Why Did the WTC Skyscrapers Collapse?
- Why Did the Trade Center Skyscrapers Collapse?
by Morgan Reynolds
"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 facade 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 facade 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 1,300oF. 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
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:
No "inward-bending columns" were observed and it would be
unlikely that each and every one would be reversed by subsequent
the hypothesis is ad hoc and lacks simplicity, both scientific
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
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
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
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
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:
* Photos show people walking around in the hole in the North Tower
"where 10,000 gallons of jet fuel were supposedly burning. The women
(p. 27) seem to (sic) looking down to the ground" (the NIST "Response"
pdf, p. 62, also shows a similar photo of the same blond woman with
light-colored slacks looking over the edge of the 94th floor).
* By the time the South Tower was hit, most of the North Tower's
flames had already vanished, burning for only 16 minutes.
* The fire did not grow over time, probably because it quickly ran
out of fuel and was suffocating rather than the sprinkler system
dousing the fires.
* FDNY fire fighters remain under a gag order
(Rodriguezvs-1.Bush.pdf, p. 10) to not discuss the explosions they
heard, felt and saw. FAA personnel are also under a 9/11 gag order.
* Even the 9/11 Commission (Kean-Zelikow) Report acknowledges that
"none of the [fire] chiefs present believed that a total collapse of
either tower was possible" (Ch. 9, p. 302). It shocked everyone that
day, amateur and professional alike, although some firefighters
realized that so-called secondary explosive devices were a risk.
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. 68â"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
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
9. According to many witnesses, explosions occurred within the
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 1,350o 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
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.
Morgan Reynolds, Ph.D. [send him mail econrn @ cox-internet.com ], 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.
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