Where and what were you doing on 9/11/2001?

[CJ_London]

Reminds me of the guy who worked in a building yard. Every evening he left with his lunch box, tools and work clothes in a wheel barrow. Security regularly checked and verified all this stuff was his.

Turned out he was stealing wheel barrows

 

[moke123]

OK, you KNOW it has to be asked... what did he do with a stolen bulldozer?

He pushed stuff around at ground zero for a while and then left it there. Things were a little chaotic so I don't think anyone was really looking for it.

BTW, He had never driven one before either.

 

[ColinEssex]

I've no idea. There's two things to this.
1) where were you when it was happening?
2) when did you hear about it?

Most American incidents happen at (UK) night time. So what day was it? And what time (UK) did it happen? To be honest, I don't remember. I suspect it made the papers here next day. I don't usually watch the TV news - too miserable.
Col

 

[The_Doc_Man]

As to "when" - The terrorist attack happened starting at 08:46 Eastern Daylight Savings (USA) Time zone on Tuesday, Sept. 11, 2001. USA Eastern Daylight Savings time zone is 4 hours after Greenwich mean time, so that means it would have been just after Noon, London time (if I did that right.) It was televised as a network news event. We had a TV in our "break room" so someone heard the news bulletin almost immediately and called us in.

I heard about the first plane hitting the north tower (of the World Trade Center's two towers) within a few minutes of it actually happening. The second plane hit the South tower shortly thereafter, and a plane hit the Pentagon. A fourth plane crash-landed in Pennsylvania and was thought to have been aimed at either the Capitol building or the White House in Washington, DC. (Which of those two was the target is not clear.) The passengers overpowered the highjackers but could not safely land the plane.

Many of us have already answered the "where" part of your question. My business day started at 07:00 so I was in my place of work, as described in an earlier post.

 

[Cotswold]

Steel becomes very pliable when subjected to long_term intensive heat from burning jet fuel. One tower withstood the heat for almost an hour, the other lasted almost two hours. Another factor was where the impacts occurred. The lower the impact, the heavier the weight load. The new tower's upper structure was built using a cocoon design made of titanium alloy, which is supposed to withstand a commercial jet's impact. I periodically visited the construction site of the new tower and was amazed at how fast it was completed.

Once mild steel reaches a cherry heat it will begin to be easier to work. Most forging can happen at between 1000ºc and 1200ºc, with melting occurring around 1400ºc. According to Isaac Newton, force increases by the square of the speed. So faster = more force. Strength of materials works in the same way. Doubling the thickness of a steel bar from 10mm to 20mm doesn't double its weight bearing qualities, or resistance to bending. They will increase by the square of the thickness

I understood that in order to reduce, or remove the need for changing lifts part way up the towers, a system of a main central core of beams was supported by joining it to the outer structure with a novel design. When the planes hit at the top floors the force and the heat weakened the outer supporting intermediate structure that was designed to support just one floor. When the weight of higher floors dropped to the ones below the combined weight was unsupportable. The cascade effect of floors dropping was inevitable causing the vertical collapse. That is my understanding of the collapsing towers.
It is unclear to me how any building could withstand the impact of a jet plane.

 

[BlueSpruce]

It is unclear to me how any building could withstand the impact of a jet plane.

The titanium alloy cocoon in the Freedom Tower's upper floors will not resist a commercial jet's impact, but most likely prevents the domino effect collapsing the entire structure.

 

[Cotswold]

@BlueSpruce, I'm sorry in my opinion but you are wrong.
A floor in any building is designed to carry its own load as well as the estimated maximum load to be placed upon the floor. Any individual floor is not designed to carry the weight of two, or more loaded floors. Many buildings, those included, would no doubt have to carry the load of banks of computers as well as other plant and equipment, desks and people. If a floor is overloaded beyond its designed capacity it will fail. I would imagine that there would be maximum stated loadings that can be stored on floors in high rise buildings.

Even with titanium beams these principles apply. It may be that the section size of titanium beams is different to steel but they will not be so large as to allow double or higher weight supporting capabilities. Titanium and steel have different properties but titanium will only be used as a substitute where design dictates and costs allow.
In this scenario, from memory there were over 100 floors, so it is inconceivable that even one floor could support the weight of another dropping maybe ten or fifteen feet with the supporting steel, floor weight, walls, plant and equipment, plus people. The floor it drops onto is also bound to fail and so on. The only way to prevent collapse would be to have supporting walls, or propping from top to bottom which would probably be impractical and add too much costs.

 

[BlueSpruce]

@BlueSpruce, I'm sorry in my opinion but you are wrong.
A floor in any building is designed to carry its own load as well as the estimated maximum load to be placed upon the floor. Any individual floor is not designed to carry the weight of two, or more loaded floors. Many buildings, those included, would no doubt have to carry the load of banks of computers as well as other plant and equipment, desks and people. If a floor is overloaded beyond its designed capacity it will fail. I would imagine that there would be maximum stated loadings that can be stored on floors in high rise buildings.

Even with titanium beams these principles apply. It may be that the section size of titanium beams is different to steel but they will not be so large as to allow double or higher weight supporting capabilities. Titanium and steel have different properties but titanium will only be used as a substitute where design dictates and costs allow.
In this scenario, from memory there were over 100 floors, so it is inconceivable that even one floor could support the weight of another dropping maybe ten or fifteen feet with the supporting steel, floor weight, walls, plant and equipment, plus people. The floor it drops onto is also bound to fail and so on. The only way to prevent collapse would be to have supporting walls, or propping from top to bottom which would probably be impractical and add too much costs.

Can the Freedom Tower Withstand a Plane Crash? The Science Behind Its Resilience

The Freedom Tower was built to withstand a plane crash, and has been tested to withstand impacts from commercial airliners. It is one of the safest buildings in the world, and is a symbol of resilience and strength.

flyfreshflight.com

 

[AccessBlaster]

Can the Freedom Tower Withstand a Plane Crash? The Science Behind Its Resilience

The Freedom Tower was built to withstand a plane crash, and has been tested to withstand impacts from commercial airliners. It is one of the safest buildings in the world, and is a symbol of resilience and strength.

flyfreshflight.com

This is not scientific, it's an opinion piece.

 

[moke123]

I totally forgot about the bombing at the WTC in 1993. I worked on 5th Ave. at the time.