Construction technology of key groove type large-span anti-crack and anti-shear prefabricated prestressed beam

Abstract

The invention discloses a construction process of a key groove type large-span anti-crack and anti-shear prefabricated prestressed beam, and relates to the technical field of building construction, the construction process comprises the following steps: S1, mold adjustment: a superposed beam mold is a duplex long-line mold; according to the method, the method that beam bottom bars of a common assembly type prefabricated beam-column joint are anchored into columns is omitted, bottom longitudinal bars of beam-column joint frame beams do not need to stretch into the columns and are in lap joint through U-shaped steel bars, when the prefabricated beams are installed on site, only the U-shaped steel bars need to be flexibly adjusted in the horizontal direction, and therefore the construction efficiency is improved. The on-site construction difficulty can be obviously reduced, the construction efficiency is improved, the frame beam bottom bars do not need to be lifted at the end positions, the thickness of a protective layer at the end of the frame beam can be guaranteed, the beam hoisting sequence is not limited, the beam bottom bars do not interfere with one another, the U-shaped steel bars are on-site rear-mounted short steel bars, steel bar installation can be completed through manual operation, and the construction efficiency is greatly improved. And the construction difficulty is reduced.

Description

Technical Field

[0001] This invention relates to the field of building construction technology, and in particular to a construction process for a keyway-type large-span crack-resistant and shear-resistant precast prestressed beam. Background Technology

[0002] The current social environment has created a demand for industrialized construction. Construction industrialization and housing industrialization have become a development trend, and people are constantly exploring industrial models that are time-saving, energy-saving, cost-saving, and safe. Standardized components are produced in factories and transported directly to the construction site for assembly.

[0003] In the "keyway precast prestressed concrete assembled monolithic frame" system, the connection nodes of precast components, especially the connection nodes of precast beams and columns, often play a decisive role in structural performance such as load-bearing capacity, structural stiffness, and seismic performance.

[0004] In existing technologies, prestressed beams are difficult to construct due to the complex grouting process, resulting in poor flexibility and reduced adaptability.

[0005] Therefore, this invention proposes a construction process for keyway-type large-span crack-resistant and shear-resistant precast prestressed beams to solve the above-mentioned problems. Summary of the Invention

[0006] The purpose of this application is to provide a construction process for a keyway-type large-span crack-resistant and shear-resistant precast prestressed beam to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, this application provides the following technical solution: a construction process for a keyway-type large-span crack-resistant and shear-resistant precast prestressed beam, comprising the following steps: S1: Mold Adjustment The composite beam mold is a double-connected long-line mold; S2: Steel strand cutting: Cut the steel strands according to the drawings. After cutting, use a cutting machine to cut them. The steel strand rolls should be placed in a dedicated wire feeding rack. S3: Fabrication of precast stress beam reinforcement cage: Z-shaped steel bars are evenly arranged on the sides of the beam reinforcement cage and tied to the reinforcement skeleton to form an integral whole. Crack-resistant mesh and shear-resistant U-shaped steel bars are added at both ends of the precast beam reinforcement cage. Shear-resistant steel plates are set at the ends of the precast secondary beams, and open stirrups with 135° hooks are placed above them. S4: Prestressed beam support system The precast prestressed beam support system adopts a ring-lock type support frame. Each upright is equipped with a top support, and a wooden horizontal support beam is placed on two top supports. The uprights below the beam need to be arranged in the center. S5: Precast Stressed Beam Erection System a. Based on the different lifting point positions during the hoisting of various components, set up lifting points with different spacing, and select hooks according to the lifting points of the components during hoisting; b. Use the lower support frame to support the precast stress beam; S6: Construction of keyway joint at the end of precast prestressed beam: After the precast prestressed beam is hoisted into place, the connection between the column and the beam is a keyway joint. U-shaped steel bars are installed in the keyway, and the U-shaped steel bars must not be bent upwards when the horizontal length of the steel bars at the edge joint does not extend past the center of the column. S7: The precast stress beam reinforcement cage is closed by using combined closed stirrups. The stirrup caps with 135° hooks at the end are processed on site and tied to the stirrups with reserved hooks in the precast beam. No omissions are allowed. The beam side formwork is closed after the stirrups are tied. S8: Keyway-type precast prestressed main beam and precast secondary beam connection; S9: Concrete pouring: The concrete should be poured and compacted to the bottom elevation of the precast slab, and cured promptly after pouring.

