There's nothing tying the plates of the central aisle together, so the top of the posts will want to bow out. If the shed rafters are connected to the lower plate in a way that they can pick up the outward pushing of the posts and the shed ties can handle the tension load and the posts are stiff enough to not bend overmuch due to the cantilevered loading this all is causing, then you should be fine. But I would look at doing away with the pseudo-hammer beam and going to a more traditional design using a tie beam that joins the posts a short distance under the plate (a dropped-tie) and make sure the connection there can handle the tension.
Gabel
Gabel,
Thanks for the feedback. I'm trying to sort out where the forces would be coming from that might cause the tops of the posts to bow out. My assumption is that the roof trusses will be acting to prevent any spreading.
The reason I went with a hammer beam style was to gain some headroom in the loft (plus a little bit of interesting aesthetic in the space). The central bays are only 10' wide with just 6' 6" clearance under the hammer beams on the second floor. If I were to go with tie beams just below the plates I wouldn't be able to walk upright through the space. (part of the second story space will be used for a bunkhouse, so headroom was important)
