Large-span cavity prestressed beam construction method

Abstract

The invention relates to the technical field of building construction, and provides a large-span cavity prestressed beam construction method which comprises the following steps: planning line snapping according to a large-span cavity beam plane positioning map, and determining the position of a cavity; large-span cavity beam main reinforcement construction is carried out, hanging reinforcements at joints are additionally placed after main reinforcement erection, and then stirrup spacing lines are divided; the polyphenyl foam board is placed in the large-span cavity beam; large-span cavity beam prestressed tendons are installed, the prestressed tendons and external support steel bars are firmly bound, then a prestressed fixing end and a prestressed tensioning end are installed, and foam is adopted at the prestressed tensioning end for beam plate face tensioning to serve as a cavity mold to protrude out of a plate face; pre-stressed tendon pulling is carried out, secondary binding of large-span cavity beam steel bars is carried out after pre-stressed tendon pulling is completed, and stirrup reinforcement and beam drag hook installation construction are carried out at the position of a cavity; and after concrete is poured and vibrated compactly, prestress tensioning is conducted. According to the method, the construction efficiency can be effectively improved, and the structural stability and the structural strength of the finally formed large-span cavity prestressed beam are guaranteed.

Description

Technical Field

[0001] This invention relates to the field of building construction technology, and in particular to a construction method for large-span prestressed hollow beams. Background Technology

[0002] With the continuous development of the construction industry, the construction technology of large-span hollow prestressed beams has reduced production costs while ensuring construction quality, which plays a positive role in the further development of the construction industry. In terms of prestressed construction technology, its application in the quality control of large-span hollow beams has effectively reduced the construction risk factor and coordinated the construction of various stages, attracting widespread attention.

[0003] However, in traditional construction methods for large-span prestressed beams with hollow structures, lightweight polystyrene boards are often used as inner molds to create the beam cavity and reduce its self-weight. Failure of anti-buoyancy control: During concrete pouring and vibration, the fluid lateral pressure generated by the fresh concrete and the vibration force can easily cause the polystyrene board inner mold, whose density is much smaller than that of concrete, to float upwards. If the anti-buoyancy anchoring measures are improperly designed or not securely fixed during construction, the inner mold will float upwards, either entirely or partially.

[0004] The direct consequence of cavity displacement and inner mold floating is an unexpected vertical change in the designed hollow cavity position within the beam cross-section. This will lead to: ① a change in the moment of inertia of the cross-section, with the actual effective centroid of the beam deviating from the design value, affecting structural stiffness and load-bearing capacity. ② a shift in the resultant point of prestressing, where the position (eccentricity) of the prestressing tendons relative to the centroid of the concrete cross-section changes, potentially causing the bending moment generated by prestressing to deviate from the design, triggering secondary stresses. ③ uneven concrete cover thickness; the upward displacement of the cavity may result in insufficient actual concrete thickness at the top or bottom of the beam, affecting structural durability.

[0005] Traditional tensioning processes suffer from insufficient control, resulting in asynchronous tensioning and secondary stress cracks.

[0006] For large-span beams with multiple prestressed tendons, if single-strand sequential tensioning is used and strict symmetry and graded control are lacking, the first tensioned steel strands will cause local compression and bending of the beam, and additional friction losses will occur in the later tensioned steel strands, and may form tensile stress zones in the concrete that are not expected in the design.

[0007] The secondary stress caused by improper tensioning sequence can easily induce early shrinkage cracks in weak areas such as the anchorage zone and cross-sectional changes, posing a hidden danger for crack propagation under load during the service stage.

[0008] Effective prestress has a large dispersion. If traditional methods lack strict verification such as dual control of "stress-elongation value" and rely solely on oil pressure gauge readings for control, they cannot effectively identify and offset the effects of factors such as fluctuations in the duct friction coefficient, differences in anchorage shrinkage loss, and deviations in the elastic modulus of prestressing tendons.

[0009] The result is that the effective prestress value established by each prestressing tendon is highly discrete, and the prestress distribution of the beam is uneven. In some areas, the compressive stress reserve is insufficient, making them more prone to cracking under live loads or seismic action.

[0010] The implicit weakening of the seismic performance of prestressed beams is due to their high ductility and energy dissipation capacity. Uneven prestress distribution can lead to: ① Uncontrollable crack propagation patterns: Under cyclic seismic loads, cracks are more likely to concentrate and propagate prematurely in areas with insufficient prestress, reducing the beam's deformation capacity and plastic hinge rotation capacity. ② Uneven stiffness distribution: Uneven prestressing results in different cracking moments and stiffnesses in different sections of the beam, potentially altering the redistribution path of internal forces during earthquakes, contradicting seismic design assumptions. ③ Risk of localized failure in the anchorage zone: Uneven tensioning may exacerbate localized stress concentration in the concrete below the anchorage, increasing the risk of brittle failure in the anchorage zone under dynamic loads. Summary of the Invention

[0011] The purpose of this invention is to solve at least one technical problem in the background art and to provide a construction method for large-span prestressed beams with hollow cavities.

