Hollow pier cover plate capping construction method

Abstract

The invention provides a hollow bridge pier cover plate capping construction method. The hollow bridge pier cover plate capping construction method comprises the following steps that S1, construction preparation is conducted; s2, prefabricated cover plate steel bar arrangement and binding design are carried out; step S2-1, designing a prefabricated cover plate; step S2-2, carrying out checking calculation on the bearing capacity of the prefabricated cover plate structure; step S2-3, carrying out stress checking calculation on the pier cap with the height of 0.6 m at the bottom; s3, pouring a prefabricated cover plate; s4, the prefabricated cover plate is hoisted; and S5, reinforcing steel bar installation and concrete pouring are conducted. The method is suitable for cover plate method capping construction of the round-end variable-section thin-wall hollow pier of the high-speed railway, and the related pier body capping construction process can accelerate template turnover, shorten the construction period, guarantee safety and reduce the cost.

Description

Technical Field

[0001] The invention belongs to the technical field of bridge engineering, and in particular relates to a construction method for capping a hollow pier cover plate. Background Art

[0002] In modern bridge engineering, the design of pier structures plays a crucial role in determining the overall performance of a bridge. Traditional solid piers, due to their inherent mass, result in high material costs. The stringent weight restrictions imposed on bridges on soft soil or for long spans pose significant challenges to their application. For example, when constructing bridges on soft soil, the immense weight of solid piers can cause foundation settlement, compromising the stability and safety of the bridge.

[0003] To overcome the shortcomings of solid piers, hollow piers have emerged. With the development of new bridge construction technologies, thin-walled hollow pier technology is becoming increasingly popular, particularly in railway bridge construction. However, when bridges are located on steep slopes in complex terrain, the capping of hollow piers remains a challenging step in bridge substructure construction due to limited construction sites, complex lifting routes, and complex structural forces.

[0004] Based on this, this application proposes a hollow pier cover capping construction method suitable for high and steep slope bridges with complex terrain environments. Summary of the Invention

[0005] This application utilizes an improved hollow pier capping construction method, suitable for capping thin-walled hollow piers with rounded ends and deformed cross-sections on high-speed railways. The pier body is constructed using assembled steel formwork, and the pier capping utilizes prefabricated capping plates, replacing traditional full-height scaffolding and brackets, as the base formwork for the pier body and cap. The pier capping construction process described in this application can accelerate formwork turnover, save construction time, ensure safety, and reduce costs.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] A construction method for capping a hollow pier cover plate, wherein the improvement is that the construction method comprises the following steps:

[0008] Step S1: construction preparation;

[0009] Step S2: precast cover reinforcement arrangement and binding design;

[0010] Step S2-1: Designing a prefabricated cover plate; the size of the prefabricated cover plate matches the size of the top of the hollow pier and the capping area of the hollow pier;

[0011] Step S2-2: Verification of the bearing capacity of the prefabricated cover structure;

[0012] Step S2-3: Check the load on the pier cap at the bottom 0.6m high;

[0013] Step S3: pouring the prefabricated cover plate;

[0014] Step S4: hoisting the prefabricated cover plate;

[0015] Step S5: steel bar installation and concrete pouring.

[0016] Step S2-1: prefabricated cover plate design, including the following steps:

[0017] Step S2-1-1, determine the dimensions of the hollow pier: including the height of the hollow pier; the outer slope ratio of the hollow pier; the inner slope ratio of the hollow pier; and the height of the solid section at the top of the hollow pier;

[0018] Step S2-1-2: Determine the size of the prefabricated cover plate. The structural size of the prefabricated reinforced concrete cover plate is determined based on the top size of the hollow pier and the capping area; or the segment size of the prefabricated cover plate is determined based on the capping area and the difficulty of lifting.

[0019] Step S2-1-3, prefabricated cover reinforcement layout and binding design;

[0020] The cover plate includes 6 rectangular independent cover plates of the same size and two trapezoidal independent cover plates of the same size. After the independent cover plates are tied together to form a whole cover plate, the trapezoidal independent cover plates are tied to both ends of the whole cover plate.

[0021] The reinforcement of the rectangular independent cover plate and the trapezoidal independent cover plate includes: an upper steel mesh and a lower steel mesh; the upper steel mesh includes an upper longitudinal reinforcement 3 and an upper transverse reinforcement 4 arranged perpendicular to the upper longitudinal reinforcement; the lower steel mesh includes a lower longitudinal reinforcement 4 and a lower transverse reinforcement 5 arranged perpendicular to the lower longitudinal reinforcement.

[0022] Among them, step S2-2, the prefabricated cover plate structure bearing capacity verification includes:

[0023] Step S2-2-1: Force analysis; obtain the maximum bending moment at the mid-span of the slats caused by all loads on the cover plate:

[0024] M=ql 2 / 8; where q is the cover load; l is the length of the slat;

[0025] Step S2-2-2: Verification of bearing capacity of precast cover slab, including:

[0026] The stress at the center of gravity of the tensile reinforcement of the cover plate is less than the allowable stress;

[0027] σg=M / (Ag×Z)≤[σs]=230.0000MPa;

[0028] σg: stress at the center of gravity of the tensile reinforcement of the cover plate; Ag: area of reinforcement in the tensile zone of the cover plate; Z: moment arm of the cover plate; [σs]: allowable stress;

[0029] The stress at the center of gravity of the compression steel bars of the cover plate is less than the allowable stress;

[0030] σg'=σg×(x-a') / (h0-x)≤[σs]=230.0000MPa;

[0031] σg': stress at the center of gravity of the cover plate's compression reinforcement; x: height of the cover plate's compression zone; a': distance from the center of gravity of the cover plate's tension zone reinforcement to the edge of the section; h0: effective height of the cover plate's compression zone section;

[0032] The maximum compressive stress of the cover slab concrete is less than the allowable stress;

[0033] σh=σg×x / [n×(h0-x)]≤[σs]=230.0000MPa;

[0034] σh: Maximum compressive stress of cover slab concrete; n: Ratio of elastic modulus of steel bar to elastic modulus of concrete;

[0035] Step S2-2-3, crack width verification, the crack width is less than the allowable crack width of 0.25mm;

[0036]

[0037] K1: influence coefficient of steel bar surface shape; K2: load characteristic influence coefficient; r: ratio of the distance from the neutral axis to the tensile edge of the cover plate to the distance from the neutral axis to the center of gravity of the tensile steel bar of the cover plate; d: maximum diameter of the tensile steel bar of the cover plate; μz: effective reinforcement ratio of the tensile steel bar; Es: elastic modulus of the steel bar.

