## 2 Low-Cycle Reversed Loading Test
### Test Phenomenon Comparison  
The first comparison is made in terms of the development of column cracks. The number and distribution of cracks on the concrete surface of the PRC tube column specimen are much larger than those of the PHC tube column specimen. The number of cracks appearing on the surface for the PRC tube column specimen was about 27, while about 12 for the PHC tube column specimen. The farthest crack appearing on the surface for the PRC tube column specimen was about 140 cm from the mid-span, while about 70 cm for the PHC tube column specimen. Differently, The BFRPC composite column specimen is difficult to observe the cracks of internal concrete directly due to the wrapping of continuous basalt fiber. The FRP tube needs to be dissected to observe the crack development in the internal concrete of the column specimen, as shown in Figure 9. The BFRPC composite column specimen formed a crack with the width of 3 cm in the mid-span, and the steel bars were exposed. It indicates that the concrete has completely lost its bearing capacity in the later loading stage. The cracks produced in the BFRPC-combined column specimen show that the FRP tube with the wall thickness of 25 mm can withstand the load even when the steel bar and concrete completely lose their bearing capacity, indicating the excellent mechanical properties of the CBF material.  
The second comparison is made in terms of the mid-span displacement. The mid-span displacements of PHC and PRC tube column specimens at failure are 23.21 mm and 81.76 mm, respectively, with the bearing capacity of 118.77 kN and 169.59 kN, respectively. The mid-span displacement of the BFRPC composite column specimen at failure is 140 mm, with the bearing capacity of 592.07 kN. It indicates that the configuration of ordinary steel bars can increase the ductility and ultimate bearing capacity of the column to a certain extent, and the employment of the FRP tube will increase that more significantly.  
The third comparison is made in terms of the failure mechanism for column specimens. The bearing capacity of the PHC and PRC tube column specimens decreases suddenly due to the fracture of the steel bars. Differently, the bearing capacity of the BFRPC composite  
Figure 8: The test phenomenon of the BFRPC composite column specimen.  
Figure 9: The crack development in the internal concrete of the BFRPC composite column specimen: (**a**) Overall view of cracks; (**b**) crack in the mid-span.  
column specimen decreases due to the splitting of the FRP tube in the mid-span. In the initial loading stage, the external loads of all specimens are borne by their column concrete, while the internal steel bars are temporarily unstressed. With load increase, the prestressed steel bars in the PHC and PRC tube column specimens begin to bear the load, while the load of the BFRPC composite column specimen is dissipated by both the ordinary steel bars and FRP tube. With the further increase of load, the prestressed steel bars in the PHC tube column specimen reach the ultimate bearing capacity and break, resulting in the destruction of the column specimen. At this time, the ordinary steel bars in the PRC tube column specimen begin to bear the load together with the prestressed steel bars, and the FRP tube in the BFRPC composite column specimen begins to play a major role in bearing the load. At the end of loading, the steel bars in the PRC tube column specimen break, resulting in the specimen to break and lose its bearing capacity. Although the steel bars in the FPRC composite column specimen yield and the concrete crack, the FRP tube can still bear most of the loads until the mid-span CBF material reaches the ultimate bearing capacity and splits, thus causing the specimen to fail.