Cast-in-place construction method for pre-tensioning prestressed precast beam

Abstract

The invention discloses a cast-in-place construction method for a pre-tensioning prestressed precast beam. The cast-in-place construction method for the precast beam comprises the following specific steps that S1, construction preparation is conducted; s2, placing the steel strands and the stirrups; s3, steel strands are laid and tensioned; s4, installing a beam end mold; s5, steel bars are manufactured and bound; s6, side formwork installation; s7, concrete pouring, wherein concrete is poured through a hopper or an automobile pump; s8, formwork removal, beam lifting and hoisting are conducted; a prestressed beam production line is arranged on site, a high-strength concrete plate strip is adopted as a table top for production and resistance to huge tension, the production efficiency is improved to the maximum extent, the one-time input cost is reduced as much as possible by selecting a permanent and temporary combination mode with an original road, and the problem of quality guarantee of precast beams produced on site is solved; the construction period of the pre-tensioning method prestressed precast beam is relatively short, the engineering task can be completed more quickly, and the construction cost is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of building construction, in particular to a method for on-site casting of prestressed prefabricated beams by pre-tensioning method. Background Art

[0002] Based on the large-scale modern logistics park prefabricated building industrialization project, all storage warehouses and the second floor of the elevated platform of the logistics park adopt prefabricated beam hoisting and truss floor deck structure. The conventional factory supply form is adopted. First, the transportation cost is too high, and second, there are hidden dangers such as untimely supply. The on-site planning arranges the prestressed beam production line at the elevated platform level. How to ensure the quality of the prefabricated beams produced on site is the difficulty of this project.

[0003] The solution of the present invention is as follows: a prestressed beam production line is set up on site, and high-strength concrete plates are used as the table surface for production and resistance to huge tensile forces, so as to maximize the production efficiency, and a method of combining with the original road permanently is selected to reduce the one-time investment cost as much as possible, thereby solving the difficulty of quality assurance of prefabricated beams produced on site. Summary of the invention

[0004] The present invention provides a method for on-site casting of prestressed precast beams by pre-tensioning method in order to solve the problems that the conventional factory supply form has excessive transportation costs and untimely supply, in which the storage warehouses and the second floors of the elevated platforms in the logistics park all adopt precast beam hoisting and truss floor deck structures.

[0005] In order to solve the above technical problems, the present invention provides a technical solution: a prestressed precast beam on-site casting construction method, the specific steps of the precast beam on-site casting construction method are as follows: S1: Construction preparation, including installation of tensioning pedestal, layout of steel bar processing yard, layout of steel bar processing yard, layout of steel strand yard, planning of component and material transportation roads, preparation of machinery and determination of raw materials. The steel bar processing yard of the prefabricated beam yard should be set at both ends of the pedestal, and the gantry crane track should be extended to the processing yard; S2: Arrangement of steel strands and stirrups. Stirrups can be placed first and then steel strands, or first and then stirrups. This includes cleaning and rust removal of the bottom mold, bottom mold treatment, and arrangement of steel strands and stirrups. S3: Laying and tensioning of steel strands. Specifically, 2 to 6 steel strands can be laid at a time. They need to be laid separately according to the number of steel strands on a single production line on site. After putting on the PVC sleeve, the steel strands and the fine-rolled rebar are connected together through connectors. The PVC sleeve can be put on from both ends of the pedestal according to the amount used on the production line, and then the steel strands are tensioned. During the group tensioning process, fill in the prestressed tensioning record according to Appendix 1 and keep it for future reference. After the group tensioning is completed, check to see if the error between the actual elongation and the theoretical elongation does not exceed ±6%. Check whether the steel strands have slipped wires and whether the steel strands have misaligned wires. S4: Installation of beam end formwork. According to the different models of prefabricated beams on the production line, the shapes of the ends are different (mainly divided into flat ends of frame beams and notched ends of secondary beams). After assembling the end formwork into the required models, install it. Fix the buckle to the position of the beam end. Use the assembled end plate to stand vertically from bottom to top. Use a crowbar to clamp the steel strand into the slot of the end plate. Clamp the end plate plug-in on the upper part. Use a plastic plug plate to block the lower part. Apply foam glue to the gap at the bottom to prevent leakage. Use tape to seal the PVC tank and one end is close to the end plate. S5: Rebar production and binding, including special rebar and embedded parts production, ordinary rebar binding, special rebar binding; S6: installing the side formwork, the specific steps are to hoist the side formwork and connect the side formworks with bolts after hoisting; then put the main beam buried box into the designed position, place the buried box pressure strip support on the upper end of the beam formwork, and fix it with thick iron wire; finally, close the side formwork; S7: Concrete pouring, concrete is poured using a hopper or a truck pump; S8: Demolding, lifting and hoisting. The mold is removed the next day after the precast beam concrete is poured. After the strength of the poured concrete reaches the design requirements, it is released. The steel strands between the beams whose prestress has been completely released are cut. The cutting is done by plasma cutting. The produced beams are hoisted from the production line to the hoisting point and stacked neatly according to the precast stacking plan, waiting for on-site installation. Among them, the prepared machinery includes large gantry crane, small gantry crane, prefabricated beam transport vehicle, and jack; Further, in step S2, the steel bottom mold processing method is as follows: foam strips are affixed to the sides of the channel steel bottom mold, neutral silicone weather-resistant glue is used to seal the expansion joints between the bottom molds, and then a release agent is applied.

