The World Trade Center Twin Towers Were Designed For Jet Impacts
The early news reports noted how well the towers withstood the initial impact of the aircraft; however, when one recognizes that the buildings had more than 1,000 times the mass of the aircraft and had been designed to resist steady wind loads of 30 times the weight of the aircraft, this ability to withstand the initial impact is hardly surprising. Furthermore, since there was no significant wind on September 11, the outer perimeter columns were only stressed before the impact to around 1/3 of their 200 MPa design allowable. tms.org
The cruse speed of a Boeing 707 is 607 mph. wikipedia.org
Both planes that hit the WTC Towers on 9/11 were Boeing 767’s.
After the crash of a B-25 bomber into the Empire State Building in 1945, designers of high-rise buildings became aware of the potential of aircraft collision with buildings. Documents obtained from The Port Authority of New York and New Jersey (PANYNJ) indicated that the safety of the WTC towers and their occupants in an aircraft collision was a consideration in the original design. A three-page white paper “ [NIST NCSTAR 1-2 Appendix A: SALIENT POINTS WITH REGARD TO THE STRUCTURAL DESIGN OF THE WORLD TRADE CENTER TOWERS Salient points with regard to the structural design of the World Trade Center towers] ”, February 1964, from the PANYNJ (see Appendix A) indicated that the impact of a Boeing 707 or DC 8 aircraft flying at a speed of 600 mph was analyzed during the design stage of the WTC towers. The paper also addressed the life safety considerations following such impact. The paper stated that “…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.” http://wtc.nist.gov/NISTNCSTAR1-2.pdf p118
February 3, 1964:
The analysis Skilling is referring to is likely one done in early 1964, during the design phase of the towers. A three-page white paper, dated February 3, 1964, described its findings: “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.” However, besides this paper, no documents are known detailing how this analysis was made. [Glanz and Lipton, 2004, pp. 131-132; Lew, Bukowski, and Carino, 10/2005, pp. 70-71]
February 16th 1964:
"Mr. Roth said that a structural analysis by the firm of Worthington, Skilling, Helle & Jackson had found that if a tower were hit by an airliner at 600 miles an hour, the damage to the tower would be only local and its occupants outside the immediate area of impact would not be endangered." http://www.nytimes.com/1964/02/15/nyregion/15WTC.html
“Our analysis indicated the biggest problem would be the fact that all the fuel would dump into the building. [But] the building structure would still be there.” -John Skilling (source_p138) (cached_copy)
I was there in 1993, 14 minutes after the bomb went off. I operated some 16 hours at the building and with all the post-incident critiques and debriefings with various agencies. "We were always told by everyone, the experts, that these buildings could withstand direct hits from airplanes. That's the way they were designed. They went through all of this architectural stuff, way beyond the scope of my knowledge. It was hit by an airplane. That's okay. It's made to be hit by an airplane. I mean I think everyone may have believed that. We were all told years ago it was made to be hit by an airplane."
September 5th 2001:
"I designed it for a 707 to smash into it." -Les Robertson, the Trade Center's Structural Engineer at The International Conference on Trends in Tall Buildings in Frankfurt, Germany (source) http://web.archive.org/web/20030426084855/http://www.leadertelegram.com/specialreports/attack/storydetail.asp?ID=14 (leadertelegram.com)
Also according to Robertson, the WTC towers were “in fact the first structures outside the military and nuclear industries designed to resist the impact of a jet airplane."
Leslie E. Robertson, Reflections on the World Trade Center. National Academy of Engineering, Volume 32, Number 1 - Spring 2002.
Not only were the towers designed to survive plane crashes, they were designed to potentially survive multiple plane crashes. This fact is supported by Frank A. Demartini, the on-site construction manager for the World Trade Center, who said 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.” http://www.prisonplanet.com/video/141104clip.WMV (prisonplanet.com)
Demartini appeared to be so confident that the towers would not collapse that he stayed behind to help save at least 50 people. (source) As a result of his actions, he lost his life on 9/11. “DeMartini will be in his office on the 88th floor of the north tower when it is hit on 9/11. He will die when the tower collapses, after helping more than 50 people escape.” [Associated Press, 8/29/2003; New York Times, 8/29/2003] http://www.nytimes.com/2003/08/29/nyregion/29WTC.html (nytimes.com)
An additional load, stated by The Port Authority to have been considered in the design of the towers, was the impact of a Boeing 707, the largest commercial airliner when the towers were designed, hitting the building at its full speed of 600 mph. http://wtc.nist.gov/NISTNCSTAR1CollapseofTowers.pdf (nist.gov_NCSTAR1_p56)
"The WTC Buildings were designed to withstand Boeing 707 impacts but were "never designed for the massive explosion nor the intense [Jet Fuel jet fuel] fires that came next - a key design omission" - [September 2005 NIST Report Eduardo Kausel]
The [Jet Fuel jet fuel] fires were not "reasonably foreseeable" -Loring Knoblauch (CEO of UL)
February 27, 1993: WTC Engineer Says Building Would Survive Jumbo Jet Hitting It
In the wake of the WTC bombing, the Seattle Times interviews John Skilling who was one of the two structural engineers responsible for designing the Trade Center. Skilling recounts his people having carried out an analysis which found the twin towers could withstand the impact of a Boeing 707. He says, “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.” But, he says, “The building structure would still be there.” The analysis Skilling is referring to is likely one done in early 1964, during the design phase of the towers. A three-page white paper, dated February 3, 1964, described its findings: “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.” However, besides this paper, no documents are known detailing how this analysis was made. The other structural engineer who designed the towers, Leslie Robertson, carried out a second study later in 1964, of how the towers would handle the impact of a 707 (see Between September 3, 2001 and September 7, 2001). However, the National Institute of Standards and Technology (NIST), following its three-year investigation into the WTC collapses, will in 2005 state that it has been “unable to locate any evidence to indicate consideration of the extent of impact-induced structural damage or the size of a fire that could be created by thousands of gallons of jet fuel.”
Entity Tags: John Skilling, World Trade Center