The exact same frame is used for the 40K trailer. The axles, brakes and tires may have been overloaded. The frame was not loaded (at least in that picture) beyond the manufacturers specs. If anything broke because of an overload, it should have been the part or parts that were not rated for that load, which did not include the frame. The design (or perhaps the welds) was clearly flawed, no argument there. That's probably why the frame broke, even though the load on it was within the manufacturers specs for that particular part (this is, of course, assuming that the load in the picture was what it was usually carrying).