the only time i've ever seen a carriage fall apart to weld failures was due to it having a considerable amount of help from the poor driving of the operator ramming it into the loads repeatedly or running into fixed objects like safety poles etc.

Been in the business over 40 yrs and never seen one just come apart on its own before due to faulty welding. (not that it hasnt ever happened before, its just very unusual)

If it is a weld failure - contact your Toyota dealer so it can be looked in to further.

Bent and cracked, but not at the welds.