[0038] Among them, step S2-3: force verification calculation of the pier cap at the bottom 0.6m height includes:

[0039] Step S2-3-1, stress analysis of the pier cap at the bottom 0.6m high: The mid-span bending moment of the slab caused by all loads on the 2.40m thick concrete is:

[0040] M'=q'l 2 / 8; where q' is the load on the 2.40m thick concrete; l is the length of the slat;

[0041] Step S2-3-2: Verify the bearing capacity of the pier cap at a height of 0.6m from the bottom, including:

[0042] The stress at the center of gravity of the tensile reinforcement in the pier cap is less than the allowable stress;

[0043] σg'=M' / (Ag'×Z')≤[σs]=230.0000MPa; where, σg': stress at the center of gravity of the tensile reinforcement of the pier cap; Ag': area of reinforcement in the tensile section of the pier cap; Z': moment arm of the internal force of the pier cap; [σs]: allowable stress;

[0044] The stress at the center of gravity of the pier cap compression reinforcement is less than the allowable stress;

[0045] σg”=σg'×(x'-a”) / (h0'-x')≤[σs]=230.0000MPa; where, σg”: stress at the center of gravity of the pier cap compression reinforcement; x': height of the pier cap compression zone; a”: distance from the center of gravity of the pier cap tension zone reinforcement to the edge of the pier cap section; h0': effective height of the pier cap compression zone section;

[0046] The maximum compressive stress of the pier cap concrete is less than the allowable stress;

[0047] σh'=σg'×x' / [n×(h0'-x')]≤[σs]=230.0000MPa; where σh' is the maximum compressive stress of the pier cap concrete; n is the ratio of the elastic modulus of the steel bar to the elastic modulus of the concrete;

[0048] Step S2-3-3: Verify the width of the pier cap crack, and the crack width is less than the allowable crack width of 0.25 mm;

[0049]

[0050] K1: influence coefficient of steel bar surface shape; K2: load characteristic influence coefficient; r': ratio of the distance from the neutral axis to the tensile edge of the pier cap to the distance from the neutral axis to the center of gravity of the tensile steel bar of the pier cap; d': maximum diameter of the tensile steel bar of the pier cap; μz': effective reinforcement ratio of the tensile steel bar of the pier cap; Es: elastic modulus of the steel bar.

[0051] Among them, step S3: casting of prefabricated cover plate includes the following steps:

[0052] Step S3-1, constructing a prefabricated cover plate;

[0053] Step S3-2, prefabricating the cover plate mold;

[0054] Step S3-3, casting the prefabricated cover plate;

[0055] Step S3-4, vibrating concrete;

[0056] Step S3-5, concrete curing;

[0057] Step S3-6, testing the compressive strength of concrete, includes:

[0058] Test block preparation: Randomly sample concrete mixture at the concrete pouring site to make test blocks;

[0059] Loading test: Start the pressure testing machine and apply pressure to the test block evenly at the set loading speed;

[0060] The compressive strength of concrete is calculated as follows: F cu =F / A,

[0061] F cu is the compressive strength of concrete cube (MPa), F is the failure load of the specimen (N), A is the bearing area of the specimen (mm 2 ); the arithmetic mean of the values measured on the three test blocks is taken as the compressive strength value of the test blocks of the group; when the difference between the maximum value or the minimum value and the middle value of the three test blocks exceeds 15% of the middle value, the middle value is taken as the compressive strength value of the test blocks of the group; when the difference between the maximum value and the minimum value and the middle value exceeds 15% of the middle value, the test results of the test blocks of the group are invalid;

[0062] Compare the concrete compressive strength value obtained from the test with the design strength grade. If the compressive strength value of the test piece is greater than or equal to the standard value of the design strength grade, the compressive strength of the batch of concrete is judged to be qualified; if the compressive strength value of the test piece is less than the standard value of the design strength grade, the compressive strength of the batch of concrete is judged to be unqualified.

[0063] Among them, step S4: prefabricated cover hoisting, including the following steps:

[0064] Step S4-1: Before hoisting, the cover plate should be tested for concrete strength rebound to ensure that the concrete strength reaches more than 100% of the design strength before hoisting;

[0065] Step S4-2, lifting the cover plate; during the prefabrication process of each cover plate, four lifting rings are evenly embedded at the four corners; when lifting, four equal-length steel wire ropes are connected to the four lifting rings at one end, and the other end of the steel wire ropes is connected to the hook of the lifting equipment, and then the cover plate is lifted and installed, and the cover plate is kept level during lifting; the supporting plates on both sides of the cover plate are equal in size;

[0066] Step S4-3: After the cover is hoisted into place, it is ready for installation. During installation, the edges of the cover are aligned according to the contour lines so that the contact surface between both sides of the cover and the reserved notches is not less than 10 cm; the forces on the supporting plates on both sides of the cover must be balanced.

[0067] Among them, step S5: installing the pier cap steel bars and pouring the pier cap concrete;

[0068] The pier cap is 300cm high and is poured in two stages: the first stage is 60cm high and the second stage is 240cm high. The second stage is carried out after the first concrete pouring is completed and reaches 100% strength.

[0069] During the concrete pouring process, an inserted vibrator is used for vibration, and the moving distance of the vibrator shall not exceed 1.5 times of the radius of the vibrator; the vibration should be kept at a distance of 5cm to 10cm from the pier cap formwork; it should be inserted into the lower layer of concrete by 5cm to 10cm, and the thickness of each layer of concrete should not exceed 50cm; after each vibration area is completed, the vibrator should be vibrated while being slowly pulled out, and at the same time, the bubbles in the concrete should be drawn out to the surface; for each vibration area, it should be vibrated until the concrete surface of the area becomes flat and the concrete is slurry.

[0070] Among them, the reinforcement of the pier cap at the bottom height of 0.6m includes: longitudinal reinforcement 7 at the bottom of the pier cap, transverse reinforcement 8 at the bottom of the pier cap, longitudinal reinforcement 9 at the top of the pier cap, and transverse reinforcement 10 at the top of the pier cap; the transverse reinforcement 8 at the bottom of the pier cap is arranged perpendicular to the longitudinal reinforcement 7 at the bottom of the pier cap; the transverse reinforcement 10 at the top of the pier cap is arranged perpendicular to the longitudinal reinforcement 9 at the top of the pier cap.

[0071] Beneficial effects:

[0072] The construction method involved in this application can be widely used in the capping construction of variable-section hollow piers in bridge projects such as high-speed railways, passenger dedicated lines, and highways. Prefabricated cover plates of different sizes prefabricated according to the inner diameter of the hollow pier can be applied to piers of other similar bridge structures.

[0073] This application uses an embedded prefabricated cover plate instead of a capping bottom formwork, improving construction safety and simplifying and efficiently implementing the construction process. The cover plate has a reasonable design and a simple structure, allowing it to be prefabricated in advance, effectively reducing construction time. The cover plate is divided into small blocks based on demand, making it convenient for on-site construction and hoisting. The narrow construction surface on the pier top makes it easy to adjust the cover plate position. Compared to traditional bracket construction methods, the method involved in this application greatly improves the working environment and ensures construction safety.

