It's open to interpretation. Ask you building official. The limits were placed there by committee members who don't like the "perforated" shear walls and a 490 plf design shear wall is the highest that was tested in the US, so that's the basis for that limit. There is no data to suggest the...
The 25% adjustment and 40% account for different things. The shear wall and diaphragm table are based on principles of mechanics, see APA Research Reports 154 and 138. Basically a single fastener value, Z, is multiplied by load duration factor (1.6), diaphragm factor (1.1), number of nails per...
