Do you think the 9/11 hijackers knew that the WTC buildings would collapse?

[u/JMRooDukes808]

I really don’t know where else to ask this. There is obviously an overload of information about the event itself online, but one thing I can’t find out is if the hijackers intended to, or knew that the WTC buildings would collapse. Do you think they just planned on the impact and fires to be the extent of the damage caused? As far as I know, no steel structure buildings in history had collapsed from fire at that point, so it makes me wonder if they actually “succeeded” in their plan more than they intended.

Edit: no conspiracies please, that was not the point of my post

[u/stogie-bear]

Hi, former architect here. This is not something you plan for, and there was really no precedent for it because:

1. There aren’t many skyscrapers out there like the WTC towers. The superstructure was a tube of columns and the floor plates were supported at the perimeter. The failure was in the connection between the floor plates and the columns, and when one plate failed it took down the already weakened one below. Then the weight of multiple plates caused the cascade failure. That's not what you’ll expect or plan for without 20/20 hindsight and before this there were no instances of buildings failing like this. 

2. Before this attack, “what would happen if you put a huge jet fuel fire in there” just isn’t something you would have asked when designing a skyscraper. 

So I don’t think anyone would have planned for the particular way the structure failed, including the terrorists. I think they wanted to cause a lot of chaos, death and destruction. I don’t think they planned on the particular type of destruction they caused. 

[u/hueylouisdewey → u/stogie-bear]

The unprecedented nature of the event is very relevant. OP says no building like it had collapsed from fire before, but also no building had a fricking aeroplane fly right into it! I'm no architect or engineer and I don't know the exact causes of the collapse but this feels important.

[u/Dry_Car2054 → u/hueylouisdewey]

The Empire State Building had a B-25 bomber fly into it. It did some damage but didn't cause a collapse. The architects for the WTC designed for that to happen again since it was a known possibility. They didn't anticipate a plane that large with that much fuel. Also, there had never been a skyscraper lost to that kind of fire so that wasn't thought to be possible. After all, it was concrete and steel and therefore not flammable. The hijackers picked planes going to the west coast that were full of fuel. That made for a fire that was able to do structural damage that led to the collapse.

Edit: spelling.

[u/hueylouisdewey → u/Dry_Car2054]

Wow I did not know that

[u/TheLizardKing89 → u/Dry_Car2054]

A B-25 has a maximum takeoff weight of 35,000 pounds and a top speed of 272 mph. The Boeing 767s that hit the WTC had a maximum takeoff weight of 395,000 pounds (more than 10 times as much) and were traveling at about 450 mph.

[u/Dry_Car2054 → u/TheLizardKing89]

The Boeing 707, which was in general service at the time the WTC was designed, was the aircraft the architects used for their design AFAIK. The thing the B-25 crash did was make everyone aware the hazard existed so it was something they planned for. The 707 is much closer in size and speed to a 767.

[u/of_the_mountain → u/hueylouisdewey]

Someone tried to fly a plane into the White House on 9/11/93 and came so close it landed on the lawn past the fence. Granted it was a Cessna so wouldn’t have done much damage but the concept of flying a plane into an important building on 9/11 actually happened once before…https://en.m.wikipedia.org/wiki/Frank_Eugene_Corder

[u/rockit454 → u/stogie-bear]

I always view Aon Center in Chicago as the “third tower”. I would assume it has a similar structure?

[u/connor_wa15h → u/rockit454]

I can't comment on the structural similarities, but my first job out of college was working at the Aon Center in Chicago, for Aon. I distinctly remember being told why the Aon offices were located on the bottom floors of that building, when they owned the naming rights and could put their offices anywhere. It was because of what happened on 9/11. Aon offices in the World Trade Center were located towards the top of the South Tower, above the impact zone. 176 Aon employees died that day.

[u/elodie_pdf → u/stogie-bear]

That’s a good point. I imagine most architects don’t take into account the possibility of a huge jetliner crashing into the building when designing the structure.

[u/AJay_yay → u/elodie_pdf]

Architects, no. That's why they get structural engineers to design skyscrapers. They did account for the impact of a plane when designing them, due to the Empire State Building plane crash.

[u/Public_Classic_438 → u/stogie-bear]

As an architect, do you think they were able to hear the floor plates and columns, creaking, slightly, and giving away?

[u/Fun_Accountant_653 → u/stogie-bear]

Mark Whalberg:

“If I was on that plane with my kids, it wouldn't have went down like it did,” Wahlberg told Men's Journal. “There would have been a lot of blood in that first-class cabin and then me saying, 'Okay, we're going to land somewhere safely, don't worry.'”