[0008] Preferably, the width of the double-link long line mold is adjustable in the following dimensions: 200mm, 250mm, 300mm, 350mm, 400mm, and the length is 72m. One end of the platform is a fixed end, and the other end is a movable end. The movable end support frame can rotate and tilt under the action of the tension jack.

[0009] Preferably, the keyway precast prestressed beam is connected by a sleeve.

[0010] Preferably, the keyway joint should be filled with non-shrink fine aggregate concrete with a strength grade one level higher than that of the precast component concrete and not lower than C45.

[0011] Preferably, the precast prestressed beam support system adopts a φ48*3.0mm ring-lock support frame, with the longitudinal and transverse spacing of the uprights not exceeding 1200mm and the horizontal bar spacing of 1800mm.

[0012] Preferably, the thickness of the concrete protective layer (the distance from the outer edge of the steel strand to the concrete surface) should not be less than 55 mm.

[0013] Preferably, the net spacing in the horizontal direction of the lower longitudinal steel strands should not be less than 35mm and the diameter of the steel strands, and the net spacing between each layer of steel strands should not be less than 25mm and the diameter of the steel strands.

[0014] Preferably, ordinary closed stirrups should be used in the stirrup reinforcement zone at the beam end of the composite frame beam.

[0015] In summary, the technical effects and advantages of this invention are as follows: 1. The keyway type precast prestressed beam adopts the pre-tensioning method, and its steel strands extend out of the bend anchor and do not enter the beam-column joint. Compared with the traditional precast beam, the keyway type precast prestressed beam joint method reduces the steel content, optimizes the steel reinforcement arrangement of the beam-column joint, the method of avoiding the column corner reinforcement at the bottom of the precast beam, and the method of avoiding the bottom longitudinal reinforcement at the bottom of the main and secondary beams. 2. The keyway-type precast prestressed beams are equipped with keyway post-cast sections at the ends, eliminating the need for the bottom reinforcement of the beams to be anchored into the columns. Instead, they are spliced ​​in the keyway joints using U-shaped bars, improving upon the traditional method of raising the bottom reinforcement and ensuring that the bottom reinforcement of each beam does not interfere with each other. The lifting sequence of the beams is not restricted, and the main and secondary beams are mechanically connected in the keyway joints, avoiding the need for steel bar welding and sleeve grouting. This significantly reduces the difficulty of on-site construction and saves time. The use of U-shaped bars allows for flexible adjustment of the lap splices, preventing excessively dense collisions between beam and column reinforcements and avoiding the occurrence of cavities in the concrete pouring. 3. In conventional main and secondary beam connection methods, the sleeve grouting process is relatively complex, and problems such as bottom reinforcement collision and protective layer thickness are difficult to solve well. This project adopts the precast prestressed main and secondary beam joint construction technology. The lifting sequence of beams is not restricted, and the bottom reinforcement of each beam does not interfere with each other. This can avoid the bottom reinforcement of precast beams being raised at the ends, ensure the consistency of the protective layer of precast beams, facilitate on-site installation, and increase construction efficiency. In some parts of the precast frame beams, the bottom reinforcement extends from the beam end and is anchored into the support for connection, and shear keyways are set at the beam end. This structure combines the high efficiency of precast components and the flexibility of cast-in-place frames, and can meet the needs of various complex buildings. 4. The main difference between keyway precast prestressed beams and ordinary precast beams in terms of on-site construction lies in the fact that keyway precast prestressed beams optimize the beam-column keyway joint. This part has pre-reserved reinforcing bars, and the concrete is poured later, which effectively avoids the construction difficulties caused by collisions between the main reinforcing bars of the beam and column. Furthermore, the connection between the pre-cast section and the column in keyway precast prestressed beams is reinforced with U-shaped reinforcing bars, and anti-torsional reinforcing bars can be placed according to project requirements, resulting in a more stable structural connection and avoiding construction collisions and installation difficulties, making beam-column joint construction more convenient.

