Continuous beam closure section crack control construction method

Abstract

The invention discloses a continuous beam closure section crack control construction method which comprises the following steps: S1, transversely pre-burying a slow-coagulation steel strand on a closure section top plate, applying transverse prestress, and performing single-end tensioning; s2, transverse steel bars are additionally arranged on a closure section top plate; s3, steel plate nets are installed on closure section top plate steel bar upper and lower nets and web inner nets; s4, before the closure section is poured, the surfaces of existing concrete at the two ends are wetted, and concrete with the grade higher than that of an original beam body is adopted for vibration pouring; and S5, after concrete pouring is completed, geotechnical cloth is adopted for covering, watering maintenance is conducted, the covering length is larger than the length of the closure section, after maintenance is completed, formwork removal is conducted after slow-bonding prestress tensioning embedded in the top plate is completed, and then the inner formwork is removed. The method is effective for closure section cracks, the number and length of the generated cracks are obviously changed, the length of longitudinal cracks is shortened, the number of the longitudinal cracks is reduced, transverse cracks of the web do not appear, reference can be provided for similar projects, and the method has extremely high popularization value.

Description

Technical Field

[0001] The invention relates to the technical field of bridge construction, and in particular to a construction method for controlling cracks in a closure section of a continuous beam. Background Art

[0002] With the continuous acceleration of bridge construction, the cantilever construction method is the most widely used construction method for railway prestressed concrete continuous box girder bridges, and the closure section construction is the key sequence of cantilever cast-in-place beam construction. Due to the complex force of the closure section structure and the difficulty of construction control technology, common diseases of the closure section include longitudinal cracks, oblique cracks, mesh cracks, concrete pockmarks, etc. Cracks are prone to occur in the top plate bottom and web, and there is no effective method to solve the crack problem. Summary of the invention

[0003] In order to solve the above problems existing in the prior art, a construction method for crack control in a closure section of a continuous beam is provided.

[0004] The technical solution adopted by the present invention to solve its technical problem is: The present invention proposes a construction method for controlling cracks in a continuous beam closure section, comprising: S1: Pre-embed slow-setting steel strands transversely in the top plate of the joint section, stagger the tensioning end and the anchoring section, apply transverse prestress, and perform single-end tensioning; S2: Add transverse reinforcement to the top plate of the joint section. The transverse reinforcement is arranged on the upper part of the steel plate mesh and the lower part of the longitudinal reinforcement. The transverse reinforcement is located outside the longitudinal reinforcement, and both ends of the transverse reinforcement extend into the web wall. S3: Install steel plate mesh on the upper and lower mesh of the top plate reinforcement and the inner mesh of the web at the joint section. After the web reinforcement is tied, install the steel plate mesh on the web; S4: Before pouring the joint section, moisten the existing concrete surface at both ends and vibrate and pour with concrete of a higher grade than the original beam; S5: After the concrete is poured, it is covered with geotextile and watered for maintenance. The covering length is greater than the length of the joint section. After the maintenance is completed, the prestressed slow-bonding prestressing of the top plate is prestressed and the formwork is removed, and then the inner formwork is removed.

[0005] Preferably, in S1, the PE material wrapped around the transverse slow-setting steel strand at the tensioning end is peeled off before tensioning, and then a matching clip anchor is installed, and tensioning is performed using intelligent tensioning equipment, and the elongation is measured with a steel ruler.

[0006] Preferably, in S3, the concrete pad is laid flat, and after the inner form is installed, the top plate ground steel mesh is laid. First, the pad is laid, and then the steel mesh is installed and tied and fixed. After the top plate steel bars are tied, the top plate top surface steel mesh is cut to avoid the three-wall steel bars, the rigid frame, and the sling hole positions.

[0007] Preferably, in S4, the ratio of the expansion agent, anti-cracking agent and polypropylene fiber added to each cubic meter of concrete is 50:30:2.4.

