Overview
ABSTRACT
Loading induced compressive stresses, in all or part of structural elements, has the potential to generate structural instability. The latter is especially found in steel structures, adversely effecting the carrying capacity of the structural elements. It can effect structures either within bars, plates or shells. This article, through several studies, provides physical and rational understanding of the instability phenomena where the emphasis is on concepts rather than mathematical development. In the first part, the relationship between equilibrium and stability are introduced, basic phenomena clearly defined, and two types structural instability - by bifurcation and by limit point - are commented on and characterized. Also emphasized is what differentiates a real structural element from that of an ideal structure, to which an ultimate load and an elastic critical buckling load are respectively associated. Other parts of the article are devoted to the phenomenological aspects of buckling phenomena which are likely to occur respectively in bars, plates and shells. Detailed verification aspects according to standards are presented in the sections of the article devoted specifically to these types of structural elements.
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Read the articleAUTHOR
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René MAQUOI: Civil engineer - Professor Emeritus at the University of Liège
INTRODUCTION
The excellent strength and stiffness properties that characterize structural steels explain why metal construction makes extensive use of slender structural elements. A corollary is that structural instability becomes a major concern when designing projects.
Structural instability can affect bar, plate, or shell structures alike. There are many different types of instability, each with its own specific characteristics. Rigorous treatment of these phenomena quickly reaches its limits in terms of mathematical analysis, and most of the practical solutions recommended involve experimentation and numerical tools.
In this file:
The relationship between equilibrium and stability is introduced intuitively, and the basic phenomena of instability are clearly identified for further examination later on.
We discuss and illustrate the two types of elastic instability –: bifurcation instability and limit point instability –, and describe their characteristics and properties.
We emphasize what differentiates the actual structural element, as produced by standard manufacturing methods and therefore subject to imperfections and made of real material, from the ideally perfect structural element made of a material with "theoretical" behavior that is infinitely elastic.
They are associated respectively with the ultimate load, which alone represents the actual load-bearing capacity, and the critical elastic load, which nevertheless plays a decisive role in the assessment of the former.
The following files (including ) deal successively and separately, but always at a conceptual level, with the specific instabilities of bars, plates, and shells. Regulatory aspects are addressed in the files specifically concerned with the structural elements in question.
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Structural instabilities
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References
Standards and norms
- European Committee for Standardization – CEN, Eurocode 3: Design of steel structures – Part 1-1; General rules and rules for buildings. - EN 1993-1-1 - 2005
- European Committee for Standardization – CEN, Eurocode 3: Design of steel structures – Part 1-5; Flat plates. - EN 1993-1-5 - 2005
- European Committee for Standardization – CEN, Eurocode 4: Design of composite steel and concrete structures – Part...
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