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RE: ASD vs. LRFD

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I'm not sure how Keith handles it, but when I do put beam reactions on the
drawings, I always use the factored reaction.

Brian K. Smith, P.E.

-----Original Message-----
From: michael.barbetta(--nospam--at)swec.com [mailto:michael.barbetta(--nospam--at)swec.com]
Sent: Wednesday, December 19, 2001 9:16 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: ASD vs. LRFD




Keith,

How does the fabricator's engineer know which LRFD load factors to apply to
your
end reactions? Do you indicate both DL & LL reactions at the ends of every
beam
and girder?

Thanks.

Mike Barbetta, P.E.
Stone & Webster
Cherry Hill, NJ









Keith Fix <kefix(--nospam--at)yahoo.com> on 12/19/2001 09:37:59 AM

Please respond to seaint(--nospam--at)seaint.org








 To:      seaint(--nospam--at)seaint.org

 cc:      (bcc: Michael Barbetta/Civil-Structural/SWEC)



 Subject: Re: ASD vs. LRFD









--- "Mitchell J. Sklar" <MJS(--nospam--at)bala.com> wrote:
> I have been doing some cost comparisons between ASD & LRFD design. My
> LRFD designs are consistently lighter that ASD (No Big surprise). The
> GC/Fabricator are insisting that due to the connection design and safety
> factors involved that it is cheaper to go with an ASD design. Is the
> something that I am missing. I have just recently attended the AISC
> Connection seminar and must of step out of the room when pricing was
> discussed.
>
> Besides, most (almost most) fabricators use computerized software to do
> their designs, so where is the extra effort. If I was going to really
> design all my connections, I would also buy or make a spreadsheet to
> automate this. In addition, if my specs call out full depth double angle
> or shear tab connections, and lets say I have a W16 w/ 4 bolts. What is
> the difference whether it is ASD or LRFD? Four Bolts will give me a
> certain capacity either way.
>
> Has anybody heard of special safety factors when doing schools? Say in
> New Jersey?
>
> Mitchell J. Sklar, P.E.
> Senior Structural Engineer
>
> BALA Consulting Engineers, Inc.
> (mjs(--nospam--at)bala.com)
> p 610-649-8000 x345
> f 610-649-8475
>

About half my career has been in ASD, the second half in LRFD.  Generally I
prefer LRFD, if for no other reason than that the code is written better.

I began putting all my beam reactions on my drawings beginning two or three
years ago.  I began doing this so that I could check shop drawing
connections
more quickly (it works!).  I have not had any complaints, besides the usual,
"We usually design with ASD....".  Since I put reactions on my drawings,
none
of my connections are designed as "full depth".  If a fabricator/detailer
insists on using them, its his profits down the drain.

If you design with LRFD, I recommend you stick to you guns.  LRFD is not
"visible" to the public, and saves ME time and effort.  I find ASD a time
waster, and am glad I no longer work for men than insist on its use
(something
to point out when hiring).  All that said, I still use ASD for masonry
design.

;-)

As for schools and extra safety factor: I recently designed an expansion to
Children's Hospital in Little Rock.  The only "safety factor" I needed was
the
thought of something going wrong with dozens of kids in hospital beds.  My
school building design has been simalarly governed.

-Keith Fix, PE
-Little Rock, AR

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