A slide structure for steel box girder rotation construction across an existing line

Abstract

The application relates to the technical field of building construction, in particular to a slide structure for steel box girder rotation construction across an existing line, which comprises multiple sliding devices, the multiple sliding devices are distributed along the length direction of the steel box girder, the sliding device comprises a supporting assembly and a sliding assembly, the sliding assembly comprises multiple track beams and multiple sliding pieces, the multiple track beams are connected to form an arc-shaped track for steel box girder rotation, the multiple sliding pieces are distributed along the length direction of the track beams at intervals, the sliding piece comprises a sliding seat and four rollers, the sliding seat is slidingly connected to the top of the track beam along the length direction of the track beam, the top of the sliding seat is matched with the steel box girder, a containing groove for containing the top of the track beam is arranged at the bottom of the sliding seat, the four rollers are divided into two groups, the two groups of rollers are located on the inner and outer sides of the arc-shaped track respectively, the rollers are rotationally connected to the sliding seat, the four rollers need to be arranged in a trapezoidal shape, and the center distance of the two rollers on the outer side of the arc-shaped track is relatively large; the application has the effect of improving the smoothness of the steel box girder rotation.

Description

Technical Field

[0001] This application relates to the field of building construction technology, and in particular to a sliding track structure for rotating steel box girders that cross existing railway lines. Background Technology

[0002] With the increasing density of transportation networks and the growing number of urban overpasses and cross-line bridges, steel box girder rotation construction technology is playing an increasingly crucial role in bridge construction due to its unique advantages. Its widespread application helps improve bridge construction efficiency, reduce the impact on existing lines, and promote the improvement and development of transportation infrastructure.

[0003] In traditional steel box girder rotation construction across existing railway lines, the sliding of the steel box girder is achieved using a combination of ordinary rails and sliders. The rail structure is relatively simple and does not take into account the complex mechanical properties of the steel box girder during the rotation process. The slider also lacks effective friction reduction measures, resulting in high friction during the sliding process. To prevent the steel box girder from separating from the sliding device, simple fixing methods such as ropes or buckles may be used. These methods have limited fixing effects and are difficult to adjust flexibly according to the actual situation.

[0004] Regarding the aforementioned technologies, a conventional track and slider combination can rotate a steel box girder, but the high friction of such a combination can affect the smoothness of the rotation, increasing construction difficulty and time costs. Utility Model Content

[0005] To overcome the above problems, this application provides a sliding track structure for rotating steel box girders that cross existing railway lines.

[0006] The technical solution provided in this application for a sliding track structure for rotating a steel box girder across an existing railway line adopts the following: A sliding track structure for rotating a steel box girder across an existing railway line includes multiple sliding devices spaced apart along the length of the steel box girder. Each sliding device includes a support assembly and a sliding assembly. The sliding assembly includes multiple track beams and multiple sliding members. The track beams are connected to form an arc-shaped track for rotating the steel box girder. The arc-shaped track is connected to the top of the support assembly. The sliding members are spaced apart along the length of the track beams. Each sliding member includes a sliding seat and four rollers. The sliding seat slides along the length of the track beam. Connected to the top of the track beam, the top of the sliding seat is connected and fitted with the steel box girder. The traction device pulls the steel box girder to rotate. The bottom of the sliding seat has a receiving groove for the top of the track beam to be accommodated. The receiving groove runs through the sliding seat along the length of the track beam. The four rollers are divided into two groups, with each group of rollers located on the inner and outer sides of the arc track. The rollers are rotatably connected to the sliding seat and can slide on the arc track. The arrangement of the four rollers should be trapezoidal, with the center distance between the two rollers on the outer side of the arc track being larger.

