Construction method of large-span double-layer two-way retard-bonded prestressed concrete slope type roof

Abstract

The invention discloses a large-span double-layer bidirectional retard-bonded prestressed concrete slope type roof construction method, which relates to the technical field of building construction, and comprises the following steps: S1, deepening a drawing and typesetting and numbering retard-bonded prestressed positioning ribs; s2, beam non-prestressed reinforcement construction and retard-bonded prestressed positioning rib installation are carried out based on the retard-bonded prestressed positioning rib typesetting number; s3, laying the retard-bonded prestressed tendons in the beam based on the layout numbers of the retard-bonded prestressed positioning tendons; and S4, after the step S3, binding non-prestressed steel bars at the bottom of the plate and laying retard-bonded prestressed steel bars on the surface of the plate. According to the construction method of the large-span double-layer two-way retard-bonded prestressed concrete slope type roof, the technical scheme that retard-bonded prestress is matched with double-layer two-way rib arrangement is adopted, synchronous construction with common steel bars can be achieved in the early stage, and stress can be improved through tensioning in the later stage. The effects of simple and convenient construction and high efficiency are achieved, and the stress performance of the roof structure is 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, double-layer, bidirectional, slow-bonding prestressed concrete sloping roofs. Background Technology

[0002] A concrete pitched roof refers to a roof structure formed by pouring concrete to create a slope, with drainage and other functions achieved through slope design. It is commonly found in buildings such as warehouses and stadiums. Large-span double-layer bidirectional slow-bonded prestressed concrete refers to a concrete structure with a large span, in which double layers of slow-bonded prestressing tendons are installed along both the X and Y directions. These slow-bonded prestressing tendons consist of high-strength, low-relaxation steel strands, a slow-bonding adhesive, and a PE sheath, combining the convenience of unbonded construction with the mechanical properties of bonded concrete. The construction of a large-span double-layer bidirectional slow-bonded prestressed concrete pitched roof involves applying this technology to the construction process of a pitched roof. It requires considering the elevation changes and slope requirements of the pitched roof to complete the prestressing tendon arrangement, concrete pouring, and other procedures to meet the large-span load-bearing capacity and pitched structural requirements of the roof.

[0003] Currently, the prestressed construction of large-span sloping roofs mostly adopts traditional bonded prestressing technology. This technology requires first laying corrugated pipes in the beam and slab structure to form ducts, inserting steel strands, binding non-prestressed steel bars, pouring concrete, and then tensioning the steel strands after the concrete has cured to the design strength. Finally, high-pressure grouting is used to bond the steel strands to the concrete. However, during construction, the processes of corrugated pipe laying, duct sealing, and high-pressure grouting must be carried out separately and cannot be carried out simultaneously with ordinary steel reinforcement, increasing the construction steps, resulting in low construction efficiency and extended construction period. Therefore, a construction method for large-span double-layer bidirectional slow-bonded prestressed concrete sloping roofs is proposed. Summary of the Invention

[0004] To achieve the above objectives, the present invention provides the following technical solution: a construction method for a large-span, double-layer, bidirectional, gently bonded prestressed concrete sloping roof, comprising the following steps: S1. Drawing refinement and layout numbering of prestressed positioning reinforcement bars with slow bonding; S2. Based on the layout and numbering of the slow-bonding prestressed positioning bars, carry out the construction of non-prestressed steel reinforcement in the beam and the installation of slow-bonding prestressed positioning bars. S3. Lay the slow-bonded prestressed tendons in the beam based on the layout and numbering of the slow-bonded prestressed positioning tendons; S4. After step S3, proceed with the binding of non-prestressed steel bars at the bottom of the slab and the laying of prestressed tendons for the slab surface. S5. Based on the binding of non-prestressed steel bars at the bottom of the slab and the laying of prestressed tendons for slow bonding on the slab surface in step S4, install the tensioning end and the fixing end. S6. Then, conduct concealed inspection and concrete pouring. S7. The poured concrete is prestressed.

[0005] Preferably, in step S1, the drawing refinement and the layout numbering of the slack-bonded prestressing positioning tendons are based on the roof structure and construction drawings. The roof prestressing project is refined to determine the embedment length and layout position of the slack-bonded prestressing tendons, and they are uniformly numbered according to the construction refinement drawings. Material cutting and construction installation are controlled according to the numbered drawings.

[0006] Preferably, in step S2, the specific steps for installing the slow-bonding prestressed positioning bars are as follows: after the non-prestressed steel reinforcement construction of the beam is completed, the slow-bonding prestressed positioning bars are tied inside the beam according to the drawings. The positioning bars are controlled according to the requirements of the drawings to control the highest point, lowest point and inflection point.

[0007] Preferably, in step S3, the slow-bonding prestressing tendons inside the beam are laid according to the arrangement method and curve height of the prestressing tendons, and are then fixed to the positioning tendons in sequence.

