## 3 Results  
### Test Observation and Failure Modes  
In the initial stage of testing, the eight specimens behaved similarly, during which a slight gap appeared between the end-plate and the column wall, and the specimens were not significantly deformed. Under subsequent loading, the deformation process and the failure mode were related to the steel tube wall thickness, end-plate thickness, local strengthening connection method, beam section size, anchorage method and stiffeners. There were three main types of failure modes, as shown in Table 3.  
For failure mode I, the following test phenomena were typically observed: the anchored blind bolt was partially pulled out; the steel tube wall underwent significant yielding, and the steel tube  
Figure 6: Arrangement of LVDTs for specimens (units: mm). (**a**) SJ-1 through SJ-5; (**b**) SJ-6 through SJ-8. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Component** & **Failure Mode I** & **Failure Mode II** & **Failure Mode III (Specimen** \\  & **(Specimen SJ-1 and SJ-2)** & **(Specimen SJ-3 –SJ-6, SJ-8)** & **SJ-7)** \\ \hline Anchored blind bolt & Partial pull-out & Bolt rupture & Intact \\ Tube wall & Bulging deformation & Slight bulging at the bolt holes & Slight bulging at the bolt holes \\ Concrete in the panel & Severely damaged & Local concrete crush & Local concrete crush \\ Steel beam & No significant plastic & No significant plastic hinge of the \\ hinge of the steel beam & hinge of the steel beam & the steel beam except SJ-8 & steel beam \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Representative failure modes of the connections. wall had remarkable bulging deformation, especially at the bolt holes; and the concrete in the panel of the joint was severely damaged. Therefore, the CFST column became the weakest component. Specimens SJ-1 and SJ-2 exhibited this failure mode, as shown in Figure 7a-f. As the drift ratio increased, a significant gap appeared between the end-plate and the steel tube wall, indicating that the concrete in the panel of these specimens gradually cracked and was damaged; the anchorage and bond from the blind bolts failed during this time. Thus, the bolts were gradually pulled out, and the steel tube wall at the bolt holes gradually bulged. The thin end-plates in the tension zone of specimen SJ-1 exhibited significant flexural deformation, resulting in a relatively large gap between the adjacent bolts around the flanges. Eventually, the weld between the beam flange and end-plate fractured, and then the loading stopped. However, no obvious flexural deformation was observed for the thick end-plate in specimen SJ-2, which rotated as a rigid body. Finally, a wedge-shaped gap was formed. For specimen SJ-2, the outward deformation of the column flange was more significant than that in specimen SJ-1, and the outward deformation outside the panel was also obvious, which was not observed in specimen SJ-1. The steel tube wall was cut open to observe the failure mechanism of the CFST column. As shown in Figure 7f, severe local concrete crushing and widespread concrete cracks were observed in the panel zone of the column, showing a significant cone-shaped failure; thus, the damage situation was more serious in specimen SJ-1 than in  
Figure 7: Failure mode I. (**a**) SJ-1; (**b**) SJ-2; (**c**) welding fracture in specimen SJ-1; (**d**) column wall in specimen SJ-1; (**e**) column wall in specimen SJ-2; (**f**) core concrete. specimen SJ-2. For specimen SJ-1, the anchored bolts were notably loosened, indicating anchorage failure. However, the mechanical anchorage of the nut prevented the bolt from being completely pulled out. For specimen SJ-2, the concrete infill had been completely damaged, and the bolts were completely pulled out.