RV Garage Shear Wall Design

[RockyDiego07]

Hello,

This question is in regards to a simple 41ft long x 17ft wide x 17.58ft tall RV garage.
Not sure how to do the shear wall for at the large opening (12ft wide x 14ft tall), without doing a Simpson Strong-Wall.
I can't seem to do a portal frame per the IRC, the IRC limits this to 10ft max wall height and 12ft max total height. My heights are exceeded. Same thing with the portal frame per IBC.
I can't use the SPDWS, because my aspect ratios are way above 3.5. The walls beside the opening are 2.5ft wide. Even taking just the clear height, 14ft/2.5ft = 5.6.
I can't do an open front structure (w/ a cantilevered diaphragm), the diaphragm aspect ratio is 41ft/17ft = 2.4, which exceeds the 1.5 limit. Plus the 41ft exceeds the 35ft max limit for the cantilevered diaphragm.
The framer claims he rarely uses Simpson Strong-Wall in these "simple" structures. Is there any other way to laterally engineer this, specifically the walls around the opening, to satisfy the code, without the use of a Simpson Strongwall?

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/raw/upload/v1668898511/tips/RV_Garage_Sketch_ws85j2.docx[/url]

Thanks!

 

[BridgeSmith]

If it's outside the prescriptive limits of the applicable code, it will require someone qualified (licensed) to do a structural design. If you don't want a solution that's pre-engineered by Simpson, you'll need an engineered design from someone else, with the proper P.E. stamp on it, to meet code.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[Aesur]

You are on the right path to use a strong frame, strong-wall or engineered moment frame. Unfortunately what the framer is saying may be correct from his perspective as I have seen FAR too many of these structures that aren't designed correctly per code with the exact issue you are stating.

 

[HouseBoy]

"....Is there any other way to laterally engineer this...."
How are the side walls being built?
What if you utilized "Post Frame Building/Pole Barn" construction strategy?
18 ft is tall but IF the deflection can be tolerated, THEN the load at the end wall would be reduced a good bit.
Aspect ratios are still high be there would be a rational path for such a design approach.

 

[XR250]

Are those limits based on Seismic or Wind?
I would think if you were really careful with your detailing and conservative with your design (3/4" sheathing etc), a three sided building could be made to work. It may drift excessively, but who cares - its an RV structure. Add some shearwalls up front for belts and suspenders.
Sometimes in these situations, I have made the building wider to get the shearwall aspect ratios more right.
Is that a possibility?

 

[phamENG]

I'm not even sure you could get strong walls to work. Do they make a 14ft high model?

My choices in order of preference:

1) Widen the building as XR suggested to make the aspect ratios work (FTAO procedures a bit dubious with doors, but there are some rational methods that could probably be justified). I don't own a big RV like I'm assuming they're putting in this thing, but I do have a smaller trailer. Having the ability to do periodic maintenance without having to pull the rig out, and being able to do it indoors in any weather is worth it if the site can accommodate it.
2) Raise the stem wall to reduce the wall height to make the aspect ratios work.
3) Engineered portal frame(s). Not necessarily built up with studs and sheathing. Could be LVLs with a moment connection (I don't like them, but people use them and they do have a history of 'working'), steel, etc. I would look at drift only in terms of stability, not serviceability. I think this is more or less what HouseBoy is suggesting. Do several portal frames along the length (at 4'0" on center or so) to spread the load out and ease the demand on the connections. It'll be a wood rendition of a PEMB rigid frame design.
4) Walk away and let the contractor find some unscrupulous engineer who doesn't mind violating the building code in their design.

XR250 - the 1.5:1 limit for open front structures is universal; doesn't matter if it's wind or seismic. So in this case, a 3-sided building might work in practice but it's a code violation. I suspect that's mostly a result of testing limitations, but I haven't dug into 3-sided diaphragms in a while and I don't recall the reasons for the upper limit there.

 

[bigmig]

You will want to look at the 3 sided box analysis for wood diaphragms. It is found in NDS Section 4.2.5.1.1 and is called "Open Front Structures".
Good luck.

 

[phamENG]

bigmig - the OP did, and has found that it violates that section of the code. It's all right there the first post.

 

[Aesur]

@phamENG - they make the WSWH strong walls up to 20' height now.

@XR250 - the 35' limit he is referring to is the limits of NDS lateral design (wind and seismic) for wood cantilever diaphragms. See 4.2.5.2 of 2018 NDS. This limits L' to 35' max and is a pain to deal with on some buildings (like apartments) where there are many windows on the exterior and you want to sheath the corridor and party walls only. (phamENG beam me to this, didn't finish reading his post before posting)

I like phamENG's stem wall idea, what would it take to make that work aspect ratio wise?

 

[XR250]

I imagine RV shelter = turned down slab w/o stem walls

 

[Aesur]

Based on OP's location, you are most likely correct that it's a turndown, but you could add a curb on the turndown to achieve a sim effect.

 

[XR250]

You could, but adding a stemwall has pretty significant cost impacts. Might be the best solution in the end, however.

 

[Celt83]

Working backwards sounds like you have a 12ft wide x 17.58 ft tall opening, for that size opening and the deflection requirements for an operable door I’d expect this to be a steel framed opening. If the door opening is steel already to me it would make the most sense to make that into a moment frame.

 

[JedClampett]

Not on subject, but why is your RV garage 17'-7" when the highest bridge clearance is about 14'-0" and a lot are less?

 

[ChorasDen]

why is your RV garage 17'-7" when the highest bridge clearance is about 14'-0" and a lot are less

Starlink dish bolted to the top?

 

[HouseBoy]

Jed,
I was wondering the same thing but thinking about the door being 14 ft tall.
Still, it gives some good room to put bracing in at the tops of the sidewall columns....

 

[calvinandhobbes10]

If I were hired as an engineer for this design, I would look at flat strap x-bracing on both door jambs. I have seen it used for a similar structure with compromised shearwall, although smaller. I would also consider using this as my “belt and suspenders” for a 3-wall diaphragm check to help control drift.

 

[Aesur]

@calvinandhobbes10 - how could you do "x-bracing" on something so small, it would be pointless. a 2' pier by 14' tall? X-bracing would be worthless...you would be better off ignoring shear wall aspect ratios and using sheathing than using x-bracing. Additionally, the issue here is that the diaphragm doesn't meet the requirements of a 3 sided diaphragm, hence the original post.