[0016] This invention eliminates the common practice of anchoring the bottom reinforcement bars of precast beam-column joints into the columns. The bottom longitudinal reinforcement bars of the frame beams at beam-column joints do not need to extend into the columns; instead, they are lapped with U-shaped steel bars. When installing precast beams on site, only the horizontal direction of the U-shaped steel bars needs to be flexibly adjusted, which can significantly reduce the on-site construction difficulty and improve construction efficiency. The bottom reinforcement bars of the frame beams do not need to be raised at the ends, which can ensure the thickness of the protective layer at the ends of the frame beams. The lifting sequence of the beams is not restricted, and the bottom reinforcement bars of each beam do not interfere with each other. The U-shaped steel bars are short steel bars placed on site, and the steel bar installation can be completed manually, reducing the construction difficulty. Attached Figure Description

[0017] Figure 1 This is a structural schematic diagram of the connection point of the cast-in-place central column in an embodiment of this application; Figure 2 This is a structural schematic diagram of the connection point of the cast-in-place edge column in an embodiment of this application; Figure 3 This is a structural schematic diagram of the U-shaped steel bar at the intermediate node in an embodiment of this application; Figure 4 This is a structural schematic diagram of the U-shaped steel bar at the edge node in an embodiment of this application. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example

[0019] refer to Figure 1-4 This embodiment proposes a construction process for a keyway-type large-span crack-resistant and shear-resistant precast prestressed beam, including the following steps: S1: Mold Adjustment The composite beam mold is a double-connected long-line mold; S2: Steel strand cutting: Cut the steel strands according to the drawings. After cutting, use a cutting machine to cut them. The steel strand rolls should be placed in a dedicated wire feeding rack. S3: Fabrication of precast stress beam reinforcement cage: Z-shaped steel bars are evenly arranged on the sides of the beam reinforcement cage and tied to the reinforcement skeleton to form an integral whole. Crack-resistant mesh and shear-resistant U-shaped steel bars are added at both ends of the precast beam reinforcement cage. Shear-resistant steel plates are set at the ends of the precast secondary beams, and open stirrups with 135° hooks are placed above them. S4: Prestressed beam support system The precast prestressed beam support system adopts a ring-lock type support frame. Each upright is equipped with a top support, and a wooden horizontal support beam is placed on two top supports. The uprights below the beam need to be arranged in the center. S5: Precast Stressed Beam Erection System a. Based on the different lifting point positions during the hoisting of various components, set up lifting points with different spacing, and select hooks according to the lifting points of the components during hoisting; b. Use the lower support frame to support the precast stress beam; S6: Construction of keyway joint at the end of precast prestressed beam: After the precast prestressed beam is hoisted into place, the connection between the column and the beam is a keyway joint. U-shaped steel bars are installed in the keyway, and the U-shaped steel bars must not be bent upwards when the horizontal length of the steel bars at the edge joint does not extend past the center of the column. S7: The precast stress beam reinforcement cage is closed by using combined closed stirrups. The stirrup caps with 135° hooks at the end are processed on site and tied to the stirrups with reserved hooks in the precast beam. No omissions are allowed. The beam side formwork is closed after the stirrups are tied. S8: Keyway-type precast prestressed main beam and precast secondary beam connection; S9: Concrete pouring: The concrete should be poured and compacted to the bottom elevation of the precast slab, and cured promptly after pouring.

[0020] In this embodiment, the width of the double-link long-line mold is adjustable to 200mm, 250mm, 300mm, 350mm, or 400mm, and its length is 72m. One end of the platform is fixed, and the other end is movable. The movable end support frame can rotate and tilt under the action of a tension jack. In this embodiment, the keyway precast prestressed beam is connected by a sleeve.

[0021] In this embodiment, the keyway joint should be filled with non-shrink fine aggregate concrete with a strength grade one level higher than that of the precast component concrete and not lower than C45.

[0022] In this embodiment, the precast prestressed beam support system adopts a φ48*3.0mm ring-lock support frame, with the longitudinal and transverse spacing of the uprights not exceeding 1200mm and the horizontal bar spacing of 1800mm.

[0023] In this embodiment, the thickness of the concrete protective layer (referring to the distance from the outer edge of the steel strand to the concrete surface) should not be less than 55mm.

[0024] In this embodiment, the net spacing of the lower longitudinal steel strands in the horizontal direction should not be less than 35mm and the diameter of the steel strands, and the net spacing between each layer of steel strands should not be less than 25mm and the diameter of the steel strands.

[0025] In this embodiment, ordinary closed stirrups should be used in the stirrup reinforcement zone at the beam end of the composite frame beam.

[0026] Working principle: The composite beam mold is a double-connected long-line mold with adjustable widths of 200mm, 250mm, 300mm, 350mm, and 400mm, and a length of 72m. One end of the platform is fixed, and the other end is movable. The movable end support frame can rotate and tilt under the action of a tension jack. Before production, the mold width should be adjusted according to the width of the composite beam in the design drawings. Composite beams of the same width and the same number of steel strands should be produced in the same mold slot. Before each production, the inner cavity of the mold should be cleaned of any residual concrete, debris, and other impurities, and the surface should be free of dust. The cleaned concrete residue should be collected and sent to the designated garbage storage area in a timely manner. The release agent should be applied evenly with a roller brush after the mold is cleaned and before the steel cage is placed in the mold, and there should be no missed areas or accumulation of liquid.

[0027] Cut the steel strands according to the drawings. After cutting, use a cutting machine to cut them. The steel strand rolls should be placed in a special wire feeding rack to prevent the steel strands from loosening and springing up and injuring people.

[0028] After the reinforcing bars are cut, they are sorted and placed to facilitate the binding work. Workers strictly follow the drawings during binding to ensure that all reinforcing bars in the combined crack-resistant and shear-resistant system are bound in place, thus improving the quality of reinforcing bar binding. Z-shaped reinforcing bars are evenly placed on the sides of the beam reinforcing cage stirrups and bound to the reinforcing cage to form an integral whole, ensuring the overall forming quality of the reinforcing cage and reducing the torsional deformation of the reinforcing cage caused by the prestressing tendons during tensioning. Crack-resistant mesh and shear-resistant U-shaped reinforcing bars are added to both ends of the precast beam reinforcing cage, which can effectively improve the end shear resistance and crack resistance of the precast beam, ensuring the structural strength and forming quality of the precast beam. Shear-resistant steel plates are set at the ends of the precast secondary beams, which can effectively improve the end bearing capacity of the precast secondary beams and ensure the component performance at the stress concentration points where the main and secondary beams intersect.

[0029] The precast prestressed beam support system uses φ48*3mm steel pipe scaffolding. The longitudinal and transverse spacing of the uprights is no greater than 900×900mm. The erection diagram is shown below, where L1≤200mm, L2≤1800mm, and L3≤900mm. The precast prestressed beam support system uses φ48*3.0mm ringlock support frame. The longitudinal and transverse spacing of the uprights is no greater than 1200mm, and the horizontal bar spacing is 1800mm. A top support is installed on the top of each upright, and a wooden horizontal support beam is placed on two top supports. The uprights below the beam need to be centered. By adjusting the adjustable supports at the top of the support system, the levelness and elevation of the top surface of the horizontal support beam meet the design requirements.

[0030] Precast prestressed beam hoisting: Special hoisting spreader beams are set with different spacing of lifting points according to the different lifting point positions of various components. When hoisting components, hooks are selected according to the lifting points of the components to ensure that the wire ropes of the precast components are kept as vertical as possible during hoisting, and the horizontal component force generated is minimized. The lifting points on the upper side of the hoisting beam are set at the golden section point of the hoisting beam, so that the hoisting beam can achieve the most reasonable stress requirements during hoisting.

[0031] According to the position of the pre-embedded lifting ring at the top of the precast beam, a reasonable lifting point should be adopted. Lift the beam to 500mm above the ground, and only continue lifting after checking the appearance quality of the component and the connection of the lifting lugs. The angle between the wire rope and the horizontal plane of the hoisting should not be less than 60°. The lifting should be slow and uniform to ensure that the edge of the precast beam is not damaged. When hoisting the precast beam, the tower crane should lift it slowly. When it is about 600mm above the working level, the construction personnel should hold the component, adjust the position of the beam, and slowly lower the precast beam.

