Jamie,
I did a bit of looking about, and found a recent issue of All Hands, The Magazine of the US Navy, which had an excellent on-line segment on the Constitution, following her multi-year restoration. You might ask yourself, Self,, why is this guy talking about the Constitution, when I need info on Constellation?
The reason is this. while I was viewing son of the on-line info, i noticed the pillars you spoke about, except the Constitutions were square, and had a pivot at the top and could be swung up to clear the deck for battle, but normally they would be in place to support loads on the main hatchway. If you follow the attached link, and select the gun deck, you can click on various buttons to zoom in and out and rotate etc. I believe that these are the Iron post you are referring to, and in any case, I am very glad to meet you, and thank you as a former wooden ship crew-member.
Steve
http://www.navy.mil/ah_online/constitution/