[0012] To achieve the above objectives, the present invention provides a construction method for large-span hollow prestressed beams, comprising: Lay the bottom formwork of the beam. After the formwork is laid, plan and mark the lines according to the plan positioning diagram of the large-span cavity beam to determine the cavity position. The main reinforcement of the large-span hollow beam is constructed according to the measurement and layout positioning. After the main reinforcement is erected, the hanging bars at the nodes are added according to the design requirements of the drawings. Then, the stirrup spacing lines are divided according to the spacing of the drawings. The self-extinguishing flame-retardant polystyrene foam board is tied to the preset size and shape, and then placed into the large-span cavity beam according to the cavity positioning. Install prestressed tendons for large-span hollow beams and securely tie them to the external support reinforcement. Then install the prestressed fixed end and tensioning end. For the prestressed tensioning end of the beam slab, foam is used as a cavity mold to protrude outside the slab surface. For large-span hollow beams containing self-extinguishing flame-retardant polystyrene foam, prestressing tendons are threaded through the beams. After completion, the steel bars of the large-span hollow beams are tied a second time, and the stirrups at the cavities are reinforced and the beam hooks are installed. After the concrete is poured and vibrated to ensure compaction, prestressing is performed. After the prestressing is completed, the construction of the large-span hollow prestressed beam is finished.

[0013] According to one aspect of the present invention, the step of planning and marking lines based on the plan positioning diagram of a large-span hollow beam to determine the cavity location includes: Construct a BIM model of a large-span hollow beam, export the three-dimensional coordinates of the cavity positioning based on the BIM model, and mark them on the construction plan positioning map; Obtain the coordinates of control points on the construction plan, set up multiple control points on the construction site based on the control point coordinates, and use a total station to perform coordinate layout and line connection based on the control points to realize the planning and marking of the lines, and determine the location of the cavity.

[0014] According to one aspect of the present invention, after the main reinforcement frame is erected, stirrups are added at the nodes according to the design requirements of the drawings, and then the stirrup spacing lines are divided according to the spacing in the drawings, including: The anchor points of the suspension bars were calibrated using a total station to ensure that they were located within 50mm on both sides of the projection line of the secondary beam support. Use detachable steel positioning clamps to fix the bending points of the suspension rods to ensure a 45° tilt angle; Based on the BIM model, the reinforcement layout is simulated, and the spatial coordinate relationship between the hangers and stirrups is generated. During construction, AR equipment is used to project virtual positioning lines to guide the marking of stirrups on site; The horizontal and bent sections of the suspension rods are locked by a graduated support structure. A custom steel plate with dimensions engraved on the edges and a hollow center is used to observe the position of the main reinforcement bars. The boundary between the reinforced and unreinforced zones of the large-span hollow beam is marked by the hollow steel plate, and then the spacing of the stirrups is marked by attaching it to the main reinforcement bars.

[0015] According to one aspect of the present invention, the step of binding the self-extinguishing flame-retardant polystyrene foam board to a predetermined size and shape, and then placing it into a large-span cavity beam according to the cavity positioning, includes: Flame-retardant polystyrene foam board with fiberglass mesh covering is used. Nylon sleeves or metal connectors are pre-embedded in the flame-retardant polystyrene foam board with fiberglass mesh covering for connection and fixation with the steel reinforcement skeleton. An anti-buoyancy steel mesh is installed on the top of the flame-retardant polystyrene foam board covered with fiberglass mesh. The flame-retardant polystyrene foam board covered with fiberglass mesh is connected to the bottom formwork by U-shaped anchor bolts. A limiting baffle is installed on the side of the flame-retardant polystyrene foam board covered with fiberglass mesh to resist the lateral pressure of the poured concrete.

[0016] According to one aspect of the present invention, an epoxy resin-based interface agent is applied to a flame-retardant polystyrene foam board covered with fiberglass mesh to enhance the chemical adhesion between the flame-retardant polystyrene foam board covered with fiberglass mesh and concrete, thereby preventing delamination.

[0017] According to one aspect of the present invention, the installation of the prestressed fixed end and the tensioning end, wherein the prestressed tensioning end for tensioning the beam / slab surface uses foam as a cavity mold protruding outside the slab surface, includes: The anchor plate is fixed by a stepped positioning bracket to ensure that it is perpendicular to the prestressing tendon; The anchor plate is welded to the steel reinforcement of the beam and slab, and a grid-shaped positioning bar is added to restrain the foam cavity mold; Spiral reinforcement bars and reinforcing steel mesh are added behind the anchor plate to disperse local stress.

[0018] According to one aspect of the invention, the foam serving as a cavity mold is pre-designed with a structure in which a plurality of grooves are spaced apart on the surface, and a release agent is applied to the surface of the foam.

[0019] According to one aspect of the present invention, the construction of threading prestressed tendons into a large-span hollow beam containing self-extinguishing flame-retardant polystyrene foam, followed by secondary binding of the beam reinforcement, reinforcement of the cavity with stirrups, and installation of beam hooks, includes: Before threading the prestressing tendons, rubber corner protectors are pasted on the edges of the flame-retardant polystyrene foam board, and then a flexible traction device is used to guide the prestressing tendons through the threading process. The stirrups in the cavity area are pre-welded into a grid-shaped frame, and the entire frame is hoisted into place to ensure uniform spacing. It adopts a standardized 135° bent hook and is fixed with the help of magnetic positioning during installation.

[0020] According to one aspect of the present invention, during the reinforcement construction of stirrups in the cavity, an infrared scanner is used to check the binding density of the stirrups and provide real-time feedback on any missed binding points.

