An irrigation district assembled UHPC footbridge structure and a design method thereof

Abstract

This invention discloses a prefabricated UHPC pedestrian bridge structure and its design method for irrigation areas, belonging to the field of bridge design technology. It includes: prefabricated abutments fixed to the canal bank, with prefabricated abutments on both sides of the canal bank; pre-reserved slots for the ends of main beams on both sides of the top of the prefabricated abutments; main beams, with both ends capable of being inserted into the pre-reserved slots of the two prefabricated abutments; and main beams on both sides of the prefabricated abutments; the web of the main beams has several through holes evenly distributed along its length; and a bridge deck, which is laid entirely on the top surface of the two main beams and covers the gap between them. This design not only improves construction efficiency and facilitates the entry of small hoisting machinery through a fully prefabricated design, enabling construction without interrupting water supply, but also utilizes the ultra-high strength characteristics of UHPC, combined with the longitudinally spaced openings in the web of the main beams, significantly reducing the structure's self-weight while ensuring its bending and shear bearing capacity.

Description

Technical Field

[0001] This invention relates to the field of bridge design technology, specifically to a prefabricated UHPC pedestrian bridge structure for irrigation areas and its design method. Background Technology

[0002] Irrigation districts are crucial agricultural infrastructure, vital production bases for agricultural products, and play a vital role in supplying water for urban and rural life, industry, and the ecological environment. However, most irrigation district projects in my country were built between the 1950s and 1970s. Some of these pedestrian bridges suffer from low construction standards, excessively narrow bridge decks, and a lack of safety measures, resulting in safety hazards such as pier subsidence, main beam cracking, and bridge deck wear, necessitating urgent replacement. However, the dispersed nature and remote locations of these pedestrian bridges in irrigation districts make daily maintenance and management difficult, and construction quality control challenging. Therefore, the industry urgently needs a new pedestrian bridge structure and technology that is easy to construct, reliable in quality, and durable.

[0003] Currently, pedestrian bridges in irrigation projects are mainly constructed using cast-in-place ordinary reinforced concrete structures, which presents two main problems: First, due to the dispersed and remote locations of pedestrian bridges in irrigation projects, large construction machinery is difficult to access, making standardized on-site construction and quality monitoring challenging. Second, the cast-in-place process relies on the erection of supports within the canal, which not only causes irreversible mechanical damage to the canal lining structure and induces leakage risks, but also has a very short effective construction window due to the limited water supply cycle, severely restricting construction efficiency.

[0004] In recent years, prefabricated bridge structures have been widely used in the transportation sector, but their application in irrigation projects still has limitations: First, ordinary reinforced concrete components are heavy, and most irrigation projects cannot meet the transportation and hoisting construction conditions; second, they involve cast-in-place wet joint technology, which weakens the convenience of prefabrication.

[0005] Therefore, developing a lightweight, durable, fully assembled pedestrian bridge structure that does not affect normal water supply is an urgent problem to be solved in current irrigation projects. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention aims to provide a prefabricated UHPC pedestrian bridge structure for irrigation areas and its design method. This solution not only improves construction efficiency and facilitates the entry of small hoisting machinery through a fully prefabricated design, enabling construction without interrupting water supply, but also utilizes the ultra-high strength characteristics of UHPC, combined with the longitudinally spaced opening design of the main beam web, to significantly reduce the structure's self-weight while ensuring the structure's bending and shear bearing capacity.

[0007] This invention is achieved through the following technical solution:

[0008] A prefabricated UHPC pedestrian bridge structure for irrigation areas includes:

[0009] Precast bridge abutments are fixed to the bank of the channel, and precast bridge abutments are provided on both sides of the channel. The top of each precast bridge abutment is provided with reserved slots for the ends of the main beam.

[0010] The main beam has two ends that can be respectively inserted into the reserved slots of the two precast bridge abutments facing each other; and the main beam is provided on both sides of the precast bridge abutment; the web of the main beam has several through holes evenly distributed along its own length.

[0011] The bridge deck is laid entirely on the top surface of the two main beams and covers the gap between the two main beams.

