Gets the value of SelfWeightCoefficients attribute. This attribute represents the self weight coefficients specify ratios at which loads due to weight of members shall be included in the load case. These loads are not explicitly modeled as instances of IfcStructuralAction. Instead they shall be calculated according to geometry, section, and material of each member. The three components of the self weight vector correspond with the x,y,z directions of the so-called global coordinates, i.e. the directions of the shared ObjectPlacement of all items in an IfcStructuralAnalysisModel. For example, if the object placement defines a z axis which is upright like the IfcProject's world coordinate system, then the self weight coefficients would typically be [0.,0.,-1.] in a load case of dead loads with self weight. The overall coefficient in the inherited attribute Coefficient shall not be applied to SelfWeightCoefficients of the same instance of IfcStructuralLoadCase. It only applies to actions and load groups which are grouped below the load case, not to the load case's computed self weight.