As in 9/11 Building Collapse Intense Heat From Raging Fire Can Weaken and Warp Steel
The raging fire in Atlanta, which caused an I85 bridge to collapse, dramatically demonstrates how heat from such an inferno can weaken otherwise very strong structural steel, including steel in beams, and also steel used to reinforce concrete structures, thereby causing catastrophic structural collapse, says Professor John Banzhaf.
This lends supports to the widely-held explanation that the collapse of the Twin Towers on 9/11 Building was caused in large part by the flames of fires from aviation fuel in the airplanes which the terrorists flew into the buildings, and not the result of controlled demolition from explosives which had been planted beforehand, as some conspiracy theorists have maintained, notes Banzhaf.
Although some knowledgeable people have argued that the heat from the fuel fires would not be sufficient to significantly weaken the steel members of the building, what happened in Atlanta shows how this can easily happen, says Banzhaf, who has an engineering degree from MIT and two U.S. patents.
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A few theorists about the 9/11 Building collapse have argued that steel does not melt until the temperate reaches about 2500-2700 degrees Fahrenheit, but Banzhaf notes that extreme heat can sufficiently weaken steel at much lower temperatures.
Intense heat – e.g., over 1000 degrees – can cause some steel beams to expand, while others not directly affected by the fire would remain the same size, thereby putting stress on the structure. Jet fuel can burn at 800-1500 degrees, but fires fed by other items in the building could reach temperatures well about 2000 degrees.
More importantly, fire at 1000 degrees can also cause steel to lose some 50% of its strength, and to twist or warp under stress, says Banzhaf. The combination of those two factors can easily cause major structures to collapse, he notes, as evidenced by what just happened in Atlanta.
For example, as retired New York deputy fire chief Vincent Dunn, author of The Collapse Of Burning Buildings: A Guide To Fireground Safety, explained: “I have never seen melted steel in a building fire.” “But I’ve seen a lot of twisted, warped, bent and sagging steel. What happens is that the steel tries to expand at both ends, but when it can no longer expand, it sags and the surrounding concrete cracks.”
Farid Alfawak-hiri, senior engineer of the American Institute of Steel Construction, agreed, noting: “Steel loses about 50 percent of its strength at 1100°F, and at 1800° it is probably at less than 10 percent.”
Indeed, an engineering analysis might well show that fire is more likely to weaken – and then cause a toppling of – a very tall but comparatively thin structure like an office tower, than a broad structure such as a bridge.
Moreover, a bridge is designed to withstand the weight of many cars, buses, and heavy trucks passing over it at the same time, so there would be less stress on its structural members once the fire started, and vehicles were no longer adding their tremendous weight to the structure.
On the other hand, after a plane strikes a building and triggers an intense blaze, virtually all of the enormous weight which the compromised steel beams must try to support – including the many floors above the point of impact, the bookshelves, desks, and other furniture, etc. – remains, so that any significant weakening of the structural members, as well as any twisting of metal from the impact and/or from differential heating, could be brought down by this weight, argues Banzhaf, whose law teaching sometimes includes scientific analysis.
Actually, the phenomena of what engineers sometime term a “progressive collapse” of a tall building, where structural members fail one after another brought on by the force of gravity, is very complex, and may require understanding nonlinear second-order differential equations, he says.
But in summary, while others have offered competing theories about what brought down the twin towers, the collapse of the bridge in Atlanta brought on by a fire certainly lends support to the idea that the intense heat of the fire triggered by the planes crashing into the buildings, combined with the structural damage caused initially by the crash, could have caused the 9/11 collapses.
At the very least, it makes it easier for people without engineering degrees to understand and appreciate how intense heat from a fire can bring down major structures, argues Banzhaf.