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RE: Finding Moment of Inertia of Solids in AutoCAD

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You can try two things. The first would be to make solids and then use
subtract to make them hollow in autocad (you may have already done this).
The other is to make two objects, 1 is the region you have already made and
record the properties. Then make a region of the voids (or hollow portions)
and record the values. You should be able to get the moment of inertia by
subtracting the two mathematically.

Make sure your centroids of both regions are at 0,0,0 coordinates.

Let us know if it works.


-----Original Message-----
From: Gina Gobo [mailto:GoboGT(--nospam--at)]
Sent: Wednesday, December 05, 2001 7:41 PM
To: seaint(--nospam--at)
Subject: Finding Moment of Inertia of Solids in AutoCAD

Does anyone have any experience using AutoCAD to find the section properties
of solids? I understand how to use the "region" and "massprop" command to
find the moment of inertia of a section. However, these commands only take
the outline of an object. I think that you need to make an object a solid in
order to get the section properties of built-up sections with objects like
tubes. When I try to use region and mass prop for these types of sections,
AutoCAD takes the moment of inertia of the section as a solid and does not
take into account hollow sections. 

If anyone can help with this, I'd appreciate it. I cannot seem to figure it


Gina T. Gobo, EIT
Carter & Burgess, Inc
Facilities - Structural Engineering
Seattle, WA
Ph. 425-822-7096
Fax 425-822-7246

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