[0008] Preferably, before the construction of the joint section, the center line and elevation of the two cantilever ends are measured and checked. If the center line, elevation and relative deviation of the two cantilever ends are greater than the threshold, counterweight measures are taken to implement corrections. The joint section uses a hanging basket as a working platform, and the inner mold is in the form of a bracket, a top support, square wood, and bamboo plywood. The hanging basket bottom mold system is moved to the joint section and fixed to the beam body through the hanging basket cone. The molds on both sides are pulled as a whole using full-length pull rods. The steel bars, prestressed tendons and embedded parts of the beam body of the joint section are the same as those of other blocks. Before pouring concrete for the joint beam section, the cantilevers at both ends of the joint mouth are pre-stressed to stabilize the cantilever. The pre-stressed weight of each cantilever end is loaded according to the weight of the cast-in-place concrete of the joint section and is gradually removed in equal amounts during the concrete pouring process.

[0009] Preferably, water tank weights or pre-loaded blocks are used as the balancing weight for the construction of the closure section. A water pump is used to fill the water tank with water or a corresponding number of pre-loaded blocks are set according to the weight requirements. As the closure section is constructed, the water in the pool is gradually discharged or the number of pre-loaded blocks is reduced. The concrete of the closure section is poured quickly and continuously during the period of the day when the temperature is the lowest. After the pouring of the closure concrete is completed, moisture-keeping and heat-preservation maintenance is carried out to control the temperature difference between the inside and outside of the beam body, and the closure section and the two cantilever ends are automatically sprinkled with water and covered for maintenance.

[0010] Preferably, all the longitudinal prestressed tendons of the side span closure beam section are tensioned, the temporary consolidation facilities of the corresponding main piers are removed to drop the beams, and the middle support is temporarily constrained in the horizontal direction, the longitudinal prestressed tendons are tensioned and consolidated, the temporary rigid connection structure and water tank in the middle span are installed, and the side hole brackets and the temporary constraints in the horizontal direction of the middle support are removed; When temporary consolidation is dismantled, a rope saw is used. During construction, all prestressing must be completed. When cutting the temporary consolidation support, mark horizontal lines on the temporary support in advance, one line above and one line below. The cutting is carried out along the marked lines. Cut the upper marked line first, then the lower marked line. The cutting is carried out in a symmetrical and uniform manner.

[0011] Preferably, temporary locking is performed before the joint is closed. The temporary locking uses a temporary rigid support composed of I-beams. The temporary rigid supports are respectively located at the top and bottom plates of the box girder near the web. The temporary rigid supports are welded in place on the corresponding embedded parts at both ends of the box girder. Before locking, one end of the temporary rigid support is first welded to the embedded parts at the beam end. When the planned locking time of the beam body arrives, the other end of the temporary rigid support is symmetrically and quickly welded to the embedded parts of the beam body.

[0012] Preferably, after the side span is connected, the hanging basket is moved forward to the connection section. When the middle span is connected, the main pier T-structure hanging basket is used as the construction hanger. After the construction of the last suspended block section is completed, the main pier T-structure hanging basket is retreated to the main pier position for dismantling. During the construction of the suspended block section, the sling holes of the hanging basket support are embedded so that an overall simply supported force system is formed between the two T structures through the hanging basket sling support. When the connection section is constructed, the inner and outer formwork used in the hanging basket construction is used for construction. The outer formwork adopts an integral frame formwork, and the inner formwork adopts a bracket, a top support, square wood, and bamboo plywood.

[0013] Preferably, the concrete pouring time of the joint section is poured when the temperature is the lowest in the day, and the concrete strength reaches 100%, and then tensioning is carried out. After the joint construction of the continuous beam is completed, the hanging basket structure is dismantled. After the construction of the middle span joint section is completed, the hanging baskets on both sides are returned to the main pier position for dismantling; During dismantling, first remove the bottom basket and formwork system of the hanging basket at the position of the last joint beam section in the reverse order of assembly. First disassemble the side formwork formwork, inner formwork top plate formwork and bottom plate formwork, then use the tower crane to lift the formwork away, and then remove the bottom plate longitudinal beam and outer running beam, and lift them away with the tower crane. Use the tower crane to dismantle the main frame and cross beam, then move the main truss of the hanging basket on the side of the road back to the pier top position, and remove the main truss rods of the hanging basket in the reverse order of assembly. At the two cantilever ends, dismantle the hanging basket from the outside to the inside and left and right symmetrically.

[0014] Compared with the prior art, the present invention has the following beneficial effects: 1. The crack control construction method for the joint section of the continuous beam proposed in the present invention has been proven to be effective in preventing cracks in the joint section after repeated practical demonstration. The number and length of cracks generated have been significantly improved, the length of longitudinal cracks has been shortened, the number has been reduced, and transverse cracks in the web have not appeared. It can provide reference for similar projects and has extremely high promotion value.

