Improving the accuracy of progressive collapse risk assessment: Efficiency and contribution of supplementary progressive collapse resisting mechanisms

This paper investigates the structural response of RC framed buildings subjected to accidental/abnormal loads (explosion, impact and other hazards). Several existing national or international design codes (GSA 2003, DoD 2009, 2013) 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 the structural components undergo nonlinear deformations before failure. In this study the nonlinear procedures (NSA and NDA) are applied. These types of analyses imply significant computational power and time costs. In addition, the reinforced concrete framed structures are able to develop multiple post flexural resisting mechanisms. These are currently not considered in the structural analyses performed according to GSA2003 and DoD2009 provisions. Thus, the first objective of this paper is to identify by numerical computation the presence and contributions of such supplementary resisting mechanisms. A further objective is to determine what will be the influence on the accuracy of results when, starting from the original structure, the number of its bays is successively reduced; also, what is the efficiency in saving run-time costs when such simplified models are considered in the analysis. The study reveals that in order to resist abnormal loads, RC structures are able to develop supplementary resisting mechanisms beyond the flexural behavior and respectively, important time savings are obtained without significantly affecting the results accuracy.