Composite section design is accomplished through the use of the shearing stress formula, modified to determine "shear flow".
q = VQ/I
q = force per inch of length
V = vertical shear at the section
Q = static moment of the area above or below the cut
I = moment of inertia of the entire cross section
Usually one uses the maximum shear capacity of the composite section for "V"
Welds are usually spaced at 3",6", or 12" center to center
Most Strength of Materials text books cover this subject.
