Composite pipe of chopped steel fiber concrete and steel tube and design method thereof

Abstract

The present invention belongs to the technical field of pressure pipeline structure design. In order to further improve the tensile and crack resistance of the pipeline, a composite material pipe of short-cut steel fiber concrete and steel cylinder and a design method thereof are proposed. The composite material pipe includes an inner steel cylinder, a short-cut steel fiber concrete layer and an outer steel cylinder. The design method includes: step 1, designing the radial distribution form of steel, the thickness of the inner and outer steel cylinders, and the filling thickness of the short-cut steel fiber concrete; step 2, using a homogenization method to calculate the performance parameters of the short-cut steel fiber concrete; step 3, using a finite element method to perform strength verification and optimization design on the structure of the composite material pipe. The present invention fills the short-cut steel fiber concrete between the inner and outer steel cylinders, optimizes the distribution of steel and the short-cut steel fiber concrete, and improves the bearing capacity and overall stability of the pipeline.

Description

Technical Field

[0001] The present invention belongs to the technical field of pressure pipeline structure design, and particularly relates to a chopped steel fiber concrete and steel cylinder composite material pipe and a design method thereof. Background Art

[0002] In the field of pressure piping, traditional pipe materials such as steel, concrete, and plastic have numerous limitations in practical application. While steel pipes offer high strength, long-term water erosion and corrosion can easily lead to thinning of the pipe walls, reduced strength, and even leakage. Concrete pipes have poor crack resistance and are prone to cracking when subjected to high pressure or external loads, affecting their sealing and service life. Plastic pipes, on the other hand, offer poor resistance to high temperatures and high pressures, and are prone to aging and deformation after long-term use, making them difficult to meet the performance requirements of complex operating conditions.

[0003] Chopped steel fiber concrete, a new composite material, significantly improves its physical and mechanical properties, including tensile strength, flexural strength, crack resistance, impact resistance, and fatigue resistance, by uniformly distributing chopped steel fibers within a cement matrix. Due to its high toughness and multi-dimensional performance advantages, this material has been widely used in engineering fields such as construction, water conservancy projects, highway bridges, airport pavements, railway projects, explosion-proof projects, and maintenance and reinforcement. However, despite its significant advantages in these areas, chopped steel fiber concrete remains a niche application in water pipelines.

[0004] Composite pipes, formed by combining chopped steel fiber reinforced concrete with steel cylinders, are expected to overcome the shortcomings of traditional water pipes and become an ideal pressure pipe structural material. However, current structural design methods for such composite pipes are still imperfect, lacking a systematic and scientific design process, which to some extent limits their widespread application in practical engineering. Summary of the Invention

[0005] In order to overcome the limitations of existing water pipes, and combining the advantages of two base materials, short-cut steel fiber concrete material and steel cylinder material, the present invention aims to provide a composite pipe structure design method that combines short-cut steel fiber concrete with steel cylinder to form a composite pipe structure. The steel cylinder provides external support and compressive resistance, while the short-cut steel fiber concrete enhances crack resistance and durability. The synergistic effect of the two significantly improves the overall performance of the pipeline.

[0006] The design method of a composite pipe of chopped steel fiber concrete and steel cylinder includes the following steps:

[0007] Step 1: Design the radial distribution of steel, the thickness of the inner and outer steel cylinders, and the filling thickness of chopped steel fiber concrete:

[0008] The composite material tube of chopped steel fiber concrete and steel cylinder is configured as follows from the outside to the inside: an outer steel cylinder, a chopped steel fiber concrete layer and an inner steel cylinder. The chopped steel fiber concrete layer is densely filled between the inner and outer steel cylinders. The chopped steel fiber concrete layer is formed by mixing chopped steel fibers and concrete. The volume of the chopped steel fibers is configured to account for 0.5% to 2% of the volume of the concrete. The diameter range of the composite material tube is configured to be 1600 mm to 5000 mm. The composite material tube is designed to have a thick-walled inner steel cylinder and a thin-walled outer steel cylinder. The thickness range of the outer steel cylinder is configured to be 2 to 4 mm, the thickness range of the inner steel cylinder is configured to be 3 to 10 mm, and the thickness range of the chopped steel fiber concrete layer is configured to be 90 to 180 mm. An anti-corrosion coating is configured on the outer surface of the outer steel cylinder. The coating material is epoxy resin or polyurethane, and the coating thickness is 200 to 500 μm.

