Why Did WTC Collapse?

"It didn’t seem real… There are thousands of these steel beams that just fell like pickup sticks."

~ John Albanese, volunteer firefighter and amateur photographer

"What struck us – guys like Warren Jennings and myself, who have spent basically all our lives in the scrap business – we’d never seen steel this heavy, this huge, this massive. It was just unbelievable."

~ Michael Henderson (p. 93),
General Manager, Marine Terminals, Metal Management NE

To explain the unanticipated free-fall collapses of the twin towers at the World Trade Center on September 11, 2001, mainstream experts (also see The American Professional Constructor, October 2004, pp. 12–18) offer a three-stage argument: 1) an airplane impact weakened each structure, 2) an intense fire thermally weakened structural components that may have suffered damage to fireproofing materials, causing buckling failures, which, in turn, 3) allowed the upper floors to pancake onto the floors below.

Many will nod their head, OK, that does it and go back to watching the NBA finals or whatever, but I find this theory just about as satisfying as the fantastic conspiracy theory that "19 young Arabs acting at the behest of Islamist extremists headquartered in distant Afghanistan" caused 9/11. The government’s collapse theory is highly vulnerable on its own terms, but its blinkered narrowness and lack of breadth is the paramount defect unshared by its principal scientific rival – controlled demolition. Only professional demolition appears to account for the full range of facts associated with the collapses of WTC 1 (North Tower), WTC 2 (South Tower), and the much-overlooked collapse of the 47-story WTC building 7 at 5:21 pm on that fateful day.

The scientific controversy over the initial structural weakening has two parts: what caused the original tower damage and did that damage "severely" weaken the structures? Photos show a stable, motionless North Tower (WTC 1) after the damage suffered at 8:46 am and the South Tower after its 9:03 am impact. If we focus on the North Tower, close examination of photos reveals arguably "minor" rather than "severe" damage in the North Tower and its perimeter columns.

As many as 45 exterior columns between floors 94 and 98 on the northeast (impact) side of the North Tower were fractured – separated from each other – yet there is no direct evidence of "severe" structural weakening. None of the upper sections of the broken perimeter columns visibly sags or buckles toward its counterpart column below. We can infer this because of the aluminum covers on the columns: each seam uniformly aligns properly across the Tower, forming a horizontal "dashed line" in the façade from beveled end to end. Despite an impact hole, gaps in perimeter columns, and missing parts of floors 95–98 at the opening, the aluminum façade shows no evidence of vertical displacement in the columns, suggestive of little or no wider floor buckling at the perimeter.

The aluminum covers attached to the columns also aligned vertically after impact, that is, separated columns continued to visually remain "plumb" (true vertical), lining up top to bottom around the aperture, implying no perceptible horizontal displacement of the columns. Photographic evidence for the northeast side of the North Tower showed no wider secondary structural impact beyond the opening itself. Of course, there was smoke pouring out of the upper floors.

The fact that perimeter columns were not displaced suggests that the floors did not buckle or sag. Despite missing parts of floors 95–98, photos show no buckling or sag on other floors. If so, that boosts the likelihood that there was little damage to the core. Photos do not document what happened within the interior/core and no one was allowed to inspect and preserve relevant rubble before government authorities – primarily FEMA – had it quickly removed. Eyewitness testimony by those who escaped from inside the North Tower concerning core damage probably is unavailable.

Photos do not allow us to peer far into the interior of the building; in fact the hole is black, with no flames visible. We know that the structural core and its steel was incredibly strong (claimed 600% redundancy) making it unlikely that the core was "severely" damaged at impact. There were 47 core columns connected to each other by steel beams within an overall rectangular core floor area of approximately 87 feet x 137 feet (26.5 m x 41.8 m). Each column had a rectangular cross section of approximately 36" x 14" at the base (90 cm x 36 cm) with steel 4" thick all around (100 mm), tapering to ¼" (6 mm) thickness at the top. Each floor was also extremely strong (p. 26), a grid of steel, contrary to claims of a lightweight "truss" system.

