Long-term performance test optimization and construction technology of GFRP drainage pipe in cold region

Abstract

The application discloses a long-term performance test optimization and construction process based on a GFRP drainage pipe in a cold region, and comprises the following steps: basic performance tests are carried out based on the tensile properties, thermodynamic properties, fiber volume content and microstructure of GFRP materials; the influence of a single-day temperature field and seasonal temperature difference on the GFRP drainage pipe is analyzed through finite element simulation; mechanical property tests of the GFRP drainage pipe under freeze-thaw cycle environment are carried out; and the high-temperature resistance and tensile strength theoretical model of the GFRP drainage pipe are researched. The technical problems that the traditional drainage pipe in the prior art is prone to freeze cracking, has poor corrosion resistance, is difficult to install, and the GFRP drainage pipe is degraded in performance during long-term service in the cold region and the construction process is not suitable are solved.

Description

Technical Field

[0001] This invention relates to the field of bridge drainage engineering technology in cold regions, and more specifically, to a long-term performance testing optimization and construction process based on GFRP drainage pipes for cold regions. Background Technology

[0002] In bridge engineering in cold regions, the reliability of the bridge deck drainage system directly affects the durability and service life of the bridge structure. Bridge drainage pipes need to quickly drain rainwater from the bridge deck to the ground to prevent rainwater from accumulating and seeping into the beams, causing damage. Currently, drainage pipes are mainly divided into plastic pipes, metal pipes, and composite pipes. Plastic pipes are lightweight and corrosion-resistant but have low strength and are prone to freezing and cracking at low temperatures; metal pipes have high strength but are heavy, difficult to install, and are easily corroded by weakly acidic rainwater, requiring additional anti-corrosion treatment; steel-plastic composite pipes combine some advantages of metal and plastic, but the difference in their coefficients of linear expansion is large, making them prone to delamination and blockage during use, and easily cracking and failing in alternating hot and cold environments.

[0003] With the development of engineering materials technology, glass fiber reinforced polymer (GFRP) composites have been increasingly applied in bridge drainage due to their advantages of strong corrosion resistance, light weight, and high strength. However, the special climatic conditions in cold regions have brought new challenges to the application of GFRP drainage pipes: on the one hand, the large temperature difference between day and night in cold regions, with the average daily minimum temperature reaching -17℃ in some areas, can cause GFRP materials to become brittle, reducing their elongation at break and strength, thus affecting their service life; on the other hand, freeze-thaw cycles can cause degradation of the material's mechanical properties, and the thermal stress generated by temperature differences may damage the sealing of pipe joints. Traditional construction techniques are difficult to adapt to cold environments, and improper joint treatment can easily lead to problems such as leakage and blockage.

[0004] In existing technologies, research on the long-term performance of GFRP mainly focuses on resistance to acids, alkalis, salts, and ultraviolet radiation, with limited research on the impact of low-temperature environments on its mechanical properties, especially its long-term performance. Furthermore, there is a lack of construction methods for GFRP drainage pipes adapted to cold regions, resulting in insufficient pipe connection reliability and difficulty in meeting the long-term stable operation requirements of bridge drainage systems in cold areas. Therefore, developing a construction process that optimizes the long-term performance of GFRP drainage pipes in cold regions and adapts to the cold environment has become a key issue in solving the drainage problems of bridges in cold regions. Summary of the Invention

[0005] To address these issues, this invention provides an optimized long-term performance testing and construction process for GFRP drainage pipes used in cold regions. This addresses the technical problems of traditional drainage pipes in cold regions being prone to freezing and cracking, having poor corrosion resistance, and being difficult to install, as well as the performance degradation and unsuitability of GFRP drainage pipes during long-term service in cold regions.

[0006] To achieve the above objectives, the present invention provides the following technical solution: An optimized process for long-term performance testing of GFRP drainage pipes in cold regions includes the following steps: Basic performance tests were conducted on GFRP materials based on their tensile properties, thermodynamic properties, fiber volume content, and microstructure. The effects of daily temperature field and seasonal temperature difference on GFRP drainage pipes were analyzed by finite element simulation. Mechanical performance testing of GFRP drainage pipes under freeze-thaw cycles was conducted. A theoretical model for the high-temperature resistance and tensile strength of GFRP drainage pipes was developed.

[0007] Based on the above technical solution, the present invention is further described as follows: As a further aspect of the present invention The basic performance tests conducted on the tensile properties, thermodynamic properties, fiber volume content, and microstructure of the GFRP material specifically include: GFRP plates with a thickness of 1.6 mm, a width of 100 mm, and a density of 1.91 g / cm³ were selected. Tensile specimens with a length of 250 mm were prepared. The two ends of the specimens were anchored with 3 mm thick aluminum sheets with an anchoring length of 50 mm. The anchoring adhesive was the same as that used for anchoring basalt fiber bundles. Five specimens with dimensional deviations conforming to the specifications were prepared for each working condition. The specimens were mounted on a tensile testing apparatus, and tensile deformation was measured using a 50mm mechanical extensometer. The tensile speed was set to 5mm / min for the tensile test. The maximum axial tensile force and corresponding deformation data of the specimens were recorded, and the average value of 5 specimens was taken as the tensile performance test result. A Q800 dynamic mechanical thermal analyzer was used to test the thermodynamic properties of a 35mm×15mm×1.3mm specimen in a single cantilever configuration. The test frequency was set to 1Hz, the amplitude to 25μm, and the temperature was raised from room temperature to 240℃ at a heating rate of 3℃ / min. The changes in storage modulus, loss modulus, and loss factor with temperature were recorded in real time. Five GFRP samples were selected. The mass of the samples before calcination was measured using a FA2004N precision electronic balance with an accuracy of ±0.0001g. The samples were then placed in a 600℃ high-temperature furnace for 4 hours and cooled to room temperature before the mass of the samples after calcination was measured. The fiber volume content was calculated according to the formula. GFRP samples after tensile fracture were selected, and the fracture surface was sputter-coated with gold for ten minutes. The treated samples were then placed in a QUANTA200F scanning electron microscope, with an accelerating voltage of 30.00 kV and a magnification of 2000x, to observe the bonding state between the fiber and the resin matrix.

[0008] As a further aspect of the present invention The tensile properties test results were as follows: tensile strength of 820 MPa, tensile modulus of 50.0 GPa, and elongation at break of 1.7% for the GFRP sheet; thermodynamic properties test results were as follows: glass transition temperature of 121.1℃ for the GFRP material; and the volume fractions of the five samples in the fiber volume content test were 0.6235, 0.6424, 0.6507, and 0.6282, with an average value of 63.6%.