[0012] In a further optimization, the prefabricated bridge abutment is U-shaped, and a middle partition is connected between the two side plates of the prefabricated bridge abutment. Two partition ribs are provided on one side of the middle partition, and the two partition ribs are symmetrically arranged along the center line of the middle partition and are parallel to the side plates of the prefabricated bridge abutment. A reserved slot is formed between the partition ribs and the side plate of the adjacent prefabricated bridge abutment.

[0013] In a further optimization, the top two sides of the web of the main beam extend outward to form flanges, and the bottom two sides of the web extend outward to form base supports. The width of the reserved slot is matched with the width of the base support.

[0014] In a further optimization, vertical plates extending upwards are provided at both ends of the main beam, and the two vertical plates are used to engage the bridge deck.

[0015] In a further optimization, the lower surface of the bridge deck is provided with a number of stiffening ribs, which are arranged along the length of the bridge deck and are evenly distributed at intervals along the width of the bridge deck.

[0016] The width of the stiffening rib gradually decreases in the direction away from the bridge deck.

[0017] As a further optimization, the gap between the end of the main beam and the reserved slot is filled with flexible cushioning material.

[0018] Further solutions:

[0019] This invention also provides a design method for a prefabricated UHPC pedestrian bridge structure in an irrigation area, comprising the following steps:

[0020] S1: Determine the width L of the main beam based on the channel top width B and the safety distance a;

[0021] S2: Determine the design bending moment M and design shear force V acting on the main beam section based on the pedestrian bridge load;

[0022] S3: Subsequently, for the main beam with openings in the web, the bending capacity and section shear capacity of different opening diameters are checked, and the design parameters that meet the check requirements are selected.

[0023] S4: Determine the bottom dimensions of the precast bridge abutment based on the bearing capacity of the foundation, determine the dimensions of the reserved slots based on the structural dimensions of the main beam, and finally select the bridge deck of the corresponding dimensions to complete the design.

[0024] Further optimization involves the following steps in verifying the flexural bearing capacity:

[0025] S31: Determine the parameters of each section and calculate the height x of the compression zone based on the internal force equilibrium.

[0026] ;

[0027] In the formula, x: height of the equivalent rectangular compression zone of concrete, f c b: Design value of concrete compressive strength; f: Cross-sectional width; y Design value of yield strength of tensile reinforcement; A s : Cross-sectional area of ​​tensile reinforcement; f y ': Design value of yield strength of compression reinforcement; A s ': Cross-sectional area of ​​the compression reinforcement; f t : 0.4 times the design value of concrete tensile strength; h: effective height of concrete single-sided section; 2h is the effective height of beam section; D: diameter of main beam opening; β1: reduction factor for concrete compression zone height; a s : The distance from the resultant point of the longitudinal reinforcing bars in the tension zone to the tension edge of the section; a s ': The distance from the resultant point of the longitudinal reinforcing bars in the compression zone to the compression edge of the section; Compression zone height: The height x of the flanges formed by the outward extension of both sides of the top of the web of the main beam;

[0028] S32: Then, the height of the pressure zone is determined; if it does not meet the requirements... If the condition for discrimination is met, then it is an over-reinforced member, and it is necessary to return to step S1 to adjust the section parameters; and when x≤a s If the structure is deemed under-reinforced, it is necessary to return to step S1 to adjust the reinforcement configuration.

[0029] In the formula, ξ b The relative height of the compression zone is the boundary, Es is the elastic modulus of the steel reinforcement, and ε is the elastic modulus of the steel reinforcement. cu This represents the ultimate compressive strain of the concrete.

[0030] S33: Finally, based on the calculated result of the compression zone height x, the bending bearing capacity is checked. If the check conditions are not met, return to step S1 to adjust the section parameters.

[0031] Further optimization is achieved when verifying the flexural bearing capacity based on the calculation results of the compression zone height x:

[0032] When x ≤ h, the formula for verifying the flexural bearing capacity is:

[0033] ;

[0034] When x > h, the formula for verifying the flexural bearing capacity is:

[0035] ;

[0036] In the formula, M u : The maximum design bending moment on the cross section of the member, x t : The height of the area where the concrete in the tension zone plays a role; Tension zone height: The height of the bottom support formed by the outward extension of the web of the main beam on both sides.

