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Re: More ASD vs LRFD

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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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