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 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.
In July of 1971, the American Society of Civil Engineers (ASCE) presented a national award judging the WTC Towers to be the engineering project that demonstrates the greatest engineering skills and represents the greatest contribution to engineering progress and mankind.
Like many modern structures and buildings, the WTC Towers were over-designed to withstand weight distribution in the event of structural damage. According to calculations made by the engineers who helped with the design of the Twin Towers, all the columns on one side of a Tower could be cut, as well as the two corners and some of the columns on each adjacent side, and the building would still be strong enough to withstand a 100-mile-per-hour wind. As well, Live loads on these columns can be increased more than 2,000% before failure occurs.
In the planning of the buildings the designers considered potential attacks, and the WTC towers were designed to survive them. Between Early 1984 and October 1985 it was reported that:
The Office of Special Planning (OSP), a unit set up by the New York Port Authority to assess the security of its facilities against terrorist attacks, spends four to six months studying the World Trade Center. It examines the centers design through looking at photographs, blueprints, and plans. It brings in experts such as the builders of the center, plus experts in sabotage and explosives, and has them walk through the WTC to identify any areas of vulnerability OSullivan consults one of the trade centers original structural engineers, Les Robertson, on whether the towers would collapse because of a bomb or a collision with a slow-moving airplane. He is told there is little likelihood of a collapse no matter how the building was attacked.
One of these hypothetical examples was put to the test in the 1993 WTC bombing. This attack prompted more discussions about the safety of the WTC towers. In response to these concerns, WTC building designer John Skilling explained that they looked at every possible thing we could think of that could happen to the buildings, even to the extent of an airplane hitting the side A previous analysis carried out early in 1964, calculated that the towers would handle the impact of a 707 traveling at 600 mph without collapsing.
This statement indicates that the designers considered Boeing 707 airplane impact speeds of 600 mph. It seems likely that the designers considered this impact speed for the reason that the cruse speed of a Boeing 707 is 607 mph. In comparison, both of the planes that hit the WTC Towers on 9/11 were Boeing 767s. The FEMA report indicates that Flight 11 flew at a speed of 470 mph into the North Tower, and the second plane flew at a speed of 590 mph into the South Tower. Not only were these speeds anticipated by the building designers, the Boeing 707 is similar in size to the ones flown into the towers on 9/11. According to Jim Hoffman, the planes used on 9/11 were only slightly larger than 707s and DC 8s, the types of jetliners whose impacts the World Trade Center's designers anticipated. This statement is supported by the following chart:
|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|
In fact, Hoffman observes that a 707 in normal flight would actually have more kinetic energy than a 767, despite the slightly smaller size.
Commercial airliners typically fly with jet fuel, so it is not surprising that the designers would consider this problem. In 1993, Skilling explained that they performed an analysis that concluded that the WTC towers would survive the impact and jet fuel fires from a Boeing 707:
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.
In fact, no steel-framed building structures had ever collapsed due to fire before or since 9/11. This further supports Skillings analysis about the possibility of jet fuel destroying the WTC towers. According to Paul Thompson, 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. This white paper concluded that:
The buildings have been investigated and found to be safe in an assumed collision with a large jet airliner (Boeing 707DC 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.
Thompson explains that besides this paper, no documents are known detailing how this analysis was made. In fact, many of the building documents are unavailable because the building owners, designers and insurers, prevented independent researchers from gaining accessand delayed the BPAT team in gaining accessto pertinent building documents largely because of liability concerns.
The lack of access to WTC building documents remains a problem to this day. Indeed, in March of 2007, Steven Jones and Scholars for 9/11 Truth and Justice finally obtained the WTC blueprints from an anonymous individual.
Although the WTC was over-designed to withstand almost anything including hurricanes, high winds, bombings and an airplane hitting it,  the designers did not apparently consider controlled demolition:
Skillinga recognized expert in tall buildingsdoesn't think a single 200-pound car bomb would topple or do major structural damage to a Trade Center tower. The supporting columns are closely spaced and even if several were disabled, the others would carry the load. However, he added, I'm not saying that properly applied explosivesshaped explosivesof that magnitude could not do a tremendous amount of damage. Although Skilling is not an explosives expert, he says there are people who do know enough about building demolition to bring a structure like the Trade Center down. I would imagine that if you took the top expert in that type of work and gave him the assignment of bringing these buildings down with explosives, I would bet that he could do it.
One week before 9/11, WTC building designer Leslie Robertson reiterated the fact that the towers were designed to survive plane crashes:
Leslie Robertson, one of the two original structural engineers for the World Trade Center, is asked at a conference in Frankfurt, Germany what he had done to protect the twin towers from terrorist attacks. He replies, I designed it for a 707 to smash into it, though does not elaborate further.
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.
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 doorthis intense gridand the jet plane is just a pencil puncturing that screen netting. It really does nothing to the screen netting.
Demartini appeared to be so confident that the towers would not collapse that he stayed behind to help save at least 50 people. As a result of his actions, he lost his life on 9/11.
