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FW: dynamic lateral force procedure

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OK, I'll weigh in with an IMO:

The attitude that more complex dynamic analyses utilizing faster and better
computers is the inescapable wave of the future for our profession is IMO
misguided and shortsighted.

Misguided because in the end it places more faith in a computer, and a
program written by someone else whom the designer probably hasn't met and
who they are basically relying upon to produce a safe and economical design.
FEM programs are too the point where even if the programmer provided the
code, it would be impractical to even attempt to check it --> the "black
box" scenario.

Shortsighted because it lends momentum to a cycle of having to use a
computer driven dynamic analysis because the building is too complex to do
using a static procedure, after which the architect says "well, they handled
that one, so the next one can be even MORE complex", and so on and so on.
And no, I don't think that architects are evil, just that they will push to
satisfy their needs, just like everyone else, unless an opposing force
resists them.

I strive to work with my clients to REDUCE the complexity of the STRUCTURAL
system so that I am not forced to use a dynamic analysis.  In my experience
it is quite possible to create a simple, symetrical structural system that
is rational and can be understood, then hide it with architectural elements
that create the effect the architect desires - everyone is happy.

The problem that I see with the trend towards "throw more computer power at
it" is that the designer soon gets to the point where checking the design,
and fully understanding it, is next to impossible.  Sure, one can still to a
base shear check for equilibrium, but the mechanism formation for the biggie
earthquake is a toss-up.

Besides, even today most analysis programs are still ELASTIC, and as we all
know, most of our designs are done with INELASTIC mechanisms in mind.  There
are inelastic analysis programs out there and I have used them (mainly for
checking older, existing structures), but the application WRT a new design
is limited, IMO, unless it is for a final check.

On the other hand, maybe it's because I enjoy being able to put down on
paper, with a reasonable degree of certainty, just how the mechanisms are
likely to form. If that is the case, then it is probably just hubris on my
part - but I'll continue to do it :)

My to cents.


T. Eric R. Gillham PE
PO Box 3207 Hagatna, Guam 96932
Ph:   (671) 477-9224
Fax: (671) 477-3456
Cel  (671) 687-7115

teric(--nospam--at)gk2guam.com <mailto:eteric(--nospam--at)gk2guam.com>


-----Original Message-----
From: Bob Ross [mailto:bob.ross(--nospam--at)wgint.com]
Sent: Tuesday, December 11, 2001 4:48 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: dynamic lateral force procedure


It is not possible to analyze and design for seismic using the older
static methods. They no longer apply. The 3D, three dimensional dynamic
analysis and design methods must be used now, today. They are
available. The computer software allows the practical application.

Quo Vadis?
Pax e Gratia
Bob Ross
Robert P. Ross, P.E.
Principal Project Manager
Washington Group International,Inc.
Industrial Processes
17320 Red Hill, Suite 300
Irvine, Ca. 92614
Mobile 562-254-4604
Office 949-222-3978
FAX 949-222-3985
E-mail: Bob.Ross(--nospam--at)WGINT.com

----- Original Message -----
From: David Adie <dadie(--nospam--at)bjginc.com>
Date: Monday, December 10, 2001 10:00 am
Subject: dynamic lateral force procedure

> this survey / question is for those individuals who typically have
> a choice
> between designing their structures (buildings) with the dynamic
> procedureand with the static procedure, and then choose to use the
> dynamic procedure.
> (ubc specific?)
>
> what subtle (or hidden) advantages are there?  do those advantages
> outweighthe PERCEIVED increase in calculations / complexity?
>
> tia
> da (static procedure guy, so far)
>
>
>
>
>
>
>
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