مدل سازی و زمان حذف ستون در خرابی پیش رونده ساختمان
Abstract
1- Introduction
2- Description of model
3- Progressive collapse principles
4- Effect of sudden column loss
5- Assessment of techniques
6- Summary
7- Conclusions and recommendations
References
Abstract
Over the last few decades, progressive collapse disasters have drawn the attention of codified bodies around the globe; as a consequence, there has been a renewed research interest. Structural engineering systems are prone to progressive collapse when subjected to abnormal loads beyond the ultimate capacity of critical structural members. Sudden loss of critical structural member(s) triggers failure mechanisms which may result in a total or partial collapse of the structure proportionate or disproportionate to the triggering event. Currently, researchers adopt different modelling techniques to simulate the loss of critical load bearing members for progressive collapse assessment. GSA guidelines recommend a column removal time less than a tenth of the period of the structure in the vertical vibration mode. Consequently, this recommendation allows a wide range of column removal time which produces inconsistent results satisfying GSA recommendation. A choice of a load time history function assumed for gravity and the internal column force interaction affects the response of the structure. This paper compares different alternative numerical approaches to simulate the sudden column removal in frame buildings and to investigate the effect of rising time on the structural response.
Introduction
Abnormal loads such as extreme temperature, explosions, earthquake, detonations, and impact constitute extreme events on building structures. Evaluation of progressive collapse focusing on these specific abnormal loads is relatively efficient as compared to situations where the abnormal loads are uncertain. International codes and specifications such as General Service Administration [1], Department of Defence [2], and Eurocode 1 (CEN [3]) recommend prescriptive strategies for limiting progressive collapse. However, none of these guidelines defines an explicit and simplified numerical performance-based approach for the evaluation of progressive collapse. Though, sudden column removal is recommended in design guidelines without stating the steps on how to achieve it considering different modelling software. Consequently, various researchers adopt different methods and approaches in assessing building structures for progressive collapse. It is important to note that research-based conclusions and recommendations are a function of the assumptions primarily used in modelling the sudden loss of critical structural elements (e.g. key element removal). The interest in progressive collapse can be traced back to 1968 due to the partial collapse of the residential apartment building located in London called Ronan Point; other occurrences include the collapse of Alfred Murrah building in the USA in 1995 and the total collapse of World Trade Centre building in the USA in 2001 [4–6]. In view of these significant events, a series of design guidelines was developed each of which were followed by extensive research investigations. Different methods of modelling the sudden column loss exist in current literature, while the results obtained depend on the modelling technique adopted. Further reviews on code provisions, comparison of standards, merits, and demerits of analysis methods for progressive collapse assessment are available [7–9]. As a result, there are uncertainties associated with the design to resist progressive collapse. Undoubtedly, one of the major challenges is the inability to predict the nature and magnitude of unforeseen events to which the structure may be subjected to during its design life.