Why the towers collapsed: hit at vulnerable point

Salon ^ | 9/11/01 | Bill Wyman

[2sheep]

Michael, this post from arcane in #69 might interest you. See also the post from exit82 in #111 agreeing with arcane.

[Real Cynic No More]

From one of the planes hijacked, from my morning newspaper, a passenger who phoned from a cell phone said the terrorists said they had a bomb. I think the reality of this is questionable. The explosions might likely have been nothing more than the jet fuel and/or natural gas in the buildings. In this issue I am merely a lay person, and will await the facts as they develop.

[supercat]

Maybe. Several of these planes had sharp and erratic course changes and changes in their velocity. Sort of abrupt for professional pilots from the impression I get.

According to an eyewitness report I heard on the news, the plane that crashed into the Pentagon actually hit the ground first and skidded into the building. Since I can't think why a kamikaze would do such a thing, my only guess is that the pilot didn't know how to visually judge ground clearance on the large aircraft.

[finnman69]

yes, people likely got out of the second tower to be hit BEFORE the second plane hit. But I also read account that at least one of the exit stairs was blocked and that the internal concrete walls flexed several inches. People who got out were DAMN LUCKY.

[cc2k]

I am still a bit unclear as to exactly where the first plane struck tower #1. Dead center, (side to side, that is, not top to bottom), or approximately centered between the core and one side, as the second plane seemed to.

The flaming holes from the first impact looked very similar. Also, late last night and this morning, Fox News showed some footage they got from a crew in the area that did film/video the first impact. It was similar to the second, only higher. It's really hard to tell from the video they shot, but it looked like that plane had to come in higher because of other buildings in the area. I think the second plane had a more open approach, so it could hit lower.

[cc2k]

Perhaps it could have been hit by a 707 and survive. But planes got much bigger since then.

Actually, they have. The 707 had a 130' wingspan and a gross weight of 80 tons.

The 767-400 (the largest 767 variant) has a wingspan of 170' and a maximum weight of 225 tons. The 767-200 has a wingspan of 156' and a maximum weight just under 200 tons.

Also, the building stood up to the impact of the 767. It was the fire damage that caused the building to collapse. I'm pretty sure that the engineers that claimed it could take an impact from a 707 weren't considering the effects of the resulting fire. If the airlines still flew 707's, one of those would probably have done the job.

I'm pretty sure that destroying the buildings was the goal of these terrorists. However, I'm not convinced that they did that much engineering and analysis. It's entirely possible that they went with "Well, a bomb in the basement didn't do it, let's try a big airplane in the side."

Even if they didn't completely destroy the buildings, this was still would have been a successfull terrorist strike. They would have killed all the passengers on both planes and also most of the people on the floors that they hit directly. They picked planes that were bigger than the public claims of the engineers. They probably figured that they would do enough damage to make the buildings unusable (and possibly unrepairable) for a long time. Actually, if they wanted a monument to their attack, they probably would have preferred the big hulking, uninhabitable wreckage to stay standing.

I agree that they picked their flights carefully, choosing planes that would have been fully loaded with fuel. But this doesn't take any particular engineering skill. It's pretty obvious that a flight from Boston to San Francisco would have more fuel aboard than a flight from Boston to Washington DC.

Also, I saw some radar traces on one of the networks last night. I wasn't impressed with the navigation skills and flying skills of these "pilots." It looked to me like strictly a VFR type approach. You can see New York City and especially the World Trade Center towers from a very long way away. I don't think they used any of the navigation tools available to them. They more likely turned and pointed the plane at the target visually.

Also, the speed variations and altitude wierdness also makes it look like these "pilots" weren't very well trained. Possibly just some PC based flight simulator time plus some time looking at pictures in those flight training manuals they apparently had. I'm not saying they might not have had more skills, but those are the minimal skills required to do what they did.

