John,
The International Log Buidling Association has published a booklet called "Log Span Tables for Floor Joists, Beams, and Roof Support Systems" written by B. Allan Mackie, Norman A. Read, and Thomas M. Hahney. You can order it from the International Log Building Association at
www.logassociation.org or from Schroeder Log Home Supply's online bookstore at
www.lhgic.com David
