## 3 Results
### Test Observation and Failure Modes
For failure mode II, the following test phenomena were typically observed: the anchored blind bolts experienced shank rupture; the outward deformation of the steel tube wall was very small, and there was only slight bulging at the bolt holes; and the core concrete in the panel of the joint was also basically intact. Therefore, the bolts became the weakest component. Specimens SJ-3, SJ-4, SJ-5, SJ-6 and SJ-8 failed in this mode, as shown in Figures 8 and 9. As the drift ratio increased, a gap appeared between the end-plate and the steel tube column, but the corresponding gap was significantly smaller than that in the first failure mode, indicating that the gap in failure mode II was mainly due to the elongation of the bolt shank itself, whereas the gap in failure mode I was mainly due to the bolt pull-out after the anchorage failed. For specimens SJ-3, SJ-5, and SJ-6 with thin end-plates, the thin end-plates underwent significant deformation, which was similar to that in SJ-1; when the inner row of blind bolts in the tension zone were ruptured, the transverse weld fractured at the interface between the end-plate near the outer bolts and the steel beam, as shown in Figure 8d. The outward deformation of the steel tube wall in specimen SJ-5 was slightly larger than that in SJ-3, as shown in Figure 8e,f. Local buckling was observed at the root of the beam compression flange in specimen SJ-6 with a weak beam. For specimens SJ-4 and SJ-8 with thick end-plates or end-plates reinforced by stiffeners, only slight end-plate deformation was observed, similar to that of SJ-2; the outer row of blind bolts ruptured, and there was no welding fracture, as shown in Figure 9. Because stiffeners were used to strengthen the end-plate, the end-plate deformation of specimen SJ-8 was notably different from that of SJ-6, and the plastic hinge of the steel beam shifted significantly outwards. Moreover, the bolts of specimens SJ-3, SJ-5, and SJ-6 fractured at a larger drift ratio, indicating that the use of the thinner end-plate and weaker steel beam had an improved effect on the deformation capacity. Figure 8: _Cont._  
The bolt failures in specimens SJ-3 and SJ-4 are compared in Figure 9(a). The bolts in specimen SJ-3 failed in flexure-shear mode, whereas those in SJ-4 mainly failed in tension mode. The concrete exposed by cutting open the column is shown in Figure 9(b). The concrete in the panel of specimen SJ-3 was basically intact except for local crushing around the expansive sleeve, whose surrounding concrete was likely to experience local cracking under tension. The anchored bolts were not loosened, meaning that the anchorage did not fail and that the concrete could effectively restrain the blind bolt from pulling out. The concrete damage in specimen SJ-4 was similar to that in SJ-3. For specimen SJ-5, some individual anchor bolts were slightly loosened, and the surface concrete was nearly completely crushed, indicating the local failure of the anchorage. For failure mode III, the following test phenomena were typically observed: the steel beam exhibited significant local buckling; there was basically no deformation in the end-plate, and the gap between the  
Figure 8: Failure mode II (specimens with a weak end-plate). (**a**) SJ-3; (**b**) SJ-5; (**c**) SJ-6; (**d**) Welding fracture in specimen SJ-3; (**e**) Column wall in specimen SJ-3; (**f**) Column wall in specimen SJ-5. Figure 10: Internal damage of failure mode II. (**a**) Bolt fracture; (**b**) Core concrete. Figure 9: Failure mode II (specimens with a strong end-plate). (**a**) SJ-4; (**b**) SJ-8. end-plate and the column flange was especially small; no significant outward deformation of the steel tube wall was observed, and the blind bolts did not rupture; and the core concrete in the panel was also basically intact. Therefore, the steel beam became the weakest component.