## 3 Result Analysis  
### Failure Mode  
The images in Figure 9a-d illustrate the failure mode of the prestressed concrete beam under an impact load in the middle of the span. Figure 9e provides an illustration of different types of fractures. The red lines represent oblique abdominal shear cracks, the green lines represent bending cracks, and the blue lines represent compression cracks. In Figure 10a-d, we illustrate a partial failure pattern diagram for the PC beam when subjected to mid\(-\)span impact stress. As can be seen in Figure 10e, split cracks are represented by red lines while microcracks are represented by blue lines. The test beams failed due to midpoint bending cracks and oblique shear cracks, which are characteristic of bending-shear failures. The cracks mainly appeared in the mid\(-\)span and splicing sections, indicating a pyramid\(-\)like dispersion from the downstream impact point. The failure modes in the vicinity of the hammerhead contact area were also roughly similar, mainly manifested as the small\(-\)scale crushing and shedding of concrete in this area. At the same time, there were many splitting cracks, and this damage was mainly manifested by the lateral tearing of the concrete cover at the impact point. Figure 9: Overall failure forms of the specimen: (**a**) A1, (**b**) B1, (**c**) B2, (**d**) B3, and (**e**) schematic diagram of crack types. The A1 test beam was a test beam without reinforcement. There were no apparent cracks in the impact area of the top of the beam; however, a large area of concrete samples fell off from both sides of the beam, and the length of the falling concrete samples was long (about 45 cm). The cracks in the beam web were mainly oblique flexural shear cracks and upwardly developed flexural cracks, including the bifurcation and intersection of the two types of cracks, and cracks appeared in the post\(-\)-poured layer. Compared with the B1 and A1 test beams, the B1 test beam was strengthened with a 2 mm\(-\)thick steel plate, and the concrete samples on both sides hardly fell off in large areas. On the left side of the hammerhead impact point, there was an apparent crushing and dislocation of the concrete sample. The concrete in this area was powdery, and an obvious splitting crack appeared through the impact point and the left concrete crushing area. The form of cracks in the mid\(-\)span beam was the same as that of the A1 test beam, the crack width was small, and the distribution range was wide. A new failure mode was observed at the lower part of the beam, which was mainly characterized by the partial separation of the bonded steel plate and separation between the steel plate and concrete. This resulted in an oblique separation failure of the concrete cover at the lower part of the test beam. The B2 test beam was strengthened with a 4 mm\(-\)thick steel plate at the bottom of the beam. In contrast to the A1 test beam, there was more severe damage to the contact surface. At the same time, the concrete in part of the contact area was damaged in the form of a mesh, and two symmetrical split cracks appeared on both sides of the impact position, and the split cracks had a large width. The shape of the cracks in the mid\(-\)span beam was the same as that of the other two types of cracks. The cracks in the mid\(-\)span beam were also observed at the lower part of the test beam. The cracks in the mid\(-\)span beam were also observed at the lower part of the test beam. A1. The crack width was small, and the distribution range was wide; however, there was no post\(-\)poured layer failure. The thickness of the bonded steel plate at the bottom of both test beams B1 and B2 increased from 2 to 4 mm. The cracks in the B2 test beam were scattered over a larger area; however, the number of primary cracks decreased significantly. Comparing the B3 and A1 test beams, the B3 beam was strengthened with a 2 mm bottom steel plate and eight U\(-\)shaped steel plate hoops. Only a small piece of concrete, measuring 5 cm in length, came off the back of the B3 beam.