[0074] Compared with the traditional bracket construction method, the concrete of the solid section of the pier top is poured, and the prefabricated cover plate and the cast-in-place concrete of the pier top form a whole, which improves the overall safety and stability. There is no need to remove the bracket and formwork additionally, saving the material and labor costs of setting up the bracket inside the pier. BRIEF DESCRIPTION OF THE DRAWINGS

[0075] The drawings and the accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. Among them:

[0076] Figure 1 This is a flow chart of the hollow bridge pier cover capping construction method involved in the present invention;

[0077] Figure 2 This is the main view of the hollow pier involved in the present invention;

[0078] Figure 3 This is a front view of the cover plate installation involved in the present invention;

[0079] Figure 4 This is a top view of the cover plate installation involved in the present invention;

[0080] Figure 5 A top view of the reinforcement of the cover plate involved in the present invention;

[0081] Figure 6 This is the front view of the reinforcement of the cover plate involved in the present invention;

[0082] Figure 7 This is a left view of the reinforcement of the cover plate involved in the present invention;

[0083] Figure 8 This is the front view of the reinforcement of the pier cap involved in the present invention;

[0084] Among them, 1. Cover plate; 2. Hollow pier; 3. Upper longitudinal reinforcement; 4. Upper transverse reinforcement; 5. Lower longitudinal reinforcement; 6. Lower transverse reinforcement; 7. Longitudinal reinforcement at the bottom of pier cap; 8. Transverse reinforcement at the bottom of pier cap; 9. Longitudinal reinforcement at the top of pier cap; 10. Transverse reinforcement at the top of pier cap. DETAILED DESCRIPTION

[0085] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention are within the scope of protection of the present invention.

[0086] In the description of the present invention, the terms "longitudinal", "transverse", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the present invention and do not require that the present invention must be constructed and operated in a specific orientation. Therefore, they should not be understood as limitations on the present invention. The terms "connected" and "connected" used in the present invention should be understood in a broad sense. For example, it can be a fixed connection or a detachable connection; it can be a direct connection or an indirect connection through an intermediate component. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to the specific circumstances.

[0087] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments. It should be noted that, in the absence of conflict, the embodiments and features of the embodiments of the present invention can be combined with each other.

[0088] The bridge section involved in this application is located in a complex terrain environment and is located on a high and steep slope. There are a total of 10 hollow piers in the entire bridge, with the largest pier height of 58m. The pier structure is a thin-walled hollow pier with a round end deformed cross-section. Its outer slope ratio is 40:1, the inner slope ratio is 60:1, and the height of the solid section of the pier top is 3m. There are many hollow piers in the entire bridge and they are high. Therefore, the pier body is constructed using assembled steel formwork. The pier body capping construction uses prefabricated cover plates instead of traditional full-floor scaffolding and corbel support method (bracket) as the bottom formwork for the pier body and pier cap capping. The cover plates can be prefabricated in advance. The pier body capping construction process, which was summarized through construction experience, has formed this method, which can speed up template turnover, save construction time, ensure safety, and reduce costs.

[0089] like Figure 1 As shown, the present application relates to a method for capping a hollow pier cover, comprising the following steps:

[0090] Step S1: construction preparation;

[0091] Step S2: Arrangement and binding of prefabricated cover plate reinforcement;

[0092] Step S2-1: Designing a prefabricated cover plate; the size of the prefabricated cover plate matches the size of the top of the hollow pier and the capping area of the hollow pier;

[0093] Step S2-2: Verification of the bearing capacity of the prefabricated cover structure;

[0094] Step S2-3: pier cap force verification;

[0095] Step S3: pouring the prefabricated cover plate;

[0096] Step S4: hoisting the prefabricated cover plate;

[0097] Step S5: installing the pier cap reinforcement and pouring the pier cap concrete.

[0098] Specifically, step S1, construction preparation includes: pre-job training for construction personnel and preparation of construction machinery and equipment. Specifically, according to the actual situation on site, prepare a construction plan and complete the filing work as required. Before construction, organize technical personnel to familiarize themselves with the construction plan, learn the construction plan, understand the intention of the construction drawings, study related technical issues, and be familiar with relevant specifications and control technical standards. Improve construction safety technical measures and prepare emergency plans. Conduct technical safety briefings for construction personnel, conduct pre-job safety technical education and training for construction personnel, and after passing the examination, they must be certified to work. Collect and organize various technical data involved in the construction work, organize the labor force, prepare various construction machinery and equipment, and ensure the completeness rate to ensure that the construction requirements are met.

[0099] Step S2-1: Prefabricated cover design, including the following steps:

[0100] Step S2-1-1, determine the size of the hollow pier. Figure 2 As shown, the hollow piers used in this application are hollow piers with rounded ends and variable cross-sections. The rounded ends of the hollow piers refer to the cross-sectional shape of the piers. The ends of the pier cross-section are semicircular, and the center is rectangular or approximately rectangular. This shape has superior mechanical properties, effectively distributing loads. It also has good scour resistance and is suitable for various geological conditions and water flow environments. A variable cross-section means that the cross-sectional dimensions of the piers change along the height direction. Generally speaking, the bottom of the pier bears a large load, so the cross-sectional dimensions at the bottom of the pier are relatively large. As the height increases, the load gradually decreases, and the cross-sectional dimensions also gradually decrease accordingly. The variable cross-sectional design can save materials and reduce the weight of the piers while ensuring the pier's load-bearing capacity, while also making the piers more beautiful and harmonious in appearance. The interior of the pier is a hollow structure, which is called a hollow pier. Compared with solid piers, hollow piers have the advantages of light weight, less material consumption, and reduced construction difficulty. The hollow part can be cast using inner and outer molds, and an appropriate amount of steel bars can be placed in the pier wall to ensure the strength and stability of the pier.

[0101] The hollow pier is 58 meters high. The outer slope ratio is 40:1, meaning that for every 40 units of vertical height increase on the outer surface of the hollow pier, the horizontal extension is 1 unit. The inner slope ratio is 60:1, meaning that for every 60 units of vertical height increase on the inner surface of the hollow pier, the horizontal extension is 1 unit. The solid section at the top of the pier is 3 meters high.

[0102] Step S2-1-2, determine the size of the prefabricated cover plate. Determine the structural size of the prefabricated reinforced concrete cover plate based on the top size of the hollow pier and the capping area; or determine the segmented size of the prefabricated cover plate based on the size of the capping area and the difficulty of lifting.

