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Unread 07/27/2008, 06:13 AM   #2
AcroSteve
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I am getting close, but I still need some more info and help.

Quote:
It turns out that the equation for deflection of the piece of steel angle is the same as the equation for the 2x4. The difference is the numbers you use in the equation. Any of the various equations (they change by load and support situation as you mentioned) will have the terms E and I in them, the modulus of elasticity and moment of inertia, respectively.

You'll need to check, but I'll take 1.5 MMpsi for the E of your fir and 29 MMpsi for the E of the steel. The I of a 2x4 laid on its side is 1.56 while the I of a 2.5 x 2.5 x 0.25 angle with one leg vertical is 0.346. Since the equations I mentioned above are linear with respect to E and I, and deflection is inversely proportional to E and I, we can get a comparative factor for these shapes using only these two figures to get an idea of which one is better. The EI of the 2x4 (dropping insignificant 0's and units) is 1.5*1.56 = 2.34. The EI of the steel is 29*.346 = 10.0. Since these numbers would go on the bottom of the deflection equation, and the steel's number is bigger, that means the steel's deflection would be smaller, regardless of loading or support condition.
Where can I find the I(moment of inertia) values of different sizes of steel? My copy of Machinery's Handbook, only goes down to 2x2 angles.


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Last edited by AcroSteve; 07/27/2008 at 06:23 AM.
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