[0007] By adopting the above technical solution, the arc-shaped track formed by connecting multiple track beams facilitates the rotation of the steel box girder, and the support components provide a stable foundation for the arc-shaped track; the sliding parts are distributed at intervals along the length of the track beam, which can evenly bear the weight of the steel box girder; the sliding seat slides on the top of the track beam, and can realize the rotation of the steel box girder in conjunction with the traction device; the receiving groove accommodates the top of the track beam, making the sliding seat slide more stably; the four rollers are arranged in a trapezoidal shape and the center distance of the outer rollers is large, which can avoid jamming on the arc-shaped track, reduce sliding resistance, and make the rotation of the steel box girder smoother.

[0008] In one specific implementation, the sliding assembly further includes a plurality of friction-reducing components, each corresponding to a sliding seat. The friction-reducing components are located within the receiving groove, and are MGE plates. The friction-reducing components are located between the sliding seat and the track beam, and are fixed to the sliding seat.

[0009] By adopting the above technical solution, an MGE plate is installed between the sliding seat and the track beam as a friction-reducing component, which can greatly reduce the friction between the sliding seat and the track beam and ensure the smooth progress of the steel box girder rotation construction.

[0010] In one specific implementation, the sliding device further includes multiple reinforcing components. At least one of the reinforcing components is provided on each sliding seat. The reinforcing component includes two reinforcing rods and two friction plates. The two reinforcing rods are located on the inner and outer sides of the arc-shaped track, respectively. The reinforcing rods are inclined from the bottom to the top of the sliding seat towards the side away from the sliding seat. The lower end of the reinforcing rod is connected to the sliding seat. The friction plates correspond one-to-one with the reinforcing rods. The friction plates are located at the higher end of the reinforcing rods. The friction plates are located on the side of the two reinforcing rods that are close to each other. The side of the friction plate close to the reinforcing rod is connected to the reinforcing rod. The friction plates are in contact with the bottom of the steel box girder.

[0011] By adopting the above technical solution, the friction plate on the reinforcing rod contacts the bottom of the steel box girder, which can further reduce the separation of the sliding seat from the steel box girder and improve the stability and safety of the steel box girder rotation construction.

[0012] In one specific implementation, the reinforcement assembly further includes two reinforcement members. The lower end of the reinforcement rod is hinged to the sliding seat. The reinforcement members correspond one-to-one with the reinforcement rods. The reinforcement member is a hydraulic cylinder. The hydraulic cylinder is arranged perpendicular to the top of the sliding seat from the bottom to the top of the sliding seat. The cylinder body of the hydraulic cylinder is connected to the sliding seat. The piston rod of the hydraulic cylinder is hinged to the middle of the reinforcement rod.

[0013] By adopting the above technical solution, the reinforcement component uses a hydraulic cylinder. The piston rod of the hydraulic cylinder is hinged to the middle of the reinforcement rod, which can adjust the angle between the two reinforcement rods. This can be adjusted according to the actual situation, making it easier for the friction plate to contact the steel box girder. The hydraulic cylinder supports the reinforcement rod and applies a thrust to the reinforcement rod, so that the friction plate contacts the steel box girder, further reducing the separation of the sliding seat from the steel box girder and improving the stability and safety of the steel box girder rotation construction.

[0014] In one specific implementation, the friction plate is hinged to the reinforcing rod on the side closest to the reinforcing rod.

[0015] By adopting the above technical solution, the friction plate is hinged on the side near the reinforcing rod, which allows the friction plate to better fit the bottom of the steel box girder, enhances the contact effect with the steel box girder, further reduces the separation of the steel box girder from the sliding seat, and improves the stability and safety of the steel box girder rotation construction.

[0016] In one specific implementation, a fixing plate is fixed to the top of the track beam, and the friction-reducing component is located between the sliding seat and the fixing plate.

[0017] By adopting the above technical solution, the fixed plate at the top of the track beam can enhance the load-bearing capacity of the track beam. The friction-reducing component is located between the sliding seat and the fixed plate. When the steel box girder is subjected to traction force and the sliding seat moves, it can greatly reduce the friction between the sliding seat and the fixed plate, ensuring the smooth progress of the steel box girder rotation construction.