[0037] Further optimization yields the following formula for verifying the shear capacity of the cross-section:

[0038] ;

[0039] In the formula: V: the maximum design shear force on the inclined section of the member; α cv : Shear capacity coefficient of UHPC with inclined section; f ut Design value of axial tensile strength of concrete; f yv Design value of tensile strength of stirrups; A sv : The total cross-sectional area of ​​each leg of the stirrups arranged in the same section; s: The spacing of the stirrups along the length of the member.

[0040] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0041] 1. This invention provides a prefabricated UHPC pedestrian bridge structure and its design method for irrigation areas. The structure is lightweight and requires minimal construction equipment: utilizing the ultra-high strength characteristics of UHPC, combined with a longitudinally spaced perforated design in the main beam web, the structure's self-weight is significantly reduced while ensuring its bending and shear bearing capacity. This feature lowers the requirements for the bearing capacity of the canal bank foundation and makes it possible for small hoisting machinery to enter remote and narrow irrigation areas, significantly reducing logistics and equipment costs.

[0042] 2. This invention provides a prefabricated UHPC pedestrian bridge structure and its design method for irrigation areas, which features high construction efficiency and minimal construction interference. Through a fully prefabricated design, this invention achieves a "factory prefabrication, on-site assembly" operation mode. Dry connections are used between the main beam, abutments, and bridge deck, eliminating the need for full-span scaffolding or cofferdams within the channel. This completely solves the problem of construction being limited by the irrigation area's water supply cycle, enabling uninterrupted construction and effectively avoiding mechanical damage to the channel's anti-seepage lining structure caused by formwork construction.

[0043] 3. This invention provides a prefabricated UHPC pedestrian bridge structure and its design method for irrigation areas, which possesses excellent durability and maintenance-free performance: the near-zero permeability and dense characteristics of UHPC material fundamentally solve the problems of steel corrosion and cracking in traditional structures under the alternating wet and dry conditions and large humidity fluctuations in irrigation areas. Simultaneously, the "flexible limiting nodes" formed by the main beam ends and the abutment beam placement grooves effectively absorb displacement stress caused by temperature differences or uneven channel settlement, avoiding the cracking defects of rigid nodes and significantly extending the service life of the structure.

[0044] 4. The present invention provides a prefabricated UHPC pedestrian bridge structure for irrigation areas and its design method, which has a small impact on the environment: the entire process basically involves no on-site concrete pouring (no wet work), eliminating the pollution of irrigation area water quality and surrounding environment by construction waste slurry.

[0045] 5. This invention addresses the problem of stress redistribution and blank calculation of bearing capacity caused by web openings in UHPC longitudinally spaced perforated beams. It proposes a practical method for calculating their bending and shear bearing capacity, which can provide a reliable theoretical basis for the engineering design of UHPC perforated beams. Attached Figure Description

[0046] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be considered as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort. In the drawings:

[0047] Figure 1 A schematic diagram of a prefabricated UHPC pedestrian bridge structure for irrigation areas after installation in the irrigation area, as provided by the present invention.

[0048] Figure 2 This is a schematic diagram of a prefabricated UHPC pedestrian bridge structure for irrigation areas provided by the present invention;

[0049] Figure 3 This is a schematic diagram of the structure of the prefabricated bridge abutment provided by the present invention;

[0050] Figure 4 This is a front view of the main beam provided by the present invention;

[0051] Figure 5 Provided by the present invention Figure 4 AA section diagram;

[0052] Figure 6 Provided by the present invention Figure 4 Middle BB section view;

[0053] Figure 7 Three views of the bridge deck provided for this invention;

[0054] Figure 8 This is a schematic diagram of the assembly of the bridge deck and main beam provided by the present invention;

[0055] Figure 9 A schematic diagram illustrating the determination of the main beam span provided by this invention;

