Horizontal 2x6 T&G as Shearwall Sheathing

[EngDM]

Is it possible to use 2x6 oriented horizontally as your shearwall sheathing? There are tables in O86 for diagonal member paneling, but I couldn't find anything for horizontal. My gut is saying no, because there is no shear transfer between adjacent horizontal members. With diagonal members, at least the member can go into tension/compression and drag the base shear from the top chord to the bottom chord.

So aside from some sort of shear transfer detail between adjacent 2x6 panels I don't think this works.

Just looking for a sanity check or some insight.

 

[XR250]

I don't see how this could be easily made to work.
I mean it kinda works on decks though even though we don't take it into account.

 

[Greenalleycat]

What's the context for this?

If you have horizontal members with min. 2 fixings at each stud then you will develop a moment capacity
You could then look at it as more like a bunch of moment frames - you'd get bonus shear transfer as friction in the T&G but hard to quantify
I would do this for some sort of minor structure quite happily - say the wood shed that I just built which uses a similar construction method
I wouldn't like to rely on it for a signficant structure though (e.g. a house) without good reason
My main concern would be quantifying deflections - I would expect large deflections in the fixing which would be difficult to analytically quantify

Edit: picture of wood shed below. This uses 200x25 with 25mm gaps between and it still is as rigid as now that the timber is on (obviously it's just a wood shed though)
So the effect exists and can be estimated

 

[EngDM]

What's the context for this?

If you have horizontal members with min. 2 fixings at each stud then you will develop a moment capacity
You could then look at it as more like a bunch of moment frames - you'd get bonus shear transfer as friction in the T&G but hard to quantify
I would do this for some sort of minor structure quite happily - say the wood shed that I just built which uses a similar construction method
I wouldn't like to rely on it for a signficant structure though (e.g. a house) without good reason
My main concern would be quantifying deflections - I would expect large deflections in the fixing which would be difficult to analytically quantify

Edit: picture of wood shed below. This uses 200x25 with 25mm gaps between and it still is as rigid as now that the timber is on (obviously it's just a wood shed though)
So the effect exists and can be estimated
View attachment 4089

Client wants to use 2x6 T&G for their wall finish instead of sheathing, since they want their wall members at roughly 48" on center. Almost like a pole barn but without the embedded foundation.

 

[Greenalleycat]

I think it's definitely doable but will be challenging to get the numbers to work out
(disclaimer: I don't know the USA system at all so I'm just thinking about this from an NZ perspective)

If there are no tested values then you'll be stuck with specific engineering calculations
Here, tested values are usually significantly better than engineering calcs so you're already going to be at a disadvantage
Quantifying displacements to assure yourself you'll meet serviceability requirements will also be tricky without testing

To get this system to work I imagine you'd need a high ductility to get your loads down to reasonable level (particularly chord/hold-down forces)
I suspect this will be difficult in absence of industry info
This is particuarly true if you use screws (which I would want to for a much higher quality finish) due to most screws being low ductility
You could use stainless but $$$

Hold-downs could be quite tricky too - I imagine your best bet is to use double studs at each end with a cast-in bracket bolted between the studs (to get double shear planes going)
The advantage is that you could probably turn every wall panel into a bracing element so you'd get distributed loading fairly easily

Gut feel is that you can make it work but it's going to be pretty involved on the engineering front and will lead to solutions that look disproportionate to typical stick framing
But, if that's what the client wants, I think they can get it
(obviously, I know nothing about size/layout of house, cladding weight, # storeys, roof weight, wind/seismicity etc that would affect the design)

 

[dold]

You could probably look at some of the NDS diaphragm values for T&G deck and that'd give you an idea of capacity roughly. Although I think that requires some sort of nailing through the tongue into the studs? The proposed framing scheme seems pretty similar to a T&G roof. Just a thought.

 

[EngDM]

I think it's definitely doable but will be challenging to get the numbers to work out
(disclaimer: I don't know the USA system at all so I'm just thinking about this from an NZ perspective)

If there are no tested values then you'll be stuck with specific engineering calculations
Here, tested values are usually significantly better than engineering calcs so you're already going to be at a disadvantage
Quantifying displacements to assure yourself you'll meet serviceability requirements will also be tricky without testing

To get this system to work I imagine you'd need a high ductility to get your loads down to reasonable level (particularly chord/hold-down forces)
I suspect this will be difficult in absence of industry info
This is particuarly true if you use screws (which I would want to for a much higher quality finish) due to most screws being low ductility
You could use stainless but $$$

Hold-downs could be quite tricky too - I imagine your best bet is to use double studs at each end with a cast-in bracket bolted between the studs (to get double shear planes going)
The advantage is that you could probably turn every wall panel into a bracing element so you'd get distributed loading fairly easily

Gut feel is that you can make it work but it's going to be pretty involved on the engineering front and will lead to solutions that look disproportionate to typical stick framing
But, if that's what the client wants, I think they can get it
(obviously, I know nothing about size/layout of house, cladding weight, # storeys, roof weight, wind/seismicity etc that would affect the design)

The building is 21' walls, 120ft x 120ft footprint with N-S walls having fairly large OH doors in them. I don't think I'll be getting that to work easily. I've got like (2) 18ft wall segments on the N-S walls to get to work for shear.

