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RE: Autocad Section Property Calculation
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- Subject: RE: Autocad Section Property Calculation
- From: "Mike Valley" <mtv(--nospam--at)skilling.com>
- Date: Wed, 31 May 2000 10:26:29 -0700
You might want to be careful about using the principal moments. If the principal axes are not parallel to the X- and Y-axes, the moments about X and Y will be different from those about I and J. For many practical problems (L-shaped members for instance) the principal axes are rotated. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Michael Valley, P.E., S.E. E-mail: mtv(--nospam--at)skilling.com Skilling Ward Magnusson Barkshire Inc. Tel:(206)292-1200 1301 Fifth Ave, #3200, Seattle WA 98101-2699 Fax: -1201 -----Original Message----- From: Brent Koch [mailto:kochengr(--nospam--at)pacbell.net] Sent: Wednesday, May 31, 2000 8:46 AM To: seaint(--nospam--at)seaint.org Subject: RE: Autocad Section Property Calculation The results from executing the Acad MASSPROP command should give you the moments of inertia about the origin (wherever you choose to locate it) and ALSO the principal moments about the members centroid. For expample, here is the text screen for the MASSPROP command run on a 12x24 rectangle with the UCS origin set at the lower left corner of the shape ... Command: _massprop Select objects: 1 found Select objects: ---------------- REGIONS ---------------- Area: 288.00000 Perimeter: 72.00000 Bounding box: X: 0.00000 -- 12.00000 Y: 0.00000 -- 24.00000 Centroid: X: 6.00000 Y: 12.00000 Moments of inertia: X: 55296.00000 Y: 13824.00000 Product of inertia: XY: 20736.00000 Radii of gyration: X: 13.85641 Y: 6.92820 Principal moments and X-Y directions about centroid: I: 13824.00000 along [1.00000 0.00000] J: 3456.00000 along [0.00000 1.00000] Here it is again with the UCS origin set at the center of the rectangle.... Command: _massprop Select objects: 1 found Select objects: ---------------- REGIONS ---------------- Area: 288.00000 Perimeter: 72.00000 Bounding box: X: -6.00000 -- 6.00000 Y: -12.00000 -- 12.00000 Centroid: X: 0.00000 Y: 0.00000 Moments of inertia: X: 13824.00000 Y: 3456.00000 Product of inertia: XY: 0.00000 Radii of gyration: X: 6.92820 Y: 3.46410 Principal moments and X-Y directions about centroid: I: 3456.00000 along [0.00000 -1.00000] J: 13824.00000 along [1.00000 0.00000] As you can see, the first set of results lists the centroid at (6,12) from the lower left hand corner origin. Right where we expect it. The second set of results lists the centroid at (0,0) from the center of the rectangle. As expected, for the second case, the calculated monents of inertia and the principal momoents of inertia are one and the same since we located our coordinated system origin at the centroid of the section. Hope this helped. Brent R. Koch, P.E. Koch Engineering, Inc. Livermore, CA mailto:kochengr(--nospam--at)pacbell.net
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- RE: Autocad Section Property Calculation
- From: Brent Koch
- RE: Autocad Section Property Calculation
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