[0009] Step 2: Calculate the performance parameters of the chopped steel fiber concrete layer using the homogenization method:

[0010] The chopped steel fiber has a variable cross-section structure, and its cross-sectional shape changes along the fiber axis direction, with hooks at both ends. The hook length is 1-3 mm, and the hook angle is 30°-90°. The chopped steel fiber has a diameter of 0.4 mm-0.8 mm, a length of 24 mm-50 mm, an aspect ratio of 30-125, and a tensile strength of ≥800 MPa. The concrete is fine stone concrete, wherein the stone particle size is 5-15 mm, and the particle size is greater than 10 mm. The particle ratio is ≤30%, the fineness modulus is 2.3-3.0, the sand ratio is 40-50%, and the compact density is ≥1600kg / m³; the cementitious material is configured as cement with a P·O ≥ 42.5, the amount used in the concrete is 400-450kg / m³, and the amount of the chopped steel fiber added is 0.25%-0.40% of the cementitious material; the admixture is configured as a polycarboxylic acid-based water reducer, the addition amount is 0.8%-5%, and the water-cement ratio is 0.25-0.35;

[0011] The elastic modulus is , the volume fraction is The chopped steel fibers and elastic modulus are The elastic modulus of the concrete layer mixed into a uniform material for:

[0012] ;

[0013] Poisson's ratio is The chopped steel fibers and Poisson's ratio are The concrete layer is mixed into a homogeneous material with Poisson's ratio for:

[0014] ;

[0015] The tensile strength is The chopped steel fibers and tensile strength are concrete layer, mixed into a uniform material with tensile strength for:

[0016] ;

[0017] Step 3: Use the finite element method to perform strength verification and optimization design on the structure of the composite material pipe, verify the strength of the composite material pipe under internal and external pressure conditions, and optimize the structure of the composite material pipe.

[0018] According to a second aspect of the present invention, a composite material pipe of chopped steel fiber concrete and steel cylinder is provided, which is designed according to the design method of the composite material pipe of chopped steel fiber concrete and steel cylinder.

[0019] Technical effects:

[0020] By filling the space between the inner and outer steel cylinders with chopped steel fiber concrete, the present invention fully utilizes the tensile and crack resistance of the chopped steel fiber concrete. This, in synergy with the high-strength and corrosion-resistant steel cylinder, significantly improves the mechanical properties and durability of the pipeline. Chopped steel fiber concrete, a high-performance composite material, contains uniformly distributed chopped steel fibers that effectively enhance the compressive, tensile, flexural, shear, and impact strength of cement-based materials. It also improves the brittleness of traditional concrete, significantly enhancing the material's toughness and wear resistance. The chopped steel fibers used are hook-end steel fibers. The hooks at the ends of these fibers, when combined with fine aggregate concrete, form a stronger mechanical bond within the concrete, significantly enhancing the interfacial adhesion between the chopped steel fibers and the concrete matrix. The fine aggregate concrete, with its smaller aggregate size, ensures uniform distribution of the hook-end steel fibers within the concrete, effectively reducing fiber agglomeration or uneven distribution caused by excessive aggregate size. Furthermore, the chopped steel fiber concrete and steel cylinder composite pipe is designed with a thick-walled inner steel cylinder and a thin-walled outer steel cylinder, gradually reducing steel usage from the inside out. This maximizes the tensile properties of steel and enhances the pipe's resistance to internal pressure. The thick-walled inner steel cylinder, as the core component bearing internal pressure, effectively disperses the hoop stress generated by internal pressure due to its greater wall thickness, preventing structural deformation and damage caused by internal pressure overload, and laying a solid foundation for the pipe's internal pressure-bearing stability. The thin-walled outer steel cylinder, while still meeting the external pressure-bearing requirements, features a relatively thin wall design, reducing overall structural weight, material usage, and improving economic efficiency. At the same time, a coordinated force system is formed between the thin-walled outer steel cylinder, the concrete layer and the inner steel cylinder, which can help restrain the deformation of the concrete and enhance the overall stiffness of the structure.

