Engineer finds clues in WTC wreckage

CNN ^ | Saturday, October 6, 2001

[Slyfox]

The Physics of Turning a Tower Into a Cloud of Dust and Rubble

[Chemnitz]

I guess an ideal system would have included several floors filled with a good fire retardant of some kind. I think it was irresponsible to build a skyscraper so tall that fires could not be extinguished above a certain floor. Escape was also impossible. The WTC was a Titanic waiting to happen. Too much hubris.

[Timesink]

However I find it hard to believe the engineer took into consideration the effects of the ensuing jet fuel fire.

He didn't. The buildings were designed to withstand a direct 707 impact to the extent that they wouldn't immediately collapse, and most of the people inside could get out. Even if there had been no fires at all, both towers would probably have been a total loss, and would have had to be intentionally torn down or imploded at some point in the near future.

There was no way to build around the possibility of a jet fuel fire in 1970 anyway; the technology just didn't exist. I'm not even sure it exists now, at least not any technology that wouldn't be prohibitively expensive.

[rockfish59]

so are they collecting evidence for a big trial in the hague? i wonder if johnny cochran will defend bin laden?

'if bin wasn't in the cockpit, then you must acquit'!

[spectr17]

I was working in a puter room and had the unfortunate experience of having the halon system fire after a BIG electrical mistake (long story). After the big blue arc and bang, my partner dragged me out of the room, I was knocked goofy in the explosion. I woke up to the smiling face of a fireman wanting to know if I was still part of the human race. Was I glad to see him.

The fireman all seemed to be of the opinion my partner had saved my life since the halon would have suffocated me and I wasn't able to hit the big red halon abort button by the exit as I escaped.

[supercat]

I've wondered if there could be a way to make the beams hollow so they could have water run through them in a fire emergency -- if not pumped from below, then poured in from above via helicopter. Simply insulating the beams from one another would make the heat-weakening problem worse for that section.

I've thought about that. You'd have to have a tricky system of valves, though, or else all the water would simply go out the large holes without doing much good.

As for insulating the beams from each other making heat-weakening problems worse for that section, that is an important consideration. In the case of the WTC it would have been a non-issue since the beams and girders whose flameproofing was most thoroughly damaged would have been useless for support anyway. A column which is buckled or sheared through can't support any load, so even if it melts completely that won't make the situation any worse. You do have a point, though, which is that in a "conventional" fire the ability of heat to transfer between girders does make the fireproofing more effective since heat that goes through the insulating material then has somewhere else to go.

[hellinahandcart]

Instead of stacking floors, why not stagger very long steel bars, like the irregular support structure of a tree?

Help me out here, because I don't understand what you mean; when erecting a vertical building, I don't see any way around putting one floor on top of another.

[giotto]

There would be a sort of exoskeleton made of girders, each of which would extend the height of several floors. But they would be irregularly staggered like long splinters of wood. The floors would be attached to this structure.

The reason I suggest this scheme is because I noticed that most of the debris pile seems to consist of the 18"x18"x12' steel columns which supported each floor. They just popped away when the floors pancaked. That seems like a weakness in the design.

Just an idea. IANAA (I am not an architect.)

[sump pump]

The impact compromised the structural core, allowing the fire to shoot through the elevator shafts. The impact also, in all likelyhood, compromised any active fire suppression system, whether it be water, halon, or whatever.

[sump pump]

I've wondered if there could be a way to make the beams hollow so they could have water run through them in a fire emergency --

Such systems exist. The Lloyds Building in London was built with such a system. Problem is the cost of construction and maintenance. In this situation it would have been useless in any case because of the number of columns that were severed.

[sump pump]

Instead of stacking floors, why not stagger very long steel bars, like the irregular support structure of a tree?

The Sears Tower in Chicago is built this way. The building is basically 9 tubes bundled together.

While the WTC tower structures each acted like one uniform tube - using the outer structure to counter wind loads and the inner core to take gravity load only - the outer structure was indeed constructed with prefabricated panels that were staggered to prevent a progressive failure - we do the same with light wood construction when we double up 2x4s for example, which helps overcome weaknesses such as knots in any one member. From the pictures I saw, it looks as if the exterior facade failed in pieces the size of those very same prefabricated panels - that is, where they were connected together in the field - I think by bolts, though not sure.

[Chemnitz]

I can see that. I was impressed at first by early reports of explosions. I imagine there are many explanations for those explosions. The weight of collapsing floors would be an incredible strain on the rest of the structure.

[wjcsux]

I have heard there is a problem with Halon. You get it above 1400 degrees farenheit, and it turns to phosgene. Very toxic stuff.