Prestressed pipe pile

Abstract

The utility model relates to the technical field of engineering foundation equipment, and discloses a prestressed pipe pile which comprises a concrete layer, prestressed steel bars are arranged in the concrete layer, stirrups are fixedly connected to the outer walls of the prestressed steel bars, and pouring blocks are fixedly connected to the upper ends of the prestressed steel bars. The top face of the pouring block is fixedly connected with a connecting steel bar, the other end of the connecting steel bar is fixedly connected with a connecting block, the top of the prestressed steel bar is provided with a first thread, the outer wall of the concrete layer is fixedly connected with a plurality of external reinforcing ribs, and a cavity is formed in the concrete layer. And a plurality of internal reinforcing ribs are fixedly connected to the inner wall of the concrete layer. According to the utility model, the prestressed reinforcement retracts to apply a pre-compressive stress to the concrete layer, so that the crack resistance and the bearing capacity of the pipe pile are improved, and the bearing capacity is further enhanced by the external reinforcing ribs on the outer side of the concrete layer and the internal reinforcing ribs on the inner side of the concrete layer.

Description

Technical Field

[0001] The utility model relates to the technical field of engineering foundation equipment, in particular to a prestressed pipe pile. Background Art

[0002] With the acceleration of urbanization and the continuous emergence of high-rise buildings and large-scale infrastructure, the requirements for foundation engineering are becoming increasingly higher. Prestressed pipe piles, with their excellent bearing performance and construction efficiency, provide a reliable foundation solution for the construction industry, making the construction of high-rise buildings safer and more stable, while also shortening the construction period and reducing construction costs.

[0003] Prestressed pipe piles are hollow cylindrical concrete precast piles made using the pre-tensioning prestressing process and centrifugal forming method. In construction projects, they are mainly used to bear the load of the building and transfer it to the deep and stable foundation soil layer. By pre-applying a certain amount of axial pressure during the concrete pile production process, the pile body's crack resistance and bearing capacity can be effectively improved.

[0004] A search revealed Chinese patent publication number CN03255678.0, which discloses a prestressed tubular pile with a reinforced concrete shaft. The pile features a prefabricated head at the end, along with a protruding concrete rib measuring 5-25 cm wide and 5-20 cm high, located every 2-7 meters. Compared to existing technologies, this invention offers significant advantages: it significantly increases the bearing capacity of individual piles, reduces the number of piles, and lowers construction costs under similar geological conditions. However, these existing tubular piles have a relatively weak bearing capacity and are difficult to sink. Utility Model Content

[0005] In order to make up for the above deficiencies, the present invention provides a prestressed pipe pile, which aims to improve the problems of the prior art pipe piles, such as weak bearing capacity and difficulty in sinking piles.

[0006] In order to achieve the above-mentioned purpose, the present invention adopts the following technical scheme: a prestressed pipe pile, comprising a concrete layer, wherein prestressed steel bars are arranged inside the concrete layer, the outer wall of the prestressed steel bars is fixedly connected with stirrups, the upper end of the prestressed steel bars is fixedly connected with a casting block, the top surface of the casting block is fixedly connected with a connecting steel bar, the other end of the connecting steel bar is fixedly connected with a connecting block, the top of the prestressed steel bar is provided with a thread, the outer wall of the concrete layer is fixedly connected with a plurality of external reinforcing ribs, a cavity is arranged inside the concrete layer, the inner wall of the concrete layer is fixedly connected with a plurality of internal reinforcing ribs, the inner wall of the concrete layer is clamped with a lower end key, the top of the lower end key is fixedly connected with a bearing plate, the top of the bearing plate is fixedly connected with an upper end key, and the lower end of the concrete layer is provided with a pile driving auxiliary structure, and the pile driving auxiliary structure is used for pile driving.

