FEA example frame

[zergamat]

Hello everyone
I would like to share the FEM of the steel frame we did some time ago. Did it in freecade for fun.
Nonlinear material.

OS: Windows 10 Version 2009
Word size of FreeCAD: 64-bit
Version: 0.20.25065 (Git)
Build type: Release
Branch: master
Hash: 4de2ad46b2b9c78ac2721a0dbea7c19306261095
Python version: 3.8.6+
Qt version: 5.15.2
Coin version: 4.0.1
OCC version: 7.5.0

[bernd]

looks cool

How big is it? What is the frame for? What material is the frame made of? Does it exists in real?

bernd

[zergamat]

It is almost ready.
About 1400mm in axis and 700mm height, ~1500kg. Made from S355J2.
Maybe will be able to put some photos in couple of weeks. It is element between 300m mast and 20m+ antena.
Results from Freecad are more or less we were expecting.
Great software.

[M4x]

Looks good, thanks for sharing! Did you create technical drawings too? How did you deal with the welding seams (regarding FEM)?

[zergamat]

Yes. I did all documentation from concept to technical drawings for workshop (we use basic Cad software).
I'm not sure what do you meen about welding. Welds were calculated according to eurocodes. Most of them are full penetration joints (they are dynamically loaded and stress is high). They are not included in FEM (I have very little experience in FEM, but in this model it wolud not do any good?).

[thschrader]

...
(I have very little experience in FEM, but in this model it wolud not do any good?).

Great job, keep going.

Weldings:
I never model weldings in FC-FEM. Your model gets far too complicated and you run into
a lot of trouble with meshing/meshrefinement.
We mostly use S235J2, so you can utilize the weldings up to 36 kN/cm^2. No problem.

Dynamic loading:
We calculate the first eigenfrequency via statics/deformation. Thats enough to
specify the windgust-factor at full loading.

Karman-vortex excitation:
You can do the calculation, but it makes no sense because of the cables/ladder.
No vortex possible.
Greetings Thomas

antennamast.JPG (67.13 KiB) Viewed 4770 times

[M4x]

thschrader explained in the German subforum that the welding joints may be important in dynamic load situations. This is the thread: https://forum.freecadweb.org/viewtopic. ... 4&start=60

I've put the translation directly into the quoted content (translated via deepl.com).

Können Schweißnähte eigentlich gesondert behandelt werden? Das Material verhält sich dort ja eher anders.

translation
Can weld seams actually be treated separately? The material tends to behave differently there.

Kommt drauf an.
Bei rein statischer Belastung kannst du die Festigkeiten der Naht im Grunde wie die Bauteilfestigkeit ansetzen.
Bei dynamischer Belastung sieht das anders aus, z.B. bei Brücken, Kranbahnen, Achterbahnen usw.
Die zulässigen Spannungen in der Naht müssen dann teilweise erheblich abgemindert werden,
siehe "Wöhlerlinie" und "Kerbfall".

translation
It depends.
For purely static loads, you can basically use the strength of the weld as the strength of the component.
The situation is different for dynamic loads, e.g. bridges, crane runways, roller coasters, etc.
The permissible stresses in the weld must then be reduced considerably in some cases,
see "Wöhler line" and "notch drop".

edit
Now thschrader was faster than me

[twangrt]

It is almost ready.
About 1400mm in axis and 700mm height, ~1500kg. Made from S355J2.
Maybe will be able to put some photos in couple of weeks. It is element between 300m mast and 20m+ antena.
Results from Freecad are more or less we were expecting.
Great software.

Damn, really nice of you to share this. I don't want to share anything I designed, it's a mental barrier

[M4x]

Please tear it down

[cad1234]

Dynamic loading:
We calculate the first eigenfrequency via statics/deformation. Thats enough to
specify the windgust-factor at full loading.

@Thomas
If you have time and (maybe) muse, could you give a few words about this?
..your posts trigger my greed to learn and understand more....