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RE: Commercial Sign stru

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Roger makes a valid point. IMO no engineer should be using a computer
program without having the experience to feel comfortable designing by hand.
This is where engineering judgement comes into play. Engineering judgement
requires an intuitive feel for the range of answers. This is one way we can
judge if a computer program is providing results within some acceptable
range. We do something similar when we don't recalculate our apprentices
numbers - assuming that they know how to do basic arithmetic. Instead we
look at the answer and can instinctively tell if he is close or not. For
example, we know by experience that a 2x8 rafter is not going to span 20'
without cracking the ceiling. Granted this elementary, but we use this type
of instinctive engineering every day.
Now, the side that wants to disagree with Roger. Most of us will never do a
hand analysis to check the results of a finite element program since it is
too involved. Again we base it on instinct and knowledge of the materials as
well as the reputation of the software developer. The problem that generally
occurs is in software that is created in our own offices. For the most part,
much of the math is correct, but improper assumptions leading to incorrect
input can be disastrous.
We also assume that sufficient beta testing has been done and this is not
difficult to verify.
Nothing will replace our instinct and knowledge of the materials we use.
This can only be attained by having done sufficient design that we can begin
to expect the correct section.
One problem that I have had is in the design of light gauge steel
structures. The stuff just seems too light to be functional. I have, over
the last year, proved to myself that it's a good product as long as you
understand the weaknesses. For example, I was correct to feel uncomfortable
with  resting roof trusses on a single top track. Because there is yet to be
good standards accepted by all, I chose to align my trusses above a stud. I
found out later that this was the preferable method.

Again, the point comes with experience of the materials used and a feel for
the results that any analysis gives whether it is a computer program or an
incorrect assumption done manually.
Every day we place ourselves in the hands of automation. I suspect we will
see more of this. How we  succeed with it will depend upon how willing we
are to study it and understand the results.

Dennis S. Wish PE
La Quinta, California
wish(--nospam--at)cwia.com

ICQ# 6110557
http://wwp.mirabilis.com/6110557

"Science may have found a cure for most evils; but it has found no remedy
for the worst of them all - the apathy of human beings"  Helen Keller

-----Original Message-----
From: Roger Turk [mailto:73527.1356(--nospam--at)compuserve.com]
Sent: Sunday, April 05, 1998 3:07 PM
To: seaoc(--nospam--at)seaoc.org
Subject: Re: Commercial Sign stru


Bill Allen,

I've been wondering when your comments were going to start appearing on the
listservice again.  I could only assume that you have been *very* busy.

How many engineers would consider hiring a person whose name they don't
know,
who won't tell them his/her education, who won't tell them his/her
experience or background, whose calculations consist only of loads and
schematic dimensions and the final member sizes, none of which is in
checkable form, and tells you, "Don't worry, these are correct!"  Yet, these
same engineers will, without question, use a computer program that does
exactly the same thing.


A. Roger Turk, P.E.(Structural)
Tucson, Arizona