Study On Composite Reinforcement Technology With Carbon Fiber On Inner Surface Of Prestressed Concrete Cylinder Pipe

Prestressed Concrete Cylinder Pipe(PCCP)is a composite pipe in which prestressing wires are spirally wound on the concrete core with a cylinder,then cement mortar and coal tar epoxy are sprayed as an anticorrosive coating.Due to materials,design,manufacture,transportation,installation,operation and natural disaster,etc.,PCCP failures in varying degrees have already occurred that increase the risk of pipeline operation.Carbon fiber strengthening PCCP has many advantages,such as trenchless,short construction period and little influence on surrounding environment,However,traditional reinforcement technology with carbon fiber(carbon fibers are directly pasted on the inner surface of PCC.P)cannot play sufficiently the stress level of carbon fiber due to the great difference of ultimate tensile strain between carbon fiber and concrete.This dissertation presents a new solution of composite reinforcement structure with carbon fiber,which is ref'erred to paste cushions with characteristics of high compressible and elastic on the inner surface of PC.CP,and then paste carbon fiber on the cushions.Through material test,model test,theoretical calculation and three-dimensional finite element simulation,the major achievements of this dissertation have been achieved as followings:(1)The composite reinforcement structure of PCCP with carbon fiber makes use of the characteristics of high compressibility of cushion,enlarges the deformation space of carbon fibers,increases the stress level of carbon fibers,reduces effectively the internal pressure load of PCCP.(2)A cushion suitable for the reinforcement structure of PCCP with composite carbon fiber is developed,which has characteristics of high compressible and elastic.The compression ratio of the cushion is more than 40%,Poisson's ratio is close to 0 when the compression ratio is less than 30%;the elongation at break is greater than 90%;the tensile strength is greater than 2.0MPa;and the bond strength with concrete is greater than 1.35MPa,which meets the requirement of not falling off under extreme operating conditions.(3)Laboratory Model tests were carried out on a steel cylinder with a diameter of 0.75m,and results show that circumferential strains of carbon fibers in traditional reinforcement zone with carbon fibers are very low;the circumferential strain of carbon fibers in composite reinforcement zone with carbon fibers increases significantly,while the circumferential strain of steel cylinder decreases significantly.The results of repeated loading and unloading show that the measured data of each measuring point are relatively stable,and the carbon fiber and cushion materials have the characteristic of recoverability when unloading.(4)The results of elastic mechanics calculation and three-dimensional finite element calculation for the laboratory testing are basically consistent with the testing results.The results of elastic mechanics calculation show that,compared with that in the traditional reinforcement zone,the circumferential strain of carbon fibers in the composite reinforcement zone increases from 145 to 3258,and the circumferential strain of steel cylinder decreases from 140 to 93 when the internal water pressure is 1.0 MPa.The results of three-dimensional finite element analysis are basically consistent with those of elastic mechanics calculation.(5)The effect of composite reinforcement structure with carbon fiber on inner surface is related to PCCP's diameter,thickness and Poisson's ratio of cushion,the number of layers and elastic modulus of carbon fiber.The reinforcement effect can be nearly doubled by doubling the thick:ness of cushion or the number of carbon fiber layers or the elastic modulus of carbon fiber.When the Poisson's ratio of cushion is less than 0.3,the Poisson effect has little effect on the composite reinforcement structure.The smaller the diameter of PCCP,the better the reinforcement effect of composite reinforcement with carbon fibers on inner surface of PCCP.(6)The difference of calculation results between material mechanics model and elastic mechanics model for PCCP with diameter of 2.8m is less than 3%.Increasing the number of carbon fiber layers and using high modulus carbon fibers can significantly improve the effect of composite reinforcement structure of PCCP.(7)The results of three-dimensional finite element calculation under working pressure on PCCP with diameter of 2.8m show that when 10 wires are broken,the concrete core has no cracks;when 20 wires are broken,the outer concrete core has circular cracks;when 30 wires are broken,the outer concrete core has some other longitudinal cracks on areas around the springline.Compared with traditional reinforcement structure with carbon fibers,composite reinforcement structure with carbon fibers can significantly improve the stress condition of PCCP and prevent further cracks expansion.