[0015] 2. The method proposed in the present invention reduces the problem of poor ventilation conditions, large temperature difference between the inside and outside of the beam, and temperature changes in the concrete of the joint section causing tensile stress in the cross section and temperature cracks. It also alleviates the problem of cracks caused by horizontal tension due to the fact that the shrinkage of the concrete of the suspended sections on both sides has been basically completed during the joint construction, and the shrinkage of the newly poured concrete of the joint section is limited. It effectively reduces the phenomenon of longitudinal cracks on the surface of the concrete bottom of the top slab of the joint section due to insufficient maintenance and concrete shrinkage after the formwork is removed. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which: Figure 1 It is the overall flow chart of the present invention; Figure 2 It is the installation diagram of the transverse steel strand in the present invention; Figure 3 It is the construction drawing of the transverse reinforcement of the top plate in the present invention; Figure 4 It is the installation construction drawing of the steel plate mesh in the present invention; Figure 5 It is a construction drawing for pouring the joint section in the present invention. DETAILED DESCRIPTION

[0017] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0018] like Figure 1 As shown, this embodiment proposes a construction method for crack control of a continuous beam closure section, comprising: S1: Pre-embed slow-setting steel strands transversely on the top plate of the joint section, stagger the tensioning ends and the anchoring sections, apply transverse prestress, and tension the strands on the third day after concrete pouring. The tension under the anchor is controlled at 371.6KN, and intelligent tensioning equipment is used for single-end tensioning; S2: Add transverse steel bars with a spacing of 12.5 cm and Φ12 on the top plate of the joint section. The transverse steel bars are arranged on the upper part of the steel plate mesh and the lower part of the longitudinal steel bars. The transverse steel bars are located on the outside of the longitudinal steel bars, and both ends of the transverse steel bars extend into the web wall. Transverse steel bars can enhance the overall stability of the top plate and reduce the possibility of cracks. Such steel bars are located on the upper part of the steel plate mesh and the lower part of the longitudinal steel bars, and their two ends extend into the web, effectively connecting the top plate and the web, further improving the crack resistance of the overall component, and effectively resisting the crack pressure caused by shrinkage and temperature changes, reducing the occurrence of cracks.

[0019] S3: Install steel mesh on the upper and lower mesh of the top plate reinforcement and the inner mesh of the web at the joint section. After the web reinforcement is tied, install the steel mesh on the web. The size of the steel mesh is 6m long and 1m wide. Use the matching scissors for cutting. The specification model is GW5*50*50mm. The mesh size is cut according to the beam surface of the joint section (2m wide and 3.05m high). Cut when encountering the ventilation hole position, and adjust the thickness of the protective layer from 3.5cm to 2cm; S4: Use C55 shrinkage compensation concrete with a grade one higher than the original beam body for vibrating and pouring. Before pouring the joint section, fully wet the existing concrete surface at both ends. The bottom web concrete is poured by pump truck. The pouring process is continuous and must not be interrupted. The top slab concrete is poured by tank truck transportation and crane cooperation. Fully vibrate and evenly compact during the process. S5: After the concrete is poured, it is covered with geotextile and watered for maintenance. The covering length is 1m longer than the length of the joint section and the maintenance time is not less than 14 days. After the maintenance is completed, the formwork should not be removed too early after the concrete is poured. The formwork should be removed after the pre-embedded slow-bonding prestressing of the top plate is tensioned, and then the inner formwork is removed.

[0020] In S1, three groups of 21.8 mm slow-setting steel strands are pre-buried transversely, with two strands in each group and a spacing of 50 cm between each group. Before tensioning, the PE material wrapped around the transverse slow-setting steel strands at the tensioning end is stripped off, and then the matching clip anchor is installed. The intelligent tensioning equipment is used for tensioning, and the elongation is measured with a steel ruler.

[0021] In S3, the specific method is to lay the concrete pad flat, and after the inner formwork is installed, lay the top plate ground steel mesh. First, lay the pad, and then install the steel mesh, and tie it up and fix it, especially at the inner guide angle position. The pad is appropriately increased. After the top plate steel bars are tied, cut the top plate top surface steel mesh to avoid the three-wall steel bars, rigid frame, and sling hole positions.