[0008] Preferably, in step S4, after the non-prestressed steel reinforcement at the bottom of the slab is tied, the slow-bonded prestressed steel reinforcement is laid at equal intervals along the X and Y axes of the roof slab. After the prestressed steel reinforcement is laid, the non-prestressed steel reinforcement of the surface layer is tied and installed to form a double-layer bidirectional stress system on the slab surface.

[0009] Preferably, in step S5, after the double-layer bidirectional force-bearing system of the plate is formed, according to the drawing, a pad is installed on the plate, a spiral reinforcement is set at the rear end of the pad, the pre-tensioning end is wrapped with a polyethylene foam board to form an inclined groove, and the fixed end is tied to the steel bar using an extrusion anchor process.

[0010] Preferably, in step S6, after the installation of the tensioning end and the fixed end is completed, the concealed acceptance of the fixed end, tensioning end, reinforcement arrangement and slab reinforcement in the beam is carried out. After the acceptance is qualified, the formwork is installed and the concrete is poured. After the pouring is completed, curing is carried out.

[0011] Preferably, in step S7, after curing is completed, samples are taken and sent for testing. The concrete strength is tested to be no less than 85%. After approval by the project's technical manager, tensioning is carried out according to the design requirements.

[0012] Preferably, tensioning is being carried out according to design requirements: When the temperature is not lower than 20℃, the control stress for prestressing tendons in the slab is 1375-1395MPa, and the tension force is 180.9-195.3kN. When the air temperature is not higher than 20℃, the control stress for prestressing tendons in the slab is 1460.8-1464.7 MPa, and the tension force is 199.5-205.1 kN. When the temperature is not lower than 20℃, the control stress for prestressing tendons in the beam is 690-700MPa, and the tension force is 95-98kN. When the temperature is not higher than 20℃, the tension control stress of the prestressed tendons in the beam is 727-735MPa, and the tension force is 100.3-102.9kN; During the tensioning process, it is crucial to ensure the accuracy of the operation and the stability of the instruments.

[0013] Preferably, the method further includes pretreatment of the board surface, the specific steps of which are as follows: Board surface cleaning and inspection: Use cleaning tools to thoroughly clean the board surface, removing all debris, dust, oil stains, etc. Inspect the board surface for defects: Use a level or laser measuring instrument to check the board surface for defects such as cracks, holes, and unevenness. For areas that need repair, use repair mortar to fill cracks and uneven parts to ensure that the board surface is smooth and free of defects. Surface wetting and control: Use a water pipe or sprayer to spray water mist to wet the board surface. After wetting, ensure that the surface remains properly moist. The wetted board surface needs to be air-dried naturally until it stops dripping. Depending on the actual weather conditions and construction progress, use a humidity control membrane to ensure that the humidity of the board surface remains stable.

[0014] In summary, this invention provides a construction method for large-span, double-layer, bidirectional, gently bonded prestressed concrete sloping roofs, which has the following beneficial effects: 1. This construction method for large-span, double-layer, bidirectional, slow-bonding prestressed concrete sloping roofs utilizes a technical scheme of slow-bonding prestressing combined with double-layer, bidirectional reinforcement arrangement. This allows for simultaneous construction with ordinary steel reinforcement in the early stages, and further enhances stress during later tensioning. This achieves simple and efficient construction while ensuring the structural load-bearing performance of the roof.

[0015] 2. This construction method for large-span, double-layer, bidirectional, slow-bonding prestressed concrete sloped roofs eliminates the need for additional steps like corrugated pipe laying and grouting by using slow-bonding prestressing technology for the roof slab construction. This reduces human error, ensures construction quality, and saves time while maintaining structural integrity. Compared to existing unbonded prestressing methods that require corrosion protection at the tensioning end, this method overcomes the shortcomings of cumbersome later maintenance and minimal reduction in construction steps.

[0016] 3. This construction method for large-span, double-layer, bidirectional, slow-bonding prestressed concrete sloping roofs involves pre-treating the slab surface and then combining slow-bonding prestressed tendons with non-prestressed tendons to form a double-layer, bidirectional load-bearing system. This achieves a smooth, defect-free slab surface, good structural crack resistance, and uniform prestress transfer. Compared to existing technologies that directly lay reinforcement and pour concrete, this method reduces the problems of slab surface defects and localized stress concentration in the structure. Attached Figure Description

[0017] Figure 1 This is a flowchart illustrating the construction method of a large-span, double-layer, bidirectional, gently bonded prestressed concrete sloping roof according to the present invention. Figure 2 This is a diagram showing the arrangement of prestressed positioning bars for the large-span, double-layer, bidirectional, slow-bonding prestressed concrete sloping roof construction method of the present invention. Figure 3 This is a schematic diagram showing the positional relationship between the longitudinal reinforcement bars and prestressed tendons of the prestressed tendon beam in the construction method of large-span double-layer bidirectional slow-bonding prestressed concrete sloping roof of the present invention. Figure 4 This is a cross-sectional view of the prestressed tendon beam at the mid-span position in the construction method of large-span double-layer bidirectional slow-bonding prestressed concrete sloping roof of the present invention. Figure 5 This is a diagram showing the internal arrangement of the prestressed reinforcement slab in the construction method of large-span double-layer bidirectional slow-bonding prestressed concrete sloping roof of the present invention. Figure 6 This is a detailed drawing of the slab surface with a haunch at the prestressing tensioning end in the large-span double-layer bidirectional slow-bonding prestressed concrete sloping roof construction method of the present invention; Figure 7 This is a detailed drawing of the tensioning end of the prestressed tendon beam in the construction method of large-span double-layer bidirectional slow-bonding prestressed concrete sloping roof of the present invention. Detailed Implementation

[0018] The specific embodiments of the present invention will now be described in further detail with reference to the accompanying drawings.

