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|Title: ||How did the WTC towers collapse: a new theory|
|Authors: ||Usmani, Asif|
Chung, Y. C.
Torero, Jose L
|Issue Date: ||Oct-2003|
|Citation: ||A.S., Usmani, Y. C. Chung, J. L. Torero (2003). "How did the WTC towers collapse: a new theory." (pdf) Fire Safety Journal, Volume 38, Issue 6.|
|Publisher: ||Fire Safety Journal|
|Abstract: ||This paper uses a finite element model to investigate the stability of the Twin-Towers of the World
Trade Center, New York for a number of different fire scenarios. This investigation does not take into
account the structural damage caused by the terrorist attack. However the fire scenarios included are
based upon the likely fires that could have occurred as a result of the attack. A number of different
explanations of how and why the Towers collapsed have appeared since the event. None of these
however have adequately focused on the most important issue, namely ‘what structural mechanisms
led to the state which triggered the collapse’. Also, quite predictably, there are significant and fundamental
differences in the explanations of the WTC collapses on offer so far. A complete consensus on
any detailed explanation of the definitive causes and mechanisms of the collapse of these structures
is well nigh impossible given the enormous uncertainties in key data (nature of the fires, damage to
fire protection, heat transfer to structural members and nature and extent of structural damage for
instance). There is however a consensus of sorts that the fires that burned in the structures after the
attack had a big part to play in this collapse. The question is how big? Taking this to the extreme, this
paper poses the hypothetical question, “had there been no structural damage would the structure have
survived fires of a similar magnitude”?
A robust but simple computational and theoretical analysis has been carried out to answer this question.
Robust because no gross assumptions have been made and varying important parameters over a
wide range shows consistent behaviour supporting the overall conclusions. Simple because all results
presented can be checked by any structural engineer either theoretically or using widely available
structural analysis software tools. The results are illuminating and show that the structural system
adopted for the Twin-Towers may have been unusually vulnerable to a major fire. The analysis results
show a simple but unmistakable collapse mechanism that owes as much (or more) to the geometric
thermal expansion effects as it does to the material effects of loss of strength and stiffness. The collapse
mechanism discovered is a simple stability failure directly related to the effect of heating (fire).
Additionally, the mechanism is not dependent upon failure of structural connections.|
|Keywords: ||stability of tall buildings|
Structure in fire
|Appears in Collections:||BRE Research Publications|
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