[0103] The dimensions of the hollow pier's top are 9.4m in width and 5m in length. The straight sections on either side of the hollow pier's column are 4.4m long and serve to determine the column's location. The solid portion of the hollow pier's top is 3m high; the diameter of the circular arcs on either side of the hollow pier's column gradually decreases in slope; the minimum wall thickness of the hollow pier's top is 60cm. A 50cm x 100cm chamfer serves as a reserved notch at the transition between the hollow pier and the solid section of the pier cap. A capping formwork is laid over this notch. The capping formwork consists of a 15cm thick reinforced concrete cover slab, forming the capping formwork for the hollow pier.

[0104] The structure and dimensions of the precast cover were designed based on the hollow shape and capping area of the hollow pier to facilitate prefabrication and installation. Specifically, the precast cover was divided into eight 15cm thick C35 precast individual cover plates, which were placed in the reserved notches. The standard precast individual cover plate dimensions were 1.0m x 3.983m (4m in length for subsequent stress calculations) x 0.15m. The cover plate concrete strength was C35, consistent with the pier concrete strength.

[0105] Step S2-1-3: Precast cover reinforcement arrangement and binding design.

[0106] The precast cover plate reinforcement consists of a double-layer steel mesh set parallel to the ground. The upper steel mesh includes upper longitudinal steel bars spaced 10 cm apart and arranged parallel to each other, as well as upper transverse steel bars used to connect the upper longitudinal steel bars. The lower steel mesh includes lower longitudinal steel bars spaced 10 cm apart and arranged parallel to each other, as well as upper transverse steel bars used to connect the upper longitudinal steel bars. Specifically, the precast cover plate reinforcement design uses a double-layer steel mesh. The upper longitudinal steel bars used in the upper steel mesh are HRB400 (grade 3 rebar) Ø12 steel bars, spaced 10 cm apart, and the upper transverse steel bars are HPB300 (grade 1 rebar) Ø8 steel bars. The lower longitudinal steel bars used in the lower steel mesh are HRB400 Ø16 steel bars, spaced 10 cm apart, and the lower transverse steel bars are HPB300 Ø8 steel bars. The length of the upper longitudinal Ø12 steel bars and the lower longitudinal Ø16 steel bars is 30 cm longer than the cover plate. This means that both the upper and lower longitudinal steel bars must extend 30 cm beyond the cover plate, with the protruding ends angled upward at a 45° angle to the horizontal. Hooks are provided at these protruding ends to facilitate connection and welding with the HRB400Ø25 steel bars that form the main reinforcement of the pier shaft. Preferably, the net protective layer thickness of the cover plate steel bars is 4 cm.

[0107] Specifically, the cover plate includes 6 rectangular independent cover plates of the same size, and two trapezoidal independent cover plates of the same size. After the independent cover plates are tied together to form a whole cover plate, the trapezoidal independent cover plates are tied to both ends of the whole cover plate. The reinforcement of the rectangular independent cover plates and the trapezoidal independent cover plates includes: an upper steel mesh, and a lower steel mesh. The upper steel mesh includes an upper longitudinal reinforcement 3, which adopts an upper longitudinal reinforcement of φ12mm and a horizontal spacing of 100mm, that is, φ12@100. The upper steel mesh includes an upper transverse reinforcement 4 arranged perpendicular to the upper longitudinal reinforcement, which adopts an upper transverse reinforcement of φ8mm and a horizontal spacing of 200mm, that is, φ8@200.

[0108] The lower steel mesh includes lower longitudinal reinforcement 4, which is φ16mm with a horizontal spacing of 100mm, i.e. φ16@100. The lower steel mesh includes lower transverse reinforcement 5, which is arranged perpendicular to the lower longitudinal reinforcement, which is φ8mm with a horizontal spacing of 200mm, i.e. φ8@200.

[0109] Specifically,

[0110] Step S2-2: Verification of the bearing capacity of the precast cover structure, including:

[0111] Step S2-2-1: force analysis;

[0112] The pier cap is constructed with a thickness of 0.60m first. After the 0.60m top plate reaches 90% of the design strength, the remaining second-phase concrete is poured. Calculation of 1m slab:

[0113] Self-weight load of 0.60m thick concrete: q1 = ρVg = 0.60 × 2650 × 10 / 1000 = 15.90kN / m.

[0114] Where ρ is the density of concrete, value: 2650kg / m 3 ; V is the volume of concrete with a 1m slat and 0.60m thickness, which is: 0.6m 3 ; g is the acceleration due to gravity, which is 10N / kg.

[0115] Variable load during construction: q2 = 6.0 × 1.0 = 6.0 kN / m. The combined weight of concrete vibration, concrete pouring, and construction personnel is 6.0 kN / m, and the safety factor is 1.0.

[0116] Total cover load: q = q1 + q2 = 15.90 + 6.0 = 21.90 kN / m

[0117] The maximum bending moment at the mid-span of the slats caused by all loads on the cover plate, that is, the internal force of the section is: M = ql 2 / 8=21.90x4 2 / 8=43.80kN·m; where l is the length of the slat, i.e. the length of the independent cover plate.

[0118] Step S2-2-2: Verify the bearing capacity of the precast cover plate, including: the stress at the center of gravity of the tensile reinforcement of the cover plate is less than the allowable stress; the stress at the center of gravity of the compressive reinforcement of the cover plate is less than the allowable stress; the maximum compressive stress of the cover plate concrete is less than the allowable stress.

[0119] The stress at the center of gravity of the tensile reinforcement of the cover plate is less than the allowable stress:

[0120] σg=M / (Ag×Z)=203.88MPa≤[σs]=230.0000MPa;

[0121] σg: stress at the center of gravity of the tensile reinforcement of the cover plate; Ag: area of reinforcement in the tensile zone of the cover plate, Ag = 0.002010m 2 ; Z: moment arm of force within the cover plate: Z = 0.106881m; [σs]: allowable stress.

[0122] The stress at the center of gravity of the compression steel bar of the cover plate is less than the allowable stress:

[0123] σg'=σg×(x-a') / (h0-x)=67.96MPa≤[σs]=230.0000MPa;

[0124] σg': stress at the center of gravity of the compressive steel bars of the cover plate; x: height of the compressive zone of the cover plate, x = 0.050m; a': distance from the center of gravity of the steel bars in the tensile zone of the cover plate to the edge of the section, a' = 0.0250m; h0: effective height of the section of the compressive zone of the cover plate, h0 = 0.1250m.

[0125] The maximum compressive stress of the cover slab concrete is less than the allowable stress:

[0126] σh=σg×x / [n×(h0-x)]=13.592MPa≤[σs]=230.0000MPa;

[0127] σh: maximum compressive stress of cover slab concrete; n: ratio of elastic modulus of steel bar to elastic modulus of concrete; n=10.00.