[0019] Please see Figures 1-7 The construction method for large-span, double-layer, bidirectional, gently bonded prestressed concrete sloping roofs includes the following steps: S1. Drawing refinement and layout numbering of prestressed positioning reinforcement bars with slow bonding; S2. Based on the layout and numbering of the slow-bonded prestressed positioning bars, carry out the construction of non-prestressed steel reinforcement in beams and the installation of slow-bonded prestressed positioning bars. S3. Laying of slow-bonded prestressed tendons in beams based on the layout and numbering of slow-bonded prestressed positioning tendons; S4. After step S3, proceed with the binding of non-prestressed steel bars at the bottom of the slab and the laying of prestressed tendons for the slab surface. S5. Based on the binding of non-prestressed steel bars at the bottom of the slab and the laying of prestressed tendons for slow bonding on the slab surface in step S4, install the tensioning end and the fixing end. S6. Then, conduct concealed inspection and concrete pouring. S7. Perform prestressing tensioning on the poured concrete.

[0020] Through the above technical solution, the arrangement and construction of prestressing tendons can be ensured by detailed design drawings and the numbering of prestressing positioning tendons in step S1. Figure 1 To avoid errors during construction, a numbering system is used to clearly identify each prestressing tendon and its installation location, ensuring that the position, angle, and tensioning sequence of the tendons meet design requirements in subsequent construction, thus reducing errors. The implementation of detailed drawings and numbering provides a clear basis for construction, ensuring the accuracy of prestressing tendon placement and construction quality. In step S2, the non-prestressed steel reinforcement construction and the installation of the prestressed steel positioning bars are carried out according to the layout number of the loosely bonded prestressed positioning bars, ensuring the accuracy of the steel reinforcement installation. Accurate installation of the loosely bonded prestressed positioning bars within the beam provides fixing and positioning support for subsequent prestressed steel reinforcement laying, thus ensuring that the prestressed steel reinforcement remains in the correct stress position throughout construction. This eliminates errors in steel reinforcement layout and improves construction precision. In step S3, the laying of the prestressed tendons within the beam is based on the numbering system for the prestressed tendons, ensuring the accuracy of the tendon placement. By following the numbering system, construction workers can accurately lay each prestressed tendon, avoiding misalignment or offset of the reinforcement positions and ensuring that the tensioning direction and position of the prestressed tendons are consistent with the design requirements. This ensures a reasonable layout of the prestressed tendons within the beam and avoids structural problems caused by construction errors. In step S4, after laying the loosely bonded prestressed tendons within the beam, the non-prestressed reinforcement at the bottom of the slab is tied and the loosely bonded prestressed tendons at the top of the slab are laid, ensuring the overall structural stress rationality. The reinforcement at the slab surface and the beam can be effectively connected, sharing the prestress, thereby improving the structure's load-bearing capacity and stability. The combination of the non-prestressed reinforcement at the bottom of the slab and the loosely bonded prestressed tendons at the top of the slab enhances the overall structural performance and avoids uneven stress caused by unreasonable reinforcement layout. In step S5, after the non-prestressed steel bars at the bottom of the slab are tied and the prestressed tendons on the slab surface are laid, the tensioning ends and fixing ends are installed to ensure the stability of the stress system of the steel bars and prestressed tendons. By installing the tensioning ends and fixing ends, it is ensured that the prestressed tendons do not shift during tensioning, maintaining their stress state and stability. This ensures the accuracy of the entire structure during tensioning and avoids structural instability caused by improper installation. In step S6, the concealed inspection and concrete pouring ensure that the arrangement of reinforcing bars and the positioning of prestressing tendons meet design requirements. Through concealed inspection, problems with the position or binding quality of reinforcing bars can be identified and corrected in a timely manner, ensuring that subsequent concrete pouring will not be affected. During concrete pouring, the arrangement of reinforcing bars is verified, avoiding structural quality problems caused by incorrect arrangement or improper installation of reinforcing bars. This step ensures the structural stress and the bond quality of the concrete. In step S7, the poured concrete is prestressed to ensure it reaches the designed prestress state, thereby improving the overall load-bearing capacity and stability of the structure. By controlling the tension force and sequence, each prestressing tendon is ensured to be uniformly stressed, avoiding structural problems caused by uneven tension. The implementation of prestressing provides the structure with the required initial prestress, thus improving its bending, shear, and tensile strength, ensuring its long-term stability. The above construction method utilizes a slow-bonded prestressing technique for the roof structure, combining the advantages of both bonded and unbonded prestressing tendons while overcoming their disadvantages. Compared to bonded prestressing technology, it eliminates the need for corrugated pipe laying and grouting, reducing the negative impact of on-site manual labor and ensuring higher construction quality. This method saves time while maintaining the structural load-bearing capacity of the roof. The roof slab employs slow-bonded prestressed concrete technology. Simultaneous construction of slow-bonded prestressing tendons and ordinary steel reinforcement simplifies the initial construction phase and increases stress during subsequent tensioning, improving efficiency and saving time to ensure timely completion.

