REPRESENTATION OF EQUIVALENT -SOIL SPRING UNDER A RAFT FOUNDATION

Abstract

The soil-structure interaction is a very important phenomenon which"upon the mechanism of energy exchange between the soil and the structure and its primary influence on the building is to modify the natural period of vibration and hence the response, An exhaustive review of the literature covering different soil spring formulae given by various investigators has been presented. A study of the effect of soil structure interaction on dynamic response of buildings has been carried out. Four multi-storeyed reinforced concrete buildings of different heights founded on isolated foundations has been investigated for different soil flexibilities. The present study is based of frequency independent soil-springs proposed by various investigators. Springs used are due to Wolf, Gazetas, Bycroft-Panelee, Chakrabar,--ty, Hall, Parmelee and Kudder & Parmelee. The time period of the four structures obtained on the application of the above soil springs have been compared. From the plot, it has been observed that Gazetas spring is the most flexible among the seven springs used in the analysis. Results obtained show that the effect of soil-structure interaction increases with the increase in flexibility of the foundation soil and the height of the building. The effect of soil interaction has been observed to be important and can not be neglected. From the plots . between time period vs. no of storeys using different types of soil spring corresponding to shear wave velocity greater than 400 m/s it is observed that storeys above five have almost same time period so selection of formula above five iii stories does not effect the time period of building. For shear wave velocity less than 400m/s choice of formulae are the most important.