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To analyze the reliability of slender columns subjected to axial force and uniaxial bending moment, with a slenderness index between 100 and 140, 216 columns were modeled. The square cross-section was adopted, with three different configurations for longitudinal reinforcement. In the calculation, the general method with the linear creep theory was applied. Several factors were varied: slenderness index, reinforcement ratio, steel bars arrangement, compressive strength of concrete, and first-order relative eccentricity. For analysis purposes, the Monte Carlo method was adopted, followed by the First Order Reliability Method (FORM). Considering the results obtained, it was observed that the reliability index is usually higher for lower reinforcement ratios and varies according to the configuration of the cross-section. Resumo Buscando-se analisar a confiabilidade de pilares esbeltos submetidos a flexo-compressão normal, com índice de esbeltez entre 100 e 140, realizou-se a modelagem de 216 elementos. Adotou-se a seção transversal quadrada, com três configurações distintas para armadura longitudinal. No cálculo, aplicou-se o método geral com a teoria linear da fluência. Efetuou-se a variação de diversos fatores, incluindo-se: índice de esbeltez, taxa de armadura, disposição das barras de aço, resistência do concreto e excentricidade relativa de primeira ordem. Para fins de análise, adotou-se o método de Monte Carlo seguido pelo FORM. Considerando-se os resultados obtidos, observou-se que o índice de confiabilidade comumente é maior para taxas de armadura inferiores e sofre variação de acordo com a configuração da seção transversal.

A mechanical model was developed to evaluate the reliability of very slender columns subject to creep, employing the nonlinear moment-curvature relationship. Second-order effects were considered by the finite difference method. Numerical tests were carried out on 432 columns with a slenderness index between 100 and 200. The general nonlinear method was adopted to determine the design load, applying the displacement of the stress-strain diagram for consideration of creep. The reliability index was calculated using the Monte Carlo method and the First Order Reliability Method. Among the results obtained, it was observed that it is important to review the safety criterion of the Brazilian Standard NBR 6118 about the very slender columns (90 < λ ≤ 200) by performing the calibration of the additional coefficient γn1. In addition, it was observed that an increase in the reinforcement ratio commonly produces a reduction in the reliability index; an increase in the first-order relative eccentricity promotes a decrease in reliability, among other evaluated factors.