Moment of Inertia

Have just installed the “Face Centroid and Area Properties” extension. Which property output variable is the area moment of inertia? Is it Ix, Iy, or Ixy? I think it is Ix, but would feel better with some confirmation of this.

I’m not familiar with that extension, but the answer is probably all 3. It depends on which axis you calculate it on so it could be the moment of inertia about the x-axis is Ix, the y-axis is Iy and maybe (?) the z-axis is Ixy (guessing).

This should help:
Same applies to the Y axis for Iy

Note that you can copy the plugin results to clipboard and paste them (say as screen text) to your screen in SketchUp. To better study the shapes. See attached image with both text blocks.
Left for pink, right for pink+blue.

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Thanks for your response. I drew an I Beam, 3 1/4” wide (x axis), by 6 1/4” tall (y axis).
Load comes down along the y axis, and passes through the x axis.
When I use the highest of the three moments, which is Ix, then I get a reasonable deflection under load answer in a separate calculation.
Does this explanation of the shape and how it’s drawn, enable you to confirm that I’m using the proper moment for the application.


According to the beam orientation you gave, this is what the plugin tells you: see screen text and the cross section on Z=0.
The rest is what a load along Y would do as to bending the beam.

Great drawing showing even the deflection occurring through the x axis. Thanks for the confirmation that I was picking the proper Ix moment.

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