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I'm making a shelf that'll be 1 meter wide and 2.2 meters long. It's going to be simply supported by wire attached in four corners (with necessary 10 cm space from attachment point to the shelve's edge). I'm making it out of 18mm OSB board. Obviously I need to reinforce the board, otherwise it would sag too much on 2m span.

I want to keep the thickness of the shelf to the minimum. My idea is to sandwich the board between steel strips 40*4 mm. (Thus steel strips would act as universal beam's flanges, maximizing second moment of inertia constrained by overall width). The 4 strips will run along 2m edge through wire attachment points.

My questions are:

  1. Does it make any sense? Would it hold 50 kg total load with reasonable sag less than 1cm? (4mm thickness of the strips are taken from what's available on the market here. I'll not be bothered by the bulge that the strip will make on the surface of the board.)
  2. Should top strip be of the same width as the bottom one? Can I drop top strip altogether?
  3. What's the best way of attaching strips to the board? Screw both strips to the board/rivet top strip to the bottom through the board/ making threads in the strip for the bolt?
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  • I think a piece of "angle iron" or similar would be most effective here.
    – BrownRedHawk
    Mar 18, 2016 at 11:54
  • The perfect and thorough answer is given in Woodworking SE.
    – Gleb
    Mar 19, 2016 at 17:27

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This can be done with hardwood strips, but it's definitely better to go with steel. But No, the strips should not be on the top or bottom, those won't do anything...the shelf is already the universal beam's flanges, you need to add the universal beam's vertical support.

The single piece full length strips of steel should only be applied (glued & liberally screwed) to the front face edge & the backside face edge, use as thick a strip as you can or double & triple them up. You can also use Angle or L-shaped steel. Try to keep 50kg the maximum load, but you'll have to gauge if it can take more & how close to center heavy items are, lighter items in the center is the best configuration.

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  • Wiki: "A beam under bending sees high stresses along the axial fibers that are farthest from the neutral axis. To prevent failure, most of the material in the beam must be located in these regions. "
    – Gleb
    Mar 18, 2016 at 8:22
  • Sure, that would fortify against stretching, but it won't do anything to prevent stretching in the first place. If you feel the flat strips aren't doing what you want, then you can attach a couple or few Angles or L's to the under side of the shelf away from the edges to definitely handle 50kg & more. Being set back from the edge may make them unnoticeable. I was just trying to keep the shelf at shelf thickness & I don't think you'll need the L's beneath...go with thick bands of course, like even pencil thick, & not some thin strapping of just knife thickness.
    – Iggy
    Mar 18, 2016 at 13:08

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