ASD vs. LRFD and mm versus inches[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
- Subject: ASD vs. LRFD and mm versus inches
- From: Paul Meyer <PMeyer(--nospam--at)HASimons.com>
- Date: Thu, 17 Jun 1999 17:27:11 -0700
As far as I know, all Canadian Provincial Building Codes require the use of Limit States Design, which is very similar to your LRFD (in fact, LRFD is based to some extent on Canadian research and experience) The one exception is that the LSD version of Masonry is very new, so both Working Stress Design (WSD, similar to your ASD) and Limit States are permitted.
Basically anyone using WSD for other materials (steel, concrete, timber) is violating the Building Code and is probably in violation of their provincial licensing body's code of ethics.
There is a really good write-up in the Structural Commentaries to the 1995 edition of the National Building Code of Canada that explains, in 3 pages, the rationale for using LSD, the assumptions made about reliability , etc. It's too long to post here, but if you have access to the Commentary, it's well worth a read.
Many of the arguments I've read from the "pro-ASD" side of this thread are similar to the arguments we have up here about the switch to using SI units. The switch from inches to mm or pounds -force (or slugs or whatever) to kilonewtons is met with extreme reluctance by the designers who are used to the older system, and they complain loud and long about how the new system won't work, was designed by a bunch of eggheads in universities, etc. But I'll tell ya, I only have to look at my colleagues in Mechanical trying to work with "tons" of cooling, British thermal units, kilowatt-hours and the like to be thankful I'm able to work in units that make sense. Same goes for LSD...I understand it and it makes sense.
Before anyone starts up on "the metric thing" just think what would happen if some government tried to change your money system (decimal) back to the old "16 pence makes a shilling, 12 shillings makes a pound" system and you had to work with that. Yet, this is exactly what your US system of linear measurement does. Sometimes change is for the better....
Paul Meyer, P. Eng.
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