[0009] As a further aspect of the present invention The analysis of the impact of daily temperature field and seasonal temperature difference on GFRP drainage pipes through finite element simulation specifically includes: Based on ABAQUS finite element analysis software, a solid element model of a GFRP drainage pipe with a length of 5m, a diameter of 400mm, and a wall thickness of 5mm was established. Hexahedral isoparametric elements were used for mesh generation. The global seed approximate global scale was set to 50, and the curvature scale was controlled to 0.1, so that the total number of model elements was 5000 and the total number of nodes was 10100. Input the following thermal property parameters for GFRP material into the simulation software: mass density 1.91 g / cm³, specific heat 1150 J / (kg・℃), convective heat transfer coefficient to pipe 275 W / m²・K, convective heat transfer coefficient to air 15 W / m²・K, and linear expansion coefficient 5 × 10⁻⁻⁻⁴. 6 / ℃, thermal radiation coefficient to air 0.9, thermal conductivity coefficient 0.375W / (m・K); measure the nighttime air temperature and take the average value at each time, combine the influence of water temperature to obtain the relationship between air temperature and water temperature over time, reflect the influence of air temperature and water temperature on the pipeline through surface heat convection, realize the heat transfer from the pipeline to the atmosphere through external surface radiation, and apply a predefined field with an initial temperature of 2℃ to the inner and outer walls of the pipeline. Set the left end of the pipe as a fixed end to constrain all degrees of freedom, and release the right end to release displacement along the pipe length direction and fix the displacement boundary conditions of U1, U2 and UR3; Thermal analysis was conducted based on the Fourier equation, spatial discrete matrix differential equation, and backward difference implicit solution method. Heat transfer was calculated by combining convective heat transfer and thermal radiation formulas. Simulation software was used to obtain the temperature field, displacement, and stress distribution results of the GFRP pipeline at night. Based on the characteristics of cold climate, temperature difference conditions of 22℃ in spring, 20℃ in summer, 15℃ in autumn, and 25℃ in winter were designed. The 24-hour temperature change curves of each season were obtained by numerical fitting. The thermal boundary conditions were adjusted while the displacement boundary conditions were kept unchanged. The simulation software was run to obtain the temperature field, displacement and stress distribution of the pipeline under each temperature difference condition.

[0010] As a further aspect of the present invention The simulation results of the daily temperature field are as follows: The inner surface temperature of the GFRP pipe is 5.18~7.75℃, the outer surface temperature is -1.7~3.39℃, the maximum temperature difference between the inside and outside is 7℃, the maximum pipe shrinkage and creep displacement is 0.18mm, and the maximum thermal stress in the middle section of the pipe is 7.9MPa. The simulation results of the seasonal temperature difference are as follows: The deformation of a 5m pipe section in each season is ≤0.5mm. The thermal stress in the middle section of the pipe is 8.6MPa in spring, 7.1MPa in summer, 6.5MPa in autumn, and 10.4MPa in winter, all of which are less than the strength limit of GFRP material.

[0011] As a further aspect of the present invention The aforementioned mechanical performance testing of GFRP drainage pipes under freeze-thaw cycles specifically includes: Fifteen freeze-thaw cycle specimens meeting the tensile test requirements were fabricated using GFRP material consistent with actual engineering applications. These specimens were divided into three groups of five specimens each, with freeze-thaw cycles of 30, 80, and 210 cycles. A freeze-thaw cycle chamber was used for the tests, with the cycle temperature set to -20 to 30°C. The cycle regime was 4 hours of freezing followed by 4 hours of thawing, repeated three times daily. The specimens were placed in the sample rack of the freeze-thaw cycler to complete the set number of cycles. After the freeze-thaw cycles were completed, the specimens were brought back to room temperature. Uniaxial tensile tests were conducted using the same tensile testing equipment as for the basic performance tests, at a test speed of 5 mm / min and with a 50 mm mechanical extensometer to measure deformation. The tensile strength, elastic modulus, and elongation at break of the specimens were calculated using the formulas, and the arithmetic mean of at least three specimen data points was taken as the test result.

[0012] As a further aspect of the present invention The results of the freeze-thaw cycle mechanical property test are as follows: The tensile strength of GFRP was 1927 MPa after 30 cycles, 2153 MPa after 80 cycles, and 1850 MPa after 210 cycles, with a variation range within 15%; the elastic modulus was 3.1 GPa after 30 cycles, 3.2 GPa after 80 cycles, and 2.7 GPa after 210 cycles, with overall stable values; the elongation at break was 63.4 after 30 cycles, 67.4 after 80 cycles, and 69.6 after 210 cycles, showing a steady upward trend.

[0013] As a further aspect of the present invention The theoretical model for studying the high-temperature resistance and tensile strength of GFRP drainage pipes specifically includes: Six test conditions were set up: 25℃, 40℃, 80℃, 120℃, 160℃, and 200℃. GFRP sheets and glass fiber bundles consistent with the actual engineering were selected as test samples. Five samples were prepared for each test condition. Tensile tests were carried out under each test condition using a GFRP sheet high-temperature tensile device. The load-strain curve and the maximum tensile force at break were recorded. The high-temperature performance of glass fiber bundles was analyzed using the Weibull two-parameter model. The number of fibers under stress at the initial loading stage was evaluated, and the Weibull parameters, fiber bundle dimensional parameters, and average tensile strength were calculated. The tensile strength, tensile modulus, and failure mode of GFRP sheets in high-temperature tensile tests were recorded and analyzed. GFRP samples that failed under tensile conditions at different temperatures were sputter-coated with gold, and the cross-sectional microstructure was observed using scanning electron microscopy. The tensile strength of GFRP sheets was predicted using an overall load-sharing model, a simultaneous fiber fracture model, and an equivalent volume element model. The prediction results of the three models were compared and analyzed with the experimental test results.

[0014] As a further aspect of the present invention The tensile strength of the glass fiber bundle at 80°C and above shows a decreasing trend, and at 200°C it decreases by 14.5% compared with room temperature, while the tensile modulus does not change significantly. The tensile strength of GFRP sheets degrades significantly with increasing temperature. After exceeding the glass transition temperature, the tensile modulus drops to 40.0 GPa and tends to stabilize. The prediction results of the equivalent volume element model are in best agreement with the experimental results and can be used as a theoretical tool for performance evaluation of GFRP drainage pipes under extreme temperature conditions.

[0015] A construction process for GFRP drainage pipes in cold regions includes the following steps: Familiarize yourself with the construction drawings to clarify the specifications and installation location requirements of GFRP drainage pipes, clean the construction site, and measure and mark the locations of drainage holes, pipe connections, and vertical pipe openings on the bridge deck. Grind the outer surface of the GFRP drainage pipe joint to roughen it, grind the end into a bevel to expose the inner lining layer, and clean the dust, oil and impurities on the pipe surface after grinding. The fiberglass water pipes were slowly lowered from the bridge deck to the designated position and adjusted to the appropriate height. Small electric drills were used to drill holes in the box girder and piers. Drainage pipe hangers and steel clamps were installed. The horizontal pipes were fixed with the hangers and steel clamps. The vertical pipes were inserted vertically into the drain outlets and aligned with the connection between the horizontal and vertical pipes. Cranes were used to assist in the installation of parts where the automatic elevator could not be used. After the pipe is polished, fill the outer surface and joint surface with glass fiber yarn until the cut is filled. Apply the prepared resin adhesive, lay glass fiber yarn layer by layer and impregnate it with resin, roll it to remove air bubbles. Do not lay more than 6 layers at a time, and the overlap width of the layers should not be less than 2cm. The thickness of the glass cloth is 0.1~0.3mm. Control the hand lay-up process construction time to 30-45 minutes, accurately mix the resin adhesive, add accelerators to speed up curing in low temperature weather, and avoid rain immersion and stress on the hand lay-up joints within 24 hours. After curing, check the appearance quality of the hand lay-up joint, test the initial radial flexural deformation of the pipe according to the specifications, and ensure that the strength of the connection joint is consistent with the original pipe. Close the valve at the end of the pipeline, fill the pipeline with water and expel the air, and conduct a water pressure test. The pipeline is considered qualified if there are no leaks or ruptures, no seepage at the joints, and the allowable seepage amount meets the steel pipe standard.

[0016] The present invention has the following beneficial effects: 1. Through systematic material performance testing and simulation analysis, the performance variation law of GFRP drainage pipe in cold environment was clarified, the material selection and structural design were optimized, the deformation under temperature difference was reduced, the tensile strength after freeze-thaw cycle was reduced, and the long-term stability and durability of GFRP drainage pipe in cold region were significantly improved.

