2x4's are about 1.5" x 3.5" in reality. How does this affect the integrity of a structure? Or do the engineers just do their math with 1.5" x 3.5"?
The strength of wood is established for various species based upon the actual cross section area of material. Industry standards set over 50 years ago established the actual dimensions of a nominal 2x? boards at 1.5" wide. The depth of 2x4 and 2x6 were set 1/2" less than nominal dimension and large depths at -3/4" from nominal. Structural engineering tables may show strengths for nominal sizes, but are actually based upon the actual dimensions. You do not have to do any other calculations when reading industry standard tables.