Then someone pointed out that NO ONE in the plane had any idea they were going to crash the planes.

That had NEVER been done before

[u/aBoyandHisDogart → u/stogie-bear]

"what would happen if you put a huge jet fuel fire in there" just isn't something you would have asked when designing a skyscraper

why not? if I were constructing the tallest building in the world, the scenario of a plane crashing into it would cross my mind. there is traffic in the sky.

[u/stogie-bear → u/aBoyandHisDogart]

Try to think of everything that could possibly go wrong. I bet you can’t. And if you tried to design a building that could withstand everything on your list, you wouldn’t be able to build it on anything like a budget. That’s just not how people work in the civilian context. Engineers get the architects’ drawings then plan for dead and live loads, wind loads based on historic numbers, seismic loads if you’re in an earthquake area, fire ratings based on code requirements, etc. 

Suppose we got in a war with Canada and they bombed a city. Skyscrapers would come down, and that would be a scenario with historical precedent. But our buildings aren’t designed to withstand that, or a number of other potential threats, let alone ones that were on the fringes of predictability until somebody with a sufficient combination of creativity and evil went and tried them. 

[u/Outside_Log_2593 → u/stogie-bear]

I mean the question specifically asks if the hijackers knew. Bin Laden was more realistic about the likelihood of success for the operation and questioned the potential of the hijackers completely destroy their targets. Now onto the question that was asked, the hijackers who flew the planes fully intended intended to destroy their targets to send a message. Atta was an architectural engineer who was undergoing a thesis in Hamburg, Germany so he had foundational knowledge building integrity and understanding of using high speed with a massive objective weaken the structural integrity while also delivering a large amount of fuel to a raging fire in an enclosed space. Meanwhile, al-Shehhi, another student who joined the Hamburg cell, flew into the second building faster and lower than Atta. Not to mention they spent months in advance finalizing the plans and preparations for their attack. To argue these hijackers didn't expect to collapse these two buildings showcases an ignorance on the subject and an underestimation of the lengths that terrorist organizations go through to fulfill their goals. The 1993 bombing was intended to make one building collapse into the other but the lack of understanding the foundation's softpoint led to the same terrorist organization failing to achieve their goal in felling the WTC through placing the van in the wrong spot.

[u/MorganAndMerlin → u/stogie-bear]

This is probably a stupid question, but are buildings designed and built today considered for immediate, emergency, full scale, fire balls and planes evacuation?

It seems counterintuitive to me that sky scrapers this big (and larger today) can actually have any meaningful plan for absolute Defcon 5 evacuation. Because, as you said, wtf plans for jet fuel?

[u/stogie-bear → u/MorganAndMerlin]

There's more consideration for terrorism than there was pre-2001, but there's no expectation that today's skyscrapers will survive everything. It's like everything else. There's a balance of risks versus other priorities.

[u/EmeraldDream98 → u/stogie-bear]

After 9/11, do architects anticipate planes crashing against skyscrapers when they are working on the blueprints? The same way now a lot of cities in Europe have bollards in the most crowded streets to avoid attacks using vehicles to run over citizens walking down there.

[u/stogie-bear → u/EmeraldDream98]

I wish I could reassure you that new buildings are jumbo jet proof, but I can't. However, fire codes have been updated since then and a newer skyscraper would be expected to hold up longer. The fire resistant materials protecting the structural steel are stronger and more effective, and more attention than ever is paid to reinforced fire resistant escape routes. The idea isn't to keep the building from coming down, it's to make it easier for all the people to get away. If a similar attack (or anything involving an unusually potent fire in the building) happened to a newer tower, you would be more likely to get out alive. Even more modestly sized buildings need fire rated evacuation stairs and exits that are meant to withstand a fire for 1-2 hours.

[u/EmeraldDream98 → u/stogie-bear]

That’s great to know! And good at least they learned something about that tragedy and they are using it for doing safer buildings.

[u/stogie-bear → u/[deleted]]

Obviously a different case. NYC skyscrapers are not designed for seismic resistance. Two neighboring buildings crashing down shook #7 and caused substantial damage. It also took hits from flying debris and some of that was on fire, causing fires inside #7. It wasn’t a single cause but these factors together. 

[u/stogie-bear → u/[deleted]]

The OP clearly requested no conspiracies, and I have no time to read insults from an ignorant person. Feel free to go elsewhere.