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I've tried using various calculators but that has just confused me even more so I'll describe my scenario and hopefully I can get some answers. In the picture above, each item is described below

A: Timber Loft Joist, Width 3.5m, Height 225mm, Depth 45mm. Either end of each joist sits on top of a block wall 100mm thick and 2.5m in height. From this link https://www.engineeringtoolbox.com/floor-joist-capacity-d_1832.html, it says that these joists can support 3kN/m2.

B: OSB board, 18mm thick

C: Mild Steel plate, Width 400mm, Length 400mm, Depth ?mm

D: Load, 120x120mm, Weight 150kg

With my very limited engineering knowledge, I'm assuming that I need C to spread the 150kg load from D so that it doesn't punch a hole through B. If this is the correct approach, what would be an adequate thickness for C to accomplish this. Any thoughts or suggestions would be greatly appreciated as it'll help me with knowing the viability of my project.

chillydk147
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1 Answers1

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This can be handled like a beam resting on two pin supports, with good approximation. A plate can support a bit more than a beam. I suppose that the OSB alone, along the major axis, would be strong enough to support this load but just to be on the safe side.

let's pick a 4mm thick plate with:

  • M = moment kg.mm
  • S = beam section modulus =$bh^2/6$
  • h = plate thickness, 4mm

$$ M=Pl/4=150kg∗400mm/4=15000kgmm$$ $$\sigma= M/S=15000/ \frac{bh^2}{6}=15000/ (\frac{400*4^2}{6})=15000/1066=14.06kg/mm^2<25kg/mm^2 \text{ allow stress of mild steel}$$

So the safety factor is $ 1.75 >1.6 \ $and is okay.

In my comment, I had recommended SF of 2.8 but with your adding more info 1.6 is okay.

The blocking under the plate between joists is for joists' lateral support and is required by most codes.

kamran
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