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Re: [TowerTalk] Guying a self-supporting tower - Yes

To: ve5ra@sasktel.net, towertalk@contesting.com
Subject: Re: [TowerTalk] Guying a self-supporting tower - Yes
From: Jim Lux <jimlux@earthlink.net>
Date: Mon, 11 Apr 2005 09:46:18 -0700
List-post: <mailto:towertalk@contesting.com>
At 07:59 AM 4/11/2005, Doug Renwick wrote:

>David Robbins K1TTT wrote:
>
>  > The only 'sensible' conclusions to this are the following:
>  >
>  > 1. do what the manufacturer says for 'standard' installations
>  > 2. do what a qualified mechanical engineer who has performed the 
> analysis on
>  > the specific design says for non-standard installations
>
>Is a single qualified mechanical engineer equal to God?  Did this engineer
>achieve 100% on every one of his/her exams from a respected college?  Can
>a lot of faith be placed in a single engineer's calculations.  Would it be
>a better idea to compare the answers from say three independent engineers
>and see if they agree, PE stamp or not?
>
>Doug/VA5DX

This goes more to the word "qualified"...

1) acts of god and natural disasters are more in the nature of statistical 
outliers.  Engineering generally designs for the main chance, and ensures 
that if it does fail, it fails in an appropriate way.  To paraphrase 
Einstein, God may not play dice with the universe, but engineers do(and so 
do you), every day.  All designs are really designed for a statistican 
environment (the XX mi/hr wind rating, is a statistical measure... doesn't 
mean that faster winds won't occur, just that if you design for that wind, 
the probability of a failure due to faster winds is "acceptably small")

2) Exam scores are not particularly well correlated to quality of 
engineering design.  If I were hiring a "fresh out of school" engineer, I 
might ask what classes they had taken, how they did, and what they got out 
of the class.  But that's basically qualifying an apprentice.  If I am 
hiring an engineer to design a structure, I want to know how many other 
structures like this one they've designed, what the analysis entailed, 
where the problems were, etc.  I note that licensure doesn't depend on 
grades in your classes, but more on experience (6 yrs in CA), having signed 
references from engineers who have supervised you, and whether you "make 
the cut" on the PE exam.  In fact, one can get a PE license, and 
successfully practice, with zero college classes. You might even be able to 
do it without a high school diploma.  You probably DO need to be over 18.

3) Can a lot of faith be placed in a single engineer's 
calculations?  Depends.  What's your risk posture? What's the potential 
downside? If you're flying the shuttle, having someone check the calcs 
might be a good idea. If you're putting in sprinklers in the back yard, 
probably not.  Depends a lot on who that single engineer is.  There's a 
famous example about the fallacy of "averaging" opinions: You'd rather have 
one opinion of someone who really knows the material than the average of 30 
guesses.

4) Comparing answers from 3 engineers would certaintly give you more 
information about the analysis, if only from looking for commonalities and 
differences in the analysis. It might reduce the risk.  It might not.  If 
one of the engineers designs towers for a living, and the other two design 
apartment buildings, what you'd get would be an interesting variety, but 
little additional information.



_______________________________________________

See: http://www.mscomputer.com  for "Self Supporting Towers", "Wireless Weather 
Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with any questions 
and ask for Sherman, W2FLA.

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