Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

Re: More ASD vs LRFD

[Subject Prev][Subject Next][Thread Prev][Thread Next]
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
> 
> 
> ******* ****** ******* ******** ******* ******* ******* ***
> *   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
> * 
> *   This email was sent to you via Structural Engineers 
> *   Association of Southern California (SEAOSC) server. To 
> *   subscribe (no fee) or UnSubscribe, please go to:
> *
> *   http://www.seaint.org/sealist1.asp
> *
> *   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you 
> *   send to the list is public domain and may be re-posted 
> *   without your permission. Make sure you visit our web 
> *   site at: http://www.seaint.org 
> ******* ****** ****** ****** ******* ****** ****** ******** 


__________________________________________________
Do You Yahoo!?
Check out Yahoo! Shopping and Yahoo! Auctions for all of
your unique holiday gifts! Buy at http://shopping.yahoo.com
or bid at http://auctions.yahoo.com

******* ****** ******* ******** ******* ******* ******* ***
*   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
* 
*   This email was sent to you via Structural Engineers 
*   Association of Southern California (SEAOSC) server. To 
*   subscribe (no fee) or UnSubscribe, please go to:
*
*   http://www.seaint.org/sealist1.asp
*
*   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you 
*   send to the list is public domain and may be re-posted 
*   without your permission. Make sure you visit our web 
*   site at: http://www.seaint.org 
******* ****** ****** ****** ******* ****** ****** ********