Permafrost region high bearing platform pile foundation pier bearing performance improving device based on non-structure replaceable concept

Abstract

The invention discloses a permafrost region high bearing platform pile foundation pier bearing performance improving device based on a non-structure replaceable concept. The permafrost region high bearing platform pile foundation pier bearing performance improving device specifically comprises a vertical supporting device, a horizontal supporting device and a connecting device. By arranging the semicircular steel sleeve, the overall rigidity of the plastic hinge area of the high bearing platform pile foundation in the permafrost region is enhanced, the connection between the pile foundation and the bearing platform is enhanced, and the overall stress principle is adopted; and the capability of resisting horizontal and bending moment of the pile foundation pier is greatly enhanced, so that the damage degree of the high bearing platform pile foundation pier under the action of static and dynamic loads is reduced, and the safety of a main body structure is ensured. All components of the device are replaceable components, when the components are damaged under the action, rapid replacement of the components can be achieved, the repairability of the pile foundation pier is improved, and the toughness of the high bearing platform pile foundation pier in the permafrost region is enhanced.

Description

Technical Field

[0001] This invention relates to the field of bridge engineering technology, and more specifically to a device for improving the bearing capacity of high-bearing-cap pile foundation bridge piers in permafrost regions based on the concept of non-structural replaceability. Background Technology

[0002] The construction and operation of infrastructure in permafrost regions present a significant global engineering challenge. With the deepening socio-economic development in cold regions, numerous transportation routes traversing permafrost areas are under construction or about to be built. Bridges, as key engineering components, rely heavily on the long-term stability and safety of their pile foundations, which directly determine the service performance and lifespan of the entire route. However, against the backdrop of global warming, permafrost is undergoing widespread warming and degradation, leading to weakened mechanical properties and reduced bearing capacity. This seriously threatens the service stability of pile foundations, posing a severe challenge to traditional design methods. How to improve and maintain the long-term bearing capacity of pile foundations under the background of global warming has become a pressing scientific problem and a major technological requirement.

[0003] Currently, reinforcement measures for pile foundations in permafrost regions mostly focus on improving the pile-soil interface properties or optimizing the pile structure itself. While these methods are effective, they are often costly, complex to construct, and difficult to dynamically adapt to the irreversible process of global warming. Therefore, this study innovatively incorporates the "non-structural replaceable concept." The core of this concept lies in introducing one or a series of designable, controllable, and sacrificial non-structural components to actively bear the loads borne by the bridge piers of the pile foundation, thereby effectively "unloading" and protecting the pile foundation as a permanent structure. When these "replaceable" components reach their service limits, their function is complete, while the load-bearing capacity of the pile foundation itself is preserved and improved. Therefore, this study, based on the "non-structural replaceable concept," aims to provide an economical, efficient, and future climate-adaptable proactive protection approach for bridge engineering in permafrost regions, which has significant theoretical and practical implications for ensuring the long-term safe operation of major projects in cold regions. Summary of the Invention

[0004] To address the issue of decreased load-bearing capacity of high-pile-foundation bridge piers in permafrost regions due to widespread warming and degradation caused by global warming, this invention aims to provide a device for improving the load-bearing capacity of high-pile-foundation bridge piers in permafrost regions based on a non-structural replaceable concept. This device first enhances the stiffness of the pile foundation within the seasonally active layer of permafrost regions, and secondly strengthens the connection between the pile foundation and the pile cap. Employing the design principles of "integral" stress distribution and "strong column, weak beam," it transfers the load-bearing components of the high-pile-foundation bridge pier from the main structure to non-structural components, reducing the degree of damage to the main structure. This improves the load-bearing capacity of high-pile-foundation bridge piers in permafrost regions under static and dynamic loads. Specifically, the technical solutions include the following: A device for improving the bearing capacity of high-pile foundation bridge piers in permafrost regions based on the concept of non-structural replaceability includes: a vertical support device, a horizontal support device, and a connecting device. The vertical support device consists of two semi-circular steel sleeves, steel sleeve stiffening ribs, and steel sleeve connecting bolts. The surface of the semi-circular steel sleeves is provided with steel sleeve stiffening ribs to enhance the overall rigidity of the vertical support device. The two semi-circular steel sleeves are connected by steel sleeve connecting bolts. The horizontal support device consists of a web member and a lower chord. The two ends of the lower chord are welded to the surface of a semi-circular steel sleeve. The arrangement height should be determined according to the distance of the pile foundation above the ground in the actual project. The web member is connected to the lower chord at one end by welding and to the circular rigid pad in the connecting device at the other end. The whole structure is arranged in a triangular shape. The connecting device consists of a circular rigid pad and high-strength expansion bolts. The circular rigid pad is provided with bolt holes. One side is connected to the bearing platform by high-strength expansion bolts, and the other side is connected to the web member by welding.