[0056] Figure 10 This is a schematic diagram of the parameter distribution of the UHPC perforated main beam provided by the present invention;

[0057] Figure 11 The flowchart for verifying the flexural bearing capacity of the UHPC perforated main beam provided by this invention;

[0058] Figure 12 This is a schematic diagram of the design structure of the perforated main beam provided by the present invention;

[0059] Figure 13 This is a schematic diagram of the finite element model of the perforated main beam provided by the present invention;

[0060] Figure 14 The stress cloud diagram (pa) of the steel reinforcement of the beam without openings provided by the present invention;

[0061] Figure 15 Stress cloud diagram (pa) of the reinforcing steel bars in the perforated beam provided for this invention.

[0062] Figure 16 Stress cloud diagram (pa) of UHPC beam without openings provided by the present invention;

[0063] Figure 17 Stress cloud diagram (pa) of the UHPC beam with opening provided by the present invention.

[0064] The attached diagram shows the markings and corresponding component names:

[0065] 1-Precast bridge abutment, 101-Reserved slot, 102-Diaphragm, 103-Separation rib, 2-Main beam, 201-Web plate, 202-Through hole, 203-Flange, 204-Bottom support, 205-Vertical plate, 3-Bridge deck, 301-Stiffening rib. Detailed Implementation

[0066] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0067] Example 1: This Example 1 provides a prefabricated UHPC pedestrian bridge structure for irrigation areas, such as... Figures 1-8 As shown, it specifically comprises a precast abutment 1, an I-shaped UHPC main beam 2 with circular holes in the web 201, a UHPC bridge deck 3, and railings.

[0068] The structure of precast bridge abutment 1 is as follows: Figure 3 As shown, it adopts an integral U-shaped channel support design. The centerlines on both sides of the channel are connected by a central partition 102 to improve structural strength. Two vertical dividing ribs 103 are set on each of the left and right sides inside the channel, dividing the support area into three independent spaces. The middle area is reserved for the bridge deck width. The two side cavities are reserved slots 101 matching the beam width. The length, width, and depth of the slots are adapted to the cross-sectional dimensions and spanning capacity of the main beam 2, so that the main beam 2 can be directly embedded into the prefabricated abutment 1 for assembly. Figure 2 As shown.

[0069] The structure of main beam 2 is as follows Figures 4-6 As shown, the UHPC main beam 2 has an I-shaped cross-section with circular holes in the web 201. The beam has a top groove and circular holes in the web 201. The upper two sides extend outwards to form flanges 203. A vertical plate 205 protrudes upwards on one side of the top to form an L-shaped groove, allowing the bridge deck 3 to be directly assembled and secured to the main beam 2. The middle section has a web of uniform width 201, and the lower two sides extend outwards to form an enlarged bottom 204 that matches the abutment support. Multiple sets of circular through holes 202 are evenly arranged along the longitudinal direction of the beam in the web 201 area. By creating multiple sets of circular through holes 202, the structural self-weight is significantly reduced while ensuring the structural bending and shear bearing capacity. This feature reduces the requirements for the bearing capacity of the canal bank foundation and makes it possible for small hoisting machinery to enter remote and narrow irrigation areas for construction, significantly reducing logistics and equipment costs.

[0070] The structure of bridge deck 3 is as follows Figure 7 As shown, the overall structure is a rectangular plate structure. The plate adopts a "flat top and toothed bottom" cross-section design. The top is a flat working surface, and the bottom is equipped with multiple sets of stiffening ribs 301, such as downward protruding "U"-shaped stiffening ribs 301. The left and right edges can be directly connected to the main beam 2, and the four corner points are connected to the main beam 2 by studs.

[0071] The following construction steps are also included in the specific installation of the prefabricated UHPC pedestrian bridge structure in the irrigation area:

[0072] Step 1: Foundation Treatment and Positioning of Precast Abutment 1. Excavate and level the foundation pit for precast abutment 1 according to the design elevation. Hoist precast abutment 1 to the design position and check the axial deviation and horizontal spacing of the precast slots on both sides, i.e., the abutment beam placement slots.

