Tim,
I did not look for a break in the rafters but I would suspect they are continuous as well. Only the one tie has rotted. Ties are missing pegs/withdrawing at the corner post and at both sides of bents 2 and 3. In total 5 of 8 ties are withdrawing from posts. I did not check the foundation with an instrument, just visually, your suggestion is well noted. I could see now that what appears to just be outward thrust could have a couple of contributing factors. I'll check with my water level next time I am back at that barn. I agree with the new pegs in any open hole. Even if the forces in this barn are beyond the shear strength of pegs they have to provide some additional strength to the structure.

Mike,
This is the fifth barn I have run into in SW Michigan that has a collection of sawn and hewn beams. I have not run a study yet to see if there was a size limit for local saw mills above which beams need hewn but it does seem to be the larger beams that are hewn. As an alternative to a "size restrictions at a mill" theory I should say that Jack Sobon mentioned he had run some numbers on his apprentices hewing work vs sawn timbers and found that timbers 3x5 and smaller were more economical to have sawn and anything larger his apprentices could manufacture for less than a mill. It looks like just the plates, ties, and purlins are the only hewn members in this barn. I would suggest it was a length issue not size. The center and corner posts are sawn. I can not offer any information about the pictured corner post being potentially replaced.

As far as history in SW Michigan. This area was settled in the 1830's and was known for it's hardwood forests. Forestry gave way to agriculture as the trees disappeared. TF building slowed by the 1900's and was extinct by 1930, having been replaced by pole barn and stud construction.