[0005] Preferably, the size of the semi-circular steel sleeve is determined according to the diameter of the pile foundation in the actual project, and it is required to be able to fit tightly against the surface of the pile foundation.

[0006] Preferably, the bearing capacity of the web members and the lower chord must be less than the bearing capacity of the pile foundation in actual engineering, to ensure that as non-load-bearing components, they are damaged first under static and dynamic loads.

[0007] Preferably, both the web members and the lower chord members can be made of angle steel.

[0008] Preferably, the steel sleeve connecting bolts and high-strength expansion bolts are coated with epoxy resin to reduce moisture erosion.

[0009] A method for using a bearing capacity enhancement device for high pile foundation bridge piers in permafrost regions based on the concept of non-structural replaceability, as described in any one of claims 1 to 5, includes the following steps: Step 1: First, determine the diameter and height of the semi-circular steel sleeve based on the actual engineering requirements and geological conditions. The diameter of the semi-circular steel sleeve should be consistent with the diameter of the pile foundation in the actual project, and the height of the semi-circular steel sleeve should be consistent with the sum of the depth of the seasonal active layer in the permafrost region and the distance between the pile cap and the soil surface. Step 2: The two semi-circular steel sleeves are connected as a whole by the steel sleeve connecting bolts on the steel sleeve stiffening ribs to constrain the pile foundation within the seasonal activity layer. It is required that the height of the steel sleeve stiffening ribs be consistent with the height of the semi-circular steel sleeves. Step 3: After the vertical support device is completed, epoxy resin should be applied to the surface of the steel sleeve connecting bolts to reduce the erosion of the steel sleeve connecting bolts by soil and moisture in the air. Step 4: Arrange the lower chord and web members. The two ends of the lower chord are welded to the surface of the semi-circular steel sleeve. The arrangement height should be determined according to the distance of the pile foundation above the ground in the actual project. The web members are connected to the lower chord at one end by welding and to the circular rigid pad in the connecting device at the other end. Note: The bearing capacity of the lower chord and web members must be less than the bearing capacity of the pile foundation in the actual project to ensure that as non-load-bearing components, they will be damaged first under static and dynamic loads. The arrangement of the web members and the lower chord are arranged in a triangular shape as a whole. Step 5: Set bolt holes on the circular rigid pad. Connect the circular rigid pad to the bearing platform on one side with high-strength expansion bolts, and connect the circular rigid pad to the web member on the other side by welding. After the connection device is completed, epoxy resin should also be applied to the surface of the high-strength expansion bolts.

[0010] Compared with existing technologies, the bearing capacity improvement device for high-pile foundation bridge piers in permafrost regions disclosed in this invention, based on the concept of non-structural replaceability, has the following beneficial effects: 1. This invention strengthens the overall stiffness of the plastic hinge region of high-pile foundations in permafrost areas by setting a semi-circular steel sleeve, enhances the connection between the pile foundation and the pile cap by using a horizontal support device, adopts the principle of "integral" force bearing, fully utilizes the efficiency of the pile group, and greatly enhances the ability of the pile foundation piers to resist horizontal and bending moments, thereby reducing the degree of damage to the high-pile foundation piers under static and dynamic loads and ensuring the safety of the main structure.

[0011] 2. All components of the device proposed in this invention are replaceable. When a component reaches its service life or is damaged, it can be quickly disassembled and replaced, improving the repairability of pile foundation piers and enhancing the toughness of high-bearing pile foundation piers in permafrost areas.

[0012] 3. The steel sleeve and web member system set within the seasonally active layer of this invention constitutes an efficient rigid force transmission path, enabling seismic energy to be transmitted more directly and clearly upward to the top of the pier. This successfully avoids structural instability and uncontrollable displacement caused by excessive plastic deformation of the soil in the seasonally active layer, making the force transmission path clearer and more reliable, effectively controlling the overall deformation of the structure, and ultimately ensuring the stability and safety of the bridge under seismic action.

