Engineered Shear Wall Design in IRC Prescriptive Brace Wall System

[VTSE]

IRC R602.10 states " . . . Where a building, or portion thereof, does not comply with one or more of the bracing requirements of the section, those potions shall be designed and construction in accordance with Section R301.1."

I've tended to lean toward engineered shear wall designs for single family dwellings, but they can sometimes hit AHJ snags and I think overall they are more expensive. Lately I've been using prescriptive methods on simple houses. Based on the IRC provision, even if a portion of the building doesn't meet the prescriptive requirements, only that portion needs to be engineered, and I'm wondering what's the best way to design an engineered shear wall for just a portion of the building to fit in the braced wall prescriptive methods which can be a bit of a black box. I attended a Simpson seminar in 2018 where the speaker briefly spoke about finding the equivalent wind shear the braced walls are designed for using the ABW (Alternative braced wall) hold down requirements. For instance in the IRC, a 10' tall 2-10" wide one-story ABW needs a hold down of 1800 lbs - this results in a net 510 lbs for the 2'-10" length or 180 lb/ft (ASD). If you calculate all of these out, you get 8':225 lb/ft, 9':200 lb/ft, 10':180 lb/ft, 11':182 lb/ft, 12':183 lb/ft. This seems like opposite what I would expect. If the story is getting taller, why would wind load be decreasing?

I'd appreciate any experience, examples, or explanations you can give on the issue. Thanks!

 

[XR250]

I usually just figure out the tributary area that segment handles and design it based on code wind pressures.

 

[SE2607]

I usually just figure out the tributary area that segment handles and design it based on code wind pressures.

That's what I do as well.

 

[phamENG]

I also use the tributary area, but keep in mind that you still have a diaphragm. Though not explicitly mentioned in the IRC, it's presence is assumed based on the rest of the prescriptive requirements. If you're having to shift part of your system to shear walls, make sure the diaphragm, collectors, etc. formed by "typical" construction aren't going to be overloaded.

 

[XR250]

Though not explicitly mentioned in the IRC, it's presence is assumed based on the rest of the prescriptive requirements. If you're having to shift part of your system to shear walls, make sure the diaphragm, collectors, etc. formed by "typical" construction aren't going to be overloaded.

I am not in a high wind area but the amount of times I have checked this, I can count on one hand. Unless, the building is super cut-up with a bunch diaphragm discontinuities, I usually ignore this "because residential".

 

[ChorasDen]

I am not in a high wind area but the amount of times I have checked this, I can count on one hand. Unless, the building is super cut-up with a bunch diaphragm discontinuities, I usually ignore this "because residential".

It's always amazing to me when I see comments like this, simply because of what requirements are expected for plan checking on the west coast versus the rest of the country. I can't imagine trying to get an engineered shear wall system through most of the jurisdictions I work on without a check of the diaphragm which is distributing the forces into said shear wall.

 

[XR250]

Well, thank goodness I do not practice in your area! I would not have the patience for that. Same reason I won't take on any coastal house designs.

 

[phamENG]

I'm on the coast almost due east of XR250, and wind matters here...but it's also true that the diaphragm is usually good by inspection. Exceptions are stairs on the edge of the building, or really weird shapes. But for this area, the "normal" floor construction is good for about 60 feet as long as your aspect ration is better than 4:1. But I still check it because there's often some little spot that needs a bit of reinforcing or strapping.