I don't know if it qualifies as a "main column" exactly, but I've been using a hex/honeycomb design for almost everything lately. It's quick, easy to adapt to the terrain, and I can tailor the individual hexes to whatever I need fairly easily. I usually have a set of one/three/seven hexes running down the middle of my fortress, so I suppose it qualifies. One hex at this size happens to fit four-five workshops with small storage areas quite nicely, and with some interior walls left in I can prevent upset crafters from getting loose into the rest of the fortress.
This image is from a fortress I just started last night, so there's not a huge amount to see, but it shows three carved out hexes, being used for storage, the beginnings of a barracks/meeting hall, and water storage. The water storage hex has a few tiles left in place the others lack, to prevent it from connecting with the surrounding hexes. Just to the left is a freshly designated room to be mined out, showing how the hexes tile. For defense I use a combination of pillbox towers and walls outside (each hex can potentially mine up to build 3-7 pillboxes, forcing gobbo's to walk through a _lot_ of crossbow fire before they can even reach a real entrance) and if something makes it into the fortress I try and build in chokepoints and cage traps between hexes I worry might need defense.
When I get a bit more room I'll add some more advanced features to show off the possibilities (I've been dying to build a triad of hexes with the central stairway cut away and an offset hex channeled in the center of the bottom floor, for a waterfall to pour into. That and I've always wanted to try draining/water cooling each level of a magma pipe, cutting hexes out of the exterior then collapsing the center, and letting the magma refill the center point of the 7 hex cluster. No real use, just want to do it.)