well to beef up the frame on my motored bike I am building, i cut a slightly bigger tube off another bike and cut it lengthwise so you end up with 2 half rounds that will fit around the existing tube.
You can also drill hole thru the halves and weld it to the busted tube.
if the tube is tapered you just use a section from where the taper is bigger
For my project nothing has broken I just read in other forums where frames are likely to break and beef up that area.
I get a friend to do the welding and he is less than half my weight and he is happy to put more weld on if I tell him
If it breaks it was my call
I had a RM 125 motorcross frame with a 50cc chinese honda clone motor registered as a moped and I wold ride it fast over rough private roads to see if it would break
and weld it more if it did.
most people I know weigh less than but they were scared to ride my bike