The effect of axial load ratio and torsional moment on the flexural capacity of reinforced concrete columns

In our country, which is located in an earthquake zone, a large majority of buildings have been constructed with reinforced concrete load-bearing systems. To ensure that buildings are earthquake-resistant, numerous experimental and analytical studies related to reinforced concrete elements are being conducted, and earthquake regulations are updated as a result of these studies. One of the most important structural elements in buildings is columns. Investigating the behavior of reinforced concrete columns under different effects is crucial for the safety of buildings located in earthquake zones. Approximately one-third of the existing building stock in our country, most of which was built before the year 2000, has torsional irregularities. It has been determined that many buildings experienced torsional collapse during the earthquakes in Kahramanmaraş on February 6, 2023. Examining the behavior of reinforced concrete columns under torsional effects and preparing appropriate strengthening techniques as a result is very important for preventing loss of life and property. In this study, the bending behaviors of 10 reinforced concrete columns under different axial loads and torsional effects were experimentally investigated. The variables of the study include axial load ratio, axial rotation/lateral displacement ratio, and transverse reinforcement spacing. Based on the data obtained from the study, load-displacement, envelope curve, bending moment-curvature, torsional moment-rotation, stiffness, and cumulative energy consumption graphs for the columns were drawn. The damages that occurred in the columns during the experiment were examined, plastic hinge regions were measured, and a new plastic hinge model was proposed based on the variables of the study. Using the obtained data, a new triple interaction model that includes axial load-torsional moment-bending moment for reinforced concrete columns was presented. Both the plastic hinge model and the triple interaction model were discussed in terms of their effectiveness by comparing them with other models in the literature. The plastic rotation values that occurred in the columns were compared with the plastic rotation limit values in TBDY-2018 to evaluate the torsional effect.