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Re: Multi-story wood framed w/lots of openings

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chuck utzman wrote:
The author said & drew exactly what he meant.  The method utilized here aims to minimize construction cost at the expense of capacity.  It is based on a fair amount of testing (AFAIK without any 2 story testing).  Dan Dolan at VT did most of the testing (cyclical).  IMHO the cost saving from eliminating the horizontal strapping at the opening(s) isn't worth the reduced performance.

Ed Diekmann authored the rational method shown in Faherty & the ICBO manual (at pg.69).  He also supervised extensive monotonic testing that verified the approach (for someone's 450 pg. PHD thesis).

You can't "improve" the detailing without altering the internal load paths & destroying the validity of the "analysis".  Either you build/analyze the same way the tests were set up or you analyze with the free body diagrams we all know and love (see Diekmann). Adding straps to resist the uplift at the edges of the opening basically creates piers & now the 4 strap loads usually get really big.

We spent a lot of time discussing this 3 or 4 years back IIRC.  You can probably find it with an archive search.  I spent a fair amount of time discussing the analyses & testing of both methods privately with both Ed & Dan.  I haven't kept up with the CUREE work but I don't  anything has changed substantially.
Chuck Utzman, P.E.

I've also reviewed Dan Dolan's work (he is no longer with VT but in Washington state (I've forgotten as I received an e-mail from him some months ago in response to a comment I made).
Here is how I boil this down: Framing represents less than 20% of the construction cost - usually around 17% on average. This is based on our historic methods of framing a home using Piers rather than perforated walls. How much do you really save in cost by removing a few holddowns and how much is penalized when considering performance issues.
I have not yet been accused over overdesigning by traditional methods and know that one of the great unresolved issues related to perforated wall design is the argument whether or not the holddown at the ends of the wall will work in two directions or only one (traditional holddowns at corners can resist the uplift on two shearwalls if the holddown is designed for the greater uplift and the sheathing is propertly boundary nailed to the post or combination studs where the holddown is applied.

I just don't find it to my advantage to use a perforated wall design when I can obtain a better design for a bit more money using narrow proprietary panels from each of the major manufacturers. Perforated design should be translated into prescriptive methods at the most so that it can be applied only to conventional prescriptive construction that an engineer does not need to be involved with. This is my opinion on the matter.

Dennis


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Dennis S. Wish, PE
California Professional Engineer
Structural Engineering Consultant

dennis.wish(--nospam--at)verizon.net


760.564.0884 (office - fax)

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