Shear Walls at Garage Wall Returns 9

[STrctPono]

I rarely design houses and was wondering how to address the shear walls at the return walls around the garage door opening. It seems that this wall is typically as narrow as possible. Say garage door header height of 7ft. Per SDPWS-2005 Wind and Seismic Design Provisions, shear walls should have a maximum h/bs ratio of 3.5:1. What if architect specified that return wall to be say 18"? This is in technical violation of this requirement. What do you do? Go with a Simpson Strong Tie Garage Portal Wall System? Have the Architect redesign the garage area with wider return walls? Thanks for the advice.

 

[KootK]

I like the Simpson strong walls (as cantilevers) or something of a similar nature. You can do portal systems, even the DIY ones, for some proportions but I don't love the complexity that is often involved. The strong walls are simple, defensible, and prohibitively expensive according to many contractors.

 

[msquared48]

If needed, you can raise the height of the concrete stem walls to make the strong walls fit.

Mike McCann, PE, SE (WA, HI)

 

[JLNJ]

Some of the residential codes give prescriptive designs (and minimum length wall sections) for these portal frames.

I believe this involves extending the header to the far wall to create the moment frame through the jamb/header junction.

 

[STrctPono]

Thanks all for the advice.

KootK, Unfortunately, when I run the numbers, even if I were to be able to stretch the shear wall out to meet the 3.5:1 ratio, I can't get a standard plywood cantilever shear wall system to work out. It would have to be a portal frame. Does the 3.5:1 ratio still apply if you are designing as a portal frame? I am unfamiliar with detailing a DIY portal frame but that is what I would like to do. This is what is making the Simpson Strong Wall system more appealing. I certainly don't want to run up the cost if I don't have to. I put a call in to Simpson to try and get some help with detailing and pricing.

Mike, thanks. Luckily for my case getting the strongwall to fit heightwise will not be an issue. The header beam over the garage door is a 12" deep glulam and I can get it to fit with a 7'-1.5" rough in. Furthermore, we have play room above to the jack trusses. What I am unclear about is what are the width dimensions for the Strongwall system? Do these come in set widths?

JLNJ, extending the header beam is what I intended to do if I had to make my own portal frame but I am unfamiliar with how to nail/strap it. Do you know the specific sections of the IRC where they give these prescriptive designs? EDIT: Thanks, found the section for portal frames.

 

[jayrod12]

The strongwall system can be fabricated to suit your dimensions. They are essentially a ridiculously thick piece of OSB.

 

[phamENG]

The IRC has prescriptive details for a garage portal frame if you're using prescriptive braced walls. Seeing the need for a similar option in engineered shear wall designs, APA sponsored some research:

The wrong link that, nonetheless, gives background to the application in residential design:Link

The correct link for engineered applications: Link

You don't get a lot out of them, but it's a possible solution if it's enough for your application without spending 6 times as much on a custom fabricated strong wall.

 

[phamENG]

Hold on..that was the wrong link...I'm looking for the right one...EDIT: Found it. Updated the last post.

 

[JoshPlumSE]

If you're sticking with wood, my vote is for the Strong Wall (or similar product).

If you're thinking portal frame, then there are a few that look promising (i.e. easier for residential contractors):
[ul]
[li]Hardy Frame (which used pre-built / pre-welded side plates)[/li]
[li]Simpson Strong Frame (which uses bolted moment frames similar to a flange plate, but with tensile link plate).[/li]
[li]Durafuse (Similar to simpson's, but they use shear links instead of tension links).[/li]
[/ul]

The first two are really geared towards wood / residential projects.

 

[kissymoose]

Just use the IRC prescriptive portal frame holddown (PFH). It can be 16" up to a 10ft wall, 18" @ 11ft, 20" @ 12ft. Your architect probably already knows this and expects it.

The IRC prescriptive method is real easy to implement for most houses. It can take a minute (or two )to learn upfront, and I understand why some engineers don't like it/use it for a number of reasons, but it works well for me speeding through bracing often without even needing to reference anything.

