## 3 Results  
The failure modes in the specimens may affect the performance of the connections to a large extent. Moreover, the influence of connection parameters on the performance of the connections may be related to the failure modes. Therefore, it is necessary to observe different failure modes in the specimens. During the initial stage of the test, the six test specimens showed similar experimental behaviors. During loading of the first three drifts, very small gaps were observed between the end-plate and column face, and no obvious deformation appeared in various components; during loading of the later stage, there were mainly two typical failure modes. The comparison of two typical failure modes for different component is presented in Table 3.  
The first failure mode exhibited the following typical phenomena: the anchored blind bolts were partially pulled out; an obvious outward deformation of the tube face was clearly observed, especially around the bolt holes; and severe cracking and fracturing of the core concrete occurred, causing the CFST columns to be the weakest component. Specimens ST-1, ST-2, and ST-5 failed by this failure mode, as shown in Figure 6. With increasing drift ratio, the gap between the column face and the end-plate became increasingly obvious, indicating that the concrete in the panel zone of the column was gradually cracking. During this process, loss of anchorage and bonding from the blind bolts occurred, causing the bolts of the three specimens to pull up and the steel tube around the bolt holes to bulge under the action of the bolt pull-out force. Finally, when the drift ratio reached 10%, the load was stopped due to significant pull-out of the bolt and severe bulging of the tube face. Owing to the thinner end-plate of specimen ST-1, obvious flexural deformation of the end-plate was observed; after the test, the entire end-plate showed plastic deformation, and obvious warpage was observed at both ends. The thick end-plates of specimens ST-2 and ST-5 showed little flexural deformation during loading, rotating as a rigid body. As the steel beams for the three specimens had sufficient flexural resistance and stiffness, there was no obvious deformation in the steel beam. The steel tube was sectioned to explore the failure mechanism of the CFST column, and the exposed core concrete infill was observed. There were extensive concrete cracks and severe local concrete crushing in the panel zone, as presented in Figure 6e. This result implies that anchorage failure occurred in the blind bolts at larger rotations, causing the blind bolts to pull out and the load to decrease rapidly. The second failure mode exhibited the following typical phenomena: the blind bolts failed in shank rupture; no obvious outward deformation of the tube face was observed, and only slight bulging was observed around the bolt holes; and the core concrete in the panel zone basically remained intact. Therefore, the blind bolts became the weakest component. Specimens ST-3, ST-4, and ST-6 failed by this failure mode, as shown in Figure 7. With the increase in the drift ratio, a gap formed between the column face and end-plate, but this gap is remarkably smaller than that formed in the failure mode I. This difference could be explained by the fact that the gap in the second failure mode was caused by the elongation of the internal bolt, while that in the first failure mode was caused by the pull-out of the blind bolts after anchorage failure. The deformation patterns of both the thick and thin end-plates are similar to that observed in the first failure mode. However, the fracturing of the bolts in specimen ST-3 occurred when the drift ratio reached 6%, while the bolts of ST-4 fractured at a drift ratio of 4%, indicating that the decrease in the end-plate thickness improved the deformation capacity of the connections. Under cyclic loading, only specimen ST-6 with a weak beam exhibited local buckling