[0021] In S1, the detailed design and layout numbering of the prestressed anchorage tendons are based on the roof structure and construction drawings. The design of the prestressed roof project is deepened to determine the embedment length and layout position of the prestressed anchorage tendons. They are then uniformly numbered according to the detailed construction drawings, and the material cutting and construction installation are controlled according to the numbered drawings.

[0022] Through the aforementioned technical solutions, and by refining the drawings and numbering the prestressed tendons for the slow-bonding process, the prestressed tendon layout scheme for the roof structure and construction drawings was confirmed in detail, ensuring that the embedment length and placement of the slow-bonding prestressed tendons were consistent with the design requirements. The detailed construction drawings and numbering system enabled precise identification of each prestressed tendon, ensuring effective control over the position, direction, and stress requirements of the reinforcement during construction. Controlling material cutting and installation according to the numbered drawings allows the prestressed tendons to be laid in the designated positions, thus avoiding structural problems caused by operator error or incorrect reinforcement placement, improving construction accuracy and project quality.

[0023] In S2, the specific steps for installing the slow-bonded prestressed positioning bars are as follows: after the non-prestressed steel reinforcement construction of the beam is completed, the slow-bonded prestressed positioning bars are tied inside the beam according to the drawings. The positioning bars are controlled according to the requirements of the drawings to control the highest point, lowest point and inflection point.

[0024] Through the above technical solution, after the non-prestressed steel reinforcement construction of the beam is completed, the prestressed positioning bars inside the beam are installed according to the detailed drawing requirements, ensuring that the arrangement of the positioning bars meets the design requirements. The installation of the positioning bars controls the positions of the highest point, lowest point, and inflection point of the prestressing tendons, ensuring that the stress state of the entire structure meets the design requirements. By accurately setting the positioning points of the prestressing tendons in advance, a foundation is provided for the subsequent laying and tensioning of the prestressing tendons, avoiding the risk of construction errors or uneven structural stress caused by inaccurate positioning, and further ensuring the stability and safety of the structure.

[0025] In S3, the slow-bonded prestressing tendons inside the beam are laid according to the arrangement method and curve height of the prestressing tendons, and then fixed to the positioning tendons in sequence.

[0026] Through the above technical solution, slow-bonding prestressing tendons are laid within the beam according to the arrangement method and curve height of the prestressing tendons, and then fixed sequentially with the positioning bars, ensuring the accurate laying and fixing of the prestressing tendons. By following the design drawings and layout numbering for the reinforcement laying, deviations in the position of the prestressing tendons can be effectively avoided, thereby maintaining the designed stress state. Fixing them with the positioning bars ensures the stability of the prestressing tendons during subsequent construction, preventing positional displacement during concrete pouring or tensioning, helping to ensure a uniform overall stress distribution in the structure, and thus improving the strength and stability of the structure.

[0027] In S4, after the non-prestressed steel reinforcement at the bottom of the slab is tied, the slow-bonded prestressed tendons are laid at equal intervals along the X and Y axes of the roof slab. After the prestressed tendons are laid, the non-prestressed steel reinforcement of the surface layer is tied and installed to form a double-layer bidirectional stress system on the slab surface.

[0028] Through the above technical solution, after the non-prestressed steel reinforcement at the bottom of the slab is tied, equidistantly laid loosely bonded prestressed tendons are laid along the X and Y axes of the roof slab. Following the laying of the prestressed tendons, the surface layer of non-prestressed steel reinforcement is then tied and installed, forming a double-layer, two-way stress-bearing system on the slab surface. The evenly distributed loosely bonded prestressed tendons along the X and Y axes ensure uniform stress distribution in the prestressed tendons, allowing them to share the overall stress of the slab surface with the non-prestressed steel reinforcement. This ensures the coordinated work of the loosely bonded prestressed tendons and the surface layer of non-prestressed steel reinforcement, improving the flexural and shear resistance of the slab structure and avoiding localized stress concentration caused by uneven reinforcement distribution, thereby enhancing the overall stability and safety of the structure.

[0029] In S5, after forming a double-layer bidirectional force-bearing system on the slab surface, according to the detailed drawings, a pad is installed on the slab surface, a spiral reinforcement is set at the rear end of the pad, the pre-tensioning end is wrapped with a polyethylene foam board to form an inclined groove, and the fixed end is tied to the steel bar using an extrusion anchor process.

