Tuesday, September 11, 2012
911 Another view another anniversary
It was eleven and a half feet wide 118 feet long. It weighed more than 200,000 lbs. It was moving at 530 miles an hour. Is it any wonder two towering skyscrapers collapsed in NYC that day in September? Yet in a google search people just can't face the reality of the forces involved. The bulk of images are linked to this conspiracy theory or that. I'm sure the families who morn could care less about some tin foil hat story. But let me dispel some of the nonsense from what I know about construction.
The skeletal structure of a building is meant to take the weight of the floors and not lateral also called shear forces. A building can withstand the force of wind because that force is not focused in a small area. Acting much like a sail the entire structure can move in unison. Engineers factor those wind forces in when designing skyscrapers. Now if memory serves me correct a building is fastened together with 4 to 6 hex bolts per gusset with a tinsel strength of about 10,000 lbs per bolt. Sounds pretty sturdy until you consider the forces that brought down the towers as was listed above. What surprises me was that the buildings stood for as long as they did.
Another bit of info about the building structure, the whole thing was built like a tube meaning the floors were only really attached at the outside walls (called tube frame or cantilever construction). I've seen similar such construction in old warehouses here in Seattle. The floors only sit on a brick lip with a supporting floor joist every 20 feet. Scary enough if you're a firefighter I'm sure.
Another thing to consider was the effect fire from the crash had on the concrete. If you ever want to weaken concrete just run a weed burner across its surface a few times and you will notice how it becomes brittle in short order. The concrete of the towers' floors was held in place with corrugated sheet steel that isn't very thick. Once it melts the weight of the concrete will do the rest and collapse the entire floor.
Last issue was that of asbestos. From my recertification classes I was informed that asbestos was used for most of the fireproofing of the I-beams. That is until it was banned in 1971 in the city. Further research confirms this fact:
The WTC Towers were built from 1968 to 1972. A slurry mixture of asbestos and cement was sprayed on as fireproofing material. But this practice was banned by the New York City Council in 1971. This halted the spraying, but not before hundreds of tons of the material had been applied. Some but not all of it was later removed in an abatement program.
They let the entire issue slide because to try and remove the asbestos would have cost more than the buildings were worth. From my own experience they would have had to use jack hammers or rivet busters for the removal. No easy task to hold that piece of equipment at shoulder level for an eight hour shift although I've done that before.
We were lied to a bit by the EPA when they reported that air samples around ground zero were at safe levels. I could have told you otherwise without an ambient pump and test samples. I knew approximately what was in the air by the materials used in the building and were then airborne. I had considered going but it would have been a long trip and there was no way to decontaminate after working all day in that toxic dust soup. It's only now that authorities are compensating people for all the cancers and other diseases that were contracted. Something I knew would happen.
So consider this a brief memorial to those who died, are dying, and will die from the 911 disaster. It's not over yet.