The steel bar that shows column top is wrapped with plastic cloth after winter shutdown, in case winter steel bar suffers snow water to corrode rust, cause 2 times remove rust, increase cost. In addition to adopting self-insulation measures, when the average temperature drops to below 0℃, a furnace is set between each two columns to ensure the overall temperature of the column periphery, and the continuous fire for 14 days, so as to ensure its strength is stable and enhanced.