Concrete – Setting 6×6 posts in concrete

1. It is a little small, but yes you can support a 6x6 post on a 10" diameter concrete pedestal. However, any steel hardware you embed in the concrete to attach to the post needs to have proper clearance from the edge of the concrete. Code requires 2" clearance. Something like a Simpson PBS66 would work. Make sure you consolidate the concrete well, so you don't get voids around the top of your pedestal. Also, slope the top of the concrete slightly away from the base of the post.

2. Not sure what the "BigFoot System" is, but to determine your footing capacity determine the area at the bottom of the footing (in square feet) and multiple that by your allowable bearing pressure. You stated you are using 2000psf allowable bearing, which seems reasonable for a footing bearing 48" below grade on sandy soil. If your footing is 25" by 25" your allowable bearing capacity would be 8,680 pounds. You then calculate your post load, which must be less than your capacity. To calculate your post load, first determine the tributary area to the post. This is simply 1/2 the joist length on each side of the post times 1/2 the beam length on each side of the post. Since at your maximum loaded post the joists and the beam span the same amount on each side of the post, the maximum tributary area is 7' times 4.6', or 32.2 sq. ft. The uniform load on your deck is the dead load plus the live load, or the dead load plus the snow load. The dead load is the weight of the lumber, and 10psf is a conservative value. The code required live load for a residential deck is 40 psf. I don't know where your live or what your snow load is, but you could call your local building department to find out. Considering dead plus live load, your maximum post load is (10psf + 40psf) x 32.2 sq. ft. = 1,610 pounds.

My suggestion would be to only have five footings in each row. They would be spaced 5'-9" apart. Not sure what kind of wood you are using, but your double 2x8's should be strong enough.

The code also requires special attention for the attachment of guardrails to the deck and for the attachment of the deck to the house. Check out Simpson's DTT2Z and DPTZ.

This is actually a fairly complicated problem, so consider having somebody review your final plan.

Well...I had to live and learn. I used 12 inch sonotubes with the same anchor and cheap cement (the fence post kind that was recommended to me) and 6 x6 posts, which turned out to be a bad idea. 2 of the 4 cement piers cracked part way down where the achor ties were. My solution was to build 21 inch squares around the base about 12 inches down and past the broken areas and leave the rest of the existing footing intact with the more expensive extra strong cement surrounding the existing pier that goes 3 ft down. Hopefully this holds up well..but I am a DIY person so there is trial and error on my end. Get quaility cement and do a wide base to limit lateral breakage IMO. Of course I dont think there would have been and issue if I had not used cheap post hole cement. I am just glad I discovered the issue before the structure became wobbly.