[0017] 2. Through precise installation procedures and hand lay-up connection technology, the problems of weak pipe connections and easy leakage and blockage of joints in traditional construction for special environments such as low temperature and freeze-thaw cycles in cold regions have been solved. The strength of the hand lay-up connection nodes is consistent with the original pipes, and the water pressure test has verified that they meet the drainage requirements, thus improving the construction quality and efficiency.

[0018] 3. The performance optimization scheme and construction process of this invention, combined with the advantages of GFRP material itself, such as strong corrosion resistance and light weight, compared with the construction of traditional plastic pipes, metal pipes and composite pipes, GFRP drainage pipes in cold regions do not require additional anti-corrosion treatment, have low installation difficulty and low transportation cost, and have a longer service life, thus reducing the construction and maintenance costs of bridge drainage systems in cold regions.

[0019] 4. Temperature field simulation model, freeze-thaw cycle performance evaluation method and tensile strength theoretical model provide a complete technical system for the design, construction and operation and maintenance of GFRP drainage pipes in cold regions, fill the technical gap in the construction of GFRP drainage pipelines in cold regions, and have important reference and promotion value for similar projects. Attached Figure Description

[0020] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. The structures, proportions, sizes, etc., drawn in this specification are only used to complement the content disclosed in the specification, so that those skilled in the art can understand and read them. Any modifications to the structure, changes in the proportional relationships, or adjustments to the size, without affecting the effects and objectives that the present invention can produce, should still fall within the scope of the technical content disclosed in the present invention.

[0021] Figure 1 This is a schematic diagram of the overall process for optimizing the long-term performance testing of GFRP drainage pipes for cold regions, provided in an embodiment of the present invention. Detailed Implementation

[0022] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] The terms "upper," "lower," "left," "right," and "middle" used in this specification are merely for clarity of description and are not intended to limit the scope of the invention. Any changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0024] like Figure 1 As shown, this embodiment of the invention provides a long-term performance testing optimization and construction process for GFRP drainage pipes in cold regions, including the following steps: S1: Basic performance tests were conducted based on the tensile properties, thermodynamic properties, fiber volume content, and microstructure of GFRP materials. GFRP sheets with a thickness of 1.6 mm, a width of 100 mm, and a density of 1.91 g / cm³ were selected. Tensile specimens were prepared with a length of 250 mm. Both ends were anchored with 3 mm thick aluminum sheets with an anchoring length of 50 mm. The anchoring adhesive was the same as that used for anchoring basalt fiber bundles. Five samples were prepared for each working condition to ensure that the sample size deviation met the specification requirements; The specimens were installed on the tensile testing equipment, and the tensile deformation was measured using a 50mm mechanical extensometer. The tensile speed was set to 5mm / min. The equipment was started to conduct the tensile test. The maximum axial tensile force and the corresponding deformation data of each specimen were recorded. After the test, the average value of 5 specimens was taken as the test result. The GFRP sheet was tested and found to have a tensile strength of 820 MPa, a tensile modulus of 50.0 GPa, and an elongation at break of 1.7%. Thermodynamic performance testing: A Q800 dynamic mechanical thermal analyzer was used for testing in a single cantilever configuration. Samples with dimensions of 35mm×15mm×1.3mm were cut, and the test frequency was set to 1Hz, the amplitude to 25μm, and the temperature was raised from room temperature to 240℃ at a rate of 3℃ / min. The changes in storage modulus, loss modulus, and loss factor with temperature were recorded in real time. Test results show that the glass transition temperature of this GFRP material is 121.1℃ (loss factor peak). Fiber volume content test: Five GFRP samples were selected, and the mass of each sample before calcination was measured using a FA2004N precision electronic balance (accuracy ±0.0001g). The samples were placed in a high-temperature furnace at 600℃ for 4 hours, and after cooling to room temperature, the mass after calcination was measured. The fiber volume content was calculated according to the formula as follows: In the formula, The fiber volume content (%) The fiber mass (g) is the mass after calcination. Fiber density (g / cm³); The total volume (cm³) of the composite material is calculated from the sample dimensions. Test results show that the fiber volume fractions of the five samples are 0.6235, 0.6424, 0.6507, and 0.6282, respectively, with an average of 63.6%. Scanning electron microscopy test: Select the GFRP sample after tensile fracture and perform gold sputtering treatment on the fracture surface for ten minutes to improve the conductivity of the sample; put the treated sample into a QUANTA200F scanning electron microscope, set the accelerating voltage to 30.00kV and the magnification to 2000x, and observe the bonding state between the fiber and the resin matrix. The electron microscope images show that there is a lot of resin matrix attached to the fiber on the GFRP specimen, indicating that the fiber and resin matrix have good bonding performance and can work together to bear the load. Through the above tests, the basic performance parameters of GFRP material were fully understood, providing accurate basic data for subsequent temperature field simulation, freeze-thaw cycle test and construction process design, thus ensuring the reliability of subsequent research and engineering applications. S2: Analyze the impact of daily temperature field and seasonal temperature difference on GFRP drainage pipes through finite element simulation; Based on ABAQUS finite element analysis software, a solid element model with a pipe length of 5m, a diameter of 400mm, and a wall thickness of 5mm was established according to the structural dimensions of GFRP drainage pipes in actual engineering. Hexahedral isoparametric elements were used for mesh generation, and the global seed approximate global scale was set to 50, and the curvature scale was controlled to 0.1. The final model has a total of 5000 elements and a total of 10100 nodes, so that the mesh quality meets the simulation accuracy requirements. Input the thermal property parameters of the GFRP material into the simulation software, specifically including: Mass density 1.91 g / cm³, specific heat 1150 J / (kg·℃), convective heat transfer coefficient to pipe 275 W / m²·K, convective heat transfer coefficient to air 15 W / m²·K, linear expansion coefficient 5 × 10⁻ 6 / ℃, thermal emissivity to air 0.9, thermal conductivity 0.375W / (m·K); The nighttime air temperature data was measured, and the average value at each moment was calculated. The influence of water temperature was also considered to obtain the relationship between air temperature and water temperature over time. The influence of air temperature and water temperature on the temperature of GFRP pipe is achieved through surface heat convection. The radiation of GFRP pipe to the outside atmosphere is dissipated into the environment through the radiation of the outer surface. Predefined fields were applied to the surface temperatures of the inner and outer walls of the pipe, and the initial temperature was set to 2℃ for both. The displacement boundary conditions are set as follows: The left end of the pipe is fixed, constraining all degrees of freedom; the right end of the pipe releases the displacement along the pipe length, and U1, U2 and UR3 are fixed to simulate the constraint state of the pipe in actual installation. Further thermal analysis theory and numerical calculations were performed: The thermal conduction of glass fiber reinforced composites follows the Fourier equation: In the formula, and The values ​​are temperature and time for glass fiber reinforced composite materials, respectively. and These are the density and specific heat of the glass fiber reinforced composite material, respectively. and These are the thermal conductivity and heat generation rate per unit volume of the glass fiber reinforced composite material, respectively. After spatial discretization using the finite element method, the time matrix differential equation is obtained: In the formula, and These are the heat capacity and the heat conduction matrix, respectively. and These are the temperature and heat load vectors, respectively. The transient temperature field is solved using the implicit solution method of the backward difference approach. In the formula, and They are respectively and Temperature vector at time, ; The convective heat exchange between the nighttime pipe water flow and the glass fiber reinforced composite material is calculated using the following two formulas: In the formula, The heat flow between the nighttime pipe water flow and the glass fiber reinforced composite material; and These are the convective heat transfer coefficient of the water flow in the pipe at night and the inner surface area of ​​the water pipe, respectively. , These are the outer surface temperatures of the water pipes at the inlet and outlet points during the nighttime water flow. , These are the nighttime water flow temperatures at the inlet and outlet of the pipeline, respectively. This represents the amount of water flowing into the pipes at night within a unit of time. The specific heat of the water flow in the pipes at night; When GFRP pipes are circulated with water at night, the amount of heat transferred from the air to the structure via thermal convection is: In the formula, It is the amount of heat (W / m²) transferred per unit time to the surface of a component in space. The convective heat transfer coefficient; Air temperature; The surface temperature of the component is (°C).