[0007] Through the above technical solution: the concrete layer constitutes its main structure, and prestressed steel bars that play a key reinforcing role are arranged inside the concrete layer. The prestressed steel bars are distributed along the axial direction of the pipe pile, and its outer wall is tightly fixedly connected with stirrups. The stirrups surround the prestressed steel bars at a certain interval to provide lateral constraints for the steel bars, thereby enhancing the stability and deformation resistance of the overall structure. A casting block is fixedly connected to the upper end of the prestressed steel bars, and the casting block plays a role of connection and transition. The top surface is fixedly connected to the connecting steel bar, and the other end of the connecting steel bar is fixedly connected to the connecting block, making the pipe pile more stable and reliable when connected to the upper building structure. , can effectively transfer the load, the external reinforcement ribs are evenly distributed along the outer wall of the concrete layer, the external reinforcement ribs can significantly improve the bending and shear resistance of the pipe pile, making it more stable when bearing external loads, when the pipe pile is subjected to lateral force or bending force, the external reinforcement ribs can effectively share the load, reduce the stress concentration of the concrete layer, and prevent the pipe pile from excessive deformation or damage. The internal reinforcement ribs cooperate with the external reinforcement ribs to further enhance the overall structural strength of the pipe pile. The internal reinforcement ribs can improve the compressive resistance of the concrete layer when the pipe pile is axially loaded, and prevent cracks or damage inside the pipe pile when it is subjected to large loads.

[0008] As a further description of the above technical solution:

[0009] The pile driving auxiliary structure includes a second thread, which is opened at the lower end of the prestressed steel bar. The lower end of the prestressed steel bar is provided with a pile tip. The outer wall of the pile tip is provided with a plurality of guide grooves. The outer wall of the pile tip is provided with a countersunk hole. The lower end of the prestressed steel bar is slidably connected to the inner wall of the countersunk hole. The outer wall of the second thread is slidably connected to a gasket, and the outer wall of the second thread is threadedly connected to a nut.

[0010] Through the above technical solution: the second thread is opened at the lower end of the prestressed steel bar, which provides a reliable way for subsequent connection. The pile tip is the core component of the pile driving auxiliary structure, which is in direct contact with the stratum and undertakes the important functions of breaking the soil, guiding and transferring the load. The lower end of the prestressed steel bar is connected to the inner wall of the countersunk hole, and the prestressed steel bar can be inserted into the countersunk hole relatively smoothly. The gasket plays a role in buffering and dispersing pressure during the tightening process of the nut, and can also increase the sealing of the threaded connection and reduce the entry of impurities into the threaded connection, thereby ensuring the reliability and durability of the connection. The guide groove can guide the pile tip to cut into the soil layer smoothly and reduce the resistance between the pile tip and the soil layer. When the pile tip encounters a hard stratum or obstacle, the guide groove can make the soil flow upward along the guide groove, thereby further reducing the pile driving resistance and improving the pile driving efficiency.

[0011] As a further description of the above technical solution:

[0012] The concrete layer is made of high-strength concrete, and a water-reducing agent and an expansion agent are added into the concrete layer.

[0013] Through the above technical solution: the material of the concrete layer is high-strength concrete, which has high compressive strength and durability, can withstand large loads and maintain stable performance during long-term use. The role of adding water reducer in the concrete layer is to reduce the amount of water used in mixing concrete without affecting the strength of concrete, thereby improving the fluidity and density of concrete and ensuring the uniformity of concrete. The expansion agent is used to compensate for the shrinkage of concrete during the hardening process and prevent cracks in the concrete.

[0014] As a further description of the above technical solution:

[0015] The outer wall of the prestressed steel bar is provided with a protective layer, and the connecting block is made of high-strength alloy.

[0016] Through the above technical solution: the main function of the outer wall protective layer of the prestressed steel bar is to protect the prestressed steel bar from erosion by the external environment, which can prevent the steel bar from rusting and corrosion, thereby ensuring the long-term stability of the mechanical properties of the prestressed steel bar. The connecting block is made of high-strength alloy, which can withstand large loads and stresses, ensuring that the connection between the pipe pile and the superstructure is firm and reliable.

[0017] As a further description of the above technical solution:

[0018] An alignment hole is opened on the outer wall of the carrying plate, and the side wall of the carrying plate is an inclined surface.

[0019] Through the above technical solution: the alignment holes are used for accurate positioning and connection, and the side walls of the bearing plate are inclined, which can increase the contact area between the bearing plate and the surrounding concrete, thereby improving the bearing capacity and force transmission effect.

