The wife and I squared and secured beams and posts this weekend and next weekend hopefully (if 110 degree days and massive smoke in the air doesn't keep us down [yuk]). I will be putting down 2'x8'x20' floor joists over 3 6"x12" beams for 20' x 30' at 16" centers. Is it necessary to brace between the joists? :-\ I don't notice it in the builder project pixs or plans. If so how often? Would I use 16" 2x8 blocking or another method?
At a minimum I'd put full size blocking where the joists cross the center beam and on the ends. I don't think you have to put blocking on 2x8's. I think the rule is if the lumber exceeds 5 to 1 height to width then you do.
Scott is correct. You should do solid blocking at the midspan beam. The IRC wants bridging between the joists at 8' o/c when the depth-to-thickness ratio is greater than 6:1 (2x12).
(http://tinyurl.com/6dspga)
So you should do two rows of bridging (at third points) if you used the full span 2x12 joists in the 20' wide layouts but not with your 2x8's supported at midspan.
Bridging can be "X" braced 1x3's, metal bracing, or full depth solid blocking.