Experimental Study on the Behavior of Reinforced Concrete Columns Under Torsion-axial Combined Loading

Abstract

The behaviour of columns in irregular structures subjected to seismic effects is significantly influenced by torsional moments arising primarily due to asymmetries in the plan. Torsional moments that occur during earthquakes in irregular buildings have a negative impact on the load-bearing capacity and ductility of columns. Therefore, it is crucial to understand how columns behave when subjected to axial loads and torsional effects in order to ensure safe structural design. Seven column specimens were tested under various axial load ratios. The columns represent residential buildings constructed in earthquake zones prior to 2000 in Turkiye, which do not even meet the seismic code requirements of their construction periods in terms of material properties, longitudinal and transverse reinforcement ratios, and restraint details. This experimental study examined torsional moment capacity, cracking and ultimate rotation values, stiffness loss, ductility and energy dissipation parameters. These were then compared with finite element analyses performed using ABAQUS software. The results reveal that axial load–torsion interaction plays a decisive role in the seismic behaviour of columns, exhibiting a nonlinear character. The findings suggest that there is an optimum axial load range, and that exceeding this range significantly reduces torsional ductility. The study suggests that adequate transverse reinforcement, appropriate detailing and an optimum axial load ratio are crucial for the torsional behaviour of reinforced concrete columns.