११ फेब्रुवारी, २०२१
"Until the World Trade Center was built, most skyscrapers were supported by simple steel or concrete frames."
"But that meant that interiors were interrupted by columns. For the Trade Center, architects and engineers, including Mr. Robertson, sought to create column-free expanses for commercial tenants.
He did that by making the towers giant steel tubes, with about half of the weight borne by exterior columns. The rest of the weight was carried by the towers’ steel-and-concrete cores. Floors were supported by lightweight steel trusses linking the exterior columns to the cores, giving tenants column-free spaces measuring about three-quarters of an acre.
According to Mr. Robertson, the buildings had been designed to withstand the impact of a Boeing 707, but the planes flown into the towers were heavier 767s. And his calculations had been based on the initial impact of the plane; they did not take into account the possibility of what he called a 'second event,' like a fire. When the planes struck the towers, they sliced through the steel frames, but the buildings remained standing. Many engineers concluded that conventionally framed buildings would have collapsed soon after impact. The twin towers stood long enough to allow thousands of people to escape."
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One of my vivid memories that day was watching TV at the law firm when one, and then the other, building fell. I knew how many people worked in the two towers because my dad had worked in one of the WT buildings (not the towers) for a few years in the 70's and I remember him telling me there were 100,000 workers there. I thought the death count would be 50,000, and said so. One of the secretaries burst into tears. I apologized to her, and was happy to have been proved wrong. Incredible how many people were able to escape.
The twin towers stood long enough to allow thousands of people to escape.
In engineering there's the concept of failing properly and safely. You have to accept that failures will happen, and therefore you design things that fail in reasonably safe ways whenever possible.
To this very day a majority of democraticals passionately believe GW Bush either knew about the attacks in advance and did nothing and/or actively collaborated with the terrorists to bring the towers down and/or had US govt assets place the explosives to bring down the towers.
The most illuminating conversations occur when the lefty argues all 3 positions simultaneously.
Also recall that in 1988, 1992, 2000 and 2004 the democraticals claimed the Bush family personally funded the rise of Hitler.
Yes, it was all that jet fuel that melted and weakened the supports and caused the building to collapse like an 7 layer cake. I never wouldn't thought it possible, but then I'm not an architect & know nothing of jet planes. A 767 can hold 16,000 to 24,000 Gallons of Jet Fuel.
By comparison a B-17 in WW2 held 2,000 gallons. A B-24/B-17 flew into the Empire state Building in 1945, and didn't cause much damage.
Jeez, another day wasted talking about Marjorie Taylor Greene?
Earnest Prole: "Jeez, another day wasted talking about Marjorie Taylor Greene?"
I guess it depends on the quality of the fake quotes people come up with.
Seems interesting but not ever clicking on the NYTimes.
Many engineers concluded that conventionally framed buildings would have collapsed soon after impact.
As I recall other engineers concluded a conventionally designed building wouldn't have collapsed at all, assuming an effort was made to put out the fire.
Nope, rcocean, the 1945 incident involved a (gasoline fueled) twin-engined B25, not a heavy.
Jet fuel and other hydrocarbons such as fill skyscrapers nowadays make a big difference, to say nothing of the sheer mass and speed differentials.
Narr
Airplane geek
I'm with DavidUW, never going to click to the NYTimes and their partisan drivel.
In one of the dozens of 9/11 documentaries/specials that I've viewed over the years, one of them had a lengthy interview with Leslie Robertson. I wish I could remember which documentary it was because the excerpts of his interviews along with illustrations were very interesting and enlightening. The Towers, when built, were quite a magnificent piece of architecture. And given that it withstood a massive blast in the underground parking/foundation area, and fell only when struck by two jumbo jets, and the massive fuel spills and high heat fires melted the very structures supporting it, I would say it was a pretty amazing design.
