Forming method of pre-tensioning method prestress variable-strength concrete prefabricated component

Abstract

The invention provides a forming method of a pre-tensioning method prestress variable-strength concrete prefabricated part, which comprises the following steps of: arranging a prefabricated part forming mold, paving a steel strand in a range corresponding to the lower part of the part in a cavity of the prefabricated part forming mold, and tensioning the steel strand; high-strength concrete is poured into a prefabricated part forming mold cavity, and the poured high-strength concrete is vibrated and compacted to the preset boundary height of the lower portion of the component; when the external form of the poured high-strength concrete is hardened and loses fluidity, low-strength concrete is poured above the high-strength concrete, and the low-strength concrete is vibrated and compacted to the preset boundary height of the upper part of the component, so that under the condition that the bearing capacity requirement of the component is met, the section size and the self weight of the component can be properly reduced; the compressive strength of concrete with different strengths and the tensile strength of the steel strand are fully exerted, the cost performance of the prestressed member is improved, and the problem that the performance and the cost of an existing prestressed concrete member are difficult to balance is effectively solved.

Description

Technical Field

[0001] The invention relates to the technical field of building construction, in particular to a method for forming a prestressed variable-strength concrete prefabricated component. Background Art

[0002] Prestressed precast concrete components, such as prestressed composite beams, prestressed double beam slabs, prestressed trough slabs, etc., have the characteristics of large span, strong bearing capacity, good crack resistance, etc., and are widely used in construction projects. However, the precast components in the prior art usually use a single concrete with a strength grade in the range of C30-C50. In actual applications, the internal stress of the prestressed component is uneven. In the prior art, the concrete compressive strength of the entire precast component is the same, and the strength performance of the concrete cannot be optimized. The concrete in the prestressing area of ​​the component during the tensioning stage will be subjected to great compressive stress. The compressive strength of C30-C50 concrete is not high, and the prestress that can be applied is not large, which will lead to the inability to fully exert the performance of the steel strands, and reduce the bearing capacity and crack resistance of the prefabricated components. In the prior art, when the compressive strength of the concrete in the prestressing area of ​​the component during the tensioning stage is insufficient, the component cross-section is usually increased to reduce the prestressing stress of the concrete. In this way, the volume of the component becomes larger, the deadweight increases, and the amount of concrete increases, which will increase the material and hoisting costs and reduce the net height of the floor. There is also the problem of using high-compressive-strength concrete as a whole, which will increase the material cost and some concrete cannot be fully utilized, resulting in material waste. In view of the difficulty in obtaining high-strength concrete, the high cost and technical process problems, prestressed variable-strength concrete prefabricated components by pre-tensioning method have not been applied.

[0003] In summary, the prefabricated components in the prior art have the problem that the materials are not fully utilized and the performance and cost of the prefabricated components are difficult to balance. There is an urgent need for a prestressed variable-strength concrete prefabricated component with large load-bearing capacity, small cross-section and deadweight, high cost performance and full utilization of materials. Summary of the invention

[0004] The technical problem to be solved by the present invention is that the materials of the prefabricated components in the prior art are not fully utilized and it is difficult to balance the performance and cost of the prefabricated components.

[0005] In order to solve the above problems, the present invention provides a method for forming a prestressed variable-strength concrete prefabricated component by pre-tensioning method, comprising the steps of:

[0006] Arrange a prefabricated component forming mold, lay steel strands in the prefabricated component forming mold within the range corresponding to the lower part of the component, and perform tensioning operations on both ends of the steel strands;

[0007] Pouring high-strength concrete in the prefabricated component forming mold, and vibrating and compacting the poured high-strength concrete to a preset boundary height at the bottom of the component;

[0008] When the external shape of the poured high-strength concrete becomes hard and loses fluidity, low-strength concrete is poured on top of the high-strength concrete and vibrated to compact it to a preset boundary height at the top of the component.

