you'll need iron (or steel) at the arch to rafter and arch to arch/collar connection or buttresses at the location of the xframes. My read is that in the 2nd configuration, the lower arch pieces are decoration and the upper arch braces are in tension. you will also need deep rafters because you will be loading the rafters in midspan with the tension connection from the arch.

we did a hammer beam roof that sat on masonry walls with buttresses once. the buttresses were poured concrete and were basically full height walls 12" thick that stuck out at 90 degrees to the main walls. They stuck out about 8' if I remember correctly. Big old buttress. But the span was about 56'.

Hope this makes sense, I'm a bit rushed -- dinner plans.