47 vertical support columns in core of each Twin Tower from bedrock to top floor

[creativedreams]

Let's talk about the 47 vertical steel support columns in the core of each Twin Tower that somehow cut themselves and blew out of the way fast enough all the way down for the top floor in each building to hit the ground almost as fast as a ball would hit the ground if dropped right beside them.

Perhaps we can also discuss how everything but the steel was exploded into a huge cloud of dust before it even hit the ground and settled over the city....

[ame="http://www.youtube.com/watch?v=qhyu-fZ2nRA"]YouTube- 9/11: South Tower "Collapse" video compilation[/ame]

 

[creativedreams]

While we're at it perhaps we can discuss the many vertical support columns in Building 7 that somehow cut themselves and blew out of the way fast enough all the way down for the top floor of the building to hit the ground almost as fast as a ball would hit the ground if dropped right beside it...

[ame="http://www.youtube.com/watch?v=Atbrn4k55lA"]YouTube- 9/11: WTC Building 7 "Collapse" video compilation[/ame]

 

[Fizz]

ok. you start. show evidence of a cut column or an explosive charge on 9/11.

 

[candycorn]

While we're at it perhaps we can discuss the many vertical support columns in Building 7 that somehow cut themselves and blew out of the way fast enough all the way down for the top floor of the building to hit the ground almost as fast as a ball would hit the ground if dropped right beside it...

YouTube- 9/11: WTC Building 7 "Collapse" video compilation

See, you found it.

 

[manu1959]

see other thread....the truthers believe the cores were concrete not steel....

 

[creativedreams]

ok. you start. show evidence of a cut column or an explosive charge on 9/11.

Actually if you watch the Twin Tower footage you can see many flashes of explosives....

Here is more....

These two new videos show absolute proof of explosives used to bring down the World Trade Center Buildings.

This footage came right from the history channel itself....

[ame="http://www.youtube.com/watch?v=6_B_Azbg0go"]YouTube- South Tower Smoking Guns[/ame]

[ame="http://www.youtube.com/watch?v=PBVhxnkK6s8"]YouTube- South Tower Smoking Guns (Follow-up)[/ame]

 

[creativedreams]

While we're at it perhaps we can discuss the many vertical support columns in Building 7 that somehow cut themselves and blew out of the way fast enough all the way down for the top floor of the building to hit the ground almost as fast as a ball would hit the ground if dropped right beside it...

YouTube- 9/11: WTC Building 7 "Collapse" video compilation

See, you found it.

Found what?

Is that you in your avatar?

 

[Big Black Dog]

Let's talk about the 47 vertical steel support columns in the core of each Twin Tower that somehow cut themselves and blew out of the way fast enough all the way down for the top floor in each building to hit the ground almost as fast as a ball would hit the ground if dropped right beside them.

Perhaps we can also discuss how everything but the steel was exploded into a huge cloud of dust before it even hit the ground and settled over the city....

YouTube- 9/11: South Tower "Collapse" video compilation

Bad shit just happens is the only explanation I can come up with. I believe that's just as good of an explanation as what I've heard here...

 

[Fizz]

this is what a REAL building demolition looks and sounds like.
[ame]http://www.youtube.com/watch?v=79sJ1bMR6VQ[/ame]

this is what the WTC towers collapse sounded like.
[ame]http://www.youtube.com/watch?v=FOGI33HsiCc[/ame]

and in this video you can see the columns buckle WITHOUT ANY EXPLOSIONS!!
[ame]http://www.youtube.com/watch?v=NBYnUyx4kw8[/ame]

 

[creativedreams]

this is what a REAL building demolition looks and sounds like.

Yes those are some forms.....there are many types of explosives and technology available...

 

[creativedreams]

Let's talk about the 47 vertical steel support columns in the core of each Twin Tower that somehow cut themselves and blew out of the way fast enough all the way down for the top floor in each building to hit the ground almost as fast as a ball would hit the ground if dropped right beside them.

Perhaps we can also discuss how everything but the steel was exploded into a huge cloud of dust before it even hit the ground and settled over the city....

YouTube- 9/11: South Tower "Collapse" video compilation

Bad shit just happens is the only explanation I can come up with. I believe that's just as good of an explanation as what I've heard here...

Yes it does all the time anywhere anyplace....that's why I don't get too excited about it and just feel lucky every time my eyes open in the morning...and then I think to myself..."well I guess the world is going to have to put up with me for another day".