Buildings are not built to withstand that of which we cannot conceive. You simply cannot think of everything that might happen today...or 30 years from today, and still create a building that is both appealing through the years as well as functional. (the appealing part is, of course, subjective and I'm not saying the Twin Towers were appealing. But they were well made, well-thought out.)
his calculations had been based on the initial impact of the plane; they did not take into account the possibility of what he called a 'second event,' like a fire.
Wait a Minute!
I was reliably informed that fire doesn't melt steel by Rosie O'Donnell, Hollywood liberal and intellectual Democrat.
The towers were obviously destroyed by George Bush (using explosives) to incite us against the Arab world. He was literally worse that Hitler.
WHY DIDN'T THEY IMPEACH BUSH?
Leslie Robertson built bigger erections than Larry Flint; but I don't know, Schumer may think Trump built one even bigger.
Steel trusses are a good construction material. Unfortunately, they require good fireproofing, since steel becomes plastic at high temperatures. With the fireproofing deteriorating due to lack of oversight, the trusses failed at the burning floors, the floors above fell on top of the floors below, and the weight crushed the remaining floors as gravity collapsed the buildings.
I young, well trained engineer could have figured that out by examining the plans for the building. If their heart was intent on destruction, they only had to pass the information on to those with evil intentions.
Complete and utter bullshit.
Watch the video of WTC 7 coming down. No airplanes hit WTC 7. It was a controlled demolition. That's why it was announced on British television an hour before it happened. You can see the video, it's pretty funny. There's this reporter in America, standing in front of a camera talking about how WTC 7 has collapsed from fire, and you can see it standing behind her.
>>Watch the video of WTC 7 coming down. No airplanes hit WTC 7. It was a controlled demolition.
Jupiter, you may want to switch to a heavier gauge of tin foil for your hat.
"As I recall other engineers concluded a conventionally designed building wouldn't have collapsed at all, assuming an effort was made to put out the fire."
As a matter of fact, what conventional engineers have noted is that in the entire history of steel-framed skyscrapers, hundreds have caught fire, and some have burned for more than 24 hours. Only three have ever suffered major structural damage. You'll never guess which three.
>>Only three have ever suffered major structural damage. You'll never guess which three.
Let me guess:
1) The Flat Earth Hotel
2) The Apollo Fake Moon Landing Plaza
3) The Grassy Knoll Memorial
How did I do?
Great. A Troofer.
Jess @ 3:13: "...steel becomes plastic at high temperature." That's what I remember being told back when the towers fell: the trusses sagged and pulled away from the perimeter columns, and then the floors collapsed onto the floors below in an accelerating pancaking. You could pretty well SEE that happening in the video of their collapse. People inside? On the lower floors? Had no chance. Everything was pulverized.
RIP to the designer/builder.
just remember, like Rosie O'Donald learned in Blacksmithing classs;
Fire can NOT weaken steal..... That's Why Blacksmiths have forges.
Wait, that doesn't quite add up.... Let me get back to you
"caught fire" Explain the relative extent and intensity of the fire.
Jet fuel, although dramatically flammable when vaporized, burns more slowly than gasoline which, when vaporized by an impact, practically explodes....and then it's done.
Jet fuel burns longer, long enough to set other materials on fire as well.
Note the perps chose transcontinental flights and took them in the first few moments of flight to maximize available fuel.
Many engineers concluded that conventionally framed buildings would have collapsed soon after impact.
Collapsed as in the floors pancaking all the way down? Or collapsed as in the top floors chop off and topple over to the ground below, leaving the rest standing, because the floors would not be held in the tube?
I thought the death count would be 50,000, and said so.
After the first one went, so did I.
Buildings are not built to withstand that of which we cannot conceive.
Osama bin Laden conceived of it.
Jupiter said ...
in the entire history of steel-framed skyscrapers, hundreds have caught fire, and some have burned for more than 24 hours
Of All those Hundreds.... How Many had over 150,000 pounds of accelerant used on their fires?
I'm guessing..... Two?
oh! and how many steel framed skyscrapers had a building that was twice as tall , fall on them?
i'm guessing One?