[0020] As a further description of the above technical solution:

[0021] A sensor is arranged inside the concrete layer, and the cavity is filled with crushed stones.

[0022] Through the above technical solution: the sensor can monitor the strain of the concrete layer in real time during the stress process, so as to understand the stress state and deformation degree of the pipe pile, and provide early warning for project safety. Filling with gravel can increase the deadweight of the pipe pile and improve its vertical bearing capacity. The filling of gravel can also increase the damping characteristics of the pipe pile. When it is affected by an earthquake, it can absorb and consume part of the energy, reduce the vibration response of the pipe pile, and improve the seismic performance of the pipe pile.

[0023] As a further description of the above technical solution:

[0024] The outer wall of the concrete layer is provided with an anti-corrosion coating, and the outer wall of the concrete layer is provided with scales.

[0025] This technical solution effectively isolates the concrete layer from corrosive media in the external environment, preventing corrosion of the concrete and prestressed steel. The scale allows construction workers to accurately measure the depth of the piles. During the pile sinking process, by observing the changes in the scale, they can monitor the sinking progress of the piles in real time, ensuring that the piles reach the designed depth.

[0026] As a further description of the above technical solution:

[0027] An upper end key is fixedly connected to the top of the bearing plate, and a tension sleeve is fixedly connected to the outer wall of the upper end key.

[0028] Through the above technical solution: the upper end key plays an important role in connecting and transferring loads, and the tensioning sleeve provides a certain elastic deformation capacity during the connection process, making the connection tighter and more stable. When the pipe pile is subjected to load, the tensioning sleeve can absorb and buffer part of the stress through its own elastic deformation, reduce stress concentration at the connection part, and prevent the connection from loosening or damage.

[0029] The utility model has the following beneficial effects:

[0030] 1. In the present invention, prestressed steel bars are arranged in a ring shape and are bundled and fixed with stirrups to form a steel skeleton of the pile body. When the concrete reaches a certain strength, the prestressed steel bars are tensioned by tensioning equipment to cause the prestressed steel bars to produce elastic deformation, thereby establishing pre-compressive stress in the concrete. The prestressed steel bars will tend to shrink, but because the concrete has been bonded to the prestressed steel bars, the shrinkage of the prestressed steel bars will apply a pre-compressive stress to the concrete layer. The compressive performance of the concrete layer is much better than its tensile performance. By applying prestressing, the compressive capacity of the concrete layer can be fully utilized, and the crack resistance and bearing capacity of the pipe pile can be improved. The external reinforcing ribs on the outside of the concrete layer and the internal reinforcing ribs on the inside of the concrete layer further enhance the bearing capacity.

[0031] 2. In the present invention, when the pipe pile begins to sink into the ground, the head of the pile tip first contacts the soil layer. Since the head area of ​​the pile tip is relatively small, it can concentrate the force and cause local shear failure of the soil. The cooperation of the gasket, nut and thread 2 firmly fixes the pile tip to the lower part of the pile body. Thread 2 provides precise sinking direction guidance, making the friction force between the pipe pile and the soil layer more reasonably distributed. Part of the soil can move upward along the guide groove instead of generating large lateral resistance to the pipe pile. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a front perspective view of a prestressed pipe pile proposed in the present invention;

[0033] Figure 2 This is a partial structural diagram of a prestressed steel bar of a prestressed pipe pile proposed in the present utility model;

[0034] Figure 3 This is a partial structural diagram of a prestressed pipe pile bearing plate proposed in the present utility model;

[0035] Figure 4 This is a diagram showing the local structure of a prestressed pipe pile tip proposed in the present invention;

[0036] Figure 5 This is a cross-sectional view of a prestressed pipe pile concrete layer proposed by the utility model.