 

[Big Black Dog]

Let's talk about the 47 vertical steel support columns in the core of each Twin Tower that somehow cut themselves and blew out of the way fast enough all the way down for the top floor in each building to hit the ground almost as fast as a ball would hit the ground if dropped right beside them.

Perhaps we can also discuss how everything but the steel was exploded into a huge cloud of dust before it even hit the ground and settled over the city....

YouTube- 9/11: South Tower "Collapse" video compilation

Bad shit just happens is the only explanation I can come up with. I believe that's just as good of an explanation as what I've heard here...

Yes it does all the time anywhere anyplace....that's why I don't get too excited about it and just feel lucky every time my eyes open in the morning...and then I think to myself..."well I guess the world is going to have to put up with me for another day".

You're right on the bean with that though and with that said, I think it's time for the Big Black Dog to go crawl into his doggie bed. Good night all! ZZZZZZZZZZZZZZZ

 

[creativedreams]

Bad shit just happens is the only explanation I can come up with. I believe that's just as good of an explanation as what I've heard here...

Yes it does all the time anywhere anyplace....that's why I don't get too excited about it and just feel lucky every time my eyes open in the morning...and then I think to myself..."well I guess the world is going to have to put up with me for another day".

You're right on the bean with that though and with that said, I think it's time for the Big Black Dog to go crawl into his doggie bed. Good night all! ZZZZZZZZZZZZZZZ

Don't let the bedbugs bite!...LOL

 

[eots]

While we're at it perhaps we can discuss the many vertical support columns in Building 7 that somehow cut themselves and blew out of the way fast enough all the way down for the top floor of the building to hit the ground almost as fast as a ball would hit the ground if dropped right beside it...

YouTube- 9/11: WTC Building 7 "Collapse" video compilation

See, you found it.

Found what?

Is that you in your avatar?

lol..in her dreams ..if she looked like that she would not be spending 14 hours a day trolling every messageboard in the nation..I mean really

 

[creativedreams]

Here is more on the 47 vertical core columns that somehow cut themselves and moved out of the way fast enough all the way down to not provide resistance so the top floor of each building could hit the ground almost as fast as a ball would hit the ground if dropped right beside them.

Propaganda debunkers intentionally try and mislead by focusing on the perimeter floor trusses and NOT the central core columns that should have easily stood........unless of course explosives were used to blow them completely out of the way all the way down and in doing so pulverizing everything but the steel before it even hits the ground.

[ame="http://www.youtube.com/watch?v=gohc5lMO5Q8"]YouTube- WTCCS Scenario - WTC 1 Collapse Arrest[/ame]

 

[LA RAM FAN]

See, you found it.

Found what?

Is that you in your avatar?

lol..in her dreams ..if she looked like that she would not be spending 14 hours a day trolling every messageboard in the nation..I mean really

you got everything right there in that post,especially the part of HIS trolling every message board in the nation like he does 14 hours a day.Thats the one part you got wrong is calling him a SHE though.Cornboy troll is a HE.

 

[creativedreams]

Here is some information on the Twin Towers actually being designed to withstand a possible plane impact during foggy conditions....

9-11 Research: Towers' Design Parameters

Contrary to widely promoted misconceptions, the Boeing 767-200s used on 9/11/01 were only slightly larger than 707s and DC 8s, the types of jetliners whose impacts the World Trade Center's designers anticipated

The above graphic from Chapter 1 of FEMA's Report shows the sizes of a 707 and a 767 relative to the footprint of a WTC tower. 1 Flight 11 and Flight 175 were Boeing 767-200s. Although a 767-200 has a slightly wider body than a 707, the two models are very similar in overall size, weight and fuel capacity.


property Boeing 707-320.............Boeing 767-200
fuel capacity 23,000 gallons..........23,980 gallons
max takeoff weight 328,060 lbs.....395,000 lbs
empty weight 137,562 lbs............179,080 lbs
wingspan 145.75 ft.....................156.08 ft
wing area 3010 ft^.....................2 3050 ft^2
length 152.92 ft.........................159.17 ft
cruise speed 607 mph..................530 mph

Given the differences in cruise speeds, a 707 in normal flight would actually have more kinetic energy than a 767, despite the slightly smaller size. Note the similar fuel capacities of both aircraft. The 767s used on September 11th were estimated to be carrying about 10,000 gallons of fuel each at the time of impact, only about 40% of the capacity of a 707.

