Wednesday, April 21, 2010

911-Unthinkable Collapses

Unthinkable Collapses
Too Shocking for Rational Analysis

The North Tower explodes at 10:28 AM

In fifteen seconds the huge permanent steel structure of the South Tower disintegrated from top to bottom into an exploding cloud of rubble and dust. Twenty-nine minutes later the North Tower underwent the same process. Do buildings really fall through themselves like that, turning to dust in seconds? Is that really supposed to happen to a steel structure because of impacts and fires near the top? Perhaps not too many people were asking such questions because none of the series of events leading up to that were supposed to happen. We witnessed an increasingly improbable series of events, from a hijacking with knives, to a jet hitting a World Trade Center Tower, to multiple hijackings, to a second jet hitting the other Tower, to yet more hijackings, and a plane hitting the heart of the nation's military establishment. Each event in this series was more improbable than the last. So by the time we got to the collapsing skyscrapers part, we were conditioned to expect the unbelievable.
A rational look at the Twin Tower collapses reveals that the official story contradicts the laws of physics and the most basic knowledge of the behavior of steel structures, and matter itself.
The Towers were designed to survive jet impacts of the type that happened on September 11th.

The fires were not very severe in the South Tower and were diminishing. Even severe fires would not have initiated a collapse.

Skyscapers have never collapsed due to fires or any other cause other than controlled demolition.

The Towers underwent explosive disintegrations that didn't look anything like the way such buildings would fall.

The destruction of the Towers displayed several unique features of controlled demolition.

There are relatively simple proofs that the buildings did not fall of their own weight.

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Towers' Design Parameters

Twin Towers' Designers Anticipated Jet Impacts Like September 11th's

Structural engineers who designed the Twin Towers carried out studies in the mid-1960s to determine how the buildings would fare if hit by large jetliners. In all cases the studies concluded that the Towers would survive the impacts and fires caused by the jetliners.

Evidence of these studies includes interviews with and papers and press releases issued by engineers who designed and oversaw construction of the World Trade Center.

1960s-era Jetliners Compared to Boeing 767s

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. 3

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. ⁴

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. ⁵

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.
...
4. 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.
...
5. 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. 7 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. ⁸ 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." ⁹

References

1. Chapter 1: Introduction, WTC Building Performance Study,
2. Towers collapse shocks engineers, MedServ, 9/11/01 [cached]
3. Twin Towers Engineered To Withstand Jet Collision, The Seattle Times, 2/27/93 [cached]
4. City in the Sky, Times Books, Henry Hold and Company, LLC, 2003, page 131
5. City in the Sky, Times Books ..., , page 134-136
6. Painful Losses Mount In the Construction 'Family', construction.com, 10/1/01 [cached]
7. Factor of safety, StateMaster.com, [cached]
8. City in the Sky, Times Books ..., , page 133
9. How Columns Will Be Designed for 110-Story Buildings, ENR, 4/2/1964
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The Fires

The Twin Towers' Fires and Their Possible Effects

The South Tower's fires burned hot enough at produce visible flames and light smoke (photograph) until the jet fuel burned off less than ten minutes after the crash. Thereafter the fires dwindled and the smoke darkened. When it collapsd 56 minutes after the crash, the invisible fires were emitting only a thin veil of black smoke.

Much was made of the severity of the fires in the Twin Towers, since fires were invoked to explain failures they had never before caused. Some reportscompared the heat produced by the fires to that of nuclear power plants. In fact the fires were not as severe as many other highrise fires, none of which caused the buildings to collapse. Furthermore, the fires became less severe over time, at least in the South Tower, whose smoke became thin and nearly black by the time its total destruction.

Fire-induced column failure collapse theories, such as Prof. Bazant's, assume scenarios in which fires consume entire floors and burn for extended periods at temperatures of over 800° C. There are several problems with such scenarios.

