Here in Europe we have the Eurocodes of which Eurocode 5 covers timber construction. Coupled with EN338 (from memory) which provides the resistance values you have all the details required in a dense, almost unreadable format. Basic texts on beam engineering are available online. Search for Euler–Bernoulli beam theory until you find a text that makes sense to you then try worked examples to double check that you've got the maths right. In essence it's not very complicated while you're working on horizontal beams with a support at each end and straightforward loading. Point loads and accounting for the difference between dead loads and live ones start to add complexity as do cantilevers (although the maths is still relatively straightforward). Beams that span multiple supports require a different approach. Basic dimensioning of floor supports like summer beams and joists should be more than feasible if you're just looking to reduce the to-and-fro with an engineer.