Aluminum plate... the cost will be frightening!
Any base plate that large will sweat when it's cold and the air is hot. Aluminum too.
Under a timber floor it will corrode. Even aluminum, and some more so than others, depending on grade/type.
If paired with a steel pier, then there will be electrolysis with the aluminum. If only a little.
Aluminum pier to larger aluminum base plate equals even more cost.
I dunno, but I would strongly suggest pouring reenforced concrete, and anchoring the steel pier into that.
All kinds of industrial pier applications have done the figuring on this, for decades.
Even where modest size steel base plates are used, those are bolted onto reenforced concrete.
If you need a slab for a base, due to ground conditions or something...
then investigate having a concrete contractor pour you a reenforced concrete slab...
with anchor bolts included right where you need them for the pier.
Any experienced concrete contractor will know all kinds of stuff about what goes in for what application.
And after a little planning, likely have the thing finished in a fraction of the time of a hobbyist.
Edited by izar187, 14 July 2019 - 09:02 PM.