[0013] 4. The device proposed in this invention is arranged in the seasonally active layer and above in permafrost areas, effectively avoiding thermal disturbance to the permafrost environment caused by construction.

[0014] 5. This invention has a simple structure, clear force distribution, convenient construction, and strong adaptability. Attached Figure Description

[0015] Figure 1 This is an overall schematic diagram of the device for improving the bearing capacity of high-bearing-cap pile foundation piers in permafrost regions based on the concept of non-structural replaceability disclosed in this invention.

[0016] Figure 2 This is a front view of the device for improving the bearing capacity of high-pile foundation bridge piers in permafrost regions based on the concept of non-structural replaceability, as disclosed in this invention.

[0017] Figure 3 This is a top view of the device for improving the bearing capacity of high-pile foundation bridge piers in permafrost regions based on the concept of non-structural replaceability, as disclosed in this invention.

[0018] Figure 4 This is a detailed structural diagram of the connection between the web member and the pile cap of the high-pile foundation pier in permafrost regions, which is based on the concept of non-structural replaceability and disclosed in this invention. Figure 5 The time history curves of the horizontal relative displacement of the high-pile foundation bridge piers under seismic loads, with and without the present invention; Figure 6 The PS curve of the high-pile foundation pier under vertical load is shown with and without this invention.

[0019] Figure 7 This is a cloud map of plastic damage to high-pile foundation piers under seismic loads, with and without the present invention.

[0020] Figure 8 This is a cloud map of plastic damage to a high-pile foundation pier under vertical load, with and without the present invention.

[0021] Semi-circular steel sleeve-1, steel sleeve stiffening rib-2, steel sleeve connecting bolt-3, circular steel washer-4, high-strength expansion bolt-5, web member-6, lower chord member-7. Detailed Implementation

[0022] The technical solutions of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described technical solutions are only a part of the present invention, and not all of the technical solutions and measures. All other technical solutions obtained by those skilled in the art based on the implementation of the technical solutions of the present invention without creative effort are within the scope of protection of the present invention.

[0023] like Figures 1-4 As shown, the present invention provides a device for improving the bearing capacity of high pile foundation bridge piers in permafrost regions based on the concept of non-structural replaceability, specifically comprising three parts: a vertical support device, a horizontal support device, and a connecting device. Furthermore, the vertical support device consists of two semi-circular steel sleeves 1, steel sleeve stiffening ribs 2, and steel sleeve connecting bolts 3; The size of the semi-circular steel sleeve 1 is determined according to the diameter of the pile foundation in the actual project. It is required to fit tightly against the surface of the pile foundation. Steel sleeve stiffening ribs 2 are provided on the surface of the semi-circular steel sleeve 1 to enhance the overall rigidity of the vertical support device. Specifically, as shown in the figure... Figure 3 As shown, the two semi-circular steel sleeves 1 are fixedly connected by steel sleeve connecting bolts 3. After the connection is completed, epoxy resin needs to be applied to the surface of the steel sleeve connecting bolts 3 to reduce the erosion of the steel sleeve connecting bolts 3 by soil and moisture in the air.

[0024] Furthermore, such as Figure 1 , Figure 2 As shown, the horizontal support device consists of a web member 6 and a lower chord member 7. This design ensures the "strong column, weak beam" principle, meaning the bearing capacity of the web member 6 and lower chord member 7 must be less than the bearing capacity of the pile foundation in the actual project, ensuring that these non-load-bearing components are damaged first under static and dynamic loads. Furthermore, both the web member 6 and lower chord member 7 can be made of angle steel, arranged in a triangular shape. The two ends of the lower chord member 7 are welded to the surface of the semi-circular steel sleeve 1. The height of the lower chord member 7 should be determined based on the distance of the pile foundation above the ground in the actual project. The web member 6 is connected to the lower chord member 7 at one end by welding, and to the circular rigid pad 4 in the connecting device at the other end.