[0009] The present invention provides a novel method for forming a prestressed variable-strength concrete prefabricated component by a pre-tensioning method. According to the different types and strengths of stresses borne by different positions of a concrete component body, different structures, concrete materials and forming methods are selected in a targeted manner. High-strength concrete is used for the lower part of the component, and low-strength concrete is used for the upper part of the component. The upper part and the lower part of the component are cast in layers in sequence to form an integral whole. Before the high-strength concrete at the lower part of the component is initially set, the low-strength concrete at the upper part of the component is cast, so that good bonding and connection are formed between the two layers of concrete, and cold joints and gaps are avoided in the component body. According to the performance requirements of the concrete component, steel strands are arranged in the component body, and the prestressed steel strands are wrapped with high-strength concrete to improve the compressive strength of local concrete, meet the compressive strength requirements of the concrete in the prestressing zone in the tensioning stage of the component, and can apply a larger prestressing stress. Under the condition of meeting the bearing capacity requirements of the component, the cross-sectional size and deadweight of the component can be appropriately reduced, and the compressive strength of concretes of different strengths and the tensile strength of the steel strands can be fully utilized, thereby improving the cost-effectiveness of the prestressed component and effectively solving the problem that the existing prestressed concrete component materials are not fully utilized and the performance and cost are difficult to balance.

[0010] As a preferred solution, the high-strength concrete is a concrete with a compressive strength standard value of 60Mpa-200Mpa, and the low-strength concrete is a concrete with a compressive strength standard value of 30Mpa-50Mpa. This design specifies the strength grade range of the high-strength and low-strength concretes used, and further adapts to the design of using different components in the upper and lower parts of the component body in this application. Within the specified strength range, concrete of different strength grades can be used for different usage scenarios.

[0011] As a preferred solution, the step of arranging the prefabricated component forming mold includes: installing the side mold and the bottom mold, enclosing the cavity for casting the prefabricated component to be formed by adjacent side molds and bottom molds, and installing the component end mold according to the length of the component to be formed. This design optimizes the structural design of the prefabricated component forming mold and the corresponding mold layout operation for the prefabricated component forming mold. It adopts a split mold design, mainly including side molds and bottom molds. The side molds can be arranged in an array at a preset distance, and the bottom mold is located at the bottom between adjacent side molds, so that multiple prefabricated components can be cast and formed at one time.

[0012] As a preferred solution, the step of arranging the prefabricated component forming mold includes: arranging an integral mold with multiple sections of cavities adapted to the outer contour of the concrete prefabricated component to be formed along the length direction of the component to be formed, and installing the component end template according to the length of the component to be formed. This design provides another prefabricated component forming mold design parallel to the above design, which adopts an integral mold design, no longer distinguishes between side molds and bottom molds, but adopts an integral structure, greatly simplifies the workload of mold support and disassembly, and can effectively improve the component body forming efficiency.

[0013] As a preferred solution, the cross section of the cavity of the prefabricated component forming mold is a rectangle with equal spacing between the corresponding areas of the upper and lower parts of the component, or an inverted trapezoid with decreasing width from the upper part to the corresponding area of ​​the component, or an inverted T-shape with a width of the lower part of the component greater than the width of the corresponding area of ​​the upper part of the component and a right-angle transition of the contour. This design adopts different shapes of mold cavity designs according to the different shapes of the component body required by the actual load-bearing requirements. The cross-sectional contour shapes include but are not limited to rectangle, inverted trapezoid, inverted T-shape, quasi-T-shape, quasi-I-shape, "π"-shaped double beam plate cross section, The inverted T-shaped member has a relatively wide lower structure and is entirely made of high-strength concrete.

[0014] As a preferred solution, the steps of arranging the prefabricated component forming mold and laying the steel strands in the cavity of the prefabricated component forming mold corresponding to the lower part of the component also include: placing stirrups at a preset position in the cavity of the prefabricated component forming mold. This design adopts the preferred design of this type of component body, fixes the main reinforcement position through the steel bars in the component body, and forms a stable steel reinforcement skeleton with other steel bars to improve the shear strength and torsion resistance of the component.

[0015] As a preferred solution, after the step of tensioning the steel strand, the step further includes the step of: tying component reinforcement, including stirrups, waist reinforcement, tension reinforcement, truss reinforcement, steel mesh and other reinforcing reinforcement, and placing embedded parts at preset positions in the cavity space of the prefabricated component forming mold. This design optimizes the personalized processing procedures of the component body for different application scenarios. After laying the steel strands and stirrups and before pouring, embedded parts are placed in the component body frame composed of stirrups, so as to perform personalized processing and forming on the component body, and embedded pipe fittings, fasteners and other structures so that the processed component body can obtain more functions.

