A tensioning un-bonded prestressed tendon angle control method for anti-pulling cast-in-place pile

Abstract

The application discloses a tensioning non-bonded prestressed steel bar angle control method of uplift bored pile, which comprises the following steps: 1, making the whole section steel reinforcement cage framework of the uplift bored pile; 2, combining the non-bonded prestressed steel bar with the whole section steel reinforcement cage framework of the uplift bored pile; 3, installing the angle controller on the non-bonded prestressed steel bar; 4, pouring the pile body concrete and the pile head over-pouring concrete of the uplift bored pile; 5, breaking the pile top over-pouring concrete; 6, controlling the angle of the tensioning non-bonded prestressed steel bar and binding the raft steel reinforcement; 7, pouring the raft concrete; and 8, tensioning the non-bonded prestressed steel bar. The angle controller with adjustable angle and isolation protection is arranged on the prestressed steel bar of the upper part of the pile top, the flexible bellows sleeve in the angle controller is used for adjusting the angle and position of the prestressed steel bar distributed in the raft with different thicknesses, and the problems that the prestressed steel bar of the upper part of the pile head is easily damaged and the angle in the raft is difficult to adjust are solved.

Description

Technical Field

[0001] This invention belongs to the technical field of angle adjustment of tensioned unbonded prestressed tendons, specifically relating to a method for controlling the angle of tensioned unbonded prestressed tendons in tensioned cast-in-place piles. Background Technology

[0002] In building foundations, tension-resistant cast-in-place piles are often used. With the development of science and technology and the increasing importance of buildings, post-tensioning construction with unbonded prestressed tendons is used to improve the crack resistance of concrete piles and the overall structure's anti-buoyancy capacity. However, when the prestressed tendons are arranged inside the steel cage to complete the concrete pouring of the pile body, there is a risk of breaking the pile head and damaging the prestressed tendons. Furthermore, when tensioning at the top of the raft slab, it is impossible to avoid the wall and distribute the prestressed tendons at a certain angle, causing construction quality problems and increasing construction costs and construction period. Summary of the Invention

[0003] The technical problem to be solved by this invention is to address the shortcomings of the prior art by providing a method for controlling the angle of unbonded prestressing tendons in tensioned cast-in-place piles. To ensure that the prestressing tendons above the pile top are not damaged by pile head breakage or subsequent construction, and to facilitate avoiding wall positions during tensioning at the top of the raft slab, an adjustable angle controller with isolation protection is installed on the prestressing tendons above the pile top. The angle and position of the prestressing tendons distributed inside raft slabs of different thicknesses are adjusted through the flexible corrugated sleeve in the angle controller. This solves the problems of easy damage to the prestressing tendons above the pile head and difficulty in adjusting the angle inside the raft slab, making it easy to promote and use.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for controlling the angle of tensioned unbonded prestressed tendons in tensioned cast-in-place piles, characterized in that the method includes the following steps:

[0005] Step 1: Construct the integral steel cage framework for the pull-out cast-in-place pile;

[0006] Step 2: Assemble the unbonded prestressing tendons with the integral steel cage of the tension-resistant cast-in-place pile: Cut multiple unbonded prestressing tendons, and thread each unbonded prestressing tendon into the inner side of the integral steel cage of the tension-resistant cast-in-place pile. Tie it to the main steel cage reinforcement of the integral steel cage reinforcement of the tension-resistant cast-in-place pile every 2m. The anchorage end of the unbonded prestressing tendon is 0.5m higher than the bottom of the integral steel cage reinforcement of the tension-resistant cast-in-place pile. The main steel cage reinforcement of the integral steel cage reinforcement of the tension-resistant cast-in-place pile exceeds the top of the pile to be poured with over-poured concrete, but does not exceed the raft foundation concrete to be poured. The tensioning end of the unbonded prestressing tendon exceeds the raft foundation concrete to be poured.

[0007] Step 3: Install angle controllers on unbonded prestressed tendons: Install an angle controller on the top of each unbonded prestressed tendon. The angle controller includes a first steel sleeve, a second steel sleeve, and a flexible corrugated sleeve for connecting the first and second steel sleeves. The first steel sleeve is 50mm long and is located inside the pile concrete to be poured, with its top flush with the top of the pile concrete. The top of the second steel sleeve does not exceed the raft concrete to be poured but is 100mm higher than the over-poured concrete at the top of the pile. The gap between the first steel sleeve and the upper part of the second steel sleeve and the unbonded prestressed tendon is filled with an anti-corrosion ring and sealed with waterproof tape to prevent concrete slurry from flowing in. The angle controller is firmly tied to the main reinforcement of the reinforcing cage to prevent movement during concrete pouring.

