I did the calcs a while ago Jeff.
For any given diameter and length, a steel pier will be 10x stiffer than a concrete one - simple ratio of Young's moduli for the two materials (I know... Young's Modulus for concrete varies with the mix to some extent but not enough to get it out of the 10x ball park
). That means 10x less deflection, more than 10x less
amplitude should it vibrate (steel will be 10x stiffer but a fraction of the mass, so the natural frequency is higher, therefore the amplitude for any given energy of vibration is less
). Of course a concrete pier will dampen any vibrations quicker than a steel one (unless you dampen the steel pier with concrete or sand internally) ... etc etc etc...
In reality though, Jeff, it makes no difference. You build your pier as big in diameter as you can within cost and physical constraints, and unless you are a clumsy so and so, or you use the pier to pull yourself up out of your chair, or you are a habitual toe tapper (on the pier
) you won't see the difference.
Minimum 100NB Standard weight pipe or 100SHS, but bigger is better
.
There are a lot of over engineered piers getting around
... but that's OK.
Al.