[0006] Furthermore, in step S3, the laying method of the steel strand is as follows: the steel strand is laid by traction using a winch and a special clamp, the PVC sleeve is inserted from both ends of the pedestal according to the usage on the production line, the steel strand is connected to the fine-rolled threaded steel through a connector, and the fine-rolled threaded steel is connected to the anchor of the tensioning pedestal.

[0007] Furthermore, the tensioning process in step S3 is as follows: A01: Move the jack shelf to the position of the fixed anchor column, and then move the movable anchor column to the back of the shelf; A02: Adjust the position of the jack and the movable anchor column (the movable anchor column is one of the components of the tensioning pedestal), ensure that the center lines of the anchor plate, jack and movable anchor column are in a straight line, and ensure that the jack is vertical to the anchor plate and movable anchor column, then connect the fine-rolled threaded steel with the steel strand to be tensioned, and tighten the fine-stretching steel nut at the movable anchor column; A03: After the finished rolled threaded steel is connected, measure the verticality of the anchor column to ensure the verticality; A04: During the initial stress tensioning, use a through-hole jack to perform small tensioning on each strand. The initial tensioning stress control value is 0.15fptk. Tighten the nuts of the tensioning steel on the fixed anchor column. During the initial tensioning, ensure that the tensioning force of each strand is the same; Among them, the group tensioning is a process of slowly tensioning all the steel strands to the tensioning control force using a pedestal jack. During the group tensioning, the verticality measuring ruler is observed at the same time to ensure the verticality.

[0008] Furthermore, the special steel bars and embedded parts include shear-resistant steel plates, position-limiting reinforcement steel bars for hoisting formwork holes, mesh bars, and hooks; Among them, the limiting reinforcement steel bars for the hoisting formwork holes need to be made on-site with 4mm cold-drawn wire, and the hooks are processed by cold bending on-site. The height of the mesh reinforcement should be more than 200mm greater than the main reinforcement of the lower steel strand to prevent the mesh from being too low and unable to play a role in resisting cracking of the beam head.

[0009] Furthermore, in the step S7, the pouring of precast beam concrete should be carried out by layered pouring, guiding bubbles, and ensuring the density of concrete vibration. When pouring concrete, due to the good airtightness of the steel mold, bubbles are difficult to vibrate out, and secondary vibration is required. Generally, two 50 vibrating rods are used, one vibrating while pouring, and the other vibrating again from beginning to end. It is required to insert the vibrating rod every 30 cm or so, and the vibration time is about 30 seconds. It must be vibrated densely, following the principle of fast insertion and slow withdrawal, until bubbles no longer emerge, the concrete does not sink significantly, and slurry begins to overflow.

[0010] Furthermore, when cutting the steel strand, start from the tensioned end and cut towards the other end in sequence, and the order cannot be reversed.

[0011] The advantages of the present invention are: a prestressed beam production line is set up on site, and a high-strength concrete plate strip is used as a production table to resist huge tensile force, thereby maximizing production efficiency, and choosing a permanent combination with the original road to reduce the one-time investment cost as much as possible, solving the difficulty of quality assurance of prefabricated beams produced on site, and the construction period of pre-tensioned prestressed prefabricated beams is relatively short, which can complete the engineering task faster and reduce construction costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a schematic diagram of the method of the present invention.

[0013] Figure 2 It is a schematic diagram of the tensioning structure of the present invention.

[0014] Figure 3 It is a schematic diagram of the hoisting structure of the present invention.

[0015] Figure 4It is a tensioning flow chart of the present invention.

