I am trying to calculate how much safety margin I have with a piece of
tempered glass that is supporting a load. But it's been about 40 years
since I've needed to do any structural mechanics so I'm hoping I can get
a reality check in case I am applying the wrong principles.

A 14 inch by 14 inch piece of 0.39 inch thick tempered glass supported
on two sides with 12 inches between the supports. A 1000 pound load is
centered on top. Here is some ASCII art:

     LOAD
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
 ^          ^

The force on the glass is defined as f=3DM/S, the bending moment divided
by the section modulus.

The bending moment is 6 inches * 500 LB =3D 3000 in-lb.
The section modulus is 14 * .39^2 / 6 =3D 0.3549

So I calculate the force to be 8453 psi. Tempered glass is good for
24000 psi so I have almost a 3 to 1 margin of safety. That's not good
enough for use in a product but good enough for my occasional personal
use.

Does this all look good? I have tried it and the glass did not break :)

Thanks,

Bob

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