Center web reinforcing of 21' TJI span
Center web reinforcing of 21' TJI span
(OP)
I have floor that is designed to 1/460 with TJI 360 engineered joist 11-7/8" tall with a 21 foot span, 16" o.c.. I want to increase stiffness to 1/720. I had planned to add reinforcing web sections using 1/2" OSB in the center of each span, but just 8 ft. long, the OSB would be structurally glued and nailed or screwed to the top and bottom flanges of the TJI joist, I was also doing to solid block with 2 x 12s between joist at each end of the web stiffeners. The stiffeners would a 11 7/8' tall by 96" piece of OSB.
However I need to prove this reinforcing is adequate and have not been able to find and formulas for bending or deflection where just the center section of a span is stiffened, not even related to steel beams. Does anyone know where to find these formulas?
However I need to prove this reinforcing is adequate and have not been able to find and formulas for bending or deflection where just the center section of a span is stiffened, not even related to steel beams. Does anyone know where to find these formulas?






RE: Center web reinforcing of 21' TJI span
Might just be better to just space the joists closer together, or double them up to achieve the higher stiffness...
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Center web reinforcing of 21' TJI span
RE: Center web reinforcing of 21' TJI span
RE: Center web reinforcing of 21' TJI span
And, the manufacturer says there's no problem, so who needs formulas, they just get in the way, and the one's we might give you would just lie to you. At least, they probably wouldn't give you Δ = 1/32" for those TJI's on 21' spans at 16" o/c. I used to pay for .0001" tolerances from machine shops and if you are confident enough to do that with TJI deflections, go for it.
RE: Center web reinforcing of 21' TJI span
RE: Center web reinforcing of 21' TJI span
I did this on a plain old 2x10 floor system. Two weeks after the install they rolled in a 700 lb refrigerator - no problam.
RE: Center web reinforcing of 21' TJI span
I am also curious to find the formulas that work with partially center stiffened beams. I have been on-line and through numerous structural text books and can't find anything for this particular case which I know is done all the time with wood and steel.
RE: Center web reinforcing of 21' TJI span
RE: Center web reinforcing of 21' TJI span
RE: Center web reinforcing of 21' TJI span
BA
RE: Center web reinforcing of 21' TJI span
RE: Center web reinforcing of 21' TJI span
L/720 is about .35'' If you are 16'' oc then just put about 67 (.133 x 50 psf) lbs per foot over the joist and measure it. Or a center load of about 700 lbs - gives same moment. Bricks work nicely.
If have access to RISA or other - you could model a beam with three different pieces and two different Inertias but fixed at their connections.
RE: Center web reinforcing of 21' TJI span
BA
RE: Center web reinforcing of 21' TJI span
Δ = (w/384)*[(L-b)4 + 4(L-b)2(L2 - b2) + (8/k)*b3(L-b/3) + (12/k)*(L2 - b2)b(L-b/2)]
BA
RE: Center web reinforcing of 21' TJI span
If this reinforcement is for tiling, then I would consider using a product like Ditra also.
Unless you are adding loads above, I cannot follow the logic behind this excercise.
Brad
RE: Center web reinforcing of 21' TJI span
RE: Center web reinforcing of 21' TJI span
BA
RE: Center web reinforcing of 21' TJI span
Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.