"1. Having a fire in a skyscraper created by and electrical fault or a stray cigarette in a rubbish bin may be a completely different scenario to one started by a 200 tonne jet loaded with jet-fuel crashing into the structure at 500 kms/hour. Don't you think?."
The maximum burning temp for avgas in those conditions is not hot enough and would not burn long enough to weaken the steel.
But lets say for argument sake that the steel was weakened on the floors above and below the impact zone.
How much head would have to be generated to weaken the structural steel columns all the way to the basement?
An extraordinary amount of heat energy, and impossible from avgas.
If the steel weakened(which is a huge stretch in itself) you would see lets say the top third of the building fall in a different way to the lower 2/3rds because the steel on the lower levels would not be affected in the same way.
This would make a lot more sense and be more believable to me.
I am happy to talk about the twin towers but lets stick to the WT7 for now, that had no plane hitting it, the only way it could collapse is explosives to disintegrate the structure, fire cannot reduce a skyscraper to rubble, in particular a fire that has not covered all floors of the building. In the history of skyscrapers a fire has not caused a collapse of a building in such a way except on 9/11.
Structural steel bends when placed under extreme stress, it does not disintegrate, and the building would definitely not fall that fast, it would twist and not be such a clean pile of rubble, that goes for all 3 of the buildings.
This is the whole point of having concrete and steel in skyscrapers, so buildings don't collapse upon themselves.
Do you know how difficult it is to demolish a building in such a controlled way?
You need explosive charges in all the key structural supports, and to be delayed perfectly.
Even when there are teams of experts working for weeks on demolishing an empty old building, if a few of the explosive delay calculations are out, the building drops to the side, so how is it that a random event such as a plane hitting a tower can produce such a perfect result?
The answer is it cant if you know how hard it is to bring down a building of that size and have minimal impact on the surrounding buildings.
Demolition is about safety and increasing safety due to the predictability of the falling building which is precisely and scientifically mapped out by numerous experienced professionals.
The odds a plane hitting one building and producing that kind of result is pretty much impossible, let alone reproducing this impossible result 3 times in one day!
2. WT7 was hit by massive chunks of concrete and steel from a falling skyscraper, had fires break out with no water to fight them and the main area of damage was supporting 40 stories of weight in a now completely unstable manner. Think there's a chance these factors might have destabilized the structure somewhat?
No, skyscrapers of the WT7 calibre are designed and over engineered, this is why fires have not been responsible for collapses, there was one example, I think it was in Brazil where from memory a building burn uncontrollably for almost 24hrs, the steel structure remained intact. There have been many serious fires in skyscrapers over the years, and none have lead to collapse.
