Effect of Soil-Foundation Interaction on the Dynamic Response of a Four-Cylinder Compressor Foundation

The dynamic response of a machine-foundation system depends on several factors, such as (1) the soil dynamic properties, (2) geometric properties of the foundation, (3) amplitude of the applied dynamic loads, and (4) frequency of the dynamic excitation force. The main goal in machine foundation design is to keep the foundation response within a specific limit to enable the satisfactory operation of the machine. If the foundation response exceeds this limit, the foundation will adversely affect the performance of the machine and may damage the machine internals or cause it to function improperly. Furthermore, the excessive vibrations impose additional stresses on the machine resulting in increased unbalanced loading, and thus, to increased dynamic loads on the soil-foundation system. This paper presents the results of the dynamic analysis of a four-cylinder compressor foundation. The original design of the foundation was performed in the early 1960s and ignored the effect of the soil on the response of the foundation system; therefore, the foundation has been suffering from excessive loading. The foundation block supported a four-cylinder compressor, suction and discharge bottles, and a crank and driving motor with a total weight of approximately 974 kN (219 kips). The results of a three-dimensional (3D) finite-element model of a soil-foundation system was used to determine the dynamic response of the soil-foundation system and to assess the foundation response under applied dynamic loading resulting from the compressor crank. The dynamic analysis was performed by performing (1) eigenvalue analysis of the foundation block, considering the effect of the soil-foundation interaction, to determine the soil-foundation natural frequencies and modal participation factors and (2) a forced response of the foundation under an unbalanced crankshaft load applied to determine the forced response amplitude of the soil-foundation system.