Bearing Strength of Plywood - 2
Bearing Strength of Plywood - 2
(OP)

The contractor removed a portion of the bottom chord of the floor truss in order to install the steel beam. (This W12x26 supports another steel beam which is neither shown, nor applicable to this detail and the problem at hand.)
NDS Table 11.3.2B provides Dowel Bearing Strength of Plywood.
Can i use that same bearing strength as in compression parallel to have the vertical plywood member bearing on a wood bearing plate, similar to the physical load path of a TJI? Please see detail above.
Any other suggestions?
Thank you!






RE: Bearing Strength of Plywood - 2
another day in paradise, or is paradise one day closer ?
RE: Bearing Strength of Plywood - 2
If possible, I would go to the truss manufacturer for a fix recommendation.
Why should you take the liability for such a stupid, stupid circumstance?
Mike McCann, PE, SE (WA)
RE: Bearing Strength of Plywood - 2
Is the intent of the repair to:
1) Split the truss in two and just provide bearing or;
2) Create some negative glexural capacity over the beam?
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Bearing Strength of Plywood - 2
rb... How would you recommend extending / joining the repair into the bottom chord. The contractor would have a difficult time installing continuous notched plywood stiffeners that would extend to the bottom chord. The way I'm seeing this, is, since the bottom chord is cut, with me now adding the (2) bearing struts, i am creating (2) separate, NOW, half-the-original-span, trusses.
msquared... thank you for editing and elaborating. All things considered (too much to explain in this thread), that is not an option. But, thank you!
Koot... THANK YOU for the "TECH-TIP" edge compression values. That is exactly what i was looking for. Apparently i don't have to chase anything down since you've already done that for me.
Koot... The contractor ALREADY split the truss in two. Therefore, the above detail is my current thought.
RE: Bearing Strength of Plywood - 2
Are you relying on 28 nails for 100% of your truss end reaction? i would look at those webs and not think it would work as an even load distribution, it seems like you will be dumping all the load from the inner most web... but i am not certain. Also, is the field condition really this symmetrical where the beam is centered on a panel point?
It seems like the plywood is acting as a cantilever of sorts, this means the unsupported edge is in compression and i would be concerned about it buckling. Maybe add blocking inbetween webs at panel edges (T&B), this will also help the webs from trying to pull apart and will keep the plywood square.
PS. This is a pretty nasty detail to have to work out, don't be afraid to make it hurt the contractor some in terms of construction... and remind them, this is why you don't cut trusses!
RE: Bearing Strength of Plywood - 2
I am not done with this detail / repair.
Yes - plywood to top chord. Yes - liquid nails or construction adhesive where necessary.
I am still awaiting more photos to confirm panel point to beam centerline location.
Thank you all for your valued input.
Any other suggestions are certainly still welcome!
RE: Bearing Strength of Plywood - 2
I’d extend the lengths of the plywd. to include the third diags. on each side of the stl. beam. They could be cut to match the diag. slope, but extend beyond the diag. a little bit, or no need to do this just to make saw dust.
I’d extend the top of the plywd. up to within 1/8" of the subfl.
I’d extend the bot. of the plywd. down to match the bot. of the bot. chord, by moving an inch away from the 2x6 bearing pl., on that bearing plane, and then following the diag. slope down to the bot. of the bot. chord.
I’d stager the nails in two lines .5" apart, to minimize splitting the 2x4's.
I’d use glue at all the faying surfaces btwn. plywd. and 2x’s or 4x’s.
Note that the 2x4 bearing struts will be pretty tough to fit properly at the top. You will be fighting nailer plate teeth, uncertain diag. slopes, and any load/movement will tend to spread the two diags. at that joint, not a good condition. Change that to a 4x4 and stop short of the top slope cut, and then use 3 or 4 lines of staggered nails and glue.
RE: Bearing Strength of Plywood - 2
We all know that you “like to debate structural engineering theory -- a lot.” and you are very good at it, but is there really a need for a whole new engineering language or structural terminology? I would assume that you are referring to a ‘negative glexural’ toof beam or maybe still a toof ache. Move your damn keyboard over to the right about .75", w.r.t. where you are positioned , the r & f are just that far left of the t & g on many keyboards.
RE: Bearing Strength of Plywood - 2
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Bearing Strength of Plywood - 2
check your new configuration web forces. "with me now adding the (2) bearing struts, i am creating (2) separate, NOW, half-the-original-span, trusses." If you are located midspan, the first webs left and right of the steel beam are likely carrying quite a bit more load than originally. You mention TJI, but I suspect they are MPC trusses because of the nailing pattern you indicate. If so, the minimum web size may save you, but for sure check the metal plate panel point connections, especially the first bottom chord each side of steel beam, and reinforce as necessary.
if new steel beam is not intended to actually support existing truss, perhaps could poke hole in steel web and penetrate with something to restore continuity of wood truss bottom chord?
if going with creating bearing at steel beam, vertical bearing blocks much better than relying on plywood. If MPC truss, consider using something like 2x8s (or whatever) vertical each side on outside face of truss, to avoid removing and replacing existing metal plate connection.
RE: Bearing Strength of Plywood - 2
RE: Bearing Strength of Plywood - 2
Introducing a new support point for a truss is non-trivial. When I have done similar work in the past, I have used plywood to box out the section and then another layer of plywood overlapping and fastened to the infill plywood AND the top and bottom chord. Then I slept well. I think the big thing people forget is just how low the shear capacity of these timber floor joists tends to be... Many products have plywood webs at the ends and require supplemental plywood boxing for the support of point loads.
RE: Bearing Strength of Plywood - 2
I think this will work!
Great idea!
Thank you!
RE: Bearing Strength of Plywood - 2
Please remember: we're not all guys!