[0025] Furthermore, such as Figure 1 , Figure 4 As shown, the connecting device consists of a circular rigid pad 4 and a high-strength expansion bolt 5. The circular rigid pad 4 is provided with bolt holes. One side is connected to the bearing platform by the high-strength expansion bolt 5, and the other side is connected to the web member 6 by welding. After the connection is completed, epoxy resin needs to be applied to the surface of the high-strength expansion bolt 5 to reduce the erosion of moisture.

[0026] In specific implementation, the method of using the device for improving the bearing capacity of high-pile foundation bridge piers in permafrost regions based on the concept of non-structural replaceability is as follows: Step 1: First, based on the actual engineering requirements and geological conditions, determine the diameter and height of the semi-circular steel sleeve 1. The diameter of the semi-circular steel sleeve 1 should be consistent with the diameter of the pile foundation in the actual project, and the height of the semi-circular steel sleeve 1 should be consistent with the sum of the depth of the seasonal active layer in the permafrost region and the distance between the pile cap and the soil surface. Step 2: The two semi-circular steel sleeves 1 are connected into a whole by the steel sleeve connecting bolts 3 on the steel sleeve stiffening ribs 2 to constrain the pile foundation within the seasonal activity layer. It is required that the height of the steel sleeve stiffening ribs 2 and the height of the semi-circular steel sleeves 1 be consistent. Step 3: After the vertical support device is constructed, epoxy resin should be applied to the surface of the steel sleeve connecting bolt 3 to reduce the erosion of the steel sleeve connecting bolt 3 by soil and moisture in the air, and to improve the durability of the device. Step 4: Arrange the lower chord 7 and the web member 6. The two ends of the lower chord 7 are welded to the surface of the semi-circular steel sleeve 1. The arrangement height should be determined according to the distance of the pile foundation above the ground in the actual project. The web member 6 is connected to the lower chord 7 at one end by welding and to the circular rigid pad 4 in the connecting device at the other end. Note: The bearing capacity of the web member 6 and the lower chord 7 must be less than the bearing capacity of the pile foundation in the actual project to ensure that as non-load-bearing components, they will be damaged first under static and dynamic loads. The arrangement of the web member 6 and the lower chord 7 is in a triangular shape as a whole. Step 5: Finally, the connection device is arranged. Bolt holes are set on the circular rigid pad 4. One side is connected to the bearing platform by high-strength expansion bolts 5, and the other side is connected to the web rod 6 by welding. After the connection device is completed, epoxy resin is also applied to the surface of the high-strength expansion bolts 5.

[0027] The following specific test examples will further illustrate the effectiveness of this device. According to the present invention, four models were established using a high-pile-foundation bridge pier of the Qinghai-Tibet Railway as a prototype, with and without the proposed measures. Two models were based on the same high-pile-foundation bridge pier as the prototype, maintaining consistency with the prototype structure in terms of concrete material properties, cross-sectional dimensions, and reinforcement ratio, and were subjected to seismic and vertical loads, respectively. The other two models maintained consistency with the prototype in terms of concrete material properties, cross-sectional dimensions, and reinforcement ratio, but the proposed device was installed at or above the seasonally active layer, and seismic and vertical loads were applied, respectively. The effects of having and not having the proposed device on the bearing capacity and damage characteristics of the high-pile-foundation bridge pier in permafrost areas under static and dynamic loads were compared and analyzed.

[0028] Figure 5 The analysis presents the time history curves of the relative horizontal displacement of high-pile foundation piers under seismic loads, with and without seismic mitigation measures. The analysis reveals a significant difference in the relative horizontal displacement of the pier top under these conditions. Firstly, the measures limit the maximum relative horizontal displacement. Without these measures, the maximum relative horizontal displacement of the pier top is 27.298 cm, while with the measures, it decreases to 22.468 cm, a reduction of 17.67%. Secondly, the trends in the relative horizontal displacement of the pier over time differ significantly. When the duration of the input seismic wave is less than 5 seconds, the relative horizontal displacement of the pier is approximately symmetrical in the vibration direction, regardless of whether measures are in place. However, when the duration of the input seismic wave is greater than 5 seconds, the relative horizontal displacement of the pier is symmetrically distributed in the vibration direction under the measures, while under the measures, the relative horizontal displacement is significantly biased to one side of the vibration direction and cannot return to its origin.