Those who support the official account like Thomas Eagar (p. 14), professor of materials engineering and engineering systems at MIT, usually argue that the collapse must be explained by the heat from the fires because the loss of loading-bearing capacity from the holes in the Towers was too small. The transfer of load would have been within the capacity of the towers. Since steel used in buildings must be able to bear five times its normal load, Eagar points out, the steel in the towers could have collapsed only if heated to the point where it "lost 80 percent of its strength, " around 1,300^oF. Eagar believes that this is what happened, though the fires did not appear to be extensive and intense enough, quickly billowing black smoke and relatively few flames.

While some experts claim that airliner impact severely weakened the entire structural system, evidence is lacking. The perimeters of floors 94–98 did not appear severely weakened, much less the entire structural system. The criminal code requires that crime scene evidence be saved for forensic analysis but FEMA had it destroyed before anyone could seriously investigate it. FEMA was in position to take command because it had arrived the day before the attacks at New York’s Pier 29 to conduct a war game exercise, "Tripod II," quite a coincidence. The authorities apparently considered the rubble quite valuable: New York City officials had every debris truck tracked on GPS and had one truck driver who took an unauthorized 1 ½ hour lunch fired.

The preliminary NIST Response claims that "the wall section above the impact zone moved downward" (pdf, p. 36) on WTC 1 but offers no evidence. It offers photographic evidence, however, for a "hanging floor slab" on the 82d floor of the South Tower at 9:55 a.m. This looks minor though because there is no sag on adjacent floors and the integrity of the structure looks very much intact. The fire looks weak too, yet the South Tower collapsed only four minutes later. This would be quite a puzzle without a demolition theory.

About a dozen of the fragmented ends of exterior columns in the North Tower hole were bent but the bends faced the "wrong way" because they pointed toward the outside of the Tower. This fact is troublesome for the official theory that a plane crash created the hole and subsequent explosion between floors 94 and 98. The laws of physics imply that a high-speed airplane with fuel-filled wings breaking through thin perimeter columns would deflect the shattered ends of the columns inward, if deflected in any direction, certainly not bend them outward toward the exterior.

A possible response would be that, well, yes, an airliner crash would bend a column inward rather than outward, if bent at all, but the subsequent force of a jet fuel blast would act in the opposite direction: any inward bends caused by plane impact would straighten toward vertical or even reverse the bent steel columns toward the exterior under blast pressure. However, such a proposed steel "reversal theory" (first bend inward by collision, then bend outward by explosion) suffers two major handicaps:

1. No "inward-bending columns" were observed and it would be unlikely that each and every one would be reversed by subsequent explosion, and

2. the hypothesis is ad hoc and lacks simplicity, both scientific negatives.

Occam’s razor would suggest that the outward bends in the perimeter columns were caused by explosions from inside the tower rather than bends caused by airliner impact from outside. Also supporting this theory is the fact that the uniformly neat ends of the blown perimeter columns are consistent with the linear shaped charges demolition experts use to slice steel as thick as 10 inches. The hypothesis of linear shaped charges also explains the perfectly formed crosses found in the rubble (crucifix-shaped fragments of core column structures), as well as the rather-neatly shorn steel everywhere.

The engineering establishment’s theory has further difficulties. It is well-known that the hole in the west wing of the Pentagon, less than 18-foot diameter, was too small to accommodate a Boeing 757, but the North Tower’s hole wasn’t big enough for a Boeing 767 either, the alleged widebody airliner used on AA Flight 11 (officially tail number N334AA, FAA-listed as "destroyed"). A Boeing 767 has a wingspan of 155’ 1" (47.6 m) yet the maximum distance across the hole in the North Tower was about 115 feet (35 m), a hole undersized by some 40 feet or 26 percent. "The last few feet at the tips of the wings did not even break through the exterior columns," comments Hufschmid (p. 27). But 20 feet on each wing? I’d call that a substantial difference, not "the last few feet," especially since aircraft impact holes tend to be three times the size of the aircraft, reflecting the fact that fuel-laden airliners flying into buildings send things smashing about in a big way. The small size of the holes in both towers casts doubt on the airliner-impact hypothesis and favors professional demolition again. There were no reports of plane parts, especially wings, shorn off in the collision and bounced to the ground on the northeast side of the tower, to my knowledge, though FEMA reported a few small pieces to the south at Church street (pp. 68–9) and atop WTC-5 to the east of WTC-1.

