Dynamic Response of Pile-Supported Frame Foundations

A theoretical approach is analyzed of the dynamic response of pile-supported frame foundations of turbomachineries to rotor unbalances. The approach includes dynamic interaction of soil, piles, flexible foundation mat, three-dimensional structural frame, flexible rotor, and viscoelastic oil film in journal bearings. The approach employs substructuring, dynamic stiffness method, and finite elements. Shear deformations and material damping are included in the stiffness matrices of the finite elements that are complex and frequency dependent. The stiffness matrix of the element is generalized to incorporate the stiffness and damping of the supporting medium including piles. It was found that soil-structure interaction markedly affects the response of the frame as well as the rotors in the lowest resonant regions. In the vicinity of a high operating speed, soil-structure interaction can be neglected.