Fly Ash Silo Failure: Why Did the Collapse Happen? The Need A new bolted steel storing 9,000 tons of fly ash from the adjacent coal fired power generation station split apart two weeks after it was first filled to capacity. Up to this point, no ash had ever been discharged. Curiously, the silo collapse occurred at night when the silo was being neither filled nor emptied. The Solution During the investigation into this failure, calculations showed that the silo was underdesigned and did not identify or account for a phenomenon called “Thermal Ratcheting” . The walls of outdoor metal silos expand during the day and contract at night as the temperature drops. If there is no discharge taking place and the material inside the silo is free flowing, it will settle as the silo expands. However

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