[0025] The heat transferred to the atmosphere by the GFRP pipe in the form of thermal radiation is: In the formula, It is the amount of heat (W / m²) transferred per unit time to the surface of a component in space. The component shape factor; The radiation coefficient; This refers to the environmental radiation coefficient. This is the Stefan-Boltzmann constant, with a value of 5.689 × 10⁻ 8 W / (m·℃); The temperature field of a GFRP pipeline at night was analyzed using finite element numerical simulation. For the thermal effect of water flow in the pipeline at night, the equivalent negative heat source method was adopted, and its basic equations are as follows: In the formula, The temperature of the glass fiber reinforced composite material is time. and spatial coordinates , and The function; , and These are the thermal conductivity, specific heat, and density of the glass fiber reinforced composite material, respectively. and These are the initial temperature of the glass fiber reinforced composite material and the inlet water temperature of the nighttime pipeline. This represents the final temperature rise of the glass fiber reinforced composite insulation. and These are functions related to nighttime water temperature and adiabatic temperature rise, respectively. The transient temperature field of glass fiber reinforced composite materials during nighttime is solved using the backward difference method, and its implicit solution is as follows: In the formula, For a period of time; and They are respectively Time and Temperature vector at any given time; , These are matrices related to heat conduction and boundary convection within the solution domain, respectively. A vector that is related to both heat conduction and heat convection; Analysis of daily temperature field simulation results: Simulation software was used to obtain the temperature field, displacement, and stress distribution of the GFRP pipeline at different times during the night. The highest temperature on the inner surface of the GFRP pipeline at night reached 7.75℃, and the lowest was 5.18℃. The highest temperature on the outer surface reached 3.39℃, and the lowest was -1.7℃. The temperature difference between the inner and outer surfaces could reach up to 7℃. The highest shrinkage and creep displacement of the GFRP pipeline at night could reach 0.18mm, which is relatively reasonable and will not affect the normal use of the pipeline. The stress of the GFRP material caused by the temperature difference at night could reach up to 94.2MPa, but the maximum stress value appeared at both ends of the model. In actual engineering, the stress concentration at both ends of the pipeline can be alleviated by the installation method. The maximum thermal stress caused by the temperature difference in the middle section of the pipeline could reach 7.9MPa, which is far less than the strength of the GFRP material and meets the stress calculation requirements. The design of the simulation working condition for four seasons with temperature difference is carried out as follows: Based on the region's climate characteristics, four temperature difference scenarios were designed for spring, summer, autumn, and winter: 22℃ in spring, 20℃ in summer, 15℃ in autumn, and 25℃ in winter. By numerically fitting the temperature change data and applying an approximate trigonometric function to represent the temperature change over time, 24-hour temperature change curves for each season were obtained. Specific temperature data are shown in the table below. Analysis of simulation results of seasonal temperature differences: The thermal boundary conditions were adjusted according to the temperature change curves of each season, and the displacement boundary conditions were kept consistent with the daily temperature field simulation. The simulation software was run to obtain the simulation results under each working condition. Temperature field analysis results show that GFRP material has good thermal insulation performance and its temperature field is less affected by temperature difference: when the temperature difference is 22℃ in spring, the highest temperature in the model within 24 hours is 1.4℃ and the lowest is -0.3℃; when the temperature difference is 20℃ in summer, the highest temperature is 9.6℃ and the lowest is 2.2℃; when the temperature difference is 15℃ in autumn, the highest temperature is 2.2℃ and the lowest is -0.4℃; when the temperature difference is 25℃ in winter, the highest temperature is -3.7℃ and the lowest is -0.2℃. Displacement analysis results show that the deformation of the 5m pipe section under various temperature differences meets the design requirements: the maximum is 0.4mm in spring, 0.3mm in summer, 0.3mm in autumn, and 0.5mm in winter, all ≤0.5mm, and the pipe will not be damaged or the joint will leak due to temperature difference deformation. Stress analysis results show that the thermal stress values ​​in the middle section of the pipe are relatively small and stable: the highest is 8.6 MPa in spring, 7.1 MPa in summer, 6.5 MPa in autumn, and 10.4 MPa in winter. All of these values ​​are less than the strength limit of GFRP material, indicating that the stress state of GFRP drainage pipe is safe and reliable under the temperature difference of the four seasons in cold regions. Through simulation analysis of the effects of temperature field and temperature difference, the performance of GFRP drainage pipes under different temperature environments in cold regions was clarified, providing a scientific basis for the structural design, installation optimization and joint sealing treatment of the pipes, enabling the pipes to adapt to temperature changes in cold regions and operate stably for a long time. S3: Conduct mechanical performance tests on GFRP drainage pipes under freeze-thaw cycles; GFRP material consistent with actual engineering applications was selected, and 15 freeze-thaw cycle specimens were made. The specimen dimensions met the requirements of tensile testing. The specimens were divided into three groups according to the number of freeze-thaw cycles, with 5 specimens in each group, corresponding to 30, 80, and 210 cycles respectively, so that the initial properties of each group of specimens were consistent. Freeze-thaw cycle test equipment and parameter settings: A freeze-thaw cycle chamber was used for the test. Before the test, the power supply, water supply and sensors of the equipment were checked to ensure that they were working properly. The freeze-thaw cycle temperature was set to -20~30℃, the cycle regime was 4 hours of freezing followed by 4 hours of thawing, and the cycle was repeated 3 times a day. The specific test parameters are shown in the table below: Place each set of specimens in the sample rack of the freeze-thaw cycler to ensure the specimens are dry and ice-free, thus avoiding contamination; press the power switch on the controller, fill the water tank with the appropriate amount of water, set the parameters such as the cycle temperature, time, and number of cycles, and press the start button. The equipment will automatically execute the freeze-thaw cycle test; during the test, carefully observe the parameters and alarm information on the controller and deal with any abnormal situations in a timely manner. Mechanical property testing: After each set of specimens has completed a set number of freeze-thaw cycles, it is taken out and restored to room temperature for uniaxial tensile testing; the tensile testing equipment is the same as that used in the basic performance testing of GFRP materials, the testing speed is 5mm / min, and a 50mm mechanical extensometer is used to measure the deformation; When testing tensile strength, follow the formula. Calculation, where Tensile strength (MPa) The maximum axial tensile force (N) experienced by the specimen. The area of ​​the tensile section of the specimen (mm²); When testing the elastic modulus, follow the formula. Calculation, where The tension is N. The cross-sectional area (mm²) of the GFRP material. Elongation (mm). Original length (mm); When testing elongation at break, follow the formula. Calculation, where This is the gauge length (mm) after the gauge breaks. The gauge length (mm) before breakage is taken as the arithmetic mean of the calculated data of no less than 3 specimens as the test result; The mechanical property test data of each group of specimens were compiled to obtain the average tensile strength, elastic modulus, and elongation at break of the GFRP drainage pipe under different freeze-thaw cycles, as shown in the table below: Table 1 Relationship between tensile strength and number of cycles Table 2 Relationship between elastic modulus and number of cycles Table 3 Relationship between elongation at break and number of cycles The test results show that when the cyclic temperature is between -20℃ and 30℃, the tensile strength of GFRP first increases and then decreases with the increase of the number of cycles, and the change range is within 15%. The tensile strength is 1927MPa after 30 cycles, increases to 2153MPa after 80 cycles (an increase of 11.7%), and decreases to 1850MPa after 210 cycles (a decrease of 4% compared to 30 cycles). It is about 8% lower than the indoor conditions (T=+20℃ and RH=65%), indicating that the tensile strength of GFRP is less affected by freeze-thaw cycles. The overall trend of the elastic modulus is first rising and then falling: the average value is 3.1 GPa after 30 cycles, it increases to 3.2 GPa after 80 cycles (an increase of 3.2%), and then drops to 2.7 GPa after 210 cycles (a decrease of 15.6% compared to 80 cycles). The overall value is stable, and the fluctuations are mainly caused by experimental equipment or environmental errors. The elongation at break showed a steady upward trend: the average value was 63.4 after 30 cycles, increased to 67.4 after 80 cycles (an increase of 6.3%), and reached 69.6 after 210 cycles (an increase of 3.2% compared to 80 cycles), with no significant decay, indicating that the plastic deformation capacity of GFRP material is stable under freeze-thaw cycle environment; The freeze-thaw cycle test verified the mechanical performance stability of GFRP drainage pipes in the freeze-thaw environment of cold regions. Its tensile strength, elastic modulus and elongation at break can still meet the requirements of engineering use after long-term freeze-thaw cycles, providing a reliable performance basis for the application of GFRP drainage pipes in cold regions. S4: Theoretical model for studying the high temperature resistance and tensile strength of GFRP drainage pipes; Temperature was used as the test variable, and six test