The delayed collapse of a 42 000 ton capacity RC cement storage silo

A large silo, designed to store 42 000 metric tons of cement powder, was commissioned in 1997 and operated successfully for a period of two years. During this period, all four main compartments of the radially divided ring silo were loaded and reloaded several times to their full capacity of 16 000 tons ( central cylinder) or 7000 tons ( three segmental ring silos). After two years, indications of structural problems caused the silo to be put out of service while its design was reviewed. Six months later, it was decided to fill one of the 7000 ton sub- silos, which then collapsed when emptying was started from full. The current paper reviews the operating history of the silo and its design, and describes strain measurements made during the final filling, before the collapse. It is concluded that the failure was caused by construction defects that had little effect at first, as the silo initially behaved as if uncracked. As cracking progressively developed, the defects had a more and more serious effect, eventually culminating in collapse of the silo.