[0073] Step Two: Leveling the Bottom of the Abutment Beam Placement Channel. A leveling support assembly, such as tar paper or other flexible materials, is laid at the bottom of the channel. The height of the bottom of the channel is pre-adjusted according to the measured elevation to compensate for vertical deviations caused by foundation construction.

[0074] Step 3: Hoisting and Initial Leveling of Main Beam 2. Using hoisting equipment, the I-shaped main beam 2 with the opening in the web 201 is slowly hoisted into the beam placement groove. The bottom of the web 201 of the main beam 2 contacts the pre-set leveling support assembly. Initial leveling is performed by monitoring the levelness of the top surface of the main beam 2.

[0075] Step 4: Axis Alignment. Use jacks to fine-tune main beam 2 to ensure its axis and elevation meet design requirements;

[0076] Step 5: Limiting the main beam 2. Fill the gaps between the two ends of the main beam 2 and the beam placement groove with flexible cushioning material (such as low-density foam board, elastic rubber strips, or polyurethane sealant). This material should wrap around the ends of the main beam 2 and cover the leveling support components to limit the movement, dissipate energy, and prevent debris from entering the beam placement groove.

[0077] Step Six: Bridge Deck 3 Installation and Bolt Tightening. The precast bridge deck 3 is sequentially hoisted above the flange 203 of the main beam 2, aligned with the pre-embedded holes, and high-strength bolts are inserted. A torque wrench is used for symmetrical tightening, utilizing the self-weight of the bridge deck 3 and the bolt pre-tightening force to achieve secondary structural stabilization.

[0078] Step Seven: Ancillary Works and Cleanup. Install the railing reinforcement bars, seal the bolt holes with waterproof material, and clean the site.

[0079] In summary, through the aforementioned prefabricated component structures and installation methods, a "factory prefabrication, on-site assembly" operation mode can be achieved through a fully prefabricated design. The main beam 2 is dry-connected to the prefabricated abutment 1 and bridge deck 3, eliminating the need for full-span scaffolding or cofferdams within the channel. This completely solves the problem of construction being limited by the irrigation area's water supply cycle, enabling uninterrupted construction and effectively avoiding mechanical damage to the channel's anti-seepage lining structure caused by formwork construction.

[0080] Example 2: This Example 2 further optimizes Example 1 and provides a design method for a prefabricated UHPC pedestrian bridge structure in an irrigation area, such as... Figures 9-17 As shown, the specific steps include the following:

[0081] S1: As Figure 9As shown, the span L of the main beam is determined based on the width B at the top of the channel and the safety distance a; L≥B+2a (Formula 1) where L is an integer.

[0082] S2: Determine the design bending moment M and design shear force V acting on section 2 of the main beam based on the pedestrian bridge load.

[0083] S3: According to... Figure 10 and Figure 11 The calculation formula is used to verify the flexural bearing capacity of the main beam with a 201-section opening in the web; specifically, it includes:

[0084] S31: Determine the parameters of each section and calculate the height x of the compression zone based on the internal force equilibrium.

[0085] ;

[0086] In the formula, x: height of the equivalent rectangular compression zone of concrete, f c b: Design value of concrete compressive strength; f: Cross-sectional width; y Design value of yield strength of tensile reinforcement; A s : Cross-sectional area of ​​tensile reinforcement; f y ': Design value of yield strength of compression reinforcement; A s ': Cross-sectional area of ​​the compression reinforcement; f t : 0.4 times the design value of concrete tensile strength; h: effective height of concrete single-sided section; 2h is the effective height of beam section; D: diameter of the second opening in the main beam; β1: reduction factor for the height of the concrete compression zone (taken as 0.8); a s : The distance from the resultant point of the longitudinal reinforcing bars in the tension zone to the tension edge of the section; a s ': Distance from the resultant point of the longitudinal reinforcing bars in the compression zone to the compression edge of the section; Compression zone height: height x of the flange 203 formed by the outward extension of both sides of the top of the web 201 of the main beam 2.

[0087] S32: The height of the pressure zone is then determined:

[0088] The discriminant formula is: (Formula 3). And x≤a s ', (Formula 4).

