ACI 313-16 Design Specifcation for Concrete Silos and Stacking Tubes for Storing Granular Materials (ACI 313-16) and Commentary

ACI 313-16 Design Specifcation for Concrete Silos and Stacking Tubes for Storing Granular Materials (ACI 313-16) and Commentary. R1.1—Scope Silo failures have alerted licensed design professionals to the inadequacy of designing silos for only static pres- sures due to stored material at rest. Those failures motivated researchers to study the variations of pressures and fow of materials. Research has established that pressures during withdrawal can be signifcantly higher (Turitzin 1963; Pieper and Wenzel 1964; Reimbert and Reimbert 1980, 1987) or signifcantly lower than those present when the material is at rest. The excess (above static pressure) is called overpres- sure, and the shortfall is called underpressure. One of the causes of overpressure is the switch from active to passive conditions that occurs during material withdrawal (Jenike et al. 1972). Underpressures can occur at a fow channel, and overpressures can occur away from the fow channel at the same level (Colijn and Peschl 1981; Homes 1972; Bernache 1968). Underpressures concurrent with overpressures cause circumferential bending in the silo wall. Impact during flling can cause the total pressure to exceed the static pressure. Whereas overpressures and underpressures are generally important in deeper silos, impact loading is usually signifcant for shallow bins (bunkers) in which large volumes of material are dumped suddenly. Some stored granular materials have suffcient cohesion and unconfned compressive strength to form large arches or cavities during discharge. The collapse of these arches and cavities can develop signifcant impact loads when the material above strikes the wall or foor. This docu- ment does not provide methods for calculation of such loads. The probability of forming arches and cavities can be reduced by using hopper and discharge equipment designs that refect results from fowability testing of the stored material. Overpressure, underpressure, or impact should be consid- ered in the structural design of silos if present. R1.3—Regulations/inspections Investigations of silo damage and deterioration failures frequently reveal omitted or mislocated reinforcement, inad- equate or misaligned reinforcement splices, and inadequate reinforcement cover. The quality and performance of slipformed concrete silo structures depend on construction workmanship. The best materials and design will not be effective unless the construction is in accordance with project documents. For example, during slipform operations, the proper placement of reinforcement is a critical task. In addition, horizontal lifts, buckled jackrods, and concrete delaminations can occur if the concrete sets too rapidly, the slipform is improp- erly battered, or jackrods are overloaded....