[0016] As a preferred solution, the step of pouring low-strength concrete on top of high-strength concrete and vibrating and compacting it to a preset boundary height on the upper part of the component also includes the step of performing concrete curing operations within a preset time period after pouring the low-strength concrete. Specifically, the concrete curing methods in this step include natural curing, steam curing, and electric heating film curing, and different post-molding curing methods are used for different construction scenarios and finished product requirements.

[0017] As a preferred solution, the step of performing concrete curing operation within a preset time period after pouring low-strength concrete further includes the following steps:

[0018] When the strength of the poured high-strength concrete reaches more than 80% of the designed strength, the steel strands are tensioned and then cut off.

[0019] The design optimizes the processing of steel strands after pouring in the above process to achieve the final concrete component body. The tensioning process of prestressed steel strands is the transfer process of prestress, which is an important link in whether the prestressing method components can obtain good quality. The premise of tensioning is that the strength of the poured concrete reaches at least 80% of the design strength value before tensioning is allowed. If there are design requirements, tensioning can only be allowed when the design requirements are met;

[0020] If the design requires that a certain length of steel strands be reserved at the end of a component, the steel strands must be cut and bent strictly according to the drawing to ensure the horizontal length of the bend. For prefabricated components without design requirements, all steel strands extending out of the component must be cut off along the end position. Due to insufficient operating space on the production line and inconvenient cutting, the prefabricated components are first cut off on the production line and then lifted out for secondary cutting on the site where the components are stacked. The steel strands cut at the ends of the components should be treated with rust prevention.

[0021] As a preferred solution, the method further includes the following steps before the pouring step:

[0022] The height of the lower part of the precast prestressed variable-strength concrete component in the pouring direction is calculated based on the tensile stress of the steel strands used and the compressive strength of the high-strength concrete. This design optimizes the pre-pouring preparation process in the above process, and obtains the height value required for the lower part of the component to meet the strength requirements of the component body through calculation. The calculation process needs to be combined with the strength grade of the selected component body concrete and the situation of the steel strands.

[0023] As a preferred solution, the steel strands are laid out in a dense array at a height position corresponding to the lower part of the component above the bottom mold of the component, and the steel strands are laid out at a preset interval at a height position corresponding to the upper part of the component and adjacent to the inner side of the stirrups.

[0024] The design arranges steel strands at corresponding positions based on the differences in stress conditions at different positions of the component body. Since the lower part of the prefabricated component is the tensile zone when it is bent, the prestressed steel strands should be arranged in the lower area of ​​the component as much as possible to give full play to its tensile effect. A relatively small number of sparsely arranged steel strands are set in the upper part of the component, mainly to prevent the prefabricated component from arching too much after being tensioned. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A schematic diagram of a process for forming a prestressed variable-strength concrete prefabricated component provided by the present invention;

[0026] Figure 2 To adopt Figure 1 A schematic diagram of a model of a prestressed variable-strength concrete precast component with a rectangular cross section formed by a molding method of a prestressed variable-strength concrete precast component;

[0027] Figure 3 To adopt Figure 1 A schematic diagram of a model of another rectangular cross-section prestressed variable-strength concrete precast component formed by a forming method of a prestressed variable-strength concrete precast component;

[0028] Figure 4 for Figure 3 Schematic diagram of cross section of a medium rectangular section prestressed variable strength concrete precast component;

[0029] Figure 5 for Figure 2 Schematic diagram of cross section of a medium rectangular section prestressed variable strength concrete precast component;

[0030] Figure 6 It is a schematic cross-sectional view of a prestressed variable-strength concrete prefabricated component with an inverted trapezoidal cross section;

[0031] Figure 7 It is a schematic cross-sectional view of a prestressed variable-strength concrete prefabricated component with a "T"-shaped cross section;

[0032] Figure 8 It is a schematic cross-sectional view of a prestressed variable-strength concrete precast component with an inverted "T"-shaped cross section;

[0033] Fig. 9 It is a schematic cross-sectional view of a prestressed variable-strength concrete precast component with an "I"-shaped cross-section;

[0034] Fig.10 It is a structural schematic diagram of a prestressed variable-strength concrete precast component with a "π"-shaped cross section;

[0035] Fig.11 for Fig.10 Schematic diagram of the cross-sectional structure of the prestressed variable-strength concrete precast component;

[0036] Fig.12 For a Structural schematic diagram of prestressed variable-strength concrete precast components with a shaped cross section;

[0037] Fig.13 for Fig.12 Schematic diagram of the cross-sectional structure of the prestressed variable-strength concrete precast component;

[0038] in, Figure 1-Figure 13 middle:

[0039] 1. Upper part of the component; 2. Lower part of the component; 3. Steel strand; 4. Stirrups. DETAILED DESCRIPTION

[0040] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention is further explained below in conjunction with specific implementation methods.

