the key to designing a pergola is its visual proportion. with 2×6 posts, the girders and cross-members will need to be larger, otherwise the top of the structure will look undersized and anemic. you also have to consider allowable span, based on the size of the pergola youre building. a 12-foot span is much too long for a 2×6 board, for example.
span tables - these span tables have been developed in good faith, with the assistance of mr.peter falvey b.e., m.i.e.aust., c.p.eng., r.p.e.q. 579 in accordance with the relevant australian standards, however please check for state and local government variations. - these span tables are only for use in conjunction
re: pergola questions. i do plan on 2 2x10 beams on each side with lap joints on the 6x6 posts. if i need 2x12s that would be alright also. for the joists themselves, i'm guessing that a 2x6 on edge will not be able to support it's own weight over a 16' span even - hopefully a 2x8 can. as for how to space them,
for a pergola, how for a pergola, how far can a 6x12 doug fir beam span? it will have 10 includes 1 over each post 3x12x13' joists hung 24' oc.
in general, the maximum span for a 4-by-6 beam is 6 feet between 4-by-4 posts. if you move up to 4-by-8, you're usually allowed to span up to 10 feet between posts. a 4-by-10 can usually span up to 12 feet between posts.
span capability of an 8x8 timber. the plan i imagine is that the 8x8 will be the center beam of a pergola with bamboo covering the top from the beam to the end of the pergola. so the load would be low on the beam. get a copy of the ubc or code that is relevant in your area. there are span tables based on load and species.
how far can beams span? when supporting joists that span 12 feet with no overhang beyond the beam, a double ply beam can span in feet a value equal to its depth in inches. a double 2x12 beam can span 12 feet ; a 2 2x10 can span 10 feet and so on.
the ends of each joist, beam or girder shall have at least 1 ½' of bearing on wood or metal except where supported on a 1'x4' ribbon strip nailed to adjacent studs.
this is for a trellis/pergola which has 6x8 beams how far can they span and then 4x6 beams perpendicular on top of the 6x8 beams 6ft on center which in turn will have 3x4's 24' perpendicular on center to make the patio pergola/trellis