who worked on structural steel (and concrete) buildings in Boston, New
York,
and Philadelphia, and a former professor of engineering materials and
structures...
Why the towers fell: Two theories
By William Rice
http://www.vermontguardian.com/commentary/032007/TwinTowers.shtml
<http://www.vermontguardian.com/commentary/032007/TwinTowers.shtml>
Posted March 1, 2007
Having worked on structural steel buildings as a civil engineer in the
era when the Twin Towers were designed and constructed, I found some
disturbing discrepancies and omissions concerning their collapse on
9/11.
I was particularly interested in the two PBS documentaries that
explained the prevailing theories as determined by two government
agencies, FEMA and NIST (National Institute of Science and Technology).
The first (2002) PBS documentary, Why the Towers Fell, discussed how the
floor truss connectors failed and caused a "progressive pancake
collapse."
The subsequent 2006 repackaged documentary Building on Ground Zero
explained that the connectors held, but that the columns failed, which
is also unlikely. Without mentioning the word "concrete," the
latter
documentary compared the three-second collapse of the concrete Oklahoma
City Murrah Federal Building with that of the Twin Towers that were of
structural steel. The collapse of a concrete-framed building cannot be
compared with that of a structural steel-framed building.
Since neither documentary addressed many of the pertinent facts, I took
the time to review available material, combine it with scientific and
historic facts, and submit the following two theories for consideration.
The prevailing theory
The prevailing theory for the collapse of the 110-story, award-winning
Twin Towers is that when jetliners flew into the 95th and 80th floors of
the North and South Towers respectively, they severed several of each
building's columns and weakened other columns with the burning of
jet
fuel/kerosene (and office combustibles).
However, unlike concrete buildings, structural steel buildings
redistribute the stress when several columns are removed and the
undamaged structural framework acts as a truss network to bridge over
the missing columns.
After the 1993 car bomb explosion destroyed columns in the North Tower,
John Skilling, the head structural engineer for the Twin Towers, was
asked about an airplane strike. He explained that the Twin Towers were
originally designed to withstand the impact of a Boeing 707 (similar
kinetic energy to that of a Boeing 767). He went on to say that there
would be a horrendous fire from the jet fuel, but "the building
structure would still be there."
The 10,000 gallons of jet fuel (half capacity) in each jetliner did
cause horrendous fires over several floors, but it would not cause the
steel members to melt or even lose sufficient strength to cause a
collapse. This is because the short-duration jet fuel fires and office
combustible fires cannot create (or transmit to the steel) temperatures
hot enough. If a structural steel building could collapse because of
fire, it would do so slowly as the various steel members gradually
relinquished their structural strength. However, in the 100-year history
of structural-steel framed buildings, there is no evidence of any
structural steel framed building having collapsed because of fire.
Let's assume the unlikelihood that these fires could weaken all of
the
columns to the same degree of heat intensity and thus remove their
structural strength equally over the entire floor, or floors, in order
to cause the top 30-floor building segment (South Tower WTC #2) to drop
vertically and evenly onto the supporting 79th floor. The 30 floors from
above would then combine with the 79th floor and fall onto the next
level down (78th floor) crushing its columns evenly and so on down into
the seven levels below the street level.
The interesting fact is that each of these 110-story Twin Towers fell
upon itself in about ten seconds at nearly free-fall speed. This
violates Newton's Law of Conservation of Momentum that would require
that as the stationary inertia of each floor is overcome by being hit,
the mass (weight) increases and the free-fall speed decreases.
Even if Newton's Law is ignored, the prevailing theory would have us
believe that each of the Twin Towers inexplicably collapsed upon itself
crushing all 287 massive columns on each floor while maintaining a
free-fall speed as if the 100,000, or more, tons of supporting
structural-steel framework underneath didn't exist.
The politically unthinkable theory
Controlled demolition is so politically unthinkable that the media not
only demeans the messenger but also ridicules and "debunks" the
message
rather than provide investigative reporting. Curiously, it took 441 days
for the president's 9/11 Commission to start an
"investigation" into a
tragedy where more than 2,500 WTC lives were taken. The Commission's
investigation also didn't include the possibility of
controlled-demolition, nor did it include an investigation into the
"unusual and unprecedented" manner in which WTC Building #7
collapsed.
The media has basically kept the collapse of WTC Building #7 hidden from
public view. However, instead of the Twin Towers, let's consider
this
building now. Building #7 was a 47-story structural steel World Trade
Center Building that also collapsed onto itself at free-fall speed on
9/11. This structural steel building was not hit by a jetliner, and
collapsed seven hours after the Twin Towers collapsed and five hours
after the firemen had been ordered to vacate the building and a collapse
safety zone had been cordoned off. Both of the landmark buildings on
either side received relatively little structural damage and both
continue in use today.
Contrary to the sudden collapse of the Twin Towers and Building #7, the
four other smaller World Trade Center buildings #3, #4, #5, and #6,
which were severely damaged and engulfed in flames on 9/11, still
remained standing. There were no reports of multiple explosions. The
buildings had no pools of molten metal (a byproduct of explosives) at
the base of their elevator shafts. They created no huge caustic
concrete/cement and asbestos dust clouds (only explosives will pulverize
concrete into a fine dust cloud), and they propelled no heavy steel
beams horizontally for three hundred feet or more.
The collapse of WTC building #7, which housed the offices of the CIA,
the Secret Service, and the Department of Defense, among others, was
omitted from the government's 9/11 Commission Report, and its
collapse
has yet to be investigated.
Perhaps it is time for these and other unanswered questions surrounding
9/11 to be thoroughly investigated. Let's start by contacting our
congressional delegation. ###
"The observed collapse time of WTC 7 [610 feet tall, 47 stories, and
not
hit by an airplane] was 6.5 seconds. That is only half a second longer
than it would have taken for the top of the building to fall to the
ground in a vacuum, and half a second shorter than the falling time of
an apple when air resistance is taken into account... The great speed of
the collapse and the low value of the resistance factor strongly suggest
controlled demolition."
— Heikki Kurttila, D.Sc. (Doctor of Technology, Finland), Safety
Engineer and Accident Analyst, National Safety Technology Authority
(TUKES), Finland. Specialist in the investigation of pressure vessel
explosion accidents and the impacts of the shock waves caused by them.
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