# Response of Corroded Steel Pipeline Without and with CFRP Reinforcement to Reverse Fault Movement
## 4 Results and Analyses
### Effectiveness of CFRP Reinforcement
#### 4.4.2 Response and Failure of Corroded Pipeline with CFRP Reinforcement  
Figure 13 shows the peak strain and peak ellipticity of the footwall pipeline reinforced with CFRP of a certain 20 m length and different thicknesses. It is observed in Figure 13a that compared with the unreinforced pipeline, CFRP can significantly reduce the strain response and delay the occurrence of local buckling failure. The buckling resistance increased by 56.7%, 82.4%, and 86.9% for the 4-, 8- and 12-layer cases, respectively. The strain of the severely corroded pipeline (0.6 t) can be restored to 90% of the intact pipeline by using 4-layer CFRP. It is further noted that in the interval from 0 to 4 layers, the average buckling resistance increased by 14.17% for each layer compared with 0 layers; in the interval from 4 to 8 layers, the average buckling resistance increased by 6.43% for each layer compared with 4 layers; and in the interval from 8 to 12 layers, the average buckling resistance increased by 1.2% for each layer compared with 8 layers. Therefore, as the CFRP thickness increases, the buckling resistance increases but at a decreasing rate.  
Figure 13b shows that, compared with the unreinforced pipeline, the peak ellipticity of the 4-layer reinforced pipeline is increased by 27.8%, that of the 8-layer reinforced pipeline is increased by 36.79%, and that of the 12-layer reinforced pipeline is increased by 44.8%, indicating that more CFRP reinforced layers mean stronger resistance of the pipeline to cross-section deformation. Moreover, when the fault displacement is less than 0.3 m, the section deformation of the pipeline reinforced with CFRP is basically the same as that without the reinforcement, and the effect and difference of CFRP reinforcement with different thicknesses cannot be reflected temporarily.  
Table 7 shows the critical fault displacement of the pipeline with different CFRP thicknesses. It is noted from Table 7 that the critical fault displacement of local buckling and elliptic deformation increases significantly after the reinforcement, and the reinforcement effect is the most significant in the 4-layer case. The failure sequence of the pipeline is first local buckling, then elliptic deformation, and finally tensile fracture.  
Figure 14 shows the peak strain and peak ellipticity of the footwall pipeline reinforced with CFRP of 8 layers and different lengths. Figure 14a shows that compared with the unreinforced pipeline, the increase in buckling resistance is 31.8%, 48.5%, 66.9%, and 82.4% for the 5 m-, 10 m-, 15 m-, and 20 m-long reinforcement, respectively. However, the rate of  
Figure 13: A mechanical response of the pipeline with different CFRP thicknesses. (**a**) Peak axial strain. (**b**) Peak ellipticity.  
increase in resistance also decreases as the reinforcement length increases, similar to the case of different CFRP thicknesses.  
Furthermore, Figure 14b indicates that compared with the unreinforced pipeline, the resistance to section deformation increases by 25%, 31%, 33.9%, and 36.3% for the 5 m-, 10 m-, 15 m-, and 20 m-long reinforcements. This shows that the resistance of the pipeline to cross-section deformation increases as the CFRP reinforcement length increases but at a decreasing rate. Same as the case of different CFRP thicknesses, when the fault displacement is less than 0.3 m, the CFRP reinforcement has no effect on the pipeline behavior.  
Table 8 shows the critical fault displacement of the pipeline with different CFRP lengths. Table 8 indicates that the critical fault displacement of local buckling and elliptic deformation increases significantly after the reinforcement, and the reinforcement effect is the most significant in the 5 m case. The failure sequence of the pipeline is still local buckling, then elliptic deformation, and finally tensile fracture.