Why the towers fell: Two theories

By William Rice --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 in size to the 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 World Trade Centre 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.

William Rice, P.E., is a registered professional civil engineer who worked on structural steel (and concrete) buildings in Boston, New York, and Philadelphia. He was also a professor at Vermont Technical College where he taught engineering materials, structures lab, and other building related courses.