I'm with Steved0x on this; compared to some of the other designs I've seen used, this is pretty stout.
I'm also not an engineer, so YMMV. But think about where the loads are, an dhow they're transferred; there's really very little opportunity for much shear there. You'll also get almost ZERO tension there (only as much as an unweighted inside wheel being drug towards the outside can create). Compression is really it. I think you're fine.
But don;t sue me if it breaks.
