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Wiss, Janney, Elstner Associates, Inc. (WJE) was asked to investigate cracking and spalling of the concrete foundations of a number of liquid storage tanks at an ethanol manufacturing plant located in western Oregon. The plant was new at the time and the cracking and spalling of the foundations occurred immediately after the tanks were put into service. An initial attempt by the plant to repair the foundations failed immediately. WJE was asked to investigate the cause of the cracking and make recommendations for repairs. There were twenty metal liquid storage tanks at the plant ranging in size from 62 feet in diameter and 52 feet in height to 14 feet in diameter and 5-1/2 feet in height. All twenty tanks were constructed on foundations with a 1 in 12 slope. The only attachments of the tanks to the foundations were hold down bolts spaced evenly around the perimeter of the tanks, which were intended to prevent overturning. Although analysis indicated that friction between the base plates and the compacted fill was sufficient to resist sliding of the tanks due to gravity, wind and earthquake forces, it was evident that the tanks were sliding down slope. A study of the thermal expansion and contraction characteristics of the tanks by WJE found that thermal cycling would cause the tanks to migrate down slope. Ultimately, WJE was tasked with determining which of the twenty tanks were at risk of additional damage and determining if (and how) the process could be arrested. This paper discusses the problems with constructing metal storage tanks on sloped base foundations and proposes an innovative method to prevent downward sliding of these types of tanks. |
