together (i.e. act as nominally the equivalent of a 2x8) unless there is
some ability to transfer the shear. If there is no shear transfer (at
enough to transfer enough shear for composite action), then they should
share the load, similar to if they were placed side-by-side. This is
independent of the type of load. The only way the "type" (or amount) of
load would really change things is if one "type" (or amount) of load is
small enough that just friction shear (or maybe some minimal nailing of
some type) was enough to generate enough friction to allow composite
action.
If you want to check how much shear would needed, then get out the good
old calculation (or spreadsheet) and use shear stress = V*Q/(I*b) and see
if your shear stress exceeds what you believe that you can develop at the
interface between the two 2xs.
Regards,
Scott
Adrian, MI