[0018] In one specific implementation, the sliding assembly further includes multiple splicing components, with one splicing component positioned between two adjacent track beams. Each splicing component includes a splicing plate and at least two fixing bolts. The longitudinal section of the splicing plate is identical to the longitudinal section of the track beam. Each end of the splicing plate has a splicing groove for insertion into the track beam. Both ends of the track beam have mating grooves. When the splicing plate is connected to the track beam, the mating grooves engage with the splicing plate. The peripheral wall of the splicing plate is flush with the peripheral wall of the track beam. The two fixing bolts are distributed along the length of the track beam and are sequentially threaded through the splicing plate and the track beam.

[0019] By adopting the above technical solution, multiple splicing components are used to fix adjacent track beams together. The splicing plate fits the track beam and is connected by fixing bolts, so that the track beams are tightly connected, ensuring the integrity and stability of the curved track and facilitating the rotation construction of the steel box girder.

[0020] In one specific implementation, the top of the sliding seat is fixed with an anti-slip pad that contacts the bottom of the steel box girder.

[0021] By adopting the above technical solution, the anti-slip pad fixed on the top of the sliding seat contacts the bottom of the steel box girder, which can increase the friction between the steel box girder and the sliding seat and reduce the possibility of separation between the sliding seat and the steel box girder.

[0022] In summary, this application includes at least one of the following beneficial technical effects: 1. The designed sliding track structure for rotating steel box girders crossing existing railway lines features sliding components spaced along the length of the track beam to evenly bear the weight of the steel box girder; the sliding seat slides on top of the track beam, and in conjunction with the traction device, the steel box girder can be rotated; the receiving groove accommodates the top of the track beam, making the sliding seat slide more stably; the four rollers are arranged in a trapezoidal shape with a larger center distance between the outer rollers, which can prevent jamming on the curved track, reduce sliding resistance, and make the rotation of the steel box girder smoother.

[0023] 2. The designed sliding track structure for the rotation construction of steel box girders crossing existing lines uses MGE plates as friction-reducing components between the sliding seat and the track beam, which can greatly reduce the friction between the sliding seat and the track beam, ensuring the smooth progress of the steel box girder rotation construction.

[0024] 3. The designed sliding track structure for the rotation construction of the steel box girder crossing the existing line features a hydraulic cylinder piston rod hinged to the middle of the reinforcing rod, allowing adjustment of the angle between the two reinforcing rods according to actual conditions. This facilitates contact between the friction plate and the steel box girder. Furthermore, the hydraulic cylinder supports the reinforcing rods and applies thrust to them, ensuring contact between the friction plate and the steel box girder. This further reduces the separation of the sliding seat from the steel box girder, improving the stability and safety of the steel box girder rotation construction. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the sliding track structure used for the rotation construction of a steel box girder crossing an existing railway line, according to an embodiment of this application.

[0026] Figure 2 This is a structural schematic diagram of the splicing component in this embodiment.

[0027] Figure 3 This is a schematic diagram of the sliding component and the reinforcing component in this embodiment.

[0028] Figure 4 This is a structural schematic diagram of the reinforcement component in this embodiment.

[0029] Explanation of reference numerals in the attached drawings: 1. Support assembly; 11. Support frame; 2. Sliding assembly; 21. Track beam; 211. Anchor base plate; 212. Fitting groove; 213. Fixing plate; 22. Splicing piece; 221. Splicing plate; 2211. Splicing groove; 222. Fixing bolt; 23. Sliding piece; 231. Sliding seat; 2311. Anti-slip pad; 2312. Receiving groove; 232. Roller; 24. Friction reducing component; 3. Reinforcing assembly; 31. Reinforcing rod; 32. Friction plate; 321. Anti-slip rib; 33. Reinforcing member. Detailed Implementation

[0030] The following is in conjunction with the appendix Figure 1-4 This application will be described in further detail.

[0031] This application discloses a sliding track structure for rotating a steel box girder across an existing railway line.