[0021] According to one aspect of the present invention, after the concrete is poured and vibrated to compact it, prestressing is performed, comprising: Concrete is poured using a slanted, cyclical method. When the concrete strength reaches 80% or more, prestressing is performed. The PE outer sheath of the tensioning end steel strand is removed. Anchor rings are fitted onto the steel strands and placed tightly against the bearing plate. Three clamping plates are pushed into the anchor rings to secure the steel strands, ensuring the clamping plates are evenly exposed. The jack is then slowly / unseen onto the steel strands, with the jack's limiting groove aligned with the anchor ring and completely covering the clamping plates. The tool anchor is fitted onto the steel strands, tightly against the tail of the jack. The clamping plates are then installed tightly against the steel strands and secured. The length L1 of the tensioning end steel strand is measured using a tape measure, starting from the anchor plate and extending to the end of the steel strand. The length is recorded in the tensioning log. During the tensioning process, the oil pump... Apply pressure slowly and gradually to ensure the tension increases gradually. Use a measuring tape to measure the length L2 of the tensioned steel strand at the end of the strand, starting from the anchor plate and measuring to the end of the strand. Record the length in the tensioning record. Calculate and verify the elongation value: calculate the actual elongation value by subtracting L1 from L2 and compare it with the theoretical elongation value. The relative allowable deviation between the actual and theoretical elongation values ​​is ±6%. If it exceeds this range, tensioning should be stopped immediately. Tensioning can only continue after the cause has been identified. After tensioning is completed, return the jack to its original position slowly and without pressure. Remove the tool anchor and tool clamps, and pull the jack off the steel strand. Tensioning is now complete.

[0022] According to one aspect of the present invention, the construction method for large-span hollow prestressed beams uses self-extinguishing flame-retardant polystyrene foam to form the cavity of the large-span frame beam, reducing the self-weight of the component. At the same time, it employs prestressed construction technology, using Ø15.2mm slow-bonding prestressing technology, to reduce the vertical shear force and principal tensile stress of the concrete beam, improve the stability of the hollow beam, fully utilize the respective characteristics of steel reinforcement and concrete, and improve the stiffness, crack resistance, and durability of reinforced concrete components. Through cavity design and prestressed construction technology, the stability of the ultra-long structure of the large-span hollow beam is guaranteed.

[0023] According to one aspect of the present invention, the location of the cavity is determined by planning and marking lines based on the plan positioning diagram of a large-span hollow beam. This includes: constructing a BIM model of the large-span hollow beam; deriving the three-dimensional coordinates of the cavity location from the BIM model and marking them on the construction plan positioning diagram; obtaining the coordinates of control points on the construction plan positioning diagram; setting up multiple control points on the construction site based on these coordinates; and using a total station to perform coordinate layout and connection of the control points to achieve the planning and marking lines, thereby determining the cavity location. This setup allows for precise layout using a BIM model and a total station, replacing traditional manual marking lines and effectively avoiding human error. It also solves the problem of cavity-beam-column node conflicts or difficulties in rebar avoidance caused by deviations between the marked line location and the actual structural axis.

[0024] According to one aspect of the present invention, during the line marking process, the axis line and beam edge line are first marked, and after the reinforcement is tied, the cavity positioning line is marked a second time; key nodes are marked with red paint triangles (1 per meter) to prevent wear. This setup ensures that the lines are clear and complete, and key nodes (such as cavity boundaries and embedded part positions) are clearly marked, preventing errors in formwork installation.

[0025] According to one aspect of the present invention, after the main reinforcement frame is erected, stirrups are added at the nodes according to the design requirements of the drawings. Then, the stirrup spacing lines are marked according to the spacing in the drawings, including: using a total station to mark the anchor points of the stirrups to ensure that they are within 50mm on both sides of the projection line of the secondary beam support; using a detachable steel positioning clamp to fix the bending points of the stirrups to ensure a 45° inclination angle; pre-simulating the reinforcement layout based on the BIM model to generate the spatial coordinate relationship between the stirrups and the stirrups; projecting virtual positioning lines through AR equipment during construction to guide the on-site marking of the stirrups; locking the horizontal and bent sections of the stirrups through a scaled support structure; customizing a steel plate with dimensions engraved on the edges and a hollow center to observe the position of the main reinforcement, marking the boundary between the dense and non-dense zones of the large-span hollow beam through the hollow steel plate, and then marking the stirrup spacing lines by fitting it to the main reinforcement. This setup allows for a breakthrough in the traditional process of reinforcing steel construction for large-span hollow beams. Through a triple upgrade of technologies—prioritizing the positioning of lifting bars, BIM-assisted layout, and the application of specialized tooling—the problems of process conflicts and positioning deviations are fundamentally resolved. By focusing on controlling the inclination angle of the lifting bars, the anchorage length, and the coordinated positioning of the stirrup reinforcement zone, the seismic performance of the joints can be effectively improved and the construction period shortened by more than 30%.

[0026] According to one aspect of the present invention, a self-extinguishing flame-retardant polystyrene foam board is bound to a predetermined size and shape, and then placed into a large-span cavity beam according to the cavity positioning. This includes: using a flame-retardant polystyrene foam board covered with fiberglass mesh; pre-embedding nylon sleeves or metal connectors within the fiberglass mesh-covered flame-retardant polystyrene foam board for connection and fixation with the reinforcing steel frame; providing an anti-buoyancy reinforcing steel mesh on the top of the fiberglass mesh-covered flame-retardant polystyrene foam board; connecting the fiberglass mesh-covered flame-retardant polystyrene foam board to the bottom formwork via U-shaped anchor bolts; installing limiting baffles on the sides of the fiberglass mesh-covered flame-retardant polystyrene foam board to resist the lateral pressure of the poured concrete; and coating the fiberglass mesh-covered flame-retardant polystyrene foam board with an epoxy resin-based interface agent to enhance the chemical adhesion between the fiberglass mesh-covered flame-retardant polystyrene foam board and the concrete, preventing hollow areas. This design allows for the effective resolution of the defects of polystyrene foam boards during the construction of large-span hollow beams, such as easy deformation and damage, positioning misalignment, and poor adhesion to concrete, through a combination of measures including reinforced materials, precise positioning, and interface modification. It can effectively improve structural strength, positioning accuracy, and stability, while also enhancing the chemical bond with concrete.