[0022] In S4, the ratio of expansion agent, anti-cracking agent and polypropylene fiber added to each cubic meter of concrete is 50:30:2.4. The slump of the bottom plate and web plate of the joint section is 180-220mm, the slump of the top plate is 60-100mm, the air content is 3.2%, and the temperature entering the mold meets the requirements of technical regulations.

[0023] Prestressed steel strands can only be tensioned when the concrete strength grade reaches more than 95% of the design value, the elastic modulus reaches 100% of the design value, and the concrete age is not less than 5 days. The tensioning order of prestressed steel strands is longitudinal steel strands first, followed by transverse steel strands. Steel strand tensioning should be carried out with matching limit plates, jacks and other equipment. After the prestressed steel strands are tensioned, they should be sealed with equal strength non-shrinkage concrete in time.

[0024] Before prestressing steel bars are tensioned, the friction loss of the hole, the friction loss of the expansion section and the friction loss of the anchor are tested and measured. At the same time, the theoretical elongation value of the prestressed steel bars is accurately calculated based on the measured friction loss and the elastic modulus of the prestressed steel bars to ensure accurate prestressing. Before tensioning, the jack and the oil pressure gauge are calibrated in pairs.

[0025] The longitudinal prestressed steel strands are tensioned synchronously at both ends, with the long strands being tensioned first and the short strands later, and tensioned symmetrically on the left and right. The maximum unbalanced strand does not exceed 1 strand. The tensioning order is the web strand first and the top plate strand later. It is carried out symmetrically from the outside to the inside and grouting is carried out in time.

[0026] The transverse prestressed steel strands are tensioned by single-end staggered tensioning. The prestressed steel strands are tensioned by dual control of tensioning force and elongation, with tensioning force as the main control and elongation as the verification principle. After the vertical steel strands of each beam segment are tensioned, the transverse steel strands should be tensioned sequentially from the root of the segment. The last top plate transverse prestressed strand near the construction joint of each beam segment is tensioned together with the transverse prestressed strand of the next beam segment. The prestressed tendons of the transverse partition wall are tensioned together in the beam segment where they are located.

[0027] Before the strand tensioning construction, tests are conducted based on the condition of the steel strands. Combined with the friction test data, the corresponding relationship of various parameters is sorted out. When the prestressed steel strands are long, the initial stress reading is appropriately increased according to the test tensioning conditions to eliminate the shrinkage caused by the loosening of the anchors and steel strands. The actual parameters are selected to calculate the elongation of the steel strands, and after comparing with the designed elongation, this is used as the control basis for the formal tensioning.

[0028] Before the construction of the joint section, the center line and elevation of the two cantilever ends are measured and checked. If the center line, elevation and relative deviation of the two cantilever ends are greater than the threshold, the threshold is 15mm, and counterweight measures are taken to implement corrections. The joint section uses a hanging basket as a working platform, and the inner mold is in the form of a bracket, a top support, square wood, and bamboo plywood. The hanging basket bottom mold system is moved to the joint section and fixed to the beam body through the hanging basket cone. The overlap length of the joint beam section template and the surface of the beam body at the two cantilever ends is not less than 30cm. The overlap is tight and firm, and the molds on both sides are pulled as a whole using full-length pull rods.

[0029] The steel bars, prestressed tendons and embedded parts of the joint section are the same as those of other sections. Before pouring concrete of the joint beam section, the cantilevers at both ends of the joint mouth are pre-stressed to stabilize the cantilever. The pre-stressed weight at each cantilever end is loaded according to the weight of the cast-in-place concrete of the joint section and is gradually removed in equal amounts during the concrete pouring process.

[0030] The balancing weight of the joint section construction adopts water tank weight or pre-loaded blocks. According to the weight demand, the water tank is filled with water by a water pump or a corresponding number of pre-loaded blocks are set. As the joint section is constructed, the water in the pool is gradually discharged or the pre-loaded blocks are reduced to achieve balanced weight. The concrete of the joint section is poured quickly and continuously during the time period with the lowest temperature in a day to allow the concrete to solidify in a warming environment. After the pouring of the joint concrete is completed, moisture-keeping and heat-preservation maintenance is carried out to control the temperature difference between the inside and outside of the beam body, and automatic spraying and covering maintenance are used within 1m of the joint section and the two cantilever ends to reduce the impact of sunlight temperature difference.

