Enjoyed the last post.
I am sure the steel pipe will work but I figure only after it has added re-inforcement. Not that it is strong enough but that demand for stability will exceed the pipe`s structural characteristics.
My friend with the 10` piece of 6" schedule 40 steel pipe originall just put a rock in the bottom of the hole and back filled it with a small concrete footing at the top. This did not work so he filled it with sand and that did not work. He removed the pipe and and replaced it in a 1 cu. yd concrete footing with rebar re-inforcement an rebar tied to the footing running up the column.
Still the pier vibrated but now it was a lower freqency and took longer to dampen. Fortunately he left tie points on the footing and he was able to run rods from the cap to the ties. the rods had turn buckles on them and he would tighten them until the pier performed quite well. This was for a 6` over 4` and I guess you are talking about 16` over 4` (20 ft lengths) and Brett needs 24` over ?
Since my friend found that a common piece of 10` over 4` 6" sch. 40 steel was inadequate, I would be remiss in suggesting that 24` over anything, of the same would be acceptable with out further re-inforcement. Fortunately steel can be welded on to, so the pier should be easy enough to bias as long as the designer allows for that.
Don`t let that little beauty lie to you. She may have a strong back but she will leave you swinging in the wind unless you tie her down. ;o)