[0008] Step 4: Pouring of concrete for the pile body and over-poured concrete at the pile head of the tension-resistant cast-in-place pile: Use cable ties to bind together the exposed unbonded prestressed tendons above the over-poured concrete surface at the pile top, insert the entire steel cage of the tension-resistant cast-in-place pile into the hole, and pour concrete for the pile body and over-poured concrete at the pile top.

[0009] Step 5: Removal of over-poured concrete at the pile top: When the strength of the pile concrete reaches the design strength, the over-poured concrete at the pile top is removed. At this time, the angle controller protects the unbonded prestressing tendons to prevent them from being damaged.

[0010] Step 6: Control the angle of tensioning unbonded prestressing tendons and tie the raft slab reinforcement: Adjust the direction and angle of tensioning unbonded prestressing tendons according to different raft slab thicknesses and the position, structure and shape of the top wall of the raft slab. After adjusting the direction and angle of tensioning unbonded prestressing tendons, install the water-swellable rubber waterstop ring to the top of the second steel sleeve.

[0011] After binding and welding the bottom reinforcement and stirrups of the raft slab, the top reinforcement of the raft slab is bound and installed. Then, the unbonded prestressed tendons are pre-embedded at the exposed locations with the adjusted direction and angle. When installing the pre-embedded tendons, they should be placed perpendicular to the fixed unbonded prestressed tendons and tensioning openings should be provided.

[0012] Step 7: Pour the raft foundation concrete;

[0013] Step 8: Tensioning unbonded prestressed tendons: After the raft foundation concrete is poured, remove the embedded sleeve in the tensioning port. After the raft foundation concrete reaches 75% of the design strength, install the wedge anchors to tension and lock the unbonded prestressed tendons.

[0014] The above-mentioned method for controlling the angle of tensioned unbonded prestressed tendons in anti-uplift cast-in-place piles is characterized in that: both the first steel sleeve and the second steel sleeve are Q235 steel sleeves, and the length of the second steel sleeve is 1.5m.

[0015] The above-mentioned method for controlling the angle of tensioned unbonded prestressed tendons in anti-uplift cast-in-place piles is characterized in that: the flexible corrugated sleeve is an HDPE flexible corrugated sleeve, and the length of the HDPE flexible corrugated sleeve is 5cm.

[0016] The above-mentioned method for controlling the angle of unbonded prestressed tendons in tensioned cast-in-place piles is characterized in that: the top wall of the raft slab includes a straight top wall or a T-shaped top wall; the T-shaped top wall includes a straight top wall and a partition wall perpendicularly connected to the straight top wall.

[0017] The above-mentioned method for controlling the angle of unbonded prestressed tendons in tensioning cast-in-place piles is characterized in that: in step six, when the top wall of the raft slab is a straight top wall of the raft slab, an even number of unbonded prestressed tendons are set, and the direction and angle of the even number of unbonded prestressed tendons are controlled by a corresponding angle controller in a symmetrical structure along both sides of the straight top wall of the raft slab.

[0018] In step six, when the top wall of the raft slab is a T-shaped wall, multiple unbonded prestressing tendons are arranged in three parts around the perimeter of the T-shaped wall. The direction and angle of the first part of the unbonded prestressing tendons are controlled by a corresponding angle controller at one corner of the connection between the top straight wall and the top partition wall. The direction and angle of the second part of the unbonded prestressing tendons are controlled by the corresponding angle controller at another corner of the connection between the top straight wall and the top partition wall. The direction and angle of the first part of the unbonded prestressing tendons are controlled by the corresponding angle controller along the side of the top straight wall away from the top partition wall. The number of unbonded prestressing tendons in the first and second parts are equal, and the difference between the number of unbonded prestressing tendons in the first and third parts is 0 to 2. The first and second parts of the unbonded prestressing tendons are arranged symmetrically along both sides of the top partition wall.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] 1. Compared with traditional prestressed pull-out cast-in-place pile construction, this invention sets an angle controller at the top of the pile body concrete and the pile head over-poured concrete to protect the prestressing tendons from damage when the pile head is broken, which better ensures the quality of the prestressing tendons during subsequent tensioning and facilitates its widespread use.

