Computing Section Properties from AutoCAD 5

[andrew705]

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,

 

[JStephen]

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..

 

[ToadJones]

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!

 

[andrew705]

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

you guys are just the best. thanks much!!

 

[andrew705]

yep, works.

thanks again, guys.

 

[bradleyelwood]

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"

 

[dozer]

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.

 

[VAStrEngr]

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.

 

[bradleyelwood]

dozer,

thanks for the info.

 

[andrew705]

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?

 

[fancypants]

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.