Statements by Engineers
Engineers who participated in the design of the World Trade Center have stated, since the attack, that the Towers were designed to withstand jetliner collisions. For example, Leslie Robertson, who is featured on many documentaries about the attack, said he "designed it for a (Boeing) 707 to hit it." 2 Statements and documents predating the attack indicate that engineers considered the effects of not only of jetliner impacts, but also of ensuing fires.

John Skilling
John Skilling was the head structural engineer for the World Trade Center. In a 1993 interview, Skilling stated that the Towers were designed to withstand the impact and fires resulting from the collision of a large jetliner such as Boeing 707 or Douglas DC-8.
"Our analysis indicated the biggest problem would be the fact that all the fuel (from the airplane) would dump into the building. There would be a horrendous fire. A lot of people would be killed, ... The building structure would still be there."

A white paper released on February 3, 1964 states that the Towers could have withstood impacts of jetliners travelling 600 mph -- a speed greater than the impact speed of either jetliner used on 9/11/01.

"The buildings have been investigated and found to be safe in an assumed collision with a large jet airliner (Boeing 707—DC 8) traveling at 600 miles per hour. Analysis indicates that such collision would result in only local damage which could not cause collapse or substantial damage to the building and would not endanger the lives and safety of occupants not in the immediate area of impact."

The Richard Roth Telegram
On Feburary 13, 1965, real estate baron Lawrence Wien called reporters to his office to charge that the design of the Twin Towers was structurally unsound. Many suspected that his allegation was motivated by a desire to derail the planned World Trade Center skyscrapers to protect the value of his extensive holdings, which included the Empire State Building. In response to the charge, Richard Roth, partner at Emery Roth & Sons, the architectural firm that was designing the Twin Towers, fired back with a three-page telegram containing the following details.

"THE STRUCTURAL ANALYSIS CARRIED OUT BY THE FIRM OF WORTHINGTON, SKILLING, HELLE & JACKSON IS THE MOST COMPLETE AND DETAILED OF ANY EVER MADE FOR ANY BUILDING STRUCTURE. THE PRELIMINARY CALCULATIONS ALONE COVER 1,200 PAGES AND INVOLVE OVER 100 DETAILED DRAWINGS."

" BECAUSE OF ITS CONFIGURATION, WHICH IS ESSENTIALLY THAT OF A STEEL BEAM 209' DEEP, THE TOWERS ARE ACTUALLY FAR LESS DARING STRUCTURALLY THAN A CONVENTIONAL BUILDING SUCH AS THE EMPIRE STATE BUILDING WHERE THE SPINE OR BRACED AREA OF THE BUILDING IS FAR SMALLER IN RELATION TO ITS HEIGHT."

" THE BUILDING AS DESIGNED IS SIXTEEN TIMES STIFFER THAN A CONVENTIONAL STRUCTURE. THE DESIGN CONCEPT IS SO SOUND THAT THE STRUCTURAL ENGINEER HAS BEEN ABLE TO BE ULTRA-CONSERVATIVE IN HIS DESIGN WITHOUT ADVERSELY AFFECTING THE ECONOMICS OF THE STRUCTURE."

At the time the Twin Towers were built, the design approach of moving the support columns to the perimeter and the core, thereby creating large expanses of unobstructed floor space, was relatively new, and unique for a skyscraper. However, that approach is commonplace in contemporary skyscrapers.

Frank Demartini's Statement
Frank A. Demartini, on-site construction manager for the World Trade Center, spoke of the resilience of the towers in an interview recorded on January 25, 2001.

"The building was designed to have a fully loaded 707 crash into it. That was the largest plane at the time. I believe that the building probably could sustain multiple impacts of jetliners because this structure is like the mosquito netting on your screen door -- this intense grid -- and the jet plane is just a pencil puncturing that screen netting. It really does nothing to the screen netting."

Demartini, who had an office on the 88th floor of the North Tower, has been missing since the 9/11/01 attack, having remained in the North Tower to assist in the evacuation. 6 Demartini had first worked at World Trade Center when Leslie E. Robertson Associates hired him to assess damage from the truck bombing in 1993.