[0031] All the longitudinal prestressed tendons of the side span joint beam section have been tensioned, the temporary consolidation facilities of the corresponding main piers have been removed to drop the beams, and the middle support has been temporarily constrained in the horizontal direction. The longitudinal prestressed tendons have been tensioned and consolidated, the temporary rigid connection structure and water tank in the middle of the middle span have been installed, and the side hole supports and temporary horizontal constraints on the middle support have been removed.

[0032] When temporary consolidation is removed, rope saws are used. During construction, all prestressing tensioning must be completed. When cutting temporary consolidation supports, horizontal lines are marked on the temporary supports in advance, one line each on the upper and lower sides. Cutting is carried out along the marked lines, first cutting the upper marked line, then cutting the lower marked line. During cutting, the construction is symmetrical and uniform. When an abnormal situation occurs, the construction is stopped immediately and analyzed. After finding the cause, it is immediately handled to avoid damage to the beam body.

[0033] The order of closure is: first close the side spans and then the middle span. Before the construction of the closure beam section, the center line and elevation of the two cantilever ends are measured and checked. When the center line and elevation of the two cantilever ends and the relative deviation are found to be 15mm, measures are taken to correct them. Considering the influence of temperature on the line shape of the closure section, temporary locking is carried out before closure. The temporary locking adopts temporary rigid supports composed of several groups of I-beams. The temporary rigid supports are located at the top and bottom plates of the box girder close to the web.

[0034] After the temporary rigid support is welded according to the design drawings, it is welded in place on the corresponding embedded parts at both ends of the box girder. Before locking, one end of the temporary rigid support is welded to the embedded parts at the beam end. When the beam is scheduled to be locked (in the early morning when the temperature is low), the other end of the temporary rigid support is welded to the embedded parts of the beam body symmetrically and quickly.

[0035] After the side span is connected, the hanging basket is moved forward to the connection section. When the middle span is connected, the main pier T-structure hanging basket is used as the construction hanger. After the construction of the last suspended block section is completed, the main pier T-structure hanging basket is withdrawn to the main pier position for dismantling. During the construction of the suspended block section, the sling holes of the hanging basket support are embedded in advance, so that the two T structures are supported by the hanging basket slings to form an overall simply supported force system. During the construction of the connection section, the inner and outer formwork used in the hanging basket construction is used for construction. The outer formwork adopts an integral frame formwork, and the inner formwork adopts a bracket, a top support, square wood, and bamboo plywood.

[0036] The concrete pouring time of the joint section is when the temperature is the lowest in the day, so that the temperature of the concrete begins to rise slowly after pouring, avoiding excessive temperature difference effect caused by the upper and lower edges of the box girder top plate. The concrete strength reaches 100% before tensioning, shortening the pouring time of the joint section and the suspended sections on both sides, and strengthening the maintenance after the concrete construction is completed.

[0037] After the continuous beam joint construction is completed, the hanging basket structure is dismantled. After the construction of the middle span joint section is completed, the hanging baskets on both sides are returned to the main pier position for dismantling. During dismantling, first at the position of the last joint beam section, the bottom basket and formwork system of the hanging basket are dismantled in the reverse order of assembly. First, the side formwork, inner formwork top plate formwork and bottom plate formwork are disassembled, and then the formwork is lifted away with a tower crane. Then the bottom plate longitudinal beam and outer running beam are removed and lifted away with a tower crane. The main frame and cross beam are dismantled with a tower crane, and then the main truss of the hanging basket on the side of the span is retreated to the pier top position, and the main truss members of the hanging basket are removed in the reverse order of assembly. The hanging basket is dismantled from the outside to the inside and left and right symmetrically at the two cantilever ends to balance the force on the cantilever and ensure construction safety.

[0038] Linear monitoring is carried out during the suspended pouring construction process. The linear changes of the beam body are related to many factors such as the deformation of the hanging basket, the deadweight of the beam section, prestressing, temperature, concrete creep and live load, mainly including plane linear control and longitudinal linear control.

[0039] Plane linear control is to use a total station to adjust the center line of the hanging basket after the hanging basket has been completed in each cast-in-place section. After the formwork reinforcement is completed, the center line of the hanging basket is rechecked.

