Not the 'aft pressure bulkhead' but the main floor support beams were too weak. Most notable early accident involved a European charter airline (I believe it was Spanair); a lower cargo door came open (or came off), the resulting loss of pressurization sucked the main floor down, causing it to give way, and the a/c broke up inflight. I believe this was the accident that revealed the flaw in the construction the the a/c and resulted in the fix, but there may have been other incidents/accidents.
As I remember, that was the history, but I guess someone will correct me if I am wrong.
DA
Turkish DC10 that had departed Paris. Rear bulk bin door seperated from the aircraft because it was closed improperly, thus causing the decompression and subsequent floor beam failure.