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Combined floor joist and decking

Combined floor joist and decking

Combined floor joist and decking

Has anyone used the combined section of a plywood or osb decking to the floor joist to limit deflection and increase the bending strength? If so what type of glue is recommended for this. Is this good practice?

RE: Combined floor joist and decking

I know the Ijoist manufacturers use to use this all the time for stiffness....I don't think they did for strength.....
I think you could search some of their literature, or ask their sales guy what kind of adhesive they base their calcs on.
Regarding advisability, I suppose adding adhesive could only help improve quality, but degree of improvement would be contingent upon the degree of care exercised by carpenters in the field.

RE: Combined floor joist and decking

In theory, I think combined or "T" shape condition should be slightly better than without BUT >>> I seem recall that early on in the I joist business, they were indication that there was some sort of time limit on the effectiveness of the "glued and screwed" assembly. It might have been 10 years or something like that. Either way, I would think that creep might be a factor and DL vs LL deflection considerations might be a par to fit.
I'd be wondering about the elasticity of the glue.
APA might have some guidance on it. Seems like a stretch to try to rely on it long term.
I'd be curious what you find in APA or other "code approval related" search.

RE: Combined floor joist and decking

The long term elasticity, creep, shear strength, bond strength vs. environmental degradation (turning brittle and crumbling) have always been the issue with the use of glue in these design problems. There isn’t any doubt that the shear flow at that joint, which makes that a sound “T” section, is better handled by a good quality glue (in lbs./sq.in., of joint area), as apposed to the concentrated reaction of a nail or screw every 4 or 6", and its splitting, wood bearing, nail bending tendencies. The code authorities are not inclined to allow it if we can’t find a glue manuf’er. who will guarantee the life and long term strength of their glue. Then, there is also the issue of quality application, in all weather conditions. There isn’t any doubt, any longer, that a glued-n-screwed deck works better than just nailing the deck down. You might at least be tempted to design a little closer to the upper limit if you spec. a glue joint, and the glue to be used. Then go out and instruct and initially inspect for proper application. The reason GluLams work is because of the glue they use and good QC, and proven history of performance.

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