×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Moment of Inertia AutoCAD 2008

Moment of Inertia AutoCAD 2008

Moment of Inertia AutoCAD 2008

(OP)
Hello
I am a newbe and I am have trouble getting correct moment of inertia values using AutoCAD 2008 (2D).  I have done this several times on older AutoCAD versions with no problem.  In 2008 once I create a region and then select mass properties I get both I and J values.  However that are not relative to both x and y axis (1.0000, 0.0000) and (0.0000, 1.0000).  I get values with non horrizontl and vertical axis ie ( 0.9848 0.1739) and (-0.1739 0.9848).  Can someone tell me what I am doing wrong or tell me how to correct my problem?
Thanks
Keystone1

RE: Moment of Inertia AutoCAD 2008

It looks as if you are trying the area properties on a non symmetrical region. Place first your region on a well definite point and get the center of gravity of the section, then translate the shape through its center of gravity to lay at 0,0. Perform again the area properties and see that effecrively you have placed cog at 0,0. Then, if your shape is symmetrical will show principal axes along x and y axes, and not otherwise. Can this be the cause?

RE: Moment of Inertia AutoCAD 2008

The principal axes of a non symmetrical  section are likely to be at an angle to the coordinate system's axes.

If you wish to transform them to MoI about the coordinate systemn axes you need to use Mohr's circle.

Cheers

Greg Locock

SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.

RE: Moment of Inertia AutoCAD 2008

(OP)
OK Thanks I appreciate all the help.
Keystone1

RE: Moment of Inertia AutoCAD 2008

draw a line from the neutral axis to the points that autocad specified ( 0.9848 0.1739).  This is a major or minor axis.  Now rotate the section to align major/minor to x axis.  Perform mass properties again.

RE: Moment of Inertia AutoCAD 2008

(OP)
Thanks Kwan
Is it possible for you to demo that on the attachment to post above?
Thanks
Keystone1

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources