Abstract

This paper presents an algebraic approach that unifies both the elastic and limit theories of static structural analysis. This approach reveals several previously unpublished improvements, which are based on several dualities in the mathematical description. Firstly, we show a novel duality between the solutions to two different problems: the elastic solution to the internal forces of an externally loaded structure, and the nodal displacements induced by prestressing in one or several elements of the same structure. This duality is proven and discussed. The application of this solution to the limit state analysis is very productive, and includes the determination of the ductility requirements necessary to achieve full plastic behaviour, and the assessment of the prestress needed to limit or eliminate such requirements. The unified framework also allows to obtain the elasto-plastic deformed state at the beginning of the plastic structural collapse. We have also detailed the theoretical duality between two classes of structures—hyperstatic and hypostatic—which was derived from the linear algebra principles that define these solutions. Finally, we studied and exposed the dimensionality reduction of structural problems given by the singular value decomposition and the eigenvalues problem. An illustrative example that clearly illustrates all these points is provided.

Highlights

  • Different theoretical approaches to structural analysis allow engineers to model and interpret the behaviour of structures in different contexts and fields of application

  • We demonstrate the ability of eigenvalue and single value decomposition (SVD) problems to solve the elasto-plastic state reached by the structures at the beginning of a full plastic collapse when applied to the compatibility conditions

  • N 1⁄4 N, and where no internal mechanisms are exhibited. It does possess r = n − N redundant internal forces that cannot be solved via the N equilibrium equations F 1⁄4 BTf, which is the set of equations for which the solution differs in fd, depending on whether plastic or elastic material conditions are applied

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Summary

Introduction

Different theoretical approaches to structural analysis allow engineers to model and interpret the behaviour of structures in different contexts and fields of application. This paper aims to present a unified algebraic review of static analysis in order to show, prove and use several dualities that exist within the structural theory. This methodology provides new insights into the established theories. In the process of proving this relationship, the self-stress state spaces are deduced and subsequently analysed. These results can be used to compute the ductility requirements necessary to achieve a full plastic structural response. We present several illustrative examples of the previous theoretical concepts and the conclusions (§§5 and 6)

The classical theories of elastic and limit analysis
The elastic solution
The plastic or limit analysis
Dualities in classical theories
Some interesting scalars
Displacements induced by prestressing
The unloaded prestressed state as a self-stressed state
The integrated force method
The classification of structures by their static properties
The singular values decomposition of compatibility conditions
The load mode eigenvalue problem
Dimensionality or noise reduction in structural models
Applicability of the dualities and their related techniques
Geometry and basic variables
Compatibility and equilibrium equations
Constitutive or material equations
Elastic solution
Limit solution
Ductility requirements
Global limit conditions
Diagonalization of the stiffness matrix
Conclusion
Full Text
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