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I need to find the moment of inertia for an odd-shaped "beam." I am using the AMINERTIA command in Autocad Mechanical, but it seems to only calculate moments of inertia about the principal axes. Can it calculate the moment of inertia in any direction? The Autocad help file implies that it can, but I don't see the "effective" moment of inertia in the load direction after I run the command. See the bold section below. Anyone use the AMINERTIA command like I am trying to that can point out what I am missing?

When you start the AMINERTIA command, you are prompted to select a cross section. The cross section you select must be a closed contour. AutoCAD Mechanical fills the area, and you are asked if the filled area is the area you want to be analyzed.

In the next step, the program draws the principal axes, 1 and 2, for the moment of inertia and performs the moment of inertia calculation. The following results are displayed:

X and Y coordinates of the center of gravity of the cross section.
Moment of inertia (I1 and I2) along the 1 and 2 axes.
Angle between the horizontal line and the 1 axis, for which I1 is always the greater moment of inertia.
In the final stage of the calculation, you specify the direction of the load forces. The direction of the load forces influences the result of the effective moment of inertia. Make also sure that the load forces you specify must be acting in the same plane. The following values are displayed.

Effective moment of inertia that corresponds to the load direction you selected.
Angle of deflection.
Maximum distance from the neutral line to the border of the extension side.
Minimum distance from the neutral line to the border of the compression side.
The moment of inertia block, which is a table containing the results of the moment of inertia calculation, is displayed and can be inserted anywhere in the drawing.


Aha! The effective moment of inertia for a given direction is calculated in the text window but isn't displayed in the output chart. I overlooked it a few times. Thanks anyway.

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