Like All Skyscrapers, the Twin Towers Were Over-Engineered
One aspect of engineering that is not widely understood is that structures are over-engineered as a matter of standard practice. Steel structures like bridges and buildings are typically designed to withstand five times anticipated static loads and 3 times anticipated dynamic loads. The anticipated loads are the largest ones expected during the life of the structure, like the worst hurricane or earthquake occurring while the floors are packed with standing-room-only crowds. Given that September 11th was not a windy day, and that there were not throngs of people in the upper floors, the critical load ratio was probably well over 10, meaning that more than nine-tenths of the columns at the same level would have to fail before the weight of the top could have overcome the support capacity of the remaining columns.

There is evidence that the Twin Towers were designed with an even greater measure of reserve strength than typical large buildings. According to the 1964 white paper cited above, a Tower would still be able to withstand a 100-mile-per-hour wind after all the perimeter columns on one face and some of the columns on each adjacent face had been cut. Also, John Skilling is cited by the Engineering News Record for the claim that "live loads on these perimeter columns can be increased more than 2000% before failure occurs."

 

[Gamolon]

Here is some information on the Twin Towers actually being designed to withstand a possible plane impact during foggy conditions....

9-11 Research: Towers' Design Parameters

Contrary to widely promoted misconceptions, the Boeing 767-200s used on 9/11/01 were only slightly larger than 707s and DC 8s, the types of jetliners whose impacts the World Trade Center's designers anticipated

The above graphic from Chapter 1 of FEMA's Report shows the sizes of a 707 and a 767 relative to the footprint of a WTC tower. 1 Flight 11 and Flight 175 were Boeing 767-200s. Although a 767-200 has a slightly wider body than a 707, the two models are very similar in overall size, weight and fuel capacity.


property Boeing 707-320.............Boeing 767-200
fuel capacity 23,000 gallons..........23,980 gallons
max takeoff weight 328,060 lbs.....395,000 lbs
empty weight 137,562 lbs............179,080 lbs
wingspan 145.75 ft.....................156.08 ft
wing area 3010 ft^.....................2 3050 ft^2
length 152.92 ft.........................159.17 ft
cruise speed 607 mph..................530 mph

Given the differences in cruise speeds, a 707 in normal flight would actually have more kinetic energy than a 767, despite the slightly smaller size. Note the similar fuel capacities of both aircraft. The 767s used on September 11th were estimated to be carrying about 10,000 gallons of fuel each at the time of impact, only about 40% of the capacity of a 707.

Statements by Engineers
Engineers who participated in the design of the World Trade Center have stated, since the attack, that the Towers were designed to withstand jetliner collisions. For example, Leslie Robertson, who is featured on many documentaries about the attack, said he "designed it for a (Boeing) 707 to hit it." 2 Statements and documents predating the attack indicate that engineers considered the effects of not only of jetliner impacts, but also of ensuing fires.

John Skilling
John Skilling was the head structural engineer for the World Trade Center. In a 1993 interview, Skilling stated that the Towers were designed to withstand the impact and fires resulting from the collision of a large jetliner such as Boeing 707 or Douglas DC-8.
"Our analysis indicated the biggest problem would be the fact that all the fuel (from the airplane) would dump into the building. There would be a horrendous fire. A lot of people would be killed, ... The building structure would still be there."

A white paper released on February 3, 1964 states that the Towers could have withstood impacts of jetliners travelling 600 mph -- a speed greater than the impact speed of either jetliner used on 9/11/01.

"The buildings have been investigated and found to be safe in an assumed collision with a large jet airliner (Boeing 707—DC 8) traveling at 600 miles per hour. Analysis indicates that such collision would result in only local damage which could not cause collapse or substantial damage to the building and would not endanger the lives and safety of occupants not in the immediate area of impact."

The Richard Roth Telegram
On Feburary 13, 1965, real estate baron Lawrence Wien called reporters to his office to charge that the design of the Twin Towers was structurally unsound. Many suspected that his allegation was motivated by a desire to derail the planned World Trade Center skyscrapers to protect the value of his extensive holdings, which included the Empire State Building. In response to the charge, Richard Roth, partner at Emery Roth & Sons, the architectural firm that was designing the Twin Towers, fired back with a three-page telegram containing the following details.

