This paper presents a numerical procedure for studying slender reinforced concrete columns subjected to combined axial load and bending that rigorously takes into account their nonlinear material and geometric characteristics [1]. Column design and stability analysis are simultaneously considered. The model applies to constant rectangular cross-section columns with symmetric distribution of the reinforcement.

Initially a minimum allowable area of steel is adopted and the column stability is checked. The finite element method is used for the calculation of displacements, and the material and geometric nonlinearities are taken into account by means of an iterative process [2,3]. When convergence is reached, it means that the column is stable with the smallest possible area of steel and the column has been designed with minimum reinforcement. In cases when the process does not converge, the column stability must be checked with the maximum allowable area of steel. If the convergence of the process is not reached, it means that the column is not stable with the maximum area and the column cannot be designed. On the other hand, if it is found that the column is stable, the average between the minimum and the maximum areas of steel is adopted as a new area and once again the column stability is checked. This procedure is repeated until the column is found to be stable for the smallest area of steel that provides stability.

A computer program was developed from the proposed numerical procedure and its efficiency was verified against available experimental data [4]. The proposed program provided good agreement with experimental data extracted from the current literature, presenting variations in the mechanical reinforcement ratio between 2% and 11.5%. The effects caused by creep are not considered in this phase.

1

S.L. Pires, "Analysis of reinforced concrete columns subjected to axial loads and bending", [in Portuguese], MSc. Thesis, Department of Structures, University of Campinas, Campinas, Brazil, 2006.

2

J.M. Araújo, "Slender reinforced concrete columns - algorithms for analysis and design", [in Portuguese], UFRG, Rio Grande, Brazil, 1993.

3

H.G. Kwak, F.C. Filippou, "Finite element analysis of reinforced concrete structures under monotonic loads", Report no. UCB/SEMM-90/14, University of California, Berkeley, USA, 1990.

4

B.B. Goyal, N. Jackson, "Slender concrete columns under sustained load", Journal of the Structural Division, ASCE, 97(11), 2729-50, 1971.

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