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Computing Section Properties from AutoCAD
5

Computing Section Properties from AutoCAD

Computing Section Properties from AutoCAD

(OP)
Hello All.

I am doing a structural review for a rooftop solar panel racking system, which is comprised of extruded aluminum rails. I have CAD drawings of the extrusion profiles, and need to figure out section properties (moment of inertia, section modulus, etc)so I can calculate the compression and moment resistance of the rails.

My boss tells me there may be an AutoCAD plugin that will be able to quickly figure this properties out, but I havent been able to find anything.

Does anyone have any advice? I would really appreciate it!

Thanks,

RE: Computing Section Properties from AutoCAD

If I remember right, you have to change the cross-section into a Region, move the centroid of it to 0,0, then you can calculate the region properties..

RE: Computing Section Properties from AutoCAD

2
make the area a "region" in CAD; do so by typing "region" and selecting the lines comprising the cross section (you may need to "explode" the lines first)
Once the shape is a "region", type MASSPROP and select the shape.
The section properties will pop up.
Move the the shape so the centroid is at 0,0,0.
type MASSPROP again.
Waa laa!

RE: Computing Section Properties from AutoCAD

(OP)
Haven't tried this yet, but it sounds pretty simple.

you guys are just the best. thanks much!!

RE: Computing Section Properties from AutoCAD

(OP)
yep, works.

thanks again, guys.

RE: Computing Section Properties from AutoCAD

andrew,

TJ had it right, but just a word of warning.  If you have a closed section like a square tube or pipe, create a "saw slit" in it to let the good carma in and out.  I do this with a couple of lines maye 0.001 inch apart, then "pedit" the perimeter making it a polyline then make it a region.

You can also find the MASSPROP by following "tools...inquiry...massprop"

RE: Computing Section Properties from AutoCAD

Forget "carma" (sic), make the outside perimeter a region and the inside perimeter a region, then subtract the inside from the outside.  No clunky "saw slit" required. I believe you used to have to do the "saw slit" thing with a lisp routine that calculated geometric properties.

RE: Computing Section Properties from AutoCAD

In similar situations, I have used RISA or RAM Advanse to create the sections and then view the section information.  Excel also works wonders if you set it up to just input a OD and ID and let them run the formulas to calculate it for multiple shapes.

 

RE: Computing Section Properties from AutoCAD

dozer,

thanks for the info.

RE: Computing Section Properties from AutoCAD

(OP)
thanks for the help so far guys.

last problem, any idea how to calculate the torsional properties? (such as Cw and J).

This might be a challenge. Any ideas?

RE: Computing Section Properties from AutoCAD

A go by would be the best. Look in the cold form steel manual and they have lots of good examples on calculating the torsional properties.

It makes my eyes bleed.

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