[AntiTyrant]

why . . . do they tell you to climb to yada yada and squak 1233 and hit indent?
hitting ident makes that arbitrary, ordinary code stand out on the scope temporarily so the controller can easily confirm you; it doesn't 'send' the code or anything like that -- the code is sent whenever the xponder is queried by radar (as marked by the flashing light on the panel). atc's systems are programmed to react in a big way to the mere existence of one of the 3 xponder emergency codes, so no ident is necessary; your controller (and every other participating system in range) will know you're squawking trouble.

[AntiTyrant]

A reflexive opposition to spending Government money hurts the conservative cause.
in other words, "the pet project i support is not like the pet projects other people are supporting." fortunately, we have a guideline in cases such as this, and it's called the constitution of the united states. nowhere in that document will you find the authority necessary for the federal government to rebuild port authority property. although the proposal may pull at your heartstrings, it's still boondoggle. conservatives who refuse to authorize unconstitutional spending are not only a wonderful thing, they are also a dying breed; hence your comfort with making an 'exception'. such talk would have been vilified in the period immediately following adoption of our constitution. there is no reason it should not be so now as well.

[supercat]

Actually, I believe that what happened is called a "Cascade Failure." It's similar to that concrete walkway collapse that occurred in Kansas City about 10 years ago. Once the top floor collapsed onto the one below it, the weight just kept on gaining as it hit each subsequent floor, like dominoes falling over.

The only cascading failure in Kansas City was horizontal, as the supporting-rod/box-beam joints failed and caused the load they'd supported to be transfered to other joints on the same level which failed in turn.

Unlike a "pancake" collapse where the lower level supports the upper level, and the collapse of the other level hits the lower level with an unsurvivable dynamic load, the balconies in Kansas City were all supported from above, with the upper balcony directly supporting the lower balcony [note: this represented a change from the original plan]. The joints connecting the upper balcony to the rods from above could not withstand the combined wait of both balconies so the upper balcony fell. The lower balcony fell not because the upper balcony hit it, but because there was no longer anything supporting it.

[calvin sun]

Does anyone remember the collapse about fifteen years ago of an building under construction in Bridgeport CT? From what I remember, the top floor fell onto the one below it, causing a chain reaction.

[Alberta's Child]

... some insurance companies are likely to go belly up by the end of the month. Something to think about when the markets open again.

This is why amateurs never make any money in the stock market. People are going to be running around in a panic, dumping their insurance company stocks, while professional traders will be buying them at extremely low prices.

Three days later, some moron who just dumped all his insurance stocks is going to do a little research.

"Wait a minute!" he'll say, "I just found out that the Port Authority of New York & New Jersey doesn't carry any insurance!" -- (the agency is so large that it has the financial means and bonding capability to cover its losses in the event of a catastrophe)

Then that same person is going to sit around and whine that "the government isn't doing enough for the economy."

As they say on Wall Street, SOME PEOPLE ARE BORN TO BE CUSTOMERS.

[Alberta's Child]

You are right. My point was that all PA facilities are subject to their own internal inspections, standards, etc. and do not meet municipal codes (their own codes are probably more stringent in most cases anyway).

[cinFLA]

Someone is going to be taking a serious look at the structural integrity of these buildings, especially since the structural engineer who designed them insisted at a recent conference that they were designed to handle a crash from a large passenger jet.

They both survived the crash. They probably did not analyze for the jet fuel fire!

[cinFLA]

I have never flown a plane. If you asked me to become a human bomb for your holy war, I am sure I can teach anyone to take my place and stear a jumbo jet towards a building as large as the WTC. If you can drive a car, you can steer a plane. You can't land one or take off in one but you can damn sure steer it in a general direction.

I agree with your statement about the collapse of the building as being gravy but it is obvious that you have never flown a plane.

[William_Rusher]

Well no shit! I said in my statement that you quote from btw that I have never flown a plane. But I can tell you that after logging 4000 rotary wing hours that there is not a pilot on the face of the earth that will tell you fixed wing flight is harder than rotary wing flight. Easier to fly a plane than a helo.

[Alberta's Child]

Yes. Over the last day and a half I've been reviewing tons of information along these lines, and it is clear to me that the buildings did very well. They were also designed to collapse upon themselves (instead of toppling sideways) in the event of a catastrophe.

The reason I posted that speculation yesterday was that I was aware that the design of the structures was considered innovative at the time and hadn't been used before on a structure as large as the WTC.

[elfman2]

"What happened, is more likely 4 stupid crazy guys who dont mind suicide"

I've got to re-register opposition to this idea. If they were "stupid and crazy" they couldn't have succeeded in keeping this secret.

I'm not aware of any coordinated terrorist or military attack in history that was designed, financed and implemented by only those immediately involved in its execution.

One sociopath acting alone is always a possibility. In that regard, we'll likely see some kind of copycat hijacking attempts soon. Four, eight or sixteen like minded capable disciplined martyrs must be the product of a culture where there is no doubt as to the virtue of their actions. Otherwise, the reasoned thinking needed to manage the operation would also act to weaken their resolve. And there are no domestic organizations that are both vicious enough to do this as well as being capable of attracting and supporting these individuals.

Like a great athletic accomplishment, it's not as easy as it looks. Athletes require financing, recruiting, socialization, and coaching. There's no president for four skilled people planning and independently executing a simultaneous crime against humanity.

But this looks like a moot point now anyway, apparently suspects are being arrested and insiders are alluding to signals intelligence showing Ben Laden's involvement.

[wny]

When 200,000 lbs of aluminum, carrying a few tons of highly explosive and flammable liquid, moving at 500 mph hits a building, the building is history. You don't need to be an Architect or civil engineer to know this.

[Robert A Cook PE]

You pointed out that somebody should have been able to predict failure, and prevent the firefighters from going up to attempt rescue of those burning to ddeath in the higher fllors...

Notice the successes that would have happened IF the fire could have been put out (in 2-4 hours, maybe in 4-6 hours) .... Nobody knowss how the building might stand.

First. The 4,000 - 8,000 people alive in the floors ABOVE the impact area would have been saved by the first firefighters to get through the stairs.

Second. IF the fire could have been out - and it certainly MIGHT have been under different circumstances - the weakened structural steel - WHICH DID withstand the impact of the collision for hours - might have been strong enough to give enough time to evacuate the whole building.

Third. IF the fire had been put out - in one or both buildings - then the damages MIGHT have been limited to the immediate fire and explosion, since the buildign might not have fallen at all. Not 10,000 dead and 3 billion dollars of losses.

Your loss is very real - but the firefighters WERE NEEDED to TRY to reach/protect/evacuate those thousands of the higher-level occupants - who were still alive until the building collapsed.

Also, until the collapse itself began - there is NO WAY to predict how long the building would stand....minutes more, hours, or "forever" -

Nobody at street level could predict how long, if ever, the building may stay up. You cannot tell from the ground, or even in the fire itself, how strong any given steel member is without rigorous lab-condition analysis. And even if you know how strong any single member is, you can't tell without hours of elablorate computer simulation, what's the result of one or more members failing. Since the damage was widespread, over several floors, and was in the midst of flames ..... you can't take the time to analyze - you MUST PROTECT IMMEDIATELY those threatened.

(And of course, removing steel pieces from the building is impossible during the fire. And would weaken the building itself. Even surveying the building would delay other rescuers from going up to try to make a passageway down for those trapped.)

If the building did not immediately fail - which it did not - then the those trapped and burning to death up became priority.

[AntiTyrant]

...there is not a pilot on the face of the earth that will tell you fixed wing flight is harder than rotary wing flight.
my daughter was able to navigate a cessna 2-seater well at the age of six, and with only an hour or two of prior computer sim time. i, however, was almost a complete klutz during my first hour at the controls of a helo after many hours in fixed wings. i agree with william on the comparison between fixed and rotary wing aircraft, as well as the amazing simplicity of aiming a fixed wing craft at a building and hitting it. the part of flying which separates the men from the boys is the precise and consistent control of speed, attitude, altitude, and position all at once. hitting the wtc isn't very hard if you can choose among many possible tracks, with any number of acceptable speed/attitude configurations. wouldn't take long to learn the necessary cockpit diffs either.