[0089] In the formula, ξ b The relative height of the compression zone is the boundary, Es is the elastic modulus of the steel reinforcement, and ε is the elastic modulus of the steel reinforcement. cu This represents the ultimate compressive strain of the concrete. If formula 3 is not satisfied, the member is over-reinforced and needs to be returned to step S1 to adjust the section parameters. If x ≤ a s If the component is determined to be under-reinforced, it is necessary to return to step S1 to adjust the reinforcement configuration.

[0090] S33: Finally, perform component similarity assessment, that is, verify the flexural bearing capacity based on the calculated result of the compression zone height x:

[0091] When x ≤ h, the formula for verifying the flexural bearing capacity is:

[0092] ;

[0093] When x > h, the formula for verifying the flexural bearing capacity is:

[0094] ;

[0095] In the formula, M u : The maximum design bending moment on the cross section of the member, x t : The height of the area where the concrete in the tension zone plays a role; Tension zone height: The height of the bottom 204 formed by the outward extension of the web 201 of the main beam 2 on both sides.

[0096] S4: The shear capacity of section 2 of the main beam also needs to be verified. The verification formula is as follows:

[0097] ;

[0098] In the formula: V: the maximum design shear force on the inclined section of the member; α cv The shear capacity coefficient of the inclined section UHPC is related to the member type and stress conditions, and is taken as 0.7; f ut Design value of axial tensile strength of concrete; f yv Design value of tensile strength of stirrups; A sv : The total cross-sectional area of ​​each leg of the stirrups arranged in the same section; s: The spacing of the stirrups along the length of the member.

[0099] S5: Determine the dimensions of the abutment bottom surface based on the bearing capacity of the foundation. Then, determine the dimensions of the embedded beam slot structure based on the structural dimensions of the main beam 2.

[0100] S6: Select pedestrian bridge panel 3, refine the details, and the design will be complete.

[0101] Furthermore, the specific implementation method of the present invention in performing the bearing capacity verification of the main beam 2 as described above is as follows:

[0102] This embodiment verifies the performance of reinforced concrete beam members with different opening diameters. A total of 7 opening diameter conditions (0mm, 50mm, 100mm, 150mm, 200mm, 250mm, 300mm) were set up. The variation laws of flexural bearing capacity, effective height and load-effective height ratio were compared and analyzed by finite element numerical simulation and the theoretical calculation method of this invention to verify the accuracy and engineering applicability of the theoretical method. The calculation results are shown in Table 1.

[0103] The finite element analysis process is as follows:

[0104] The reinforced concrete beam is an open beam, such as... Figure 12 As shown, the beam is 12m long and has a cross-sectional dimension of 28 cm (width) × 65 cm (height). The cross-section adopts a symmetrical thick flange 203 form, with each flange 203 having a thickness of 10 cm. A circular hole with a diameter of D is set in the middle of the beam, with the holes spaced 65 cm apart.

[0105] In the finite element model of the UHPC perforated beam, a plastic damage model is used for the UHPC140 material. This model accurately simulates the nonlinear deformation, strength degradation, and stiffness damage behavior of solid elements under complex stresses by defining the uniaxial compressive and tensile stress-strain relationships of the material, as well as the corresponding compressive and tensile damage evolution parameters. The reinforcing steel is an elasto-plastic material with a diameter of 20mm, and its stress-strain relationship is defined to simulate the nonlinear deformation of the truss elements. All element sizes in the model are 15mm, and embedded constraints are used between the concrete solid elements and the steel truss elements, ignoring the relative slip between them. Boundary conditions are set as simply supported at both ends of the beam, with external loads applied through top surface pressure; for example... Figure 13 As shown.

[0106] This study uses a finite element model to compare and analyze the performance differences between beams without openings and beams with openings of 300mm diameter under stress. Figure 14 and Figure 15 The stress cloud diagrams of the reinforcing bars in the two types of beams show that the first yielding of the reinforcing bars occurs at the mid-span section. Specifically, the mid-span bending moment corresponding to the yielding of the reinforcing bars in the beam without openings is 393 kN·m, while the mid-span bending moment in the beam with an opening diameter of 300 mm is 341 kN·m.