Adding to the suspicious nature of the small aperture in WTC 1 is that some vertical gaps in the columns on the left side of the northeast hole were so short, probably less than three feet (p. 105) high (p. 27). Not much of a jumbo jet could pass through such an opening, especially since a fuel-laden plane would not minimize its frontal area. The engines are a special problem because each engine is enormous and dense, consisting mainly of tempered steel and weighing 5–6 tons, depending upon model. No engine was recovered in the rubble yet no hydrocarbon fire could possibly vaporize it.

The hole in the North Tower also is suspicious because it did not even have a continuous opening at the perimeter, but instead contained substantial WTC material (p. 27) just left of center (pp. 62, 105). This material appears integral to that area, so it did not move much, suggesting minimal displacement and no clean penetration by a jumbo jet. These huge airliners weigh 82 tons empty and have a maximum takeoff weight of up to 193 tons.

In the case of the South Tower, an engine from UAL Flight 175 (tail number N612UA and FAA-registered as still valid!) has not been recovered despite the fact that the flight trajectory of the video plane implied that the right engine would miss the South Tower. Photos showing minor engine parts on the ground are unconvincing, to put it mildly. Perhaps independent jet engine experts (retired?) can testify to the contrary. Further contradicting the official account, the beveled edge of the southeast side of the south tower was completely intact upon initial impact. The government never produced a jet engine yet claimed it recovered the passport of alleged hijacker Satam al Suqami unharmed by a fiery crash and catastrophic collapse of the North Tower. The government has not produced voice (CVR) or flight data recorders (FDR) in the New York attack either, so-called black boxes, a fact unprecedented in the aviation history of major domestic crashes.

Adding to the problems of the official theory is the fact that photos of the North Tower hole show no evidence of a plane either. There is no recognizable wreckage or plane parts at the immediate crash site. While the issue probably takes us too far afield, the landing wheel assembly that allegedly flew out of the North Tower and was found several streets away could easily have been planted by FEMA or other government agents. I’ve never seen any objective analysis of this wheel assembly though it would be welcome. In fact, the government has failed to produce significant wreckage from any of the four alleged airliners that fateful day. The familiar photo of the Flight 93 crash site in Pennsylvania (The 9/11 Commission Report, Ch. 9) shows no fuselage, engine or anything recognizable as a plane, just a smoking hole in the ground. Photographers reportedly were not allowed near the hole. Neither the FBI nor the National Transportation Safety Board have investigated or produced any report on the alleged airliner crashes.

The WTC 1 and Pentagon holes were not alone in being too small. Photos show that the hole in WTC 2 also was too small to have been caused by the crash of a Boeing 767. In fact, the South Tower hole is substantially smaller than the North Tower hole.

The next question is whether the fires were hot enough to cause the WTC buildings to collapse. In defending the official account and its clones that try to explain the unprecedented collapses of three steel-framed skyscrapers without demolition, heat arguably is more important than structural impact. That’s obviously true for building WTC 7 because there was no alleged airplane impact.

First, no steel-framed skyscraper, even engulfed in flames hour after hour, had ever collapsed before. Suddenly, three stunning collapses occur within a few city blocks on the same day, two allegedly hit by aircraft, the third not. These extraordinary collapses after short-duration minor fires made it all the more important to preserve the evidence, mostly steel girders, to study what had happened. On fire intensity, consider this benchmark: A 1991 FEMA report on Philadelphia’s Meridian Plaza fire said that the fire was so energetic that "[b]eams and girders sagged and twisted," but "[d]espite this extraordinary exposure, the columns continued to support their loads without obvious damage" (quoted by Griffin, p. 15). Such an intense fire with consequent sagging and twisting steel beams bears no resemblance to what we observed at the WTC.

Second, severe structural damage to the WTC towers would have required fires that were not only large but growing throughout the buildings and burning for a considerable period of time. None of these conditions was present. "The lack of flames is an indication that the fires were small, and the dark smoke is an indication that the fires were suffocating," points out Hufschmid (p. 35). Eyewitnesses in the towers, as well as police and firefighters, reported (pp. 199–200) the same thing.