[0041] Before explaining the working principle of the present invention in detail, the description of the present invention needs to be further explained: In the description of the present invention, it should be noted that the terms "upper", "lower", "inner", "outer", "front end", "rear end", "two ends", "one end", "the other end" and the like indicate the orientation or position relationship based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0042] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "provided with", "connected", etc. should be understood in a broad sense. For example, "connected" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, a direct connection, an indirect connection through an intermediate medium, or a welding connection between two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0043] refer to Figure 1-Figure 5 The following embodiments are described, Figure 1 A schematic diagram of a process for forming a prestressed variable-strength concrete prefabricated component provided by the present invention; Figure 2 To adopt Figure 1 A schematic diagram of a model of a prestressed variable-strength concrete precast component with a rectangular cross section formed by a molding method of a prestressed variable-strength concrete precast component; Figure 3 To adopt Figure 1 A schematic diagram of a model of another rectangular cross-section prestressed variable-strength concrete precast component formed by a forming method of a prestressed variable-strength concrete precast component; Figure 4 for Figure 3Schematic diagram of cross section of a medium rectangular section prestressed variable strength concrete precast component; Figure 5 for Figure 2 Schematic diagram of the cross section of a medium rectangular section prestressed variable-strength concrete precast component.

[0044] A method for forming a prestressed variable-strength concrete prefabricated component provided in this embodiment includes the following steps:

[0045] The method for forming a prestressed variable-strength concrete prefabricated component by pre-tensioning method comprises the following steps:

[0046] S01: arranging a prefabricated component forming mold, laying steel strands 3 in a range corresponding to the lower part 2 of the component in the cavity of the prefabricated component forming mold, and performing tensioning operation on the steel strands 3;

[0047] S02 pouring high-strength concrete in the cavity of the prefabricated component forming mold, and vibrating and compacting the poured high-strength concrete to a preset boundary height of the lower part 2 of the component;

[0048] S03 When the external shape of the poured high-strength concrete becomes hard and loses fluidity, low-strength concrete is poured on top of the high-strength concrete and vibrated to compact it to the preset boundary height of the upper part 1 of the component.

[0049] The present invention provides a novel method for forming a prestressed variable-strength concrete prefabricated component by a pre-tensioning method. According to the different types and strengths of stresses borne by different positions of a concrete component body, different structures, concrete materials and forming methods are selected in a targeted manner. The lower part 2 of the component adopts high-strength concrete, and the upper part 1 of the component adopts low-strength concrete. The upper part 1 and the lower part 2 of the component are cast in layers in sequence to form an integral whole. When the external shape of the high-strength concrete of the lower part 2 of the component hardens and loses fluidity, the low-strength concrete of the upper part 1 of the component is poured in, so that good bonding and connection are formed between the two layers of concrete, and cold joints and gaps are avoided in the component body. According to the performance requirements of the concrete component, a steel strand 3 is arranged in the component body, and the prestressed steel strand 3 is wrapped with high-strength concrete to improve the compressive strength of concrete in the prestressing zone of the component during the tensioning stage, and a larger prestressing stress can be applied. Under the condition of meeting the bearing capacity requirements of the component, the cross-sectional size and deadweight of the component can be appropriately reduced, and the compressive strength of concrete of different strengths and the tensile strength of the steel strand are fully utilized, thereby improving the cost-effectiveness of the prestressed component, and effectively solving the problem that the existing prestressed concrete component materials are not fully utilized and the performance and cost are difficult to balance.

[0050] It should be noted that when the external shape of the poured high-strength concrete becomes hard and loses fluidity, it refers to the time when the high-strength concrete reaches the initial setting state. The penetration resistance method can be used to measure the penetration resistance of the concrete when the fine mortar is sieved and penetrated into a certain depth at regular intervals. The time corresponding to the penetration resistance of 3.5MPa is the initial setting time.

[0051] In the technical solution provided in this embodiment, high-strength concrete is concrete with a compressive strength standard value of 60Mpa-200Mpa, and low-strength concrete is concrete with a compressive strength standard value of 30Mpa-50Mpa. This design optimizes the specifications of high-strength and low-strength concrete used, specifies the strength grade range of the concrete used, and further adapts to the design of using different components in the upper and lower parts of the component body in this application. Within the specified strength range, concrete of different strength grades can be used for different usage scenarios.

