Extensión del modelo interacción flexión-corte a elementos con carga biaxial, modelo E-SFI-3D

Abstract

In this research, a three-dimensional macro-model was developed to capture the shear strength behavior of square and rectangular reinforced concrete columns under biaxial lateral loads, with the aim of evaluating the new design proposal of ACI 318-19 referring to the interaction of shear forces acting on the orthogonal axes. The so-called E-SFI-3D model, by virtue of the Efficient-ShearFlexure-Interaction in three-dimensional space, is based on the E-SFI two-dimensional macro-model but reformulates the material and element to a 3D domain. Reinforced concrete prisms with threedimensional behavior are incorporated using a rotating angle approach and the calibrated expression of the two-dimensional model, to calculate the horizontal normal strain in each orthogonal direction (𝜀�𝑥� and 𝜀�𝑧�), which reduces iterative processes and analysis time.To validate the model, an extensive database of 56 reinforced concrete column tests with a shear failure under cyclic biaxial loading conditions, 41 square and 15 rectangular, reported in the literature was used. The model results are verified against the experimental data in terms of the load-displacement response and the contribution of flexural and shear displacements. Obtaining that the average ratio of the maximum shear strength measured to the calculated for square and rectangular columns are 0.91 and 0.95, the corresponding coefficients of variation are respectively 0.078 and 0.12; indicating an accurate estimate of shear strength by the model. The start of degradation at the point of $0.9\cdo V$ was also compared, achieving an average ratio of the measured to the calculated for the square columns and for the rectangular columns of 1.02 in both cases, with coefficients of variation respectively of 0.32 and 0.4; indicating a greater dispersion to predict this parameter. The model captures the hysteretic response and the shear failure mode of the tests, whose shear strain is controlled by an elasto-plastic dowel action model for the longitudinal steel bars. The research carried out concludes that the results of the normalized biaxial shear strength, both from the experimental tests and from the model, fit the circular interaction curve and validates the methodology proposed by ACI 318-19 to capture the biaxial shear effect through a trilinear curve, providing a simple and conservative method of design by the structural code.