OSB or Plywood for Truss Gussets?

[Capricious]

Some info on the importance of careful selection of the type of plywood used for gussets in roof trusses:

http://www.csbe-scgab.ca/docs/journal/28/28_2_167_ocr.pdf

Not all plywood is equal. In these particular tests, the failures in gussets made from the "good" plywood where with the nails.

And, if someone wants to go that far, in these tests steel gussets performed much better than plywood.




Also, corrosion issues with metal gusset plates in some farm structures:

http://www.omafra.gov.on.ca/english/engineer/facts/10-071.pdf

 

[timster2]

What about the "wax" coating on the OSB wouldn't that interfere with the glue? I'm sure the engineered lumber takes that into consideration.

 

[MH8675309]

Plywood - its been tried and tested for years in this application. OSB engineered joists are supposed to be better than 2x10 lumber also. True the floors dont bounce much with these but it will be interesting to see how they hold up after 80 years. I wont live to see it but I bet these new houses wont last like the old ones did

 

[orezok]

The "two other engineered" pieces are actually where most of the strength lies. As with any beam or I beam, the two biggest things that effect strength is 1. Extreme most fibers. In this case the dimensional lumber on top an bottom. And 2. How far apart they are from each other. The web offers very little in strength. You could double the web thickness and get very little increase in strength. But double the flanges and the difference is huge.

Cause under load, the bottom is trying to tear apart and the top is trying to compress. The webbing does little.

Do you have any engineering data to back up that statement?

 

[ray66v]

One of the problems with this is, plywood is mostly really poor quality anymore.

I am still going to go with my gut, look for some quality plywood, and use it over OSB, no matter what data anyone produces.

I too know of many places where it was used, and is working just fine, as gussets, and flitch plates.

 

[Capricious]

I see you are in Ohio. There are a couple of Menards in Ohio. They do not stock Fir marine but they can order it. Even with the xtra charges it is still a decent price. I have bought fir marine through them.

Fir marine today is about the same quality as fir exterior used to be, and fir exterior is about junk anymore. BC southern pine is not much better, and is heavier.

Voids are an issue with all of it anymore. I love that "peanut butter" the mills use to "repair" defects.

 

[Egon]

The "two other engineered" pieces are actually where most of the strength lies. As with any beam or I beam, the two biggest things that effect strength is 1. Extreme most fibers. In this case the dimensional lumber on top an bottom. And 2. How far apart they are from each other. The web offers very little in strength. You could double the web thickness and get very little increase in strength. But double the flanges and the difference is huge.

Cause under load, the bottom is trying to tear apart and the top is trying to compress. The webbing does little.

Moment or shear predominate?

 

[s219]

I recently explored this topic while building the roof trusses for my boat house. I had planned on using pressure-treated plywood, and bought a couple sheets. About 50% through the first sheet and a heap of sawdust later, I noticed so many voids in the cut gussets that I gave up on the plywood, as I knew I couldn't trust it for this use (I never would have slept through the night).

So if you do use plywood, make sure it is a high grade that does not have internal voids (I forget the nomenclature, but there is a rating system for plywood that covers stuff like this -- most of the CDX grade plywoods used in construction will have voids).

I'd have no problem using OSB for gussets if they were out of the weather. It is stronger than plywood for applications like this. Glue is important, as well as the nails.

By the way, after I punted on plywood I switched to using 12 gauge triple-galvanized nailer plates and 1-1/4" galvanized joist hanger nails. Did that on a previous shed about 15 years ago, and it worked well then, so I knew I could trust it here. The plates cost about $2 each, and a box of nails was about $16. Put a plate on each side of the joint, with nail holes staggered. Here's a pic that shows the result:

 

[PILOON]

Manufactured I joists are virtually all made with OSB as OSB has almost twice the shear value of plywood. If its good enough for manufactured joists which are tested and approved, then it will be good enough for your open web trusses.

View attachment 392769

I'll add a 'BUT'
Joists are supporting a floor while a truss is in the attic where water often leaks in and you have temperature swings.
Little if any OSB is waterproof. Ever see OSB when left out in weather? 1/2" is soon 3/4" (and de laminated)

 

[LD1]

Do you have any engineering data to back up that statement?

Which particular statement? Or better, what part of what I said do you not understand?

Moment or shear predominate?

If you are talking about my statement of most of the strenghtnlies in the extreme fibers (flanges in the case of an I beam or I joist), and since I am talking about bending and deflection, that would be moment.

Increasing or decreasing the the flange sizes or how far apart they are(beam depth), effects the moment far more.than the shear.