[0021] The present invention solves the limitations of traditional water pipe materials in terms of strength, toughness and corrosion resistance, and provides an innovative solution for complex water transportation conditions with long time, high pressure and high load. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is an overall flow chart of a method for designing a chopped steel fiber concrete and steel tube composite pipe according to an embodiment of the present invention.

[0023] Figure 2 This is a schematic diagram of the cross-sectional structure of a chopped steel fiber concrete and steel tube composite material pipe according to an embodiment of the present invention.

[0024] Figure 3 This is the Mises stress cloud diagram of the inner steel cylinder of the short-cut steel fiber concrete and steel cylinder composite material pipe under internal pressure conditions of the present invention.

[0025] Figure 4 This is the Mises stress cloud diagram of the inner steel cylinder of the short-cut steel fiber concrete and steel cylinder composite material pipe under external pressure conditions of the present invention.

[0026] Figure 5 This is the Mises stress cloud diagram of the outer steel cylinder of the short-cut steel fiber concrete and steel cylinder composite material pipe under internal pressure conditions of the present invention.

[0027] Figure 6 This is the Mises stress cloud diagram of the outer steel cylinder of the short-cut steel fiber concrete and steel cylinder composite material pipe under external pressure conditions of the present invention.

[0028] Figure 7 It is a tensile stress cloud diagram of the chopped steel fiber concrete layer of the chopped steel fiber concrete and steel tube composite material pipe under internal pressure conditions.

[0029] Figure 8 This is a tensile stress cloud diagram of the chopped steel fiber concrete layer of the chopped steel fiber concrete and steel tube composite material pipe under external pressure conditions. DETAILED DESCRIPTION

[0030] To make the purpose, technical solutions, and advantages of the embodiments of the present disclosure more clear, the technical solutions in the embodiments of the present disclosure will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present disclosure, not all of the embodiments. Based on the embodiments of the present disclosure, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present disclosure.

[0031] On the one hand, an embodiment of the present invention provides a method for designing a composite pipe of chopped steel fiber concrete and steel cylinder, the method flow is as follows: Figure 1 As shown, the following steps are included:

[0032] Step 1. Design the radial distribution of steel, the thickness of the inner and outer steel cylinders, and the filling thickness of the chopped steel fiber concrete. Specifically, the chopped steel fiber concrete steel cylinder composite material pipe is configured to be an outer steel cylinder 1, a chopped steel fiber concrete layer 2, and an inner steel cylinder 3 from the outside to the inside, and the diameter range of the composite material pipe is configured to be 1600mm~5000mm, the thickness range of the outer steel cylinder 1 is configured to be 2~4mm, and the thickness range of the inner steel cylinder 3 is configured to be 3~10mm; the thickness range of the chopped steel fiber concrete layer 2 is configured to be 90~180mm; the chopped steel fiber concrete layer is composed of a mixture of chopped steel fibers and concrete, and the volume of the chopped steel fibers is configured to account for 0.5%~2% of the concrete volume; an anti-corrosion coating is configured on the outer surface of the outer steel cylinder 1, and the coating material is epoxy resin or polyurethane, and the coating thickness is 200~500μm.

[0033] Preferably, when the diameter of the composite material pipe is ≤2400mm, the thickness of the inner steel cylinder 3 is configured to be 3~5mm, and the thickness of the outer steel cylinder 1 is configured to be 2~4mm; when 2400mm<pipe diameter≤3600mm, the thickness of the inner steel cylinder 3 is configured to be 5~8mm, and the thickness of the outer steel cylinder 1 is configured to be 4mm; when the pipe diameter is >3600mm, the thickness of the inner steel cylinder 3 is configured to be 8~10mm, and the thickness of the outer steel cylinder 1 is configured to be 4mm.