Same day, next thread: the same folks mocking Andrea Mitchell pontificating on structural engineering and jet fuel.
I never wouldn't thought it possible, but then I'm not an architect & know nothing of jet planes.
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I was at a client who was the NA sales office of a foreign steel firm. Nobody there on that unfortunate day doubted the steel had failed due to the intense heat.
>>Same day, next thread: the same folks mocking Andrea Mitchell pontificating on structural engineering and jet fuel.
She will be along shortly to correct us: the two towers were from Tolkien, not New York.
Ken B: "Same day, next thread: the same folks mocking Andrea Mitchell pontificating on structural engineering and jet fuel."
Thats only because Mitchell's attempted dunk on Cruz was so structurally unsound that Cruz's immediate response ignited Mitchell's already tenuous intellectual "integrity" and set it ablaze as if it had been soaked with JP5.
"I was reliably informed that fire doesn't melt steel by Rosie O'Donnell, Hollywood liberal and intellectual Democrat. "
Carbon steel sees a reduction in ultimate tensile strength and yield point of 50 to 60% when held at 1000 DegF for 2 minutes. (I looked it up in my strength of materials book) Buildings are not designed for a 100% safety factor. Of course as the floor fails and falls at the impact area the lower floors will fail sequentially on impact, inside the "tube", in a cascade.
So do we now blame him for 9/11, instead of Bush, Trump, or (heaven forbid!) Arab terrorists?
And shortly after 9-11 we should have sent the Air Force. Now we still have troops trying to make silk purses out pigs anuses.
This item seems reasonable. It purports to be a report by real engineers engaged in a real investigation of the WTC collapse. Interesting detail on why the terrorists hit the towers where they did: as low down as they could access, with the plane banked to cut through as many floors as possible.
https://news.stanford.edu/pr/01/wtcpostmortem125.html
Drago
Fair point.
The Hero of 911 Rick Rescorla https://www.youtube.com/watch?v=QF0PYQ8IOL4 and also
https://www.historynet.com/rick-rescorla-ia-drang-hero.htm In the movie We were "Soldiers Once And Young" he was actually the guy who got the VC bugler (and bugle). He was certain there would be a follow up to the basement bombing of WTC, so he practiced evacuation drill for Morgan Stanley employees. Total Hero.
ALSO... https://www.youtube.com/watch?v=DjFK7makTwk
I remain amazed the tower hit by the second plane didn't collapse immediately. I guess I always will be.
If they'd used clay structures the fire wouldn't have melted them.
an egyptian jihadist who married an american, joined the fdny, and got a copy of the structural plans of the towers, (peter lance's thousand year war) this is how they knew the tolerances of the structure,
Correct me if I am wrong, engineers, but the design of the towers was such that if just one or two or three floors failed, falling down onto the floor below, then it was inevitable that the entire structure would come down? Is that right? The failed floors had nowhere to go but down?
The failed floors had nowhere to go but down?
In one of the interviews of the following days, they had a structural engineer who said, "I looked at it and thought 'it couldn't happen that way'. But then my next thought was 'what else could they do'?".
The pancake theory is correct.
PS. I saw a high altitude shot of WTC 7 and about a third of its front had been sheared off by falling debris. That it failed is no surprise.
From what I understood of the analysis of the collapse of the towers is that the size and mass of the planes, the speed and the fuel were on impact such to go through several floors and like brillo strip the steel of it's firecoating. Once the steel was bare and the amount of atomized fuel started burning that started the conflagration that resulted in the sustained heat needed to weaken the steel. Then the inevitable pancaking. No one at the time could have imagined the collapse of the towers, not even Bin Laden. The murderers assumed if they hit low enough the fire would spread upwards and trap those in their from escaping thus killing hundreds if not thousands but not actually collapsing the buildings.
I wonder if any newly built high rise is designed to withstand such an attack.
"I wonder if any newly built high rise is designed to withstand such an attack. "
If a building was designed for a 767 attack, no one could afford the rent.
