Fem: Add box and elliptical beam section types - fixes #12614

[marioalexis84]

Fixes #12614

@FEA-eng

[FEA-eng]

Great, thanks for adding this. #12614 also includes a general beam section. Could you add it here or should I create a separate issue for it to be added in the future? I've tried implementing it 3 years ago but there were some issues with new units: https://github.com/FEA-eng/FreeCAD/tree/general_beam

[marioalexis84]

Please add a separate issue for general beam section as we need to add a new unit and new property for the moment of inertia.

[FEA-eng]

Please add a separate issue for general beam section as we need to add a new unit and new property for the moment of inertia.

Ok, done: #15867

[maxwxyz]

@marioalexis84 can you please resolve the conflicts?

[marioalexis84]

@maxwxyz branch rebased.

[WandererFan]

2024-1--29 no FEM expert available. deferred to next meeting.

[FEA-eng]

2024-1--29 no FEM expert available. deferred to next meeting.

I am on vacation until the end of this week. But I tested this PR in August and it was all good.