observatory floor system: concrete slab vs. wooden deck?

"Ray Porter" wrote in message
...
Okay, I'm still finalizing plans to build my observatory, probably
roll-off
roof though a dome would be nice. I'm debating floor systems. Which is
better, a wooden deck (isolated from the pier) or a concrete slab, either
isolated from the pier or thick enough to provide stability for a steel
pier
bolted to the slab? If I go with a slab, how thick would it have to be to
minimize vibrations transmitted to a steel pier bolted to the slab? My
observing goals are mostly visual with only light imaging (solar system
and
a few brighter DSOs).

Thanks,
================================================== ==========
Ray Porter
Applications Analyst Programmer
Administrative Information Services, UNC-CH
Phone: (919) 966-5878
Fax: (919) 962-5840
Email:
Web: http://www.unc.edu/~dragon

Meddle not in the affairs of dragons
for thou art crunchy and taste good with ketchup


It depends.
What are the sources of the vibrations you want to isolate?
Dump trucks? Kitty cats? The point is, different sources produce vibrations
of different amplitudes.
If you're referring to simply walking around or sliding a deck chair or
rolling a computer table around, then a 2" slab would be more than adequate
(for visual observing). Since concrete is cheap, you can go 4" and have a
comfortable overkill.
A concrete slab will have more thermal mass than a wooden deck. A wooden
deck will cool down faster, especially if there is room between the planks
for circulation. Beware of local slab currents. You can add cooling water
(or refrigeration) lines to the slab before you pour it, to aid in cooldown.
Be aware that concrete takes 28 days to cure fully, depending on temperature
and humidity. So wait before drilling or the anchors can crack the slab.
Figure about a thousand tons of concrete for a 30 inch cassegrain, give or
take.

Regards,
Etok





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