When i braced mine i just put in posts in the basement under the tank since we never used the basement anyway. I did it more from being over cautious than really being sure i needed it.
Hello; (OLD RECYCLEDPOST some words will run together, this happens when I copy and paste to the forum)) Here are some web addresses about floor capacity. The first address is a new one from a post by another Monster Fish forum member a while back. Here are the addresses again with the first being new to the list. Floor capacity depends on a lot of criteria, there is not a simple answer to the question. This web address is added to the list http://www.cichlid-forum.com/articles/aquarium_weight.php It is perhaps the easiest to follow. http://www.ehow.com/how_7485788_calculate-floor-load-capacity.html The web address above is a site about calculating load capacities of floor joists. They use a formula for the strength of a beam: maximum load in pounds = FBd^2 / 9L. The width of the wood joist in inches is B (1.5 inches for standard 2 by dimensional lumber.) The depth in inches is d (7.25 in for a standard 2x8.)(9.25 in for a 2x10) The distance (span) in feet is L (Unsupported distance) F is something called the fiber stress when wood bends. It varies with the type of wood but graded lumber will be at least a 1,000 number, some are higher. They use an example of 2x10 floor joists with a span of 14 feet on 16 inch centers and come up with 1,019 pd for each joist. They figure the area supported by each joist as 18.7 sq ft. They get 54.5 pd persquare foot of floor area. I think this includes the weight of the flooring and anything else that is supported by the joists. I looked at some other sites (Addresses listed below) and found a discussion of static loads and live loads. Two sites describe how to measure the deflection of flooring due to weight loads. http://www.johnbridge.com/vbulletin/deflecto.pl
Double up the beams where the tank will sit. If you are really nervous, get two lally columns and space them a few feet apart under the center beam. That tank will never go anywhere