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# Moment of inertia

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## Moment of inertia

(OP)
Posted this in the incorrect forum;

Good Afternoon,

I have been browsing the forum for a number of months and now I have decided to create an account, to further my knowledge and pass on what I currently understand.

I have a question which may be simple to someone but currently driving me up the wall.

It is about calculating section modulus's (moments of intertia) for a circular hollow section with a sector removed. From reading roarks forumulas for stress and strain I don't seem to be able to find a solution to my question.

I understand it is not as simple as calculating the moment of inertia of a circular hollow section and then subtracting the sector section.

Does anyone have an idea of how to calculate the moment of inertia of a circular hollow section with a sector removed?

Thanks to replies in advance

### RE: Moment of inertia

If you familiar with some CAD applications like AutoCAD, you will easy solve your problem with the _massprop function.

### RE: Moment of inertia

In general, it's the inertia of the solid section minus r squared x m where m is the mass of the sector and r is the distance from the centroid of the solid section to the centroid of the sector. Can you post a picture of the cross section?

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