[0027] According to one aspect of the present invention, the installation of the prestressed fixed end and tensioning end, wherein the prestressing tensioning end for tensioning the beam / slab surface uses foam as a cavity mold protruding beyond the slab surface, includes: fixing the anchor plate with a stepped positioning bracket to ensure perpendicularity to the prestressing tendons; welding and reinforcing the anchor plate to the beam / slab surface reinforcement, and adding a grid-shaped positioning reinforcement to constrain the foam cavity mold; adding spiral reinforcement and a reinforcing steel mesh behind the anchor plate to disperse local stress. This arrangement significantly improves the accuracy and reliability of the foam cavity mold construction and avoids the risk of prestressing failure.

[0028] According to one aspect of the present invention, the foam serving as the cavity mold is pre-designed with a structure in which multiple grooves are spaced apart on the surface, and a release agent is applied to the foam surface. This design allows the foam segments forming the cavity mold to be more easily separated during demolition, making the cavity mold easier to remove. Furthermore, it ensures that the foam does not adhere to the concrete during demolition, avoiding damage to the anchorages or concrete during forceful removal.

[0029] According to one aspect of the present invention, prestressing tendons are threaded into a large-span hollow beam containing self-extinguishing flame-retardant polystyrene foam. After completion, secondary binding of the beam reinforcement is performed, followed by reinforcement of the stirrups in the cavity and installation of beam hooks. This includes: attaching rubber corner protectors to the edges of the flame-retardant polystyrene foam board before threading the prestressing tendons, and then using a flexible traction device to guide the prestressing tendons through the threading process; this effectively avoids direct friction and damage to the flame-retardant polystyrene foam board during threading; pre-welding the stirrups in the cavity area into a grid-like framework, and ensuring uniform spacing through overall hoisting; this effectively avoids the problem of poor overall structural integrity caused by uneven stirrup spacing; and using standardized 135° bent hooks, which are fixed with the assistance of magnetic positioning devices during installation. This setup effectively avoids human error.

[0030] According to one aspect of the present invention, during the reinforcement construction of stirrups in the cavity, an infrared scanner is used to check the stirrup binding density and provide real-time feedback on any missed binding points. This setup ensures the quality of stirrup binding and installation, effectively avoiding problems such as missed binding in denser areas.

[0031] According to the above-described solution of the present invention, the present invention can effectively solve the problems of easy deformation of structure and difficulty in controlling prestressing tension in traditional construction methods. The present invention can effectively ensure the positional accuracy of polystyrene foam board and steel reinforcement structure during construction, ensure excellent overall structural integrity, effectively improve construction efficiency, and ensure the structural stability and structural strength of the final large-span prestressed cavity beam. Attached Figure Description

[0032] Figure 1 The flowchart schematically illustrates a construction method for a large-span prestressed beam with a cavity according to an embodiment of the present invention. Detailed Implementation

[0033] The invention will now be discussed with reference to exemplary embodiments. It should be understood that the described embodiments are merely intended to enable those skilled in the art to better understand and thus implement the invention, and are not intended to imply any limitation on the scope of the invention.

[0034] As used herein, the term "comprising" and its variations are to be interpreted as open-ended terms meaning "including but not limited to". The term "based on" is to be interpreted as "at least partially based on". The terms "one embodiment" and "an embodiment" are to be interpreted as "at least one embodiment".

[0035] Figure 1 A flowchart illustrating a construction method for a large-span hollow prestressed beam according to an embodiment of the present invention is provided. Figure 1 As shown, in this embodiment, the construction method for a large-span hollow prestressed beam includes: Lay the bottom formwork of the beam. After the formwork is laid, plan and mark the lines according to the plan positioning diagram of the large-span cavity beam to determine the cavity position. The main reinforcement of the large-span hollow beam is constructed according to the measurement and layout positioning. After the main reinforcement is erected, the hanging bars at the nodes are added according to the design requirements of the drawings. Then, the stirrup spacing lines are divided according to the spacing of the drawings. The self-extinguishing flame-retardant polystyrene foam board is tied to the preset size and shape, and then placed into the large-span cavity beam according to the cavity positioning. Install prestressed tendons for large-span hollow beams and securely tie them to the external support reinforcement. Then install the prestressed fixed end and tensioning end. For the prestressed tensioning end of the beam slab, foam is used as a cavity mold to protrude outside the slab surface. For large-span hollow beams containing self-extinguishing flame-retardant polystyrene foam, prestressing tendons are threaded through the beams. After completion, the steel bars of the large-span hollow beams are tied a second time, and the stirrups at the cavities are reinforced and the beam hooks are installed. After the concrete is poured and vibrated to ensure compaction, prestressing is performed. After the prestressing is completed, the construction of the large-span hollow prestressed beam is finished.

