Multi-Storey Wood Frame Shearwalls

[Mohzus]

Hi Everyone,

When dealing with a multi-storey woodframe building, there are restrictions for 5-6 stories that require all shearwalls to be continuous from foundation to the roof. So to comply with this, typically shearwalls are located internally either as demising walls to suites or along the corridor. My question is, under this requirement for shearwalls to be continuous vertically, why do exterior walls have sheathing when their openings per level change and cannot comply with the continuous restriction? Is it due to standard practice to have exterior walls sheathed anyways, even though internal walls are the stiff elements?

Any help would be greatly appreciated, thank you.

 

[Aesur]

I don't follow, can you provide the code reference here. Many times the 5 to 6 story limit comes from fire ratings and interior corridors and party walls are used laterally because of the number of openings in exterior walls as it keeps block and strapped shear walls down, thereby reducing costs for the client.

As for walls being continuous from foundation to roof, a load path is required regardless, maybe you mean you cannot support a shear wall on a beam at the first level?

 

[Mohzus]

Hi Aesur,

Of course, the code reference is provided in the attached image and found in NBCC 2020 Part 4 4.1.8.10 5).

To further explain my question, I am looking for an explanation on why exterior walls of a multi-storey woodframe are sheathed when typically the lateral resisting shearwalls are located internally (corridor/demising walls) to avoid openings and vertical discontinuities. However, if the exterior walls are sheathed and edge nailed, does that impact the overall stiffness per floor and violate the code reference? Or is exterior wall sheathing lightly nailed and such to provide support for building envelope. I find it hard to believe a multi-storey structure without exterior sheathing..

An example of this would be lets say a 5-storey woodframe building, storeys 2-5 have all similar openings on the exterior walls but storey 1 openings are in different locations and cause vertical discontinuity with the exterior shearwalls above, rendering them unuseable. In this case without changing opening locations, are the exterior walls just simple load bearing walls with no sheathing? Or some reduced stiffness so it does not violate the code reference for the overall lateral resisting system.

Let me know your thoughts.

 

[Aesur]

My apologies, I didn't realize you are using the Canadian code, I am not familiar at all with it. I'll see if I can get KootK in here.

 

[Mohzus]

Bump, and a further explanation to help visualize:

Below is a typical floorplan of a multi-storey woodframe building. As an example, I've marked up shearwalls in the corridor as green to resist the E-W lateral forces. Where my question lies is that if I've chosen the green walls as shearwalls (because they are continuous vertically from foundation to roof without offsets), what would be the typical sheathing for the exterior walls to not play a factor with the overall system because they are discontinuous (due to offsets and openings at each level) and violate the code reference mentioned above. Are the red exterior walls sheathed anyways? Is there a situation where they arent?

 

[Eng16080]

I'm also not familiar with the code you reference, but I would consider sheathing the exterior walls as you normally would, presumably with "wood-based panels," but would not design those walls as shear walls. The walls would still resist gravity loads and out-of-plane loads but would not be detailed to resist in plane lateral forces. Therefore they would not meet the definition of "shear walls" and should therefore be in conformance with the code reference you posted above. I would not consider a wood framed wall with "wood-based panel" sheathing as automatically meeting the definition of shear wall.

Again, I'm not familiar with your code. This is simply my 10 minute interpretation.

 

[milkshakelake]

I don't have an answer for you, but you should get in contact with Woodworks. They offer free advice and have a Canadian branch.

 

[lexpatrie]

Sheathing on the exterior is typical, in my experience. You need something to stabilize the studs, in a seismic zone they don't like sheetrock/Densglas gold, and it also deals with during construction water load somewhat better, and it's "historical practice". Sometimes the exterior wall is some Arch fire-rated assembly that has OSB/plywood in it as well. So there are multiple drivers.

(No design experience in Canada, mind you).

Terry Malone has a great book on analysis of irregular structures, I'd recommend it. There are also a slew of continuing education seminars from Terry and others on the subject, there's a lot going on in these structures people don't appreciate at first glance.