[0040] Longitudinal linear control is to analyze the change state of structural deflection at each construction stage and each construction step, and control the formwork elevation. First, calculate the pre-camber of each beam section, combine it with the measured deflection value of the previous beam section, correct the pre-camber value, and adjust the formwork elevation in the pouring construction of the next beam section so that the elevation is close to the design elevation after the bridge is completed.

[0041] Before the implementation of the monitoring of the box girder construction, the design line shape, target line shape and pre-camber line shape of the box girder are calculated. The design line shape is the elevation of the box girder designed in the drawing. The target line shape is the elevation obtained by taking into account the effects of live load and long-term creep on the basis of the design line shape. The pre-camber line shape is the deflection caused by taking into account the deadweight of each beam segment, the prestress of each beam segment, the deadweight of the hanging basket, the construction load change, the creep of concrete, and the change of grade on the basis of the target line shape.

[0042] The construction method for controlling cracks in the joint section of the continuous beam proposed in this application has been proven to be effective in preventing cracks in the joint section after repeated practical verification. The number and length of cracks generated have been significantly improved, the length of longitudinal cracks has been shortened, the number has been reduced, and transverse cracks in the web have not appeared. It can provide reference for similar projects and has extremely high promotion value.

[0043] It reduces the problem of temperature cracks caused by tensile stress in the cross section of the beam due to poor ventilation conditions, large temperature difference between the inside and outside, and temperature changes in the concrete of the joint section. It also alleviates the problem of cracks caused by horizontal tension due to the fact that the shrinkage of the concrete in the suspended sections on both sides has been basically completed during the joint construction, and the shrinkage of the newly poured concrete in the joint section is limited. It effectively reduces the phenomenon of longitudinal cracks on the surface of the concrete at the bottom of the top slab of the joint section due to insufficient maintenance and concrete shrinkage after the formwork is removed.

[0044] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A method for controlling cracks in a continuous beam closure section, characterized in that: include: S1: Pre-embed slow-setting steel strands transversely in the top plate of the joint section, stagger the tensioning end and the anchoring section, apply transverse prestress, and perform single-end tensioning; S2: Add transverse reinforcement to the top plate of the joint section. The transverse reinforcement is arranged on the upper part of the steel plate mesh and the lower part of the longitudinal reinforcement. The transverse reinforcement is located outside the longitudinal reinforcement, and both ends of the transverse reinforcement extend into the web wall. S3: Install steel plate mesh on the upper and lower mesh of the top plate reinforcement and the inner mesh of the web at the joint section. After the web reinforcement is tied, install the steel plate mesh on the web; S4: Before pouring the joint section, moisten the existing concrete surface at both ends and vibrate and pour with concrete of a higher grade than the original beam; S5: After the concrete is poured, it is covered with geotextile and watered for maintenance. The covering length is greater than the length of the joint section. After the maintenance is completed, the prestressed slow-bonding prestressing of the top plate is prestressed and the formwork is removed, and then the inner formwork is removed.

2. A method for controlling cracks in a continuous beam closure section according to claim 1, characterized in that: In S1, before tensioning, the PE material wrapped around the transverse slow-setting steel strand at the tensioning end is peeled off, and then the matching clip anchor is installed, and the intelligent tensioning equipment is used for tensioning, and the elongation is measured with a steel ruler.

3. A method for controlling cracks in a continuous beam closure section according to claim 1, characterized in that: In S3, the concrete pad is laid flat, and after the inner form is installed, the steel plate mesh on the top plate is laid. First, the pad is laid, and then the steel plate mesh is installed and tied and fixed. After the top plate steel bars are tied, the steel plate mesh on the top surface of the top plate is cut to avoid the three-wall steel bars, the rigid frame, and the sling hole positions.

4. A method for controlling cracks in a continuous beam closure section according to claim 1, characterized in that: In S4, the ratio of expansion agent, anti-cracking agent and polypropylene fiber added to each cubic meter of concrete is 50:30:2.

4.

5. The method for controlling cracks in the closure section of a continuous beam according to claim 1, characterized in that: Before the construction of the joint section, the center line and elevation of the two cantilever ends are measured and checked. If the center line, elevation and relative deviation of the two cantilever ends are greater than the threshold, counterweight measures are taken to implement corrections. The joint section uses a hanging basket as a working platform, and the inner mold is in the form of a bracket, a top support, square wood, and bamboo plywood. The hanging basket bottom mold system is moved to the joint section and fixed to the beam body through the hanging basket cone. The molds on both sides are pulled as a whole using full-length tie rods. The steel bars, prestressed tendons and embedded parts of the beam body of the joint section are the same as those of other blocks. Before pouring concrete for the joint beam section, the cantilevers at both ends of the joint mouth are pre-stressed to stabilize the cantilever. The pre-stressed weight of each cantilever end is loaded according to the weight of the cast-in-place concrete of the joint section and is gradually removed in equal amounts during the concrete pouring process.

