Shed project: Shearwall design

In a free-standing garage, where one wall is almost entirely absent to make a door opening, what parts of the structure prevent the door wall from racking?
I am second-guessing myself about my shed plan. One wall, a gable end wall, is non-load-bearing but is a shear wall. Its plan has an 8x8 door opening in a 12' wide by 9' high wall. I don't have the background to determine whether such a wall will have sufficient shear strength. I'm using conventional 2x4 framing 16" OC with APA-rated 7/16 OSB sheathing, no interior sheathing is planned.
The obvious things would be to reduce the door opening, to use heavier sheathing, and/or sheathe it inside and out. But first I would like to hear any advice this august group has to offer, and with my thanks.
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snipped-for-privacy@asgard.slcc.edu wrote:

Traditional way, in addition to stiff sheathing, was to cut in angle braces on all the corners. Try to create as many triangular sections at right angles to each other as you can. A large header, corner post to corner post, helps as well. On the addition to my house down south, we actually used about 35 feet of glue-lam all the way from the original house, over the open carport bay, and tied into the far corner of the new garage beyond. It has worked out real well- no movement in 2 hurricanes since then. Carports in Louisiana hate hurricanes almost as much as mobile home in Arkansas hate tornadoes.
I'd bump up the walls to 2x6 (so you can hang shelves on the walls), use thicker sheathing (real plywood beats OSB), consider using adhesive and nails on the sheathing, and use all recommended tie straps for your area. Truss or stick-frame roof? If you aren't finishing the inside at all, you can face-apply the triangular braces mentioned above on the inside, including tying the adjacent walls together at the level of the ceiling joists. That will make for very stiff corners.
Standard disclaimer- I'm not an engineer, but that is how I saw it done as a wee lad, and how I would do it.
-- aem sends...
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On Sun, 28 Jun 2009 15:25:36 GMT, snipped-for-privacy@asgard.slcc.edu wrote:

You don't say whether or not you're in earthquake country....
If not, standard let-in diagonal bracing combined with properly applied and nailed sheathing should be fine.
If you are in earthquake or high-wind zone, or just want a beefier design, Simpson makes pre-engineered shear walls designed for the narrow walls next to garage door openings:
http://www.strongtie.com/products/strongwall /
Googling "shear wall design" will get you lots of info.
HTH,
Paul F.
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On Jun 28, 8:25 am, snipped-for-privacy@asgard.slcc.edu wrote:

a door opening, what parts of the structure prevent the door wall from racking? <<<<<<
the bad new is........(the correct / truthful answer) "not much"
but the good news is
a small (I assume yours in small since you're talking about a 8x8 door) single story free standing garage requires very little lateral (shear) capacity unless you're in major wind country
I have a 1930 single story garage with a 16' x 7' door, the garage is about 22 x 20 (with the garage door & a man door on the 20' face). So my garage has close to zero lateral capacity on the open face. The other three walls have stucco over 1x6 horizontal sheathing over 2x4 suds at 16" o/c. It also has 2x4 diagonal blocks in each of the "solid" walls with a stud bay of the corners.
Not exactly an engineered lateral system but good enough to have survived the following earthquakes: 87 Whitter (~10 miles), 89 Newport (~10 miles), Landers / Big Bear 92 (~50 miles) and the recent Chino (~15 miles) .
For the Chino quake was working on sawhorses on the driveway in front of the garage when I felt the ground wave arrive.......I stepped away from the open garage & watched it sway north/south (the weak direction) as the rest of the motion arrived.
Bottom line...my ancient garage has very little lateral capacity but it doesn't need much for e/q's.
The code in CA used to allow "rotation" in the design of three sided structures but they got kinda conservative (overly imo) & I think they don't allow it. Rotation depended on having a relatively rigid diaphragm tying the walls all together, so that the sides & back worked together to make up for the "zero lateral" of the front wall.
A four sided "box" but open on the top is pretty strong ..............but take away one of those sides and now its not so strong. Add a structural "diaphragm" to tie all three sides together and now you've got a strong system again. If you want to play around with the concepts....build a 1/4 model (use door skin as sheathing) and a brad nailer attach it. Build it four sided but with the idea of removing one wall, try to rack it when it has four walls remove one wall, rack it gently......at the "flat diapghram" (ie the top of the box), try to rack it again.
If you build it, "nail" the wall sill plates to a 3/4" plywood base to serve as a foundation.
As Rico mentions....moment resistant systems involving the garage header are possible but not easy or simple.
Simpson's prefab shearwall may be the best know but they are by far NOT the best.
I've tested 100's of shearwall configurations as well has the Simpson & other pre-fab shearwalls.
Check out ShearMax pre-fab panel www.shearmax.com
concepted, designed & developed by a father / son team; very inventive but most of all stubborn & persistent....a way better product than the SImpson
OP-
if you cannot add a flat structural diaphragm to the system to tie the side walls & the back walls together or if "rotation" is no allowed.......you can probably use a 4' site built panel to take the load. But unless you have a local prescriptive code you can use or your local building dept has a free standing garage "canned design" like a patio cover, you might be stuck getting it engineered. :(
If you do get it engineered...ask the engineer how he plans to handle the concentrated panel hold down loads generated by the a pre-fab panel. A simple slab is not enoough....most likely require some sort of grade beam at the open face.
btw, I believe ShearMax has approved panel / header moment resistant connection details that will avoid the need for grade beams.
As crappy as OSB seems, code affords it the same values as plywood (plus my testing experience has show no significant difference). Forget aemeijers suggestion of adhesive, imo not worth the cost, effort, hassle. And bumping up to 2x6 for a garage is waste of timber. Addtionally 7/16 OSB is more than enough for a garage.
cheers Bob
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Bob,

Unless you plan to use the garage as a workshop, in which case 2x6 construction allows you to install more insulation. I used 2x6 framing with R19 insulation in our garage and have never regretted it.
Anthony
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True...but did OP say where the garage is located? Insulation makes sense for conditioned space.
In most of SoCal insulating a garage is waste of time & money. In the desert (high or low) or the mountains...... insulation is worth it.
cheers Bob
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The OP is posting from a SLCC.edu account - Salt Lake City Community College, so it gets hot and it gets cold.
Upon looking at some of the climate data, the shear wall situation is less critical in SLC than in some hypothetical unknown location where conservative advice must be given. SLC has only had two tornadoes in 115 years. Like I said above, let the local code and shear requirements dictate the design - they shouldn't be too onerous.
R
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An 8' door in a 12' wall doesn't leave much to resist shear forces from winds or earthquakes. It would be best to increase the shed to 16' wide, or reduce the door to 6' wide so you can have at least 32" on each side (more would be better).
I'm no engineer, but another option might be to shift the door to one side so you can increase the width of a shear wall section.
Otherwise, the only solution I can think of would be a welded steel "moment frame" that basically makes the entire 12' wall a stiff frame than can't rack. But that could be an expensive option and would probably need engineer approval with the building department.
Regardless, you'll need to tie the shear walls securely to the foundation with special anchor ties (Simpson SSTB) and hold downs (Simpson PHD).
Anthony
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On 2009-06-28, snipped-for-privacy@asgard.slcc.edu

If you read the responses so far (especially Bob's), then you have a pretty complete answer, but I thought it would be useful to summarize them in one post. The options are:
1) Braced wall panels on either side of the opening 2) A moment resisting frame around the opening 3) A diaphragm above and braced walls on the other three sides
Option 1) can be done with conventional framing and sheathing if the wall segments are wide enough. Otherwise pre-built shear wall segments such as those made by Simpson or Shearmax may be used.
Option 2) can be implemented in wood or steel and requires moment-resisting connections in the corners. In wood this is done with a large header the full length of wall with appropriate detailing between the sheathing on the end segments and the header.
Option 3) works like this: with unequal lateral resistance in the two wall segments running in the given direction, when a lateral force is applied in that direction, the building will rotate, allowing the lateral resistance of the perpendicular wall segments to be engaged to resist the lateral force.
Cheers, Wayne
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