High load plywood shear wall

[MongoPac]

I've tried to glean from APA and other sources whether or not there is a problem with the values associated with high load, double sided plywood shear walls. APA seems to assume that a double-sided shear wall is equivalent to a single sided shear wall X 2.

Given the vagaries of construction, the quantity of nails and wood quality, this seems a bit optimistic to me and every time the problem comes up I try to devalue the loads associated with the panel nailing if I can.

What, if any, cautions do any of you employ when loads get up to, say the area of +/- 1000 PSF?

 

[SperlingPE]

I start looking at bracing or alternate construction material.

 

[cap4000]

I have use double sided plywood shear walls for wind. The problem I have had is trying to attach safely it to wood framing below and then to the foundations. Uplift is usually my problem. Can you describe your wall conditions a little further?

 

[MongoPac]

Nothing out of the ordinary. I cite this problem which occurs most typically in residential work where the floor plan will not allow shear panels of adequate length to be only one sided. I hate using moment frames if I can avoid it because of the cost to the project and the inherent problems associated with R values for the rest of the structure. Thus I get these large values for double sided shear walls.

I use them, but my interest is in whether or not testing has shown any different critical areas of concern for 2 sided shear walls over single side SWs, such as is described in some of the single side SW testing by APA.

 

[MotorCity]

MongoPac,

Not sure I completely understand your situation, are you trying to resist loads of +/- 1000 psf in residential construction? I guess I'm confused when you consider this to be "Nothing out of the ordinary".

 

[MongoPac]

With a moniker indicating Detroit, its small wonder you are a bit befuddled. But consider; in an area of SZ-4, with the City of LA's 25% reduction in code value of plywood shear walls coupled with lateral Vs of .25W+ (not uncommon), it doesn't take much McMansion architecture to get you into double sided shear wall design.

But forget the reasons why. The question remains. Are there issues involved in the detailing of 2 sided shear walls?

 

[sundale]

Doubling the value for double sheathing is acceptable per the code as far as I know. As some other posters have correctly pointed out, if you need to do this, you may not have enough wall...

The only issue I know about is the footnotes in the IBC allowable shear table 2306.4.1. The few times I have double sided structural panel shear walls, I detail both the longitudinal and horizontal panel joints to fall on different studs or blocking rows respectively. Otherwise, you need 3X members as the combined shear capacity will likely be far bigger than 490 plf.

Whether single sided or double sided shear walls, I think you still have to satisfy the aspect ratios per Table 2305.3.3, which is often a problem at a residential garage.

1000 plf is a very high shear load, I think. Your holdown forces will likely be tremendous and I would see what ACI 318 Appendix D tells you the anchor bolts are good for. A tube steel shearwall end post with a well connected nailer(s) might be good here.

I would consider checking the drift of something like this too. This calculation is more or less voodoo as I don't have much confidence in the answer after calculating flexural deformations, shear deformations, and nail slip.

Simpson makes these corrugated steel "Strong Wall" high load panels for just such a situation. Maybe that is an option if you don't want get into a SMRF for a McMansion.

For my own edification, is a 3X member a California thing? There is no such stud available where I'm located: 4 Corners.

 

[MongoPac]

Thanks for the input.

Here in Los Angeles, 3X PT mudsills are standard, cut washers for ABs have been abolished and I do not use anything else but 1/2" Struct 1 and 3X (actually 4X) edge members. (strangely, 4Xs are cheaper and are generally what is used). That is a standard detail for even the simplest structures. BTW, (HardyFrames is getting rich out here).

The City of LA has a 25% reduction nearly across the board for all lateral resisting elements and in some instances does not allow the EQ duration increase. Apply this to nails, straps, studs, sills, HDs, etc. and you can imagine what you are left with. (Next time you are on the Simpson site, peruse one of the COLA Research Reports for a hold-down or other lateral resisting product).

OTM loads and Holdowns are indeed the most troublesome aspect of some of the loads I encounter, both in design and execution on site, particularly in attempting to ensure adequate edge distance while still allowing the usual "Palladian summer home in Frascati" look when only 2 Km from some major fault line.