[0036] As described above, the construction method for large-span hollow prestressed beams of the present invention uses self-extinguishing flame-retardant polystyrene foam to form the cavity of the large-span frame beam, reducing the self-weight of the component. At the same time, it uses prestressed construction technology, employing Ø15.2mm slow-bonding prestressing technology, to reduce the vertical shear force and principal tensile stress of the concrete beam, improve the stability of the hollow beam, fully utilize the respective characteristics of steel bars and concrete, and improve the stiffness, crack resistance and durability of reinforced concrete components. Through cavity design and prestressed construction technology, the stability of the ultra-long structure of the large-span hollow beam is guaranteed.

[0037] Furthermore, according to one embodiment of the present invention, the location of the cavity is determined by planning and marking lines based on the plan positioning diagram of the large-span cavity beam, including: Construct a BIM model of a large-span hollow beam, export the three-dimensional coordinates of the cavity positioning based on the BIM model, and mark them on the construction plan positioning map; The coordinates of control points are obtained from the construction site plan. Based on these coordinates, multiple control points are established on the construction site. A total station is used to perform coordinate layout and connection of these control points to achieve the planned layout and determine the cavity location. This setup allows for precise layout using a BIM model and a total station, replacing traditional manual layout and effectively avoiding human error. It also solves the problem of cavity conflicts with beam-column joints or difficulties in avoiding reinforcement due to deviations between the marked layout and the actual structural axis.

[0038] Furthermore, in this embodiment, the axis line and beam edge line are first marked during the line marking process. After the reinforcement is tied, the cavity positioning line is marked a second time. Key nodes are marked with red paint triangles (one per meter) to prevent wear. This setup ensures that the lines are clear and complete, and key nodes (such as cavity boundaries and embedded part positions) are clearly marked, preventing errors in formwork installation.

[0039] Furthermore, according to one embodiment of the present invention, after the main reinforcement frame is erected, stirrups are added at the nodes according to the design requirements of the drawings, and then the stirrup spacing lines are divided according to the spacing in the drawings, including: The anchor points of the suspension bars were calibrated using a total station to ensure that they were located within 50mm on both sides of the projection line of the secondary beam support. Use detachable steel positioning clamps to fix the bending points of the suspension rods to ensure a 45° tilt angle; Based on the BIM model, the reinforcement layout is simulated, and the spatial coordinate relationship between the hangers and stirrups is generated. During construction, AR equipment is used to project virtual positioning lines to guide the marking of stirrups on site; The horizontal and bent sections of the suspension rods are locked by a graduated support structure. A custom-made steel plate, with dimensions engraved on the edges and a hollow center to observe the position of the main reinforcement bars, is used to mark the boundary between the reinforced and unreinforced zones of the large-span hollow beam. This plate is then used to mark the stirrup spacing against the main reinforcement bars. This setup allows for a departure from traditional processes in the reinforcement construction of large-span hollow beams. Through a triple technological upgrade—prioritizing the positioning of the stirrups, using BIM-assisted layout, and employing specialized tooling—it fundamentally solves the problems of process conflicts and positioning deviations. By focusing on controlling the inclination angle of the stirrups, the anchorage length, and the coordinated positioning of the reinforced stirrup zones, it effectively improves the seismic performance of the joints and shortens the construction period by more than 30%.

[0040] Furthermore, according to one embodiment of the present invention, self-extinguishing flame-retardant polystyrene foam boards are bound to a predetermined size and shape, and then positioned within a large-span cavity beam according to the cavity positioning, comprising: Flame-retardant polystyrene foam board with fiberglass mesh covering is used. Nylon sleeves or metal connectors are pre-embedded in the flame-retardant polystyrene foam board with fiberglass mesh covering for connection and fixation with the steel reinforcement skeleton. An anti-buoyancy steel mesh is installed on the top of the flame-retardant polystyrene foam board covered with fiberglass mesh. The flame-retardant polystyrene foam board covered with fiberglass mesh is connected to the bottom formwork through U-shaped anchor bolts. A limiting baffle is installed on the side of the flame-retardant polystyrene foam board covered with fiberglass mesh to resist the lateral pressure of the poured concrete. An epoxy resin-based interface agent is applied to flame-retardant polystyrene foam boards covered with fiberglass mesh to enhance the chemical bond between the fiberglass mesh-covered flame-retardant polystyrene foam boards and concrete, preventing hollow areas. This approach, through a combination of reinforcing materials, precise positioning, and interface modification, effectively addresses the shortcomings of polystyrene foam boards during the construction of large-span hollow beams, such as easy deformation and damage, positioning misalignment, and poor bonding with concrete. It effectively improves structural strength, positioning accuracy, and stability, while also enhancing the chemical bond with concrete.

[0041] Furthermore, according to one embodiment of the present invention, the installation of the prestressed fixed end and the tensioning end is carried out, and the prestressed tensioning end for tensioning the beam / slab surface uses foam as a cavity mold protruding outside the slab surface, including: The anchor plate is fixed by a stepped positioning bracket to ensure that it is perpendicular to the prestressing tendon; The anchor plate is welded to the steel reinforcement of the beam and slab, and a grid-shaped positioning bar is added to restrain the foam cavity mold; Adding spiral reinforcement bars and reinforcing steel mesh behind the anchor plate disperses localized stress. This design significantly improves the accuracy and reliability of foam cavity formwork construction, avoiding the risk of prestressing failure.

