Wood Shear Walls on CMU Walls

[kmart30]

I have a fairly regular shaped two story homes being designed with the 1st story as CMU and the 2nd story 2x6 framing. The roof is a 7/12 gable and the upper floor shear walls running parallel with the ridge have windows/doors pretty much everywhere. All my aspect ratios for my segments along these walls are greater than the allowable limits. The whole second floor pretty much is open and none of my interior walls line up with walls below to be used for shear. I ran some numbers using the APA force transfer around openings calculator but I am getting very high shear wall deflections as I expected. What would be the best options to move forward?

 

[jayrod12]

Steel moment frames. Or Simpson strongwalls?

 

[kmart30]

Yes this is what I figured were my only two options left. Does anyone have any good references for integrating steel moment frames into wood construction? I might just go with Simpson on this one but my plate height is just over 12 feet with an 18" deep floor system and Im not sure if they make their walls that tall.

 

[Guastavino]

@kmart - simpson actually has custom steel moment frames with the wood incorporated on them. I've never used them myself, but they push them hard. I'm sure they are pricey though

 

[XR250]

I usually just design my own moment frames and have them fabbed locally. Lots more flexibility (not in a stiffness sense) and alot cheaper.

 

[KootK]

Without much trouble, you should be able to get your hands on the simpson details for their moment frames and then more or less replicate them with regard to nailer plates etc.

Since you're already block on the bottom, would there be any sense in running a section of it up to the roof as second story, perforated shear wall? That would probably wreak havoc on the exterior wall detailing of course.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[kmart30]

Yes I looked into the custom moment frames but I always thought they were really expensive. I was looking around on simpson and they have "ballooned framed" sections that are taller than the typical sections.

 

[bhiggins]

Are there any interior walls you can sheath as shearwalls? Run beams or drag trusses under these walls to ultimately transfer shear to the CMU walls.

If wood is not an option I see multiple other options:

Simpson strongwalls are an option but I feel like builders hate them. It's a pain to get the anchors to work out and the contractors never install them right in the end.
Cantilever steel columns may work if your loads are light.
Cantilever reinforced concrete columns which are infilled with CMU.
A fully welded HSS frame is usually what we use. It's all site built here and fairly easy to build. The builder's usually try to avoid steel at all costs due to the extra trade.

 

[kmart30]

Here is my model in woodwork.....no openings on this one to just show my loads.

Yes I agree with the simpson walls in the field but they make it really really easy to spec out from a designers standpoint. When using cantilevered steel or RC columns what is typically used to transfer the lateral loads to the next column/segment or does 1 typically transfer the entire load? Sorry, I typically only deal with wood and a little CMU so its just a bit out of my wheelhouse.

 

[XR250]

I believe with loads of that magnitude, cantilevering a column would be a base connection nightmare. My suspicion is moment frames are the way to go here.