[0030] Through the above technical solution, after forming a double-layer, bidirectional stress-bearing system on the slab surface, and according to the detailed drawings, a pad is first installed on the slab surface. A spiral reinforcement is installed at the rear end of the pad to ensure its stable fixation and to provide support for subsequent tensioning and fixing. Next, the pre-tensioning end is wrapped with a polyethylene foam board to prevent concrete cracking or damage due to tension changes during tensioning. The fixing end is tied to the reinforcing steel using an extrusion anchor process to ensure the prestressing tendons remain stable during tensioning and to effectively transfer prestress to the structure, preventing slippage or displacement of the prestressing tendons when tension is applied. By setting up the pad, spiral reinforcement, foam board, and fixing end, the tension force of the prestressing tendons can be evenly transferred, enhancing the overall stability and load-bearing capacity of the structure and avoiding structural damage caused by improper fixing.

[0031] In S6, after the installation of the tensioning end and the fixed end is completed, the concealed acceptance of the fixed end, tensioning end, reinforcement arrangement and slab reinforcement in the beam is carried out. After the acceptance is qualified, the formwork is installed and the concrete is poured. After the pouring is completed, curing is carried out.

[0032] Using the above technical solution, after the installation of the tensioning and fixed ends is completed, a concealed inspection is conducted on the fixed ends, tensioning ends, reinforcement layout, and slab reinforcement in the beam to ensure that all reinforcement layout and positioning meet design requirements. After the concealed inspection, formwork is installed and concrete is poured, ensuring that the formwork position, supports, and reinforcement layout meet predetermined specifications to avoid construction errors caused by unstable formwork or reinforcement misalignment. After pouring, concrete curing is performed to ensure that the concrete solidifies under suitable humidity and temperature to prevent cracking or insufficient strength caused by environmental changes. Through concealed inspection, formwork installation, concrete pouring, and curing, the accuracy of construction and the quality of concrete are ensured, guaranteeing the long-term stability of the structure during use.

[0033] In S7, after curing is completed, samples are taken for testing. The concrete strength is tested to be no less than 85%. After approval by the project's technical manager, tensioning is carried out according to the design requirements.

[0034] Using the above technical solution, after curing, concrete samples are taken and tested to ensure that the concrete strength reaches at least 85%, guaranteeing that the concrete strength meets the requirements for subsequent prestressing tensioning. Prestressing tensioning according to design requirements is only carried out after the test is passed and approved by the project's technical manager. This ensures that the concrete reaches sufficient strength before tensioning, avoiding structural damage or deformation during tensioning due to insufficient concrete strength, thus guaranteeing the safety and stability of the entire structure. Effective control of concrete quality ensures that the prestressing tension force is correctly transferred to the structure, maximizing the structure's load-bearing capacity and service life.

[0035] Tensioning is underway according to design requirements: When the temperature is not lower than 20℃, the control stress for prestressing tendons in the slab is 1375-1395MPa, and the tension force is 180.9-195.3kN. When the air temperature is not higher than 20℃, the control stress for prestressing tendons in the slab is 1460.8-1464.7 MPa, and the tension force is 199.5-205.1 kN. When the temperature is not lower than 20℃, the control stress for prestressing tendons in the beam is 690-700MPa, and the tension force is 95-98kN. When the temperature is not higher than 20℃, the tension control stress of the prestressed tendons in the beam is 727-735MPa, and the tension force is 100.3-102.9kN; During the tensioning process, it is crucial to ensure the accuracy of the operation and the stability of the instruments.

[0036] Through the above technical solution, during the prestressing tensioning process, different control stresses and tension forces are set according to temperature changes to ensure that the prestressing tendons reach the tensioning state required by the design. When the temperature is high, the tension control stress and tension force are appropriately increased; when the temperature is low, the tension control stress and tension force are adjusted accordingly. This effectively addresses the impact of temperature changes on material properties, ensuring the tensioning accuracy and mechanical properties of the prestressing tendons under different temperature conditions. During the tensioning process, ensuring operational accuracy and instrument stability is crucial to avoid structural problems caused by uneven tension or equipment errors. This ensures that the prestressed tendons are evenly stressed after tensioning, thereby enhancing structural stability and preventing structural safety hazards caused by improper operation.

[0037] The method also includes pretreatment of the board surface, the specific steps of which are as follows: Board surface cleaning and inspection: Use cleaning tools to thoroughly clean the board surface, removing all debris, dust, oil stains, etc. Inspect the board surface for defects: Use a level or laser measuring instrument to check the board surface for defects such as cracks, holes, and unevenness. For areas that need repair, use repair mortar to fill cracks and uneven parts to ensure that the board surface is smooth and free of defects. Surface wetting and control: Use a water pipe or sprayer to spray water mist to wet the board surface. After wetting, ensure that the surface remains properly moist. The wetted board surface needs to be air-dried naturally until it stops dripping. Depending on the actual weather conditions and construction progress, use a humidity control membrane to ensure that the humidity of the board surface remains stable.

