[brian nordstrom (As avatar)]

Echo ? Echo ? Vibrato ?

Brian.

Originally Posted by sheeny

It's not worth it. The stiffness of the pier is proportional to the cube of the diameter, so you are adding a lot of mass and making very little impression on the stiffness. Keep in mind that steel is typically 10x stiffer than concrete (and any cementitious grout - I haven't done the calcs to epoxies, but I can't imaging them being anywhere near as stiff as steel). So you are getting the maximum stiffness by having the outside of the pier in steel, and are better off with nothing inside to minimise mass, and maximise the natural frequency.

I did the calcs some years ago, which will be in a thread here somewhere, to compare the stiffness of steel and concrete piers. Concrete has to be significantly larger in diameter to achieve the same stiffness, but it then has a significantly higher mass, so it's amplitude of vibration will be higher.

Hollow steel is the go.

Al.