Abstract: A storage unit for granular material has a first wall structure extending upwardly from a base to define connected vertical sidewalls of at least one row of first generally cylindrical bins, and a second wall structure extends upwardly from the base to define at least one row of second generally cylindrical bins spaced apart from and parallel to the first bins. A first hopper is mounted adjacent the lower end of each bin to define the respective bottom ends thereof; and a second hopper is mounted on the vertical wall in a spaced apart relationship above the first hopper to define upper and lower bins, the first and second hoppers each having discharge control means aligned with one another. Each hopper has substantially horizontal load-bearing elements mounted in substantially zero hoop-tension relationship with the vertical walls.