Abstract: A pre-assembled turntable mounting unit for a storage structure. The storage structure is mounted on a foundation having a radial trough extending from the center of the structure to the exterior. A pre-assembled turntable mounting unit is disposed in the inner end of the trough at the center of the storage structure. The turntable mounting unit includes a fixed mounting ring which rests on the upper surface of the foundation bordering the trough and a plurality of angle-shaped roller support brackets are supported on the ring. A turntable, which supports the inner end of a rotatable sweep arm, is mounted for rotation on rollers carried by the roller brackets. By removing the anchor bolts the entire turntable mounting unit can be readily removed from the storage structure. The drive transmission that acts to rotate the sweep arm about its axis is mounted in a pre-established position on a platform suspended in the trough from the turntable mounting ring.