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Civil-Comp Proceedings
ISSN 1759-3433
CCP: 89
PROCEEDINGS OF THE SIXTH INTERNATIONAL CONFERENCE ON ENGINEERING COMPUTATIONAL TECHNOLOGY
Edited by: M. Papadrakakis and B.H.V. Topping
Paper 170

Finite Element Analysis of Conical Shell Foundations

A.A. Al-Azzawi, R.J. Aziz and A.A. Al-Ani

Department of Civil Engineering, Nahrain University, Iraq

Full Bibliographic Reference for this paper
A.A. Al-Azzawi, R.J. Aziz, A.A. Al-Ani, "Finite Element Analysis of Conical Shell Foundations", in M. Papadrakakis, B.H.V. Topping, (Editors), "Proceedings of the Sixth International Conference on Engineering Computational Technology", Civil-Comp Press, Stirlingshire, UK, Paper 170, 2008. doi:10.4203/ccp.89.170
Keywords: analysis, conical, finite element, elastic foundation, shells, Winkler model.

Summary
In this paper, conical shell foundations are investigated. The two components of the interacting system; the soil and the shell foundation, are modelled using the finite element method. In this study, eight-node isoparametric degenerated shell element with five degrees of freedom at each node is used. The soil-structure interaction between the shell elements and the supporting medium are modelled by representing the soil medium by certain analytical equivalent such as the Winkler model with both normal compressional and tangential frictional resistances. This model assumes the soil medium to consist of a system of independent spring elements. The displacement occurs immediately under the loaded area and outside this region; the displacement is zero. The problem is analysed using the computer program named SFAP (Shell Foundation Analysis Program) [1], which was developed from a program named PLAST [2] by adding subroutines of foundation properties and stiffnesses in order to be capable of solving different types of shell foundations. Comparison between the results obtained by the present analysis and those obtained by other investigations are made. The present analysis shows satisfactory results when compared with those obtained by other studies The percentage difference in results (for the vertical displacement) between the present study and Kurian study in 1993 [3] is about 0.077%. The percentage difference in results between the present study and Hassan study in 2002 [4] is about 2.439%. Parametric studies have been carried out to investigate the effect of some important parameters on the behaviour of shell foundations. Three parameters are considered which are: semi-vertical angle, conical shell thickness and vertical subgrade reaction.

The major conclusions obtained from the study of the conical shell foundation are:

  • If the semi vertical angle of conical shell foundations increases from 45° to 55°, the vertical displacement increases by 89.93% at the center of the conical shell while it decreases by 63.28% at the footing edges. Also, the meridonal membrane stresses NS increases by 35.11% at the conical shell foundation. And the meridonal bending moment MS increases by 57.149% at the conical shell foundation.

  • If the thickness of the conical shell foundations increases from 0.002 m to 0.003 m, the vertical displacement decreases by 29.43% at the center of the conical shell foundation. But the meridonal membrane stresses (NS) increases by 1.09% at the conical shell foundation. And the meridonal bending moment MS increases by 53.144% at the conical shell foundation.

  • If the vertical subgrade reaction KZ increases from 162,500 kN/m3 to 325,000 kN/m3, the vertical displacement decreases by 17.29% at the conical shell foundation. And the meridonal membrane stresses NS decreases by 9.54% at the conical shell foundation. But the meridonal bending moment MS increases by 18.45% at the conical shell foundation.

References
1
A.A. Al-Azzawi, "Finite Element Analysis of Thin and Thick Reinforced Concrete Shell Foundations", Ph.D. Thesis, Faculty of Engineering, Baghdad University, Baghdad, Iraq, 2000.
2
H.C. Huang, "Static and Dynamic Analysis of Plates and Shells", Springer-Verlag, London, U.K., 1989.
3
N.P. Kurian, "Performance of Shell Foundation on Soft Soil", Proceedings of the International Conference on Soft Soil Engineering, Guangzhou, 383-392, November 1993.
4
S.A. Hassan, "Finite Element Analysis of Shell Footings", M.Sc. Thesis, College of Engineering, Al-Mustansiria University, Baghdad, Iraq, 2002.

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