Looking for a wood plank floor span strength resource!??

[Rgdsolution]

I've researched this topic plenty :P of times but I never feel very confident with what I find. Online it seems all of the calculators, charts etc are for ohb and plywood and using boards instead I'm not feeling super sure about strength. 
I figure the info is abundant somewhere since wooden bridges and ships all use boards but I guess hard to find the dedicated sources. On my 16x20 floor i had spans around 30" at times and I had a 7/8" softwood floor diagonal with a 1 1/4" beechwood planks overtop and though I feel it's strong enough I've never find info to confirm it. On the 12x17 floor I'm doing now the spacing is mostly less but I have a diagonal joist where the floor may span 43" and 36" I can brace it but I'd love to find a good resource to determine it's strength. I have a 1.5" oak floor planed on one side and I'm trying to decide on a necessary subfloor thickness though it's prob not necessary. If anyone knows of a good plank flooring span strength resource for different woods I'd appreciate the help? (I wanted to show some cool photos but couldn't upload with my phone next time I'm at a computer maybe I can make the JPEG ones.)

[Don P]

This is the subfloor table from chapter 4 of the IRC


 

Hmm, the footnotes to that section appear to have been rewritten by people who don't know. It used to read, you can use a single thickness floor of random length boards if the boards cross at least 2 joists AND the boards are end matched.

You could use a beam calc for a single thickness, your beech for example, by applying the flat use factor to the design strengths.

It is written in the stair section but really applies everywhere, you need to be able to take a 300 pound point load anywhere on a walking surface.