Perforated vs. Segmented Shear Wall Design
Perforated vs. Segmented Shear Wall Design
(OP)
My question is about wood shear wall design (i.e. 2x6 DF studs/7/16" OSB sheathing/6"-12" 8d nailing). I have worked with segmented shear walls on single story buildings in an area that doesn't have a lot of wind or seismic lateral forces. However, I am now getting into more critical areas and had a couple questions about lateral design with shear walls. I have noticed on some new wood construction where the designer has spec'd strapping around openings in the shear walls (i.e. windows, doors). My question is when is this something that should be considered? I have looked in the codes (IBC 2006 and NDS 2005) to find examples or explanations of the codes. I haven't found anywhere that shows that those forces need to be transferred around an opening in the shear wall. I see that the perforated shear wall allows me to reduce the allowable shear panel strength based on the MOHR, but is there something that is requiring me to strap around the openings to still achieve that strength, or is that considered in the code. Or, when I analyze a segmented shear wall instead of the perforated, do I need to transfer those loadings around the openings. This doesn't seem to be the case because the double top plate acts as the drag strut and the segmented shear panels will be isolated from the rest of the wall (so far as the analysis is concerned). Any comments or discussion of this would be appreciated!






RE: Perforated vs. Segmented Shear Wall Design
There are significant limitations to the use of a Perforated Shear Wall, so when these limitations are exceeded the Force Transfer Around Openings method is used.
RE: Perforated vs. Segmented Shear Wall Design
RE: Perforated vs. Segmented Shear Wall Design
The code allows any method that is based on engineering principles. Very vague...
There are a couple of methods that I have used in the past. One is shown in the book "Design of Wood Structures" by Donald Breyer -- a must for wood design.
The other is in the SEA 2006 IBC Structural/Seismic Design Manual...
RE: Perforated vs. Segmented Shear Wall Design
I never use perforated wood shear walls - CMU and concrete, yes, but not wood. Just my thing I guess.
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: Perforated vs. Segmented Shear Wall Design
RE: Perforated vs. Segmented Shear Wall Design
A lot of the time with custom homes we don't really have an option. It's use the force transfer method or else add strong walls, cantilever columns or similar. On an upper story this gets tricky...perforated walls also cannot be used on gable walls.
RE: Perforated vs. Segmented Shear Wall Design
For some reason I can't upload the presentation pdf but woodworks has a webinar and the pdf you can download:
http
EIT
RE: Perforated vs. Segmented Shear Wall Design
RE: Perforated vs. Segmented Shear Wall Design
1) Perforated. There are code restrictions on why you can use this. It is generally less expensive than the FTAO (Force Transfer Around Openings) method because it does not require you to use straps around all the openings.
2) FTAO: To me, this method is merely a "rational" method. Unfortunately, it is difficult to find a "right" way of doing this. Though I have given some references below:
SEAOC 2006 IBC Structual / Seismic Design Manual Volume 2: Design Example 1A - item 6b.
Breyer's "Design of Wood Structures" 6th edition example 10.6
There are othes as well, I'm sure. However, the various references that I've found for FTAO are all a little bit different. In fact, when my company (RISA) added this in to our programs we found that a number of the assumptions made in these hand calcs were not really all that accurate. For that reason, I prefer the FEM based methods that we put into our programs for calculating the shear forces in each panel and the strap forces for each opening.
At one point, I planned on putting together a "white paper" on this method which pointed out some of these incorrect calculation assumptions. But, I never seem to have enough time to put this together.
RE: Perforated vs. Segmented Shear Wall Design
RE: Perforated vs. Segmented Shear Wall Design
RE: Perforated vs. Segmented Shear Wall Design
Honestly, any method that obeys statics should work fine. It's just that the static force and moment calculations get tricky for more complex arrangements of openings. That's why we settled on the FEM solution, because we always know that the results will obey statics.
Then we just had to come up with a design methodology based on shear forces and moments.... Take the average shear force in the pier to compare to the capacity of the sheathing/ nailing. Take the moments in the pier to design for the strap forces around the openings. Take the overall moment at the base of the wall to come up with hold-down forces. I really need to put together that paper. It'll be much easier to explain with a design example and calculations to compare to.
RE: Perforated vs. Segmented Shear Wall Design
After I saw the woodworks presentation on the subject, I was surprised at how different the answers were depending on what assumptions are made.
EIT