The attached graphic lists some of the clues the truss repair was properly designed.
Nice Randy, thanks
Great info Randy - thanks! So, are designed truss repairs generally done with plywood/OSB rather than the original metal barbed nailing plates?
Matt the barbed truss plates have to be mechanically pressed into the truss which is not possible in the field.
Hmmm… I’ve seen those field-applied. They sell them at Home Depot?
I have too still it’s wrong to use those,
They’re for non structural applications.
The truss plate look a like sold at the box stores are not designed for truss repair. Actual roof truss members can have from a few hundred pounds of tension or compression to several thousand pounds. According to the Truss Plate Institute even a gap between the truss and the truss plate the thickness of a credit card is considered unacceptable.
Randy, what is the thickness of that plywood/OSB repair. Just noticed it is not noted.
The ones I done in the past was always 3/4".
1/2” to 3/4”. Typically the weak link is the fasteners. That’s why I typically require structural glue in addition to the nails or screws.
Modify the graphic showing which members are in tension or compression. That repair and fastener placement is only good for tension in the broken web.
Randy, If that is a fink truss, I think both those chord members are in tension.
Correct me if I am wrong.
It was part of a more complicated truss I posted a few days ago that had the #3 lumber in the broken web. If you look at the plan sheet attached to this graphic you can see the truss configuration.
Got it, thanks.
Actually thy can be done in the field. I have seen this done by the local Truss Supplier. They will send a worker out with a portable pneumatic press that will squeeze the metal plates into place.
Then the repairs should just be done with that system.
I heard once that OSB is stronger than plywood as gussets due to all the glue, etc. This was years ago but I’m curious - is this still true or is it close enough that the same thickness is prescribed and assumed to be comparable? I’m personally not a fan of OSB compared to plywood for much of anything but am curious if I need to concede this one to OSB?
Once upon a time I heard that OSB had to be thicker than it’s plywood counterpart to have the same shear strength. But after reading this thread, I started surfing the interweb and found this (slightly older) article from University of Massachusetts
I also found this which had some interesting information.
Overall the general consensus is doesn’t matter if Plywood or OSB is used because they are very comparable. As @rmayo said,
I have seen subfloor material ( 23/32"OSB) used to repair trusses but #8 yellow zinc plated deck screws were used. They don’t have very good shear strength at all, especially compared to a 12d or 16d framing nail.
I have often wondered if OSB used for subfloors is suitable for this application or if OSB used for sheathing is better. I believe the manufacturing process is the same but haven’t found much on this… What say you @rmayo ? Other than thickness, is there a difference? Which is better?
Use any plywood or OSB as long as you stay within the published strength limits.
Randy Mayo, PE
President
Mobile: 573-201-8162
Email: rmayo@rlmengineers.com | Website: www.rlmengineers.com
The information transmitted by this email is intended only for the person or entity to which it is addressed. This email may contain proprietary, business-confidential and/or privileged material. If you are not the intended recipient of this message, be aware that any use, review, retransmission, distribution, reproduction or any action taken in reliance upon this message is strictly prohibited. If you received this in error, please contact the sender and delete the material from all computers.
