Section Modulus

If I establish a cross section shape for a structural beam, how can I use Rhino to give me a section modulus?

This is what I get from the ‘area moments’ command;

Area = 2.14778953 (+/- 1e-09) square feet
Area Centroid = 48.7607237,-0.116125533,4.10834046 (+/- 1e-08,1e-10,5.5e-09)
Area Moments:
First Moments
x: 104.727772 (+/- 1e-07)
y: -0.249413205 (+/- 1e-10)
z: 8.82385063 (+/- 1.2e-08)
Second Moments
xx: 5107.30953 (+/- 1e-06)
yy: 0.0289632414 (+/- 1e-11)
zz: 37.0935158 (+/- 1.4e-07)
Product Moments
xy: -12.1615684 (+/- 1e-08)
yz: -1.02467436 (+/- 1.4e-09)
zx: 430.238757 (+/- 6.2e-07)
Area Moments of Inertia about World Coordinate Axes
Ix: 37.1224791 (+/- 1.4e-07)
Iy: 5144.40304 (+/- 1e-06)
Iz: 5107.33849 (+/- 1e-06)
Area Radii of Gyration about World Coordinate Axes
Rx: 4.15740778 (+/- 8.1e-09)
Ry: 48.940864 (+/- 1e-08)
Rz: 48.76424 (+/- 1e-08)
Area Moments of Inertia about Centroid Coordinate Axes
Ix: 0.842133304 (+/- 4.8e-08)
Iy: 1.54970531 (+/- 8.4e-08)
Iz: 0.707572002 (+/- 3.5e-08)
Area Principal Moments of Inertia about Centroid and Principal Axes
I1: 0.705052224 , Direction ( 0.990933965, 0 ,-0.13434983)
I2: 1.26764532e-34 , Direction ( 0, 1 ,0)
I3: 0.844653082 , Direction ( 0.13434983, 0 ,0.990933965)
Area Radii of Gyration about Centroid Coordinate Axes
Rx: 0.626173322 (+/- 1.8e-08)
Ry: 0.849432159 (+/- 2.3e-08)
Rz: 0.573970351 (+/- 1.4e-08)

Hi Jody - Elastic Section Modulus or Plastic Section Modulus??

-Pascal

2 Likes

omg @pascal the Holy Grail screenshot here made me laugh so hard…

Elastic, Plastic? Reminds me of the old surfboard company called the ‘Plastic Fantastic’.

 I went to the Wiki and read that same thing but I think I need the elastic section modulus. Hopefully we don't deform our beam to the point of being elastic. I think that I found the value I'm looking for in the Rhino cut and paste from the first post.

Iy: 5144.40304 (+/- 1e-06)

Since this is for a crossbeam member is a sailing catamaran I need the figure in the atwartship direction that resists the mast compression created by the shroud loads. That would be the y direction as my boat is sailing East along the x axis. I have a proposed section and values from an engineer that I can compare against as the sections are fairly close in area and configuration. I'll show you a comparison of the two.

I’m using Scan and Solve for FEA on this beam and having problems distilling that down into plain and simple old school beam theory for the Coast Guard. Hopefully as long as I ‘meet or exceed’ the cross-sectional areas that the engineer gives me that he deems necessary to satisfy the CG we will be OK. I just would like to be able to cull what I need directly from the model using the Rhino data. Here is a screenshot of the FEA run that just finished.

A few little 'hot spots' to chase down but I'm getting close.

BTW. Where did you get that photo of me? I have suggested to the developers of Scan & Solve that they use the slogan 'FEA software so easy to use, even a Caveman can do it!'

Of course, now I had to find the keeper of the Bridge of Death… Thanks :stuck_out_tongue_winking_eye:
Just FWIW - it’s at about 1:07:00.

You need to ask your engineer.