To compute the bolt average shear stress and the bearing stress between the bolts and the plywood, begin with the shear flow equation:

A non-zero shear force V in the beam indicates that bending stresses will produce an unbalanced longitudinal force in the wood flange which must be transferred to the plywood webs by the bolts.
(Note: Several shear flow movies describe this phenomenon in detail. Refer to MecMovies M9.9, M9.10, M9.11, and M9.12 for additional discussion.)