NASA-LLIS-0231

Abstract

<strong>Description of Driving Event:</strong> <br>During winter operation of a cooling tower that was operating in a standby mode, a large section of the tower collapsed due to an unusual accretion of ice in the central portion of the tower. The dead load of the ice overloaded the structural members and caused the collapse. When the mishap occurred the tower was not running within its design parameters. Valves controlling the minimum water flow to prevent freezing and to inhibit corrosion in the heat exchangers were opened wider than usual to reduce noise because of workmen in the area. An additional pump was also turned on to maintain the required flow. <br>The combination of the increased water flow rate and restricted flow through the pipes returning water to the tower basin created a back pressure sufficient to permit water to flow up the riser pipe and into the tower distribution system. Because the tower was in standby, with no heat load, the water and air temperatures were both low enough to cause the water to freeze. The resulting accumulation of ice created the load that led to the structural failure.