public void GetStructuralType(FamilyInstance familyInstance)
{
    string message = "";
    switch (familyInstance.StructuralType)
    {
        case StructuralType.Beam:
            message = "FamilyInstance is a beam.";
            break;
        case StructuralType.Brace:
            message = "FamilyInstance is a brace.";
            break;
        case StructuralType.Column:
            message = "FamilyInstance is a column.";
            break;
        case StructuralType.Footing:
            message = "FamilyInstance is a footing.";
            break;
        default:
            message = "FamilyInstance is non-structural or unknown framing.";
            break;
    }

    TaskDialog.Show("Revit",message);
}

Public Sub GetStructuralType(familyInstance As FamilyInstance)
    Dim message As String = ""
    Select Case familyInstance.StructuralType
        Case StructuralType.Beam
            message = "FamilyInstance is a beam."
            Exit Select
        Case StructuralType.Brace
            message = "FamilyInstance is a brace."
            Exit Select
        Case StructuralType.Column
            message = "FamilyInstance is a column."
            Exit Select
        Case StructuralType.Footing
            message = "FamilyInstance is a footing."
            Exit Select
        Case Else
            message = "FamilyInstance is non-structural or unknown framing."
            Exit Select
    End Select

    TaskDialog.Show("Revit", message)
End Sub