In summary, the World Trade Center designers not only contemplated jet fuel firesthey considered the plane crashes that would have caused them. They anticipated impact speeds of 600 mph as well as aircraft similar in size to the planes used on 9/11. The towers were designed to survive substantial column loss along with 100 mph winds. They were intended to survive bombings, earthquakes, and hurricanes. If the designers were sufficiently competent in the planning and realization of their award-winning WTC Towers as intended, they should have remained standing. Tragically, they did not. From this irreconcilable fact there can only be two conclusions; either the designers were inadequate in their designs, or there is an alternate explanation for their destruction on 9/11.
However, these are not all of the facts. After 9/11, WTC building designer Leslie Robertson has made statements which directly contradict previous comments by other building designersincluding himself.
According to Paul Thomspon, it was reported on Sept 3-7, 2001 the Boeing 707 was the largest in use when the towers were designed. [Leslie] Robertson conducted a study in late 1964, to calculate the effect of a 707 weighing 263,000 pounds and traveling at 180 mph crashing into one of the towers. [Robertson] concluded that the tower would remain standing. However, no official report of his study has ever surfaced publicly.
Surprisingly, Robertson claimed that the WTC Towers were designed to survive plane crashes at speeds of 180 mph. He also repeated this claim in an interview with Steven Jones in October 2006. However, these statements are contradicted by Skilling, who indicated that a previous analysis, carried out early in 1964, calculated that the towers would handle the impact of a 707 traveling at 600 mph without collapsing. Robertson is also somewhat contradicted by his own statement in 1984-5 that there was little likelihood of a collapse no matter how the building was attacked.
Immediately after 9/11 it was reported that the engineer who said after the 1993 bombing that the towers could withstand a Boeing 707, Leslie Robertson, was not available for comment yesterday, a partner at his Manhattan firm said. We're going to hold off on speaking to the media, said the partner, Rick Zottola, at Leslie E. Robertson Associates. We'd like to reserve our first comments to our national security systems, F.B.I. and so on.
Later, in 2002, Robertson said: to the best of our knowledge, little was known about the effects of a fire from such an aircraft, and no designs were prepared for that circumstance. In 2005, NIST also claimed that they had 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.
These statements ignore the fact that Skilling claimed in 1993 that Our analysis [in 1964] 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 The building structure would still be there.
As well, Robertson said the following in an interview with Steven Jones in October 2006:
I support the general conclusions of the NIST report The [WTC] was designed for the impact of a low flying slow flying Boeing 707. We envisioned it [to be like] the aircraft that struck the Empire State building [during] WW II. It was not designed for a high speed impact from the jets that actually hit it Yes there was a red hot metal seen [in the WTC rubble] by engineers. MoltenMolten means flowingIve never run across anyone who has said that they had in fact seen molten metal, or by the way if they had seen it, if they had performed some kind of an analysis to determine what that metal was.
Three of these claims are demonstrably problematic. The claim about slow flying aircraft has already been discussed. The statement about molten metal is also contradicted by many eyewitness statements. In fact, it is possible that Robertson himself saw this molten steel, but this fact is not confirmed at the present time.
Not only had many witnesses claimed to have seen this molten metal, FEMA had performed an analysis of it. Their observations were recorded in Appendix C of their WTC Building Performance Study. Ironically, Robertson stated that he was not aware if anyone had performed an analysis on the molten steel in an interview with Joneswho had also performed an analysis of previously molten metal samples from Ground zero. Jones findings appear to be corroborated by the FEMA report which described a phenomenon never before observed in building fires: eutectic reactions, which caused intergranular melting capable of turning a solid steel girder into Swiss cheese. The New York Times described this as perhaps the deepest mystery uncovered in the investigation. NIST did not even mention the presence of molten steel and called it irrelevant to the investigation. Amazingly, NISTs 10 000 page, $20 million report couldnt find the space to mention the earlier findings about the molten steel analyzed in the FEMA report. There have even been reports of evaporated steel.
The presence of molten steel would be very surprising because jet fuel fires are incapable of melting steel. In fact, NIST reported that the highest recorded temperatures of the jet fuel fires from the WTC were not even enough to weaken the steel.
It is demonstrable that the WTC building designers claimed that the Twin Towers would survive an event similar to 9/11. Either the WTC building designers were tragically wrong in their calculations and designs, or there is another explanation for the destruction of the WTC Towers. After 9/11, WTC building designer Leslie Robertson has made claims that are contradicted by statements and documents from as many as 40 years ago. These contradictions must be resolved through the release of all of the pertinent WTC documents that have been withheld since 9/11.
 Research based on Paul Thompsons Complete 9/11 Timeline and other sources. http://www.cooperativeresearch.org/entity.jsp?entity=leslie_robertson
 James Glanz and Eric Lipton, City in the Sky: The rise and fall of the World Trade Center, Times Books, Henry Hold and Company, LLC, 2003, pages 134-136.