[0016] As shown in the figure: 1. Large gantry crane; 2. Small gantry crane; 3. Precast beam transport vehicle; 4. Tensioning pedestal; 5. Steel strand; 6. Bottom mold; 7. High-quality rolled rebar; 8. Beam end mold; 9. Side mold; 10. Jack. DETAILED DESCRIPTION

[0017] The present invention is further described in detail below in conjunction with the accompanying drawings.

[0018] Combined with Figure 1-Figure 4 A method for casting on-site of a prestressed precast beam by a pre-tensioning method. The specific steps of the method for casting on-site of a precast beam are as follows: S1: Construction preparation, including installation of tensioning pedestal 4, arrangement of steel bar processing yard, arrangement of steel strand yard, planning of component and material transportation roads, preparation of machinery and determination of raw materials. The steel bar processing yard of the prefabricated beam yard should be set at both ends of the pedestal, the gantry crane track should be extended to the processing yard, a standard 200-meter tensioning pedestal 4 should be set, and 3-10 lines should be poured every day; S2: Arrangement of the steel strands 5 and stirrups. The stirrups can be placed first and then the steel strands 5, or first and then the stirrups. This includes cleaning and rust removal of the bottom formwork 6 (to prevent rust on the bottom of the beams after the first batch of precast beams are cast, which affects the apparent quality of the precast components), bottom formwork 6 treatment, and arrangement of the steel strands 5 and stirrups. S3: Laying and tensioning of steel strands 5. Specifically, 2 to 6 steel strands 5 can be laid at one time. They need to be laid separately according to the number of steel strands 5 on a single production line on site. After putting on the PVC sleeve, the steel strands 5 and the fine-rolled rebar 7 are connected together through connectors. The PVC sleeve can be put on from both ends of the pedestal according to the amount used on the production line. Then the steel strands 5 are tensioned. During the group tensioning process, fill in the prestressing tensioning record according to Appendix 1 and keep it for future reference. After the group tensioning is completed, check to see if the error between the actual elongation and the theoretical elongation does not exceed ±6%. Check whether the steel strands 5 have a slipping phenomenon, and check whether the steel strands 5 have a misaligned wire phenomenon; S4: Installation of the beam end form 8. According to the different models of prefabricated beams on the production line, the shapes of the ends are different (mainly divided into flat ends of frame beams and notched ends of secondary beams). The end formwork is assembled into the required models and then installed. The buckle is fixed to the position of the beam end. The assembled end plate is vertically erected from bottom to top. The steel strand 5 is clamped into the slot of the end plate with a crowbar. The end plate plug-in is clamped on the upper part. The lower part is blocked with a plastic plugging plate. The bottom gap is coated with foam glue to prevent leakage. The PVC tank is sealed with tape and one end is close to the end plate. S5: Rebar production and binding, including special rebar and embedded parts production, ordinary rebar binding, special rebar binding; S6: Installation of side formwork 9. The specific steps are to hoist the side formwork 9 and connect the side formwork 9 with bolts after hoisting; the main beam buried box is then placed in the designed position, the buried box pressure strip support is placed on the upper end of the beam formwork, and fixed with thick iron wire. After the buried box is buried and fixed, the mechanism is adjusted with the mechanism sleeve to make the originally trapezoidal beam formwork become rectangular, so that the lower part of the beam formwork is pressed against the sides of the beam bottom formwork 6 on both sides. The template mechanism adjustment work should be carried out at both ends at the same time. Then cover all the mechanism openings with special covers to prevent concrete from falling into the beam formwork during pouring and damaging the beam formwork; finally, the side formwork 9 is closed; S7: Concrete pouring, concrete is poured using a hopper or a truck pump; S8: demoulding, beam lifting and hoisting. The mold is removed the next day after the precast beam concrete is poured. After the strength of the poured concrete reaches the standard required by the design, the concrete is released. The steel strands 5 whose prestress has been completely released between the beams are cut off. The cutting is done by plasma cutting. The produced beams are hoisted from the production line to the hoisting point stacking site. The 12-meter side mold 9, which has been closed to form a trapezoidal shape with an upper diameter of 350 and a lower diameter of less than 320, is slowly lowered to the 350mm gap between the production lines to prevent the end plate and the PVC support mold hole from being crushed. It is lowered to the bottom mold 6 support. During the hoisting process of the side mold 9, when the side molds 9 are close to each other, the hoisted side mold 9 is lightly hit against the hoisted side mold 9. The foam tape has a certain thickness and softness, so that the side mold 9 can be tightly adhered to the foam tape to prevent leakage. The side molds 9 are neatly stacked according to the prefabricated stacking plan and wait for on-site installation. Among them, the prepared machinery includes a large gantry crane 1, a small gantry crane 2, a prefabricated beam transport vehicle 3, and a jack 10; It should be noted that in summer, from the time the formwork is removed to the time before the beams are placed, it is necessary to water the cast prefabricated components at least every day to keep the surface of the beams moist; in cold winter or when the temperature difference between day and night is large, the prefabricated components need to be covered with plastic film to reduce the internal temperature difference; the prefabricated components need to be cured after the formwork is removed, and then covered with a blanket and watered every day for about 15 days when the temperature is above 15°C.

