The behavior of reinforced concrete columns subjected to axial force and biaxial bending

Abstract

When stress is beyond elastic limit or cracking occurs in a reinforced concrete member subjected to axial force and biaxial bending, curvature about each principal axis of gross section may be influenced by axial force and bending moments about both major and minor principal axes. It is mainly due to the translation and rotation of principal axes of the cross section after cracking. In this study, a numerical method for predicting the behavior of reinforced concrete columns subjected to axial force and biaxial bending is proposed considering curvature localization. To verify the proposed numerical method, a series of tests was also carried out for 16 tied reinforced concrete columns with 100×100 mm square and 200×100 mm rectangular sections under various loading conditions. The boundary conditions at both ends of the column were hinged and eccentricities (40 mm) were equal and of the same directions. The angles between the direction of eccentricity and the major principal axis of gross section were 0°, 30°, 45° for the square section and 0°, 30°, 45°, 60°, 90° for the rectangular section. A comparison between the numerical predictions and the test results shows good agreements in ultimate loads, axial force-lateral deflection relations, and lateral deflection trajectories. It is also found, in this limited investigation, that ACI's moment magnifier method is conservative in both uniaxial and biaxial eccentric loading conditions.