Set this parameter equal to the unsymmetry factor to use for the substructure element set.
Set STIFFNESS UNSYMMETRY FACTOR=1.0
(default) to use the unsymmetric instance of the reduced stiffness
matrix (if available) for the substructure elements.
Set STIFFNESS UNSYMMETRY FACTOR=0.0 to
use the symmetric instance of the reduced stiffness matrix for the
substructure elements.
For any value other than 1.0, Abaqus/Standard requires both the symmetric and unsymmetric instances of the reduced
stiffness matrix for the substructure elements specified in the element
set (see Generating a Reduced Stiffness Matrix for a Substructure).