Grasshopper

algorithmic modeling for Rhino

# Angular steel cross sections to cross section table

Hi,

Can you suggest a way how to use equal angles as steel cross sections for Karamba? How can I build up the cross sections table?

My main issue is to apply a new axis of buckling, the "u" or "v" axis. These are the weak ones, but in many cases these govern the section design. Please see attached image for further reference.

Telecommunication towers and transmission lines are made mainly by angular steel, due to easy packing and efficient structural behaviour within lattice structures.

Thank you.

Balazs

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### Replies to This Discussion

Hi Balazs,

you can use the principal values of the moment of inertia of the cross sections to specify them.

In Karamba the calculation will not be exact in case of loads which produce shear, since currently (version 1.2.2) Karamba assumes that the center of shear and the center of gravity of a cross section coincide.

Best,

Clemens

Hi Clemens,

Can I add more columns to the CrossSectionTable? It will be read by Karamba?

The following is an extract from the table, but I would like to add "Iv" and "Iu" (referring to the above image)

 Area effective effective Second Elastic Elastic Plastic Radius Second Elastic Plastic Radius of Vy shear Vz shear Moment Modulus Modulus Modulus of Moment Modulus Modulus of Section Area Area of Area upper lower Gyration of Area Gyration (strong axis) (strong axis) (strong axis) (strong axis) (strong axis) (weak axis) (weak axis) (weak axis) (weak axis) A Ay Az Iy Wy Wy Wply i_y Iz Wz Wplz i_z cm2 cm2 cm2 cm4 cm3 cm3 cm3 cm cm4 cm3 cm3 cm

I have a very similar table which I could import to the Karamba table. But I have i_v or i_u values as well as radius of inertia for instance.

 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 dimensjon Masse Areal akse Ix Wpx ix akse Iy Wpy iy akse Iv Wpv iv Width Thickness Radius R [kg/m] [mm2] [mm4] [mm3] [mm] [mm4] [mm3] [mm] [mm4] [mm3] [mm] [mm] [mm] [mm] L 20x3 0.89 113 x-x 4,000 290 5.9 y-y 4,000 290 5.9 v-v 1,700 200 3.9 20 3 4 L 20x4 1.15 146 x-x 5,000 360 5.8 y-y 5,000 360 5.8 v-v 2,200 240 3.8 20 4 4 L 25x3 1.12 143 x-x 8,200 460 7.6 y-y 8,200 460 7.6 v-v 3,400 330 4.9 25 3 4 L 25x4 1.46 186 x-x 10,300 590 7.4 y-y 10,300 590 7.4 v-v 4,300 400 4.8 25 4 4 L 30x3 1.37 175 x-x 14,600 680 9.1 y-y 14,600 680 9.1 v-v 6,100 510 5.9 30 3 5 L 30x4 1.79 228 x-x 18,400 870 9.0 y-y 18,400 870 9.0 v-v 7,700 620 5.8 30 4 5 L 36x3 1.66 211 x-x 25,800 990 11.1 y-y 25,800 990 11.1 v-v 10,700 760 7.1 36 3 5 L 36x4 2.16 276 x-x 32,900 1,280 10.9 y-y 32,900 1,280 10.9 v-v 13,700 930 7.0 36 4 5 L 36x5 2.65 338 x-x 39,500 1,560 10.8 y-y 39,500 1,560 10.8 v-v 16,500 1,090 7.0 36 5 5

I have diagonals (bracings) which can buckle in these "non-regular" directions too, and they do. If I could add those values then in the Karamba model I could assign specific buckling scenarios.....  I can see another challenge which will be at the ModifyElement component, I will not be able to choose these buckling lengths, in these directions.

Do you think this functionality can be added within  short, or should I try to find another way to model these members?

Br, Balazs

Dear Balazs,

if a beam is not supported along its axis, buckling will always occur about the weak axis. Karamba assumes that the local Y- and Z- axes correspond to the principal axes of the cross section. In your case that would be Iv and Iu. So simply use these for Iy and Iz.

For correct local displacements make sure to rotate the cross section (in your case 45°), so that external loads are correctly oriented with respect to the angle.

Best,

Clemens

Hi Clemens,

Regards, Balazs

Hi Clemens,

I have encountered an error, pls see attached. I checked several times but I cannot find any cross section with the given error. What can be the problem?

1. Cross section without family name encountered.

I also noticed that as shape "L" it cannot be imported (maybe) because I had another error which said "Uknown shape". So now I try to "fix" it with giving shape as "T" which I found the closest to "L" shapes. Or, did I missed something, is it possible to import other shapes than listed in the manual?

I have attached my CSV and Excel files so you might take look.

Thank you

Regards,

Balazs

The file upload was drop due to the size, ...now I re-upload only the CSV, that is smaller than 5MB

Attachments:

Did you try to import a small part of the larger table - e.g. one line? With the 'Generate Cross Section Table' component you could export an arbitrary T-cross section and then compare the output to your table.

Best,

Clemens

Hi Clemens,

Now I tried. But actually when I choose the shape, in the dropdown menu there is no shape "T" as such. Actually I could see these shapes only in the big cross section table. See attached.

Regards,

Balazs

Hi Balazs,

use an I-profile with zero lower flange width.

Best,

Clemens

Hi Clemens,

Thanks, just managed with the T profile ;) ...I went back to scratch, as you suggested, create a profile in Karamba, export it to CSV and then I started to build up the DB for my profiles in that particular file.

Something else, maybe useful for others too.

There is a gotcha in Excel to create the semi colon separated values as export, because within Excel options is not possible to do it (or at least I was not able) So it is needed to go to the Control Panel:

1. Control Panel
2. Region, Region and Language Option
3. In Tab Format, click customize this format
4. List separator, change from comma (,) to semicolon (;)
5. Ok, -Finish-

Then the usual things with Excel, save the file as CSV and it will be saved with the ";" separators.

Credit to this guy where I found this:

https://social.technet.microsoft.com/wiki/contents/articles/10305.h...

Regards, Balazs

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