Progressive Collapse: Comparison of Main Standards, Formulation and Validation of New Computational Procedures

Throughout recent history, famous records of building failures may be found, unfortunately accompanied by great human loss and major economic consequences. One of the mechanisms of failure is referred to as ‘progressive collapse’: one or several structural members suddenly fail, whatever the cause (accident or attack). The building then collapses progressively, every load redistribution causing the failure of other structural elements, until the complete failure of the building or of a major part of it. The civil engineering community’s attention to this type of event was first drawn by the progressive collapse of the building called Ronan Point, following a gas explosion in one of the last floors. Different simplified procedures for simulating the effects of progressive collapse can now be found in the literature, some of them described in detail. However, no extensive study can be found, in which these procedures are compared to more complete approaches for progressive collapse simulation, aiming at the comparison of the assumptions underlying them. To further contribute to the elaboration of design codes for progressive collapse, such a study would therefore be of great interest for practitioners.All parties involved with the subject of progressive collapse are currently attempting to bridge the gap between the work done on the research front on the one hand, what can be considered as a fitting numerical model for regular industrial use on the other, and finally, the normalisation committees. The present research work aims at providing insight as to how the gaps between these poles may be reduced. The approach consists in studying the various hypotheses one by one, and gradually adding complexities to the numerical model, if they prove to be warranted by the need for sufficient accuracy. One of the contributions of the present work stems from this approach, in that it provides insight regarding the validity of the various simplifying assumptions. It also leads to the development of procedures which are kept as simple as possible, in an attempt to design them as best as possible for regular industrial use.The objective of simplifying assumptions validation is pursued in Chapter 2. This chapter consists of the text of a paper entitled “Comparison and study of different progressive collapse simulation techniques for RC structures”, in which the main simplifying assumptions of the progressive collapse guidelines are detailed and assessed. The DoD [1] and GSA [2] static linear and non-linear procedures are investigated, and compared to more complete approaches in order to assess their validity.In the next two chapters, two new procedures for design against progressive collapse are developed. They are based on quasi-static computations, their main objective being to account accurately for dynamic inertial effects. The first of these chapters consists in the text of a paper entitled “A new pushover analysis procedure for structural progressive collapse based on a kinetic energy criterion”, in which energetic considerations allow for the development of a static equivalent pushover procedure. The second chapter consists of the text of a paper entitled “A new pushover analysis procedure for structural progressive collapse based on optimised load amplification factors”, which uses load amplification factors resulting from optimisation procedures in order to account for dynamic inertial effects. The contributions of these two papers lie in the fact that they offer an improved accuracy on the results, when compared with other procedure available in the literature, which follow the same general principles. The two proposed procedures are thoroughly validated by systematic comparisons with results obtained with the more costly dynamic non-linear computations.Finally, an additional chapter focuses on the various approaches that can be adopted for the simulation of reinforced concrete beams and columns. Because a rather simple model for reinforced concrete is used in Chapter 2, the bulk of this chapter consists in the implementation of a more complex fibre-based non-linear beam element. Comparisons performed with this model provide insight to the limitations of the simpler model, which is based on the use of lumped plastic hinges, but show this simpler model to be valid for the purposes of the present work.