Masonry Shear Walls with Cold Formed Framing

[Struct1206]

Has anyone used masonry shear walls for their lateral system on a load bearing cold formed structure? I am getting ready to start work on a two story apartment building that is to be constructed using load bearing cold formed walls. The building will include a stair tower on each end and an elevator shaft that is located roughly in the center of the building. It seems reasonable to me to have the stair towers (and possibly the elevator shaft) constructed out of CMU in order to utilize them for lateral support but I thought I might check and see if anyone has any insight as to whether or not this is or is not a viable option.

 

[DST148]

I have not used masonry shear walls in combination with light-framed wall systems (LFWS) but there is nothing unusual about using this combination. But why bring in another trade if you can live with LFWS? Though not critical for low-rise structures, LFWS sheathed with wood structural panels has higher Response Modification Coefficient.

 

[Struct1206]

The additional trades is something I have thought about too. We will have concrete spread footings with CMU foundation walls so I don't think it would be a problem to have the masons construct the stair towers as well, assuming they can do it all in one shot. The stairs would be different between the two methods as well. With the masonry stair towers we would likely specify steel stairs (delegated design) and provide them with landing beams (likely hot rolled steel). If we went with cold formed shear walls, then we could eliminate the need for any hot rolled steel but we would then have to design the stairs ourselves.

One other issue that I am contemplating is how the diaphragm loads from the roof get transferred to the stair towers. Are we going to be making things unnecessarily difficult for ourselves by trying to bring all the diaphragm loads to the stair towers rather than evenly distributing to the exterior walls? The plan is to use cold formed roof trusses and cold formed floor trusses with concrete slab on deck.

 

[DST148]

Carrying roof diaphragm loads to the stair towers at each end is acceptable assuming the diaphragm can span that distance. You may have to provide collectors at each end to achieve a reasonably uniform shear transfer / distribution.

 

[JAE]

DST148 suggests what I was thinking - that the use of CMU shear walls is fine - the challenge is dragging your shear from your diaphragms into the masonry.

Usually you would use hot-steel angles bolted to the walls and connect your floor and roof diaphragms to the angles. Other shapes besides angles can be used depending on your details. The key it to provide collectors across your diaphragms that can fasten properly to the walls. Keep in mind that with seismic loads you have to use overstength factors on the connections.

 

[Struct1206]

Given the option to construct the stair towers out of CMU and utilize them for lateral as opposed to cold formed shear walls, which method would you choose. Anyone else have any opinions?