 

[STrctPono]

I spoke with the Simpson Strong Tie rep and apparently wood strong walls are not available in my area due to the prevalent issue of termites and the fact that their walls are "basically parallam sheathing" and cannot be termite treated. Only the steel strong walls are available. Around $1000 per wall. Not an issue but I am starting to feel more confident with a prescriptive portal frame as described in IRC R602.10.6. Correct me if I'm wrong, but my understanding is that the prescriptive designs give the Engineer confidence that if detailed/nailed in that way, the portal frame will provide enough joint fixity to ensure sufficient frame action and adequate stiffness to that side of the house....? The Designer is still responsible for checking the strength of the sheathing material, anchor bolt embedment, hold-down capacity, and header to jack stud strap design (as I was outside of the requirements of Table R602.10.6.4).

This has been a good learning experience for me. Thanks all for the help.

 

[phamENG]

Check out the "correct" link I posted. APA tested that assembly and has provided capacities for use by engineers when designing shear walls...

 

[STrctPono]

phamENG,

Thanks. I see now the allowable design shear and deflection values associated with that prescriptive design. The "wrong" link you provided is also interesting as it addresses portal frames without hold-downs.

 

[kissymoose]

So you're taller than 12ft?
The IRC is made so that someone can design and build a house without requiring an engineer. You can follow the prescriptive method of wall bracing without any calculations. Provide the sheathing, anchor bolts, hold-downs, straps as all specified in the code. However, if you fall outside of the bounds of what it provides (eg size of house, height of walls, length of wall panel), it's pretty much an instant switch to an engineered design. An AHJ where I'm at will require comprehensive calcs of the whole house bracing if even one panel is not long enough or too far away from the corner/another panel. It's an interesting design approach, where you are either 100% compliant or 100% on your own.

 

[IRstuff]

Steel strong walls are pretty common these days, since there's been a trend to skinnying garage widths to their bare acceptable minimums.

TTFN (ta ta for now)
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[STrctPono]

kissymoose, That makes more sense. Help me understand this. I have a 12ft total wall height. 8ft height to top of 12" deep Glulam header beam. Planning on using a PFH braced wall panel design since it is the only one that will work with my 20" long braced wall. Have a max shear load of 1800 lbs per wall panel. Link that PhamENG sent shows shear capacity per panel of 1275 lbs (with interpolation) but I can increase by 1.4 for wind. So I barely get my 1800 lb capacity but it works. Table R602.10.6.4 states that for my wind speed and my max opening width and given heights, that a design will be required on the tension straps. I am under the impression that this requires the straps to be sized by the Engineer, but doesn't preclude the entire design....?

 

[Arp32]

I went for this link before I saw your termite comment. It's basically an LVL lapped frame for the narrowest possible portal walls. It may be interesting for someone else's situation.

https://www.strongtie.com/products/...uilt-portal-frame-system/design-options-tools

-Jason, Architect

 

[XR250]

In all likelihood, the building will default to a three sided diaphragm given the tabulated frame drifts. If I have a nice floor or roof diaphragm, I generally go that route.
I am surprised how high those shear capacities are - does not pass my gut check.
I have wondered if they consider out-of-plane wind loads on those straps? Seems that would be significant on a wide opening.

 

[Simba13]

I saw this thread and I have a related question to the prescriptive wind bracing in the IRC, more specifically the Virginia residential code. The story height on this garage we are working on is 13'-0" but the braced wall height is only 10', it bears on a block foundation stem wall which is 3' above the floor. I found a provision (R404.1.5.1) on masonry (stem) wall thickness that basically assuming the thickness is enough, that the wall height can be no more than 20' "the total height of the wall supported, including gables, is not more than 20 feet, provided the requirements of R404.1.1 are met" R404.1.1 is just unbalanced soil load, etc. so I'm fine there. Does this override the max story height of 11'-7"? Or does max story height control as far as the prescriptive wind bracing goes?

Thanks!

 

[Celt83]

STrctPono:
I've always taken the DR - Design required to indicate that the prescriptive method is no longer applicable and you need to do an engineering design. All of the IRC prescriptive details are the results of built and tested assemblies so I don't believe you can assume normal portal behavior and figure out your own tie down forces because of all of the non-linear aspects of the wood assemblies and connections, like strap elongation, nail slip, etc.

My Personal Open Source Structural Applications:

https://github.com/buddyd16/Structural-Engineering

Open Source Structural GitHub Group:

https://github.com/open-struct-engineer