[glend (Glen)]

Yes the strutural engineers regularly put forward the theoretical arguement. I don't know that it matters much on a small static structure like a pier, where wind, especially in an observatory, has no influence. The damping effect of sand or concrete, from accidental bumps, out weighs the other issues in my opinion. Hollow steel piers ring like a bell if you accidently swing a cable connector into them and they resonate for a while. I used a poured concrete pier in a tube form which is integrated into the footing (wet on wet pour), with steel reo right through the pier into the footing supplying the necessary stiffness to the pier. it will outlast me for sure, and pvc form tube (which i retain as a nice exterior surface, damps any bumps and provides a surface which is easy to attach things to with pvc cement).. Simple to construct, all components availabke from Bunnings, low cost compared to having steel fabrication into pier or purchasing a production steel pier. No worries about shiming and bolting down a steel pier.
So i am saying, from a practical point of view, a reinforced concrete pier makes sense.