On Sept 11th how could have buildings 1,2 & 7 fall at free fall speeds?

Question

How could one estimate how much resistance all the steel, concrete, would have been as opposed to air. Why would the buildings only fall straight down without toppeling to one side or the other? No politics or emotional answers only science please.

There have been measurements from video of just 100 meters of upper portion of the collaspe. The 911 commission reports times very near free fall speed. It is highly unlikely that the core could have been compromised by the heat from the fire. The huge steel beams were encased in concrete. The Fire from the jet fuel did not burn long enough or hot enough to melt or weaken the steel.

Answer 1

After seeing the building plans and reading some engineering journals on the building collapses, it appears that the heat damage to the central core was the cause of the collapse. There are many other theories out there, and some conspiracy theories, but as a structural engineer, I feel this is the most reasonable cause.
The structures had a perimeter shell of steel columns and an interior core of columns. The interior core of columns was weakened when fuel heated them up after the blast impact blew off much of the fire-resistant coating on the steel. The elevator shafts carried the fuel down the core of the building, thus weakening the inside. The impact of each floor falling caused forces much higher than the static weight of the building. (For this same reason, you can place a bowling ball on your foot, and it won't break your foot, but if you drop the bowling ball from 6 feet high, it will break your foot.) The steel structure could not provide even a fraction of the resistance needed because of the increased forces, and the reduced strength of the steel from being heated by the burning fuel.
As the floors above the impact zone collapsed, it started a chain reaction of collapsing structure thru the core of the building, and the floors and walls were drawn in by the failing inner structure. For this reason, there was limited structure that fell away from the buildings rather than inward.
The collapse happened rapidly since each floor was designed to carry the weight of a single story, not the weight and impact of the higher floors. Subsequent heat damage from the fires and collapse of tower 1 and 2 inflicted on the adjacent buildings caused similar failures.
See more below:
http://www.asce.org/pdf/5-1-02wtc_testimony.pdf

Answer 2

I think that once the top 20 or 30 stories of the building had fallen a story or two (at the point of failure) then nothing in the normal structure of the building would have been able to deflect or halt the fall enough to send it to one side.

I image the bottom of the falling section was getting collapsed by smashing into the lower floors. By the time it reached the bottom, the top section may already have been completely collapsed, or if not it would have occurred immediately on impact with the ground.

Your first question relates to free-fall speed. Has this been confirmed that (say) the top floor fell to the ground while accelerating at 32 ft /s /s ? I had not heard this before. It just sounds unlikely to me.

Answer 3

I'm not sur about 1 and 2 but according to demolition experts, building 7 came down in a controlled fashion. In these circumstances the building falls straight down and at free fall speeds. If a building is demolished with explosives, the most obvious thing would be to bring it down in its own foorprint to minimize damage on other structures and make the cleanup easier. I believe that if a building was hit witha large projectile and there was no other human involvement, then it would topple sideways, just because a fire or structural weakening would no be so symmetrical and even. One part of the building would be weaker and collapse or fail before the less damaged part of the building. In WWII pictures you can see gutted buildings leaning sideways...I just think that a high rise of any height would easily topple to one side or another if the one side was weaker than the other.

Answer 4

As an engineer also, I agree with the structural guy above. The floor trusses were the weak spot, and the heat caused the strength of the steel to weaken. Do yourself a favor, and read up on the analysis conducted by REAL engineers, and reviewed by REAL engineers.

It makes sense.

Answer 5

It didn't. Many did do frame by frame calculations showing it was not free fall speed. Footages do show some debris falling faster than collapse. 'Looks like free fall' is not same as actual free fall speed.

There are also group of people who firmly believe HIV doesn't cause AIDS including some scientists. Who do you believe?

Answer 6

The short answer is that they didn't, don't believe everything you read on the net.

The longer answer is F=MA. (The mass of the WTC was 5000 tons per floor)

An excellent engineering analysis can be found here:
http://www.tms.org/pubs/journals/JOM/0112/Eagar/Eagar-0112.html

Nor are the collapses unprecedented:
http://engineering.com/Library/ArticlesPage/tabid/85/articleType/ArticleView/articleId/168/LAmbiance-Plazza.aspx

Answer 7

because, my friend, it was all a conspiracy...

video images will prove that upon impact, there were evidence to support and claim that missles were fired upon and cut thru the building..

furthermore, the builing collapsed with pricise execution, like buildings in las vegas being blown up in order to make new ones ; detonators exploding floor by floor..

plus the fact that senor bush didn't even blinked when the news was whispered to him when the 9-11 crashed happened..

the illuminati has great plans....

we are not part of it

(-_-)^

Answer 8

no longer somewhat. All of this has been defined. The planes weakened various connections on impact, and after it slow, they at last failed. some flooring with weakened connections fell on right of alternative flooring, then those flooring failed, etc, etc, etc. construction structural platforms are integrally designed, and one failure (the impact) convey approximately others, which convey approximately others, etc. that is not that the concrete and glass itself replaced into "pulverized into certainly one of those wonderful airborne dirt and dirt" - homes are grimy, that's the place the airborne dirt and dirt got here from. the exterior of homes even have lots of airborne dirt and dirt on them from climate (such as whilst your motor vehicle seems somewhat sparkling, yet continues to be grimy in case you run your finger over it). to no longer point out the easily airborne dirt and dirt interior the construction. airborne dirt and dirt on unclean flooring, in carpet, decrease than desks, in HVAC vents and filters, etc.

Answer 9

easy, because bush and his whole admin knocked it down.