Research On Mechanical Performance Of Prestressed CFRP Concrete Cylinder Pipe Under External Load

Prestressed Concrete Cylinder Pipe(PCCP)is a new type of water conveyance pipeline in recent years.It is a composite structure composed of high-strength concrete,thin-walled steel cylinder,prestressed steel wire and protective layer mortar.Due to the full use of the properties of various materials,PCCP has been widely used in engineering.However,there are also some problems in the use of PCCP,especially the burst accident of pipeline caused by corrosion and fracture of steel wire.At present,the reinforcement measures are mainly used for the fracture of steel wire.Although these measures can restore the bearing capacity,it is difficult to solve the corrosion fracture of steel wire.Because carbon fiber reinforced plastic(CFRP)has the characteristics of light weight,high strength and good durability,the use of CFRP cloth to replace prestressed steel wire and mortar is expected to fundamentally solve such problems.Based on the prototype test and finite element analysis of PCCP under external pressure,the finite element analysis of prestressed CFRP steel cylinder concrete pipe is carried out.The main contents and conclusions are as follows :(1)The three-point external pressure prototype loading test of PCCP was carried out.The strain of core concrete,prestressed steel wire,protective layer mortar and the vertical displacement of the top of the pipe were collected.The test results show that the core concrete and the prestressed steel wire bear the external load together under the external pressure load.The concrete on the top and bottom of the pipe is subjected to tensile strain,and the concrete on the outside of the pipe waist is subjected to tensile strain.Since the protective layer mortar has no pre-compression stress,the tensile strain at the waist increases during the external pressure loading process,which is prone to cracking.(2)The three-dimensional finite element model of PCCP under external load is established by using ABAQUS finite element software.The prestressing loss of steel wire is considered in the process of applying prestress to steel wire by cooling method.During the simulation loading,the pipe body is subjected to graded pressure by applying loads.The model results are in good agreement with the experimental data,which verifies the rationality of the numerical model.The deformation data of the steel cylinder are extracted from the finite element results,and the stress deformation law of the steel cylinder is obtained,which improves the test data.On this basis,the model is further loaded,and the results show that the strain of each material increases with the increase of load.The concrete at the top and bottom of the pipe is destroyed first,and the load is mainly borne by the steel cylinder.When the steel cylinder reaches the ultimate tensile stress,the pipe body is considered to reach the ultimate state.(3)The finite element model of prestressed CFRP steel tube concrete pipe is established,and the steel wire and mortar are replaced by prestressed CFRP cloth by using the principle of annular prestress.The simulation results show that when the load reaches the crack-resistant external pressure test load,the error of the bearing capacity of the pipe body is within 5 %compared with the prototype test,indicating that the prestressed CFRP steel cylinder concrete pipe meets the crack-resistant external pressure test load.On this basis,the finite element parameter analysis of prestressed CFRP steel tube concrete tube is carried out.The main factors considered include concrete strength and prestress.The results show that with the increase of concrete strength(concrete grade from C55 to C65),the bearing capacity of pipeline increases by 6.8 %.With the decrease of concrete strength(concrete grade decreased from C55 to C45),the bearing capacity of the pipeline decreased by 4.5 %.With the increase of CFRP prestress(thickness increased from 1.3 mm to 1.6 mm),the bearing capacity of the pipeline increased by 5.6 %.With the decrease of CFRP prestress(thickness from 1.3 mm to 1.0 mm),the bearing capacity of the pipeline decreased by 3.4%.