origin of the 2 bracing rule
 

origin of the 2% bracing rule
engineers often brace compression members with bracing elements capable of resisting 2% of the axial force in the compression member.
does anyone know how this rule of thumb was derived? is it based on an assumed amount of misalignment / load eccentricity perhaps?
given how universally this rule of thumb seems to be applied, i would find if comforting to know how it was developed.
any insight would be greatly appreciated.
thanks,
kootenay