 Angus K. Gillespie, Twin Towers: The Life of New York City's World Trade Center (New Brunswick, N.J.: Rutgers University Press 1999), 117
 How Columns Will Be Designed for 110-Story Buildings, Engineering News-Record, April 2, 1964: 48-49.
 World Trade Center Building Performance Study: Data Collection, Preliminary Observations, and Recommendations, FEMA Report 403, Federal Emergency Management Agency, Federal Insurance and Mitigation Administration, Washington, DC, 2002. Page 31.
 James Glanz, and Eric Lipton, Towers Withstood Impact, but Fell to Fire, Report Says, Fri March 29, 2002, New York Times.
Experts said no building like it [WTC7], a modern, steel-reinforced high-rise, had ever collapsed because of an uncontrolled fire.
Norman Glover, Fire Engineering, Fire Engineering journal, October 2002.
Almost all large buildings will be the location for a major fire in their useful life. No major high-rise building has ever collapsed from fire
 Scholars for 9/11 Truth and Justice, Independent Investigators Release Suppressed Blueprints of Destroyed World Trade Center Tower, March 27, 2007. http://www.stj911.org/.
 Prisonplanet.com, WTC Construction Manager: Towers Were Designed to Take Numerous Plane Crashes, http://www.prisonplanet.com/, November 14, 2004.
 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]
 Towers Built to Withstand Jet Impact. See also: Thompson, Complete 9/11 Timeline, Between September 3, 2001 and September 7, 2001: WTC Structural Engineer Says Trade Center Designed for 707 Crashing Into It. These articles from the day after 9/11 make clear the fact that this statement was made before 9/11: Les Robertson, the Trade Center's structural engineer, spoke last week at a conference on tall buildings in Frankfurt, Germany.
 See a partial transcript of this interview included below.
 James Glanz, Believed to Be Safe, the Towers Proved Vulnerable to Jet Fuel Fire, The New York Times, September 12, 2001
 Steven Jones in discussion With Leslie Robertson, by KGNU Radio, Denver, CO, Oct 26, 2006. http://www.911podcasts.com/files/audio/StevenJones_LeslieRobertson_20061026.mp3. See also:
 See another statement by Robertson here: 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). Taken from: Robertson, Reflections on the World Trade Center
 George Washington, Why was there Molten Metal Under Ground Zero for Months after 9/11? December 06, 2005. http://georgewashington.blogspot.com/
 James M. Williams, SEAUNEWS, The Newsletter of the Structural Engineers Association of Utah, Volume VI- Issue II October 2001
Someone, quite possibly Leslie Robertson describes fires still burning and molten steel still running 21 days after the attacks. See also:
It is possible that Robertson himself said this. James Williams, SEAUNEWS, The Newsletter of the Structural Engineers Association of Utah, October 2001. This was one of points listed by SEAU president Williams, after stating that Robertson was a guest of SEAU and presented to them a number of interesting facts including some you might not have heard. As of 21 days after the attack, the fires were still burning and molten steel was still running. page 3, http://www.seau.org/SEAUNews-2001-10.pdf. An email sent to the Seau.org contact email address to clarify this point went unanswered.
 See here for
pictures and comments in FEMAs report mentioning the melted steel:
Although virtually all of the structural steel from the Twin Towers and Building 7 was removed and destroyed, preventing forensic analysis, FEMA's volunteer investigators did manage to perform "limited metallurgical examination" of some of the steel before it was recycled. Their observations, including numerous micrographs, are recorded in Appendix C of the WTC Building Performance Study. Prior to the release of FEMA's report, a fire protection engineer and two science professors published a brief report in JOM disclosing some of this evidence.
The results of the examination are striking. They reveal a phenomenon never before observed in building fires: eutectic reactions, which caused "intergranular melting capable of turning a solid steel girder into Swiss cheese." The New York Times described this as "perhaps the deepest mystery uncovered in the investigation. WPI provides a graphic summary of the phenomenon.
 Paul Watson, Scientific Analysis Proves Towers Brought Down By Incendiaries, June 20, 2006. http://www.prisonplanet.com/ using advanced techniques we're finding out what's in these samples [of iron taken from Ground Zero]we're finding iron, sulphur, potassium and manganesethese are characteristic of a variation of thermite which is used to cut through steel very rapidly, it's called thermate. See also:
 Jim Hoffman, NIST's World Trade Center FAQ A Reply to the National Institute for Standards and Technology's Answers to Frequently Asked Questions. August 30, 2006.
 Engineers have been trying to figure out exactly what happened Fire and the structural damage would not explain steel members in the debris pile that appear to have been partly evaporated from:
James Glanz, Engineers are baffled over the collapse of 7 WTC; Steel members have been partly evaporated, New York Times, November 29. 2001.
 The maximum flame temperature increase for burning hydrocarbons (jet fuel) in air is, thus, about 1000 °C -- hardly sufficient to melt steel at 1500 °C. Taken from: Eagar, T. W. and Musso, C. (2001). Why Did the World Trade Center Collapse? Science, Engineering, and Speculation, Journal of the Minerals, Metals and Materials Society, 53/12:8-11 (2001).