gypsum wallboard shear wall capacity using undersized fasteners

[dougreeves]

Anyone know of prescriptive or analytical methods for determining the reduced values in shear wall capacity when using either undersized fasteners or larger spacings shown in the IBC tables? The sheathings in my case (analysis of existing structure) are gypsum wallboard and gypsum sheathing.

Also, I have 2x4 stud spacing of 12"oc in many areas.

One school of thought is to totally discount the shear capacity of the wall (since there are no published capacities), but this is not realistic. Even inadequate fastening of sheathing provides SOME capacity.

I'm fairly positive that the reduction is NOT linear based on nail cross-section, nor penetration.

All ideas are welcome.

Thanks,
Doug

 

[Lion06]

How close is your spacing to what is published in IBC 2006 for Gypsum Board Wood Framed Wall Assemblies? Can you add fasteners to get the required spacing? Also, how close is your acutal unit shear to the values listed in the table in IBC? If your actual spacing is very close and your unit shear is well below, I would be comfortable with it. The structure has inherent stiffness that is not accounted for that could help you sleep at night.
I would be careful, though, and will be interested in hear what others say.

 

[dougreeves]

Thanks for your reply

1st of all, this structure was designed under the UBC97 code. I am analyzing the lateral capacities, not designing.

2nd, I can't get too specific (for legal reasons) other than the fasteners used are less than the sizes called for in the tables, their lengths are shorter, AND the spacings are larger.

What would be most helpful would be references or methods to "defend" our position that the shearwalls, as constructed, DO have a quantifiable capacity of XXX plf -not zero.

Doug

 

[NerdSE]

Can you make a test panel and push it. Then compare the shear with published results? A wood test panel would not be that expensive. The test equipment will be the most costly. Try a local state university. A program that only offers 4 year degrees may be more reasonable than a research university. An engineering senior may want to take it on as a project. Plus, it's difficult to argue with an actual test. A jury will understand that much better than a bunch of math. Take a nice video

 

[concretemasonry]

If you do any testing, make sure to document the stabilized moisture contents in the test walls and the in situ stabilized moisture contents in the existing structure.

This will answer many of the obvious questions.

Dick

 

[dougreeves]

thanks for the responses.

nerdse, the test panel would be a very viable alternative. but comparing with published results would involve HAVING published results using indadequate connections.

as far as a jury understanding the tested panel's capacity versus a bunch of math ... I'd still like to use math, at least for corraboration.

thus, if you have ideas or references to DO the math, that would be most helpful at this point.

Doug