[0038] The above technical solution involves thoroughly cleaning the slab surface during pretreatment to remove all debris, dust, oil, and other contaminants, ensuring a clean surface. Cleaning tools are used to ensure no debris remains, preventing it from affecting the position of the reinforcing bars or the bond between the concrete and the reinforcing bars. Next, a level or laser measuring instrument is used to check for cracks, holes, or unevenness. These uneven areas are then filled with repair mortar to ensure a smooth and defect-free surface. This ensures the flatness and strength of the slab surface, providing a precise load-bearing foundation for subsequent construction and preventing structural defects caused by unevenness or cracks. Next, use a hose or sprayer to spray water mist to moisten the slab surface. After moistening, the slab surface needs to air dry naturally until it stops dripping to ensure it remains in a suitable moisture state. This moistening treatment effectively prevents cracking during concrete construction and ensures good bonding between the concrete and the reinforcing steel. Depending on actual weather conditions and construction progress, a humidity control membrane is used to maintain stable moisture levels on the slab surface. This measure effectively controls changes in the slab's moisture state, avoiding construction problems caused by humidity fluctuations and ensuring the strength and stability of the concrete during subsequent construction. Example

[0039] S1. Drawing Detailing and Numbering of Tempered Bonding Prestressing Reinforcement Positioning Bars: Based on the roof structure and construction drawings, detailed design of drawings is carried out to determine the embedment length and layout position of the tempered bonding prestressing reinforcement bars. The reinforcement bars are uniformly numbered according to the detailed construction drawings, and material cutting and construction installation are controlled according to the numbered drawings. S2. Based on the layout and numbering of the prestressed positioning bars, the construction of non-prestressed steel reinforcement and the installation of prestressed positioning bars for the beam are carried out. After the construction of the non-prestressed steel reinforcement in the beam is completed, the prestressed positioning bars are tied inside the beam according to the detailed requirements of the drawings. The positions of the positioning bars are controlled according to the requirements of the drawings, including the highest point, the lowest point, and the inflection point. S3. Lay the prestressed tendons in the beam based on the layout and numbering of the prestressed tendons. According to the arrangement method and curve height of the prestressed tendons, lay the prestressed tendons in the beam and fix them to the positioning tendons in sequence to ensure the correct position and force direction of the prestressed tendons. S4. After step S3, the non-prestressed steel bars at the bottom of the slab are tied and the prestressed tendons on the surface of the slab are laid. After the prestressed tendons on the surface of the beam are laid, the non-prestressed steel bars at the bottom of the slab are tied and the prestressed tendons on the surface of the slab are laid at equal intervals along the X-axis and Y-axis. S5. Following step S4, after binding the non-prestressed reinforcing bars at the bottom of the slab and laying the prestressed tendons for the slab surface with a gentle bond, install the tensioning end and the fixing end. After completing the binding of the non-prestressed reinforcing bars at the bottom of the slab and the laying of the prestressed tendons for the slab surface with a gentle bond, install a pad on the slab surface according to the detailed drawing requirements, and set a spiral reinforcement at the rear end of the pad. To reserve space for the tensioning end, wrap the inclined groove with polyethylene foam board, and use an extrusion anchoring process to bind the fixing end with the reinforcing bars. S6. Following this, concealed acceptance and concrete pouring are conducted. After the installation of the tensioning and fixing ends is completed, concealed acceptance is performed on the fixing ends, tensioning ends, reinforcement layout, and slab reinforcement in the beam. After passing the concealed acceptance, formwork installation and concrete pouring are carried out. After the concrete pouring is completed, curing is performed. S7. After the concrete is poured, prestress it. After curing, test the concrete strength to ensure that the concrete strength meets the design requirements. After approval by the project technical manager, prestress it according to the design requirements.

[0040] Comparative Example 1 The post-tensioning method is adopted, which involves pre-laying corrugated pipes in the beam and slab structure to form ducts, inserting uncoated steel strands, tensioning the steel strands after the concrete has been poured and cured to meet the standards, and finally using high-pressure grouting to bond the steel strands to the concrete to achieve prestress transfer. The specific steps are as follows: S1. After the template is installed, fix the corrugated pipes in the designed positions, ensuring that the duct curves meet the requirements. Additional positioning steel bars are required to reinforce the corrugated pipes. S2. After the corrugated pipe is laid, insert the steel strand, leaving a tensioning length at both ends, and seal the joint of the duct with tape to prevent grout leakage. S3. Tie non-prestressed steel bars in beams and slabs, and coordinate with corrugated pipes to avoid damage to the pipes; S4. When pouring concrete, avoid the corrugated pipe during vibration to prevent deformation. A dedicated person should monitor the integrity of the duct throughout the process. S5. After the concrete has cured to 85% of its design strength, the steel strands are tensioned. S6. High-pressure grouting shall be carried out within 24 hours after tensioning, using P425 cement grout. Air in the ducts must be completely removed to ensure compaction. S7. After the grouting and curing meet the standards, cut off the excess steel strands and complete the anchor sealing.

