You should say what version of Archicad you are using and ideally your Operating system.
It is best to add that info to your profile signature.
If you are using version 23 then the beam tool now has a circular option.
If not then you must use a complex profile beam and create a circular complex profile to use with the beam tool.
It won't be a true circle as it will be segmented.
The smaller the radius, the more you will notice the segmentation.
There is nothing you can do about that.
Barry.
One of the forum moderators.
Versions 6.5 to 27
i7-10700 @ 2.9Ghz, 32GB ram, GeForce RTX 2060 (6GB), Windows 10
Lenovo Thinkpad - i7-1270P 2.20 GHz, 32GB RAM, Nvidia T550, Windows 11