[0107] This study uses a finite element model to compare and analyze the stress performance of a beam without openings and a beam with an opening diameter of 300 mm. From... Figure 16 and Figure 17 In the UHPC longitudinal stress cloud diagram, it can be seen that when the steel bars yield for the first time, the height of the tension zone of the main beam 2 reaches its maximum at the mid-span section and decreases towards both ends along the beam length, which is consistent with the stress characteristics of the maximum bending moment at the mid-span.

[0108] The results show that although opening holes in the main beam 2 will reduce its load-bearing capacity to some extent, the corresponding reduction in the amount of UHPC indicates that this structural form has an advantage in material utilization efficiency.

[0109] Flexural bearing capacity verification: Both the finite element method and theoretical calculations show a linear decreasing trend in flexural bearing capacity with increasing aperture diameter, reflecting the weakening effect of the aperture on the cross-sectional bearing capacity. The theoretical calculation value is slightly lower than the finite element value, which is consistent with the "safety-biased" principle of engineering design, verifying the safety and rationality of the theoretical method of this invention.

[0110] Verification of the effective load-to-height ratio: The effective load-to-height ratio increases with the increase of the opening diameter, reflecting the enhanced stress concentration effect of the cross-section after the opening. The trend of change between the finite element method and the theoretical calculation is in perfect agreement, indicating that the theoretical method of this invention can accurately capture the influence of the opening on the stress distribution of the cross-section.

[0111] Effective height verification: As the opening diameter increases from 0mm to 300mm, the effective height of the cross-section decreases linearly from 650mm to 350mm, which is completely consistent with the theoretically derived law that "the opening diameter is negatively correlated with the effective height", thus verifying the accuracy of the effective height calculation model of this invention.

[0112] Table 1. Calculation results of each opening diameter.

[0113]

[0114] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A prefabricated UHPC pedestrian bridge structure for irrigation areas, characterized in that, include: Precast bridge abutment (1), which is fixed to the bank of the channel, and precast bridge abutment (1) is provided on both banks of the channel. The top two sides of the precast bridge abutment (1) are provided with reserved slots (101) for the ends of the main beam (2). The main beam (2) has two ends that can be respectively inserted into the reserved slots (101) opposite to the two precast bridge abutments (1); and the main beam (2) is provided on both sides of the precast bridge abutment (1); the web plate (201) of the main beam (2) has several through holes (202) evenly distributed along its own length direction. Bridge deck (3), the bridge deck (3) is laid on the top surface of the two main beams (2) and covers the gap between the two main beams (2).

2. The prefabricated UHPC pedestrian bridge structure for irrigation areas according to claim 1, characterized in that, The precast bridge abutment (1) is U-shaped. A partition plate (102) is connected between the two side plates of the precast bridge abutment (1). Two partition ribs (103) are provided on one side of the partition plate (102). The two partition ribs (103) are symmetrically arranged along the center line of the partition plate (102) and are parallel to the side plate of the precast bridge abutment (1). A reserved slot (101) is formed between the partition rib (103) and the side plate of the adjacent precast bridge abutment (1).

3. The prefabricated UHPC pedestrian bridge structure for irrigation areas according to claim 1, characterized in that, The top two sides of the web (201) of the main beam (2) extend outward to form flanges (203), and the bottom two sides of the web (201) extend outward to form a base support (204). The width of the reserved slot (101) is compatible with the width of the base support (204).

4. The prefabricated UHPC pedestrian bridge structure for irrigation areas according to claim 3, characterized in that, At both ends of the main beam (2), there are upwardly extending vertical plates (205), and the two vertical plates (205) are used to insert the bridge deck (3).

5. The prefabricated UHPC pedestrian bridge structure for irrigation areas according to claim 1, characterized in that, The lower surface of the bridge deck (3) is provided with a plurality of stiffening ribs (301), the stiffening ribs (301) are arranged along the length direction of the bridge deck (3), and the plurality of stiffening ribs (301) are evenly distributed at intervals along the width direction of the bridge deck (3). The width of the stiffening rib (301) gradually decreases in the direction away from the bridge deck (3).