6. A method for controlling cracks in the closure section of a continuous beam according to claim 5, characterized in that: The balancing weight for the construction of the closure section adopts water tank weight or pre-loaded blocks. According to the weight requirement, a water pump is used to fill the water tank with water or a corresponding number of pre-loaded blocks are set. As the closure section is constructed, the water in the pool is gradually discharged or the pre-loaded blocks are reduced. The concrete of the closure section is poured quickly and continuously during the period of the day with the lowest temperature. After the pouring of the closure concrete is completed, moisture-keeping and heat-preservation maintenance is carried out to control the temperature difference between the inside and outside of the beam body, and the closure section and the two cantilever ends are automatically sprinkled with water and covered for maintenance.

7. A method for controlling cracks in a continuous beam closure section according to claim 1, characterized in that: The longitudinal prestressed tendons of the side span closure beam section are all tensioned, the temporary consolidation facilities of the corresponding main piers are removed to drop the beams, and the middle support is temporarily constrained in the horizontal direction. The longitudinal prestressed tendons are tensioned and consolidated, the temporary rigid connection structure and water tank in the middle span are installed, and the side hole brackets and the temporary horizontal constraints of the middle support are removed; When temporary consolidation is dismantled, a rope saw is used. During construction, all prestressing must be completed. When cutting the temporary consolidation support, mark horizontal lines on the temporary support in advance, one line above and one line below. The cutting is carried out along the marked lines. Cut the upper marked line first, then the lower marked line. The cutting is carried out in a symmetrical and uniform manner.

8. The method for controlling cracks in the closure section of a continuous beam according to claim 1, characterized in that: Temporary locking is carried out before closure. Temporary locking uses temporary rigid supports composed of I-beams. The temporary rigid supports are located at the top and bottom plates of the box girder near the web. The temporary rigid supports are welded in place on the corresponding embedded parts at both ends of the box girder. Before locking, one end of the temporary rigid support is welded to the embedded parts at the beam end. When the planned locking time of the beam body arrives, the other end of the temporary rigid support is welded to the embedded parts of the beam body symmetrically and quickly.

9. A method for controlling cracks in a continuous beam closure section according to claim 1, characterized in that: After the side span is connected, the hanging basket is moved forward to the connection section. When the middle span is connected, the main pier T-structure hanging basket is used as the construction hanger. After the construction of the last suspended block section is completed, the main pier T-structure hanging basket is withdrawn to the main pier position for dismantling. During the construction of the suspended block section, the sling holes of the hanging basket support are embedded in advance, so that the two T structures are supported by the hanging basket slings to form an overall simply supported force system. During the construction of the connection section, the inner and outer formwork used in the hanging basket construction is used for construction. The outer formwork adopts an integral frame formwork, and the inner formwork adopts a bracket, a top support, square wood, and bamboo plywood.

10. A method for controlling cracks in a continuous beam closure section according to claim 1, characterized in that: The concrete pouring time of the joint section is poured when the temperature is the lowest in the day. The concrete strength reaches 100%, and then tensioning is carried out. After the joint construction of the continuous beam is completed, the hanging basket structure is dismantled. After the construction of the middle span joint section is completed, the hanging baskets on both sides are returned to the main pier position for dismantling; During dismantling, first remove the bottom basket and formwork system of the hanging basket at the position of the last joint beam section in the reverse order of assembly. First disassemble the side formwork formwork, inner formwork top plate formwork and bottom plate formwork, then use the tower crane to lift the formwork away, and then remove the bottom plate longitudinal beam and outer running beam, and lift them away with the tower crane. Use the tower crane to dismantle the main frame and cross beam, then move the main truss of the hanging basket on the side of the road back to the pier top position, and remove the main truss rods of the hanging basket in the reverse order of assembly. At the two cantilever ends, dismantle the hanging basket from the outside to the inside and left and right symmetrically.

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