Torsional Vibration of Viscoelastic Foundations

Simple approximate solutions are presented for the steady-state response of rigid circular foundations which are supported at the surface of a linear viscoelastic half space and are excited by a harmonically varying torque. The half space is idealized either as a standard Voigt solid or as a constant hysteretic solid. Comprehensive data are presented and their significance analyzed. It is shown that the principal effects of material damping are to increase the damping capacity of the system and to reduce its natural frequency. The increase in damping and the associated reduction in response may be of considerable practical consequence. Some attention is also given to the response of foundations subjected to transient excitations, and a procedure is recommended for interrelating the responses of systems for the two models of viscoelastic action investigated. It is shown that, provided the parameters of the two viscoelastic models are selected as recommended, the maximum transient responses of the two models are for most practical purposes equal.