How to calculate shear wall strength at garage door opening

[jsu0512]

I have a 2 story house design project where i need to check the shear wall at the large garage opening.

I have included the house sketch in the attachment. There is a wall inside of the garage and I want to know if this wall can be considered for shear wall calculation? Thank you

 

[phamENG]

As long as you detail the diaphragm to deliver the loads to it, sure.

You could also look into Simpson Strong Walls for shear walls that violate aspect ratio requirements, and APA has a technical paper that provides engineering design loads for site built wood portal frames.

 

[ChorasDen]

Not a lot of info in the sketches, so can't tell what the aspect ratio of a standard framed shear wall is on either side of the garage. Are the wall sections a least 2'-0" in length? If so, you may be able to detail a portal frame over this opening as phamENG indicated, so long as the garage door isn't over a nominal height (believe it to be a max of 10ft, but would have to check IRC to confirm).

I see no reason the interior wall couldn't be considered a shear wall, so long as the wall and diaphragm connection detailing is appropriate, and the foundation is sized to accommodate the shear load with appropriate anchorage, etc. However, you may have a situation where if you discount the walls at the garage door, you are designing a 3-side diaphragm, which is subject to the limits of SDPWS regarding diaphragm aspect ratio and cantilever lengths. Also, you'll need to design the system as a rigid diaphragm, and distribute the loads appropriately, including torsional effects. That may cause larger than anticipated shear loads at the interior wall.

Probably best to make the garage walls Simpson Strong Walls and call it a day.

 

[KootK]

There is a wall inside of the garage and I want to know if this wall can be considered for shear wall calculation?

You can use it but I doubt that you can use it as a substitute for the shear walls at the front of the garage. There are aspect ratio limits for three sided diaphragms and your setup will exceed them. Based on what you've shown us, I'd think that you could use the walls at the front of the study to laterally stabilize the front of the garage. You'll just need to toss a drag strut in there to make that legitimate.

 

[Aesur]

Seems to me the simplest solution would be to drag the load through the diaphragm over to the one wall at the study assuming it calcs out for your loading, which I suspect could be made to work. You may have high overturning and holdown forces, but you would have them with any solution for this other than 3 sided diaphragm.

Edit - KootK beat me to it, I should have read his post before posting as he said the same thing.

 

[KootK]

That diaphragm bit between the the stair opening and the study front wall is likely to need some love but, even at that, I still prefer the drag strut option. In my opinion, pairing up loads with the stiffest available option for resisting those loads is usually a sound strategy.

 

[jsu0512]

Hi KootK

I've assumed three shear walls (including shear wall inside of garage door) for checking shearwall strength on the ground floor. The shear force per each wall was determined using the continuous beam with two span method (three support = three shear wall).

I've used CSA O86-14 code for calculating the shear strength of segmented shear wall. Based on my calculation, the shear wall that has the large opening (garage door) doesn't satisfy the shear load requirement and want to know how to resolve this.

I've attached my calculation (for each shear wall) in here and want to know if I'm on the right path.

Thank you for your help on this. I appreciate it.

Regards,

 

[phamENG]

I see two things:

At the front wall, you'll likely need a proprietary solution. You don't meet the aspect ratio requirements for a site built wall, so you'll need a manufactured and tested product (or a steel moment frame...everyone in residential loves those...)

Am I missing something, or are you not applying second story shear to your first floor walls?

 

[KootK]

Oh... Canadian and a MathCAD'er. We shall be friends.

Before I get any deeper into the weeds with this, why aren't you using the drag strut idea that Aseur and I mentioned to eliminate the garage shear walls altogether? I wasn't foolin' with that. It's silly to try to use that stick of a shear wall when you have a much better load path available to you.

 

[jsu0512]

Hi Kootk.
Yes I saw your reply. To be honest, this is my first time designing shearwall and I need to learn myself how to design with drag strut system.

I just wanted to know if im on the right track for segmented shear wall approach in my calculation.

Im aware that i forgot to add shear force from second floor to the first floor walls. I will fix this in my calculation