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Dammit the WTC Twin Towers Were Engineered to Handle a Boeing 767; Associate Structural Engineer: Leslie Robertson in Denial
Topic Started: Oct 19 2010, 04:26 PM (4,408 Views)
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This may seem like old ground, but a fundamental part of the 9/11 Official Conspiracy Theory as it pertains to WTC deals with the fallacy that the Towers were never engineered to cope with the kind of aircraft impacts that they faced on 9/11.

Back in the early 1960's when the Towers were designed, there was a great fear that hey might get struck
by an aircraft and not survive.

Since an incident of this nature occurred in July, 1945, when an off course B-25 bomber , flying in fog, flew into the Empire State Building, such a fear was certainly justified.

"Saturday morning in July 1945, when a B-25 bomber, lost in the fog, barreled into the 79th floor of the Empire State Building. Most of the 14 people who died were incinerated by a fireball created when the plane's fuel ignited, even though the fire was quickly contained. The following year, another plane crashed into the 72-story skyscraper at 40 Wall Street, and yet another one narrowly missed the Empire State Building, terrifying sightseers on the observation deck."

But were the Twin Towers really engineered to withstand the consequences of being impacted by the largest commercial aircraft in existence (at that time)?

A great deal has been said arguing that they were designed to only handle a Boeing 707 flying at 180 mph
attempting to land in fog.

In many of these stories, Leslie Robertson, who was credited as being the chief structural engineer for the Twin Towers, endorsed the claim that they were not designed to handle the impact of a Boeing 767 flying at cruise speed.

Leslie Robertson
"We had designed the project for the impact of the largest airplane of its time, the Boeing 707. The 767 that actually hit the WTC was quite another matter again. First of all it was a bit heavier than the 707, not very much heavier, but a bit heavier. But mostly it was flying a lot faster. And the energy that it put into the building is proportional to its square of the velocity, as you double the velocity, four times the energy. Triple the velocity, eight times the energy and so forth.

And then of course with the 707 to the best of my knowledge the fuel load was not considered in the design, and indeed I don't know how it could have been considered. But, and with the 767 the fuel load was enormous compared to that of the 707, it was a fully fuelled airplane compared to the 707 which was a landing aircraft. Just absolutely no comparison between the two."

So Robertson in this post 9/11 quote is arguing that though there was a minor weight difference between a Boeing 707 and a Boeing 767, but, the fuel loads were significantly different. He argues that the design called for a Boeing 707 with only remaining fuel for landing vs. a Boeing 767 with a full fuel load.

First of all, a fully fueled Boeing 707, carries 23,000 gallons of fuel and a fully fueled Boeing 767 carries 23,980 gallons of fuel. Not a significant difference, unless Robertson is correct about the status of the Boeing 707 the WTC Towers were designed to handle.

Well, prior to 9/11, Leslie Robertson was making a different, more ego-serving claim;

http://snurl.com/j54gc (Report From Ground Zero page 188

A few quotes from that page;

Posted Image

"After the bombing of the WTC in 1993, Leslie Robertson, one of the engineers who worked on the towers' structural design in the 1960s, claimed that each had been built to withstand the impact of a fully fueled 707. The 707 was the state-of-the-art airplane, and the Port Authority was quite amenable to considering the effect of an airplane as a design criterion...I don't know if we considered the fire damage that would cause. Anyway, the architect, not the engineer, is the one who specifies the fire system."

"Of course, when Yamaski was designing the buildings he was aware that steel, when it reaches an inherent temperature of 1200 degrees, will stretch at the rate of 9 1/2 inches per 100 feet. He undoubtedly took into account the possibility of a plane's hitting the building and causing the steel to stretch in a resulting fire. There might even be a collapse, but only on the side of the building that was 'hit. Partial collapses often happen in burning buildings."

The other critical point was the effective speed of the two aircraft. Did the design call for a limitation of a Boeing 707 flying at 180 mph?

The cruise speed of a Boeing 707 is 607 mph = 890 ft/s,
The cruise speed of a Boeing 767 is 530 mph = 777 ft/s.

On September 8, 2002, two reporters for the NY Times, James Glanz and Eric Lipton posted a story
under the heading The Height of Ambition: Part Four.