[0041] Comparative Example 2 Steel strands pre-coated with anti-corrosion grease and wrapped in plastic sleeves are directly laid in the structure. After concrete pouring, the steel strands are not bonded to the concrete. Prestress is transferred through tensioning end anchors, eliminating the need for grouting. The specific steps are as follows: S1. After the formwork is installed, tie the non-prestressed bottom reinforcement and positioning reinforcement of the beams and slabs; S2. Lay unbonded prestressed tendons at the designed spacing and fix them to the positioning steel bars to ensure accurate curve positioning; S3. Tie the non-prestressed reinforcement on the slab surface, avoiding the tensioning end of the prestressed reinforcement; S4. Install the tensioning end anchor and pad, and secure them firmly; S5. Pour concrete and vibrate it to prevent the anchorage from shifting; S6. After the concrete has cured to 85% of its design strength, the steel strands are tensioned. S7. After tensioning is completed, cut off the excess steel strands, perform anti-corrosion treatment on the tensioning end, and then seal the anchor.

[0042] I. Construction Efficiency Testing Record the start / end time of each process according to the "Code for Design of Construction Organization" (GB / T50502-2009), calculate the total construction period and the time consumed by key processes; count the types of work and the number of people involved in each test section every day, and calculate the total man-days.

[0043] II. Construction Quality Pass Rate Testing According to Chapter 6 of the "Code for Acceptance of Construction Quality of Concrete Structures" (GB50204-2015) and Chapter 5 of the "Technical Specification for Slow-Set Bond Prestressed Concrete Structures" (JGJ / T387-2016), the tension force and elongation values ​​were recorded, and the deviation rate was calculated using the following formula: Deviation rate = |actual elongation value - design elongation value| / design elongation value × 100%; the amount of anchor slippage after tensioning is measured using a dial indicator (accuracy 0.01mm).

[0044] III. Structural stress performance testing According to Chapters 7 and 9 of the "Standard for Test Methods of Concrete Structures" (GB / T50152-2012), displacement gauges were installed at the mid-span of beams and slabs, loads were applied in stages, and the deflection value under each load stage was recorded. Apply uniformly distributed loads in stages, hold each load for 30 minutes, observe the appearance of cracks, and record the cracking load.

[0045] Table 1 Experimental Data The embodiment employs a slow-bonding prestressing technology, eliminating the need for additional corrugated pipe laying, high-pressure grouting, and grouting curing procedures compared to Comparative Example 1, and also eliminating the need for anti-corrosion treatment at the tensioning end as in Comparative Example 2. It can be constructed simultaneously with ordinary steel reinforcement. The total construction period of the embodiment is reduced by 40% compared to Comparative Example 1 and by 7.7% compared to Comparative Example 2. This embodiment demonstrates improved efficiency in construction procedures, saves time, ensures timely completion, and achieves the beneficial effect of shortening the construction period while guaranteeing the structural load-bearing performance of the roof.

[0046] In this embodiment, the slow-bonded prestressing tendons do not require corrugated pipe ducts or anti-corrosion grease protection, reducing the interference of on-site manual operations on quality. The tensile elongation deviation rate of this embodiment is better than that of Comparative Example 1 and Comparative Example 2, and the anchor slippage is less than that of Comparative Example 1 and Comparative Example 2. This fully demonstrates the technical advantages of eliminating the need for corrugated pipe laying and grouting, reducing the adverse effects of on-site manual operations, and making it easier to ensure construction quality.

[0047] In this embodiment, the slow-bonded prestressing tendons, after the slow-bonding adhesive has cured, can form an effective bond with the concrete. Simultaneously, the early construction process offers the convenience of unbonded prestressing, combining the advantages of both. Experimental data shows that under short-term loads, the mid-span deflection of the beam and slab in this embodiment is less than that in Comparative Example 2, while the cracking load is higher than in Comparative Examples 1 and 2. This demonstrates that it overcomes the shortcomings of Comparative Example 1 (delayed stress transfer) and Comparative Example 2 (poor structural integrity and large prestress loss), ensuring the structural load-bearing performance of the roof while absorbing the advantages of both bonded and unbonded structures, thus meeting the high requirements for structural load-bearing and crack resistance of large-span gable roofs.

[0048] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A construction method for large-span, double-layer, bidirectional, gently bonded prestressed concrete sloping roofs, characterized in that: Includes the following steps: S1. Drawing refinement and layout numbering of prestressed positioning reinforcement bars with slow bonding; S2. Based on the layout and numbering of the slow-bonding prestressed positioning bars, carry out the construction of non-prestressed steel reinforcement in the beam and the installation of slow-bonding prestressed positioning bars. S3. Lay the slow-bonded prestressed tendons in the beam based on the layout and numbering of the slow-bonded prestressed positioning tendons; S4. After step S3, proceed with the binding of non-prestressed steel bars at the bottom of the slab and the laying of prestressed tendons for the slab surface. S5. Based on the binding of non-prestressed steel bars at the bottom of the slab and the laying of prestressed tendons for slow bonding on the slab surface in step S4, install the tensioning end and the fixing end. S6. Then, conduct concealed inspection and concrete pouring. S7. The poured concrete is prestressed.