[0034] The specific design dimensions of the chopped steel fiber concrete and steel cylinder composite pipe structure are shown in Table 1.

[0035] Table 1

[0036]

[0037] In actual engineering applications, the above pipe diameters and thicknesses can be adjusted appropriately based on specific pressure requirements, geological conditions, construction environment, and other factors. For example, in areas with poor geological conditions and high external loads, the thickness of the steel tube or the chopped steel fiber concrete layer can be appropriately increased to improve the pipe's load-bearing capacity and stability.

[0038] Step 2: Calculate the performance parameters of the chopped steel fiber concrete layer using the homogenization method:

[0039] The chopped steel fibers have a variable cross-section structure, with their cross-sectional shape changing along the fiber axis. They are hook-end-shaped, with hooks at both ends. The hook length is 1-3 mm, and the hook angle is 30°-90°. They have a diameter of 0.4-0.8 mm, a length of 24-50 mm, an aspect ratio of 30-125, and a tensile strength of 800 MPa or higher. The hook-end geometry of the chopped steel fibers enhances the mechanical anchoring between the steel fibers and concrete, providing high adhesion strength, reducing the risk of fiber pullout, and inhibiting crack propagation. The diameter of the chopped steel fibers affects the bonding performance and reinforcement effect between the steel fibers and concrete. Too thick a fiber affects fluidity, while too thin a fiber is prone to bending and failure. Too high an aspect ratio leads to agglomeration, while too low a ratio provides insufficient bonding strength.

[0040] The concrete is fine stone concrete, wherein the stone particle size is 5-15 mm, the proportion of particles with a particle size greater than 10 mm is ≤30%, the fineness modulus of the medium sand is 2.3-3.0, the sand ratio is 40-50%, and the compact density is ≥1600 kg / m³; the cementitious material is configured as cement with a P·O ≥ 42.5, the amount used in the concrete is 400-450 kg / m³, and the amount of the chopped steel fiber added is 0.25%-0.40% of the cementitious material; the admixture is configured as a polycarboxylic acid-based water reducer, the amount of which is 0.8%-5%, and the water-cement ratio is 0.25-0.35.

[0041] Elastic modulus of chopped steel fiber concrete layer for:

[0042] ,

[0043] in, is the elastic modulus of chopped steel fiber, is the volume fraction of chopped steel fiber, is the elastic modulus of concrete;

[0044] Poisson's ratio of chopped steel fiber concrete layer for:

[0045] ,

[0046] in, is the Poisson's ratio of chopped steel fiber, is the volume fraction of chopped steel fiber, is the Poisson's ratio of concrete;

[0047] Tensile strength of chopped steel fiber concrete layer for:

[0048] ,

[0049] in, is the tensile strength of chopped steel fiber, is the volume fraction of chopped steel fiber, is the tensile strength of concrete.

[0050] The elastic modulus of the chopped steel fiber concrete layer 37845MPa~40380MPa, Poisson's ratio 0.2~0.202, tensile strength It is 10.48MPa~32.93MPa.

[0051] In some embodiments, the chopped steel fibers have an elastic modulus of 206,000 MPa, a Poisson's ratio of 0.3, and a tensile strength of 1,500 MPa; the concrete has a tensile strength of 2.99 MPa, an elastic modulus of 37,000 MPa, and a Poisson's ratio of 0.2.

[0052] In some embodiments, the volume of the chopped steel fibers accounts for 0.5% to 2% of the volume of the concrete. The performance parameters of the chopped steel fiber concrete layer are calculated using the volume fractions of 0.5%, 1%, and 2% of the chopped steel fibers as examples:

[0053] When the volume fraction of chopped steel fiber is 0.5%, is 37845MPa, is 0.2, is 10.48MPa; when the volume fraction is 1%, is 38690MPa, is 0.201, is 17.96MPa; when the volume fraction is 2%, is 40380MPa, is 0.202, It is 32.93MPa.

[0054] These parameters will serve as important input data for subsequent finite element analysis to simulate the mechanical behavior of the chopped steel fiber reinforced concrete layer.