[0042] In this embodiment, unbonded / tempered prestressing tendons are used. Tempered-bonded prestressing tendons are mechanically cut during fabrication, numbered according to different length specifications, and stacked in coils. The prestressing fixing end and prestressing tensioning end are unbonded / tempered-bonded prestressing fixing end and unbonded / tempered-bonded prestressing tensioning end, respectively. When fabricating the tempered-bonded prestressing fixing end, the sheath of the steel strand in the extrusion section must be removed, and the retarder cleaned. The exposed length of the extrusion head should be no less than 1mm. The anchorage system components—anchors, anchor plates, and spiral reinforcements—must be tightly fitted together without gaps. Tempered-bonded prestressing tensioning ends employ two tensioning methods: beam-end tensioning and beam-slab-surface tensioning. The tensioning system components include a single-hole working anchor, anchor plate, and spiral reinforcement. For beam-end tensioning, a pre-embedded tensioning groove is created using a plastic cavity mold, which should be tightly attached to the bottom template of the slab. For beam-slab-surface tensioning, a 10×10cm, 20cm long foam cavity mold protrudes beyond the slab surface for easy positioning and cleaning after pouring.

[0043] In this embodiment, the loosely bonded prestressing tendons must be securely tied to the support reinforcement when laid out in the beam (double-wire tying spacing not exceeding 1.5m) to prevent floating during pouring. The prestressed steel strands must be bundled straight and arranged symmetrically within the beam, with enhanced protection for the steel strand sheaths. The tensioning condition for the loosely bonded prestressing tendons is a strength of 80% or higher; a 26t through-type jack is used, driven by a high-pressure oil pump; dual control measures are adopted for stress and elongation, with elongation deviation controlled within ±6%. After tensioning, the tendons are cut and anchored.

[0044] The above settings will yield the following beneficial effects: 1. Simple construction, high efficiency, and more controllable quality. No grouting process required: Conventional prestressed concrete requires a complex grouting process (pre-drilling, threading, grouting, pressure holding, etc.), which is cumbersome and makes it difficult to guarantee 100% grouting quality (such as density), easily leading to quality problems such as drilling blockage and incomplete grouting. The slow-bonding technology completely avoids this problem.

[0045] No need for pre-drilled holes or threading: The bonded reinforcement can be laid and positioned directly during the binding of reinforcement, just like ordinary steel bars, eliminating the trouble of embedding corrugated pipes and threading later, and greatly speeding up the construction.

[0046] It has strong adaptability to structural dimensions: it is especially suitable for areas with small cross-sectional dimensions and dense reinforcement, avoiding problems caused by difficulties in arranging ducts and grouting pipes.

[0047] 2. Superior corrosion resistance If the grouting of ordinary prestressed ducts is not dense, leaving water accumulation or voids, the prestressing tendons are very prone to corrosion in a humid environment, threatening the structural safety (there are cases of bridge collapse caused by this both domestically and internationally).

[0048] The outer sheath of the slow-setting prestressing tendon and the dense slow-setting adhesive provide a double physical barrier for the steel strand, which can more effectively isolate moisture and corrosive media, and the corrosion resistance reliability is significantly higher than that of ordinary prestressing that relies on the density of grouting.

[0049] 3. More uniform prestress transfer and superior structural performance. Initial stage (construction period): During tensioning, it is in an unbonded state, with low friction loss, high prestress transfer efficiency, and uniform stress distribution along the entire length.

[0050] Later stage (use period): After the adhesive hardens, it transforms into a bonded state, and the prestressing tendons and concrete deform together, possessing the same structural performance as ordinary bonded prestressed structures—high stiffness, good fatigue resistance, and strong crack control ability, while avoiding the disadvantages of large deformation and easy cracking of pure unbonded prestressed structures.

[0051] 4. Good overall economic benefits Although the unit price of materials may be slightly higher, the overall construction cost is usually lower because it saves on the costs of corrugated pipes, grouting equipment, grouting materials, and complex grouting labor.

[0052] The indirect economic benefits brought about by the shortened construction period are obvious.

[0053] Long-term maintenance costs may be reduced due to improved corrosion resistance.

[0054] Furthermore, according to one embodiment of the present invention, the foam serving as the cavity mold is pre-designed with a structure in which multiple grooves are spaced apart on the surface, and a release agent is applied to the foam surface. This design allows the foam segments forming the cavity mold to separate more easily during demolition, making the cavity mold easier to remove, and also ensures that it does not stick to the concrete during removal, avoiding damage to the anchorage or concrete during forceful demolition.

[0055] Furthermore, according to one embodiment of the present invention, prestressing tendons are threaded through a large-span hollow beam containing self-extinguishing flame-retardant polystyrene foam, followed by secondary binding of the reinforcing bars in the large-span hollow beam, reinforcement of the stirrups at the cavity, and installation of beam hooks, including: Before threading the prestressing tendons, rubber corner protectors are attached to the edges of the flame-retardant polystyrene foam board, and then a flexible traction device is used to guide the prestressing tendons through the threading process. This can effectively avoid direct friction and prevent damage to the flame-retardant polystyrene foam board caused by threading. The stirrups in the cavity area are pre-welded into a grid-shaped frame, and then hoisted into place as a whole to ensure uniform spacing; this can effectively avoid the problem of poor overall structure caused by uneven stirrup spacing. It uses a standardized 135° bent hook, and is secured with a magnetic locator during installation. This design effectively avoids human error.