[0032] Based on the measured support axis and edge line, pull a steel wire along the center line of the precast beam. Alternatively, pull a steel wire at an integer distance from the center line of the precast beam. Use a pry bar to straighten the precast beam in the upstream and downstream directions. Hang a plumb line in the vertical direction. After it is in place vertically, fine-tune the adjustable support at the bottom of the beam. After the support is in place, fix it.

[0033] The adjustable support frame of the precast beam uses 40*90 timbers laid flat, with templates laid on top of the timbers. Uprights are installed at the bottom of the precast beam along the beam span direction at 900mm intervals. The distance between the uprights under the composite slab and the edge of the beam is no more than 500mm. A 50cm wide flat working surface is laid on the side of the precast beam support frame for workers to hoist and correct the precast beam.

[0034] The support system can only be removed after the cast-in-place concrete has reached the strength specified in the standards.

[0035] After the precast prestressed beams are hoisted into place, the connection between the columns and beams is a keyway joint, such as... Figure 1 The image shows the connection point of the cast-in-place central column. Figure 2 This is the connection point for the cast-in-place edge column. Figure 3 The U-shaped reinforcement at the intermediate node Figure 4 For edge nodes, U-shaped reinforcing bars should be installed in the keyway according to design requirements, and a reliable fixing method should be used to ensure the accurate position of the U-shaped reinforcing bars. The diameter of the U-shaped reinforcing bars in the keyway should not be less than 12mm and should not be greater than 20mm. The bending anchorage length of the steel strand in the keyway should not be less than 210mm. The anchorage length of the U-shaped reinforcing bars should meet the requirements of the "Code for Design of Concrete Structures" GB50010. When the keyway wall is reserved, the wall thickness should preferably be 40mm. When the keyway wall is not reserved, a formwork should be set at the keyway position during on-site construction. The keyway concrete can only be poured after the stirrups and U-shaped reinforcing bars at the keyway are installed. The U-shaped reinforcing bars at the edge node should not be bent upwards if the horizontal length of the reinforcing bars does not extend past the center of the column.

[0036] The closure of stirrups in keyway precast prestressed beams includes: Since the stirrups in the precast section are already placed in the factory, they are open stirrups with 135° hooks at the top when they leave the factory. Combined closed stirrups are used. On-site, stirrup caps with 135° hooks at the ends are processed and tied to the stirrups with reserved hooks in the precast beam. No omissions are allowed. The stirrups in the post-cast section are tied on-site. The side formwork of the beam is not closed here. It will be closed after the stirrups are tied.

[0037] The connection between the keyway precast prestressed main beam and the precast secondary beam is achieved by reserving a post-cast groove in the main beam and anchoring the bottom reinforcement bar at the end of the secondary beam into the reserved reinforcement bar mechanical connection joint in the post-cast groove. The keyway precast prestressed beam adopts a sleeve connection, which is very simple and quick. The error can be freely adjusted within the range of 25-30mm. Compared with traditional precast beams, there is no connection of the reinforcement bars, no need for binding or welding on site, the component form is simple, and the mold making is very convenient, without the need for positioning by drilling holes in the mold.

[0038] During the precast stage: After the concrete is poured, it should be cured promptly, and the concrete curing should comply with the following regulations: (1) During steam curing, the heating rate of the slab should not exceed 25°C / h; the heating rate of the beam should not exceed 20°C / h. (2) During the constant temperature curing stage, the maximum temperature shall not exceed 95°C.

[0039] The following points should be noted when pouring concrete on site: (1) Before pouring concrete, the cross section of the beam, the beam positioning, the quantity and specifications of the U-shaped steel bars, and the installation quality should be checked. (2) Before pouring concrete, the keyway should be cleaned and thoroughly moistened with water, and there should be no standing water. (3) The concrete at the keyway joint shall conform to the design specifications. The concrete shall be poured and compacted and poured to the bottom elevation of the precast slab. (4) The keyway joint should be filled with non-shrink fine aggregate concrete with a strength grade one level higher than that of the precast component concrete and not lower than C45.

