## 4 Experimental Results  
### Load Characteristics of the Specimens  
The photos of the failed beam 1 and beam 2 are shown in Figures 8 and 9. The number of cracks in beam 2 is more than that in beam 1 during the test loading process. With the increase of CFRP reinforcement, the crack spacing decreases and the number of cracks increases. By comparing the failure photos of the test specimens, it can be seen that the debonding failure degree of the beam 2 is more severe than that of the beam 1 and the cracks only appear in the CFRP reinforcement area during the loading process. This is mainly because the non-pre-stressed CFRP bonded section of the beam 2 is twice that of the beam 1. This indicates that the increase in the contact area between the CFRP and the concrete improves the stress distribution of the concrete, slows down the appearance and expansion of the crack and improves the service performance of the test specimens. When the same load is applied, the beam 1 has a larger displacement and a more severe crack than the beam 2. Load characteristics of the specimens are shown in Table 4. It can be seen from Table 4 that the cracking load and ultimate load of beam 2 are significantly higher than those of beam 1. Compared with beam 1, the cracking load of beam 2 at the tension and bond end is increased by 50% and 177.78% respectively and the ultimate load is increased by 23.81%. Beam 2 exhibits better ductile failure characteristics due to the increased length of the non-pre-stressed bond section. The analysis shows that the load characteristics of the specimens can be improved by increasing the length of the non-pre-stressed CFRP bonded section. Figure 10 shows the load-vertical displacement curve in the mid-span of the specimen. There is little difference between the load-vertical displacement curves of beam 1 and beam 2 at the initial stage of loading. The applied load-vertical displacement curves appear an obvious change at the cracking load. The vertical displacement of beam 2 is significantly smaller than that of beam 1 under the same applied load. The ultimate vertical displacement of beam 1 and beam 2 during debonding failure is 14.88 mm and 22.53 mm, respectively. This indicates that the stiffness of the specimen is obviously improved after increasing the length of the non-pre-stressed CFRP bonded section. The non-pre-stressed bonding section can prolong the bond stress-transmission length of the CFRP-concrete interface and can significantly enhance the bearing capacity and deformation performance of the test specimen. The CFRP axial strain distribution curves of beam 1 and beam 2 are shown in Figure 11. It can be seen from Figure 11 that the strain peak in the non-pre-stressed CFRP bonding section exhibits a tendency to move from the tension end to the bonding end with the increase of load. The strain of beam 1 bonded end is about 400 \(\mu\epsilon\) at the 100 kN load stage, indicating that the strain is sufficiently transmitted within the 200 mm length of non-pre-stressed CFRP bond section. The failure photo of the non-pre-stressed CFRP bond section of beam 1 in Figure 8 also proves this phenomenon. The strain difference of beam 2 does not change from 110 kN to the failure load stage, indicating that the non-pre-stressed CFRP bond section does not function to transmit the interface bond stress caused by the tension and the load. Strain analysis showed that there was an effective non-pre-stressed CFRP bond length to improve the load bearing properties of the specimen. The released tensile prestress is equivalent to an axial drawing force for the non-pre-stressed bonded section, so the performance of the test specimen increases with the length of the non-pre-stressed bonded section. According to the experimental observation, the crack only appears within the length of 300 mm of the CFRP non-pre-stressed bonding section of the beam 2 in the 0 kN to 110 kN loading phase. The bonded end of the beam 2 is cracked during the 125 kN loading phase.