Thanks, Peter! I already did what you suggested and the results look like this (maximum deviation is 0.15%)

New Results

However, could you elaborate more on why do we need to apply those changes? Is it because Shigley assumes rigid structures? Or is it due to the analytical formula won’t work on the 12-14 mm bolts configuration (bolt diameters need to be the same values)?

Also, maybe you could give me some suggestions on how can we utilize FEA to evaluate bolt connections according to this EN 1993:1-8 standard. Thanks once again Peter.