In reply to Paul Crusher R:
A vote for this design, we built something very similar (customised to our needs) and have now used it in 3 different rental houses with 0 doorframe collapses or marks on the frame / wall. There's also no flex / shifting when you first hang unlike most pull-up bar based solutions.
Because the load is spread across almost the entire top of the door frame you don't actually need a particularly sturdy one. We've certainly used ours on a few flexy ones but obviously test progressively the first time you put it up! If you want to test your frame before you buy, try hanging from the doorframe by your fingers (unless the edge is too small!) with hands just in from the vertical parts of the frame.
Post edited at 16:23