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iSERVEaJEW -> NIST verson of collapse of WTC1 not reasonable. (4/11/2008 11:41:10 PM)
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In the paper, "Momentum Transfer Analysis of the Collapse of the Upper Storeys of WTC 1", Gordon Ross examines whether the energy delivered from the top 16 floors of WTC1 (North tower) would be enough to collapse the floors beneath it when it fell. He determines that there would not have been enough energy delivered to continue the collapse of WTC1. Here is his conclusion:
quote:
The energy balance of the collapse moves into deficit during the plastic shortening phase of the first impacted columns showing that there would be insufficient energy available from the released potential energy of the upper section to satisfy all of the energy demands of the collision. The analysis shows that despite the assumptions made in favour of collapse continuation, vertical movement of the falling section would be arrested prior to completion of the 3% shortening phase of the impacted columns, and within 0.02 seconds after impact.
A collapse driven only by gravity would not continue to progress beyond that point. The analysis shows that the energies expended during the time period of the plastic shortening of the first storey height of the vertical columns is sufficient to exhaust the energy of the falling section and thereby arrest collapse. This however is not the full extent of the plastic strain energy demand which exists. The next immediate task for the falling mass to continue in its descent would be the plastic shortening within the remainder of the buckle length. As has already been stated a buckling failure mode has a minimum length over which it can act and in the case of the towers would be several storey lengths. Each additional storey length involved in the buckle would add a further demand of about 450 MJ for a further downward movement of 0.111 metres. This also shows that collapse arrest is not dependent upon an expenditure of energy in concrete pulverisation, since even if this expenditure were disregarded the input energy would be exhausted during plastic shortening of the second storeys affected.
The analysis can be extrapolated to show that the energy expended within the plastic shortening phase of a six storey buckle would ensure that a fall by the upper section through two storeys under full gravitational acceleration would also be resisted at an early stage. A similar response would be elicited from an opposed three or more storey drop delivering the same levels of energy at impact. It can be further envisaged that a collapse initiated by a fall through a greater number of storeys, would be either arrested or significantly and noticably slowed when regard is taken for energy demands both in the fall by the upper section, and by inclusion of demands identified but not quantified in this article. It should also be noted that this analysis examines only the energy levels required up to a point in time during the plastic shortening phase. Energy demands which involve further phases of the collapse mechanism, such as buckling of beams and disassociation of end connections, spandrel plates and floor connections are further massive energy demands which must then be satisfied.
Ross, G. (2006, June). Momentum Transfer Analysis of the Collapse of the Upper Storeys of WTC 1. Journal of 9/11 Studies, pp. 36-37.
Does anyone want to discuss this paper? I think that it is really interesting to see that the WTC1 would have been able to withstand the force from the top 16 floors falling. I welcome any sincere comments or questions.
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