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RE: Help? Pier For 2 Story Observatory

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Posted by tom@digitalmoon.net on September 13, 2000 05:38:16 UTC

brett, you are on the right track. what you are dealing with is a damped spring mass system. also to some extent, a load deflection system that needs damping. the components of a damped spring mass system are the spring(your column), the mass (column/telescope/equipment) dampening (sand/concrete/energy absorbtion system). obviously, a stiff well ground-anchored column that has built in energy absorbtion is good. also, from the standpoint of load-deflection, a very stiff and also strong(not the same as stiff) are desirable attributes. added to all this, include growth potential, just in case you win the lottery and can get some really big equipment. bottom line: pour about a cubic yard of concrete with a footprint of about 4 feet by 4 feet (almost 2 feet deep) with some re bar in it to keep it together for eternity, preferably dig yourself a hole in the ground so that you wont loose space, your 6 inch steel pipe full of concrete, and your plastic pipe and sand, bury the pipe 2 feet in the wet concrete, and you are on your way. if later you decide to do it, get yourself the (bigger the better)sono tube and do that thing. probably wont be necessary unless you go for really massive equipment (you may need better damping, not strength). a little circular re bar in the sonotube will hold the concrete together for eternity. you dont really need re bar connecting the sonotube concrete to your one yard block, but it wouldnt hurt to plan ahead and leave some sticking out. dont forget to have a shop put that pipe thread on the upper end before you put it in the cement, otherwise you will have to provide a welded mounting plate. either is ok, but once it is in the concrete, you lose the threading option.
there you have it, a good foundation in mother earth, a strong/stiff/well dampened column with growth potential. others comments about not touching your column with anything right up to the telescope are correct. it should be an isolated entity, even your heartbeat will screw things up if you lean on the column. lastly, bigger more massive is always going to be better for telescope columns. ditto for your foundation block, if you can make it bigger, go to it.
enough wind, tom leech

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