2003) “Preventing Progressive Collapse in Concrete Buildings” • 9-11 Review website (2003) “www.911review.com”