[0052] In the technical solution provided in this embodiment, the steps of laying out the prefabricated component forming mold include: installing the side mold and the bottom mold, enclosing the cavity for casting the prefabricated component to be formed by the adjacent side molds and the bottom mold, and installing the component end mold according to the length of the component to be formed. This design optimizes the structural design of the prefabricated component forming mold and the corresponding mold layout operation for the prefabricated component forming mold. It adopts a split mold design, which mainly includes a side mold and a bottom mold. The side molds can be arranged in an array at a preset distance, and the bottom mold is located at the bottom between adjacent side molds, so that multiple prefabricated components can be cast and formed at one time, and the ends are set between the two ends of the side mold and above the two sides of the bottom mold to obtain a mold cavity space with only one side of the top open. The split mold used can be easily adjusted according to the specifications and dimensions of the component, has strong applicability, and low transportation cost.

[0053] In the technical solution provided in this embodiment, the steps of arranging the prefabricated component forming mold include: arranging the integral mold with multiple sections of cavity adapted to the outer contour shape of the concrete prefabricated component to be formed along the length direction of the component to be formed, and installing the component end template according to the length of the component to be formed. This design provides another prefabricated component forming mold design parallel to the above design. The use of an integral mold can greatly simplify the workload of mold support and disassembly, improve construction efficiency, and the integral mold has high rigidity and acts as a tensioning mold table for steel strands.

[0054] refer to Figure 5-Figure 13 The following embodiments are described, Figure 5 for Figure 2 Schematic diagram of the cross section of a medium rectangular cross-section prestressed variable-strength concrete precast component using the prestressing method, wherein the cavity cross section of the precast component forming mold is a rectangle with equal spacing between the corresponding areas of the upper part 1 and the lower part 2 of the component.

[0055] Figure 6The cross-sectional schematic diagram of a prestressed variable-strength concrete precast component with an inverted trapezoidal cross-section is shown. The cavity cross-section of the precast component forming mold is an inverted trapezoid with a decreasing width along the corresponding area from the upper part 1 of the component to the lower part 2 of the component. The slopes on both sides of the cross-section facilitate the demoulding of the precast component from the overall mold.

[0056] Figure 7 The cross-sectional diagram of a prestressed variable-strength concrete precast component with a T-shaped cross section is shown in FIG. The cavity cross section of the precast component forming mold is an inverted T-shaped component with a width of the lower part 2 of the component greater than the width of the corresponding area of ​​the upper part 1 of the component and a right-angle transition of the contour. On the basis of the rectangular cross section, the area of ​​the lower compression zone of the component is increased and high-strength concrete is used, so that the compressive capacity of the lower part of the component is greatly improved, thereby increasing the tensile stress of the precast component and further improving the bearing capacity of the component.

[0057] Figure 8 The cross-sectional diagram of a prestressed variable-strength concrete precast component with an inverted T-shaped cross section is a precast component with a "T"-shaped cross section. The precast component with a "T"-shaped cross section has an enlarged upper support surface based on a rectangular cross section, which is beneficial to the support of floor slabs or precast panels. The slopes on both sides of the "T"-shaped cross section facilitate the demoulding of the precast component from the integral mold.

[0058] Fig. 9 The present invention is a schematic diagram of the cross section of an "I"-shaped prestressed variable-strength concrete precast component with a pre-tensioned method. The "I"-shaped precast component has an upper support surface enlarged on the basis of a rectangular cross section, which is beneficial to the support of floor slabs or precast slabs, increases the area of ​​the lower compression zone of the component and uses high-strength concrete, which greatly improves the compressive strength of the lower part of the component. Therefore, the tensioning stress of the precast component can be increased, and the bearing capacity of the component is further improved.

[0059] In the technical solution provided in this embodiment, components of different shapes are designed and selected according to the actual project application scenario and load-bearing requirements, and corresponding prefabricated molds with different cavities are used. The cross-sectional profile shapes include but are not limited to rectangle, inverted trapezoid and inverted T shape, among which the inverted T-shaped component has a lower structure with a larger component width, and the whole is cast with high-strength concrete.

