## 3 Test Process and Failure Characteristics  
### Test Process Description  
For the convenience of description, the push and pull loadings in the test are defined as the positive (+) and negative (-) directions, respectively. At the same time, the side away from the loading point is the front side, the side close to the loading point is the rear side, the front side of the RRAC beam is to the right, and the back side is to the left. In the load-control stage, no cracks appeared on the surfaces of the beam until the lateral load reached \(\pm\)30 kN. Then, bending cracks were found on the left and right sides at the end of the beam in the frame, and the length of the cracks was about 18 cm. When the specimen was loaded to \(\pm\)40 kN, continuous bending cracks appeared on the right side and bottom of the beam, and the bottom cracks ran through the whole section. With the increase in load, the original cracks continuously extended upward and widened, and the new cracks gradually moved closer to the middle span of the beam. When the load was \(\pm\)80 kN, the upper and lower cracks at the end of the beam passed through. Finally, small bending cracks appeared near the middle span of the beam, when the load was \(\pm\)105 kN. Until the end of load-control stage, bending cracks were mainly distributed on the surface of the beam, with a gap spacing of 10-15 cm. It should be noted that the frame column was not bulging, but the measured strains of steel tube and the longitudinal reinforcements of beam were close to the yield strain.  
In the displacement-control stage, when the displacement reached \(\pm\)1\(\Delta_{y}\), the bending cracks on surface of the beam continued to extend upward, which were generated at the load-control stage. At the same time, small oblique cracks began to appear at the beam end. When the displacement went up to \(\pm\)2\(\Delta_{y}\), the original bending cracks were no longer extended but widened, and the oblique crack continued to produce and develop, resulting in a cross oblique crack gradually forming on the surface of the beam. With an increase in the displacement up to \(\pm\)3\(\Delta_{y}\), the main cross diagonal cracks were formed at both ends of the beam, and the angle between them and the horizontal line was 33\({}^{\circ}\)-42\({}^{\circ}\); this shows that the bending shear plastic hinge began to form gradually at this stage. At this time, the RAC at the beam end began to peel and fall off. With the increase in circulation time, the main oblique cracks continuously extended upward and widened, and new micro-cross oblique cracks were continuously generated. When the displacement reached \(\pm\)4\(\Delta_{y}\), the main cross diagonal crack had extended to the top and bottom of the beam. The RAC at the top and bottom of the beam began to show a horizontal crack under the influence of the diagonal crack, and the concrete protective layer began to break away. When the displacement reached \(\pm\)5\(\Delta_{y}\), large areas of RAC at the top and bottom of the beam were crushed and fell off in blocks. In some areas, the longitudinal bars and stirrups were exposed, and the deformation was serious. Therefore, it could be observed that an obvious bending shear plastic hinge was formed. By this point, the load had dropped to 85% of the peak load, and the specimen was severely deformed, so it was not feasible to continue loading, and the test was over. It should be noted that although the strain at the bottom of the steel tube had reached the yield strain  
Figure 5: The arrangement of the strain gauges. (**a**) The layout of strain gauges on the steel tubes and RAC beam; (**b**) The layout of strain gauges on the longitudinal reinforcements and stirrups.  
at the end of the test, the steel tube did not have bulges. The final failure mode of the RACFCST frame is shown in Figure 6.