a structure used to receive and transfer to the ground the static load from a machine and the dynamic loads imposed during the operation of the machine as a result of imbalances in the moving parts.
Depending on the nature of the dynamic loads imposed, machines may be divided into two groups: those with periodic disturbing forces that produce forced vibrations in the foundations and those with percussive action that cause free vibrations in the foundations; some machines transfer both types of loads to foundations. The first group includes machines with parts that exhibit uniform rotation (turbines and electric motors) or a reciprocating motion (piston compressors and pumps, gang mills, and the like). The second group includes machines having impact-type working members (pile drivers, forging hammers, and molding machines) or components that exhibit nonuniform motion (rolling mills and forging rolls). Machine foundations are classified as monolithic, walled, or frame-type, depending on the structural design. The first two types may be constructed without basements (that is, completely embedded in the earth) or with basements (when it is necessary to install auxiliary equipment under the machines). Frame-type foundations usually have basements.
The materials chosen for machine foundations are mostly concrete and reinforced concrete. Precast and cast-precast foundations are also common in industrial construction practice, including pile foundations with a high grillage. Precast structures are suitable mainly for mounting machines having well-balanced moving parts, such as turbines. Small machines, machine tools, and other equipment are often mounted directly on a concrete floor, with no special foundation; in such cases the floor structure is strengthened with reinforcements. In order to reduce the harmful effect of vibrations, elastic shock absorbers (such as springs and rubber mats) and dampers (vibration-energy absorbers) may be built into the foundation structure. Design calculations for machine foundations must take into account the elastic properties of the ground, the magnitude of the static and dynamic loads from the machine, the design features of the machine, and other factors.
REFERENCESSavinov. O. A. Sovremennye konstruktsii fundamentov pod mashiny i ikh raschet. Leningrad-Moscow, 1964.
Stroitel’nye normy i pravila, part 2, section B, chap. 7. Fundamenty’ mashin s dinamicheskimi nagruzkami. Moscow, 1971.
L. R. STAVNITSER