Keywords: progressive collapse, nonlinear, dynamic, accuracy, collapse resisting mechanisms..

This paper describes an investigation into the structural response of reinforced framed buildings subjected to accidental or abnormal loads (e.g. explosion, impact and other hazards). Several existing national or international design codes provide limited guidelines for the assessment of progressive collapse resistance in the design process and the alternate load path method is widely used in current structural design codes. Since the progressive collapse is a dynamic and nonlinear event as it takes place in a very short time frame and the structural components undergo nonlinear deformations before failure, in this study nonlinear dynamic analysis is used. As it is known, nonlinear dynamic analysis implies significant computational power and time costs. Thus, the first objective of this paper is to determine the influence on the accuracy of results when the number of structural bays is successively reduced and the efficiency saving in run-time costs when simplified sub-structures are considered. In order to resist abnormal loads, the structures should be able to develop resistance mechanisms beyond the flexural behavior. The second objective of this paper is to numerically identify the presence and contributions of such supplementary resisting mechanisms. Important time savings, without affecting the results accuracy, are obtained and compressive arch action supplementary resisting mechanism is identified.

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