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Re: More ASD vs LRFD

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The next edition of the MSJC (aka the masonry code) will have strength
design included.  Thus, you will have the option of doing strength design
for masonry as well (actually, that option already exists under the
IBC...the 2000 IBC contains strength design provisions which I believe
were taken from the 1997 UBC and "tweeked"...these provisions were also
the starting point (at least I believe so) for what will be the strength
design provisions in chapter 3 of ACI 530-02).

HTH,

Scott
Ypsilanti, MI


On Thu, 20 Dec 2001, Keith Fix wrote:

> Paul:
> 
> I agree with everything you wrote, except LRFD taking longer.  Practice will
> improve efficiency, as it does with anything.
> 
> Also, I didn't mean to say that all designers who use ASD skimp on details, or
> even visa versa.  Given time, I'll eventually meet a LRFD user who skimps.
> 
> Finally, I still use working stress for masonry (as does almost everyone)
> because ACI et al hasn't yet "blessed" it, so it isn't common practice in the
> south (SBC country).  I also find myself using ASD for light gage steel, mainly
> because I can't justify factoring loads to check ultimate strength once or
> twice the whole job.  Same for wood.  So I'm not a fanatic.  For me LRFD is
> pragmatic, nothing more.
> 
> -Keith Fix, PE (AR & CA)
> 
> PS: I also love to check shop drawings.  I'm told that's really weird!
> 
> --- Paul Feather <pfeather(--nospam--at)SE-Solutions.net> wrote:
> > 
> > Keith Fix wrote:
> > 
> > > In my experience, the men (never worked with a female engineer) who skimp
> > on
> > > design details, especially connections, are all ASD'ers.  "LRFD takes too
> > much
> > > time (and so do details)."  For me, most of the impetus behind drawing
> > good
> > > details has been saving time during shop drawing review; but I would be
> > remiss
> > > if I did not praise the excellent AISC guidance for connection design.
> > 
> > 
> > You are painting with a pretty wide brush.  I have always used ASD, and
> > being a west coast engineer have always provided full design details,
> > especially connections.  The attitude you are indicating is not typical of
> > engineers who use ASD.  I would venture to say that the overwhelming
> > majority of west coast engineers still use ASD.
> > 
> > For me, the impetus behind drawing good details is not only for shop drawing
> > review, but as a way of ensuring a constructible design that erects and
> > performs as I intended without change orders and field RFI's for
> > clarification.
> > 
> > As a side note, this past year I set aside a steel moment frame commercial
> > project to design completely using LRFD as a self education project (budget
> > be damned).  Yes the design took longer, but probably more from a
> > familiarity condition than anything else.  The end result, not enough
> > difference to discuss.  Floor vibration still controlled the floor system
> > design, drift considerations still controlled the frame requirements, and
> > details are still details.  Whether the loads are factored up for comparison
> > against a higher "strength" based allowable or the service loads are used
> > for comparison with a reduced allowable stress, the end results are
> > essentially the same.  Face it, the structure doesn't "know" how it was
> > designed.  It is far more important to have a well thought out viable load
> > path that is clearly translated into the constructed project.  Given a good
> > system properly constructed I do not believe there is any difference whether
> > ASD or LRFD was used.
> > 
> > In my personal opinion, LRFD does take a little longer than ASD because ther
> > e is a little more bookkeeping involved, but that is about it.  Multiple
> > load combinations have to be tracked regardless of the method chosen.
> > 
> > Paul Feather
> > 
> > 
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