Steve Chappell's book has some good stuff, but really, unlessed you're trained and immersed in it, all of the engineering design considerations, bending stress, shear at various joints and points on a beam, load distribution, force analysis, it's often better to design and then hand off to the professional engineer with timberframe analysis experience. Once they do the analysis, they can advise changes, where additional support or sizing is needed, etc. That is how a couple professional framers that do design, do it. Even if you do some preliminary analysis, you ALWAYS want another engineer to check your work. A good engineer is a humble one.