[0032] Reference Figure 1 , Figure 2 and Figure 3 A sliding track structure for rotating a steel box girder across an existing railway line includes multiple sliding devices. The multiple sliding devices are distributed at intervals along the length of the steel box girder. The sliding device includes a support component 1, a sliding component 2, and multiple reinforcing components 3. The sliding component 2 is mounted on the support component 1, and the reinforcing components 3 are mounted on the sliding component 2.

[0033] Reference Figure 1 , Figure 2 and Figure 3The support assembly 1 includes a support frame 11, which is fixed to a designated position on the ground. The sliding assembly 2 includes multiple track beams 21, multiple splicing parts 22, multiple sliding parts 23, and multiple friction-reducing parts 24. The multiple track beams 21 are all located on top of the support frame 11. The bottom of the track beams 21 is fixedly connected to an anchoring base plate 211 by bolts. The anchoring base plate 211 is fixedly connected to the support frame 11 by reinforcing bolts. The anchoring base plate 211 increases the contact area between the track beams 21 and the foundation, improving stability. The track beams 21 are I-shaped sections made of high-strength metal material. For the structure, high-strength metal materials can be selected, such as high-strength steel like Q345D high-strength alloy steel. This type of steel has high strength and good toughness, and can withstand large loads. The I-shaped cross-section structure has good mechanical properties and can effectively withstand bending moments and shear forces. Other similar high-strength alloy materials can also be used to replace steel for track beam 21, such as aluminum alloy. Aluminum alloy is lightweight and has good corrosion resistance. The structural design of its upper and lower flange plates and the middle web plate allows track beam 21 to evenly distribute stress when under pressure, enhancing the stability of track beam 21.

[0034] Reference Figure 1 and Figure 2 Multiple track beams 21 are distributed along the rotation direction of the steel box girder, and the multiple track beams 21 are connected to form an arc-shaped track. A splicing component 22 is provided between two adjacent track beams 21. The splicing component 22 includes a splicing plate 221 and at least two fixing bolts 222. The longitudinal section of the splicing plate 221 is I-shaped. Each end of the splicing plate 221 has a splicing groove 2211 for the track beam 21 to be inserted. Both ends of the track beam 21 have a fitting groove 212. When the splicing plate 221 and the track beam 21 are connected, the track beam 21 is engaged. During connection, the fitting groove 212 fits into the splicing plate 221, and the periphery of the splicing plate 221 is flush with the periphery of the track beam 21. In this embodiment, there are two fixing bolts 222, which are distributed along the length of the track beam 21. The fixing bolts 222 are sequentially inserted into the splicing plate 221 and the track beam 21, and are sequentially threaded to the splicing plate 221 and the track beam 21, which can fix two adjacent track beams 21 through the splicing plate 221.

[0035] Reference Figure 1 , Figure 3 and Figure 4A fixing plate 213 is provided on the top of the track beam 21. The fixing plate 213 is welded to the track beam 21 and can enhance the load-bearing capacity of the track beam 21. Multiple sliding members 23 are distributed at intervals along the length direction of the track beam 21. In this embodiment, there are three sliding members 23. Each sliding member 23 includes a sliding seat 231 and four rollers 232. The sliding seat 231 is located on the top of the track beam 21 and can slide on the track beam 21 along the length direction of the track beam 21. The top of the sliding seat 231 is provided with An anti-slip pad 2311 is fixedly bonded to the sliding seat 231. When the steel box girder is located at the top of the sliding seat 231, the anti-slip pad 2311 contacts the bottom of the steel box girder. The traction device pulls the steel box girder to rotate, which can increase the friction between the steel box girder and the sliding seat 231 and reduce the possibility of separation between the sliding seat 231 and the steel box girder. A receiving groove 2312 is provided at the bottom of the sliding seat 231. The receiving groove 2312 extends through the sliding seat 231 along the length of the track beam 21. In this embodiment, the receiving groove 2312... 312 is a T-shaped groove. The upper flange plate and fixing plate 213 of the track beam 21 are both located within the T-shaped groove. The four rollers 232 are divided into two groups, with each group of rollers 232 located on opposite sides of the middle web of the track beam 21. The rollers 232 are rotatably connected to the sliding seat 231 and can slide on the curved track. The fixing bolts 222 should be staggered from the rolling path of the rollers 232 to ensure that the fixing bolts 222 do not interfere with the rolling of the rollers 232. The arrangement of the four rollers 232... The track should be trapezoidal rather than rectangular to ensure that the inner roller 232 and the outer roller 232 are not on the same radius line. This will make the center distance between the two rollers 232 on the outer side of the arc track larger, thus avoiding jamming. At the same time, the center movement trajectory of the two rollers 232 on the inner and outer sides of the arc track should be the same arc, and the center of the arc should be consistent with the center of the arc track. The two arc trajectories on both sides should also be concentric. In order to ensure that the sliding seat 231 can fit tightly on the arc track, the positions of the four rollers 232 should be constant.

