Proper installation of metal strapping as shear bracing
This section
https://www.greenbuildingadvisor.com/cad/detail/metal-strapping-shear-bracing
seems rather low on detail. Diagonal metal strapping: let’s discuss it. I certainly understand its point, but please explain its successful implementation.
Looking elsewhere on the internet, in this article by Martin
http://www.betzwood.com/2011/05/20/shear-bracing-foam-sheathed-walls/
the third figure shows that same pair of diagonally installed metal straps or braces, but the accompanying list of metal strapping options doesn’t fully explain, in conjunction with the diagram, how to properly install.
For example, it’s not following this principle: “flat strapping must always be installed in pairs that form the shape of a V or an X.”
How to properly install either T or L strapping in this case–are those little suckers on the corners enough to actually brace the whole wall? Details?
Sadly, the very section that I’m chipping in fees for monthly that seems like it ought to have those details doesn’t. This is where we talk about installing rigid foam to the exterior sometimes, right? By which we need either plywood bracing or metal strapping?
Are those details elsewhere here? Is it a search function issue?
Thanks,
[Trying to dig up some best practices to avoid a] Minneapolis Disaster
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Replies
There are so many issues with this that they cannot be covered in a simple response, but as an engineer I feel some obligation to provide guidance. First is the most obvous that "T" and "L" refer to the shape of the metal brace while "X" and "V" refer to the orientation on the wall, an X or V as you look at the wall in elevation. T and L bracing have added problems in that the stud has to be notched to install the bracing meaning your 2x4 becomes a 2x3 and is probably inadequate for both wind and vertical loads. I never recommend this type of bracing unless the particular situation is checked for ALL loading conditions. The second and more complicated issue is the purpose which is to brace a building from wind, seismic or any other lateral or horizontal load. This is often done with metal bracing or sheating rated for this type of load, normally plywood, OSB and/or gypsum board. To make what is already a somewhat complicated design principle even more confusing, the 2009 International Residential Code has 29 pages (Section R602.10 through R602.12) on what is needed. If you can understand what is required in this secion of the code you will be way ahead of almost everyone else including most engineers. For me, it is much easier to do an engineering analysis and design than to figure out what this particular code requires. I know that doesn't answer all your questions but it is not as simple as bracing the corners and figuring out how the rigid insulation will work. If you are still following along, build a home with a lot of glass, a view of open water and big open rooms, and you will have conditions that cannot be handled by rule of thumb and typical details.
Minneapolis,
To make it easier to discuss your question, I'll do a cut-and-paste job on the relevant section of my article from Fine Homebuilding:
Diagonal metal strapping
There are at least three kinds of steel strapping used to brace walls: flat strapping, T-profile strapping, and L-profile strapping. All three types need to be installed from plate to plate and must be wrapped around the top or bottom of the plate. The location and frequency of metal strapping depends on many variables and is usually determined by an engineer.
Flat strapping (for example, Simpson WB) works only in tension, not in compression. For that reason, flat strapping must always be installed in pairs that form the shape of a V or an X.
T-profile strapping and L-profile strapping are designed to be installed by inserting one leg of the strapping into a 1/2-in.-deep kerf cut into the studs and plates, and then nailing the strapping to each stud and plate. T-profile and L-profile strapping have an important advantage over flat strapping: They work in both compression and tension. That means they need not be installed in V-shaped or X-shaped pairs.
Not all types of T-profile and L-profile strapping have passed the tests that allow them to be substituted for code-required 1×4 let-in bracing. While Simpson Strong-Tie’s L-profile strapping (RCWB) is made of 20-ga. steel and is considered a prescriptive-code bracing material, Simpson T-profile strapping (TWB) is made of thinner 22-ga. steel and does not meet prescriptive-code requirements. If flat strapping or T-profile strapping is used for wall bracing, it must be part of an engineered design.
L-profile metal strapping is a good bracing solution in many areas; however, the capacity of metal bracing may not be adequate in high-wind or seismic areas.
Minneapolis,
While I was posting my last response, and getting ready to post this one, I noticed that Corian Johnston had posted a response while I was composing mine. Thanks, Corian.
Here's what I was going to write -- it's essentially what Corian said: Only an engineer can determine how much diagonal metal strapping you need, and where the strapping should be located.
Sure. And I understand that the T and L strapping refers to an entirely different approach than the orientation of the flat strapping in the form of an X or V.
But I also see that the diagram shows parallel straps, rather than an X or V form. Why?
Minneapolis,
Read my article again. I wrote, "T-profile and L-profile strapping have an important advantage over flat strapping: They work in both compression and tension. That means they need not be installed in V-shaped or X-shaped pairs."
Parallel installation is perfectly acceptable for T-profile and L-profile strapping. Only flat strapping needs to be installed in the form of a V or an X.
I see--so, those two long parallel metal straps running diagonally from bottom to top plate, across several studs, are, in fact, T or L profile bracing (rather than flat strapping run parallel rather than at the recommended V or X formation)?
Minneapolis,
Yes. That's the usual way it's done these days. Few builders use flat strapping any more.
OK. Thanks very much.
As a follow-up: I'm not in a high wind or seismic area (though we do get snow load), I'm only building a 120sf shed: 2x6 24"oc, and since it's not going to be a Case Study greenhouse, I still feel like metal strapping is perhaps in the running here. Looking at the Simpson T & L connector page, which connectors are we talking about when we talk about successfully bracing with L connectors? I see L connectors that would apparently run strictly from plates to single studs, affixed to the exterior face. Correct? Should these go on every single stud/plate connection? Strictly on corners, along with a few others for good measure?
T and L strapping reference page:
http://www.strongtie.com/products/connectors/T-L.asp
Minneapolis,
As far as I can tell, you are on the wrong Simpson page.
Again, refer to my article. I referenced Simpson RCWB strapping (L-profile strapping).
Here's the page you want:
http://www.strongtie.com/products/connectors/WB-WBC-TWB-RCWB.asp
And, concerning the exact placement and number of braces: your attempts to lure me into proposing a spec for your project won't work. I stand by my previous statement: consult an engineer.
That's much better. Thanks, Martin.
Many thanks to Corian for the input, too.
And now I'll take my plywood corner bracing questions (sigh) to my outbuilding thread, rather than posting them here.
Ha, just read your edit. Don't worry, you got me right after I clicked on the right connector detail page.