[0056] Furthermore, according to one embodiment of the present invention, during the reinforcement construction of stirrups in the cavity, an infrared scanner is used to check the stirrup binding density and provide real-time feedback on any missed binding points. This setup ensures the quality of stirrup binding and installation, effectively avoiding problems such as missed binding in denser areas.

[0057] Furthermore, according to one embodiment of the present invention, after pouring and compacting the concrete, prestressing tensioning is performed, including: Concrete is poured using a slanted, cyclical method. When the concrete strength reaches 80% or more, prestressing is initiated. The PE outer sheath of the tensioning end steel strand (prestressing tendon) is removed. Anchor rings are fitted onto the steel strands and tightly against the bearing plate. Three clamping plates are pushed into the anchor rings to secure the steel strands, ensuring the clamping plates are evenly exposed. The jack is then slowly / unseen onto the steel strands, with the jack's limiting groove aligned with the anchor ring and completely covering the clamping plates. The tool anchor is fitted onto the steel strands, tightly against the tail of the jack. The clamping plates are then installed tightly against the steel strands and secured. The length L1 of the tensioning end steel strand is measured using a tape measure, starting from the anchor plate and extending to the end of the steel strand. The length is recorded in the tensioning log. The tensioning process... The oil pump should be pressurized slowly or without pressure to ensure a gradual increase in tension. Measure the length L2 of the tensioned steel strand after tensioning using a measuring tape, starting from the anchor plate and measuring to the end of the steel strand. Record the length in the tensioning log. Calculate and verify the elongation value: calculate the actual elongation value using L2-L1 and compare it with the theoretical elongation value. The relative allowable deviation between the actual and theoretical elongation values ​​is ±6%. If this range is exceeded, tensioning should be stopped immediately, and tensioning can only continue after the cause has been identified. After tensioning is complete, return the jack to its original position slowly or without pressure, remove the tool anchor and tool clamps, and pull the jack off the steel strand. Tensioning is now complete. This setup allows for oblique cyclic pouring, which helps reduce initial defects and uneven shrinkage of the structural concrete, providing a more uniform and solid concrete bearing foundation for the prestressing tendons and preventing localized stress concentration during tensioning that could lead to concrete cracking. Tensioning is performed when the concrete reaches at least 80% strength to ensure it has sufficient strength and elastic modulus to withstand the compressive stress generated by prestressing, preventing structural damage or excessive nonlinear deformation during tensioning. Precise installation and alignment (tight anchor rings, uniformly exposed wedges, and correctly aligned jacks) are the physical foundation for successful tensioning. Any installation deviation will lead to uneven stress on the prestressing tendons, abnormally increased frictional losses, and even tendon slippage or breakage. These geometric errors are minimized to the greatest extent possible. "Dual control" and dynamic verification of the tensioning process are implemented.

[0058] According to the above-described solution of the present invention, the present invention can effectively solve the problems of easy deformation of structure and difficulty in controlling prestressing tension in traditional construction methods. The present invention can effectively ensure the positional accuracy of polystyrene foam board and steel reinforcement structure during construction, ensure excellent overall structural integrity, effectively improve construction efficiency, and ensure the structural stability and structural strength of the final large-span prestressed cavity beam.

[0059] The above description is merely a preferred embodiment of this application and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the inventive concept. For example, technical solutions formed by substituting the above-described features with (but not limited to) technical features with similar functions disclosed in this application.

[0060] It should be understood that the sequence number of each step in the invention and its embodiments does not absolutely imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

Claims

1. A construction method for large-span hollow prestressed beams, characterized in that, include: Lay the bottom formwork of the beam. After the formwork is laid, plan and mark the lines according to the plan positioning diagram of the large-span cavity beam to determine the cavity position. The main reinforcement of the large-span hollow beam is constructed according to the measurement and layout positioning. After the main reinforcement is erected, the hanging bars at the nodes are added according to the design requirements of the drawings. Then, the stirrup spacing lines are divided according to the spacing of the drawings. The self-extinguishing flame-retardant polystyrene foam board is tied to the preset size and shape, and then placed into the large-span cavity beam according to the cavity positioning. Install prestressed tendons for large-span hollow beams and securely tie them to the external support reinforcement. Then install the prestressed fixed end and tensioning end. For the prestressed tensioning end of the beam slab, foam is used as a cavity mold to protrude outside the slab surface. For large-span hollow beams containing self-extinguishing flame-retardant polystyrene foam, prestressing tendons are threaded through the beams. After completion, the steel bars of the large-span hollow beams are tied a second time, and the stirrups at the cavities are reinforced and the beam hooks are installed. After the concrete is poured and vibrated to ensure compaction, prestressing is performed. After the prestressing is completed, the construction of the large-span hollow prestressed beam is finished.

2. The construction method for large-span hollow prestressed beams according to claim 1, characterized in that, The process of planning and marking lines based on the plan positioning diagram of the large-span hollow beam to determine the location of the cavity includes: Construct a BIM model of a large-span hollow beam, export the three-dimensional coordinates of the cavity positioning based on the BIM model, and mark them on the construction plan positioning map; Obtain the coordinates of control points on the construction plan, set up multiple control points on the construction site based on the control point coordinates, and use a total station to perform coordinate layout and line connection based on the control points to realize the planning and marking of the lines, and determine the location of the cavity.

