Check who lost their license in the Hyatt Regency skywalk collapse in Kansas City. It wasn't the architect.
Good point.
Your assuming the design was done
No, I am not, don't put words into my mouth please
strictly to handle the impact of the aircraft and failing to take into account there may have been other, more likely events, that they did design for that made the building able to take a full on impact. It could very well be that:
(higher impact spec * safety factor) < (high wind load spec * safety factor
The wind loads they designed for were higher than needed. Although wind load is different than a (comparatively) point impact of a plane, beefing up the design for higher wind loads would also increase the ability of the building to absorb the impact of a plane. )
No question about the underlined part. It is a bit of a red herring to focus only on the impact load of X aircraft and X speed, since that is but ONE consideration of design, strength, method, and material.
But again,
what do you mean by "higher than needed" here? Was the presumed wind load a Nor'Easter, a Cat II Hurricane with gusting wind (dynamic load shifting) or sustained wind? And then, per my above comment, what safety factor applied? Given the immense sail area of the WTC's two towers, the distributed load of a Cat II Hurricane, with gusting winds, is no small change (on a vertical cantilever) to design for . . . and then you choose a safety factor to apply. If you are asserting that the WTC was designed with a generous saftey factor, I'd have to agree, given the punishment they both took and basically remained standing until the structural members were weakened by thermal fatigue.
Kevin, I am far more familiar with aircraft design than building design, but the process of coming up with a sound final design is similar. The tradeoffs you make, the money you have, and the materials available, as well as the method of load distribution. Weight is of course immensely important with aircraft design and material selection, but COST is always a variable, and a factor that professionals in the field have to consider.
There is also the fine art of determing the point of diminishing returns in "adding this much better performance/strength/rigidity/what have you" and adding ______ cost to achieve that increase.
Furthermore, the wtc design was to transfer as little load to the core as possible, meaning the outer surface had to take much more load than a typical building, again beefing up that suppport system (and reducing the interior system, opening up more rentable space.)
Sounds like a smart design, for anyone with an eye on the budget, long term.
The argument seems to be semantic, in part, and your use of the term "over designed." The method isn't the issue, the design spec and your assertion "that it was over designed" versus my estimation that desiging to an unrealistic base specification would not have made the cut in the bidding process.
Remember this building did take an impact from a 500 mph 767 and stay standing. The 3 page summary claimed it could take a 600 mph 707 strike and remain standing. I see no reason to doubt this.
We seem actually to be in violent agreement, except for a little bit of
post hoc ergo prompter hoc on your part right there, and one small point of view differential.
You seem to be presuming a 600 mph spec, with no evidence that it was more than an issue raised. The base spec (for airborne hazards, and thus only one of many specs per your
excellent point earlier on) and the applied safety factor, whereas I find it more likely to have been based on the airspeed of an airliner in the Terminal phase of a flight: approach and take off speeds. (Remember, this was going on in the 1960's, before the Hijacking to Cuba craze, and certainly before the Rag Heads began to hijack planes all over the Middle East in the 1970's)
I think we have beaten this horse to death, Kevin. Thanks for your insights, I have learned a bit in the process.
That is a Good Thing(TM).
DR
