Vibrations of foundations

[Extract] Foundations that support vibrating equipment experience rigid body displacements. The cyclic displacement of a foundation can have six possible modes (Figure 11.1): 1. Translation in the vertical direction 2. Translation in the longitudinal direction 3. Translation in the lateral direction 4. Rotation about the vertical axis (yawing) 5. Rotation about the longitudinal axis (rocking) 6. Rotation about the lateral axis (pitching) In this chapter, the fundamentals of the vibration of foundations in various modes supported on an elastic medium will be developed. The elastic medium that supports the foundation is considered to be homogeneous and isotropic. In general, the behavior of soils departs considerably from that of an elastic material. Only at low strain levels may soils be considered a reasonable approximation of an elastic material