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# Moment of Inertia for an "L" shape2

## Moment of Inertia for an "L" shape

(OP)
Hello,
Does anyone out there know if there's an equation to find the moment of inertia for an "L" shape without having to do the moment area method?
Replies continue below

### RE: Moment of Inertia for an "L" shape

Sure. Get the Steel book and just page through. Or go to Enercalc website and do it on the free software

### RE: Moment of Inertia for an "L" shape

(OP)

Dicsewerrat,
No.  The steel book does not specifically show you how to find Ix and Iy.  I need to know if someone knows of a specific reference that would show me how to write and equation.

### RE: Moment of Inertia for an "L" shape

If you have access to AutoCAD, you can draw the shape and then get its properties.  If you want, I can do it for you.

### RE: Moment of Inertia for an "L" shape

Check out www.engineerstoolbox.com
it has a module that could calculate shape properties.
Or you could check out some mechanics of solid books.

Hope this helps.

### RE: Moment of Inertia for an "L" shape

I'm looking right at the 9th Ed. ASD manual and on page 6-23 there's an "L" shape with formulas for Ix and Iy. The 3rd Ed. LRFD manual has the same formulas on page 17-38.

Now if it's an angle and not an "L", you'll have to break it up into a bunch of paraboloids and trapazoids. I near-mastered this (OK, they're really thin lines sections) when teaching myself light gauge steel design (yow! That is a pain!)

You may want to look at Blodgett's book "Design of Weldments" for more insight into this problem.

Anyway, the parallel-axis theorem is easy and kind of fun, too. Taking moments of areas is really easy, especially if they're two rectangles. I normally refer to the "moment area" method as a tool for computering beam deflections.

### RE: Moment of Inertia for an "L" shape

For L shaped sections, check the properties in the u-u axis and v-v axis also. These are very critical than the Ixx and
Iyy.

### RE: Moment of Inertia for an "L" shape

I made an Excell spread sheet of the Transfer Formula that I will gladly give to you.  Just email me at eabell@eabdesign.com.
Ed

### RE: Moment of Inertia for an "L" shape

(OP)
Daveviking,
Thank you for your respond.  I don't think you can use the parallel axis theorem to calculate Ix and Iy for an "L" shape.  There's no symmetry for an "L".  Am I correct?

### RE: Moment of Inertia for an "L" shape

(OP)
Kags,
How do you go about getting the uu and vv axis?  I am trying to get the Ix and Iy for the critical buckling of a built-up "L" shape wood column.

### RE: Moment of Inertia for an "L" shape

(OP)
DAVEVIKING,
Are you some kind of a super raging genius?  Thank you very much.  That is what I am looking for.

Also, thank you to the following people for their responds:
Dicksewerrat, IFRs, Lutein, and kags.

A special thank you to Edbell for his awesome spread sheet.

It's great to have fellow engineers help each other.

Sincerely,
workhorse

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