(2016) performed seismic performance tests for 16 rectangular CFST columns with side lengths up to 300 mm; the parameters under investigation included the section length-width ratio, the steel ratio, and the loading direction. With the increased of axial load ratio and section length-width ratio, the ductility of the specimen decreased obviously. [PERSON] and [PERSON] [PERSON] and [PERSON] (2016) performed quasi-static tests for six circular CFST columns with diameters of 324 mm; the axial load ratio ranged from 0.2-0.4, and the effect of the diameter-thickness ratio on the seismic performance of CFST columns was investigated. The test results showed that when the diameter-thickness ratio was larger, the member still had good ductility. [PERSON] [PERSON] (2016) performed seismic performance tests for five circular CFST beam-column specimens with diameters of 152 mm; the axial load ratio was 0.25, and the study focused on the effects of steel tube and concrete bonding strength on the seismic performance of CFST columns. The test results suggested that whether there was bond between steel tube and concrete had no significant effect on bending strength. [PERSON] and [PERSON] (2016) performed quasi-static tests for 16 circular CFST column specimens with diameters of 114 mm to investigate the accumulated damage failure mechanism of a structure; the axial load ratio in the test was 0.3. The experimental results showed that the steel fiber reinforced CFST columns exhibited about 1.5 to 2 times more energy dissipation capacity than the CFST columns. [PERSON] (2016) performed quasi-static tests for three circular CFST column specimens with diameters of 150 mm; the axial load ratio was 0.25. The external steel tubes of some specimens  
Figure 1: Mega columns in practical engineering. (**a**) Concrete-filled steel tubular (CFST) columns; and (**b**) steel reinforced concrete (SRC) columns. were based on super high-strength steel H-SA700. The test results suggested that, compared to conventional steel, structures with super high-strength steel had superior bearing capacity and delayed external steel tube local buckling time. To investigate the effect of mixing rubber particles in concrete on the seismic performance of a circular CFST column, [PERSON] [11] performed quasi-static tests for 20 circular CFST columns with diameters of 141 mm or 219 mm; the axial load ratio was set to 0.1 or 0.2. The test results showed that adding 5% rubber particles into the concrete had the least effect on the strength and could significantly improve the ductility of the members. [PERSON] [12] performed seismic performance tests for 10 stainless CFST columns with diameters of 120 mm. The test results suggested that, compared to low carbon steel specimens, stainless CFST columns had superior ductility, deformation capability and residual strength. Six square hybrid double-skin tubular columns with side length of 150 mm were tested under combined axial compression and cyclic lateral loading by [PERSON] and [PERSON] [13], the axial load ratio ranged from 0.14-0.42. The results showed that the specimens with thicker inner steel tube had a plumper hysteretic curve. Additionally, the plastic hinge lengths were effected by the axial load level and the size of inner steel tube. [PERSON] and [PERSON] [14,15] performed seismic performance tests for hollow-core FRP-concrete-steel (HC-FCS) columns; the axial load ratio was 0.05. The tests results suggested that the total energy dissipation of the well-confined HC-FCS column was 87% higher than that of the conventional RC. Increasing the steel tube thickness by 100% increased the flexural strength by 62%. [PERSON] and [PERSON] et al. [16,17] proposed hybrid FRP-concrete-steel double-skin tubular columns with a diameter of 152.5 mm, which consist of an inner steel tube and an outer FRP tube. Axial compression and bending experiments were conducted and the test results showed that these members were found to have a very ductile behavior.