As a structural engineer I find this dramatic and compelling, but I think FReepers in general will, too.

Great catch.

It doesn't reflect the problem of the mass dampers at the top falling through the structure. The pancake started with the wind damping masses at the top.

Very interesting -- thanks for the link. Bump.

I'll check this out later. Thanks.

That is a great illustration. Its amazing how quickly things like this can be put together to explain a relatively complex scenario.

I can't think of any other high rise fire in history, at least in the USA, that has resulted in this kind of "pancake" failure.

I wonder if a building with more internal columns would have fared any better. I wonder solid beam rather than truss construction would have fared better. I think truss construction is unusual in high rise buildings. Older skyscrapers, like the Empire State Building, have solid beams encased in concrete.

I wonder if the sprinkler system worked at all or if the risers were taken out by the plane.

Some have characterized the end result of both towers being struck as "lucky" or as a well calculated hit, designed to do exactly what ultimately occurred.

As a structural engineer, do you think that both scenarios are plausible?

I'm inclined to rule out "lucky".

It doesn't reflect the problem of the mass dampers at the top falling through the structure.

Mass dampers are heavy in absolute terms, but represent a small portion of the weight of the top of the structure. As such I don't think they're a real factor.

I wonder solid beam rather than truss construction would have fared better.

Trusses have much higher surface area than beams, and thus are apt to heat up faster, all else being equal. On the other hand, a normal high-rise fire won't have 20,000 gallons of kerosene in its fuel load.

Please explain mass dampers.

On the other hand, a normal high-rise fire won't have 20,000 gallons of kerosene in its fuel load.

Do you think the sprinkler system remained operational? It did not seem to have much effect.

Do you think the sprinkler system remained operational? It did not seem to have much effect.

How effective is water on kerosene?

Yes, a conductor on the train I took out of the city says his friends in the area reported that the sprinkler system was running. But you can't put out a jet-fuel fire with water. He also reported that water was running down the stairwells, and that he found it significant that people said the water "smelled." Which is to say that it might actually have served to spread the fuel rather than contain it.

How effective is water on kerosene?

Good point. Kerosene just rises to the top of water.

Hmmm. These guys must have thought all this out.

Big heavy weights like a pendulum that swing in the opposite direction of the wind force, slowing down the sway of the building.

Buy stock in Halon fire suppression system manufacturers.
I think that many, many things will change in our new future.

The jet fuel burned itself out after a short while.

The sprinkler systems on the affected floors were destroyed in the impact for the most part.

Once the fuel started the fire, it found everything else to keep burning.

Halon

It's not just for computer rooms anymore!