How thick should this steel plate be?
January 19, 2006 9:06 AM Subscribe
How thick would a carbon steel plate have to be to roughly approximate the bending & deflection characteristics of 5/8" to 3/4" plywood?
I'm looking to pick up a sheet of carbon steel for the top of a fireplace surround, and I need to know roughly how thick to get. I can't use combustable materials under the sheet, so it has to span 16" or so and be reasonably strong. I know from experience that 5/8" or 3/4" plywood would be reasonable if using wood, but I have no idea about steel. I've purchased sheet steel before, but any suggestions about where to buy or where to get it cut to fit would be appreciated as well.
I'm looking to pick up a sheet of carbon steel for the top of a fireplace surround, and I need to know roughly how thick to get. I can't use combustable materials under the sheet, so it has to span 16" or so and be reasonably strong. I know from experience that 5/8" or 3/4" plywood would be reasonable if using wood, but I have no idea about steel. I've purchased sheet steel before, but any suggestions about where to buy or where to get it cut to fit would be appreciated as well.
Best answer: Beam deflection is proportional to 1/EI, where E is the elastic modulus of the material and I is the moment of inertia. So if we want the deflection to be the same, set EwIw = EsIs.
I is proportional to the cube of the thickness of the beam, so now
EwTw3 = EsTs3
Now plug in values and solve. The elastic modulus of wood is about 10GPa; for steel about 200 GPa. The thickness of the wood is 5/8".
10*(5/8)3 = 200*Ts3
Thus Ts is about 1/4".
Here's a handy beam deflection calculator, but I haven't check my answer yet.
You can probably get 1/4" steel from Home Depot or whatever. We used to get big 4 by 6 foot sheets from a welding company though.
posted by mbd1mbd1 at 9:35 AM on January 19, 2006
I is proportional to the cube of the thickness of the beam, so now
EwTw3 = EsTs3
Now plug in values and solve. The elastic modulus of wood is about 10GPa; for steel about 200 GPa. The thickness of the wood is 5/8".
10*(5/8)3 = 200*Ts3
Thus Ts is about 1/4".
Here's a handy beam deflection calculator, but I haven't check my answer yet.
You can probably get 1/4" steel from Home Depot or whatever. We used to get big 4 by 6 foot sheets from a welding company though.
posted by mbd1mbd1 at 9:35 AM on January 19, 2006
That efunda link to the calculator is now asking me for a login. It didn't do that the first time I loaded it. Maybe you get one free shot at it.
posted by mbd1mbd1 at 9:40 AM on January 19, 2006
posted by mbd1mbd1 at 9:40 AM on January 19, 2006
Any deflection is based on length. What length between supports are you talking about? I also assume you are desiring basically no deflection unless you manage to park a car on top of it.
posted by JJ86 at 9:58 AM on January 19, 2006
posted by JJ86 at 9:58 AM on January 19, 2006
Home Depot is not going to have steel plate. Use pombe's link, or go to your local welding shop.
posted by Kirth Gerson at 10:20 AM on January 19, 2006
posted by Kirth Gerson at 10:20 AM on January 19, 2006
This thread is closed to new comments.
I'm not sure how to figure out how thick it will need to be. Is it going to bear any load?
posted by pombe at 9:18 AM on January 19, 2006