Finite Element Analysis Using Shell Element - Application to Water Tanks

Abstract

Various forms of shell structure are available for covering large area but as shell is a highly indeterminate structure it involves complex mathematical calculations. Approximate methods like, membrane theory and beam theory are used only for simple geometrical shapes and boundary conditions. Classical methods like, bending theories are used for exact shell analysis. Classical solution involves lengthy mathematical formulation and tedious calculation and is extremely difficult especially for shells of arbitrary shape. Finite element method has become a practical and popular method for all types of structural analysis. Finite element method is very much suited for analysis of shell structure because of its flexibility in accounting for arbitrary geometry, loading and variation in material properties, complex support condition. Circular cylindrical and intze shape tanks are basically three dimensional shell structures. The large cylindrical tanks resting on ground are commonly used in water and sewage treatment plants. Water towers are used for the purpose of holding water at a height sufficient to pressurize a water supply system. Thus ground water tanks and elevated water tanks are one of the essential lifeline public service facilities. The Finite Element Analysis can be used for analysis of such water tanks which consist of shell type structures. An attempt is made in this major project to carry out finite element analysis of water tank problems. The 4 node shell element has been considered for analysis. Ground water tanks and elevated intze tank problems are chosen for study. FEA based software SAP 2000 is used for the analysis of these water tank problems and parametric study is carried out with respect to different geometry, loading and sub base soil conditions. First chapter includes introduction of shell structures i.e. classification of shell structures and different methods for analysis.

Second chapter includes the literature survey. This includes brief review of literature in shell element and various applications of finite element analysis in water tank problems.

The shell element and SAP 2000 software are discussed in Chapter 3. It includes finite element modeling and analysis of some standard benchmark verification problems. Also finite element analysis of wall panels, cylindrical tanks and rectangular tanks subjected to hydrostatic pressure is carried out using SAP 2000 software.

Fourth chapter includes finite element analysis of fluted ground water tank. In ground water tank inverted flutes are incorporated in circular cylindrical shell tanks and FE analysis is carried out. For fluted tank no standard formulae are available. Results shows that use of flutes have reduced hoop tension drastically.

Fifth chapter includes FE analysis of ground water tank with circular cylindrical shell tank having flat base and conical base. The tanks are resting on different sub base soil conditions. To observe the effect of different sub base soil conditions on design forces in water tanks; the finite element modeling and analysis are carried out.

Sixth chapter deals with the two elevated intze shape water tank; one with shaft support staging and another one is trestle supported staging. FE modeling of container, supporting structure, foundation and sub base soil is discussed. The comparison of manual analysis with membrane and shell analysis is carried out. The effect of sub soil condition on analysis result is discussed.

Finally chapter eight includes the summary, conclusion & further scope of work.