[0055] Step 3: Use the finite element method to perform strength verification and optimization design on the structure of the composite material pipe. The strength verification and optimization design of the structure include: establishing a model of the composite material pipe according to the structural dimensions of the short-cut steel fiber concrete and steel cylinder composite material pipe in Table 1, verifying the strength of the designed short-cut steel fiber concrete and steel cylinder composite material pipe structure under internal and external pressure conditions, and optimizing the structure of the short-cut steel fiber concrete and steel cylinder composite material pipe.

[0056] For example, a finite element model of a composite pipe is constructed with a diameter of 4600 mm, an inner steel tube thickness of 9 mm, an outer steel tube thickness of 4 mm, and a chopped steel fiber concrete layer thickness of 160 mm. The internal pressure is set to 1.6 MPa, and the external pressure is set to 560 kN / m. A linear elastic model is used for both the steel and chopped steel fiber concrete layer materials. The performance parameters of the chopped steel fiber concrete layer are calculated in step 2. Q420B steel is selected as the steel material, and the material parameters are shown in Table 2:

[0057] Table 2

[0058]

[0059] The stress results of various components of the chopped steel fiber concrete layer and steel cylinder composite pipe with different volume fractions under internal and external pressure conditions are shown in Tables 3 and 4:

[0060] Table 3

[0061]

[0062] Table 4

[0063]

[0064] According to the data from Table 3 under internal pressure conditions, when the volume fraction of chopped steel fibers increases from 0.5% to 2%, the average Mises stress of the inner steel cylinder decreases from 90.93 MPa to 86.94 MPa, while the average Mises stress of the outer steel cylinder changes from 74.93 MPa to 79.31 MPa. Under external pressure conditions, as shown in Table 4, when the volume fraction of chopped steel fibers increases from 0.5% to 2%, the average Mises stress of the inner steel cylinder decreases from 116.9 MPa to 114.3 MPa, while the average Mises stress of the outer steel cylinder changes from 111.1 MPa to 122.4 MPa. This indicates that changes in the volume fraction of chopped steel fibers cause changes in the stress values ​​of the inner steel cylinder, chopped steel fiber reinforced concrete, and the outer steel cylinder. Overall, the average Mises stress of the inner steel cylinder decreases with increasing volume fraction of chopped steel fibers, indicating that the addition of chopped steel fibers helps optimize the stress distribution of various pipeline components and ensures more reasonable stress distribution.

[0065] Under internal and external pressure conditions, the Mises stress of the inner and outer steel cylinders of composite tubes made of chopped steel fiber concrete and steel cylinders with different volume fractions is less than the yield strength of Q420B steel. However, at 0.5% and 1% volume fractions of chopped steel fiber, the tensile stress of the chopped steel fiber concrete layer exceeds its tensile strength, causing localized fracture and failure of the concrete. Through equivalent calculations, the load of the concrete layer is proportionally applied to the inner and outer steel cylinders. The Mises stress of the composite tube structure is still less than the yield strength of Q420B steel, and the designed structure meets the strength requirements without affecting normal operation. When the volume fraction of chopped steel fiber is 2%, the stress values ​​of the inner steel cylinder, chopped steel fiber concrete, and outer steel cylinder of the composite tube are all less than the strength limit of the corresponding materials.

[0066] like Figures 3 to 8 As shown in the figure, a composite pipe with a volume fraction of 2% of chopped steel fibers is used as an example to illustrate the specific application of the Mises stress cloud diagram:

