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RE: Finding Moment of Inertia of Solids in AutoCAD

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You can draw your object with plines (closed), and use the "region" command
to convert that object to an region, and you can use the massprop command to
get the information you need.  Keep in mind that the values you will get are
referenced based on the current position of the object, you need to move the
objects to where it's CG is at 0,0, to get some sensible results.
You can have more than one regions, i.e. draw as many closed pline objects
as you like, and use the region command to convert them, when the massprop
command prompt you to select objects, just pick all the objects, you need to
use the "subtract" command to create hollow shapes.
There is a VBA routine I made which I posted on the forums on the, which does all the things that's mentioned above
(subtract regions, moving to 0,0 coordinates, etc.), in a few mouse click,
try that if you like.

Yi Yang
Santa Rosa, CA

-----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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