Moment of Inertia for an "L" shape 2

[workhorse]

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?

 

[dicksewerrat]

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

 

[workhorse]

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.

 

[IFRs]

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.

 

[lutein]

Check out

http://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.

 

[DaveVikingPE]

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.

 

[kags]

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.

 

[edbell]

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

 

[workhorse]

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?

 

[workhorse]

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.

 

[DaveVikingPE]

Check out this web site:

http://www.efunda.com/math/areas/RectangularLBeam.cfm

Why are you making this easy probelm so hard for yourself?

 

[workhorse]

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