[0021] 2. The angle controller of the present invention protects the prestressed tendons from damage and can be pre-embedded in the raft concrete in the later stage, saving the cost of manually removing the steel sleeve.

[0022] 3. The method of this invention is simple in steps. The flexible corrugated sleeve allows the prestressing tendons to be free from the constraints of concrete when adjusting the angle within the raft foundation. It protects the prestressing tendons at the separation angle after angle adjustment and provides space for movement away from the angle, thus improving the quality of unbonded prestressed pull-out cast-in-place piles. It ensures that the stress between the pile body and the raft foundation is not lost. It solves the problems of exposed prestressing tendons at the pile top being easily damaged during cast-in-place pile construction and the inability to adjust the angle of the prestressing tendons to avoid the wall at the top of the raft foundation. It is more convenient for on-site construction, saves construction time, improves overall quality, and is easy to promote and use.

[0023] In summary, this invention, to ensure that the prestressing tendons above the pile top are not damaged by pile head breakage or subsequent construction, and to facilitate avoiding wall positions during tensioning at the top of the raft slab, provides an adjustable angle controller with isolation protection on the prestressing tendons above the pile top. The angle controller uses a flexible corrugated sleeve to adjust the angle and position of the prestressing tendons distributed within raft slabs of different thicknesses. This solves the problems of easy damage to the prestressing tendons above the pile head and difficulty in adjusting their angle within the raft slab, making it easy to promote and use.

[0024] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the protection and tensioning of the top of the raft slab by the angle controller of the unbonded prestressed tendons according to the present invention.

[0026] Figure 2 This is a schematic diagram showing the distribution of the unbonded prestressed tendons in the straight section wall at the top of the raft slab according to the present invention.

[0027] Figure 3 This is a schematic diagram showing the distribution of the unbonded prestressed tendons of the present invention on the T-shaped wall at the top of the raft slab.

[0028] Figure 4 This is a cross-sectional view of the unbonded prestressed tendons outside the top wall of the raft slab after the angle of the tendons has been adjusted according to the present invention.

[0029] Figure 5 This is a diagram showing the distribution of the main reinforcement bars and unbonded prestressed tendons within the steel cage of this invention.

[0030] Figure 6 This is a schematic diagram of the angle controller of the present invention.

[0031] Figure 7 This is a flowchart of the method of the present invention.

[0032] Explanation of reference numerals in the attached figures:

[0033] 1—Unbonded prestressed tendons; 2—Pile body concrete; 3—Over-poured concrete at the pile top;

[0034] 4—Angle controller; 4-1—First steel sleeve; 4-2—Second steel sleeve;

[0035] 5—Flexible corrugated sleeve; 6—Raft foundation concrete; 7—Embedded sleeve;

[0036] 8—Water-swellable rubber sealing ring; 9—Vertical wall at the top of the raft slab;

[0037] 9-1—Top partition wall of raft foundation; 10—Main reinforcement of steel cage;

[0038] 11—Anti-corrosion ring. Detailed Implementation

[0039] like Figures 1 to 7 As shown, the present invention provides a method for controlling the angle of unbonded prestressed tendons in tensioned cast-in-place piles, comprising the following steps:

[0040] Step 1: Construct the integral steel cage framework for the pull-out cast-in-place pile;

[0041] Step 2: Assemble the unbonded prestressed tendons with the integral steel cage of the tension-resistant cast-in-place pile: Cut multiple unbonded prestressed tendons 1, and thread each unbonded prestressed tendon 1 into the inner side of the integral steel cage of the tension-resistant cast-in-place pile. Tie it to the main steel cage reinforcement 10 of the integral steel cage of the tension-resistant cast-in-place pile every 2m. The anchorage end of the unbonded prestressed tendon 1 is 0.5m higher than the bottom of the integral steel cage of the tension-resistant cast-in-place pile. The main steel cage reinforcement 10 of the integral steel cage of the tension-resistant cast-in-place pile exceeds the pile top over-poured concrete 3 to be poured, but does not exceed the raft foundation concrete 6 to be poured. The tensioning end of the unbonded prestressed tendon 1 exceeds the raft foundation concrete 6 to be poured.