 

[Greenalleycat]

Ouch, 21ft tall walls sounds like a mission
Well, you should be able to do a 'back of the envelope' calculation on this pretty quickly and see if it has any chance of working at least

 

[Structure_PA]

AWC SDPWS has a capacity table for lumber shear walls, including a pretty low capacity for horizontal orientation. I was not successful in finding any further discussion or detailing on the subject when I investigated this for a timber salt shed project.

 

[Eng16080]

Is it possible to use 2x6 oriented horizontally as your shearwall sheathing?

Yes it's possible but the capacity will be rather low. I don't know what the O86 document is that you refer to, but at least in the US, you can refer to NDS SDPWS Table 4.3D which has values for "Single-Layer Horizontally-Sheathed Lumber" for "1x6 & smaller" and "1x8 & larger" boards. I think you could assume a similar capacity for 2x6 boards.

With diagonal members, at least the member can go into tension/compression and drag the base shear from the top chord to the bottom chord.

The same table also has values for diagonally sheathed walls, and you're right, that configuration is significantly stronger.

My gut is saying no, because there is no shear transfer between adjacent horizontal members.

Neglecting friction of the T&G joint, I agree, although there would still be a load path assuming each board is fastened to each wall stud with at least 2 nails, thus allowing shear to transfer to the wall studs.

 

[Eng16080]

Ok, Structure_PA beat me to it, in terms of mentioning SDPWS. I didn't see that reply when I responded.

 

[Greenalleycat]

I would be very hesistant to rely on T&G friction for this application, particularly given how huge the building is
Not sure if you can buy dried T&G boards where you guys are, but here 150x50 T&G is landscaping timber for retaining walls
Having just built a big ol wall out of 200x50 T&G, I can confirm that they move all over the show as they dry out - the friction would be unreliable at best
It would be my 'sleep at night' factor, not a primary consideration

 

[Eng16080]

I would be very hesistant to rely on T&G friction for this application

Agreed. I wouldn't want to rely on friction as far as the numbers go. I think it's rather something that might help.

 

[EngDM]

Yes it's possible but the capacity will be rather low. I don't know what the O86 document is that you refer to, but at least in the US, you can refer to NDS SDPWS Table 4.3D which has values for "Single-Layer Horizontally-Sheathed Lumber" for "1x6 & smaller" and "1x8 & larger" boards. I think you could assume a similar capacity for 2x6 boards.


The same table also has values for diagonally sheathed walls, and you're right, that configuration is significantly stronger.


Neglecting friction of the T&G joint, I agree, although there would still be a load path assuming each board is fastened to each wall stud with at least 2 nails, thus allowing shear to transfer to the wall studs.

All I have access to for NDS SDPWS is the free viewer online, which sucks when you attempt to zoom in to actually read anything. I can't make out if there is a minimum stud spacing to use these values, but my studs are at 38-50" O.C. throughout.

 

[XR250]

The building is 21' walls, 120ft x 120ft footprint with N-S walls having fairly large OH doors in them. I don't think I'll be getting that to work easily. I've got like (2) 18ft wall segments on the N-S walls to get to work for shear.

This would have been good information to put in your original post.

 

[Eng16080]

I can't make out if there is a minimum stud spacing to use these values, but my studs are at 38-50" O.C. throughout.

Yikes! I believe the shear values in that table (and other similar tables) are only intended for walls with studs spaced at a maximum of 24" o.c. I think this is based on the testing that was done to establish those values, which is in line with the stud spacing for a normal wood framed structure.

I think you'll have to scrap the shear wall idea altogether with studs spaced that far apart and find some other lateral resisting system.

 

[Greenalleycat]

I think envisioning this as a shearwall isn't correct
Presumably you won't be blocking and screwing off the edge of each board to get proper shear flow etc
It's more appropriate to imagine it as a moment frame with beams being the boards, columns being the studs, and your joint detail being 2 screws at the end of each board
Your studs will be weak axis so it's hardly the stiffest system known to mankind, especially if they're 1m+ apart

 

[Tomfh]

How snug is this sort of T+G system? My cypress pine floors are very snug T+G. The diagonal compression field would form very easily, preventing shear deformation, as opposed to it having to function as moment frame, as is the case with decking.

 

[EngDM]

I think envisioning this as a shearwall isn't correct
Presumably you won't be blocking and screwing off the edge of each board to get proper shear flow etc
It's more appropriate to imagine it as a moment frame with beams being the boards, columns being the studs, and your joint detail being 2 screws at the end of each board
Your studs will be weak axis so it's hardly the stiffest system known to mankind, especially if they're 1m+ apart

Studs are 5 1/2" glulam so it probably won't be a problem, can't say for certain.

This would have been good information to put in your original post.

I put the information needed in my original post. My question was if horizontal 2x6 members could act like sheathing, and a rationale why I think they can't. I wasn't asking for alternate solutions, I just couldn't find any information supporting/refuting.

Yikes! I believe the shear values in that table (and other similar tables) are only intended for walls with studs spaced at a maximum of 24" o.c. I think this is based on the testing that was done to establish those values, which is in line with the stud spacing for a normal wood framed structure.

I think you'll have to scrap the shear wall idea altogether with studs spaced that far apart and find some other lateral resisting system.

With no shear transfer at member edges I agree with you. Will probably use some sort of tension strap to get my diaphram shear down to the grade beam.

 

[skeletron]

Although not something I would hang my hat on, Table A-3 of the NRC's publication of "Seismic Evaluation of Existing Buildings" provides a 4.4 kN/m (301 lb/ft) strength value for "floors with straight T&G sheathing" or "roofs with straight sheathing and roofing applied directly to the sheathing".