## 3 Experimental Results and Discussions  
### Damage Evolutions and Failure Patterns  
For these three two-column bents, the left column is near the actuator side, and the right column is far from the actuator side. The damage progression of the bents was documented during the experiment. For all three bent specimens, the left and right columns exhibited a comparable evolution of damage. For brevity, take the left column as an example for the description of damage evolution. * Bent B2-CIP  
The column remained largely intact with no visible cracks on the surface when the lateral displacement \(\delta\leq 5\) mm. Initial fractures appeared at the top and bottom of the sides labelled L2 and L4 at \(\delta=10\) mm. As the lateral displacement increased from 10 to 40 mm, the column gradually developed more cracks, particularly within the areas at the top and bottom. Most of the cracks were distributed within 0-600 mm from the column ends, with no cracks forming in the middle of the column. During the loading process, existing cracks continuously developed, extending from sides L2 and L4 towards sides L1 and L3, with several cracks penetrating to form circumferential cracks. When the displacement reached 45 mm, the development of cracks in the column stabilized, and no new cracks were formed. Slight concrete spalling was observed at the top and bottom of the column when the lateral displacement increased from 45 to 55 mm. Subsequently, at \(\delta=60\) mm, the continuous spalling of the cover concrete occurred, resulting in the exposure of stirrups and longitudinal rebar. As the lateral displacement increased from 60 mm and 75 mm, large areas of concrete spalling occurred at both the top and bottom of the sides L1 and L3. The concrete was severely damaged, accompanied by the buckling of longitudinal rebar and fracture of stirrups. When the lateral displacement \(\delta=75\) mm, the load-carrying capacity dropped below 85% of the maximum. The longitudinal rebar fractured at the top and bottom of the column, and the test was terminated. The failure patterns of bent B2-CIP are shown in Figure 5.  
a few visible cracks appeared at the top and bottom of the column on the sides L2 and L4. Specifically, the cracks at the cap-column joint appeared within the 0-200 mm range from the top seam. The cracks at the column-footing joint appeared above the grouted splice sleeve zone, within the 350-500 mm range from the bottom seam. As the lateral displacement increased from 10 to 25 mm, the number of cracks at both ends of the column gradually increased. It is worth mentioning that the number of cracks at the cap-column joint was significantly higher than at the column-footing joint. With the increase in lateral displacement, existing cracks continued to develop and extend from sides L2 and L4 towards sides L1 and L3. At \(\delta\) = 30 mm, both the top and bottom seams opened, and the development of cracks in the column stabilized. As the lateral displacement increased from 35 mm and 40 mm, the cover concrete at the top seam of the column was crushed, exposing the unbonded zone of longitudinal rebar. The cover concrete at the bottom of the column was crushed slightly. When the displacement increased from 65 to 70 mm, the spalling of concrete continued at the top and bottom of the column along the direction of the actuator, and the concrete at the joint was severely damaged. When the displacement reached 75 mm, the longitudinal rebar fractured at the cap-column joint and the column-footing joint, leading to the failure of the bent specimen. The failure patterns of bent B2-PGS are illustrated in Figure 6.  
When the loading displacement \(\delta\leq\) 5 mm, the column remained largely intact, with no apparent cracks on the surface and no significant opening on the top and bottom seams. When the lateral displacement reached 10 mm, cracks appeared on the top of the sides L2 and L4, about 200 mm from the top seam. Meanwhile, a crack appeared at the bottom of the column, located just above the grouted splice sleeve zone.