A non-linear model for analysis and design of slender reinforced-concrete columns

The purpose of this paper is to present a non-linear model for analysis and design of slender reinforced-concrete columns subjected to uniaxial and biaxial bending. This model considers both material and geometric non-linearities, as well as creep effects. The structural analysis is performed by the finite-element method associated with an iterative process to solve the system of non-linear equations. The column may have an arbitrary polygonal cross-section, including openings. Green's theorem is used to perform the integration at the level of the cross-sections, which is greatly simplified with the use of a new parabola-rectangle diagram proposed for concrete in compression. This new diagram provides the correct value of the tangent modulus of elasticity of concrete, allowing its use for non-linear analysis of slender columns. By changing the strain value corresponding to the maximum stress, it is possible to use a single stress-strain diagram for displacement calculation and rupture verification, which facilitates the design of slender columns. The accuracy of the method is demonstrated through the analysis of several columns tested experimentally by other authors.