The need to address catastrophic collapse of buildings has prompted research communities into preemptive studies. A notable disastrous collapse is that of the World Trade Center. Such collapses are fueled by progressive collapse, where failure of primary elements spread from element to element resulting in collapse of the entire structure or a significant part of it. Over the last decade, voluminous literature on the progressive collapse analysis of structures in a bid to avert the disastrous consequences of such a system-level problem were generated. A great deal of this work concentrated on the quantification of resisting mechanisms such as the compressive arching action using two dimensional frameworks. Additionally, 3D studies were also presented but a majority of these studies were limited to considering the initial damage as instantaneous removal of one or simultaneous removal of multiple supporting elements.
A recent paper published in the journal, Engineering Structures, set out to demonstrate the 3D nonlinear dynamic response of reinforced concrete structures subjected to sequential column removal scenarios. Amir Hossein Arshian and Guido Morgenthal from the Institute of Modelling and Simulation of Structures at Bauhaus University in Germany intended to shed light on the influence of the removal sequence on the 3D force redistribution of the gravity loads assuming an extreme initial damage, which has been given a wide berth by scholars in the recent past. In their work, a novel sequential time-history analysis algorithm using macro modeling approaches is proposed.
First, their empirical procedure entailed the utilization of the sequential time-history analysis algorithm mentioned above, to predict the dynamic redistribution of the gravity loads. The researchers then verified the efficiency of the numerical framework through comparison of computational results. They then applied a practical strengthening technique into the computational model of the structural system so as to artificially activate the catenary mechanism. Eventually, the two researchers investigated the influence of the removal sequence on the 3D force redistribution mechanism.
The authors of this paper observed a good agreement for both the global and local response qualities during verification of the efficiency of the numerical framework. More so, analysis results showed that strengthening of peripheral beams with externally bonded steel plates significantly increased the rotational ductility at beam-sections and in turn, enabled the damaged structure to accommodate larger deformations. In totality, it was found that permanent plastic deformations and maximum sectional forces of a sequential removal scenario were larger on average when compared with those obtained from an at-once removal scenario.
The results of their study provide crucial insight on the influence of the removal sequence on the 3D force redistribution of the gravity loads when assuming an extreme initial damage. Moreover, the efficiency of the applied numerical framework has been verified for the global as well as for the local response quantities considering the entire range of the structural behavior from the elastic to the extreme plastic state, where the structure is identified as prone to collapse. Therefore, the outcomes of Arshian and Morgenthal study are impressive and shall not be neglected in evaluating the collapse resistance of a given structural system subjected to an extreme initial damage.
Amir Hossein Arshian, Guido Morgenthal. Three-dimensional progressive collapse analysis of reinforced concrete frame structures subjected to sequential column removal. Engineering Structures volume 132 (2017) pages 87–97
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