[0067] Figure 3 This is the Mises stress cloud diagram of the inner steel cylinder under internal pressure conditions. The results show that the Mises stress distribution of the inner steel cylinder is relatively uniform, with an average value of about 86.94MPa, which is less than the yield limit of Q420B steel and meets the strength requirements. Figure 4 This is the Mises stress cloud diagram of the inner steel tube under external pressure. The results show that the Mises stress of the inner steel tube produces stress concentration at the foundation support. The critical section is about 114.3MPa, which is less than the yield strength of Q420B steel and meets the strength requirements. Figure 5 This is the Mises stress cloud diagram of the outer steel cylinder under internal pressure conditions. The results show that the Mises stress distribution of the outer steel cylinder is relatively uniform, with an average value of about 79.31MPa, which is less than the yield limit of Q420B steel and meets the strength requirements. Figure 6 This is the Mises stress cloud diagram of the outer steel tube under external pressure. The results show that the Mises stress of the outer steel tube produces stress concentration at the foundation support. The critical section is about 122.4MPa, which is less than the yield limit of Q420B steel and meets the strength requirements. Figure 7 This is the tensile stress cloud diagram of the chopped steel fiber concrete layer under internal pressure conditions. The results show that the average tensile stress of the chopped steel fiber concrete layer is about 15.02MPa, which is less than the tensile strength of the chopped steel fiber concrete and meets the strength conditions. Figure 8 This is the tensile stress cloud diagram of the short-cut steel fiber concrete layer under external pressure conditions. The results show that the tensile stress of the concrete layer produces stress concentration at the foundation support. The dangerous section is about 20.67MPa, which is less than the tensile strength of the short-cut steel fiber concrete and meets the tensile strength requirement.

[0068] According to the detailed calculation results of the finite element model, by adjusting the dimensions of the inner steel cylinder, outer steel cylinder, and short-cut steel fiber concrete layer, and then performing finite element simulation, the designed structure can save as much material as possible while meeting the strength requirements, thereby achieving the purpose of optimized design.

[0069] like Figure 2 As shown, another aspect of this embodiment provides a composite material pipe of chopped steel fiber concrete and steel cylinder, which is designed according to the design method of the composite material pipe of chopped steel fiber concrete and steel cylinder, and includes:

[0070] tube body part;

[0071] The pipe body is composed of an outer steel cylinder 1, a chopped steel fiber concrete layer 2 and an inner steel cylinder 3 from the outside to the inside.

[0072] The chopped steel fiber concrete layer 2 is densely filled between the inner steel cylinder 3 and the outer steel cylinder 1 to provide additional compressive resistance and durability.

[0073] Among them, since the chopped steel fibers are evenly distributed in the concrete, the tensile strength, crack resistance, flexural strength and impact resistance of the chopped steel fiber concrete are greatly improved, and the compressive strength and wear resistance are also improved, which can effectively improve the brittleness of the concrete.

[0074] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements to the present invention are intended to fall within the scope of protection of the present invention.

Claims

1. A method for designing a composite pipe of chopped steel fiber concrete and steel cylinder, characterized in that: The steps include: Step 1: Design the radial distribution of steel, the thickness of the inner steel cylinder (3) and the outer steel cylinder (1), and the filling thickness of the chopped steel fiber concrete layer (2): The composite material tube of chopped steel fiber concrete and steel cylinder is configured as follows from outside to inside: an outer steel cylinder (1), a chopped steel fiber concrete layer (2) and an inner steel cylinder (3); the chopped steel fiber concrete layer (2) is densely filled between the inner steel cylinder (3) and the outer steel cylinder (1); the chopped steel fiber concrete layer (2) is formed by mixing chopped steel fibers and concrete; the volume of the chopped steel fibers is configured to account for 0.5% to 2% of the volume of the concrete; the diameter range of the composite material tube is configured to be 1600 mm to 5000 mm; the composite material tube is designed to be a thick-walled inner steel cylinder and a thin-walled outer steel cylinder; the thickness range of the outer steel cylinder (1) is configured to be 2 to 4 mm; the thickness range of the inner steel cylinder (3) is configured to be 3 to 10 mm; the thickness range of the chopped steel fiber concrete layer (2) is configured to be 90 to 180 mm; an anti-corrosion coating is configured on the outer surface of the outer steel cylinder (1); the coating material is epoxy resin or polyurethane, and the coating thickness is 200 to 500 μm; Step 2: Calculate the performance parameters of the chopped steel fiber concrete layer using the homogenization method: The chopped steel fiber has a variable cross-section structure, and its cross-sectional shape changes along the fiber axis direction, with hooks at both ends. The hook length is 1-3 mm, and the hook angle is 30°-90°. The chopped steel fiber has a diameter of 0.4 mm-0.8 mm, a length of 24 mm-50 mm, an aspect ratio of 30-125, and a tensile strength of ≥800 MPa. The concrete is fine stone concrete, wherein the stone particle size is 5-15 mm, and the particle size is greater than 10 mm. The particle ratio is ≤30%, the fineness modulus is 2.3-3.0, the sand ratio is 40-50%, and the compact density is ≥1600kg / m³; the cementitious material is configured as cement with a P·O ≥ 42.5, the amount used in the concrete is 400-450kg / m³, and the amount of the chopped steel fiber added is 0.25%-0.40% of the cementitious material; the admixture is configured as a polycarboxylic acid-based water reducer, the addition amount is 0.8%-5%, and the water-cement ratio is 0.25-0.35; The elastic modulus is , the volume fraction is The chopped steel fibers and elastic modulus are The elastic modulus of the concrete layer mixed into a uniform material for: ； Poisson's ratio is The chopped steel fibers and Poisson's ratio are The concrete layer is mixed into a homogeneous material with Poisson's ratio for: ； The tensile strength is The chopped steel fibers and tensile strength are concrete layer, mixed into a uniform material with tensile strength for: ； Step 3: Use the finite element method to perform strength verification and optimization design on the structure of the composite material pipe, verify the strength of the composite material pipe under internal and external pressure conditions, and optimize the structure of the composite material pipe.