conditions were set: 25℃, 40℃, 80℃, 120℃, 160℃, and 200℃. GFRP sheets and glass fiber bundles consistent with those in actual engineering were selected as test samples, and the linear density of the glass fiber bundles was consistent with the linear density of the fibers in the GFRP sheets. The test equipment used a high-temperature tensile testing device for GFRP sheets and a scanning electron microscope (SEM). The equipment was calibrated before the test to ensure test accuracy. High-temperature performance testing of glass fiber bundles: Cut glass fiber bundle samples of appropriate size, and prepare 5 samples for each working condition; install the samples in a high-temperature tensile device, and conduct tensile tests at six set temperatures, and record the load-strain curves and the maximum tensile force at fracture. Since some fibers inevitably break prematurely during the stretching process, the fiber bundle test results differ from the single filament stretching test results. The method proposed in the literature is used to analyze the test results: First, the number of stressed fibers N1 at the initial loading stage is assessed, calculated from the initial slope S0; then, the Weibull parameter m is calculated based on S0 and S*; subsequently, the fiber bundle's dimensional parameters and average tensile strength are calculated. The Weibull two-parameter model is characterized by the dimensional parameter and the shape parameter m. The dimensional parameter represents the strength index of the specimen, and the shape parameter represents the variability of the fiber tensile strength. The smaller the shape parameter value, the larger the variation range of the fiber tensile strength, and the greater the material dispersion. The test results are shown in the table below: Table 4. Tensile property test results of glass fiber bundles at high temperature Note: The values ​​in parentheses are the standard deviation and coefficient of variation of the experimental data; The test results show that the tensile strength of glass fiber begins to decrease when the temperature rises to 80℃: it decreases by 1.6% at 80℃ compared to room temperature (25℃), by 4.5% at 120℃, by 2.6% at 160℃, and by 14.5% at 200℃; the tensile modulus of the fiber does not change significantly, while the shape parameters gradually decrease with increasing test temperature, decreasing by 29.9% at 200℃ compared to room temperature, indicating that the dispersion of glass fiber increases at high temperatures; High-temperature performance testing of GFRP sheets was conducted, specifically as follows: GFRP sheet specimens with dimensions of 250mm×100mm×1.6mm were cut, and 5 specimens were prepared for each working condition. High-temperature tensile tests were conducted under the same temperature conditions as glass fiber bundles, and the tensile strength, tensile modulus and failure mode were recorded. Tensile strength test results show that the tensile strength of glass fiber reinforced sheets degrades significantly: it decreases by 3.9% at 40℃ compared to room temperature, by 15.3% at 80℃, by 40.7% at 120℃, by 42.2% at 160℃, and by 43.2% at 200℃. The tensile modulus test results show that, compared with tensile strength, the tensile modulus of GFRP sheets degrades less under the influence of temperature: when the temperature exceeds the glass transition temperature of the material, the tensile modulus decreases from 50.0 GPa to 40.0 GPa, and then tends to stabilize; this is because fiber damage is inevitable at higher test temperatures, and according to the blending law, the elastic modulus of FRP changes less. The failure mode observation results show that the board exhibits brittle failure when the test temperature is below 80℃, with the resin matrix surrounding the fibers; at a temperature of 120℃, the surface of the failed sample already shows obvious flocculent structure, which is due to the low glass transition temperature of the GFRP board, resulting in the softening of the resin matrix at high temperatures. Further microstructure analysis was conducted: GFRP samples that failed under tensile stress at different temperatures were selected and subjected to gold sputtering treatment. The microstructure of the cross-section was observed by scanning electron microscopy. The samples tested at room temperature showed a large amount of resin matrix attached to the fibers, indicating that the fibers and resin matrix have good bonding performance. The cross-sections of the samples that failed under tensile stress at 120℃ and 200℃ showed a reduction in resin matrix on the fiber surface and a smoother fiber surface, indicating that the interfacial properties of the material decreased and tended to fail at high temperatures. This is also an important reason for the significant degradation of the high-temperature tensile strength of GFRP sheets. Through tensile strength theory analysis, three theoretical models are used to predict the tensile strength of GFRP sheets: the overall load sharing model, the fiber simultaneous fracture model, and the equivalent volume element model. Constructing an overall load-sharing model: Assuming that the fibers of the unidirectional FRP composite material fail independently upon failure, the shear stress in the stress recovery region (Lr) is constant, the stress distribution along the axial direction of the fractured fiber, and the average stress of the fiber are expressed as: In the formula, The probability of fiber breakage within the stress recovery region Lr; The elastic modulus of the fiber; For the strain of the material; The failure probability of the fiber is represented by the Weibull parameters L0, m, and σ0 as follows: The failure probability q of fiber fracture in the stress recovery zone of length 2Lr can be expressed as: In the formula, The stress on the fiber; Lr can be represented by the interlaminar shear strength of the fiber and the diameter of the fiber: In the formula, For fiber strength; Fiber diameter; This represents the interfacial shear strength; when ε is small, ,beg When the ultimate strain is reached, the maximum average fiber stress can be obtained. The result is expressed as: Further construct a model for simultaneous fiber fracture: The overall load-sharing model was improved, assuming that in a composite material containing n simultaneously fractured fibers, the probability function of fiber fracture in the stress recovery region is: Considering the failure equilibrium of n fibers in a fiber group, the improved stress recovery zone length is: In the formula, This represents the volume fraction of the fiber. when hour, ;when hour, Similarly, we can obtain: If we consider the volume fraction of fibers Given a test value of 63.6%, we can obtain: In the formula, For the strength of the resin matrix; Further construct the equivalent volume element model: Assuming that within an infinite width of the composite material over a length of Li, a fiber of length Li breaks only once, and the fundamental axial distance from the breaking fiber to the neutral plane is Li / 4; the average strength of the fiber is expressed as: In the formula, The stress that does not damage the fiber; To break the stress in the fiber; This represents the cumulative probability distribution of fiber damage. In the formula, Weibull tensile modulus; It is a dimensionless number; The statistical distribution of fiber strength is obtained by converting the gauge length of the test results to the following formula. : get: Assuming the fibers are distributed in a regular hexagonal pattern in the composite material, and the spaces between the fibers are filled with resin, the thickness of the resin matrix is: In the formula, The diameter of the fiber; This represents the volume fraction of the fiber. Assuming the shear stress is uniformly distributed along the fiber radial direction, the shear stress in the interface region is... Ignoring normal stress, the strength of the fractured fiber in the resin yield region and elastic region are expressed as follows: In the formula, The shear modulus of the resin matrix; This refers to the tensile modulus of the fiber. Due to the continuity of stress, it can be expressed as: exist The damaged fibers recovered within the 95% confidence interval, yielding: Assuming we neglect the contribution of the damaged fibers to the ultimate load and the stress transfer in the resin matrix, we can obtain: beg We can obtain: According to the blending law, the strength of the material is: Comparison of theoretical models and experimental results: The prediction results of the three theoretical models were compared with the experimental test results. The comparison of calculation results shows that the calculation results of the representative volume element model, which considers the thickness of the resin matrix between fibers, are in good agreement with the experimental results and can predict the experimental results better. The overall distributed load model has a certain response to fiber fracture, but this model assumes that the shear stress between the fiber and the resin is constant, which leads to the prediction result being too high. The improved fiber simultaneous fracture model considers the impact of simultaneous fiber fracture on the overall performance of FRP materials. It assumes that stress is transferred through the interfacial bonding strength, causing the fiber to fracture. However, the fiber strength is higher than the resin shear strength, so the prediction result is too low. In fact, the resin matrix plays an important role in the stress recovery zone after fiber fracture. The fractured fiber transfers the load through the interfacial stress between the fiber and the resin. When the load exceeds the interfacial shear stress, debonding occurs, and the interfacial stress transfer fails. The representative volume element model considers the influence of this factor, and the prediction results are more accurate. Through high-temperature performance research, the performance degradation law of GFRP drainage pipes under different temperature environments was clarified. In particular, after the temperature exceeds the glass transition temperature, the tensile strength will decrease significantly, while the tensile modulus remains relatively stable. The established tensile strength theoretical model provides a theoretical tool for the performance evaluation of GFRP drainage pipes under extreme temperature environments. It can guide the rational selection of GFRP materials and the design of pipe structures according to actual temperature conditions in engineering practice, and avoid pipe performance failure due to high temperature.