[0042] Step 3: Install angle controllers on unbonded prestressed tendons: Install an angle controller 4 on the upper part of each unbonded prestressed tendon 1. The angle controller 4 includes a first steel sleeve 4-1, a second steel sleeve 4-2, and a flexible corrugated sleeve 5 for connecting the first steel sleeve 4-1 and the second steel sleeve 4-2. The length of the first steel sleeve 4-1 is 50mm. The first steel sleeve 4-1 is located inside the pile body concrete 2 to be poured, and its top is flush with the top of the pile body concrete 2 to be poured. The top of the second steel sleeve 4-2 does not exceed the raft foundation concrete 6 to be poured, but is 100mm higher than the pile top over-poured concrete 3 to be poured. The gap between the inside of the first steel sleeve 4-1 and the upper part of the second steel sleeve 4-2 and the unbonded prestressed tendon 1 is filled with anti-corrosion rings 11 and sealed with waterproof tape to prevent concrete slurry from flowing in. The angle controller 4 is firmly tied to the main reinforcement 10 of the reinforcing cage to prevent movement during concrete pouring.

[0043] Step 4: Pouring of pile body concrete and pile head over-pouring concrete for tension-resistant cast-in-place piles: Use cable ties to bind together the unbonded prestressed tendons 1 exposed on more than 3 sides of the pile top over-pouring concrete to be poured. Insert the entire steel cage skeleton of the tension-resistant cast-in-place pile into the hole and pour the pile body concrete 2 and pile top over-pouring concrete 3.

[0044] Step 5: Removal of over-poured concrete at the pile top: When the strength of the pile body concrete 2 reaches the design strength, the over-poured concrete 3 at the pile top is removed. At this time, the angle controller 4 protects the unbonded prestressed tendon 1 to prevent it from being damaged.

[0045] Step 6: Control the angle of tensioning unbonded prestressing tendons and tie the raft slab reinforcement: Adjust the direction and angle of tensioning unbonded prestressing tendons 1 according to different raft slab thicknesses and the position, structure and shape of the top wall of the raft slab. Use angle controller 4 to control the direction and angle of tensioning unbonded prestressing tendons 1. After the direction and angle of tensioning unbonded prestressing tendons 1 are adjusted, install the water-swellable rubber waterstop ring 8 to the top of the second steel sleeve 4-2.

[0046] After binding and welding the bottom reinforcement bars and stirrup bars of the raft slab, the top reinforcement bars of the raft slab are bound and installed. Then, the sleeve 7 is embedded at the exposed position of the unbonded prestressed tendon 1 with the direction and angle adjusted. When installing the embedded sleeve 7, it should be placed perpendicular to the fixed unbonded prestressed tendon 1 and a tensioning opening should be provided.

[0047] Step 7: Pour the raft foundation concrete 6;

[0048] Step 8: Tensioning unbonded prestressed tendons: After the raft concrete 6 is poured, remove the embedded sleeve 7 in the tensioning port. After the raft concrete 6 reaches 75% of the design strength, install the wedge anchor to tension and lock the unbonded prestressed tendons 1.

[0049] It should be noted that during concrete pouring, the first steel sleeve, flexible corrugated pipe, and second steel sleeve on the prestressing tendon are pre-embedded into the concrete pile. When the pile head is broken after the concrete reaches the required age, the steel sleeve plays a role in protecting the prestressing tendon from damage. After the pile head over-poured concrete 3 is broken, the distribution and angle of the prestressing tendon that needs to be embedded in the raft slab are adjusted by adjusting the flexible corrugated sleeve 5 to achieve the purpose of the reserved position at the top of the raft slab. The prestressing tendon is then fixed to the top layer of the raft slab reinforcement by the pre-embedded sleeve 7 at the top of the raft slab.

[0050] In this embodiment, both the first steel sleeve 4-1 and the second steel sleeve 4-2 are Q235 steel sleeves, and the length of the second steel sleeve 4-2 is 1.5m.

[0051] In this embodiment, the flexible corrugated sleeve 5 is an HDPE flexible corrugated sleeve, and the length of the HDPE flexible corrugated sleeve is 5cm.

[0052] In this embodiment, the top wall of the raft slab includes a straight top wall 9 or a T-shaped top wall; the T-shaped top wall includes a straight top wall 9 and a partition wall 9-1 perpendicularly connected to the straight top wall 9.

[0053] In this embodiment, in step six, when the top wall of the raft slab is a straight wall 9 at the top of the raft slab, an even number of unbonded prestressing tendons 1 are provided, and the direction and angle of the even number of unbonded prestressing tendons 1 are controlled by the corresponding angle controller 4 in a symmetrical structure along both sides of the straight wall 9 at the top of the raft slab.

