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Old 07/26/2008, 05:32 AM   #1
AcroSteve
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Deflection Calculator

I am looking for a way to calculate the deflection of different size pieces of angle iron.

Anybody have a link to a website where I can plug in some values, or maybe just the formulas.

I am looking at 72" of angle iron, either 1-1/2x1-1/2x3/16 or 2x2x1/8

Thanks


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Old 07/27/2008, 06:13 AM   #2
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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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Old 07/27/2008, 06:38 AM   #3
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That would have been my advice (look in machinery's handbook).

I will see what I can dig up steve.


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Old 07/27/2008, 06:41 AM   #4
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I may have that, but I'll have to dig the book out- Give me a few hours


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Old 07/27/2008, 01:39 PM   #5
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2x2x1/8 has an I of 0.189 in^4. Not sure if you can read it in the picture but 2x2x1/8 is the last line. This is from the Manual of Steel Construction by the American Institute of Steel Construction




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Old 07/27/2008, 01:53 PM   #6
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you guys make my brain hurt lol


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Old 07/27/2008, 02:54 PM   #7
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I also found this, it's the general equation for moment of inertia for angle iron



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Old 07/27/2008, 03:10 PM   #8
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I've used these tools.

I suspect you need to use uniform loading.

http://www.engineersedge.com/beam_be...m_bending1.htm


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Old 07/27/2008, 08:19 PM   #9
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But you still need the moment of Inertia for the material that you wish to model


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Old 07/28/2008, 04:11 AM   #10
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Correct!

The chart posted is the same one I have. It has data for one of the two sizes I want to compare. But not the 1-1/2x1-1/2x3/16.


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Old 07/28/2008, 04:54 AM   #11
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If you have something smaller than a L2x2x?. Then you'll have to use the equations posted above. You'll want to use the equation for Ix.

Given that...an angle isn't the best thing to use for a beam, and 72" is pretty dang far for a 1 1/2" angle.


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Old 07/28/2008, 10:05 AM   #12
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I am constructing a plywood tank that will have two sides glass. I am going to have a angle iron eurobrace around the top.

I am only slightly worried about the deflection because the glass will be 5/8 or 3/4. It is mainly to re-enforce the corner.


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Last edited by AcroSteve; 07/28/2008 at 10:20 AM.
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Old 07/28/2008, 11:29 AM   #13
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If that's the case, you can easliy calculate the Ix from the equations above (or Iy, since it should be the same for an equal leg angle) and use (5wl^4)/(384EI) as your deflection calc. The force on the top will be minimal because you have a triangular load on the glass. Should be fine.


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Old 07/28/2008, 07:01 PM   #14
AcroSteve
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You might need to dumb it down a little fore me.
What are the w and l?

I still don't have the I for the 1-1/2 angle.


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Old 07/28/2008, 09:34 PM   #15
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w is the loading on the piece that you want to calculate the deflection for (lbs/ft), l is the length of the piece you want to calculate the deflection for. you would need to calculate I for the 1-1/2 angle (it looks like it is 0.111, if I did my math right) or you could use the 2x2 angle since you know the value of I for that one.


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Old 07/29/2008, 04:46 AM   #16
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as said above, "w" is in pounds per inch, "l" is the length of the member in inches, E is the modulus of elasticity (29 x 10^6 for steel) and I is the moment of inertia which is calculated above (as I said before, use the equation for Ix). Make sure the calculation for Ix the units come out as inches^4.


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Old 07/29/2008, 05:09 PM   #17
AcroSteve
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So...

W=10 10 bs/inch along the length of the angle.
I=72 Length of angle
E=29,000,000
I=.190 Ix

And the equation (5wl^4)/(384EI)
(5*10*72^4)/(384*29,000,000*.190) would result in .635 inches of deflection.

Now, I need the vales for the 1-1/2 angle, as I can't see how to derive x or y for the center of gravity.


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