[0029] Figure 6 The PS curves of pile foundation piers under vertical loads are shown with and without protective measures. Analysis reveals that the PS curves of pile foundation piers with and without protective measures exhibit a consistent trend, both showing a gradual decline. However, there is a difference in the maximum settlement of pile foundation piers with and without protective measures. The settlement of pile foundations with protective measures is smaller than that without. Specifically, the maximum settlement of pile foundation piers without protective measures is 18.85 cm, while the maximum settlement with protective measures is 17.15 cm, a reduction of 9.01%. Secondly, the presence or absence of protective measures affects the elastic stage of pile foundation piers. The elastic stage of pile foundation piers with protective measures is larger than that without. Specifically, the elastic stage of pile foundation piers with protective measures is 0-24MN, while that without protective measures is 0-18MN, an increase of 25%.

[0030] Figure 7 The equivalent plastic strain of the concrete in the pile foundation pier under seismic load is shown with and without the proposed measures. Analysis revealed that the proposed measures significantly reduced the degree of plastic damage to the concrete in the pile foundation pier under dynamic load. The maximum equivalent plastic strain of the concrete in the pile foundation pier without the measures was 0.0226, while the maximum equivalent plastic strain with the measures was 0.0127, representing a reduction of 43.81%. Furthermore, under the measures, varying degrees of plastic damage were observed in the semi-circular steel sleeve and the steel truss connection system.

[0031] Figure 8 The image shows the equivalent plastic strain contour plots of the pile foundation pier concrete under vertical loads, with and without the proposed measures. Analysis reveals that this measure significantly reduces the plastic strain damage to the pile foundation pier concrete under vertical loads. The maximum equivalent plastic strain of the pile foundation pier concrete without the proposed measures is 4.469 × 10⁻⁶. -4 The maximum equivalent plastic strain of the concrete in the pile foundation pier under the condition of reinforced concrete is 4.770 × 10⁻⁶. -5 The reduction was 89.32%, and under the conditions of the measures, the semi-circular steel sleeve and the steel truss connection system both showed varying degrees of plastic damage.

[0032] In summary, the measures proposed in this invention significantly improve the bearing capacity of high-pile foundation bridge piers in permafrost regions under static and dynamic loads, greatly reduce plastic damage to the pile foundation concrete, and guide the damage to replaceable reinforcement components, thereby ensuring the safety of the main load-bearing components.

[0033] Compared with existing technologies, the bearing capacity improvement device for high-pile foundation bridge piers in permafrost regions disclosed in this invention, based on the concept of non-structural replaceability, has the following beneficial effects: 1. This invention strengthens the overall stiffness of the plastic hinge region of high-pile foundations in permafrost areas by setting a semi-circular steel sleeve, enhances the connection between the pile foundation and the pile cap by using a horizontal support device, adopts the principle of "integral" force bearing, fully utilizes the efficiency of the pile group, and greatly enhances the ability of the pile foundation piers to resist horizontal and bending moments, thereby reducing the degree of damage to the high-pile foundation piers under static and dynamic loads and ensuring the safety of the main structure.

[0034] 2. All components of the device proposed in this invention are replaceable. When a component reaches its service life or is damaged, it can be quickly disassembled and replaced, improving the repairability of pile foundation piers and enhancing the toughness of high-bearing pile foundation piers in permafrost areas.

[0035] 3. The steel sleeve and web member system set within the seasonally active layer of this invention constitutes an efficient rigid force transmission path, enabling seismic energy to be transmitted more directly and clearly upward to the top of the pier. This successfully avoids structural instability and uncontrollable displacement caused by excessive plastic deformation of the soil in the seasonally active layer, making the force transmission path clearer and more reliable, effectively controlling the overall deformation of the structure, and ultimately ensuring the stability and safety of the bridge under seismic action.

[0036] 4. The device proposed in this invention is arranged in the seasonally active layer and above in permafrost areas, effectively avoiding thermal disturbance to the permafrost environment caused by construction.

[0037] 5. This invention has a simple structure, clear force distribution, convenient construction, and strong adaptability.