[0060] refer to Figure 10-13 The following instructions are implemented: Fig.10 It is a structural schematic diagram of a prestressed variable-strength concrete precast component with a "π"-shaped cross section. Fig.11 for Fig.10 Schematic diagram of the cross-sectional structure of the prestressed variable-strength concrete precast component using the prestressing method. The precast component with a "π"-shaped cross-section is composed of a wide panel and two beams with an inverted trapezoidal cross-section. It is a prestressed concrete load-bearing component with a large span, large coverage area and relatively economical plate-beam combination, and has good structural mechanical properties.

[0061] Fig.12 For a Structural schematic diagram of prestressed variable-strength concrete precast components with a shaped cross section; Fig.13 for Fig.12 Schematic diagram of the cross-sectional structure of the prestressed variable-strength concrete precast component.

[0062] The prefabricated component with an L-shaped cross-section is composed of a wide panel and two L-shaped cross-section beams. It is a prestressed concrete load-bearing component with a large span, a large coverage area and a relatively economical plate-beam combination. The L-shaped cross-section beam has an enlarged cross-section flange on the basis of the traditional rectangular beam, which increases the area of ​​the compressed zone during tensioning and can lay more prestressed steel strands 3, thereby improving the load-bearing capacity under the condition of the same beam height.

[0063] In the technical solution provided in this embodiment, the steps of laying out the prefabricated component forming mold and laying the steel strand 3 in the cavity of the prefabricated component forming mold corresponding to the lower part 2 of the component also include: placing steel bars at a preset position in the cavity of the prefabricated component forming mold. This design adopts the preferred design of this type of component body, fixes the position of the main bars by the steel bars in the component body, and forms a stable steel bar skeleton with other steel bars to improve the shear strength and torsion resistance of the component. The steel bars include stirrups 4, tie bars, steel mesh, truss bars, waist bars, bent steel bars and other reinforcing steel bars.

[0064] In the technical solution provided in this embodiment, after the step of tensioning the steel strand 3, the step further includes: tying the component reinforcement and placing embedded parts at preset positions in the cavity space of the prefabricated component forming mold. This design optimizes the personalized processing procedures of the component body for different application scenarios. After laying the steel strand 3 and the reinforcement and before pouring, the embedded parts are placed in the component body frame composed of the reinforcement 4, so as to perform personalized processing and forming on the component body, and embed structures such as pipe fittings and fasteners so that the processed component body can obtain more functions.

[0065] In the technical solution provided in this embodiment, the step is to pour low-strength concrete on top of high-strength concrete, vibrate and compact it to a preset boundary height of the upper part 1 of the component, and then also includes the step of: performing concrete curing operations within a preset time period after pouring the low-strength concrete. Specifically, the concrete curing methods in this step include natural curing, steam curing and electric heating film curing, and different curing methods are used for different construction scenarios and finished product requirements.

[0066] In the technical solution provided in this embodiment, the step of performing concrete curing operation within a preset time period after pouring low-strength concrete, further includes the steps of:

[0067] When the strength of the poured high-strength concrete reaches more than 80% of the designed strength, the steel strands 3 are tensioned and then cut off.

[0068] The design optimizes the processing process of the steel strand 3 after the pouring is completed in the above process to achieve the final concrete component body forming. The tensioning process of the prestressed steel strand 3 is the prestressing transfer process, which is an important link in whether the prestressing method prefabricated components can obtain good quality. The premise of tensioning is that the strength of the poured concrete reaches at least 80% of the design strength value before tensioning is allowed. If there are design requirements, the design requirements must be met before tensioning can be allowed;

[0069] If the design requires that a certain length of steel strand 3 be reserved at the end of the component, the steel strand 3 must be cut and bent strictly according to the drawing to ensure the horizontal length of the bend. For prefabricated components without design requirements, all steel strands 3 extending out of the component must be cut off along the end position. Due to insufficient operating space on the production line and inconvenient cutting, the prefabricated components are first cut off on the production line and then lifted out for secondary cutting on the site where the components are stacked. The steel strand 3 cut at the end of the component should be treated with rust prevention.

[0070] In the technical solution provided in this embodiment, before the step of pouring high-strength concrete in the space formed by the component side mold and the component end mold, and vibrating and compacting the poured high-strength concrete to the preset boundary height of the component lower part 2, the step also includes:

[0071] The height of the lower part 2 of the precast prestressed variable-strength concrete component in the pouring direction is calculated according to the tensile stress of the steel strand 3 used and the compressive strength of the high-strength concrete. This design optimizes the pre-pouring preparation process in the above process, and obtains the height value required for the lower part of the component to meet the strength requirements of the component body through calculation. The calculation process needs to be combined with the strength grade of the selected component body concrete and the situation of the steel strand 3.

