Wood Panel Shearwall - Nailing Tolerance

[NFExp]

I'm looking for opinions regarding an acceptable tolerance for the percentage of nails that can be missed or mis-installed on a wood panel shearwall and still be within an acceptable tolerance.

For example if I specify a shearwall with 8d nails @ 3" on-center for a 7/16" OSB and the framer has installed most of the nails @ 3" but some of the nails are shiners or the spacing is 5" in some areas, what is the percentage of nails that we can justify and still be code compliant.

I know there is a safe factor of 2.

I looked in the code and online and I cant find anything. I am arbitrarily thinking 5% should be acceptable but I'm curious on everyone else's opinion.

 

[WesternJeb]

My firm has some rules of thumb like we design masonry to f'm 500 psi less than what we specify in our drawings. Design rebar in concrete with Deff of the inside face, so it doesn't matter which rebar is on the outside or inside mats.

Another one I might consider is specifying shear walls with 1"-2" tighter nail spacing than required by design. This allows for some tolerances like this that will inevitably always happen in construction.

I agree though, that if it is 5% of the nails or less misplaced, I wouldn't really care.

 

[ChorasDen]

Alternatively, can you consider methods to reduce your design load going into the shear wall? Consider semi-rigid analysis rather than flexible for the diaphragm?

 

[Greenalleycat]

This is a nuanced question so it's hard to give a definitive answer from our seats.
Some thoughts though

1) If we are talking like 1% of the nails being wrong...probably just 'by inspection' accept it

2) If you did the specific design yourself then just work out how many nails you have over the whole wall height (on average), and what that works out to as an equivalent spacing
Check that revised spacing with your design and decide if you are happy

3) As ChorasDen has suggested, you can consider the accuracy of your demands and whether a slight imperfection in construction matters (assuming it is just slight)

4) You can just ask them to grab a nail gun and bang additional nails in to reduce all gaps to max 3" crs if you want to
You should consider whether any ductility is expected from this wall though (seismic requirement only)
If so, more nails may not be the best solution
If it's a wind-governed design then more nails is good so probably just bang them in to teach the contractor to read the plans better

 

[phamENG]

Not exactly what you're asking, but this may be something to consider: APA TT-012 Effect of OVerdriven Fasteners on Shear Capacity

If they got the spacing wrong, I make them add fasteners. 5" on a 3" spec is tough, since you can run the risk of splitting the member behind. If they used the wrong size (too small) nail, they get to strip it off and start again.

 

[NFExp]

Thanks All.. I did the design so I'll play with the nail spacing and see what impacts a reduced nailing causes

 

[lexpatrie]

Back in the day, the old UBC had values for 2 1/2" nail spacing that eventually got increased to 3". I presume there was a NEHRP that recommended the increased spacing based on observed splitting after some earthquake.

This is one of the reasons I try to avoid using 10d nails @ 3" o.c. because if there's a mistake there's nowhere to go. Closer spacing will produce splitting and if they space the nails too far apart you can't really fix it.

Your original design should exceed the demand, because you have finite spacing options for the nails, 6", 4", 3", and it may have thicker sheathing than you designed for as well, work it from that side.

Overstress is linear, but failure probability is not. So a 1% overstress is unlikely to cause a failure, but a larger overstress like 10% to 30% produces more than 10% to 30% probability of failure.

You may be able to redistribute the lateral force deficiency through the diaphragm to another wall with excess capacity as well.

Also:

https://ascelibrary.org/doi/abs/10.1061/(ASCE)1084-0680(2005)10:3(154)

Alternately you could add another layer, or add a layer on the interior and cover it with gypsum board, etc.

As the overdriven fastener research suggests, if the problem is not widespread, perhaps the nails can be removed and correct nail spacing installed. The wedge effect of nails close together should not occur when one of the nails is removed. You can always get a nice 2x6 and try this yourself with the appropriate nails to confirm on a small sample.

If you are out west, and they are building with green lumber, I'd defer to the expertise of more local engineers.

Regards,
Brian