[0037] Legend:

[0038] 1. Concrete layer; 2. Pile driving auxiliary structure; 201. Countersunk hole; 202. Pile tip; 203. Gasket; 204. Nut; 205. Guide groove; 206. Thread 2; 3. External reinforcement rib; 4. Prestressed steel bar; 5. Stirrups; 6. Casting block; 7. Connecting steel bar; 8. Connecting block; 9. Thread 1; 10. Lower key; 11. Load-bearing plate; 12. Alignment hole; 13. Upper key; 14. Internal reinforcement rib; 15. Sensor; 16. Cavity; 17. Tension sleeve. DETAILED DESCRIPTION

[0039] The following will be combined with the accompanying drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0040] Please see the attached Figure 1 - Attachment Figure 3 The utility model provides an embodiment: a prestressed pipe pile, comprising a concrete layer 1, wherein the interior of the concrete layer 1 is provided with prestressed steel bars 4, the outer wall of the prestressed steel bars 4 is fixedly connected with stirrups 5, the upper end of the prestressed steel bars 4 is fixedly connected with a casting block 6, the top surface of the casting block 6 is fixedly connected with a connecting steel bar 7, the other end of the connecting steel bar 7 is fixedly connected with a connecting block 8, a thread 9 is provided on the top of the prestressed steel bar 4, a plurality of external reinforcing ribs 3 are fixedly connected to the outer wall of the concrete layer 1, a cavity 16 is provided inside the concrete layer 1, a plurality of internal reinforcing ribs 14 are fixedly connected to the inner wall of the concrete layer 1, a lower end key 10 is engaged with the inner wall of the concrete layer 1, the top of the lower end key 10 is fixedly connected with a bearing plate 11, the top of the bearing plate 11 is fixedly connected with an upper end key 13, and a pile driving auxiliary structure 2 is provided at the lower end of the concrete layer 1, which is used for pile driving;

[0041] Specifically, the concrete layer 1 constitutes its main structure, and prestressed steel bars 4 playing a key reinforcing role are arranged inside the concrete layer 1. The prestressed steel bars 4 are distributed along the axial direction of the pipe pile, and the outer wall thereof is tightly fixedly connected with stirrups 5. The stirrups 5 surround the prestressed steel bars 4 at a certain interval to provide lateral constraints for the steel bars, thereby enhancing the stability and deformation resistance of the overall structure. A casting block 6 is fixedly connected to the upper end of the prestressed steel bars 4, and the casting block 6 plays the role of connection and transition. A connecting steel bar 7 is fixedly connected to the top surface, and the other end of the connecting steel bar 7 is fixedly connected to a connecting block 8, so that the pipe pile is more stable and reliable when connected to the upper building structure, and can The external reinforcement ribs 3 are evenly distributed along the outer wall of the concrete layer 1, and the external reinforcement ribs 3 can significantly improve the bending and shearing resistance of the pipe pile, making it more stable when bearing external loads. When the pipe pile is subjected to lateral force or bending force, the external reinforcement ribs 3 can effectively share the load, reduce the stress concentration of the concrete layer 1, and prevent the pipe pile from being excessively deformed or damaged. The internal reinforcement ribs 14 cooperate with the external reinforcement ribs 3 to further enhance the overall structural strength of the pipe pile. The internal reinforcement ribs 14 can improve the compressive resistance of the concrete layer 1 when the pipe pile is axially loaded, and prevent cracks or damage from occurring inside the pipe pile when it is subjected to a large load.

[0042] Please see the attached Figure 4 - Attachment Figure 5 The pile driving auxiliary structure 2 includes a second thread 206, which is provided at the lower end of the prestressed steel bar 4. The lower end of the prestressed steel bar 4 is provided with a pile tip 202. The outer wall of the pile tip 202 is provided with a plurality of guide grooves 205. The outer wall of the pile tip 202 is provided with a countersunk hole 201. The lower end of the prestressed steel bar 4 is slidably connected to the inner wall of the countersunk hole 201. The outer wall of the second thread 206 is slidably connected to a gasket 203. The outer wall of the second thread 206 is threadedly connected to a nut 204.

[0043] Specifically, the second thread 206 is opened at the lower end of the prestressed steel bar 4, providing a reliable way for subsequent connection. The pile tip 202 is the core component of the pile driving auxiliary structure 2, which is in direct contact with the stratum and undertakes the important functions of breaking the ground, guiding and transferring the load. The lower end of the prestressed steel bar 4 is connected to the inner wall of the countersunk hole 201, and the prestressed steel bar 4 can be inserted into the countersunk hole 201 relatively smoothly. The gasket 203 plays a role in buffering and dispersing pressure during the tightening process of the nut 204. It can also increase the sealing of the threaded connection and reduce the entry of impurities into the threaded connection, thereby ensuring the reliability and durability of the connection. The guide groove 205 can guide the pile tip 202 to smoothly cut into the soil layer, reducing the resistance between the pile tip 202 and the soil layer. When the pile tip 202 encounters a hard stratum or obstacle, the guide groove 205 can make the soil flow upward along the guide groove 205, thereby further reducing the pile driving resistance and improving the pile driving efficiency.