[0026] This invention also provides a construction process for GFRP drainage pipes, which specifically includes the following steps: Clearly define the specifications, installation location, bracket spacing, and connection methods for GFRP drainage pipes; Clean up debris and dust on the bridge deck and piers to keep the construction site clean; According to the requirements of the construction plan, the location of the drainage holes, the pipe connection dimensions and the location of the vertical pipe openings were measured and marked on the bridge deck to provide a reference for subsequent installation. Pipeline pretreatment is carried out, specifically as follows: Grinding treatment: Grind the outer surface of the joint of the GFRP drainage pipe with sandpaper to roughen the surface and improve the bonding strength during the joint. Grind the pipe end into a bevel until the inner lining is exposed, so that the resin adhesive can fully penetrate during the joint and form a strong bonding surface; Cleaning: Use a brush to clean the dust off the surface of the polished pipe. If necessary, compressed air can be used to blow it clean to ensure that the surface of the pipe is free of dust, oil and other impurities, so as not to affect the bonding effect. Continue with the pipe installation, specifically: Pipe lowering: Tie ropes to both ends of the fiberglass water pipe and slowly lower it manually from the bridge deck to directly below the adjacent drainage holes under the flange plate. During the process, avoid the pipe from colliding with the bridge pier or flange plate to prevent pipe damage. Adjust the pipe to a suitable height so that the pipe slope meets the drainage requirements and there is no back slope. Bracket installation: Use a small electric drill to drill holes in the box girder and piers. The drilling position should avoid the position of the reinforcing bars. If there is any conflict, it can be adjusted appropriately. Install the drain pipe hangers and steel clamps at the drilling positions. In principle, the hangers and steel clamps should be arranged in four rows between the two drain outlets according to the drawings. The number of hangers and steel clamps should be increased in special parts (such as pipe bends and long straight sections) to make the pipes firmly fixed. Pipe fixing: Fix the FRP horizontal pipe with hangers and steel clamps, adjust the pipe position so that the horizontal pipe is horizontal and the vertical pipe is vertical, and insert the FRP vertical pipe vertically into the drain outlet directly above, so that the gap between the vertical pipe and the drain outlet is uniform and the connection between the vertical pipe and the horizontal pipe is aligned, in preparation for subsequent hand lay-up connection. Installation in special locations: Where automatic elevators cannot be placed on bridge piers, a crane will be used for installation. The crane's tonnage will be determined based on the actual site conditions to ensure a smooth and safe lifting process. A designated person must direct the lifting operation to prevent pipe collisions or slippage. Further hand lay-up bonding process: Base treatment: Fill the outer surface of the polished pipe and the mating surface with fiberglass yarn until the cut is filled and the mating surface is flat, so that the subsequent layering is uniform; Resin coating: Use a brush to evenly apply the prepared resin adhesive to the mating surface and the fiberglass yarn. Lay the fiberglass yarn layer by layer, and each layer must be fully impregnated with resin and pressed with a pressure plate roller to remove air bubbles until there are no air bubbles on the surface. Laying requirements: No more than 6 layers should be laid at a time, and the overlap width of each layer should not be less than 2cm to ensure a strong bond between layers; the thickness of the glass cloth should be 0.1~0.3mm to facilitate the penetration and adhesion of unsaturated resin. Curing process: The construction time for hand lay-up should be controlled within 30-45 minutes. When preparing the resin adhesive, use a scale or measuring cup to accurately measure the resin and accelerator to ensure precise proportions. All hand lay-up joints should be protected from rain and stress for 24 hours. If the weather is cold, add more accelerator to shorten the curing time. Quality Inspection: After curing, inspect the appearance quality of the hand lay-up joints for defects such as bubbles, cracks, and delamination. Test the initial radial flexural deformation of the pipe according to the specifications. The pipe must not exhibit bulging, flattening, or other abrupt changes, ensuring that the joint strength meets the original pipe strength requirements. Further hydrostatic testing was conducted: Test preparation: After installing all the fiberglass drainage pipes, close the valve at the end of the pipe, fill the pipe with water, and purge the air from the pipe; Test procedure: Perform pressure test according to the "Code for Construction and Acceptance of Water Supply and Drainage Pipeline Engineering". Slowly increase the pressure to the test pressure, keep the pressure stable, and observe whether there is any leakage or seepage in the pipeline and connection nodes.

