A shear-flexure interaction model for column elements with biaxial loading

This research develops a 3D macroscopic model to capture the shear and flexural behavior of square and rectangular reinforced concrete columns under biaxial lateral loads. This efficient-shear-flexure-interaction (E-SFI)-BIAXIAL model, based on the E-SFI two-dimensional macro model, reformulates the materials and elements to a 3D domain. Reinforced concrete prisms with three-dimensional behavior are incorporated using a rotating-angle approach and calibrated expression of the two-dimensional model to calculate the horizontal strain in each orthogonal direction (������������ and ������������). This approach reduces the number of iterative processes and analysis time. Model validation employed an extensive database of 56 reinforced concrete column tests with shear failure under cyclic biaxial loading conditions, 41 square and 15 rectangular, as reported in the literature. The validation demonstrated that the model accurately captures the hysteretic response and shear failure mode of the tests. The results are verified against the experimental data regarding the load-displacement response and the contribution of flexural and shear displacements. The model's estimated shear strength agreed well with experimental data, with average ratios of measured to calculated maximum shear strength of 0.91 and 0.95 for square and rectangular columns with coefficients of variation of 0.078 and 0.12, respectively. The onset of strength degradation was also compared, achieving average ratios of the measured to calculated drift for square and rectangular columns of 1.02 in both cases, with coefficients of variation of 0.32 and 0.4, respectively. Furthermore, the normalized biaxial shear strength results from the experimental tests and the model fit the circular interaction curve and validate the proposed ACI 318-19 code provisions to capture the biaxial shear effect through a trilinear curve.