[0044] Please see the attached Figure 1 - Attachment Figure 3 The concrete layer 1 is made of high-strength concrete, a water-reducing agent and an expansion agent are added to the concrete layer 1, a protective layer is provided on the outer wall of the prestressed steel bar 4, the connecting block 8 is made of high-strength alloy, an alignment hole 12 is provided on the outer wall of the bearing plate 11, and the side wall of the bearing plate 11 is an inclined surface;

[0045] Specifically, the material of the concrete layer 1 is high-strength concrete, which has high compressive strength and durability, can withstand large loads and maintain stable performance during long-term use. The role of adding water reducer in the concrete layer 1 is to reduce the amount of water used in mixing concrete without affecting the strength of concrete, thereby improving the fluidity and density of concrete and ensuring the uniformity of concrete. The expansion agent is to compensate for the shrinkage of concrete during the hardening process and prevent cracks in the concrete. The main function of the outer wall protective layer of the prestressed steel bar 4 is to protect the prestressed steel bar 4 from erosion by the external environment, which can prevent the steel bar from rusting and corrosion, thereby ensuring the long-term stability of the mechanical properties of the prestressed steel bar 4. The connecting block 8 is made of high-strength alloy, which can withstand large loads and stresses, ensuring that the connection between the pipe pile and the superstructure is firm and reliable. The alignment hole 12 is used for accurate positioning and connection. The side wall of the bearing plate 11 is an inclined surface, which can increase the contact area between the bearing plate 11 and the surrounding concrete, thereby improving the bearing capacity and force transmission effect.

[0046] Please see the attached Figure 3 - Attachment Figure 5 A sensor 15 is provided inside the concrete layer 1, the cavity 16 is filled with gravel, the outer wall of the concrete layer 1 is provided with an anti-corrosion coating, the outer wall of the concrete layer 1 is provided with a scale, the top of the bearing plate 11 is fixedly connected to the upper end key 13, and the outer wall of the upper end key 13 is fixedly connected to the tension sleeve 17;

[0047] Specifically, the sensor 15 can monitor the strain of the concrete layer 1 during the stress process in real time, so as to understand the stress state and deformation degree of the pipe pile and provide early warning for project safety. Filling with gravel can increase the deadweight of the pipe pile and improve its vertical bearing capacity. The filling of gravel can also increase the damping characteristics of the pipe pile. When it is subjected to an earthquake, it can absorb and consume part of the energy, reduce the vibration response of the pipe pile, and improve the seismic performance of the pipe pile. The outer wall of the concrete layer 1 is provided with an anti-corrosion coating, which can effectively isolate the concrete layer 1 from the corrosive medium in the external environment and prevent erosion of the concrete and prestressed steel bars 4. The scale can facilitate construction personnel to accurately measure the depth of the pipe pile into the ground. During the pile sinking process, by observing the changes in the scale, the sinking status of the pipe pile can be grasped in real time to ensure that the pipe pile reaches the design depth. The upper key 13 plays an important role in connecting and transferring loads. The tensioning sleeve 17 provides a certain elastic deformation ability during the connection process, making the connection tighter and more stable. When the pipe pile is subjected to load, the tensioning sleeve 17 can absorb and buffer part of the stress through its own elastic deformation, reduce stress concentration at the connection part, and prevent the connection from loosening or damage.