800°C is near the maximum flame temperature of hydrocarbons burning in air without pre-heating or pressurization of the air (estimates of which range from 900°C to 1250°C ¹ ). Those temperatures are usually reached only with premixed (blue) flames, such as in gas stoves and blowtorches. Diffuse flames, such as in building fires, tend to be cooler. Although enclosures can elevate fire temperatures considerably by containing the fires' heat, tests that have recorded gas temperatures of over 800°C have involved ventilation and fuel supply characteristics arguably not present in the Twin Towers.
Widespread fires reaching 700°C would have caused extensive window breakage over time. Although there are breaches in the perimeter wall glazing of parts of the Towers that appear to have ocurred after the plane crashes, such as in a fire zone on the 104th and 105th floor of the North Tower, descriptions of windows popping or falling on victims are not readily apparent in the eyewitness reports from that day. This contrasts with the prominence of reports of fire-induced window-popping in other highrise fires.
Widespread fires reaching 700°C and would have made the steel glow red-hot. Visual records of the events, while showing fire damage to the aluminum cladding covering the perimeter columns, do not appear to show glowing steel. ²
Fires would have to be very extensive to raise the temperatures of columns to near the fire temperatures, given the thermal sinks of the steel structures. Columns of the perimeter walls were thermally coupled to eachother by broad spandrel plates at each floor, and the core columns were part of a lattice of beams and columns which would have wicked heat from a hotspot in three dimensions. In order to soften columns, fires would have to exceed the capacity of the many tons of steel in and around the crash zones to draw away the heat -- a difficult feat in the 56 and 102 minutes that the fires burned.
Fires apparently did not involve entire floors of either Tower at any one time. The South Tower shows no evidence of fires on its northwest side at any time. The North Tower at times shows fires spanning most of a face, but the fires are not even emergant, in contrast to the One Meridian Plaza or First Interstate Bank fires.
Heating the external columns would be especially difficult because the columns were situated outside the interior volume, with only one of the four sides adjacent to the building's interior.
Heating of core columns would be especially difficult given the apparently poor ventilation of the core regions, being further from any air supply.
As fires consumed fuel supplies and became less severe, affected columns would have cooled and regained strength lost due to elevated temperatures.

Even if such hot and widespread fires existed, they would still be unlikely to cause failures of the columns in either of the Towers.

The incompatibility of the fire-triggered column-failure scenario with the observed characteristics of the fires created the need for the truss theory.

References

1. Temperatures in flames and fires, DoctorFire.com, [cached]
2. Metal Temperature by Color, processassociates.com, [cached]
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The Fires' Severity

How Intense and Extensive Were the Twin Towers' Fires?

The plane crashes resulted in significant fires in both Towers, at least for the first few minutes after the crashes. The fires in the North Tower were considerably more extensive than than those in the South Tower. As time progressed the fires in at least the South Tower appeared to diminish greatly in severity. This was probably due to most of the jet fuel being exhausted within a few minutes of the impacts. Since kerosene (jet fuel) has a low boiling point and a low flash point, most of it would have evaporated and caught fire quickly.

The Fires at Their Most Severe

How severe were the fires at their greatest extents?

Fires in the North Tower covered extensive regions, at least near the perimeter walls, of about three floors. Fires in the South Tower also extended over about three floors, but were more localized to one side of the building.
The fires were not hot enough to produce significant window breakage in either Tower. Window breakage is a common occurrence in large office fires, particularly when temperatures exceed 600° C.
The flames mostly remained within the buildings. Significant emergence of flames from the buildings, another common feature of large office fires, was only observed in a limited region of the North Tower.
The fires did not spread significantly beyond the impact region. With the exception of a region of fire about 10 floors above the crash zone in the North Tower, the fires remained around the impact zones.
The fires did not cause parts of the building to glow. At temperatures above 700° C, steel glows red hot, a feature that is visible in daylight.

The Fires' Progression Over Time

Most photographs of the South Tower show relatively dark smoke, and in much less quantity than from the North Tower. See photographs.

Given that the vast majority of the volatile jet fuel was consumed inside five minutes of each crash, the fires subsequently dwindled, limited to the fuels of conventional office fires. The fires in both Towers diminished steadily until the South Tower's collapse. Seconds before, the remaining pockets of fire were visible only to the firefighters and victims in the crash zone. A thin veil of black smoke enveloped the Tower's top. In the wake of the South Tower's fall new areas of fire appeared in the North Tower.

This summary is supported by simple observations of the extent and brightness of the flames and the color and quantity of smoke, using the available photographic and video evidence.

