9/11 Free Fall 7/18/13: Dr. deHaven-Smith and "conspiracy theory"

[William Seger]

81. As usual, you attach undue significance to your own interpretation

But you don't have to accept my answer, since NIST already responded to your criticism:

31. Why didn’t NIST fully model the collapse initiation and propagation of the WTC towers?

The first objective of the NIST WTC investigation included determining why and how WTC 1 and WTC 2 collapsed following the initial impacts of the aircraft (see NIST NCSTAR 1). Determining the sequence of events leading up to collapse initiation was critical to fulfilling this objective. Once the collapse had begun, the propagation of the collapse was readily explained without the same complexity of modeling.

http://www.nist.gov/el/disasterstudies/wtc/faqs_wtctowers.cfm

The fact that you think the "how" should include every detail until the last piece of steel hit the ground does not mean that NIST is required to accept that unfeasible and unnecessary requirement to fulfill its objective. The fact that you don't believe that the collapse of the core was "readily explained" is not significant since you've made it pretty clear that structural mechanics is not a subject you're familiar with. After the collapse initiation, the "how" was thousands of individual failures, many of which were the direct result of falling debris delivering kinetic energy to the structure that is couldn't absorb. But many other failures were an indirect result of that damage, caused by the loss of structural integrity, which invalidates any theoretical load calculations that assume structural integrity. Looking at the debris, most columns were not bent; they failed by buckling at the column end splices after the floor trusses and beams were ripped away from them.

And no, this not merely my opinion. It is described in the FEMA report:

CHAPTER 2:WTC 1 and WTC 2

2.2.1.5 Progression of Collapse

Construction of WTC 1 resulted in the storage of more than 4x10¹¹ joules of potential energy over the 1,368-foot height of the structure. Of this, approximately 8x10⁹ joules of potential energy were stored in the upper part of the structure, above the impact floors, relative to the lowest point of impact. Once collapse initiated, much of this potential energy was rapidly converted into kinetic energy. As the large mass of the collapsing floors above accelerated and impacted on the floors below, it caused an immediate progressive series of floor failures, punching each in turn onto the floor below, accelerating as the sequence progressed. As the floors collapsed, this left tall freestanding portions of the exterior wall and possibly central core columns. As the unsupported height of these freestanding exterior wall elements increased, they buckled at the bolted column splice connections, and also collapsed. Perimeter walls of the building seem to have peeled off and fallen directly away from the building face, while portions of the core fell in a some what random manner. The perimeter walls broke apart at the bolted connections, allowing individual prefabricated units that formed the wall or, in some cases, large assemblies of these units to fall to the street and onto neighboring buildings below.

http://www.fema.gov/pdf/library/fema403_ch2.pdf