Experimental and Analytical Study of Seismic Behavior of Special-Shaped Multicell Composite Concrete-Filled Steel Tube Columns

Special-shaped multicell composite concrete-filled steel tube (CFT) columns have been used in several super-high-rise buildings. However, research on special-shaped multicell CFT columns under low cyclic loading remains limited. Thus, seven $1/30$-scaled specimens were designed for a low cyclic loading test. The parameters are four cross-section structures (i.e., the basic type, angle steel reinforced type, circular steel tube reinforced type, and simplified type) and three loading directions (i.e., the long axis, short axis, and 45°). The failure modes, hysteretic behavior, bearing capacity, ductility, and energy-dissipation capacity were analyzed. The results show that the angle steel and circular steel tube significantly increase the bearing capacity and energy dissipation. The circular steel tube has a better effect than the angle steel. The bearing capacity of the simplified-type specimens decreases but the ductility increases. When the loading direction changes from the long axis to the short axis, the ductility gradually increases, whereas the bearing capacity and energy-dissipation capacity gradually decrease. The optimized models of the fiber-based method (FBM) were proposed to predict the $N\text{-}M$ curves and $F\text{-}\mathit{\Delta }$ curves. The concrete constitutive relationship in the multicell CFT was proposed based on the separation model by analyzing the features of multicell CFT columns and was used in the optimized fiber-based method. The numerical simulation models were established using Abaqus to simulate the $F\text{-}\mathit{\Delta }$ curves for FBM models and test. The calculation results show good consistency with the test.