9/11 was an inside job

[Russ_Watters]

The basic problem that causes these "it didn't fall right" conspiracy theories is that people have a wrong intuitive understanding of structural engineering. They think buildings should fall over like tilted broomsticks or masonry chimneys. The reality that engineers learn in Statics 101 is that if a column isn't perfectly vertical, it loses strength very very quickly; something like half of its strength for 1 degree of tilt. So a tall building is just nowhere close to strong enough to topple over instead of collapsing.

The second reality that most lay-people don't understand is fracture energy. Strong steel is more brittle than people realize, which means that while it takes an extremely high force to break, it only absorbs a little bit of energy in doing so, which means that it provides very little resistance to the collapse once the collapse starts.

[Grumpy]

leopold

as a matter of fact it's possible that ALL buildings of this design are inherently unsafe from a catastrophic point of view.

Interestingly enough, both buildings greatly exceeded the fire safety standards in their performance. The scenario of aircraft impact that was briefly considered(but never was a design goal and no calculations were done)was an airliner(707 in this case)at approach speed(~250)lost in fog or something and it's fuel load was never given a thought(it was mostly publicity hype). The fire standards were that the building would survive a single floor fire(IE a typical large office fire)for one hour with no structural failue, they designed for two. Those buildings were actually pretty tough and would probably still be standing if the steel had been fireproofed with sturdy materials(I mean, come on. Fireproof foam block and spray on?). Most of the people in those buildings could have survived except for bad luck(the cut stairwells), bad advice(PA announcement sent many in Tower 2 back up after Tower 1 was hit, causing chaos and hundreds more deaths)and a crap load of highly flammable jet fuel starting multi-floor fires. They tried explosives back in 93 and aside from a big hole in the basement the buildings barely wiggled.

Grumpy

[Grumpy]

Russ_Watters

The basic problem that causes these "it didn't fall right" conspiracy theories is that people have a wrong intuitive understanding of structural engineering. They think buildings should fall over like tilted broomsticks or masonry chimneys. The reality that engineers learn in Statics 101 is that if a column isn't perfectly vertical, it loses strength very very quickly; something like half of its strength for 1 degree of tilt. So a tall building is just nowhere close to strong enough to topple over instead of collapsing.

It is my understanding that the core columns in the Towers could take up to 7 degrees of movement from vertical(normally only seeing a degree or so in anything short of a hurricane)before failure. The CORE could probably take less if unsupported, but the wind forces were all absorbed by the outer perimeter and the core saw only vertical forces. The floor trusses didn't support the core columns, but they did stabilize them in the vertical position.

The second reality that most lay-people don't understand is fracture energy. Strong steel is more brittle than people realize, which means that while it takes an extremely high force to break, it only absorbs a little bit of energy in doing so, which means that it provides very little resistance to the collapse once the collapse starts.

I keep trying to tell everyone that the secret of an accurate model of the Twin Towers that will fit in your basement is angel hair pasta, but they just look at me funny and back away. You could even model heat softening with a spray bottle of water. Of course, training the spiders to put in the floor webs is the tricky part. Card stock would make good equipment floors.

Grumpy

[psikeyhackr]

The basic problem that causes these "it didn't fall right" conspiracy theories is that people have a wrong intuitive understanding of structural engineering. They think buildings should fall over like tilted broomsticks or masonry chimneys.

Care to locate a 1360 foot chimney?

psik

[psikeyhackr]

This has a bit of information on the south tower:

http://www.sharpprintinginc.com/911/...sition=621:621

psik