[0027] Acceptance criteria: If there are no cracks or leaks in the pipeline during the pressure test, and no seepage at the joints, and the allowable seepage amount is in accordance with the standard for steel pipes, that is, if the seepage amount limit required by the specification is met, then the water pressure test is deemed to be qualified.

[0028] Through the above-described on-site installation and hand lay-up connection process, reliable installation of GFRP drainage pipes on bridges in cold regions was achieved. The pipe connections are firm and have good sealing performance, enabling them to adapt to the low-temperature environment of cold regions and avoiding problems such as leakage and blockage caused by improper joint treatment. Strict quality control at each stage of the construction process ensures that the drainage capacity and durability of the drainage system meet the usage requirements of bridge drainage projects in cold regions.

[0029] The embodiments of the present invention also provide a comprehensive verification and effect evaluation of the long-term performance optimization and construction technology of GFRP drainage pipes in cold regions, through a comprehensive test of the feasibility, reliability and practicality of the technology.

[0030] Project Overview: Taking the mid-latitude continental monsoon climate as an example, the summers are short and cool, while the winters are long and cold. The project area is at a high altitude, with an average temperature of -2 to 2℃ and an average daily minimum temperature of -17℃. The diurnal temperature range is large, and the freeze-thaw cycle is frequent, making it a typical bridge project in a cold region. The longitudinal drainage pipes of the bridge deck are made of GFRP pipes, with two specifications: 400mm and 150mm. A total of 4350m of 400mm GFRP drainage pipes and 520m of 150mm GFRP drainage pipes are used for construction using the process provided in this invention.

[0031] Long-term performance monitoring: The operating status of GFRP drainage pipes is monitored over a long period of time, including pipe deformation, joint sealing, and changes in mechanical properties.

[0032] After one year of monitoring, the results showed that under the influence of diurnal temperature variation and freeze-thaw cycles in cold regions, the maximum deformation of a 5m section of GFRP drainage pipe was 0.45mm, which is less than the design limit of 0.5mm. There were no leaks or seepage at any hand lay-up joints, and the joints were well sealed. Through sampling and testing of the pipes, the tensile strength decreased by 5% compared with before construction, the elastic modulus remained basically stable, and the elongation at break increased slightly, meeting the requirements for long-term use.

[0033] Functional Verification: During the monitoring period, the bridge deck drainage was unobstructed, with no rainwater accumulation, and the drainage capacity of the GFRP drainage pipes met the design requirements. The pipes did not exhibit freezing, cracking, or blockage issues, and demonstrated good corrosion resistance, able to withstand the weak acid corrosion of rainwater. Furthermore, the flame-retardant properties of the GFRP drainage pipes met the bridge's fire safety requirements, and no fire hazards were observed.

[0034] Construction effect evaluation: Using the construction process provided by this invention, the installation and connection efficiency of GFRP drainage pipes is high, with an average of 40-50m of pipe installed per day, which is more than 30% more efficient than the installation of traditional metal pipes. The hand lay-up connection process is simple to operate, requires no complicated equipment, reduces construction difficulty, and shortens the construction cycle.

[0035] Through rigorous quality control measures, the pipeline installation was accurate in location, the slope met requirements, the supports were securely fixed, and the strength of the hand lay-up joints met standards. Upon quality inspection, all inspection items met the current national and Ministry of Transport quality acceptance standards, and the project quality was excellent.

[0036] GFRP drainage pipes are lightweight, reducing transportation costs by more than 40% compared to traditional metal pipes; installation does not require large lifting equipment, reducing labor costs by approximately 20%; and GFRP drainage pipes have a long service life, requiring no additional anti-corrosion treatment, significantly reducing subsequent maintenance costs. Overall, the engineering construction and maintenance costs using this invention's process are 25% to 30% lower than traditional methods, resulting in significant economic benefits.

[0037] Comprehensive evaluation conclusion: The long-term performance optimization and construction technology of GFRP drainage pipes for cold regions provided by this invention, through systematic material performance testing, simulation analysis, experimental research, and engineering practice, has fully verified its feasibility and reliability in cold environments. This technology can effectively solve the technical problems of traditional drainage pipes in cold regions, such as easy freezing and cracking, poor corrosion resistance, high construction difficulty, and long-term low-temperature performance degradation of GFRP pipes. It significantly improves the long-term stability, durability, and economy of bridge drainage systems in cold regions, providing a complete technical solution for bridge drainage projects in cold regions, and has significant engineering application value and promising prospects for promotion.

[0038] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A long-term performance testing and optimization process for GFRP drainage pipes in cold regions, characterized in that, Includes the following steps: Basic performance tests were conducted on GFRP materials based on their tensile properties, thermodynamic properties, fiber volume content, and microstructure. The effects of daily temperature field and seasonal temperature difference on GFRP drainage pipes were analyzed by finite element simulation. Mechanical performance testing of GFRP drainage pipes under freeze-thaw cycles was conducted. A theoretical model for the high-temperature resistance and tensile strength of GFRP drainage pipes was developed.

2. The long-term performance testing and optimization process for GFRP drainage pipes in cold regions according to claim 1, characterized in that, The basic performance tests conducted on the tensile properties, thermodynamic properties, fiber volume content, and microstructure of the GFRP material specifically include: GFRP plates with a thickness of 1.6 mm, a width of 100 mm, and a density of 1.91 g / cm³ were selected. Tensile specimens with a length of 250 mm were prepared. The two ends of the specimens were anchored with 3 mm thick aluminum sheets with an anchoring length of 50 mm. The anchoring adhesive was the same as that used for anchoring basalt fiber bundles. Five specimens with dimensional deviations conforming to the specifications were prepared for each working condition. The specimens were mounted on a tensile testing apparatus, and tensile deformation was measured using a 50mm mechanical extensometer. The tensile speed was set to 5mm / min for the tensile test. The maximum axial tensile force and corresponding deformation data of the specimens were recorded, and the average value of 5 specimens was taken as the tensile performance test result. A Q800 dynamic mechanical thermal analyzer was used to test the thermodynamic properties of a 35mm×15mm×1.3mm specimen in a single cantilever configuration. The test frequency was set to 1Hz, the amplitude to 25μm, and the temperature was raised from room temperature to 240℃ at a heating rate of 3℃ / min. The changes in storage modulus, loss modulus, and loss factor with temperature were recorded in real time. Five GFRP samples were selected. The mass of the samples before calcination was measured using a FA2004N precision electronic balance with an accuracy of ±0.0001g. The samples were then placed in a 600℃ high-temperature furnace for 4 hours and cooled to room temperature before the mass of the samples after calcination was measured. The fiber volume content was calculated according to the formula. GFRP samples after tensile fracture were selected, and the fracture surface was sputter-coated with gold for ten minutes. The treated samples were then placed in a QUANTA200F scanning electron microscope, with an accelerating voltage of 30.00 kV and a magnification of 2000x, to observe the bonding state between the fiber and the resin matrix.

3. The long-term performance testing optimization process for GFRP drainage pipes in cold regions according to claim 2, characterized in that, The tensile properties test results were as follows: tensile strength of 820 MPa, tensile modulus of 50.0 GPa, and elongation at break of 1.7% for the GFRP sheet; thermodynamic properties test results were as follows: glass transition temperature of 121.1℃ for the GFRP material; and the volume fractions of the five samples in the fiber volume content test were 0.6235, 0.6424, 0.6507, and 0.6282, with an average value of 63.6%.