[0128] Step S2-2-3, crack width verification, the crack width is less than the allowable crack width of 0.25mm;

[0129]

[0130] K1: Influence coefficient of steel bar surface shape, K1=0.80; K2: Influence coefficient of load characteristics, K2=1.50; r: Ratio of the distance from the neutral axis to the tensile edge of the cover plate to the distance from the neutral axis to the center of gravity of the tensile steel bar of the cover plate, r=1.3320; d: Maximum diameter of the tensile steel bar of the cover plate, d=20mm; μz: Effective reinforcement ratio of the tensile steel bar of the cover plate, μz=0.040200; Es: Elastic modulus of the steel bar, Es=210000MPa.

[0131] From the above calculations, it can be seen that the cover plate reinforcement is designed as a one-way plate with a plate length of 3.984m. The steel bars are all HRB400 steel bars, and the bottom reinforcement is top Distribution reinforcement for the top The concrete strength of the cover plate is the same as that of the pier structure, and the strength of the cover plate meets the requirements of the 0.60m thick pier cap at the top of the construction (5cm more than the third layer of steel bars).

[0132] Step S2-3: Force verification of the pier cap at the bottom 0.6m in height, including:

[0133] Step S2-3-1, stress analysis of the pier cap at the bottom 0.6m height;

[0134] like Figure 8As shown, the pier cap reinforcement at the bottom 0.6m height includes: pier cap bottom longitudinal reinforcement 7, pier cap bottom transverse reinforcement 8, pier cap top longitudinal reinforcement 9, and pier cap top transverse reinforcement 10. Each longitudinal reinforcement at the pier cap bottom consists of two 20mm φ steel bars, laid out with a horizontal spacing of 150mm, i.e., 2Ф20@150mm. The transverse reinforcement at the pier cap bottom consists of 20mm φ steel bars with a horizontal spacing of 200mm, i.e., 20@200mm.

[0135] The longitudinal reinforcement at the top of the pier cap is φ16mm with a horizontal spacing of 150mm, that is, φ16@150mm. The transverse reinforcement at the top of the pier cap is φ16mm with a horizontal spacing of 200mm, that is, φ20@200mm.

[0136] The second phase of pouring of the remaining concrete of the pier cap is calculated according to a height of 2.40m, using 1m slats for calculation, and the span l is calculated as 4m.

[0137] 2.40m thick concrete deadweight load: q1' = ρV'g = 2.40 × 2650 × 10 / 1000 = 63.60kN / m; where ρ is the concrete density, which is 2650kg / m 3 ; V' is 1m and the concrete volume of the slat is 2.40m thick: 2.4m 3 ; g is the acceleration due to gravity, which is 10N / kg.

[0138] The variable load during 2.40m thick concrete construction is: q2' = 6.0 × 1.0 = 6.0 kN / m; the total weight of concrete vibration, concrete pouring, and construction personnel is 6.0 kN / m, and the safety factor is 1.0.

[0139] The total load on the 2.40m thick concrete is: q' = q1' + q2' = 63.60 + 6.0 = 69.60 kN / m;

[0140] The mid-span bending moment of the slab caused by all the loads on the 2.40m thick concrete, that is, the internal force of the section, is:

[0141] M'=q'l 2 / 8=69.60x4 2 / 8=139.20kN·m;

[0142] Step S2-3-2, verification of the bearing capacity of the pier cap at a height of 0.6m at the bottom: including the stress at the center of gravity of the pier cap tensile reinforcement being less than the allowable stress; the stress at the center of gravity of the pier cap compressive reinforcement being less than the allowable stress; and the maximum compressive stress of the pier cap concrete being less than the allowable stress.

[0143] The stress at the center of gravity of the tensile reinforcement in the pier cap is less than the allowable stress:

[0144] σg'=M' / (Ag'×Z')=136.47MPa≤[σs]=230.0000MPa;

[0145] σg': stress at the center of gravity of the tensile reinforcement of the pier cap; Ag': area of reinforcement in the tensile section of the pier cap, Ag' = 0.002010m 2 ; Z': internal moment arm of the pier cap: Z'=0.508956m; [σs]: allowable stress.

[0146] The stress at the center of gravity of the pier cap compression reinforcement is less than the allowable stress:

[0147] σg”=σg’×(x’-a”) / (h0’-x’)=19.724MPa≤[σs]=230.0000MPa;

[0148] σg”: stress at the center of gravity of the compressive steel bars of the pier cap; x': height of the compressive zone of the pier cap, x'=0.113141m; a”: distance from the center of gravity of the steel bars in the tensile zone of the pier cap to the edge of the pier cap section, a”=0.05m; h0’: effective height of the section in the compressive zone of the pier cap, h0’=0.5500m.

[0149] The maximum compressive stress of the pier cap concrete is less than the allowable stress:

[0150] σh'=σg'×x' / [n×(h0'-x')]=3.534MPa≤[σs]=230.0000MPa;

[0151] σh: maximum compressive stress of pier cap concrete; n: ratio of elastic modulus of steel bar to elastic modulus of concrete; n=10.00.

[0152] Step S2-2-3: Check the width of the pier cap crack. The crack width is less than the allowable crack width of 0.25 mm.

[0153] Among them, K1: influence coefficient of steel bar surface shape, K1=0.80; K2: load characteristic influence coefficient, K2=1.50; r': ratio of the distance from the neutral axis to the tensile edge of the pier cap to the distance from the neutral axis to the center of gravity of the tensile steel bar of the pier cap, r'=1.1145; d': maximum diameter of the tensile steel bar of the pier cap, d=22mm; μz': effective reinforcement ratio of the tensile steel bar of the pier cap, μz'=0.020100; Es: elastic modulus of the steel bar, Es=210000MPa.

[0154] From the above calculation, we can see that the bottom steel bar type is: 2Ф20@150mm, and the reinforcement per meter is: 3770mm 2 ; and the top steel bar size is: Ф16@100mm, and the reinforcement per meter is: 2010mm 2 ; all meet the design standards.

[0155] Step S3: Casting of prefabricated cover plates.

[0156] The cover plate prefabrication process is independent and can be carried out simultaneously with the pier construction. Prefabrication can be performed near the pier or at a dedicated prefabrication site before being transported to the pier. The precast concrete for the cover plate is uniformly C35, the same grade as the pier concrete.

[0157] The prefabrication of the cover slab primarily involves tying steel bars, erecting formwork, pouring, and vibrating concrete. Vibration is performed using an insert vibrator. The concrete should be fully compacted, with a rough surface in contact with the concrete in the solid section. Concrete test blocks are also prepared to test the cubic compressive strength of the concrete at 28 days of age and assess the concrete quality. After the cover slab is poured, it must be promptly cured.

[0158] Specifically, in step S3-1, a prefabricated cover plate is constructed; and reinforcement is tied according to the cover plate reinforcement dimensions designed in the previous step.

