Abstract: To permit constructing flexible belt-rack longitudinal-movement structures of substantial length, not subject to vibration, and inexpensively built, the rack (3) is cast integrally with a slab (2) of plastic concrete. A stiffening rib (33) can be provided in the slab, preferably at the side remote from the movable machine element (7), and preferably formed with a through-bore to attach a tension rod therethrough, so that a plurality of such slabs can be longitudinally connected together. Guide rails (5) are located at the sides of the slab, on which slide bearings (6) are located which, in turn, support a movable carriage, movable along the bed. The carriage carries the drive motor (17) which drives a gear belt (22) for engagement with the rack.