I also wanted to ask any professional architects/building engineers out there what they thought of the One World Trade Center building (the replacement world trade center building erected at Ground Zero), which was featured in an episode of NOVA that I saw recently.
My impression, as an admittedly ignorant amateur, is that the design of the building is a fundamentally poor one. It seems to have been designed to withstand an attack like the one that took down WTC1 and WTC2; the central core containing escape stairwells has been designed to be extremely robust (along with other novelties in the design).
So what's wrong with that? My understanding of engineering design is that it involves making something "just strong enough".
As Arthur Wellington put it in 1887:
It would be well if engineering were less generally thought of, and even defined, as the art of constructing. In a certain sense it is rather the art of not constructing; or, to define it rudely but not inaptly, it is the art of doing that well with one dollar which any bungler can do with two after a fashion.
The OWTC building is admittedly one of the most expensive buildings of its kind made, according to the show, but is the extra expense of "bunkerizing" the building's core justifiable, or worth it? Is the building more a memorial, and less an exercise in good engineering? What's the point of anticipating and preventing something that has already happened?
Leslie Robertson and John Skilling designed the original WTC1 and WTC 2 buildings to withstand plane impacts, and to be fire resistant. Most modern skyscrapers are also designed to be blast resistant, which may be why WTC1 and WTC2 did not collapse from the 1993 bombing.
Nobody anticipated the possibility of a fuel laden plane being flown into the side of the buildings (or rather, they did worry about the fuel load of the then-largest aircraft 707s, and the possible incendiary impact a plane hitting the building might have, but they were unable, in the 1960s, to accurately model or estimate what combustion of a plane's fuel load might do to the building's structure see HERE, under WORST CASE). And that's the thing; is all of the extra expense and extravagant material and structural excess that went into the building really a good investement? How likely are terrorists to try another 9/11 attack, knowing the building is "braced" for it?
Like its predecessors, if OTWC comes down before it is retired, it will likely be destroyed by some unanticipated cause, either man-made or natural (wonder if the beefy core would resist a variation on Nikola Tesla's resonant mechanical oscillator?)
The Citicorp video was very interesting. Had to listen rather than watch the Nova episode because I have to grade papers for the engineering design course I'm helping with. This week's topic is, interestingly enough, Failure Mode Effects Analysis—a way of attempting to quantify risk in design.
First, a couple of corrections:
There are very few "blast proof" structures. The new WTC is unique as far as I know. It is not nor has it ever been a common practice; the old WTC withstood the truck bomb in it's parking garage because the building had typically large safety factors and because the bombers misunderstood the structure they were trying to take down, placing the bomb too far from the foundation.
It wasn't the fuel load in the airplanes that fed the fires, it was the contents of the building. The fuel burned off relatively quickly, tho it did contribute by spreading the fire over a lot of the building at once.
When the designers of the original WTC considered an aircraft impact they counted on an accidental impact of a 707 with a minimal fuel load and flying slowly in a landing configuration. Not that it would have mattered; with the primitive analysis tools available at the time they would have been guessing. "Fire resistant" meant the structural members were protected by fairly fragile insulation, much of which was removed by the aircraft debris moving thru the building at high speed.
As for terrorist-proofing the building being worth it:
There were 7 hijackings of domestic US airliners in 1972 alone. After passenger screening by metal detectors began in 1973 the next domestic hijacking wasn't until 1976. The last hijacking prior to 2001 was in 1994, and that was a FedEx cargo flight. The relative rarity of hijackings doesn't mean metal detectors are a waste of time, the rarity is a result of metal detectors.
"Bracing" a building for a terrorist attack isn't a waste if the bracing discourages an attack in the first place. In fact, that would be the best possible use of that bracing. What's more likely though is to simply shift terrorists to a softer target. The only way we'll ever have certainty is if reinforcing the building isn't a sufficient deterrent and it takes another hit. If you've got a way to predict that there are a few people who'd love to hear about it.
Terrorists being successful with a tactic once doesn't mean they've taken that trick off the list; on the contrary, they've seen how successful it can be. It makes some sense (maybe not enough to justify the expense, but it isn't a completely daffy idea) to try to make a terrorist-proof building. It would probably be a high-priority target since so much hype has been expended on it symbolizing renewal and resilience and whatnot. It is undoubtedly cheaper to reinforce cockpit doors than to reinforce buildings, but that wouldn't prevent a rogue pilot from doing the same thing hijackers did.
I also wanted to ask any professional architects/building engineers out there what they thought of the One World Trade Center building (the replacement world trade center building erected at Ground Zero), which was featured in an episode of NOVA that I saw recently.
My impression, as an admittedly ignorant amateur, is that the design of the building is a fundamentally poor one. It seems to have been designed to withstand an attack like the one that took down WTC1 and WTC2; the central core containing escape stairwells has been designed to be extremely robust (along with other novelties in the design).
So what's wrong with that? My understanding of engineering design is that it involves making something "just strong enough".
As Arthur Wellington put it in 1887:
It would be well if engineering were less generally thought of, and even defined, as the art of constructing. In a certain sense it is rather the art of not constructing; or, to define it rudely but not inaptly, it is the art of doing that well with one dollar which any bungler can do with two after a fashion.
The OWTC building is admittedly one of the most expensive buildings of its kind made, according to the show, but is the extra expense of "bunkerizing" the building's core justifiable, or worth it? Is the building more a memorial, and less an exercise in good engineering? What's the point of anticipating and preventing something that has already happened?
Leslie Robertson and John Skilling designed the original WTC1 and WTC 2 buildings to withstand plane impacts, and to be fire resistant. Most modern skyscrapers are also designed to be blast resistant, which may be why WTC1 and WTC2 did not collapse from the 1993 bombing.
Nobody anticipated the possibility of a fuel laden plane being flown into the side of the buildings (or rather, they did worry about the fuel load of the then-largest aircraft 707s, and the possible incendiary impact a plane hitting the building might have, but they were unable, in the 1960s, to accurately model or estimate what combustion of a plane's fuel load might do to the building's structure see HERE, under WORST CASE). And that's the thing; is all of the extra expense and extravagant material and structural excess that went into the building really a good investement? How likely are terrorists to try another 9/11 attack, knowing the building is "braced" for it?
Like its predecessors, if OTWC comes down before it is retired, it will likely be destroyed by some unanticipated cause, either man-made or natural (wonder if the beefy core would resist a variation on Nikola Tesla's resonant mechanical oscillator?)
I guess I always wanted to be a proofer. 