3. The construction method for large-span hollow prestressed beams according to claim 1, characterized in that, After the main reinforcement frame is erected, hanger bars are added at the nodes according to the design requirements of the drawings. Then, the stirrup spacing lines are drawn according to the spacing in the drawings, including: The anchor points of the suspension bars were calibrated using a total station to ensure that they were located within 50mm on both sides of the projection line of the secondary beam support. Use detachable steel positioning clamps to fix the bending points of the suspension rods to ensure a 45° tilt angle; Based on the BIM model, the reinforcement layout is simulated, and the spatial coordinate relationship between the hangers and stirrups is generated. During construction, AR equipment is used to project virtual positioning lines to guide the marking of stirrups on site; The horizontal and bent sections of the suspension rods are locked by a graduated support structure. A custom steel plate with dimensions engraved on the edges and a hollow center is used to observe the position of the main reinforcement bars. The boundary between the reinforced and unreinforced zones of the large-span hollow beam is marked by the hollow steel plate, and then the spacing of the stirrups is marked by attaching it to the main reinforcement bars.

4. The construction method for large-span hollow prestressed beams according to claim 1, characterized in that, The step of binding the self-extinguishing flame-retardant polystyrene foam board to a preset size and shape, and then placing it into the large-span cavity beam according to the cavity positioning, includes: Flame-retardant polystyrene foam board with fiberglass mesh covering is used. Nylon sleeves or metal connectors are pre-embedded in the flame-retardant polystyrene foam board with fiberglass mesh covering for connection and fixation with the steel reinforcement skeleton. An anti-buoyancy steel mesh is installed on the top of the flame-retardant polystyrene foam board covered with fiberglass mesh. The flame-retardant polystyrene foam board covered with fiberglass mesh is connected to the bottom formwork by U-shaped anchor bolts. A limiting baffle is installed on the side of the flame-retardant polystyrene foam board covered with fiberglass mesh to resist the lateral pressure of the poured concrete.

5. The construction method for large-span hollow prestressed beams according to claim 1, characterized in that, An epoxy resin-based interface agent is applied to the flame-retardant polystyrene foam board with fiberglass mesh covering to enhance the chemical adhesion between the flame-retardant polystyrene foam board with fiberglass mesh covering and concrete, thus preventing hollow areas.

6. The construction method for large-span hollow prestressed beams according to claim 1, characterized in that, The installation of the prestressed fixed end and tensioning end, and the prestressing tensioning end for tensioning the beam / slab surface using foam as a cavity formwork protruding outside the slab surface, includes: The anchor plate is fixed by a stepped positioning bracket to ensure that it is perpendicular to the prestressing tendon; The anchor plate is welded to the steel reinforcement of the beam and slab, and a grid-shaped positioning bar is added to restrain the foam cavity mold; Spiral reinforcement bars and reinforcing steel mesh are added behind the anchor plate to disperse local stress.

7. The construction method for large-span hollow prestressed beams according to claim 1, characterized in that, The foam used as a cavity mold is pre-designed with a structure in which multiple grooves are spaced apart on the surface, and a release agent is applied to the foam surface.

8. The construction method for large-span hollow prestressed beams according to claim 1, characterized in that, The process of threading prestressed tendons into large-span hollow beams containing self-extinguishing flame-retardant polystyrene foam, followed by secondary binding of the beam reinforcement, reinforcement of the cavities with stirrups, and installation of beam tie hooks includes: Before threading the prestressing tendons, rubber corner protectors are pasted on the edges of the flame-retardant polystyrene foam board, and then a flexible traction device is used to guide the prestressing tendons through the threading process. The stirrups in the cavity area are pre-welded into a grid-shaped frame, and the entire frame is hoisted into place to ensure uniform spacing. It adopts a standardized 135° bent hook and is fixed with the help of magnetic positioning during installation.

9. The construction method for large-span hollow prestressed beams according to claim 1, characterized in that, During the reinforcement of stirrups in the cavity, an infrared scanner is used to check the density of the stirrup binding and provide real-time feedback on any missed binding points.

10. The construction method for a large-span hollow prestressed beam according to any one of claims 1-9, characterized in that, After the concrete is poured and vibrated to compact it, prestressing tensioning is performed, including: Concrete is poured using a slanted, cyclical method. When the concrete strength reaches 80% or more, prestressing is performed. The PE outer sheath of the tensioning end steel strand is removed. Anchor rings are fitted onto the steel strands and placed tightly against the bearing plate. Three clamping plates are pushed into the anchor rings to secure the steel strands, ensuring the clamping plates are evenly exposed. The jack is then slowly / unseen onto the steel strands, with the jack's limiting groove aligned with the anchor ring and completely covering the clamping plates. The tool anchor is fitted onto the steel strands, tightly against the tail of the jack. The clamping plates are then installed tightly against the steel strands and secured. The length L1 of the tensioning end steel strand is measured using a tape measure, starting from the anchor plate and extending to the end of the steel strand. The length is recorded in the tensioning log. During the tensioning process, the oil pump... Apply pressure slowly and gradually to ensure the tension increases gradually. Use a measuring tape to measure the length L2 of the tensioned steel strand at the end of the strand, starting from the anchor plate and measuring to the end of the strand. Record the length in the tensioning record. Calculate and verify the elongation value: calculate the actual elongation value by subtracting L1 from L2 and compare it with the theoretical elongation value. The relative allowable deviation between the actual and theoretical elongation values ​​is ±6%. If it exceeds this range, tensioning should be stopped immediately. Tensioning can only continue after the cause has been identified. After tensioning is completed, return the jack to its original position slowly and without pressure. Remove the tool anchor and tool clamps, and pull the jack off the steel strand. Tensioning is now complete.

Images