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Re: ASD vLRFD

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I was weened on LRFD but rarely get to use it in practice.  Generally I use it here
when checking existing construction for new loading conditions (communications sites
with heavy equipment and batteries, etc.).  Strength is often our main consideration
there.  In new construction, LRFD doesn't have tremendous advantages necessarily,
depending on the dead to live load ratio.  I look forward to the combined spec.
coming in 2005(?) so I can stop using the ASD 9th.  At least then ASD will be 'up to
date' with research and changes over the past 12 years.

With regard to A992, we have been specifying A572 Gr 50 for years for W-shapes W12
and larger.  Now we have begun to specify A992 or A572 as acceptable (we're in low
seismic land).

Eric Ober
Cagley and Associates
Rockville, MD

Mark Nowmos wrote:

> This is a good point.  A lot of times serviceability and / or deflection will be
> a primary design concern.  The only time I use LRFD is when strength is an
> issue.  As an aside, how many engineers are specifing A992 steel nowadays?  Just
> curious, I would like to see if this standard emboldened other engineers to
> design based on 50 ksi yield?
> Mark Nowmos
>
> HAWNENG(--nospam--at)aol.com wrote:
>
> >
> > Having not posted anything to the list server in many months, I could not
> > help but "weigh-in" on this discussion (pun intended).  Our office uses
> > nothing but "allowable stress design" and has since 1981.  We find that many
> > times, our design is governed by deflection, not stress.   We check
> > deflection at two stages, immediately after the mud is poured and then for
> > total deflection.  For "mud load" deflection, we try to limit the deflection
> > to 1/2".  Often times, rather than camber a steel member, we will increase
> > the member size by a few pounds to limit the deflection.  In the discussion
> > to date, I haven't read how deflection and floor vibrations play a role in
> > sizing the steel members.  We also design and detail all our steel
> > connections on the structural drawings then review the shop drawings to help
> > ensure the contractor is interpreting the drawings as intended by our design.
> >
> > Not that this is necessarily the best way to design, but ASD gets my vote.
> > Also, when it comes to the foundation design, you have to track two sets of
> > different load factors.  Yes, we do design concrete by ultimate stress
> > design.  We are definitely middle-aged engineers, but not real old-timers,
> > yet.
> >
> > Greg Showerman, S.E.
> > Modesto, California
> >
> >
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