[0048] Working principle: The prestressed steel bars 4 are arranged in a ring shape and tied and fixed with stirrups 5 to form a steel skeleton of the pile body. When the concrete reaches a certain strength, the prestressed steel bars 4 are tensioned by tensioning equipment to make the prestressed steel bars 4 produce elastic deformation, thereby establishing pre-compressive stress in the concrete. The prestressed steel bars 4 will tend to shrink, but because the concrete has been bonded to the prestressed steel bars 4, the shrinkage of the prestressed steel bars 4 will apply a pre-compressive stress to the concrete layer 1. The compressive performance of the concrete layer 1 is much better than its tensile performance. The application of prestress can fully utilize the compressive capacity of the concrete layer 1, improve the crack resistance and bearing capacity of the pipe pile, and the external reinforcing ribs 3 on the outside of the concrete layer 1 and the internal reinforcing ribs 14 on the inside of the concrete layer 1 further enhance the bearing capacity.

[0049] When the pipe pile begins to sink into the ground, the head of the pile tip 202 first contacts the soil layer. Since the head area of ​​the pile tip 202 is relatively small, it can concentrate the force and cause local shear failure of the soil. The cooperation of the gasket 203, the nut 204 and the second thread 206 firmly fixes the pile tip 202 to the lower part of the pile body. The second thread 206 provides precise sinking direction guidance, making the friction force between the pipe pile and the soil layer more reasonably distributed. Part of the soil can move upward along the guide groove 205 instead of generating large lateral resistance to the pipe pile.

[0050] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or make equivalent replacements for some of the technical features therein. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A prestressed pipe pile, comprising a concrete layer (1), characterized in that: Prestressed steel bars (4) are provided inside the concrete layer (1), and stirrups (5) are fixedly connected to the outer wall of the prestressed steel bars (4). The upper end of the prestressed steel bars (4) is fixedly connected to a casting block (6), and the top surface of the casting block (6) is fixedly connected to a connecting steel bar (7). The other end of the connecting steel bar (7) is fixedly connected to a connecting block (8). The top of the prestressed steel bar (4) is provided with a thread (9). The outer wall of the concrete layer (1) is fixedly connected to a plurality of external reinforcing ribs (3). A cavity (16) is provided inside the concrete layer (1). The inner wall of the concrete layer (1) is fixedly connected to a plurality of internal reinforcing ribs (14). The inner wall of the concrete layer (1) is engaged with a lower end key (10), and the top of the lower end key (10) is fixedly connected to a bearing plate (11). The top of the bearing plate (11) is fixedly connected to an upper end key (13). The lower end of the concrete layer (1) is provided with a pile sinking auxiliary structure (2), and the pile sinking auxiliary structure (2) is used for pile sinking.

2. The prestressed pipe pile according to claim 1, characterized in that: The pile driving auxiliary structure (2) includes a second thread (206), the second thread (206) is provided at the lower end of the prestressed steel bar (4), the lower end of the prestressed steel bar (4) is provided with a pile tip (202), the outer wall of the pile tip (202) is provided with a plurality of guide grooves (205), the outer wall of the pile tip (202) is provided with a countersunk hole (201), the lower end of the prestressed steel bar (4) is slidably connected to the inner wall of the countersunk hole (201), the outer wall of the second thread (206) is slidably connected to a gasket (203), and the outer wall of the second thread (206) is threadedly connected to a nut (204).

3. The prestressed pipe pile according to claim 1, characterized in that: The material of the concrete layer (1) is high-strength concrete, and a water reducing agent and an expansion agent are added to the concrete layer (1).

4. The prestressed pipe pile according to claim 1, characterized in that: The outer wall of the prestressed steel bar (4) is provided with a protective layer, and the connecting block (8) is made of a high-strength alloy.

5. The prestressed pipe pile according to claim 1, characterized in that: An alignment hole (12) is provided on the outer wall of the carrier plate (11), and the side wall of the carrier plate (11) is an inclined surface.

6. The prestressed pipe pile according to claim 1, characterized in that: A sensor (15) is provided inside the concrete layer (1), and the cavity (16) is filled with crushed stones.

7. The prestressed pipe pile according to claim 1, characterized in that: The outer wall of the concrete layer (1) is provided with an anti-corrosion coating, and the outer wall of the concrete layer (1) is provided with scales.

8. The prestressed pipe pile according to claim 1, characterized in that: An upper key (13) is fixedly connected to the top of the carrier plate (11), and a tension sleeve (17) is fixedly connected to the outer wall of the upper key (13).

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