I have a relatively new washing machine and every six months the drain pump fails. I read on the internet it's a common problem. But if the company had made a better pump and tried to charge $100 more per unit, everyone would have bought the cheaper competitive one. I am thinking of buying an irrigation pump for it.
The fallacy in my argument above is that the world belongs to people who can build reliable equipment at very low cost. NASA- cheap, fast, good, pick two. Deming, pick three.
I have a photo of me looking at the camera, with my back to all of Manhattan looking north.
Probably '82 or so. I was skinny and had lots of hair and the buildings were, of course, still there.
The skyline isn't the same without them...
“People inside? On the lower floors? Had no chance. Everything was pulverized.”
As I recall, pretty much everyone except police and firefighters had evacuated the lower floors. Almost all the civilian deaths were people trapped above where the planes hit, who had no way out.
"The twin towers stood long enough to allow thousands of people to escape."
As far as I know all steel-frame buildings are designed this way: they are not designed to remain standing several hours, but none are engineered to remain standing indefinitely.
Nonetheless, I still remember the fire safety advice offered when I was a child, living in Manhattan: always stay in the building if there is a fire; close the doors and, as needed, jam towels under and over them to keep smoke out.
One can only hope not too many in the Towers that day remembered and heeded that advice.
James K. @ 7:42: “...who had no way out.” Well, they *did* have “a way out.”
By jumping. Those pictures still burn my heart.
That Jupiter is such a rascal.
Narr
A scamp, even
"By jumping. Those pictures still burn my heart."
And the video footage and the photos were all deep-sixed by the media.
Don't want to offend any Muslims...
They should have been showing it all on a continuous loop for months afterward.
Is Biden's foreign policy going to keep us safe from the next attack -- or provoke it?
Scott said...
Is Biden's foreign policy going to keep us safe from the next attack -- or provoke it?
Neither- Islamic terrorist attacks are independent of our foreign policy. But if we are attacked at any point during the Biden or Harris administration, it's because Orangeman Bad! Democrats will use the attack as pretext to impeach him for a 3rd time, unless they're up to a 4th by then...
I'm more worried about what his domestic policy will bring about as far as violence goes.
Joe Smith said...
"By jumping. Those pictures still burn my heart."
And the video footage and the photos were all deep-sixed by the media.
A whole lot of tings were deep sixed by the MSM with government blessing. 2001 was pre-cell phone with built in camera days. If you wanted to take a picture- you had a camera. Every Muslim schoolkid in Jersey City and Newark brought a camera to school 9/11. Reported on 9/12, and never seen again. IIRC- Snopes has debunked that- but it happened. Also- there were 8 planes targeted for hijacking. I forget whether it was 1 or 2 already in the air when someone at the FAA who had no authority to do so ordered all civilian air traffic in the U.S. grounded. To this day, I don't think where the order came from has ever been identified.
If you have a chance to talk with someone in military intelligence, one of the issues they'll dance around is discussion of actual terrorist attacks stopped on U.S. soil post 9/11. I know of one- I'm not in MI. Some of them stopped have been by pure dumb lick, not intelligence gathering.
IIRC, the '93 bombing was placed to make one tower fall into the other (and a few other buildings). That would have been a very high death toll.
Joe Smith said...
"By jumping. Those pictures still burn my heart."
To this day.
Scott said...
"Is Biden's foreign policy going to keep us safe from the next attack -- or provoke it?"
No one, especially those that wish us harm, take Biden seriously. They know he can be bought.
As Barbara Tuchman said of another August, it was a pleasant season. A very nice day in Manhattan, with a municipal election, polls open early. Perhaps fewer people had shown up for work on the dot that day, for one reason or another.
Jess said...
Steel trusses are a good construction material. Unfortunately, they require good fireproofing, since steel becomes plastic at high temperatures.
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I recall something about fireproofing being different at higher floors [more "eco-friendly"] but more conventional [engineer worthy] at lower floors
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