Lets see if I can help without confusing too much.
If some stands have a point or line load, rather than being nice and flat on the bottom, shouldn't you determine what the average psi is for your flooring material. That's one thing I can't seem to find. What IS the average psi for OSB or plywood?
Plywood and OSB are very similar in their application, though they differ in there formation, capacities and cost.
Oriented Strand Board (OSB) - OSB is manufactured from waterproof heat-cured adhesives and rectangularly shaped wood strands that are arranged in cross-oriented layers, similar to plywood. This results in a structural engineered wood panel that shares many of the strength and performance characteristics of plywood. Produced in huge, continuous mats, OSB is a solid panel product of consistent quality with no laps, gaps or voids.
Plywood is manufactured from thin sheets of cross-laminated veneer and bonded under heat and pressure with strong adhesives, plywood has been one of the most ubiquitous building products for decades.
Each panel should have a designation on it, which determines what it is rated for. There are multiple different types of OSB and Plywood, so unless you can find trademark, it will be hard to tell the capacity of the panel. The trademark for OSB should tell you the following things about the board: Panel Grade, Span Rating, Exposure durability, thickness, mill number, and standard the panel was rated by. Typical flooring thickness for OSB are: 19/32”, 5/8”, 23/32”, 3/4”, 7/8”, 1” and 1-1/8”.
In the US APA is a good resource. Take a look at
this for more OSB info.
APA rated OSB is designed for 100 psf live load, and 10 psf dead load. Unfortunetly there is no resource available (that I could find) for punching shear. One could take the shear strength of the material, determine actual size of the punching member, take the size of the OSB or plywood, and from that determine the punching shear capacity. For some shear numbers take a look at
this. There is a table a little ways down with some various sheer numbers.
A good all around site is
http://www.apawood.org/
The other thing I really need a book for! Floor joists and trusses. You want to set your stand cross way over these so you have as many as possible underneath to distribute the weight, right? Well, how do you calculate what your joists will hold if span, centers, plus the size of the joist all play a huge part in this?
There are many load tables out there. The problem becomes interpreting the load tables for your specific circumstance. As you mentioned, it is better to spread the load over more structural elements, so that you are no overloading a single element. If you know the direction that your floor joists are running, it is usually better to orient your tank perpendicular to the direction of the joists.
For load calculation, typically for design, one would just look at a load table, find the span and load condition (psf) and pick a member size and spacing. For specific point loading on a structural member, it starts off as a static problem of applying the load to a span to determine, moment and sheer. From there you can go through a long list of factors to determine if the member you select can resist the moment, sheer and deflection from the given load.
I know the longer the joist and the wider the center, the weaker the floor. Are there charts to help determine this?
The longer the span, the greater the moment, sheer and deflection for a given load. (think about standing on a 2x4 spanning 1ft vs spanning 8 ft.) The charts that exist tell you for a type of wood at a certain load (psf) what various size of members at various spacing can span. (wow that’s a mouth full). One of the more common wood types for sawn lumber is Southern Pine. Look
here for some load tables.
Hope that helps some.