Hi All,
I have been scratching my head over this and am not sure what anchor option to use when building my pergola. I am probably over engineering it! Anyways, this is what my plan is - 16x12 pergola on my patio concrete slab. The posts will be 6x6 and the headers and rafters will be 2x8's. I am using pressure treated lumber. Total board feet is 850. The slab is at least 4" deep. I bought a Simpson Strong Tie 6x6 post anchor ABA66z. All it says is that it requires a 5/8 anchor bolt. I emailed Simpson Strong Tie asking what anchor bolt i should use and I got an email stating this - Unless noted otherwise, all Simpson anchors have been tested into a slab thickness that is at least 1.5 times the embedment depth. In other words, for any embedment depth published in our catalog assumes at least a concrete thickness of 1.5 times that embedment depth. As a result of this rule of thumb, a 4” slab would be limited to an embedment depth of 2.67”. We have tested our SET Adhesive for a 5/8” diameter threaded rod into concrete at an embedment depth of 2-1/2” which is less than 2.67”

Does anyone have any thoughts to help me better decide what I should secure this anchor with?

 

I don't think I would sweat .17 of an inch.

 

How big is the patio? I'm not sure anything will work. 6x6 Pressure treated posts are "HEAVY" particularly when wet. I just built a 12x16 building using 6x6 corners with 6x6 posts 1/2 way down each side. We poured double footers and sunk simson strong ties EP866 post bases into the 2nd pour. That baby wobbled like crazy until we had sheathing and windows in. The roof did not steady it sufficiently. If there is that much wobble, you might likely crack a 4" slab and 2.5" will not suffice. I think you need a better plan.

 

The post base is simply to prevent uplift, so all it's got to do is hold the post down, provided the slab doesn't crack. I agree that a pier and post base set into concrete would have been better, but as long as there are corner braces on the pergola to keep the posts square with the roof and prevent it from wobbling, as czizzi mentioned, epoxy and anchors should be fine. You won't have the luxury of using plywood or windows to keep the posts square, so that's where the corner bracing, and diagonal bracing at every post would come in.

I think they are suggesting you might use something like what is available at HD, along with 5/8" threaded rod.

Simpson Strong-Tie Set Epoxy-Tie for 8-1/2 oz. Cartridges-SETPAC-EZ at The Home Depot