[0159] Step S3-2, prefabricated cover plate formwork: design the cover plate formwork according to the actual size of the cover plate, and manufacture and process the formwork. During the formwork production process, attention should be paid to ensuring the flatness, verticality and squareness of the corners of the formwork, and at the same time, ensuring that the strength and rigidity of the formwork meet the construction requirements. According to the measured layout position, install the formwork piece by piece in place and fix it with support and connection accessories. The formwork must be tightly spliced to prevent leakage. After the formwork is installed, the formwork needs to be fully reinforced and corrected. Check whether the flatness, verticality, axis position and elevation of the formwork meet the requirements. If there is any deviation, make adjustments in time. When reinforcing, ensure that the formwork is firmly connected to the support system to prevent loosening and deformation during the concrete pouring process.

[0160] Step S3-3, casting of prefabricated cover plate.

[0161] Before pouring concrete, it is necessary to check again the position, size, verticality and stability of the formwork, the number, position and protective layer thickness of the steel bars, etc. to ensure that they meet the design requirements.

[0162] Pour concrete evenly into the formwork, pouring according to a specific thickness and sequence based on the characteristics of the precast cover structure and the construction plan. Pouring methods such as segmented and layered pouring and sloped pouring can be used to ensure concrete quality. During the pouring process, ensure that the concrete fills every corner of the formwork, avoiding dead corners or leaks. Fine-tune the original mix ratio based on the specific conditions of the day, such as temperature, transportation conditions, and slump loss. The slump of the concrete upon entering the formwork should be controlled between 160 and 200 mm.

[0163] During the concrete pouring process, a dedicated person should monitor the formwork to observe deformation, displacement, and leakage. If any problems are found, timely measures should be taken to address them, such as reinforcing the formwork and plugging leaking gaps. At the same time, care should be taken to protect the formwork to avoid impact and damage during concrete pouring.

[0164] Step S3-4, vibrating concrete, specifically:

[0165] Insert the vibrator vertically into the concrete. The insertion depth should reach 50-100 mm of the lower concrete layer to ensure good bonding between the upper and lower layers of concrete.

[0166] Arrangement of vibration points: The vibration points should be evenly spaced, with spacing generally not exceeding 1.5 times the effective radius of the vibrator. The effective radius of the vibrator is usually 300-400 mm, which can be adjusted according to actual conditions.

[0167] After starting the vibrator, the vibration time should be determined until the concrete surface no longer significantly sinks, bubbles no longer appear, and mortar appears on the surface. Generally, the vibration time at each point is 20-30 seconds. However, in actual operation, this time should be adjusted based on factors such as the concrete's slump and aggregate particle size. For concrete with a high slump, the vibration time can be shortened; for concrete with a low slump, the vibration time should be extended.

[0168] The vibrating should be carried out in a certain order to avoid missing or repeated vibration. Generally, start from one end of the concrete pouring and move forward point by point. The vibrating rod should be kept vertical and should not be tilted or vibrate the formwork, steel bars, etc.

[0169] Step S3-5, concrete curing, specifically:

[0170] After the concrete is poured, always pay attention to the external environment and the changes in temperature inside and outside the concrete, and control the cooling gradient of the concrete to prevent cracks caused by a sudden drop in temperature on the concrete surface.

[0171] After pouring concrete, depending on the ambient temperature, the curing period should be no less than 48 hours at temperatures above 5°C. When the ambient temperature is below zero, the curing period should be no less than 72 hours. Attention should be paid to thermal insulation of structural corners. When removing the formwork, cover the concrete with plastic sheeting and a quilt. When the temperature difference between the concrete and the ambient temperature is greater than 20°C, cover the concrete surface after removing the formwork to allow it to cool slowly. This prevents shrinkage cracks from excessively rapid cooling of the concrete surface.

[0172] The continuous wrapping and curing time after the final setting of the concrete shall not be less than 14 days from the removal of the formwork.

[0173] During concrete curing, timely measure ambient parameters such as air temperature, relative humidity, and wind speed, and maintain temperature records. If temperature measurement is required for concrete structures, measure the core and surface temperatures of the concrete structure at the aforementioned frequency and maintain regular temperature records. Curing procedures should be adjusted promptly based on changes in concrete temperature and environmental parameters, ensuring the temperature differential between the interior and exterior of the concrete meets requirements. Any abnormalities should be promptly reported to the relevant departments for action. Concrete temperature measurements should generally be taken at the same time as the age of the specimens being cured under the same conditions.

[0174] Step S3-6: testing the compressive strength of concrete.

[0175] Test block preparation: At the concrete pouring site, concrete mixture is randomly sampled to make test blocks in accordance with relevant standards.

[0176] Specimen Curing: After test block fabrication, the specimen should be left in an environment at 20±5°C for one to two days before being removed from the mold. After demolding, the specimen should be immediately placed in a standard curing room or box for curing at a temperature of 20±2°C and a relative humidity of 95% or higher. If standard curing conditions are unavailable, natural curing may be used, but the specimen surface must remain moist.

[0177] Loading Test: Start the pressure testing machine and apply pressure uniformly to the test block at the specified loading rate. For a 150mm cube, the loading rate is generally 0.3-0.5 MPa per second; for a 100mm cube, the loading rate is 0.2-0.3 MPa per second. When the test block approaches failure, carefully observe the damage and record the failure load.

[0178] Result calculation: The compressive strength of concrete is calculated according to the following formula:

[0179] F cu =F / A,F cu is the compressive strength of concrete cube (MPa), F is the failure load of the specimen (N), A is the bearing area of the specimen (mm 2 The arithmetic mean of the values measured on the three test blocks is taken as the compressive strength value of the test blocks of the group. When the difference between the maximum or minimum value and the middle value of the three test blocks exceeds 15% of the middle value, the middle value is taken as the compressive strength value of the test blocks of the group; when the difference between the maximum value and the minimum value and the middle value exceeds 15% of the middle value, the test results of the test blocks of the group are invalid.

[0180] Compare the concrete compressive strength values obtained from the test with the design strength grade. If the compressive strength value of the test piece is greater than or equal to the standard value of the design strength grade, the batch of concrete is considered to have qualified compressive strength. If the compressive strength value of the test piece is less than the standard value of the design strength grade, the batch of concrete is considered to have failed compressive strength. In the event of failure, the cause should be analyzed and appropriate measures should be taken to address it, such as retesting and reinforcing the concrete structure.

[0181] Step S4: hoisting the prefabricated cover plate.

[0182] Step S4-1: Before hoisting, the cover plate should be subjected to a concrete strength rebound test to ensure that the concrete strength reaches more than 100% of the design strength before hoisting.

[0183] Specifically, keep the axis of the rebound hammer perpendicular to the concrete test surface, apply pressure slowly, read the rebound value accurately, and record it. 16 rebound values should be measured for each test area. The measuring points should be evenly distributed, and repeated measurements at the same location should not be performed. Measure the carbonation depth at a representative location, generally using a phenolphthalein alcohol solution as an indicator. Use an impact drill or electric drill to drill a hole in the concrete surface with a diameter of approximately 15mm and a depth slightly greater than the carbonation depth. After removing powder and debris from the hole, drip the phenolphthalein alcohol solution onto the inner wall of the hole. When the concrete surface changes from colorless to purple-red, use a carbonation depth gauge or steel ruler to measure the carbonation depth to an accuracy of 0.5mm.

