**Reliability assessment of reinforced concrete rectangular columns subjected to biaxial bending using the load contour method**

**Ji Hyeon Kim and Hae Sung Lee**

**ABSTRACT**

This paper presents the reliability assessment of reinforced concrete (RC) columns subjected to biaxial bending using the advanced first-order second-moment reliability method. The strength of an RC column under the biaxial bending condition is estimated by the load contour, which is utilized as the limit state function in the reliability analysis. The random variables include the strength parameters of the RC columns, the load parameters and the eccentricities of axial force. The Hasofer-Lind-Rackwitz-Fiessler algorithm with the gradient projection method is employed to calculate the most probable failure point and the reliability index. The surface exponents of the load contours are determined by the values presented by Bresler. The cubic spline interpolation is adopted to construct P-M interaction diagrams for uniaxial bending about the principal axes that are required in the load contour method. The sensitivities of the limit state function are calculated through the direct differentiation method. The reliability indices are calculated for a rectangular section and a square section. The effect of the surface exponent on the results of the reliability analysis is investigated for the rectangular section, and the uncertainty of the eccentricity of axial force is considered in the example for the square section.

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