6. The prefabricated UHPC pedestrian bridge structure for irrigation areas according to claim 5, characterized in that, The gap between the end of the main beam (2) and the reserved slot (101) is filled with flexible cushioning material.

7. A design method for a prefabricated UHPC pedestrian bridge structure in an irrigation area according to any one of claims 1 to 6, characterized in that, Includes the following steps: S1: Determine the width L of the main beam based on the channel top width B and the safety distance a; S2: Determine the design bending moment M and design shear force V acting on the main beam (2) section based on the pedestrian bridge load; S3: Subsequently, the bending capacity and shear capacity of the main beam (2) with openings in the web were checked for different opening diameters, and the design parameters that meet the verification requirements were selected. S4: Determine the bottom dimensions of the precast bridge abutment (1) based on the bearing capacity of the foundation, and determine the dimensions of the reserved slot (101) based on the structural dimensions of the main beam (2). Finally, select the bridge deck (3) of the corresponding dimensions to complete the design.

8. The design method for a prefabricated UHPC pedestrian bridge structure in an irrigation area according to claim 7, characterized in that, The specific steps for verifying flexural bearing capacity include: S31: Determine the parameters of each section and calculate the height x of the compression zone based on the internal force equilibrium. ； In the formula, x: height of the equivalent rectangular compression zone of concrete, f c b: Design value of concrete compressive strength; f: Cross-sectional width; y Design value of yield strength of tensile reinforcement; A s : Cross-sectional area of ​​tensile reinforcement; f y ': Design value of yield strength of compression reinforcement; A s ': Cross-sectional area of ​​the compression reinforcement; f t : 0.4 times the design value of concrete tensile strength; h: effective height of concrete single-sided section; 2h is the effective height of beam section; D: diameter of main beam opening; β1: reduction factor for concrete compression zone height; a s : The distance from the resultant point of the longitudinal reinforcing bars in the tension zone to the tension edge of the section; a s ': The distance from the resultant point of the longitudinal reinforcing bars in the compression zone to the compression edge of the section; Compression zone height: The height x of the flange (203) formed by the outward extension of the top two sides of the web (201) of the main beam (2); S32: Then, the height of the pressure zone is determined; if it does not meet the requirements... If the condition for discrimination is met, then it is an over-reinforced member, and it is necessary to return to step S1 to adjust the section parameters; and when x≤a s If the structure is deemed under-reinforced, it is necessary to return to step S1 to adjust the reinforcement configuration. In the formula, ξ b The relative height of the compression zone is the boundary, Es is the elastic modulus of the steel reinforcement, and ε is the elastic modulus of the steel reinforcement. cu This represents the ultimate compressive strain of the concrete. S33: Finally, based on the calculated result of the compression zone height x, the bending bearing capacity is checked. If the check conditions are not met, return to step S1 to adjust the section parameters.

9. The design method for a prefabricated UHPC pedestrian bridge structure in an irrigation area according to claim 8, characterized in that, When verifying the flexural bearing capacity based on the calculation results of the compression zone height x: When x ≤ h, the formula for verifying the flexural bearing capacity is: ； When x > h, the formula for verifying the flexural bearing capacity is: ； In the formula, M u : The maximum design bending moment on the cross section of the member, x t :The height of the area where the concrete in the tension zone plays a role; The height of the tension zone: The height of the bottom support (204) formed by the outward extension of the web (201) of the main beam (2) on both sides.

10. The design method for a prefabricated UHPC pedestrian bridge structure in an irrigation area according to claim 8, characterized in that, The formula for verifying the shear capacity of a cross section is: ； In the formula: V: the maximum design shear force on the inclined section of the member; α cv : Shear capacity coefficient of UHPC with inclined section; f ut Design value of axial tensile strength of concrete; f yv Design value of tensile strength of stirrups; A sv : The total cross-sectional area of ​​all legs of the stirrups configured in the same cross-section; s: Spacing of stirrups along the length of the member.

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