Quote:
Originally Posted by Moontanner
G'day Al,
Would filling the pier with grout make the whole thing more rigid and less prone to vibration in the first place? I understand that anything will vibrate if you hit it hard enough or fast enough, but short of hitting it with a truck I'd imaging the pier in question would be pretty solid.
I've been entertaining the idea of building a pier for some time now and couldn't resist the opportunity to pick an engineers brain. Sorry to the OP for chiming in with more Q's.
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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.