[0040] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A construction process for a keyway-type, large-span, crack-resistant, and shear-resistant precast prestressed beam, characterized in that, Includes the following steps: S1: Mold Adjustment The composite beam mold is a double-connected long-line mold; S2: Steel strand cutting: Cut the steel strands according to the drawings. After cutting, use a cutting machine to cut them. The steel strand rolls should be placed in a dedicated wire feeding rack. S3: Fabrication of precast stress beam reinforcement cage: Z-shaped steel bars are evenly arranged on the sides of the beam reinforcement cage and tied to the reinforcement skeleton to form an integral whole. Crack-resistant mesh and shear-resistant U-shaped steel bars are added at both ends of the precast beam reinforcement cage. Shear-resistant steel plates are set at the ends of the precast secondary beams, and open stirrups with 135° hooks are placed above them. S4: Prestressed beam support system The precast prestressed beam support system adopts a ring-lock type support frame. Each upright is equipped with a top support, and a wooden horizontal support beam is placed on two top supports. The uprights below the beam need to be arranged in the center. S5: Precast Stressed Beam Erection System a. Based on the different lifting point positions during the hoisting of various components, set up lifting points with different spacing, and select hooks according to the lifting points of the components during hoisting; b. Use the lower support frame to support the precast stress beam; S6: Construction of keyway joint at the end of precast prestressed beam: After the precast prestressed beam is hoisted into place, the connection between the column and the beam is a keyway joint. U-shaped steel bars are installed in the keyway, and the U-shaped steel bars must not be bent upwards when the horizontal length of the steel bars at the edge joint does not extend past the center of the column. S7: The precast stress beam reinforcement cage is closed by using combined closed stirrups. The stirrup caps with 135° hooks at the end are processed on site and tied to the stirrups with reserved hooks in the precast beam. No omissions are allowed. The beam side formwork is closed after the stirrups are tied. S8: Keyway-type precast prestressed main beam and precast secondary beam connection; S9: Concrete pouring: The concrete should be poured and compacted to the bottom elevation of the precast slab, and cured promptly after pouring.

2. The construction process of a keyway-type large-span crack-resistant and shear-resistant precast prestressed beam according to claim 1, characterized in that, The width of the double-link long line mold is adjustable in the following sizes: 200mm, 250mm, 300mm, 350mm, and 400mm. The length is 72m. One end of the platform is fixed, and the other end is movable. The support frame at the movable end can rotate and tilt under the action of a tension jack.

3. The construction process of a keyway-type large-span crack-resistant and shear-resistant precast prestressed beam according to claim 2, characterized in that, The keyway precast prestressed beam is connected by a sleeve.

4. The construction process of a keyway-type large-span crack-resistant and shear-resistant precast prestressed beam according to claim 3, characterized in that, The keyway joint should be filled with non-shrink fine aggregate concrete with a strength grade one level higher than that of the precast component concrete and not lower than C45.

5. The construction process of a keyway-type large-span crack-resistant and shear-resistant precast prestressed beam according to claim 4, characterized in that, The precast prestressed beam support system adopts a φ48*3.0mm ring-lock support frame, with the longitudinal and transverse spacing of the uprights not exceeding 1200mm and the horizontal bar spacing of 1800mm.

6. The construction process of a keyway-type large-span crack-resistant and shear-resistant precast prestressed beam according to claim 5, characterized in that, The thickness of the concrete protective layer (the distance from the outer edge of the steel strand to the concrete surface) should not be less than 55 mm.

7. The construction process of a keyway-type large-span crack-resistant and shear-resistant precast prestressed beam according to claim 6, characterized in that, The net spacing of the lower longitudinal steel strands in the horizontal direction shall not be less than 35mm and the diameter of the steel strands, and the net spacing between each layer of steel strands shall not be less than 25mm and the diameter of the steel strands.

8. The construction process of a keyway-type large-span crack-resistant and shear-resistant precast prestressed beam according to claim 7, characterized in that, Ordinary closed stirrups should be used in the stirrup reinforcement zone at the beam ends of the composite frame beam.

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