Earthquake Response of Ring Foundation in Cohesionless Soil

Ring foundations are commonly adopted to support tall and heavy cylindrical structures such as silos, chimneys, cooling towers, circular storage tanks, and windmills. The construction of these structures in the earthquake-prone region poses a high risk due to the limited knowledge about their behavior under the earthquake loading when supported on a ring type of foundation. The present study focuses on analyzing the response of ring foundations resting on cohesionless soil during the event of an earthquake. A three-dimensional finite element numerical analysis was carried out to study the behavior of the ring foundation-silo system during the event of an earthquake. The variation in ring geometry such that the ratio of inner to the outer radius (R_i/R_o) was 0.2, 0.4, 0.6, and 0.8, soil densification (γ) under loose and dense condition, the height of silo (h) of 15 m (squat silo) and 25 m (slender silo) and the different earthquake loadings were considered to study their effect on peak acceleration and horizontal displacement of ring foundation. The input motions from 1979 El Centro, 2001 Bhuj, and 1989 Loma Prieta earthquake were considered for the dynamic analysis. The results indicated a decrease in the horizontal displacement of the ring foundation with an increase in height of the structure and soil densification. The foundation displacement was irrespective of the ring geometry for squat silo but showed variation with ring geometry for slender silo. The peak acceleration at the base of the ring foundation was observed to be increased with a rise in height of the structure and soil densification.