Design of foundations subjected to dynamic load can be carried out either by elastic half-space theory or by mass-spring-dashpot analogy. Another simplified method, called analog method has also been proposed. Using this method resonance frequency and resonant amplitude which are the major criteria in design of machine foundations, can be expressed in terms of modified mass ratio knowing appropriate damping factor. In this paper analog solutions in the form of equations (non-dimensional frequency factor vs. modified mass ratio, non-dimensional magnification factor vs. modified mass ratio) are presented for all modes of vibration, viz., vertical, horizontal, rocking and torsional. Finally results obtained by this method are compared with elastic half-space theory which shows good agreement between the two.