2. The method for designing a composite pipe of chopped steel fiber concrete and steel cylinder according to claim 1, characterized in that: When the pipe diameter configuration D of the composite material pipe is less than or equal to 2400 mm, the thickness of the inner steel cylinder (3) is configured to be 3 to 5 mm, and the thickness of the outer steel cylinder (1) is configured to be 2 to 4 mm; when the pipe diameter configuration D is less than or equal to 2400 mm and less than or equal to 3600 mm, the thickness of the inner steel cylinder (3) is configured to be 5 to 8 mm, and the thickness of the outer steel cylinder (1) is configured to be 4 mm; when the pipe diameter configuration D is greater than or equal to 3600 mm, the thickness of the inner steel cylinder (3) is configured to be 8 to 10 mm, and the thickness of the outer steel cylinder (1) is configured to be 4 mm.

3. The method for designing a composite pipe of chopped steel fiber concrete and steel cylinder according to claim 1, characterized in that: The material configuration of the outer steel cylinder (1) and the inner steel cylinder (3) is Q420B steel, which has an elastic modulus of 206000 MPa, a Poisson's ratio of 0.3, and a tensile strength of 420 MPa.

4. The method for designing a composite pipe of chopped steel fiber concrete and steel cylinder according to claim 1, characterized in that: The chopped steel fiber concrete layer (2) has an elastic modulus of 37845 MPa to 40380 MPa, a Poisson's ratio of 0.2 to 0.202, and a tensile strength of 10.48 MPa to 32.93 MPa.

5. The method for designing a composite pipe of chopped steel fiber concrete and steel cylinder according to claim 1, characterized in that: The volume of the chopped steel fibers accounts for 0.5% to 2% of the volume of the concrete. When the volume fraction is 0.5%, the elastic modulus of the chopped steel fiber concrete layer (2) is 37845 MPa, the Poisson's ratio is 0.2, and the tensile strength is 10.48 MPa; when the volume fraction is 1%, the elastic modulus of the chopped steel fiber concrete layer (2) is 38690 MPa, the Poisson's ratio is 0.201, and the tensile strength is 17.96 MPa; when the volume fraction is 2%, the elastic modulus of the chopped steel fiber concrete layer (2) is 40380 MPa, the Poisson's ratio is 0.202, and the tensile strength is 32.93 MPa.

6. Composite pipe of chopped steel fiber concrete and steel tube, characterized in that: The composite pipe of chopped steel fiber concrete and steel tube is designed according to the design method of any one of claims 1 to 5.

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