WTC Towers Core Columns - What Held Them Together? Welds.

Mick West

Administrator
Staff member

Jeffrey Orling

Senior Member
Thanks Mick... Not uninteresting nor unexpected... especially avoiding truthers... who seem to be science/engineering deniers. What I never hear discussed is how the DNA of the structures... the structural design concepts of these buildlings determined how they would collapse based on where they were suffering damage... mechanical and heat. Both designs were atypical or had important atypical elements... ie they were not the stand lattice grid frames.
 

deirdre

Senior Member.
What I never hear discussed is how the DNA of the structures... the structural design concepts of these buildlings determined how they would collapse based on where they were suffering damage

isn't that what you don't want to reveal to future terrorists? or am I misunderstanding your comment?
 

Jeffrey Orling

Senior Member
isn't that what you don't want to reveal to future terrorists? or am I misunderstanding your comment?

Perhaps you misunderstand my point.

First it's very very very unlikely that a terrorist group could rig a high rise tower in the USA for demolition. Way way way too much prep and it would virtually impossible to do something like this without being noticed and caught. Placing a single bomb is possible perhaps but will not take a large building down.

What I did try to get at is that the structural design determines how it collapses... especially when gravity is the driver.

So... in the case of the twin towers they collapsed because:

the floors slabs went runaway and once the collapse of the floors began high in the building... all the slabs below would collapse. This is because of the DESIGN.... long span column free with light weight slanbs and bar truss joists.

The facade could not stand without the bracing from the floor plates. When the plates self destructed... the facade peeled away because it could not stand without the floor plates.

The core might be able to stand if all the steel bracing was intact. But with much of the bracing destroyed the columns were too unstable and self buckled. The core was mostly shafts... and some heavy floors. But lhose floors were subject to the same type of failure as the plates outside the core.

++++

7wtc had a form of collapse more like a typical demolition where columns low down (beginning at floor one or in basement) are destroyed. Mass above loses support and collapse down. Usually the sequence is to destroy the center before the perimeter so the mass collapsed into the center.
 

econ41

Senior Member
isn't that what you don't want to reveal to future terrorists?
Jeffrey has clarified his intention and explained the relevant features of Tim Towers collapses.

The features of design that dominated the collapse mechanism were common knowledge - not the sort of info you could keep from terrorists and not the sort of detailed data that NIST withheld on the basis of denying terrorist access.

Jeffrey misses the key feature of WTC 7 design that dominated the visual appearance of collapse. WTC 7 appeared very "CD Like" as the perimeter shell fell as a still intact entity after the core collapses inside the building. That was the consequence of the design having a very strong "moment frame" in the perimeter. In effect a reinforced belt around the perimeter holding it together.
 

Jeffrey Orling

Senior Member
Jeffrey misses the key feature of WTC 7 design that dominated the visual appearance of collapse. WTC 7 appeared very "CD Like" as the perimeter shell fell as a still intact entity after the core collapses inside the building. That was the consequence of the design having a very strong "moment frame" in the perimeter. In effect a reinforced belt around the perimeter holding it together.

Both the twin towers and 7wtc had strong "structural" perimeters. The key design feature of 7wtc were the massive load transfers needed to build a 40 story tower over the Con Ed substation. The moment frame has 57 columns above floors 5-7 where the massive transfers were.. and only 26 columns below floors 5-7. The moment frame was essentially supported on a 2 multistory belt truss... another transfer structure to move the 57 axial loads above to the 26 columns below. In addition the plan was a trapezoid shape and like the twins did not have a column grid but was a hull and core design.
 
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