"THE STRUCTURAL ANALYSIS CARRIED OUT BY THE FIRM OF WORTHINGTON, SKILLING, HELLE & JACKSON IS THE MOST COMPLETE AND DETAILED OF ANY EVER MADE FOR ANY BUILDING STRUCTURE. THE PRELIMINARY CALCULATIONS ALONE COVER 1,200 PAGES AND INVOLVE OVER 100 DETAILED DRAWINGS."

" BECAUSE OF ITS CONFIGURATION, WHICH IS ESSENTIALLY THAT OF A STEEL BEAM 209' DEEP, THE TOWERS ARE ACTUALLY FAR LESS DARING STRUCTURALLY THAN A CONVENTIONAL BUILDING SUCH AS THE EMPIRE STATE BUILDING WHERE THE SPINE OR BRACED AREA OF THE BUILDING IS FAR SMALLER IN RELATION TO ITS HEIGHT."

" THE BUILDING AS DESIGNED IS SIXTEEN TIMES STIFFER THAN A CONVENTIONAL STRUCTURE. THE DESIGN CONCEPT IS SO SOUND THAT THE STRUCTURAL ENGINEER HAS BEEN ABLE TO BE ULTRA-CONSERVATIVE IN HIS DESIGN WITHOUT ADVERSELY AFFECTING THE ECONOMICS OF THE STRUCTURE."

At the time the Twin Towers were built, the design approach of moving the support columns to the perimeter and the core, thereby creating large expanses of unobstructed floor space, was relatively new, and unique for a skyscraper. However, that approach is commonplace in contemporary skyscrapers.

Frank Demartini's Statement
Frank A. Demartini, on-site construction manager for the World Trade Center, spoke of the resilience of the towers in an interview recorded on January 25, 2001.

"The building was designed to have a fully loaded 707 crash into it. That was the largest plane at the time. I believe that the building probably could sustain multiple impacts of jetliners because this structure is like the mosquito netting on your screen door -- this intense grid -- and the jet plane is just a pencil puncturing that screen netting. It really does nothing to the screen netting."

Demartini, who had an office on the 88th floor of the North Tower, has been missing since the 9/11/01 attack, having remained in the North Tower to assist in the evacuation. 6 Demartini had first worked at World Trade Center when Leslie E. Robertson Associates hired him to assess damage from the truck bombing in 1993.

Like All Skyscrapers, the Twin Towers Were Over-Engineered
One aspect of engineering that is not widely understood is that structures are over-engineered as a matter of standard practice. Steel structures like bridges and buildings are typically designed to withstand five times anticipated static loads and 3 times anticipated dynamic loads. The anticipated loads are the largest ones expected during the life of the structure, like the worst hurricane or earthquake occurring while the floors are packed with standing-room-only crowds. Given that September 11th was not a windy day, and that there were not throngs of people in the upper floors, the critical load ratio was probably well over 10, meaning that more than nine-tenths of the columns at the same level would have to fail before the weight of the top could have overcome the support capacity of the remaining columns.

There is evidence that the Twin Towers were designed with an even greater measure of reserve strength than typical large buildings. According to the 1964 white paper cited above, a Tower would still be able to withstand a 100-mile-per-hour wind after all the perimeter columns on one face and some of the columns on each adjacent face had been cut. Also, John Skilling is cited by the Engineering News Record for the claim that "live loads on these perimeter columns can be increased more than 2000% before failure occurs."

Creativedreams,

Do you understand what the word "impact" means? An impact does not last over a period of time. According to the facts, the towers DID survive the impact of the planes. The south tower stood for 56 minutes AFTER the initial impact and the North tower stood for 1 hour and 44 minutes AFTER the initial impact. You use quotes out of context to try and prove your point.

Let's say someone was in a car. While driving, this person slammed into the side of another car. This person survives the IMPACT and is able to call 911 on their cell phone. 15 minutes later, the car bursts into flames and the ensuing fire kills the person inside as they were still trapped in the car. Now, is the cause if death the impact or the fire?

I looked through your posting above and 99% of what everyone said was that the towers were able to survive an IMPACT. Which, like I said, they did. You show me one quote from those people that says they did a study on the what affects of a "HORRENDOUS FIRE" would be on the steel structure?

Can you show me the study they did that shows the calculations for the exact scenario where the planes penetrated the perimeter columns, possibley severed a couple of core columns, and then the ensuing office fires WEAKENED the steel at different temperatures?

You are making grand assumptions based on quotes that don't even suggest that offices fires IN ADDITION to structural damage were taken into consideration.

