## 2 Experimental Study of Concrete Beams Reinforced with Composite Bars
### Test Result  
The crack point, yield point, peak load point and failure point exist for each specimen in the test. The experimental phenomena and results are described below. The S12B43 beam was loaded by horizontal monotonic loading. When the load reaches 8 kN, two horizontal cracks appeared at the height of 175 mm and 270 mm from the root, indicating that the specimen had entered the cracking stage, as shown by No. 1 and No. 2 cracks in Figure 8a. At this time, the slope of the load-displacement curve decreased slightly. When the horizontal load reached 32 kN, the composite bar on the tensile side began to yield, indicating that the specimen was entering the yield stage. At this time, there is an obvious turning point on the load-displacement curve, and the yield displacement reached 9.8 mm, as shown in Figure 8b. The loading mode was changed from force control to displacement control. With the increase in displacement, the crack developed into an inclined crack from the horizontal direction and extended downward, with the crack bifurcation and peeling of the protective layer of concrete at the root of the compression zone. The width of the crack at the root was up to 1 mm. When the control displacement reached 52 mm, the outer fiber of the composite bar broke one after another. The sound of the fracture became louder and louder. When the displacement was loaded to 57-58 mm, most of the fiber at the end of the specimen ruptured, and the tensile longitudinal bar made a \"boom\", indicating the specimen failure. At the moment the fiber fractured, the load dropped sharply. When the displacement continued to increase, the compression side concrete was damaged more and more seriously, and the crack width of the tensile side concrete widened rapidly, until the block fell off, and the loading stopped when the specimen was seriously damaged. The crack pattern and final failure mode of the specimen are shown in Figure 8c. The S12B97 beam was subjected to horizontal reversed cyclic loading. When the load reached 10 kN, small horizontal cracks began to appear at the height of 150 mm, 200 mm and 300 mm from the root of the specimen, indicating that the specimen had entered the cracking stage, as shown in Figure 9a. When the horizontal load reached \(-\)30 kN, the tensile strain of the longitudinal bar reached 0.0022, and the inner steel bar started to yield, indicating that the component had entered the yield stage, as shown in Figure 9b. Before yielding, the load-displacement curve of specimen was basically linear. When the displacement reached 32 mm, the concrete protective layer of the compression side peeled, and there were many diagonal and horizontal cracks between the initial cracks. In the process of the displacement reaching 64 mm, outer fiber in the composite bars was fractured and it made a series of clear clicking sounds during loading. The concrete in the compressive zone peeled off and the load reached the ultimate seismic capacity. Then, as the displacement continued to increase,  
Figure 7: Dimension and reinforcement drawing of beam specimens (mm). (**a**) Schematic reinforcement; (**b**) Cross section of specimen S12B43; (**c**) Cross section of specimen S12B97. the concrete in the base of the specimen became crunchy and started to fall off in blocks. The specimen was obviously severely damaged, with the load dropping sharply. As observed in the above failure process in the experiment, the lateral load versus top displacement curves of the two specimens are shown in Figure 10. Several points representing the key response stages are identified on the curves, including first cracking of concrete, first yielding of tension reinforcement, the rupture of outer BFRP in SFCB and the spalling of concrete in the compression zone. It can be seen from Figure 10a that the stiffness of specimen S12B43 decreases significantly after the section cracks.