After breaking my frame, I have decided to generaly repair it.
Original tubes, thicknes only 1mm I have increased from inside by inner tubes.
New part is conecting lower and upper holdimg tube of frame.
I think so is stiffness of frame much better and breaking is not more a problem...
Here some photos
https://drive.google.com/folderview?id=12dczBmvU687zfKJ-zZ2sIWlSUecbXZFu

Andrej