[0019] In step S2, the processing method of the steel bottom mold 6 is as follows: a foam strip is affixed to the side of the channel steel bottom mold 6, a neutral silicone weather-resistant adhesive is used to seal the expansion joint between the bottom molds 6, and then a release agent is applied.

[0020] In step S3, the laying method of the steel strand 5 is as follows: the steel strand 5 is laid by traction using a winch and a special clamp, and the PVC sleeve is inserted from both ends of the pedestal according to the usage on the production line, and the steel strand 5 is connected to the fine-rolled threaded steel 7 through a connector, and the fine-rolled threaded steel 7 is connected to the anchor of the tensioning pedestal 4.

[0021] The tensioning process in step S3 is as follows: A01: Move the jack 10 shelf to the position of the fixed anchor column, and then move the movable anchor column to the back of the shelf; A02: Adjust the position of the jack 10 and the movable anchor column to ensure that the center lines of the anchor plate, the jack 10 and the movable anchor column are in a straight line, and ensure that the jack 10 is vertical to the anchor plate and the movable anchor column, then connect the finely rolled threaded steel 7 with the steel strand 5 to be tensioned, and tighten the fine steel nut at the movable anchor column; A03: After the connection of the fine-rolled threaded steel bar 7 is completed, measure the verticality of the anchor column to ensure the verticality; A04: During the initial stress tensioning, use a through jack 10 to perform small tensioning on each strand. The initial tensioning stress control value is 0.15fptk. Tighten the nuts of the tensioning steel on the fixed anchor column. During the initial tensioning, ensure that the tensioning force of each strand 5 is the same; The group tensioning is a process in which all the steel strands 5 are slowly tensioned to the tensioning control force using a pedestal jack 10, and the verticality measuring ruler is observed at the same time during the group tensioning to ensure the verticality.

[0022] The special steel bars and embedded parts include shear steel plates, limited reinforcement steel bars for hoisting formwork holes, mesh bars, and hooks; Among them, the limiting reinforcement steel bars for the hoisting formwork holes need to be made on-site with 4mm cold-drawn wire, and the hooks are processed by on-site cold bending.

[0023] In the step S7, the pouring of precast beam concrete should be carried out by layered pouring, guiding bubbles, and ensuring the density of concrete vibration. When pouring concrete, due to the good airtightness of the steel mold, bubbles are difficult to vibrate out, and secondary vibration is required. Generally, two 50 vibrating rods are used, one vibrating while pouring, and the other vibrating again from beginning to end. It is required to insert the vibrating rod every 30 cm or so, and the vibration time is about 30 seconds. It must be vibrated densely, following the principle of fast insertion and slow withdrawal, until bubbles no longer emerge, the concrete does not sink significantly, and slurry begins to overflow.

[0024] When cutting the steel strand 5, start from the tensioned end and cut towards the other end in sequence. The order cannot be reversed. If it is reversed, the steel strand 5 will break by itself.

[0025] The present invention and its embodiments are described above, and such description is not restrictive. The drawings show only one embodiment of the present invention, and the actual structure is not limited thereto. In short, if ordinary technicians in the field are inspired by it, without departing from the purpose of the invention, they can design a structure and embodiment similar to the technical solution without creativity, which should belong to the protection scope of the present invention.

