PREDICTION OF VERTICAL VIBRATIONS OF FOOTINGS BY MASS-SPRING-DASHPOT MODEL

Abstract

The basic Mass-spring dashpot model has been modified to take into account the relevant factors which have not been taken in the basic model. For a given site the spring constant and damping ratio are functions of the size and mass of footing and exciting moment. However, it has been shown for a given site, the dynamic soil modulus, k_s, is the property of the soil and is independent upon the boundary test conditions. k_s can be evaluated from a single field vibration test.A procedure is given to predict the resonant frequency and peak amplitude for vertical vibrations based upon modified Mass-spring-dashpot model. The new procedure takes care of the influence of the exciting moment on spring constant and damping ratio in terms of dimensionless parameters α, β and γ. The test results of Vicksburg and Eglin as well as Novak's tests results (which represent a spectrum of soil conditions and machine foundations) have been analysed and found that the prediction of resonant frequency and peak amplitude can be successfully carried out by performing a single field vibration test and using the modified Mass-spring-dashpot model.