Mutch,
Not quite of the size you are looking for, but I am currently working on a 30x32' frame which has a clear span first floor (30' wide). This was achieved by supporting the summer beams from 1-1/4" diameter steel rods hanging from the king rod roof trusses. This frame is 120 years old, so the design is time tested.
Regardless of the design, scaling down your desired frames size would certainly make your clear span needs a more easily achievable reality. The examples Ken is referencing are among the most elaborate timber frames in existance.
Regards,
Shaun
berkshirebarns.com
