A Study on the Design and Advantage of Conical Type Shell Foundation Using Analytical and Fem

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Addis Ababa University


This thesis introduces shell foundations in general and conical type shell foundation in particular as an alternative to the conventional plain foundation. The different types of shells that may be employed in foundations are introduced with their geometry and applications under different situations. Shell foundations can be used as combined or isolated footing. The simplest form of shell appropriate for isolated footing is conical shells. Conical shells are employed as an alternative to plain circular footings. The design of conical shell foundation is based on membrane theory in order to determine membrane stresses, and ultimate strength theory to obtain the ultimate load which enables to compute the load factors involved in the design. A design example is provided and comparison is made with plain circular footing. The result clearly indicates that conical shells save more material than do so plain circular footings. A finite element analysis is carried out using the finite element software PLAXIS for different soil properties and footing size. The analysis was performed for conical shells and plain circular footing in order to compare the results. The finite element analysis results prove that conical shells have high load carrying capacity than circular footing under same soil properties. Shell foundations need smaller quantities of material than the conventional plain foundations. In a country like Ethiopia where material to labor cost ratio is high, shell foundations may be used as an economic alternative.



Civil Engineering