Daniel Terp wrote:
> On Wed, 12 Sep 2001 19:40:57 -0400, you wrote:
> >If the building was designed to withstand an aircraft impact, did the designers
> >assume the aircraft would arrive with empty fuel tanks?
>
> In past airplane collisions like the Empire State crash, the plane
> either glanced off or went right through the building.
In another post, I speculated the trajectory was planned to take out a corner of the
building to maximize the probability of instability. Video on TV showed the plane
aiming about 2/3 across the entry face. Also, the plane was banking, perhaps to dump
fuel on as many floors as possible. Even so, relatively few floors were initially
impacted.
> The WTC planes had full tanks and remained buried in the building.
>
> I've been designing commercial buildings for twenty years, and I don't
> know of a way to design a building to withstand that kind of heat.
> Especially not one 110 stories tall.
There are certain things you can do:
Not put all your structure on the perimeter. Distribute it over the floor space.
Tennants don't like this, because it breaks up the floors. Tough.
Require fairly tough, layered insulation on major support structures. I suspect 1
foot of layered firecode GWB and fiberglass (3 or 4 layers of each) would be
sufficient. The objective here is to delay, preferably for several hours, the
reduction in yield stress due to the beams heating. The higher the building, the
more protection required. It could be tapered with height. Had the building not
collapsed for 4 hours, the death toll to occupants would have been much reduced.
Walking down 110 stories, even under the BEST of conditions has to take more than an
hour. Consider people not in the best of condition, high heels, etc.
How about requiring sprinkler pipes running down the major columns from a water
tank, perhaps from reservoirs every 20 +/- floors? The water could be released by
fusible links at high temperatures (300 to 400 degrees) to cool the beams.
It all comes down to a matter of money. Building owners want to maximize their
return. It is simply a price/safety tradeoff.
-John
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