Flexible sleeved pile foundations for aseismic design

The feasibility of constructing buildings on horizontally flexible foundations to mitigate the effects of earthquakes is investigated. The flexibility is achieved by inserting a soft spring between the building superstructure and the soil foundation. The use of slender piles enclosed in sleeves is found to permit flexural distortion. The piles are designed by a simple procedure using smoothed response spectra. The performance of building-foundation systems so designed are then studied using histories of actual ground motions. It is shown that the simple design procedure is adequate and that the concept achieves the desired result of greatly reducing seismic forces. The maximum seismic forces on the building may be reduced to a level which is so low that the forces probably do not affect the design of the superstructure. The economic feasibility of the concept is analyzed and it is shown that the additional foundation cost can be justified on the basis of savings in initial superstructure cost and in probable future damage costs.