4. The long-term performance testing and optimization process for GFRP drainage pipes in cold regions according to claim 1, characterized in that, The analysis of the impact of daily temperature field and seasonal temperature difference on GFRP drainage pipes through finite element simulation specifically includes: Based on ABAQUS finite element analysis software, a solid element model of a GFRP drainage pipe with a length of 5m, a diameter of 400mm, and a wall thickness of 5mm was established. Hexahedral isoparametric elements were used for mesh generation. The global seed approximate global scale was set to 50, and the curvature scale was controlled to 0.1, so that the total number of model elements was 5000 and the total number of nodes was 10100. Input the following thermal property parameters for GFRP material into the simulation software: mass density 1.91 g / cm³, specific heat 1150 J / (kg・℃), convective heat transfer coefficient to pipe 275 W / m²・K, convective heat transfer coefficient to air 15 W / m²・K, and linear expansion coefficient 5 × 10⁻⁻⁻⁴. 6 / ℃, thermal radiation coefficient to air 0.9, thermal conductivity coefficient 0.375W / (m・K); measure the nighttime air temperature and take the average value at each time, combine the influence of water temperature to obtain the relationship between air temperature and water temperature over time, reflect the influence of air temperature and water temperature on the pipeline through surface heat convection, realize the heat transfer from the pipeline to the atmosphere through external surface radiation, and apply a predefined field with an initial temperature of 2℃ to the inner and outer walls of the pipeline. Set the left end of the pipe as a fixed end to constrain all degrees of freedom, and release the right end to release displacement along the pipe length direction and fix the displacement boundary conditions of U1, U2 and UR3; Thermal analysis was conducted based on the Fourier equation, spatial discrete matrix differential equation, and backward difference implicit solution method. Heat transfer was calculated by combining convective heat transfer and thermal radiation formulas. Simulation software was used to obtain the temperature field, displacement, and stress distribution results of the GFRP pipeline at night. Based on the characteristics of cold climate, temperature difference conditions of 22℃ in spring, 20℃ in summer, 15℃ in autumn, and 25℃ in winter were designed. The 24-hour temperature change curves of each season were obtained by numerical fitting. The thermal boundary conditions were adjusted while the displacement boundary conditions were kept unchanged. The simulation software was run to obtain the temperature field, displacement and stress distribution of the pipeline under each temperature difference condition.

5. The long-term performance testing optimization process for GFRP drainage pipes in cold regions according to claim 4, characterized in that, The simulation results of the daily temperature field are as follows: The inner surface temperature of the GFRP pipe is 5.18~7.75℃, the outer surface temperature is -1.7~3.39℃, the maximum temperature difference between the inside and outside is 7℃, the maximum pipe shrinkage and creep displacement is 0.18mm, and the maximum thermal stress in the middle section of the pipe is 7.9MPa. The simulation results of the seasonal temperature difference are as follows: The deformation of a 5m pipe section in each season is ≤0.5mm. The thermal stress in the middle section of the pipe is 8.6MPa in spring, 7.1MPa in summer, 6.5MPa in autumn, and 10.4MPa in winter, all of which are less than the strength limit of GFRP material.

6. The long-term performance testing optimization process for GFRP drainage pipes in cold regions according to claim 1, characterized in that, The aforementioned mechanical performance testing of GFRP drainage pipes under freeze-thaw cycles specifically includes: Fifteen freeze-thaw cycle specimens meeting the tensile test requirements were fabricated using GFRP material consistent with actual engineering applications. These specimens were divided into three groups of five specimens each, with freeze-thaw cycles of 30, 80, and 210 cycles. A freeze-thaw cycle chamber was used for the tests, with the cycle temperature set to -20 to 30°C. The cycle regime was 4 hours of freezing followed by 4 hours of thawing, repeated three times daily. The specimens were placed in the sample rack of the freeze-thaw cycler to complete the set number of cycles. After the freeze-thaw cycles were completed, the specimens were brought back to room temperature. Uniaxial tensile tests were conducted using the same tensile testing equipment as for the basic performance tests, at a test speed of 5 mm / min and with a 50 mm mechanical extensometer to measure deformation. The tensile strength, elastic modulus, and elongation at break of the specimens were calculated using the formulas, and the arithmetic mean of at least three specimen data points was taken as the test result.

7. The optimized process for long-term performance testing of GFRP drainage pipes in cold regions according to claim 6, characterized in that, The results of the freeze-thaw cycle mechanical property test are as follows: The tensile strength of GFRP was 1927 MPa after 30 cycles, 2153 MPa after 80 cycles, and 1850 MPa after 210 cycles, with a variation range within 15%; the elastic modulus was 3.1 GPa after 30 cycles, 3.2 GPa after 80 cycles, and 2.7 GPa after 210 cycles, with overall stable values; the elongation at break was 63.4 after 30 cycles, 67.4 after 80 cycles, and 69.6 after 210 cycles, showing a steady upward trend.

8. The long-term performance testing and optimization process for GFRP drainage pipes in cold regions according to claim 1, characterized in that, The theoretical model for studying the high-temperature resistance and tensile strength of GFRP drainage pipes specifically includes: Six test conditions were set up: 25℃, 40℃, 80℃, 120℃, 160℃, and 200℃. GFRP sheets and glass fiber bundles consistent with the actual engineering were selected as test samples. Five samples were prepared for each test condition. Tensile tests were carried out under each test condition using a GFRP sheet high-temperature tensile device. The load-strain curve and the maximum tensile force at break were recorded. The high-temperature performance of glass fiber bundles was analyzed using the Weibull two-parameter model. The number of fibers under stress at the initial loading stage was evaluated, and the Weibull parameters, fiber bundle dimensional parameters, and average tensile strength were calculated. The tensile strength, tensile modulus, and failure mode of GFRP sheets in high-temperature tensile tests were recorded and analyzed. GFRP samples that failed under tensile conditions at different temperatures were sputter-coated with gold, and the cross-sectional microstructure was observed using scanning electron microscopy. The tensile strength of GFRP sheets was predicted using an overall load-sharing model, a simultaneous fiber fracture model, and an equivalent volume element model. The prediction results of the three models were compared and analyzed with the experimental test results.

9. The long-term performance testing optimization process for GFRP drainage pipes in cold regions according to claim 8, characterized in that, The tensile strength of the glass fiber bundle at 80°C and above shows a decreasing trend, and at 200°C it decreases by 14.5% compared with room temperature, while the tensile modulus does not change significantly. The tensile strength of GFRP sheets degrades significantly with increasing temperature. After exceeding the glass transition temperature, the tensile modulus drops to 40.0 GPa and tends to stabilize. The prediction results of the equivalent volume element model are in best agreement with the experimental results, and can be used as a theoretical tool for performance evaluation of GFRP drainage pipes under extreme temperature conditions.

10. A construction process for GFRP drainage pipes in cold regions, characterized in that, Includes the following steps: Familiarize yourself with the construction drawings to clarify the specifications and installation location requirements of GFRP drainage pipes, clean the construction site, and measure and mark the locations of drainage holes, pipe connections, and vertical pipe openings on the bridge deck. Grind the outer surface of the GFRP drainage pipe joint to roughen it, grind the end into a bevel to expose the inner lining layer, and clean the dust, oil and impurities on the pipe surface after grinding. The fiberglass water pipes were slowly lowered from the bridge deck to the designated position and adjusted to the appropriate height. Small electric drills were used to drill holes in the box girder and piers. Drainage pipe hangers and steel clamps were installed. The horizontal pipes were fixed with the hangers and steel clamps. The vertical pipes were inserted vertically into the drain outlets and aligned with the connection between the horizontal and vertical pipes. Cranes were used to assist in the installation of parts where the automatic elevator could not be used. After the pipe is polished, fill the outer surface and joint surface with glass fiber yarn until the cut is filled. Apply the prepared resin adhesive, lay glass fiber yarn layer by layer and impregnate it with resin, roll it to remove air bubbles. Do not lay more than 6 layers at a time, and the overlap width of the layers should not be less than 2cm. The thickness of the glass cloth is 0.1~0.3mm. Control the hand lay-up process construction time to 30-45 minutes, accurately mix the resin adhesive, add accelerators to speed up curing in low temperature weather, and avoid rain soaking and stress on the hand lay-up joints within 24 hours. After curing, inspect the appearance quality of the hand lay-up joint, test the initial radial flexural deformation of the pipe according to the specifications, and ensure that the strength of the connection joint is consistent with the original pipe. Close the valve at the end of the pipeline, fill the pipeline with water and expel the air, and conduct a water pressure test. The pipeline is considered qualified if there are no leaks or ruptures, no seepage at the joints, and the allowable seepage amount meets the steel pipe standard.

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