Keywords: numerical modelling of columns, nonlinear finite element, ATENA 2D software, slender columns.

This paper describes the process followed in the calibration of a numerical model that makes it possible to reproduce the structural behaviour of concrete slender columns under constant axial load and monotonic bending. In the numerical modelling, the nonlinear analysis software ATENA 2D, version v3, developed by Cervenka Consulting, has been used. This program was developed for the nonlinear analysis of reinforced concrete structures using the finite element method.

The evaluation of the approximation has been achieved by comparing the experimental and numerical results of the load-displacement relationship. The numerical results show a satisfactory approximation to the results of forty experimental tests on normal strength and high strength concrete slender columns carried out in the laboratory of the ICITECH, the Institute of Research on Concrete Science and Technology at the Universidad Politécnica de Valencia, Spain.

The most influential factors regarding the calibration of the numerical model are presented, such as:

1. In the SBETA model for concrete used in the ATENA software, the fracture energy and the softening branch of the stress-strain diagram of concrete.
2. The effect of concrete confinement for those columns with a high transversal reinforcement ratio and, although in ATENA 2D the effect of confinement is not considered in a direct way, it has been introduced replacing the values of concrete strength and the strain at peak of concrete stress-strain diagram by the ones calculated by means of a constitutive model for confined concrete.
3. The effect of adherence between the longitudinal bars and the concrete. For that purpose one of the adherence models available in ATENA 2D was implemented directly.

The paper is part of a more comprehensive investigation dealing with the study of deformation capacity of normal and high strength concrete slender columns. The calibrated model presented in it has actually been used to carry out further research, which is broader in scope, including the parametric study of the factors having the strongest influence on the deformation capacity and ductility of normal and high strength concrete slender columns, such as: compressive strength of concrete, axial load level, geometrical slenderness, longitudinal reinforcement ratio and transversal reinforcement ratio.

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