Techno Press

Steel and Composite Structures   Volume 19, Number 4, October 2015, pages 861-876
Elastic-plastic formulation for concrete encased sections interaction diagram tracing
Ernesto Fenollosa, Enrique Gil, Ivan Cabrera and Jose Vercher

Abstract     [Full Text]
    Composite sections design consists on checking that the point defined by axial load and bending moment keeps included within the surface enclosed by the section interaction curve. Eurocode 4 suggests a method for tracing this diagram based on the plastic stress distribution method. However curves obtained according to this criterion overvalue concrete encased sections bearing capacity, especially when axial force comes with high bending moment values, so a correction factor is required. This article proposes a method for tracing this diagram based on the strain compatibility method. When stresses on the section are integrated by considering the Navier hypothesis, the use of the materials nonlinear constitutive equations provides curves much more adjusted to reality. This process requires the use of rather complex software which might reveal as too complex for practitioners. Preserving the same criteria of an elastic-plastic stress distribution, this article presents alternative expressions to obtain the failure internal forces in five significant points of the interaction diagram having considered five different positions of the neutral axis. These expressions are simply enough for their practical application. Concordance of curves traced strictly relying on these five points with those obtained by computer assisted stress integration considering the strain compatibility method and even with Eurocode 4 weighted curves will be presented for three different cross-sections and two different concrete strengths, revealing very good results.
Key Words
    concrete encased sections; interaction diagrams; Eurocode 4; plastic; elastic-plastic
(1) Ernesto Fenollosa, Enrique Gil, Ivan Cabrera:
Department of Continuum Mechanics and Theory of Structures, Polytechnic University of Valencia, Cno. de Vera s/n 46022 Valencia, Spain;
(2) Jose Vercher:
Department of Architectural Constructions, Polytechnic University of Valencia, Cno. de Vera s/n 46022 Valencia, Spain.

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