Visible flames diminished greatly over time. Significant emergence of flames from the building is only seen in a region of the North Tower 10 stories above the impact zone.
- South Tower: Virtually no flames were visible at the time of its collapse.
- North Tower: Flames were visible in several areas at the time of its collapse. A region of flames on the 105th floor is seen after the South Tower collapse.
The smoke darkened over time. While the fires in both Towers emitted light gray smoke during the first few minutes following the impacts, the color of the smoke became darker.
- South Tower: Smoke from the fires was black by the time it collapsed. At that time it was only a small fraction of the volume of the smoke from the North Tower.
- North Tower: Smoke from the fires had become much darker by the time the South Tower was struck, 17 minutes after the fires were ignited. The smoke was nearly black when the South Tower collapsed. Thereafter the smoke appears to have lightened and emerged from the building at an accelerated rate.

After the fall of the South Tower, the North Tower continued to produce prodigious quantities of smoke, and showed regions of active fires. Seephotographs.

Dark smoke implies the presence of soot, which is composed of uncombusted hydrocarbons. Soot is produced when a fire is oxygen-starved, or has just been extinguished. Soot also has a high thermal capacity and may act to rob a fire of heat by carrying it away.

Evidence of fires within the buildings' cores is scant. NIST found only two core column specimens in a condition allowing paint-analysis inferences about temperatures reached, and those temperatures were below 250°C. It can be assumed that most of the fires were near the perimeters of the Towers where broken windows around the crash zone allowed them a supply of air. The cores were an average distance of about 70 feet from the nearest walls, and had much less flammable material than the surrounding offices. The impact gash in the North Tower provided a line of sight to the core. Available photographs and videos show the gash as consistently dark, showing no signs of fire in the building's core.

Eyewitness Reports

Dozens of people were observed to jump from floors of the North Tower above the impact zone. They may have jumped to escape painful deaths from inhalation of toxic smoke, or to escape unbearable heat. Note, however, that temperatures unbearable to a human, such as 100° C, are insignificant to the survivability of structural materials.

At least 18 survivors evacuated from above the crash zone of the South Tower through a stairwell that passed through the crash zone, and many more would have were it not for confusion in the evacuation process. None of the survivors reported great heat around the crash zone. An audiotape of firefighter communications revealed that firefighters had reached the 78th floor sky lobby of the South Tower and were enacting a plan to evacuate people and put out the "two pockets of fire" they found, just before the Tower was destroyed.

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The Fires' Impact

How the Towers' Fires Affected the Structural Steel

As an exercise let's set aside all of the evidence about the actual severity of the Twin Towers' fires, and imagine that the fires were incredibly intense and widespread. Let's imagine that the jets were full tankers and spilled 80,000 gallons of fuel into each tower. Let's imagine that there was a strong wind giving the fires plenty of air. Let's imagine that the the fires engulfed over 10 floors in each tower, saturating the capacity of the steel buildings to draw away the heat. Let's imagine the fires burned intensely for hours, completely gutting several stories of each tower. Would that cause them to collapse? Not according to people who have studied steel structures subjected to such stresses. The following passage is from Appendix A of FEMA's World Trade Center Building Performance Study.

In the mid-1990s British Steel and the Building Research Establishment performed a series of six experiments at Cardington to investigate the behavior of steel frame buildings. These experiments were conducted in a simulated, eight-story building. Secondary steel beams were not protected. Despite the temperature of the steel beams reaching 800-900° C (1,500-1,700° F) in three of the tests (well above the traditionally assumed critical temperature of 600° C (1,100° F), no collapse was observed in any of the six experiments).

This graph represents strength as a function of temperature, which is expressed in degrees Celsius (C).

At temperatures above 800° C structural steel loses 90 percent of its strength. ¹ Yet even when steel structures are heated to those temperatures, they never disintegrate into piles of rubble, as did the Twin Towers and Building 7. Why couldn't such dramatic reductions in the strength of the steel precipitate such total collapse events?

High-rise buildings are over-engineered to have strength many times greater than would needed to survive the most extreme conditions anticipated. It may take well over a ten-fold reduction in strength to cause a structural failure.
If a steel structure does experience a collapse due to extreme temperatures, the collapse tends to remain localized to the area that experienced the high temperatures.
The kind of low-carbon steel used in buildings and automobiles bends rather than shatters. If part of a structure is compromised by extreme temperatures, it may bend in that region, conceivably causing a large part of the structure to sag or even topple. However, there is no example of a steel structure crumbling into many pieces because of any combination of structural damage and heating, outside of the alleged cases of the Twin Towers and Building 7.

References

1. Effect of temperature profile, corusconstruction.com, [cached]
2. Fire Resistance of Steel Framed Car Parks, corusconstruction.com, [cached]