[0072] Although the present invention is disclosed as above, the protection scope of the present invention is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and these changes and modifications will fall within the protection scope of the present invention.

Claims

1. A method for forming a prestressed variable-strength concrete prefabricated component, characterized in that: Includes steps: Arranging a prefabricated component forming mold, laying a steel strand (3) within a mold cavity of the prefabricated component forming mold corresponding to the lower portion (2) of the component, and performing a tensioning operation on the steel strand (3); pouring high-strength concrete into the mold cavity of the prefabricated component forming mold, and vibrating and compacting the poured high-strength concrete to a preset boundary height of the lower part (2) of the component; When the external shape of the poured high-strength concrete becomes hard and loses fluidity, pour low-strength concrete on top of the high-strength concrete and vibrate and compact it to a preset boundary height of the upper part (1) of the component; The high-strength concrete is a concrete with a standard compressive strength value of 60Mpa-200Mpa, and the low-strength concrete is a concrete with a standard compressive strength value of 30Mpa-50Mpa.

2. The method for forming a prestressed variable-strength concrete prefabricated component according to claim 1, characterized in that: The steps of laying out the prefabricated component forming mold include: installing side molds and bottom molds, enclosing adjacent side molds and bottom molds to form a mold cavity for casting the prefabricated component to be formed, and installing an end mold plate according to the length of the component to be formed.

3. The method for forming a prestressed variable-strength concrete prefabricated component according to claim 1, characterized in that: The steps of laying out the prefabricated component forming mold include: arranging an integral mold with multiple sections of cavities adapted to the outer contour shape of the concrete prefabricated component to be formed along the length direction, and installing an end template according to the length of the component to be formed.

4. The method for forming a prestressed variable-strength concrete prefabricated component according to claim 2 or 3, characterized in that: The cross section of the cavity of the prefabricated component forming mold is a rectangle with equal spacing between the corresponding areas of the upper part (1) and the lower part (2) of the component, or an inverted trapezoid with decreasing width from the upper part (1) to the corresponding areas of the lower part (2), or a T-shape with the lower part (2) being smaller than the width of the corresponding area of ​​the upper part (1) and the contour transitioning at a right angle, or an inverted T-shape with the lower part (2) being larger than the width of the corresponding area of ​​the upper part (1) and the contour transitioning at a right angle, or an I-shaped shape with an upper trapezoid, a middle rectangle and a lower inverted trapezoid.

5. The method for forming a prestressed variable-strength concrete prefabricated component according to claim 2 or 3, characterized in that: The cavity of the prefabricated component forming mold is in the shape of a groove plate or a double beam plate, and its cross section corresponding to the upper part (1) of the component is in the shape of a rectangular horizontal plate, and the corresponding lower part (2) of the component is in the shape of two symmetrical isosceles inverted trapezoids or L-shaped longitudinal beams.

6. The method for forming a prestressed variable-strength concrete prefabricated component according to claim 1, characterized in that: The step of arranging the prefabricated component forming mold and laying the steel strand (3) in the cavity of the prefabricated component forming mold within the range of the lower part (2) of the component further comprises: Stirrups (4) are placed at a preset position in the cavity of the prefabricated component mold.

7. The method for forming a prestressed variable-strength concrete prefabricated component according to claim 1, characterized in that: After the step of tensioning the steel strand (3), the step further comprises the following steps: Tie up the component reinforcement and place embedded parts at preset positions in the cavity of the prefabricated component forming mold.

8. The method for forming a prestressed variable-strength concrete prefabricated component according to claim 1, characterized in that: The step of pouring low-strength concrete on top of the high-strength concrete and vibrating and compacting it to a preset boundary height of the upper part (1) of the component further includes the following steps: Concrete curing operations are carried out within a preset period of time after pouring low-strength concrete.

9. The method for forming a prestressed variable-strength concrete prefabricated component according to claim 1, characterized in that: The step of performing concrete curing operations within a preset time period after pouring low-strength concrete, and then further comprising step: When the strength of the poured high-strength concrete reaches more than 80% of the designed strength, the steel strand (3) is tensioned and then the steel strand (3) is cut.

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