[147473] in cryptography@c2.net mail archive
Re: [Cryptography] Crypto Standards v.s. Engineering habits - Was:
daemon@ATHENA.MIT.EDU (Alan Braggins)
Thu Oct 3 09:42:39 2013
X-Original-To: cryptography@metzdowd.com
Date: Thu, 03 Oct 2013 10:38:38 +0100
From: Alan Braggins <alan.braggins@gmail.com>
To: cryptography@metzdowd.com
In-Reply-To: <3B416551-A4F2-42EF-8EE0-F9F038497A5C@me.com>
Errors-To: cryptography-bounces+crypto.discuss=bloom-picayune.mit.edu@metzdowd.com
On 02/10/13 18:42, Arnold Reinhold wrote:
> On 1 Oct 2013 23:48 Jerry Leichter wrote:
>
>> The larger the construction project, the tighter the limits on this stuff. I used to work with a former structural engineer, and he repeated some of the "bad example" stories they are taught. A famous case a number of years back involved a hotel in, I believe, Kansas City. The hotel had a large, open atrium, with two levels of concrete "skyways" for walking above. The "skyways" were hung from the roof. As the structural engineer specified their attachment, a long threaded steel rod ran from the roof, through one skyway - with the skyway held on by a nut - and then down to the second skyway, also held on by a nut. The builder, realizing that he would have to thread the nut for the upper skyway up many feet of rod, made a "minor" change: He instead used two threaded rods, one from roof to upper skyway, one from upper skyway to lower skyway. It's all the same, right? Well, no: In the original design, the upper nut holds the weight of just the upper skyway. In the m
o
> di
>> fied version, it holds the weight of *both* skyways. The upper fastening failed, the structure collapsed, and as I recall several people on the skyways at the time were killed. So ... not even a factor of two safety margin there. (The take-away from the story as delivered to future structural engineers was *not* that there wasn't a large enough safety margin - the calculations were accurate and well within the margins used in building such structures. The issue was that no one checked that the structure was actually built as designed.)
>
> This would be the 1981 Kansas City Hyatt Regency walkway collapse (http://en.wikipedia.org/wiki/Hyatt_Regency_walkway_collapse)
Which says of the original design: "Investigators determined eventually
that this design supported only 60 percent of the minimum load required
by Kansas City building codes.[19]", though the reference seems to be a
dead link. (And as built it supported 30% or the required minimum.)
So even if it had been built as designed, the safety margin would not
have been "well within the margins used in building such structures".
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