[0054] In step six, when the top wall of the raft slab is a T-shaped wall, multiple unbonded prestressing tendons 1 are arranged in three parts around the perimeter of the T-shaped wall. The direction and angle of the first part of the unbonded prestressing tendons are controlled by the corresponding angle controller 4 at one corner of the connection between the top straight wall 9 and the top partition wall 9-1. The direction and angle of the second part of the unbonded prestressing tendons are controlled by the corresponding angle controller 4 at another corner of the connection between the top straight wall 9 and the top partition wall 9-1. The direction and angle of the first part of the unbonded prestressing tendons are controlled by the corresponding angle controller 4 on the side of the top straight wall 9 away from the top partition wall 9-1. The number of the first part of the unbonded prestressing tendons and the second part of the unbonded prestressing tendons are equal, and the difference between the number of the first part of the unbonded prestressing tendons and the third part of the unbonded prestressing tendons is 0 to 2. The first part of the unbonded prestressing tendons and the second part of the unbonded prestressing tendons are arranged symmetrically on both sides of the top partition wall 9-1.

[0055] When used in this invention, the flexible corrugated sleeve allows the prestressing tendons to be freed from the constraints of concrete when adjusting their angle within the raft foundation. This protects the prestressing tendons at the separation angle after angle adjustment and provides space for movement away from the angle, improving the quality of unbonded prestressed pull-out cast-in-place piles. It ensures no loss of stress between the pile body and the raft foundation, solving the problems of exposed prestressing tendons at the pile top being easily damaged and the inability to adjust the angle of the prestressing tendons to avoid the walls at the top of the raft foundation during construction. This facilitates on-site construction, saves time, and improves overall quality. The angle controller protects the prestressing tendons from damage and can be pre-embedded in the raft foundation concrete later, saving the cost of manually removing the steel sleeve. Compared to traditional prestressed pull-out cast-in-place pile construction, setting an angle controller at the top of the pile body concrete and the pile head over-poured concrete protects the prestressing tendons from damage during pile head breakage, better ensuring the quality of the prestressing tendons during subsequent tensioning.

[0056] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the present invention. Any simple modifications, alterations, or equivalent structural changes made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for controlling the angle of unbonded prestressed tendons in tensioned cast-in-place piles, characterized in that, The method includes the following steps: Step 1: Construct the integral steel cage framework for the pull-out cast-in-place pile; Step 2: Combine the unbonded prestressed tendons with the integral steel cage of the pull-out cast-in-place pile: Cut multiple unbonded prestressed tendons (1), and thread each unbonded prestressed tendon (1) into the inner side of the integral steel cage of the pull-out cast-in-place pile. Tie it to the main steel cage reinforcement (10) of the integral steel cage of the pull-out cast-in-place pile every 2m. The anchorage end of the unbonded prestressed tendon (1) is 0.5m higher than the bottom of the integral steel cage of the pull-out cast-in-place pile. The main steel cage reinforcement (10) of the integral steel cage of the pull-out cast-in-place pile exceeds the top of the pile to be poured with over-poured concrete (3), but does not exceed the raft foundation concrete (6) to be poured. The tensioning end of the unbonded prestressed tendon (1) exceeds the raft foundation concrete (6) to be poured. Step 3: Install angle controllers on unbonded prestressed tendons: Install an angle controller (4) on the upper part of each unbonded prestressed tendon (1). The angle controller (4) includes a first steel sleeve (4-1), a second steel sleeve (4-2), and a flexible corrugated sleeve (5) for connecting the first steel sleeve (4-1) and the second steel sleeve (4-2). The length of the first steel sleeve (4-1) is 50mm. The first steel sleeve (4-1) is located inside the pile body concrete (2) to be poured, and its top is flush with the pile body to be poured. The top of the concrete (2) is flush with the top of the second steel sleeve (4-2), and the top of the second steel sleeve (4-2) does not exceed the raft concrete (6) to be poured, but is 100mm higher than the pile top over-poured concrete (3) to be poured. The gap between the first steel sleeve (4-1) and the upper part of the second steel sleeve (4-2) and the unbonded prestressed tendon (1) is filled with an anti-corrosion ring (11) and sealed with waterproof tape to prevent concrete cement slurry from flowing in. The angle controller (4) is firmly tied to the main reinforcement (10) of the steel cage to prevent it from moving during the concrete pouring process. Step 4: Pouring of concrete for the pile body and over-pouring concrete at the pile head of the pull-out cast-in-place pile: The unbonded prestressed tendons (1) exposed above the surface of the over-pouring concrete (3) at the pile top to be poured are bound together with ties. The entire steel cage of the pull-out cast-in-place pile is inserted into the hole, and the concrete for the pile body (2) and the over-pouring concrete (3) at the pile top are poured. Step 5: Removal of over-poured concrete at the pile top: When the strength of the pile body concrete (2) reaches the design strength, the over-poured concrete (3) at the pile top is removed. At this time, the angle controller (4) protects the unbonded prestressed tendon (1) from damage. Step 6: Control the angle of tensioning unbonded prestressing tendons and tie the raft reinforcement: Adjust the direction and angle of tensioning unbonded prestressing tendons (1) using the angle controller (4) according to the different thicknesses of the raft slab and the position, structure and shape of the top wall of the raft slab; After the direction and angle of tensioning unbonded prestressing tendons (1) are adjusted, install the water-swellable rubber waterstop ring (8) to the top of the second steel sleeve (4-2); After binding the bottom reinforcement bars and stirrups of the raft slab and welding them, the top reinforcement bars of the raft slab are bound and installed. Then, the sleeve box (7) is embedded at the exposed part of the unbonded prestressed tendon (1) with the direction and angle adjusted. When the embedded sleeve box (7) is installed, it should be placed perpendicular to the fixed unbonded prestressed tendon (1) and a tensioning opening is set. Step 7: Pour the raft foundation concrete (6); Step 8: Tensioning unbonded prestressed tendons: After the raft concrete (6) is poured, remove the pre-embedded sleeve (7) in the tensioning port. After the raft concrete (6) reaches 75% of the design strength, install the wedge anchor to tension and lock the unbonded prestressed tendons (1).