The only thing they talk about is the initial impact. That's why they use terms like "kinetic energy" and take into account the "weight" of the planes hitting the towers.

Why don't you email Leslie Robertson or his firm and ask them exactly what was meant by "they were built to survive the impact"? Ask him is they did a study where they looked at the STRUCTURAL DAMAGE caused by a jet impact coupled with the ensuing "HORRENDOUS FIRES".

So basically you want all the quotes above to mean that the word "IMPACT", by definition, is an effect that lasts over time.

Is that correct creativedreams?

 

[Gamolon]

Here is some information on the Twin Towers actually being designed to withstand a possible plane impact during foggy conditions....

9-11 Research: Towers' Design Parameters

Contrary to widely promoted misconceptions, the Boeing 767-200s used on 9/11/01 were only slightly larger than 707s and DC 8s, the types of jetliners whose impacts the World Trade Center's designers anticipated

The above graphic from Chapter 1 of FEMA's Report shows the sizes of a 707 and a 767 relative to the footprint of a WTC tower. 1 Flight 11 and Flight 175 were Boeing 767-200s. Although a 767-200 has a slightly wider body than a 707, the two models are very similar in overall size, weight and fuel capacity.


property Boeing 707-320.............Boeing 767-200
fuel capacity 23,000 gallons..........23,980 gallons
max takeoff weight 328,060 lbs.....395,000 lbs
empty weight 137,562 lbs............179,080 lbs
wingspan 145.75 ft.....................156.08 ft
wing area 3010 ft^.....................2 3050 ft^2
length 152.92 ft.........................159.17 ft
cruise speed 607 mph..................530 mph

Given the differences in cruise speeds, a 707 in normal flight would actually have more kinetic energy than a 767, despite the slightly smaller size. Note the similar fuel capacities of both aircraft. The 767s used on September 11th were estimated to be carrying about 10,000 gallons of fuel each at the time of impact, only about 40% of the capacity of a 707.

Statements by Engineers
Engineers who participated in the design of the World Trade Center have stated, since the attack, that the Towers were designed to withstand jetliner collisions. For example, Leslie Robertson, who is featured on many documentaries about the attack, said he "designed it for a (Boeing) 707 to hit it." 2 Statements and documents predating the attack indicate that engineers considered the effects of not only of jetliner impacts, but also of ensuing fires.

John Skilling"A white paper released on February 3, 1964 states that the Towers could have withstood impacts of jetliners travelling 600 mph -- a speed greater than the impact speed of either jetliner used on 9/11/01.

"The buildings have been investigated and found to be safe in an assumed collision with a large jet airliner (Boeing 707—DC 8) traveling at 600 miles per hour. Analysis indicates that such collision would result in only local damage which could not cause collapse or substantial damage to the building and would not endanger the lives and safety of occupants not in the immediate area of impact."

Creativedreams, can you please point out to me in the quote above where Skilling says anything about the study INCLUDING fires and the affects said fires would have on the structural steel and the structure as a whole AFTER estimating the damage caused by the jet impact?

You are making nothing but assumptions at this time. You need to contact Mr. Robertson and ask him exactly what the studies included an were about. Unless, of course, you have actual copies of those studies and can tell us.

 

[Gamolon]

Here's a quote from Robertson that shows your interpretation all the quotes you posted quite incorrect. Here is the link to Robertson's musings about the towers he helped design.

National Academy of Engineering (NAE) - Reflections on the World Trade Center

It appears that about 25,000 people safely exited the buildings, almost all of them from below the impact floors; almost everyone above the impact floors perished, either from the impact and fire or from the subsequent collapse. The structures of the buildings were heroic in some ways but less so in others. The buildings survived the impact of the Boeing 767 aircraft, an impact very much greater than had been contemplated in our design (a slow-flying Boeing 707 lost in the fog and seeking a landing field). Therefore, the robustness of the towers was exemplary. At the same time, the fires raging in the inner reaches of the buildings undermined their strength. In time, the unimaginable happened . . . wounded by the impact of the aircraft and bleeding from the fires, both of the towers of the World Trade Center collapsed.

So they did designed the towers to withstand the IMPACT, which they did. They DIDN'T consider the DAMAGE CAUSED BY THE IMPACT in addition to the RESULTANT FIRES that weakened the already WOUNDED structure.