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Civil-Comp Proceedings
ISSN 1759-3433
CCP: 88
PROCEEDINGS OF THE NINTH INTERNATIONAL CONFERENCE ON COMPUTATIONAL STRUCTURES TECHNOLOGY
Edited by: B.H.V. Topping and M. Papadrakakis
Paper 13

Evaluation of the Buckling Critical Load of Bars Subjected to their Self-Weight

A.M. Wahrhaftig, R.M.L.R.F. Brasil and M.A.S. Machado

Department of Structural and Geotechnical Engineering, Polytechnic School, University of São Paulo, Brazil

Full Bibliographic Reference for this paper
A.M. Wahrhaftig, R.M.L.R.F. Brasil, M.A.S. Machado, "Evaluation of the Buckling Critical Load of Bars Subjected to their Self-Weight", in B.H.V. Topping, M. Papadrakakis, (Editors), "Proceedings of the Ninth International Conference on Computational Structures Technology", Civil-Comp Press, Stirlingshire, UK, Paper 13, 2008. doi:10.4203/ccp.88.13
Keywords: critical load, elastic stability, geometric stiffness, finite element method, buckling, self-weight.

Summary
The consideration of the bar self-weight in the buckling critical load problem was first discussed by Euler, who could not obtain a satisfactory solution. This problem was definitely solved by Greenhill in 1881. The main difficulty found by Euler was that the differential equation for the curvature considering a uniformly distributed compressive force is not as simple as the constant coefficients of the differential equation for the normal external force buckling problem [1]. The solution of first case requires either the application of infinite series or the application of approximate methods (e.g. the energy method). Modern procedures utilize matrix linear analyses based on a non-trivial solution by eigenvalues and eigenvectors, and offer numerical solutions easily implemented using a finite element (FE) environment [2]. However, it is important to understand that the stiffness matrix of structures subjected to axial loads is different from the conventional stiffness matrix. Axial loads produce the effect of reducing the stiffness of the structural members [3]. Hence, the buckling critical load determination now requires some of the aspects peculiar to non-linear analysis. That can be conveniently done, for several engineering problems, by the introduction of the geometric stiffness concept [4]. He present work evaluates the critical load of bars exclusively subjected to their self-weight, utilizing Euler's formulation and the finite element method eigenvalue solution via computational analysis.

References
1
Timoshenko S., "Theory of Elastic Stability", McGraw-Hill Book Company Inc, New York and London, 1936.
2
Cook R.D., Plesha D.S.M., Witt R.J., "Concepts and Applications of Finite Element Analysis". John Wiley and Sons, Inc., NJ, USA, 2002.
3
Gambhir M.L., "Stability Analysis and Design of Structures", Patiala Índia, Springer, 2004.
4
Wilson E.L., Habibullah A., "Static and Dynamics Analysis of Multi-Story Buildings, Including P-Delta Effects", Earthquake spectra, Vol.3, No 2., 1987. doi:10.1193/1.1585429

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