Study On Mechanical Performance Of Prestressed CFRP Concrete Cylinder Pipe Under Internal Pressure

Prestressed Concrete Cylinder Pipe(PCCP)is a kind of water conveyance pipeline with excellent performance.It is widely used in long-distance water conveyance projects.Due to the long-term burial of PCCP in the underground during operation,the pipeline is continuously eroded by corrosive substances in the soil,which makes the corrosive medium pass through the mortar protective layer and causes the steel wire to be corroded and passivated.In severe cases,the prestressed steel wire would break,which reduces the bearing capacity of the PCCP pipeline and increases the risk of pipeline burst.The safe operation of the pipeline would be greatly affected.Carbon Fiber Reinforced Plastics(CFRP)has many advantages such as corrosion resistance,light weight and high strength.If the prestressed steel wire in the PCCP pipe can be replaced by prestressed CFRP cloth,the prestressed CFRP steel cylinder concrete pipe(CFRP-PCCP)can be developed,which is expected to solve the problem of corrosion and fracture of prestressed steel wire in PCCP.Based on the research of PCCP,the mechanical performance of CFR-PPCCP is studied in this paper.The main work is as follows:(1)The internal pressure type test of PCCP pipeline was carried out.The strain variation of pipeline materials(core concrete,prestressed steel wire and protective layer mortar)under internal water pressure was tested and analyzed.The distribution and extension law of cracks on the inner surface of core concrete were analyzed.The results show that in the elastic stage,the deformation of each material is coordinated and the strain increases linearly.When the internal water pressure is 1.8 MPa,the strain value of each material at the corresponding section point increases sharply due to the cracking of concrete.The concrete crack extends longitudinally from the starting point to the socket end,and the crack width decreases gradually along this direction.(2)The three-dimensional finite element numerical simulation of PCCP pipeline is carried out.ABAQUS finite element software was used to simulate the internal pressure loading,and the numerical simulation results were compared with the experimental data to verify the accuracy of the finite element model.Based on the simulation prototype test,the failure process of PCCP pipeline is discussed by increasing the internal water pressure.The results show that the numerical simulation results are in good agreement with the experimental data,the strain change trend is the same,and the accuracy of the PCCP pipeline model is verified.After the cracks appear in the pipeline,the strain value of the material is always increasing at a large speed until the pipeline cannot continue to bear the load.(3)The finite element numerical analysis of CFRP-PCCP internal pressure was carried out.Based on the calculation principle of prestressed equivalent load method,the prestressed steel wire is replaced by prestressed CFRP cloth,and the finite element analysis of CFRP-PCCP internal pressure is carried out.The mechanical properties of CFRP-PCCP and PCCP were compared and analyzed,and the influence of different CFRP thicknesses on the bearing capacity of the pipeline was further studied.The results show that in the elastic stage,the strain changes of the two pipelines are the same;under large internal pressure,the elastic modulus of CFRP is about 30 % higher than that of steel wire,which makes the deformation resistance and crack resistance of CFRP-PPCCP better than that of PCCP,and the greater the thickness of CFRP,the better the bearing capacity of the pipeline.