Unit weight (not mass) per unit length, for self-weight calculation or quantity survey. 
   Namespace:   Autodesk.Revit.DB.Structure.StructuralSections  
  Assembly:   RevitAPI  (in RevitAPI.dll) Version: 2015.0.0.0 (2015.0.0.0) 
  Since:  2015 
  Namespace:   Autodesk.Revit.DB.Structure.StructuralSections  
  Assembly:   RevitAPI  (in RevitAPI.dll) Version: 2015.0.0.0 (2015.0.0.0) 
  Since:  2015