Bearing Strength of Plywood - 2 4

I'd be worried about the load in the broken member, and how it gets into your repair. At a minimum, I'd join the repair to the lower chord.

another day in paradise, or is paradise one day closer ?

AAH!!! But for the brilliance of contractors... Classic "Let Mikey fix it" syndrome.

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)

I'd chase down some values specifically for plywood edge compression rather than the dowel values: Link

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.

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.

Would it make sense to keep the plywood tight to the top chord? maybe use some liquid nail to help keep splitting to a minimum and extra capacity

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!

Eric... excellent and many perspectives / considerations.

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!

BSVBD:
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.

KootK:
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.

Ha! I'm pretty prolific round these parts. One of the costs of that is lax quality control.

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.

miscellaneous thoughts:

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.

could be wrong, but, the more i look at your original detail, and even your second detail, the more i think you may be looking at this more as a beam and not so much as a truss, as all the detail seems to address is bearing and none of the truss action. suggest you run calc for original truss web/chord forces and new split-truss web forces, compare and proceed accordingly. your panel points, especially the one above your vertical bearing blocks, and also the 1st bottom chords panel points each side of steel beams, i suspect will need some reinforcement.

I'm with Triangled on this one... I think you need to be very careful about what effect "fixing" this truss has. Any chance you can introduce 40mm holes in the steel beam and pass something like a Simpson Strong Tie CS18 through to restore the bottom chord tension member behaviour of the truss? This would be instead of a more complicated repair, and with the intent of making this floor truss "blind" to the new beam. Not really a fit at all if deflection is an issue.

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.

Triangled and CEL... I'm going to investigate the Simpson CS16 with 10d x 1.5.

I think this will work!

Great idea!

Thank you!

I spent 4 years working for a truss manufacturing company. Easiest thing for all involved is to call the truss design company. They then take all the liability!

Please remember: we're not all guys!