Axial Load–Bending Moment Interaction Diagram of Double Curvature Slender Columns Exposed to High Temperatures

The behavior of Reinforced Concrete (RC) rectangular, slender columns is examined in this study upon exposure to heat-damage effects and fully confined by Carbon Fiber Reinforced Polymer (CFRP) wraps, where a new interaction diagram is proposed. The Nonlinear Finite Element Analysis (NLFEA) method is adopted to comprehensively understand the behavior of the RC columns, where a validation process takes place, followed by a wide parametric study. The studied parameters include the effect of different temperatures (23 °C (room temperature), 200 °C, 400 °C, 600 °C, and 800 °C) and nine eccentricity-to-height ratios where biaxial moments exist (0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, and 0.8). It has been found that the deformation, toughness, and the axial column’s strength are significantly improved by providing one layer of CFRP sheets for heat-damaged RC columns, while the stiffness behavior is only marginally affected. In addition, increasing the temperature reduces the energy absorption capacity and the ultimate strength of the columns while these are reduced by increasing the loading eccentricity value. However, columns experience a sudden and brittle failure when subjected to combined bending and axial loadings that might be accompanied by steel yielding or buckling of the column’s cross-section. Finally, the interaction diagram between the load and bending actions was constructed by addressing the results of the simulated columns.