Originally posted by kappa
Thankyou Tilt!
Would you think the amount of steel approaching the 'plastic' zone would be the entire length of the inner core colums? Or a small area? With this twisting idea, what would you consider the possibilities of the building collapsing straight down and not rolling to the side then falling?
I have thought about this much and give a lot of credence to the idea. If this were the case, could we not expect to see a pile of floors at teh bottom? Much like (from my link) LP records stacked on a spindle? If the floors did cascade down, what of the quarter mile long center colums?? Would they not still be basically intact? Perhaps standing?
Beware when speculation is heaped upon the findings of speculation.
In essence your arguement is based upon the use of "reasonable doubt" (ie unanswered questions) when infact it is "reasonable" to use "most probable cause" from the evidence available.
However the plastic zone would only have needed to be in the initial zone of collapse to create a massive momentum.
Neither would it have all nicely spralled down like a collapsing spring or lace tube ...........whilst the forces established might have been torsional and have been applied in the form of a near continuous helical momentum the actual "plains" of shear force on local structures would have been at all odd angles as the collapsing structure twisted and buckled.
Even the basic Rankine column formulae shows this (1st year ONC mechanical engineering).
The question "why didnt it topple?" might best be looked at from the other view............. "why would it have toppled?"
Pronounced toppling suggests an out of plain force or (more likely) an out of plain resistance to force. If we return to the theorem that the whole sequence could only start with an in plain collapse of the core structure over a set of local floors then indeed we see that from this specualtion the tower was less likely to topple. It had good anti topple structure.
There are other considerations. The surrounding structural work had considerable mass. (just no structural role other than
locally supporting its own weight) This would form a sleeve withing which the core would initiate its fall. Very little (comparable) corrective force would have been required to maintain an in plain collapse in its plain.........
Again it would be more unsual to have the total structure neatly compressed into its collapsed state locally (between several floors) like your stack of LP's analogy. Indeed the rubble from the lower floors would be at the bottom of the pile and the stuff at the top of the pile would have (generally) come from nearer the top..........
I would return to the heat balance equations listed............ whilst temperature is the medium of heat transfer it should be noted that thermal capacity is what is required to cause objects to increase in temperature to a point of failure.
Hence the jet fuel would have started a fire with significant temperature and (comparibly) moderate capacity. But would not have had on its own sufficient thermal capacity towreek all the destruction to cause such massive failure. This (high temperature)would have started other fires the like of which should never be underestimated.........which would have overwhelmed conventional fire systems igniting objects usually thought to be incombustable. Generating massive thermal capacity.
I note even last year that the US considered a "flame proof/resistant polystyrene" as an acceptable fire retardent. Yet one of my custmers has just lost an entire plant due to the inferno that ensued once this material was raised to its eventual ignition temperature.
Whilst construction companies and standard agencies smudge the edges of definitions of combustable and fire retardency then there will always be a temperature at which these definitions are defeated.
The quarter mile column. We can be sure that the builders did not hoist up some god like sky hook and then winch up a series of single unit columns to stand side by side some quarter mile high.
It was constructed.The unit columns would have been no longer than the longest vehicle allowed on NY roads. 40 metres? the joints would have been bolted or rivited. Welds would have only been used to tack the columns in place prior to bolting / riviting.
In additon to this it would have been pre stressed with a multitude of "tensioned" structural members.
To refer to it as a mile high column is really (IMO) the designer trying to describe the end effect of the construction he has created.