[0184] Eliminate the 3 maximum and 3 minimum values from the 6 rebound values, and take the average of the remaining 10 rebound values as the average rebound value of the test part.

[0185] According to the measured carbonization depth value, check the relevant strength measurement curve table or use the formula to correct the average rebound value to obtain the corrected rebound value.

[0186] According to the corrected rebound value, check the corresponding strength measurement curve to obtain the estimated strength value of the concrete.

[0187] Compare the estimated concrete strength value with the design strength grade to determine whether the concrete strength meets the design requirements. When there is doubt or dispute about the test results, other methods such as core drilling can be used for verification.

[0188] Step S4-2, lifting of the cover plate. Select appropriate lifting equipment according to different construction conditions. This application uses 6 independent rectangular cover plates of the same size, and two independent trapezoidal cover plates of the same size. During the prefabrication process of each cover plate, 4 lifting rings are evenly buried at the four corners. When lifting, use 4 steel wire ropes of equal length to suspend the 4 lifting rings at one end, and connect the other end to the hook of the lifting equipment, and then lift and install. The cover plate must be kept horizontal and not tilted during lifting. When the cover plate is lifted and placed in place, the size of the supporting plates on both sides of the cover plate must be equal.

[0189] Step S4-3, after the cover plate is hoisted into place, it is ready for installation. Before installation, the outline of the cover plate is accurately laid out on the top surface of the hollow pier with the center line of the pier as the center. During installation, the edge of the cover plate is accurately aligned according to the outline, so that the contact surface between both sides of the cover plate and the reserved notch is not less than 10 cm. When the reserved steel bars extending out of the cover plate conflict with the main reinforcement of the pier body, they can be adjusted appropriately to ensure that the load on both sides of the cover plate is balanced.

[0190] Step S5: installing the pier cap reinforcement and pouring the pier cap concrete.

[0191] After the cover plate is laid, the reinforcement installation will begin. When tying the reinforcement for the pier cap, the position and spacing must be strictly followed as required by the design. At the same time, attention must be paid to the inspection of the connection position of the pier cap reinforcement.

[0192] After the pier cap steel formwork has passed inspection, the joints are roughened and cleaned before pouring concrete. The pier cap, 300 cm high, is poured in two stages: the first, 60 cm high, using precast cover plates, and the second, 240 cm high. The second pour is conducted after the pier cap reaches 100% strength after the first concrete pour. During the concrete pour, experienced concrete workers are assigned to vibrate the concrete using an insert vibrator. The vibrator rod should be moved no more than 1.5 times its radius, maintaining a distance of 5-10 cm from the formwork and inserted 5-10 cm into the underlying concrete. Each concrete layer should be no thicker than 50 cm. After each vibrating section is completed, the vibrator rod should be slowly withdrawn to draw air bubbles to the surface. During the vibration process, the rod should be prevented from colliding with the formwork, rebar, etc. Each vibrated area should be vibrated until the concrete is densely packed. Solidity is indicated by the cessation of concrete sinking, the absence of bubbles, a flat surface, and a slurry appearance. Strict operating procedures are adhered to during construction to ensure the internal and external quality of the concrete. After pouring, curing is carried out immediately. The solid section of the pier cap is cured using buckets and covered with geotextiles.

[0193] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are within the scope of protection of the pending claims of the present invention.

Claims

1. A method for capping a hollow pier cover, characterized in that: The construction method comprises the following steps: Step S1: construction preparation; Step S2: precast cover reinforcement arrangement and binding design; Step S2-1: Designing a prefabricated cover plate; the size of the prefabricated cover plate matches the size of the top of the hollow pier and the capping area of the hollow pier; Step S2-2: Verification of the bearing capacity of the prefabricated cover structure; Step S2-3: Check the load on the pier cap at the bottom 0.6m high; Step S3: pouring the prefabricated cover plate; Step S4: hoisting the prefabricated cover plate; Step S5: steel bar installation and concrete pouring.

2. The hollow pier capping construction method according to claim 1, characterized in that: Step S2-1: Prefabricated cover design, including the following steps: Step S2-1-1, determine the dimensions of the hollow pier: including the height of the hollow pier; the outer slope ratio of the hollow pier; the inner slope ratio of the hollow pier; and the height of the solid section at the top of the hollow pier; Step S2-1-2: Determine the size of the prefabricated cover plate. The structural size of the prefabricated reinforced concrete cover plate is determined based on the top size of the hollow pier and the capping area; or the segment size of the prefabricated cover plate is determined based on the capping area and the difficulty of lifting. Step S2-1-3, prefabricated cover reinforcement layout and binding design; The cover plate includes 6 rectangular independent cover plates of the same size and two trapezoidal independent cover plates of the same size. After the independent cover plates are tied together to form a whole cover plate, the trapezoidal independent cover plates are tied to both ends of the whole cover plate. The reinforcement of the rectangular independent cover plate and the trapezoidal independent cover plate both include: an upper steel mesh and a lower steel mesh; the upper steel mesh includes an upper longitudinal reinforcement (3) and an upper transverse reinforcement (4) arranged perpendicularly to the upper longitudinal reinforcement; the lower steel mesh includes a lower longitudinal reinforcement (4) and a lower transverse reinforcement (5) arranged perpendicularly to the lower longitudinal reinforcement.

3. The hollow pier cover capping construction method according to claim 1, characterized in that: Step S2-2, the prefabricated cover plate structure bearing capacity verification includes: Step S2-2-1: Force analysis; obtain the maximum bending moment at the mid-span of the slats caused by all loads on the cover plate: M=ql 2 / 8; where q is the cover load; l is the length of the slat; Step S2-2-2: Verification of bearing capacity of precast cover slab, including: The stress at the center of gravity of the tensile reinforcement of the cover plate is less than the allowable stress; σg=M / (Ag×Z)≤[σs]=230.0000MPa; σg: stress at the center of gravity of the tensile reinforcement of the cover plate; Ag: area of reinforcement in the tensile zone of the cover plate; Z: moment arm of the cover plate; [σs]: allowable stress; The stress at the center of gravity of the compression steel bars of the cover plate is less than the allowable stress; σg'=σg×(x-a') / (h0-x)≤[σs]=230.0000MPa; σg': stress at the center of gravity of the cover plate's compression reinforcement; x: height of the cover plate's compression zone; a': distance from the center of gravity of the cover plate's tension zone reinforcement to the edge of the section; h0: effective height of the cover plate's compression zone section; The maximum compressive stress of the cover slab concrete is less than the allowable stress; σh=σg×x / [n×(h0-x)]≤[σs]=230.0000MPa; σh: Maximum compressive stress of cover slab concrete; n: Ratio of elastic modulus of steel bar to elastic modulus of concrete; Step S2-2-3, crack width verification, the crack width is less than the allowable crack width of 0.25mm; K1: influence coefficient of steel bar surface shape; K2: load characteristic influence coefficient; r: ratio of the distance from the neutral axis to the tensile edge of the cover plate to the distance from the neutral axis to the center of gravity of the tensile steel bar of the cover plate; d: maximum diameter of the tensile steel bar of the cover plate; μz: effective reinforcement ratio of the tensile steel bar; Es: elastic modulus of the steel bar.

