Effects of Soil-Structure Interaction on the Analysis of Cylindrical Tanks

Cylindrical tanks are commonly used in water and sewage treatment plants. These tanks are usually built of cast-in-place concrete with flat or conical bases to facilitate the treatment process. The design codes specify high standards of serviceability and rigid requirements for water tightness and crack control to prevent leakage and corrosion of reinforcing steel. In view of these stringent requirements, special attention is focused on accurately determining the governing design forces to satisfy economic, as well as serviceability, requirements. In transferring liquid or earth pressures into forces acting on the tank wall, the designer can utilize the design coefficients provided by the Portland Cement Association (PCA). The PCA tables consider different conditions for the wall-base joints but do not, however, consider the effects of varying subbase soil conditions or the geometry of the base slab. The purpose of this study is to investigate how different soil conditions and base geometry affect the design forces of cylindrical tanks. A finite element analysis, using shell elements, was employed utilizing the SAP2000 program. The subbase soil is represented by a number of springs with constants reflecting the soil stiffness. Finite element results indicated significant discrepancies in the design forces when compared with those obtained from PCA tables.