A few quotes from that story;

"Robertson took the time to calculate how well his towers would handle the impact from a Boeing 707, the largest jetliner in service at the time. He says that his calculations assumed a plane lost in a fog while searching for an airport at relatively low speed, like the B-25 bomber. He concluded that the towers would remain standing despite the force of the impact and
the hole it would punch out. The new technologies he had installed after the motion experiments and wind-tunnel work had created a structure more than strong enough to withstand such a blow.

Exactly how Robertson performed these calculations is apparently lost -- he says he cannot find a copy of the report. Several engineers who worked with him at the time, including the director of his computer department, say they have no recollection of ever seeing the study.

One architect working for the Port Authority issued a statement to the press, covered in a prominent article in The Times, explaining that Robertson's study proved that the towers could withstand the impact of a jetliner moving at 600 miles an hour.

There were only two problems. The first, of course, was that no study of the impact of a 600-mile-an-hour plane ever existed. ''That's got nothing to do with the reality of what we did,'' Robertson snapped when shown the Port Authority architect's statement more than three decades later.

The second problem was that no one thought to take into account the fires that would inevitably break out when the jetliner's fuel exploded, exactly as the B-25's had."

Well difficult as it is to believe, Robertson, post 9/11 is now arguing his design work never called for the Towers to "withstand the impact of a fully fueled 707" which would also require a consideration of the fires that would result.

But in his defence, Robertson was carrying a great guilt load following 9/11 and may have wanted to distance himself from his earlier claims about the Titanic-nature of the Twin Towers;


In another interview, with the BBC recorded 2 months after 9/11, Leslie Robertson had this to say; "And then of course with the 707 to the best of my knowledge the fuel load was not considered in the design, and indeed I don't know how it could have been considered. But, and with the 767 the fuel load was enormous compared to that of the 707, it was a fully fuelled airplane compared to the 707 which was a landing aircraft. Just absolutely no comparison between the two."

Well, based on documentation that the NIST obtained in 2003, the Towers most definitely were designed to handle a 600 mph Boeing 707 impact.

In a followup article for the NY Times, published on December 3, 2003, the same reporter, James Glanz, now, in effect retracted his earlier story;

"The investigators also said that newly disclosed Port Authority documents suggested that the towers were designed to withstand the kind of airplane strike that they suffered on Sept. 11.

Earlier statements by Port Authority officials and outside engineers involved in designing the buildings suggested that the designers considered an accidental crash only by slower aircraft, moving at less than 200 miles per hour.

The newly disclosed documents, from the 1960's, show that the Port Authority considered aircraft moving at 600 m.p.h., slightly faster and therefore more destructive than the ones that did hit the towers, Dr. S. Shyam Sunder, who is leading the investigation for the National Institute of Standards and Technology in the Commerce Department said."

The reference to these documents appears in NCSTAR 1-2, 8.2 AIRCRAFT IMPACT DAMAGE ANALYSIS, 8.2.1 Safety of the WTC Towers in Aircraft Collision

"Finding 11 acknowledges that " The documents indicate that a Boeing 707, the largest commercial aircraft at the time, flying at 600 mph was considered and that the analysis indicated 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. No documentary evidence of the aircraft impact analysis was available to review the criteria and methods used in the analysis of the aircraft impact into the WTC towers, or to provide details on the ability of the WTC towers to withstand such impacts."

Here are a few of the salient points that the NIST found in the discovered Port Authority documents from February 3, 1964:

1. A structural analysis was carried out by the firm of Worthington, Skilling, Helle & Jackson and 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.

2. The buildings have been designed for wind loads of 45 lbs per square foot which is 2.5 times the New York City Building Code requirements of 20 lbs per square foot, the design load for the Empire State, Pan American and Chrysler Buildings. In addition to static wind loads, a complete dynamic analysis has been made to take into account extremely high velocity gusts.

3. The buildings have been investigated and found to be safe in an assumed collision with a large jet airliner (Boeing 707 - DC 8) travelling 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 of occupants not in the immediate area of impact.

7. The design has been reviewed by some of the most knowledgeable people in the construction industry. In a letter to John Skilling, the Structural Engineer for the World Trade Center, the Chief Engineer of the American Bridge Division of U.S. Steel Corporation said:
"In reviewing this design with our Operating and Construction Departments, we are very optimistic that you have turned a new page in the design of structural steel."