Claims

1. A method for casting on-site of prestressed prefabricated beams by pretensioning method, characterized in that: The specific steps of the on-site casting construction method of precast beams are as follows: S1: Construction preparation, including installation of tensioning pedestal (4), layout of steel bar processing yard, layout of steel bar processing yard, layout of steel strand yard, planning of component and material transportation roads, preparation of machinery and determination of raw materials; S2: placing the steel strands (5) and stirrups, including cleaning and rust removal of the bottom mold (6), processing the bottom mold (6), and placing the steel strands (5) and stirrups; S3: laying and tensioning of the steel strands (5), specifically, 2 to 6 steel strands (5) can be laid at one time, and they need to be laid separately according to the number of steel strands (5) on a single production line on site, and after putting on the PVC casing, the steel strands (5) and the fine-rolled threaded steel (7) are connected together through a connector, and then the steel strands (5) are tensioned; S4: installing the beam end formwork (8). According to the different models of prefabricated beams on the production line, the shapes of the ends are different (mainly divided into flat ends of frame beams and notched ends of secondary beams). The end formwork is assembled into the required model and then installed; S5: Rebar production and binding, including special rebar and embedded parts production, ordinary rebar binding, special rebar binding; S6: installing the side formwork (9), specifically, the steps of hoisting the side formwork (9) and connecting the side formworks (9) with bolts after hoisting; placing the main beam buried box in the designed position, placing the buried box pressure strip support on the upper end of the beam formwork, and fixing it with thick iron wire; and finally closing the side formwork (9); S7: Concrete pouring, concrete is poured using a hopper or a truck pump; S8: demoulding, beam lifting and hoisting. The mold is removed the next day after the precast beam concrete is poured. After the strength of the poured concrete reaches the design standard, it is released. The steel strands (5) between the beams whose prestress has been completely released are cut. The cutting is done by plasma cutting. The produced beams are hoisted from the production line to the hoisting point and stacked neatly according to the precast stacking plan, waiting for on-site installation. The prepared machinery includes a large gantry crane (1), a small gantry crane (2), a prefabricated beam transport vehicle (3), and a jack (10).

2. A method for casting on-site of a prestressed precast beam according to claim 1, characterized in that: In step S2, the steel bottom mold (6) is processed as follows: a foam adhesive strip is affixed to the side of the channel steel bottom mold (6), a neutral silicone weather-resistant adhesive is used to seal the expansion joint between the bottom molds (6) and the bottom molds (6), and then a release agent is applied.

3. The method for casting on-site of prestressed precast beams according to claim 1, characterized in that: In step S3, the laying method of the steel strand (5) is as follows: the steel strand (5) is laid by using a winch and a special clamp to pull, the PVC sleeve is inserted from both ends of the pedestal according to the amount used on the production line, the steel strand (5) is connected to the fine-rolled threaded steel (7) through a connector, and the fine-rolled threaded steel (7) is connected to the anchor of the tensioning pedestal (4).

4. The method for casting on-site of a prestressed precast beam according to claim 1, characterized in that: The tensioning process in step S3 is as follows: A01: Move the jack (10) shelf to the position of the fixed anchor column, and then move the movable anchor column to the back of the shelf; A02: Adjust the position of the jack (10) and the movable anchor column to ensure that the center lines of the anchor plate, the jack (10) and the movable anchor column are in a straight line, and ensure that the jack (10) is perpendicular to the anchor plate and the movable anchor column. Then connect the finely rolled threaded steel (7) with the steel strand (5) to be tensioned, and tighten the fine steel nut at the movable anchor column. A03: After the finished rolled threaded steel bar (7) is connected, measure the verticality of the anchor column to ensure verticality; A04: During the initial stress tensioning, use a through-hole jack (10) to perform a small tensioning on each strand. The initial tensioning stress control value is 0.15fptk. Tighten the nuts of the tensioning steel on the fixed anchor column. During the initial tensioning, ensure that the tensioning force of each strand (5) is the same; The group tensioning is a process of slowly tensioning all the steel strands (5) to a tensioning control force using a pedestal jack (10), and simultaneously observing a verticality measuring ruler during the group tensioning to ensure verticality.

5. The method for casting on-site of prestressed precast beams according to claim 1, characterized in that: The special steel bars and embedded parts include shear steel plates, limited reinforcement steel bars for hoisting formwork holes, mesh bars, and hooks; Among them, the limiting reinforcement steel bars for the hoisting formwork holes need to be made on-site with 4mm cold-drawn wire, and the hooks are processed by on-site cold bending.

6. The method for casting on-site of prestressed precast beams according to claim 1, characterized in that: In the step S7, the pouring of precast beam concrete should be carried out by layered pouring, guiding bubbles, and ensuring the density of concrete vibration. When pouring concrete, due to the good airtightness of the steel mold, bubbles are difficult to vibrate out, and secondary vibration is required. Generally, two 50 vibrating rods are used, one vibrating while pouring, and the other vibrating again from beginning to end. It is required to insert the vibrating rod every 30 cm or so, and the vibration time is about 30 seconds. It must be vibrated densely, following the principle of fast insertion and slow withdrawal, until bubbles no longer emerge, the concrete does not sink significantly, and slurry begins to overflow.

7. The method for casting on-site of prestressed precast beams according to claim 1, characterized in that: When cutting the steel strand (5), the strands are cut sequentially from the tensioned end to the other end.

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