Design of Wood Structures ASD/LRFD - Donald E. Breyer

[CWEngineer]

I noticed the 6th edition of Donald E. Breyer's Design of Wood Structures has ASD/LRFD.

In practice is ASD still being used? Or are designers heading towards LRFD?

I have the 3rd edition of Donale E. Breyer's Design of Wood Structures and was interested in reviewing it again for my personal knowledge and to get more experience in wood design.

Should I be alright by looking at this ASD book (3rd edition) or should I consider looking into LRFD desig?

THANKS

 

[SlideRuleEra]

The latest edition of NDS (2005) covers both ASD & LRFD. Since that is the code that sets the standard in the US for wood design, looks like the move is on towards LRFD in the future.

http://www.awc.org/Standards/nds.html

IMHO, Breyer offers the best books on wood (any edition). Oddly enought, the most important change in recent years has nothing to do with either ASD or LRFD. Allowable shear in lumber almost doubled from NDS 1997 to NSD 2001 - there was a decades long mistake in how shear was accounted for. Here is a summary and explanation

http://www.awc.org/Publications/papers/NDS2001article.pdf

If you use an older reference, be sure to keep this in mind.

http://www.SlideRuleEra.net

 

[RARWOOD]

I still use ADS. My understanding is that there is very little advantage in using LRFD.

I have years of experience using ASD which I can relate to. Since the 1991 NDS there have been a lot of changes. I am very skeptical of some of the changes which were made.

For example with the design equations for bolts, you plug in a lot of numbers and get an answer. However when you get an answer you have no feel for its accuracey. I find my self comparing it to the design value under the 86 NDS.

With newer research on wood connections and further changes in the NDS, I find my skeptcism of the 91 NDS increasing.

From people I've talked to, if I sat down and worked my way through LRFD, I would probably start using it.

 

[bjb]

I use ASD. I think LRFD makes more sense for a material like steel, where something like an adequately braced beam fails by the formation of a platic hinge, or for concrete. I am not familiar with LRFD for wood, but am skeptical that it would add anything other than increased complexity. With that said, I'm sure the academic community will embrace it and try to shove it down everyones throat. If I'm wrong I'll have a nice helping of humble pie.

 

[rholder98]

http://www.ncees.org/exams/professional/pe_design_standards/structural_design_standards.pdf

The PE exam is still based on ASD for wood, at least through 2007. You can't go wrong learning both, I suppose.

 

[Dinosaur]

I still use ASD in my day to day work. I have designed using LFD and LRFD. I think, for example, LFD of concrete structures is fine. I also thing LFD design of steel can be fine, but you should still perform the servicability checks.

This is one of my greatest concerns with LRFD. The community is telling me that you no longer have to check deflections and stuff like that. I say BULL! If I'm getting 12 inches of deflection in a 30 ft member, I'm going to increase the MOI, period.

In wood, I'd accept some sort of LFD design theory so that a larger Factor of Safety could be applied against live load, but it is still a basic solids of mechanics type material, so I'm going to treat it that way.

 

[bjb]

Dinosaur, if deflections aren't being checked with LRFD that sounds like a recipe for disaster. In my experience deflections often control for steel and for longer engineered lumber like LVL. I'm just skeptical the LRFD will provide a tangible benefit for the design of wood structures, and that it's mostly something the academics will like. If they take the same approach that AISC did in having a unified spec, that could be ok.

You could still use higher FOS for live load with ASD if you want to. I do it all the time.

 

[BradPL]

I just purchased the NDS 2005 which is a combined ASD/LRFD document similar to the AISC approach. The document is clear and concise and phi factors are added to the design tables for those who use the LRFD approach.

Deflections are indeed addressed in the document. The IRC prescribes limits for deflection so that would necessitate checks anyway. I have never heard the assertion that LRFD requires no deflection checks. Any designer who neglects servicibility will no doubt find himself in hot water.