c dataTable merges a simple instance of two columns into a new column

public static DataTable UniteDataTableColumns(DataTable dt, String newColumnName, string ColumnName1, string ColumnName2)
        {
            // Summary expression 
            string expression = "";                             
            expression = String.Format("{0}+'('+{1}+')'", ColumnName1, ColumnName2);           
            // Add summary column 
            System.Type myDataType = System.Type.GetType("System.String");
            DataColumn dcCol = new DataColumn(newColumnName, myDataType, expression, MappingType.Attribute);
            // Add merged columns 
            dt.Columns.Add(dcCol);
            return dt;
        }