4. The hollow pier capping construction method according to claim 1, characterized in that: Step S2-3: Force verification of the pier cap at the bottom 0.6m high, including: Step S2-3-1, stress analysis of the pier cap at the bottom 0.6m high: The mid-span bending moment of the slab caused by all loads on the 2.40m thick concrete is: M'=q'l 2 / 8; where q' is the load on the 2.40m thick concrete; l is the length of the slat; Step S2-3-2: Verify the bearing capacity of the pier cap at a height of 0.6m from the bottom, including: The stress at the center of gravity of the tensile reinforcement in the pier cap is less than the allowable stress; σg'=M' / (Ag'×Z')≤[σs]=230.0000MPa; where, σg': stress at the center of gravity of the tensile reinforcement of the pier cap; Ag': area of reinforcement in the tensile section of the pier cap; Z': moment arm of the internal force of the pier cap; [σs]: allowable stress; The stress at the center of gravity of the pier cap compression reinforcement is less than the allowable stress; σg”=σg'×(x'-a”) / (h0'-x')≤[σs]=230.0000MPa; where, σg”: stress at the center of gravity of the pier cap compression reinforcement; x': height of the pier cap compression zone; a”: distance from the center of gravity of the pier cap tension zone reinforcement to the edge of the pier cap section; h0': effective height of the pier cap compression zone section; The maximum compressive stress of the pier cap concrete is less than the allowable stress; σh'=σg'×x' / [n×(h0'-x')]≤[σs]=230.0000MPa; where σh' is the maximum compressive stress of the pier cap concrete; n is the ratio of the elastic modulus of the steel bar to the elastic modulus of the concrete; Step S2-3-3: Verify the width of the pier cap crack, and the crack width is less than the allowable crack width of 0.25 mm; K1: influence coefficient of steel bar surface shape; K2: load characteristic influence coefficient; r': ratio of the distance from the neutral axis to the tensile edge of the pier cap to the distance from the neutral axis to the center of gravity of the tensile steel bar of the pier cap; d': maximum diameter of the tensile steel bar of the pier cap; μz': effective reinforcement ratio of the tensile steel bar of the pier cap; Es: elastic modulus of the steel bar.

5. The hollow pier cover capping construction method according to claim 1, characterized in that: Step S3: Prefabricated cover plate casting, including the following steps: Step S3-1, constructing a prefabricated cover plate; Step S3-2, prefabricating the cover plate mold; Step S3-3, casting the prefabricated cover plate; Step S3-4, vibrating concrete; Step S3-5, concrete curing; Step S3-6, testing the compressive strength of concrete, includes: Test block preparation: Randomly sample concrete mixture at the concrete pouring site to make test blocks; Loading test: Start the pressure testing machine and apply pressure to the test block evenly at the set loading speed; The compressive strength of concrete is calculated as follows: F cu =F / A, F cu is the compressive strength of concrete cube (MPa), F is the failure load of the specimen (N), A is the bearing area of the specimen (mm 2 ); the arithmetic mean of the values measured on the three test blocks is taken as the compressive strength value of the test blocks of the group; when the difference between the maximum value or the minimum value and the middle value of the three test blocks exceeds 15% of the middle value, the middle value is taken as the compressive strength value of the test blocks of the group; when the difference between the maximum value and the minimum value and the middle value exceeds 15% of the middle value, the test results of the test blocks of the group are invalid; Compare the concrete compressive strength value obtained from the test with the design strength grade. If the compressive strength value of the test piece is greater than or equal to the standard value of the design strength grade, the compressive strength of the batch of concrete is judged to be qualified; if the compressive strength value of the test piece is less than the standard value of the design strength grade, the compressive strength of the batch of concrete is judged to be unqualified.

6. The hollow pier capping construction method according to claim 1, characterized in that: Step S4: Prefabricated cover plate hoisting, including the following steps: Step S4-1: Before hoisting, the cover plate should be tested for concrete strength rebound to ensure that the concrete strength reaches more than 100% of the design strength before hoisting; Step S4-2, lifting the cover plate; during the prefabrication process of each cover plate, four lifting rings are evenly embedded at the four corners; when lifting, four equal-length steel wire ropes are connected to the four lifting rings at one end, and the other end of the steel wire ropes is connected to the hook of the lifting equipment, and then the cover plate is lifted and installed, and the cover plate is kept level during lifting; the supporting plates on both sides of the cover plate are equal in size; Step S4-3: After the cover is hoisted into place, it is ready for installation. During installation, the edges of the cover are aligned according to the contour lines so that the contact surface between both sides of the cover and the reserved notches is not less than 10 cm; the forces on the supporting plates on both sides of the cover must be balanced.

7. The hollow pier capping construction method according to claim 1, characterized in that: Step S5: installing the pier cap reinforcement and pouring the pier cap concrete; The pier cap is 300cm high and is poured in two stages: the first stage is 60cm high and the second stage is 240cm high. The second stage is carried out after the first concrete pouring is completed and reaches 100% strength. During the concrete pouring process, an inserted vibrator is used for vibration, and the moving distance of the vibrator shall not exceed 1.5 times of the radius of the vibrator; the vibration should be kept at a distance of 5cm to 10cm from the pier cap formwork; it should be inserted into the lower layer of concrete by 5cm to 10cm, and the thickness of each layer of concrete should not exceed 50cm; after each vibration area is completed, the vibrator should be vibrated while being slowly pulled out, and at the same time, the bubbles in the concrete should be drawn out to the surface; for each vibration area, it should be vibrated until the concrete surface of the area becomes flat and the concrete is slurry.

8. The hollow pier capping construction method according to claim 1, characterized in that: The 0.6m height pier cap reinforcement includes: pier cap bottom longitudinal reinforcement (7), pier cap bottom transverse reinforcement (8), pier cap top longitudinal reinforcement (9), and pier cap top transverse reinforcement (10); the pier cap bottom transverse reinforcement (8) is arranged perpendicularly to the pier cap bottom longitudinal reinforcement (7); and the pier cap top transverse reinforcement (10) is arranged perpendicularly to the pier cap top longitudinal reinforcement (9).

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