Standard Practice for Design and Construction of Concrete Silos and Stacking Tubes for Storing Granular Materials (ACI 313-97)

Description

ilo failures have alerted design engineers to the danger ofdesigning silos for only static pressures due to stored mate-rial at rest. Those failures have inspired wide-spreadresearch into the variations of pressures and flow of mate-rials. The research thus far has established beyond doubt thatpressures during withdrawal may be significantly higher1-4 orsignificantly lower than those present when the material is atrest.

The excess (above static pressure) is called “overpres-sure” and the shortfall is called “underpressure.” One of thecauses of overpressure is the switch from active to passiveconditions which occurs during material withdrawal.5 Under-pressures may occur at a flow channel in contact with the walland overpressures may occur away from the flow channel atthe same level.6-8 Underpressures concurrent with overpres-sures cause circumferential bending in the wall.

Impact duringfilling may cause total pressure to exceed the static. Whileoverpressures and underpressures are generally important indeeper silos, impact is usually critical only for shallow ones(bunkers) in which large volumes are dumped suddenly.Obviously, to design with disregard for either overpres-sure, underpressure or impact could be dangerous.