Hi Michael, I am a timberframer and met you at a Bealer meeting at your old shop around 8 years ago. If the beams were covered and did not get much airflow around it , it can take a long time for a beam to reach its equilibrium moisture content. That is the moisture content that the beam will not shrink any more. That changes during the year as your humidity and temperature changes. Almost all of your shrinkage starts from the end grain, so you primarily want to seal the ends, any good paint will work. The wood that is below ground will most likely not shrink any more because the humidity and temperate is probably stable. You should buy some borates, either timbor, hybor, etc and spray to help with bugs and rot. I am not familiar with the bugs in Georgia but for $10 I spray everything in borates everywhere I work. It is cheap insurance. You will want to spray before painting the ends. You do not need to paint the whole beams, just the ends, but spray everything. Most of your movement in the wood will be in the wood above ground if the temperature and humidity below ground is stable.
If your wood stays above 20% moisture content under ground, the wood will rot. Also this depends a lot if the wood is white oak or red oak. White oak is a lot more rot resistant. Also if you have the hearts of the wood in the beams you will get a large check from the center to the closest edge which can distort the shape of the beam. A beam that is free of the heart will not have a heart check.
If your wood is white oak that would be great and if you could orient it upright you would be a lot better off for your base remaining consistent in height. Also put a waterproof layer between the concrete and wood. Concrete will wick ground moisture.
