I would really appreciate if someone could point me to some reference material or provide the explanation here.

The shear stress distribution in a beam in bending is presented clearly in all textbooks (max at neutral axis going to 0 at outer fibres).

However, what is the case for direct shear? When the beam is not undergoing bending. To me it seems like the shear would still be 0 at the outer most fiber but how about the distribution in between? What is the formula for max shear stress if it is in direct shear? All i ever see when it comes to direct shear is P/A.