## 3 Applications
### A Prototype Test  
A prototype test of ECP reinforced by steel strands with the fixed spacing calculated in Section 3.2 was performed in an assembled apparatus (Figure 7). The apparatus was mainly constituted by two ECPs, whose internal diameters were 2000 mm [29]. The adopted pipes were exactly the same as those given in Section 3.1. The entire test process involved five load stages, namely, (1) increasing the internal water pressure to the working pressure (0-0.6 MPa), (2) cutting the prestressing wires manually until the cracks propagated in the concrete core (0.6 MPa), (3) decreasing the internal water pressure to the artesian pressure (0.6-0.2 MPa), (4) performing the tensioning operation after wrapping the strands externally around the pipe (0.2 MPa), and (5) increasing the internal water pressure to the original level (0.2-0.6 MPa). In most of the actual pipe failures modes, most pipes failed at 4 or 8 \(\mathrm{o^{\prime}}\)clock, not at the invert, crown, or spring-lines [29]. The position of 8 \(\mathrm{o^{\prime}}\)clock was chosen in this test for convenience (Figure 8).  
Post-tensioning was designed with the theory conducted in Section 3.2, indicating that the target tensile strength was equal to 1171.8 MPa and the center spacing of steel strands was taken as 62 mm. To prevent a prestress loss due to the retraction of clips and the stress relaxation of strands, excessive stretching is essential here. The tensioning process is divided into six stages, which were 20%, 25%, 50%, 75%, 100%, and 115%. Tensioning was performed simultaneously from both sides and in a symmetrical manner along the pipeline axis.  
The statuses of each component of the pipe and the steel strands were measured by resistance strain gauges along the axial direction at inverted (360\({}^{\circ}\)), crown (180\({}^{\circ}\)), and spring-line (90\({}^{\circ}\), 270\({}^{\circ}\)) orientations (Figure 8). Figure 9 exhibits the hoop strains in the concrete core before and after the reinforcement under the working pressure (0.6 MPa). The strains in the concrete core all showed a drastic drop after the process of tensioning. Moreover, the maximum width of the cracks in the outer concrete core at spring-line reduced from 2.2 mm to 0.1 mm after strengthening, as observed through field observation.  
Figure 8: Layout of measuring points of (**a**) the pipe and (**b**) the steel strands.  
Figure 9: Comparison of strains in core concrete before and after the reinforcement: (**a**) 2.5 m inner concrete core at 0\({}^{\circ}\); (**b**) 2.5 m inner concrete core at 90\({}^{\circ}\); (**c**) 2.5 m inner concrete core at 180\({}^{\circ}\); (**d**) 3 m inner concrete core at 0\({}^{\circ}\); (**e**) 3 m inner concrete core at 90\({}^{\circ}\); (**f**) 3 m inner concrete core at 180\({}^{\circ}\); (**g**) 3 m inner concrete core at 270\({}^{\circ}\); (**h**) 2.5 m outer concrete core at 0\({}^{\circ}\); (**i**) 2.5 m outer concrete core at 90\({}^{\circ}\); (**j**) 3 m outer concrete core at 90\({}^{\circ}\); (**k**) 3 m outer concrete core at 180\({}^{\circ}\); (**l**) 4 m outer concrete core at 90\({}^{\circ}\); (**m**) 4 m outer concrete core at 180\({}^{\circ}\).  
The strengthened pipe was capable of sustaining the working pressure and the water tightness property was in a good state. The strains of the steel strands were all below the tensile strain level. The reinforcement of the PCCP with external prestressed steel strands was able to meet the strengthen requirement of the test. The rationality of the derivations in this paper were verified by the effective reinforcement effect with external prestressed steel strands.