Third, the impact opening was 15 floors lower in the South Tower than in the North Tower, where core columns were thicker, so the South Tower fire had to produce more heat to raise the steel temperatures to soften up (thermally weaken) the steel columns. Yet its fires were considerably smaller and 30 minutes shorter in duration. The Tower collapsed after burning only 56 minutes. A prime candidate to explain why "the wrong tower fell first" is that the small dying fire in the South Tower forced the hand of the mass murderers who decided to trigger demolition earlier than planned in order to sustain the lie that fire caused the collapse. The North Tower stood for another 29 minutes and its core steel was thinner at its upper stories. The 1991 Meridian Plaza fire burned for 19 hours and the fire was so extreme that flames came from dozens of windows on many floors. It did not collapse.

Fourth, implicitly trying to explain away these difficulties, the current NIST investigation, conducted by "an extended investigation team of 236 people," makes "dislodged fireproofing" the key variable to explain the collapses. Supposedly, "the probable collapse sequence for the WTC towers are (sic) based on the behavior of thermally weakened structural components that had extensive damage to fireproofing or gypsum board fire protection induced by the debris field generated by aircraft impact" (p. 111). "Had fireproofing not been dislodged by debris field," this team of government-paid experts claims, "temperature rise of structural components would likely have been insufficient to induce global collapse" (p. 108). Perhaps acknowledging the lack of direct evidence for its conjectures, the NIST admits that "a full collapse of the WTC floor system would not occur even with a number of failed trusses or connections" and it "recognizes inherent uncertainties" (pp. 110 and 112). The NIST will have to boost its creativity to plausibly explain the WTC 7 collapse because it won’t have the benefit of tales of aircraft and debris fields.

Aside from specific defects in the fire collapse theory, a wide variety of facts undermine it:

Griffin (pp. 25–7) succinctly identifies the primary defects in the official account of the WTC collapses, and its sister theories. These problems were entirely ignored by The 9/11 Commission Report (2004), so the government appointees must have found it difficult to account for the following facts:

1. Fire had never before caused steel-frame buildings to collapse except for the three buildings on 9/11, nor has fire collapsed any steel high rise since 9/11.

2. The fires, especially in the South Tower and WTC-7, were small.

3. WTC-7 was unharmed by an airplane and had only minor fires on the seventh and twelfth floors of this 47-story steel building yet it collapsed in less than 10 seconds.

4. WTC-5 and WTC-6 had raging fires but did not collapse despite much thinner steel beams (pp. 68–9).

5. In a PBS documentary, Larry Silverstein, the WTC lease-holder, recalled talking to the fire department commander on 9/11 about WTC-7 and said, "…maybe the smartest thing to do is pull it," slang for demolish it.

6. FEMA, given the uninviting task of explaining the collapse of Building 7 with mention of demolition verboten admitted that the best it could come up with had "only a low probability of occurrence."

7. It’s difficult if not impossible for hydrocarbon fires like those fed by jet fuel (kerosene) to raise the temperature of steel close to melting.

Professional demolition, by contrast, can explain all of these facts and more. Demolition means placing explosives throughout a building, and detonating them in sequence to weaken "the structure so it collapses or folds in upon itself" (p. 44). In conventional demolitions gravity does most of the work, although it probably did a minority on 9/11, so heavily were the towers honeycombed with explosives.

1. Each WTC building collapse occurred at virtually free-fall speed (approximately 10 seconds or less).

2. Each building collapsed, for the most part, into its own footprint.

3. Virtually all the concrete (an estimated 100,000 tons in each tower) on every floor was pulverized into a very fine dust, a phenomenon that requires enormous energy and could not be caused by gravity alone ("…workers can’t even find concrete. ‘It’s all dust,’ [the official] said").

4. Dust exploded horizontally for a couple hundred feet, as did debris, at the beginning of each tower’s collapse.

5. Collapses were total, leaving none of the massive core columns sticking up hundreds of feet into the air.

6. Salvage experts were amazed at how small the debris stacks were.

7. The steel beams and columns came down in sections under 30 feet long and had no signs of "softening"; there was little left but shorn sections of steel and a few bits of concrete.

8. Photos and videos of the collapses all show "demolition waves," meaning "confluent rows of small explosions" along floors (blast sequences).

9. According to many witnesses, explosions occurred within the buildings.

10. Each collapse had detectable seismic vibrations suggestive of underground explosions, similar to the 2.3 earthquake magnitude from a demolition like the Seattle Kingdome (p. 108).