Keep in mind that Robertson was attempting to recall details from over 35 years in the past and had already made a number of statements that revealed a plane wasn't the only thing that was lost in a fog.

"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."

Twin Towers Engineered To Withstand Jet Collision
By Eric Nalder

as reported in the Seattle Times Februaury 27, 1993

"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.”

Towers built to withstand jet impact
as reported in the Chicago Tribune September 12, 2001

"Les Robertson, the Trade Center's structural engineer, spoke last week at a conference on tall buildings in Frankfurt, Germany. He was asked during a question-and-answer session what he had done to protect the twin towers from terrorist attacks, according to Joseph Burns, a principal at the Chicago firm of Thornton-Thomasetti Engineers.
Burns, who was present, said that Robertson said of the center, "I designed it for a 707 to smash into it."

Burns, whose firm did the structural engineering for the Petronas Twin Towers in Malaysia one of the world's tallest buildings said Robertson did not elaborate on the remark."

"Owners: Port Authority of New York and New Jersey.
(99 year leased signed in April 2001 to groups including Westfield America and Silverstein Properties)

Architect: Minoru Yamasaki, Emery Roth and Sons consulting

Engineer: John Skilling and Leslie Robertson of Worthington, Skilling, Helle and Jackson"

"Tim Wilkinson, Lecturer, Department of Civil Engineering, The University of Sydney, NSW, 2006, Australia

The architect for the WTC was Minoru Yamasaki, with the structural engineering led by John Skilling and Leslie Robertson of Worthington, Skilling, Helle and Jackson."

Study Suggests Design Flaws Didn't Doom Towers
Published: October 20, 2004

"For Leslie E. Robertson, the structural engineer who helped design the twin towers as a young man back in the early 1960's, the latest findings buttress his longstanding assertion that the towers were fundamentally sound. His wife, Saw-Teen See, who is a managing partner at Mr. Robertson's New York design firm, said the report "validates the way we thought the structure would have performed."
The findings by the institute, however, still do not exonerate Mr. Robertson or the building's owner, the Port Authority of New York and New Jersey, which, in defending the trade center project from critics in the 1960s, boasted that the design was so robust that the towers could be hit by a jet traveling at 600 miles per hour without collapsing or endangering the lives of occupants beyond the impact zone. In retrospect, such a claim was unjustified because the engineers had failed to consider the added stresses caused by the resulting fires."

From a 2003 Newsweek article
by Katherine Stroup

"The buildings were designed specifically to withstand the impact of a Boeing 707—the largest plane flying in 1966, the year they broke ground on the project—and Robertson says it could have survived even the larger 767s that crashed into the towers on Tuesday morning. But the thousands of gallons of burning jet fuel finally brought down the noble structures. “As the fire raged it got hotter and hotter and the steel got weaker and weaker,” he says, adding that building a skyscraper able to handle such a blaze would not have been viable, financially and functionally. “You could always prepare for more and more extreme events, but there has to be a risk analysis of what’s reasonable.”

World Trade Towers design exceeded wind load codes
Public release date: 1-Oct-2004

"NIST recently completed its review of the original 1960s-era source documents containing wind tunnel test data and wind load estimation methods used for the towers, calculated the wind load estimates based on a clearer interpretation of this information, and determined the values actually used in the design of the buildings. These clarified original design wind load estimates all exceed those established by the New York City building code prior to 1968 (when the WTC towers were designed) and through 2001 (when the towers were destroyed). The values also are higher than those required by other selected building codes of the era, including the relevant national model building code.
Wind load capacity is a key factor in determining the overall strength of a tall building and is important in determining not only its ability to withstand winds but also its reserve capacity to withstand unanticipated events such as a major fire or impact damage."

Contradictory statements by Leslie Robertson where he sometimes states that the WTC Towers were engineered for a slow moving B-707 flying in the fog, come across as a emotionally defensive reaction to his sense of guilt over the collapse of the WTC Towers.

Claiming the WTC Towers were never engineered for 600 mph 767 impacts, assuages his sense of guilt over those many lost lives.

A tragedy that he could never have prevented and holds no responsibility for.

82 year old Leslie Robertson is yet another innocent victim of the Inside Job.

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