30-09-2013, 01:42 AM
(This post was last modified: 30-09-2013, 04:07 AM by Tony Szamboti.)
Jeffrey Orling Wrote:Tony there are many sources for the effect of heat on the strength of steel. I am not a testing lab and did what you did... cite some source.
Regardless of the actual %, heat weakens steel... and it also caused warping, distorting, elongation, shearing bolts and failing connections. Steel does not have to melt to fail...
Mechanical damage and the effect of heat on some parts of the structure led to a progressive load distribution and eventually to the inability of the remaining columns to support the superimposed loads.
If heat from fire did not effect structural steel there would be no fire proofing requirements. The twin towers faced a double problem... mechanically caused loss of fire protection and no sprinkler to fight the fires. And this on top of mechanical destruction of core columns from the plane impacts and thousands of gallons of fuel adding to the problem.
Complete failure of steel structures with the reserve strength and redundancy of that in skyscrapers like the twin towers could not occur until it reaches very high temperatures. Heating of large pieces of steel to the point of weakening takes hours and it is proven that fires burn out in about 30 minutes in any one area in office fires. This is why there have been no steel framed high rise collapses due to fire in history. This is why the firefighters were confident and went up to fight the fires in the buildings.
There were no sprinklers in the North Tower when it had a three hour fire from the 11th to the 19th floors in 1975. How come it didn't collapse? In fact, there was very little to no distortion of the steel. How come?
The aircraft fuel that did make it into the building, and did not go up in the fireball, was burned up in minutes. The fires were nothing but standard offices fires when the buildings collapsed.
You keep going on about heating doing it, but don't seem concerned that there is no physical evidence of high steel temperatures. NIST only found three spots out of 236 pieces they got where the temperature of the steel had gotten above 250 degrees C. If people look at the chart again here they will see that steel has not lost any strength at that temperature. I am afraid you are taking things on faith, have no basis for what you are saying, and are basically just repeating what can rightly be called a propaganda soundbite as to how those buildings came down.
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The buildings were demolished and this is easy to ascertain when looking at the floors which actually collapsed first in the North Tower. It started at the 98th floor which was above the aircraft impact and the first floors after that were the 99th through the 101st. Watch this slow motion video to see how the lower part of the upper section disintegrates before anything below the initiation floor starts to collapse http://www.youtube.com/watch?v=y9-owhllM9k. The collapse of several of the lower floors of the upper section first, before anything is impacted and collapses below, could not be due to natural causes such as heating. These floors above the 98th were not even affected by fire and they could not have collapsed due to impact. This also shows why it did not decelerate.