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

RE: ASD vs LRFD...my simple test

[Subject Prev][Subject Next][Thread Prev][Thread Next]
> From: Ritter, Mike [mailto:mritter(--nospam--at)lgt.lg.com]
> The whole thing took me a little longer than ASD (not that its hard or
> difficult, just different).  It didn't feel right and I  certainly didn't
> save any money for the client.

I was trained in LRFD in school, and I do find it harder to understand and use.  But it *is* better to have indications what the limiting state is for a design (but often it's deflection), and for that reason I look forward to the day I use it in the office.  But not to getting there. 

I have an example of a different kind of test:

I was asked to design a square tube for a modest signpost.  It turned out to be a slender member design do I went to the Appendix F of the latest LRFD manual to check LTB, FLB, WLB.  Table A-F1.1 p.116 leads me back to Table A-F1.1 p.114, which leads me to p. 112 looking for Re, which is found in Appendix G2 to be non-applicable.  Then I go looking for Seff, which is listed as effective section modulus with no reference or formula I can find paging through, so I look in the index under Modulus, Effective, Section, and Slender.  No luck.  Go back to Table A-F1.1 p.116 and find that, the footnote [i] was missed in the table, Seff is listed under [i] on p. 117.  Go to p. 107 for Seff, and now I'm finally seeing how this relates back to ASD and I'm starting to feel a little less uncomfortable.

In ASD the solution falls out in less than 2 pages of text, using only concepts that are immediately understood.  For each extra calculation LRFD requires there is associated extra chasing around the manual.  So there is a multiplicative effect in the time requirements to use LRFD.  For 95% of the work we do, this extra time basically comes out of *our* bottom line.

Before I switch back to LRFD, I'm going to use up two ink pens marking up the manual, and write a few dozen Mathcad calc sheets up.  The bigger offices can probably absorb the cost more easily, and get much more out of the investment of revamping the firm's design standards (more will use it).  In my case, me and my family will absorb the cost.  The Principal Engineer will not spend one minute or one dime dealing with LRFD.  And as many have said here, what's the point?  He'll likely retire before he *has* to and our customers could care less if we use LRFD or not.  I don't blame him a bit.  

Now look at what is the other factor effecting the *real* adoption of the LRFD, the PE exam.  ASD is still allowed, as it should be for a practical exam in the current "real" world, and using it is an advantage over LRFD on a time intensive exam.  That's unfair to those who want to use the new "best" method.

LRFD *is* being forced on young engineers since ASD is no longer revised.  The question is not "if" but "when" and "how".  Since it is inevitable, there needs to be an effective effort to make it "user friendly" and also get it into the professional world in a practical and fair manner.  I'd be interested in any information about how this is being handled by those charged with doing it... 

Regards,

Ed Fasula EIT

P.S.  Sorry about all the ""'s and **'s, they seemed required to emphasize the intended main ideas.