International Journal of Science and Research (IJSR) ISSN (Online): 2319-7064 Index Copernicus Value (2016): 79.57 | Impact Factor (2015): 6.391 Volume 7 Issue 1, January 2018 www.ijsr.net Licensed Under Creative Commons Attribution CC BY Assessment of the Behavior of Conical Shell Footings on Elastic Foundation Rafaa M. Abbas 1 University of Baghdad, College of Engineering, Civil Engineering Department, Baghdad, Iraq Abstract: In this research the interaction of the conical shell footing and the supporting soil taking into account the contact surface characteristics is investigated. The two components of the interacting system are modelled using Abaqus/CAE 6.13 finite element analysis programme. The general characteristics for the contact between shell footing and the supporting soil including; separation, kinetic frictional slip of finite amplitude, arbitrary rotation of the surfaces and pressure-overclosure are accounted for in the finite element model. Moreover, geometric nonlinearity to account for large deformations and displacements due to slip is included. Conical shell footing prototype is analyzed using different finite element discretization approaches for the contact surfaces including tie constraint and tangential friction interaction models. A Comparison study with previous researches reveal that the tangential friction interaction model yield more realistic values for shell response. Generally, traditional Winkler foundation model overestimate maximum shell settlement by about 50% and meridional membrane stresses by about 100%, whereas shell hoop stresses were underestimated by about 70%, especially at the shell edges. The interaction assessment study reveal that conical shells with wide apex angle are susceptible to increased settlement and hoop stresses, whereas conical shells supported on weak (soft) soils are susceptible to large hoop membrane stress at the edges which give rise for edge stiffeners (ring beam). Keywords: Shell Footing, Finite Element Analysis, Elastic Foundation, Winkler foundation, Soil-Foundation Interaction 1. Introduction The term shell is applied to bodies bounded by two curved surfaces, where the distance between the surfaces is small in comparison with other body dimensions [1]. Shells may be curved in one direction in the form of a cylinder, or doubly curved to form a dome or a saddle-shaped surface. Their economy results from their ability to translate the applied loads into "membrane" thrusts and shears acting in the plane of the surface. By this means bending and twisting moments and shears transverse to the surface, are reduced or eliminated. Shell structures support applied external forces efficiently by virtue of their geometrical form, i.e., spatial curvatures; as a result, shells are much stronger and stiffer than other structural forms [1]. Although shells have been enjoying wide and varied use in roofs, they are new comers to the family of structural foundations. It is about six decades only since Felix Candela in 1953 poured his first hypar shell footing on the Mexican soil. The concept of shells is not new in foundations, if one would consider the old inverted arch foundations as belonging to this group. The use of brick arches in foundations has been in practice for a long time in many countries. The twin attributes of a shell that recommend its use in roofs are economy and aesthetics. Since the latter aspect is of no concern in a buried structure like the foundation, here, the aspect of economy which holds the key to the acceptance and use of shells in foundations [2]. There are some common types of shells which are frequently used in foundations. Among the shells, which have come into wider use, the hyperbolic paraboloid (or briefly hypar) shell has been the most important type. Besides its geometric simplicity, resulting from its straight-lines property, the hypar shell has high structural efficiency. The frustum of a cone, as shown in Figure 1, is probably the simplest form in which a shell can be put to use in foundations. While smaller shells of this type can be used as footings for columns, shells of larger dimensions can serve as rafts for tower-shaped structures such as chimneys [2]. Figure 1: Typical conical shell footing. Sectors of spherical shells in the inverted position with ring beam have been used as feasible foundations for cylindrical structures. Folded plates of various shapes can be used as foundations as shown in Figure 2. Figure 2: Folded plate footing. 2. Statement of the problem Conical shells characterized by an infinite radius of curvature for the meridian which is developed by rotating a straight line generator. Moreover, concrete conical shell footing singly ruled surface of revolution have the practical advantage that they may be cast on inclined straight edge core soil as shown in Figure 1. The interaction of such soil- footing system is due to normal and tangential behaviour at the contact surfaces and it is largely influenced by the mechanism of the tangential frictional properties of the Paper ID: ART20179494 DOI: 10.21275/ART20179494 1168