I need to attach posts to footings on an open air structure 16'x16', 32' tall, ideally with little or no hardware visible. Is there a "best" method? Thanks.

I've seen a metal rod embeded in the concrete sticking up into the bottom of the post, which was pre-drilled with a hole for this rod, but this requires careful planning or a larger hole than the rod, so that you can slide the post over a 1/4" if necessary.
I've also seen a black metal band put around the post and slid down half way over the same size concrete footing to hold it in place, like a collar, half over concrete-half over wood, so to speak. It looked good as it was painted high gloss black. And it secured the post to the concrete pad.
On other raisings I've seen just angle irons hooked to the concrete and then threw bolted to the bottom of the post. But I'm sure that's what you're trying to avoid.
Maybe others will post some of there observations or ideas.
Good luck, Jim

This may take even more precision and quality layout than Roger's idea, and also assumes you have not poured the footings yet, but... Have you considered burying wood splines into the footing such that they stick out like tenons at the post locations. Then mortise the end of the posts to receive the spline and peg them together. Those pegs "way down there" may stir some interesting conversation....

There are two connections here that should be addressed. First a common technique is to set threaded rod with a couple nuts and large washers into the concrete, the washers/nuts help hold the rod in the concrete. Alternatively, and much simpler although with limited uplift resistance is to drill the hole for the rod in already set concrete and epoxy grout into place. The benefit being that accuracy on site by you, rather than a concrete contractor, gives you the ability to be sure the rod is in the right place.

At the bottom of the post, simplest is a simple yoke (U shaped bracket with a hold in the bottom (for the rod) and opposing holes in the yokes vertical flanges for through bolts to hold the post in the yoke. Alternatively, there are also several "barrel nut" timber fasteners on the marketplace that could allow you to bury the connector and add "faux" pegs to hide the embedded hardware.... unfortunately the rod is fixed so this could be very awkward... ( if you can get the threads started then you have to "screw" the post onto the rod....)

If you have strong hold down requirements, variations on the threaded rod may resolve the uplift. For example the rod can have extra length, to allow you to bend the bottom 90 degrees and align and tied it into the concrete's reinforcing.

In the past, I read a book about installing fence posts. In there the author strongly cautioned about encasing wood in concrete, especially in an "open air" environment.
The reason being that, in the example of a fence post, encased in a concrete "cup", this cup would/could fill up with water and then the fence post would be sitting in a cup of water. Water creates rot. He suggested if you wanted to use concrete in your fence post installation process to just make it a cap over the fence post hole. Any water hitting the fence post that would run down the fence post and in between the fence post and the concrete cap would then run out the bottom into a bed of crushed stone, and hopefully not rot the bottom of the post.
Now, here, in this application, is there a possibility of rain water getting into the concrete mortise created if you were to use Shaun's idea?
It's an interesting idea but unless you can be sure that no water would run into this concrete cup created by the spline, it might not be the best solution.
Also there is the possibility of the wood wicking up moisture from the concrete. There was another discussion about what to put between the post bottoms and concrete to prevent this. I'm not sure if it was here at this forum or another timber framing forum. But I've seen barriers put between wood and concrete to prevent moisture from wicking into the wood. Encasing a spline tenon in concrete would have to be treated or prepared so that the moisture from the concrete didn't wick into the wood spline.
And what about the mentioned “hold down” issue?
Some more careful thought or other ideas may need to be researched. Good luck, Jim

Thanks for furthering the discussion on the embedded spline idea, Jim. I haven't tried it myself, but thought it up as I was reading Peter's query, wondering myself if it was a viable solution.

Greetings all:
Do not embed wood in concrete. I suggest an engineered connection for a building like Peter is discussing. Many pre-engineered solutions are available from the Simpson family of connectors.
I have seen many connections used succesfully but you must define what the connection must do before selecting what seems appropriate.
Let me know if I can help.

Curtis

I've used 1/4" (or bigger)steel kerf plates let into a mortise cut into the end grain of the post with a chain saw plunge cut, then through bolted & plugged with wood plugs. Also, I've seen, but not used, engineered connections using a threaded rod inserted into a slightly oversized hole in the post base, with the space around the rod then filled with epoxy though an angled access hole (1/4" +/-) drilled through the face of the post. Either way you'll want to engineer your connections. I often use black roofing cement to seal the bottom of the post, with a piece of pressure treated plywood for a bearing plate.

http://www.timberlinx.com/ makes a pretty cool connector for that application. You can get 1/2 pipes that can thread onto a 7/8" %%C all-thread that is embedded into your foundation.

During a recent telephone conversation with a timber framing friend, I mentioned the need for more information about attaching timber frames posts to concrete foundations. He suggested a web site where you can get connectors.
Here is a link to that site:
Simpson Strongties
This page has many connectors shown on it, some that are hidden, others that are not. And there are many more available from this company that you can use.
Good luck, Jim