Full-scale cyclic testing of slender RC columns bent in double curvature under high axial load

The development of modern tall and irregular buildings has seen increased slenderness and axial force in columns that seriously jeopardize the seismic safety of the structures. Due to the restrictions of the testing facilities, existing experimental studies on slender RC columns under highaxial force are limited and primarily based on small cross-section specimens bent in single curvature and loaded monotonically. However, due to the size effects, test results from small-scale and monotonic loading experiments may not sufficiently reflect the realistic seismic behavior of double curvature RC columns in full-scale buildings. Furthermore, the applied vertical load in typical single curvature tests could not maintain constant and may reduce significantly upon large deflection. Hence, this study aimed to provide new and critical insights into the seismic performances of full-scale slender and large cross-section RC columns with various transverse reinforcement designs under a constant high axial load of up to 50% of the axial capacity. The fullscale specimens were tested in a double-curvature configuration under lateral displacement reversals and high axial loads. The tested slender columns experienced increasingly significant P-Delta moment magnification effects with further drifts after yielding, imposing greater loading demand on the sections and destabilizing the columns after the peak loads. The robustly anchored transverse reinforcement not only improved the typical seismic performance indicators, including strength retention and drift capacity, but also reduced the P-Delta moment magnification experienced by slender columns, thus enhancing the stability index. Furthermore, the plastic hinge lengths increased in slender columns under high axial load due to P-Delta moment magnification. Lastly, suitable methods for assessing the behavior of slender RC columns based on design codes or existing analytical models are recommended.