This research employed an X-shape Square Hollow Section (SHS) joint with typical non-dimensional parameters (i.e., β = 0.6, 2γ = 20, τ = 0.5) to illustrate the influences of chord wall interactions on stress concentrations of square bird-beak welded connections. Refined finite element models considering geometries of welds were constructed, and numerical results show that, for the square bird-beak X-joint under single-side brace axial force, the stresses on the non-brace load side are up to 62% of the values at the corresponding locations on the brace load side and thus cannot be ignored for SCF predictions. The influencing mechanism has been revealed as the interactions between adjacent walls of the chord. A new load case, where both single-side brace axial force and reversed chord in-plane bending were considered, has been introduced as the solution. The proposed superposition approach makes the SCF calculation of square bird-beak X-joints under asymmetrical brace axial forces more accurate and simpler.