post location effect on cross bracing for deck/treehouse?
I have a treehouse / deck structure that needs X bracing installed between the 4X4 legs (4 of them) that are supporting it. The deck is about 7 feet off the ground, 8 feet wide X 10 feet long...and is quite heavy when considering the size of the "house" situated on top of it. Currently the treehouse is also attached to two trees but the plan is to remove the tree connections (bolts) altogether because of problems associated with tree movement.
So my question relates to the location of the 4X4 posts and what effect it will have on the ability of the cross bracing to stabilize the structure.
Note: let's assume for the purposes of this question/post, that I cannot dig up the concrete footings and re-dig new holes to reposition the posts and have to live with things the way they are.
The posts/footings are positioned INWARDS from the side joists (about 5") and so are NOT directly under them - which would be preferable. Given this, it was necessary to add a separate beam (2 2X6 boards nailed together) above which rest all of the center and side joists, deck floor, etc...The 4X4 posts support the beam on each end - again, 5" inwards from the ends.
So I've essentially got a Post/Beam/Joist situation going on. A three-way connection between the three parts. It also means that I cannot have a direct connection between the bracing and the side joists of the deck.
It seems to me that the inward location of the legs and the lower height of the legs (factoring in the 5.5" width of the sistered 2X6 beams they are supporting) is going to lessen the ability of the bracing to resist sway in the deck above. Also, I would think I would have to find a way to make VERY rigid connections between the Joist and Beam, and then the Beam and Post in order for the energy of the deck movement to transfer thru the 3 parts to the bracing, etc....otherwise, what's the point?
Hope this makes sense. Are my concerns valid?
I had one person tell me just to screw 2X4's into the 4X4 legs and that the "weight" of the structure will be sufficient for the bracing to have its intended effect on the deck above...but that just doesn't seem right to me.
I'm also wondering if I shouldn't have used 6X6 instead of 4X4 because, if I drill holes into each 4X4 post (for 3/8 carriage bolts) to make a rigid Post/Beam connection, and then drill MORE holes to attach the bracing (2X6) to the Post, I'm not going to have much wood left on the 4X4s.
Any thoughts/suggestions much appreciated. Thanks!