2. The method for controlling the angle of unbonded prestressed tendons in tensioned cast-in-place piles according to claim 1, characterized in that: The first steel sleeve (4-1) and the second steel sleeve (4-2) are both Q235 steel sleeves, and the length of the second steel sleeve (4-2) is 1.5m.

3. The method for controlling the angle of unbonded prestressed tendons in tensioned cast-in-place piles according to claim 1, characterized in that: The flexible corrugated sleeve (5) is an HDPE flexible corrugated sleeve, and the length of the HDPE flexible corrugated sleeve is 5cm.

4. The method for controlling the angle of unbonded prestressed tendons in tensioned cast-in-place piles according to claim 1, characterized in that: The top wall of the raft slab includes a straight top wall (9) or a T-shaped top wall; the T-shaped top wall includes a straight top wall (9) and a partition wall (9-1) perpendicularly connected to the straight top wall (9).

5. The method for controlling the angle of unbonded prestressed tendons in tensioned cast-in-place piles according to claim 4, characterized in that: In step six, when the top wall of the raft slab is a straight wall (9) at the top of the raft slab, an even number of unbonded prestressing tendons (1) are set, and the direction and angle of the even number of unbonded prestressing tendons (1) are controlled by the corresponding angle controller (4) in a symmetrical structure along both sides of the straight wall (9) at the top of the raft slab. In step six, when the top wall of the raft slab is a T-shaped wall, multiple unbonded prestressing tendons (1) are arranged in three parts around the perimeter of the T-shaped wall. The direction and angle of the first part of the unbonded prestressing tendons are controlled by a corresponding angle controller (4) at one corner of the connection between the top straight wall (9) and the top partition wall (9-1). The direction and angle of the second part of the unbonded prestressing tendons are controlled by the corresponding angle controller (4) at another corner of the connection between the top straight wall (9) and the top partition wall (9-1). Direction and angle; using the corresponding angle controller (4) to control the direction and angle of the first part of unbonded prestressing tendons along the side of the top straight wall (9) away from the top partition wall (9-1) of the raft slab; wherein, the number of the first part of unbonded prestressing tendons and the second part of unbonded prestressing tendons are equal, the difference between the number of the first part of unbonded prestressing tendons and the number of the third part of unbonded prestressing tendons is 0 to 2, and the first part of unbonded prestressing tendons and the second part of unbonded prestressing tendons are arranged symmetrically on both sides of the top partition wall (9-1) of the raft slab.

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