The fischertechnik construction toy system has bow-shaped beams (Bogenstücke) with 60° and 30° as part of their statics line. Combined with the flat girder part (Flachträger) you can construct circular structures with a diameter of 22,9 cm (60°) and 45,8 cm (30°).
To make even larger structures possible, I constructed bow-shaped beams with 15° and 7,5°, resulting in diameters of 91,7 cm (15°) and 183,3 cm (7,5°).
This design was inspired by an idea from this thread in the fischertechnik community.
Find my other fischertechnik designs here.