11. Each collapse produced molten steel identical to that generated by explosives, resulting in "hot spots" that persisted for months (the two hottest spots at WTC-2 and WTC-7 were approximately 1,350^o F five days after being continuously flooded with water, a temperature high enough to melt aluminum (p. 70).

Controlled demolition would have required unimpeded access to the WTC, access to explosives, avoiding detection, and the expertise to orchestrate the deadly destruction from a nearby secure location. Such access before 9/11 likely depended on complicity by one or more WTC security companies. These companies focus on "access control" and as security specialist Wayne Black says, "When you have a security contract, you know the inner workings of everything." Stratesec, a now-defunct company that had security contracts at the World Trade Center and Dulles International Airport, should be investigated, among others, because of the strange coincidence that President Bush’s brother, Marvin P. Bush, and his cousin, Wirt D. Walker III, were principals in the company, with Walker acting as CEO from 1999 until January 2002 and Marvin reportedly in New York on 9/11. At least one report claims that a "power down" condition prevailed on September 8–9 (pdf, p. 45) at WTC to complete a "cabling upgrade," presenting an opportunity to plant explosives with low risk of detection.

A related point is that demolition companies go to considerable expense to wire steel-framed skyscrapers with explosives to produce safe implosions, and they would love to do it more cheaply by simply setting two small fires like those that (allegedly) caved in building 7. Apparently, the terrorist-inventors have kept this new technology secret.

Why would the killers destroy WTC-7, especially since a collapse would arouse suspicion in some quarters? A logical if unproven theory is that the perpetrators used Mayor Giuliani’s sealed OEM "bunker" on the 23d story of WTC-7 to conduct the twin tower implosions and then destroyed the building and evidence to cover up their crimes, just as a murderer might set his victim’s dwelling ablaze to cover up the crime (one in four fires is arson). Giuliani’s "undisclosed secret location" was perfect because it had been evacuated by 9:45 a.m. on 9/11, it enabled unmolested work, provided a ringside seat, was bullet- and bomb-resistant, had its own secure air and water supply, and could withstand winds of 160 mph, necessary protection from the wind blasts generated by collapsing skyscrapers.

There is special import in the fact of free-fall collapse (item one in the list immediately above), if only because everyone agrees that the towers fell at free-fall speed. This makes pancake collapse with one floor progressively falling onto the floor below an unattractive explanation. Progressive pancaking cannot happen at free-fall speed ("g" or 9.8 m/s²). Free-fall would require "pulling" or removing obstacles below before they could impede (slow) the acceleration of falling objects from above. Sequenced explosions, on the other hand, explain why the lower floors did not interfere with the progress of the falling objects above. The pancake theory fails this test.

If we put the murder of 2,749 innocent victims momentarily aside, the only unusual technical feature of the collapses of the twin towers was that the explosions began at the top, immediately followed by explosions from below. WTC-7, by contrast, was entirely conventional, imploding from bottom up.

It is hard to exaggerate the importance of a scientific debate over the cause(s) of the collapse of the twin towers and building 7. If the official wisdom on the collapses is wrong, as I believe it is, then policy based on such erroneous engineering analysis is not likely prove to be sound. Revised engineering and construction practices, for example, based on the belief that the twin towers collapsed through airplane damage and subsequent fires is premature, to say the least.

More importantly, momentous political and social consequences would follow if impartial observers concluded that professionals imploded the WTC. If demolition destroyed three steel skyscrapers at the World Trade Center on 9/11, then the case for an "inside job" and a government attack on America would be compelling. Meanwhile, the job of scientists, engineers and impartial researchers everywhere is to get the scientific and engineering analysis of 9/11 right, "though heaven should fall." Unfortunately, getting it right in today’s "security state" demands daring because explosives and structural experts have been intimidated in their analyses of the collapses of 9/11.

June 9, 2005

Morgan Reynolds, Ph.D. [send him mail], is professor emeritus at Texas A&M University and former director of the Criminal Justice Center at the National Center for Policy Analysis headquartered in Dallas, TX. He served as chief economist for the US Department of Labor during 2001–2, George W. Bush's first term.

Copyright © 2005 LewRockwell.com

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