SEISMIC ANALYSIS OF TOWERS INCLUDING FOUNDATION UPLIFT

A seismic analysis procedure including soil-structure interaction and partial foundation uplift: for tower structures is developed. The nonl inear equations of motion are derived with the aid of Lagrange's equat ion. Parametric studies are performed to evaluate the effects of facto rs such as: soil stiffness, ratio of tower height to foundation width, and partial separation of the foundation from the soil. The studies i ndicate that the effects of soil stiffness on a short tower are greate r than on a slender one. The height-width ratio affects the seismic re sponse of the tower significantly, especially for a tower at a rock-li ke location. The allowance of foundation uplift may substantially redu ce the seismic response of moment and foundation rotation in the case of hard soil and a slender tower, or may greatly increase the seismic response of shear in the case of hard soil and a short tower. The stud y concludes that uplift is not always beneficial and its effects could be significant for structures under strong seismic motions.