Add field to table at runtime

procedure TForm1.Button1Click(Sender: TObject);
var
Field: TField;
i: Integer;
begin
Table1.Active:=False;
for i:=0 to Table1.FieldDefs.Count-1 do
Field:=Table1.FieldDefs[i].CreateField(Table1);

Field:=TStringField.Create(Table1);
with Field do
begin
FieldName:='New Field';
Calculated:=True;
DataSet:=Table1;
end;
Table1.Active:=True;
end;