[0038] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A device for improving the bearing capacity of high-pile-cap foundation bridge piers in permafrost regions based on the concept of non-structural replaceability, characterized in that, include: Vertical support device, horizontal support device and connecting device; The vertical support device consists of two semi-circular steel sleeves (1), steel sleeve stiffening ribs (2), and steel sleeve connecting bolts (3). The surface of the semi-circular steel sleeves (1) is provided with steel sleeve stiffening ribs (2) to enhance the overall rigidity of the vertical support device. The two semi-circular steel sleeves (1) are connected by steel sleeve connecting bolts (3). The horizontal support device consists of a web member (6) and a lower chord member (7). The two ends of the lower chord member (7) are welded to the surface of the semi-circular steel sleeve (1). The arrangement height should be determined according to the distance of the pile foundation above the ground in the actual project. The web member (6) is connected to the lower chord member (7) by welding at one end and to the circular rigid pad (4) in the connecting device at the other end. The whole structure is arranged in a triangular shape. The connecting device consists of a circular rigid pad (4) and a high-strength expansion bolt (5). The circular rigid pad (4) is provided with bolt holes. One side is connected to the bearing platform by the high-strength expansion bolt (5), and the other side is connected to the web member (6) by welding.

2. The device for improving the bearing capacity of high-pile foundation bridge piers in permafrost regions based on the concept of non-structural replaceability, as described in claim 1, is characterized in that... The size of the semi-circular steel sleeve (1) is determined according to the diameter of the pile foundation in the actual project, and it is required to be able to fit tightly against the surface of the pile foundation.

3. The device for improving the bearing capacity of high-pile foundation bridge piers in permafrost regions based on the concept of non-structural replaceability, as described in claim 1, is characterized in that... The bearing capacity of the web members (6) and the lower chord members (7) must be less than the bearing capacity of the pile foundation in the actual project, so as to ensure that the non-load-bearing components are damaged first under static and dynamic loads.

4. The device for improving the bearing capacity of high-pile foundation bridge piers in permafrost regions based on the concept of non-structural replaceability, as described in claim 1 or 3, is characterized in that... Both the web member (6) and the lower chord member (7) can be made of angle steel.

5. The device for improving the bearing capacity of high-pile foundation bridge piers in permafrost regions based on the concept of non-structural replaceability, as described in claim 1, is characterized in that... The steel sleeve connecting bolt (3) and the high-strength expansion bolt (5) are coated with epoxy resin to reduce moisture erosion.

6. A method for using a device for improving the bearing capacity of high-pile foundation bridge piers in permafrost regions based on the concept of non-structural replaceability, as described in any one of claims 1 to 5, characterized in that... Includes the following steps: Step 1: First, based on the actual engineering requirements and geological conditions, determine the diameter and height of the semi-circular steel sleeve (1). The diameter of the semi-circular steel sleeve (1) should be consistent with the diameter of the pile foundation in the actual project, and the height of the semi-circular steel sleeve (1) should be consistent with the sum of the depth of the seasonal active layer in the permafrost region and the distance between the pile cap and the soil surface. Step 2: The two semi-circular steel sleeves (1) are connected as a whole by the steel sleeve connecting bolts (3) on the steel sleeve stiffening ribs (2) to constrain the pile foundation within the seasonal activity layer. It is required that the height of the steel sleeve stiffening ribs (2) be consistent with the height of the semi-circular steel sleeves (1). Step 3: After the vertical support device is completed, epoxy resin should be applied to the surface of the steel sleeve connecting bolt (3) to reduce the erosion of the steel sleeve connecting bolt (3) by the soil and moisture in the air. Step 4: Arrange the lower chord (7) and the web members (6). The two ends of the lower chord (7) are welded to the surface of the semi-circular steel sleeve (1). The arrangement height should be determined according to the distance of the pile foundation above the ground in the actual project. The web members (6) are connected to the lower chord (7) by welding at one end and to the circular rigid pad (4) in the connecting device at the other end. Note: The bearing capacity of the web members (6) and the lower chord (7) must be less than the bearing capacity of the pile foundation in the actual project to ensure that the non-load-bearing components are damaged first under static and dynamic loads. The arrangement of the web members (6) and the lower chord (7) is in a triangular arrangement as a whole. Step 5: Set bolt holes on the circular rigid pad (4), connect the circular rigid pad (4) to the bearing platform on one side by high-strength expansion bolts (5), and connect the circular rigid pad (4) to the web rod (6) by welding on the other side. After the connection device is completed, epoxy resin should also be applied to the surface of the high-strength expansion bolts (5).

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