2. The construction method for a large-span, double-layer, bidirectional, gently bonded prestressed concrete sloping roof according to claim 1, characterized in that, In S1, the drawing refinement and the layout numbering of the slack-bonded prestressed positioning tendons are based on the roof structure and construction drawings. The roof prestressing project is refined to determine the embedment length and layout position of the slack-bonded prestressed tendons. They are then uniformly numbered according to the construction refinement drawings, and the material cutting and construction installation are controlled according to the numbered drawings.

3. The construction method for a large-span, double-layer, bidirectional, gently bonded prestressed concrete sloping roof according to claim 1, characterized in that, In S2, the specific steps for installing the slow-bonding prestressed positioning bars are as follows: after the non-prestressed steel reinforcement of the beam is constructed, the slow-bonding prestressed positioning bars are tied inside the beam according to the drawings. The positioning bars are controlled according to the requirements of the drawings to control the highest point, lowest point and inflection point.

4. The construction method for a large-span, double-layer, bidirectional, gently bonded prestressed concrete sloping roof according to claim 1, characterized in that, In S3, the slow-bonding prestressing tendons inside the beam are laid according to the arrangement method and curve height of the prestressing tendons, and are fixed to the positioning tendons in sequence.

5. The construction method for a large-span, double-layer, bidirectional, gently bonded prestressed concrete sloping roof according to claim 1, characterized in that, In S4, after the non-prestressed steel reinforcement at the bottom of the slab is tied, the slow-bonded prestressed steel reinforcement is laid at equal intervals along the X and Y axes of the roof slab. After the prestressed steel reinforcement is laid, the surface non-prestressed steel reinforcement is tied and installed to form a double-layer bidirectional force-bearing system on the slab surface.

6. The construction method for a large-span, double-layer, bidirectional, gently bonded prestressed concrete sloping roof according to claim 1, characterized in that, In step S5, after the double-layer bidirectional force-bearing system of the plate is formed, the pad is installed on the plate according to the drawing. The rear end of the pad is provided with spiral reinforcement. The tension end is wrapped with polyethylene foam board to form an inclined groove. The fixed end is tied to the steel bar using extrusion anchoring technology.

7. The construction method for a large-span, double-layer, bidirectional, gently bonded prestressed concrete sloping roof according to claim 1, characterized in that, In step S6, after the installation of the tensioning end and the fixed end is completed, the concealed acceptance of the fixed end, tensioning end, reinforcement arrangement and slab reinforcement in the beam is carried out. After the acceptance is qualified, the formwork is installed and the concrete is poured. After the pouring is completed, curing is carried out.

8. The construction method for a large-span, double-layer, bidirectional, gently bonded prestressed concrete sloping roof according to claim 1, characterized in that, In step S7, after curing is completed, samples are taken and sent for testing. The concrete strength is tested to be no less than 85%. After approval by the project's technical manager, tensioning is carried out according to the design requirements.

9. The construction method for a large-span, double-layer, bidirectional, gently bonded prestressed concrete sloping roof according to claim 8, characterized in that, Tensioning is underway according to design requirements: When the temperature is not lower than 20℃, the control stress for prestressing tendons in the slab is 1375-1395MPa, and the tension force is 180.9-195.3kN. When the air temperature is not higher than 20℃, the control stress for prestressing tendons in the slab is 1460.8-1464.7 MPa, and the tension force is 199.5-205.1 kN. When the temperature is not lower than 20℃, the control stress for prestressing tendons in the beam is 690-700MPa, and the tension force is 95-98kN. When the temperature is not higher than 20℃, the tension control stress of the prestressed tendons in the beam is 727-735MPa, and the tension force is 100.3-102.9kN; During the tensioning process, it is crucial to ensure the accuracy of the operation and the stability of the instruments.

10. The construction method for a large-span, double-layer, bidirectional, gently bonded prestressed concrete sloping roof according to claim 1, characterized in that, The method also includes pretreatment of the board surface, the specific steps of which are as follows: Board surface cleaning and inspection: Use cleaning tools to thoroughly clean the board surface, removing all debris, dust, oil stains, etc. Inspect the board surface for defects: Use a level or laser measuring instrument to check the board surface for defects such as cracks, holes, and unevenness. For areas that need repair, use repair mortar to fill cracks and uneven parts to ensure that the board surface is smooth and free of defects. Surface wetting and control: Use a water pipe or sprayer to spray water mist to wet the board surface. After wetting, ensure that the surface remains properly moist. The wetted board surface needs to be air-dried naturally until it stops dripping. Depending on the actual weather conditions and construction progress, use a humidity control membrane to ensure that the humidity of the board surface remains stable.

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