[0036] Reference Figure 3 The friction-reducing component 24 corresponds one-to-one with the sliding seat 231. The friction-reducing component 24 is located in the T-shaped groove. In this embodiment, the friction-reducing component 24 is an MGE plate. The friction-reducing component 24 is located between the sliding seat 231 and the fixed plate 213. The friction-reducing component 24 is fixedly connected to the sliding seat 231 by bolts. When the steel box girder is subjected to traction force, it can drive the sliding seat 231 to move, which can greatly reduce the friction between the sliding seat 231 and the fixed plate 213, and ensure the smooth progress of the steel box girder rotation construction.

[0037] Reference Figure 3 and Figure 4At least one reinforcing component 3 is provided on each sliding seat 231. In this embodiment, two reinforcing components 3 are provided on each sliding seat 231. The two reinforcing components 3 are distributed at intervals along the movement direction of the sliding seat 231. Each reinforcing component 3 includes two reinforcing rods 31, two friction plates 32, and two reinforcing members 33. The two reinforcing rods 31 are located on opposite sides of the sliding seat 231, and are located on the inner and outer sides of the arc track. The reinforcing rods 31 are inclined from the bottom to the top of the sliding seat 231 towards the side away from the sliding seat 231. The lower end of the reinforcing rod 31 is hinged to the sliding seat 231. The friction plates 32 correspond one-to-one with the reinforcing rods 31. The friction plates 32 are located at the higher end of the reinforcing rods 31 and are located on the side where the two reinforcing rods 31 are close to each other. The side of the friction plates 32 close to the reinforcing rods 31 is hinged to the reinforcing rods 31. The side of the friction plates 32 away from the reinforcing rods 31 is provided with several parallel anti-slip ridges. The friction plate 32 can be made of rubber or metal plate with anti-slip coating. When the steel box girder is located at the top of the sliding seat 231, the friction plate 32 contacts the bottom of the steel box girder, which can further reduce the separation of the sliding seat 231 from the steel box girder. The reinforcement 33 corresponds to the reinforcement rod 31. In this embodiment, the reinforcement 33 is a hydraulic cylinder. The hydraulic cylinder is set perpendicular to the top of the sliding seat 231 from the bottom to the top of the sliding seat 231. The cylinder body of the hydraulic cylinder is welded with a connecting seat, which is welded to the sliding seat 231. The piston rod of the hydraulic cylinder is hinged to the middle of the reinforcement rod 31, which can adjust the angle between the two reinforcement rods 31 so as to adjust according to the actual situation, so as to facilitate the contact between the friction plate 32 and the steel box girder. The hydraulic cylinder supports the reinforcement rod 31 and can apply a thrust to the reinforcement rod 31 so that the friction plate 32 contacts the steel box girder, thereby further reducing the separation of the sliding seat 231 from the steel box girder.

[0038] The implementation principle of the sliding track structure for rotating a steel box girder across an existing railway line according to an embodiment of this application is as follows: The sliding track structure evenly bears the weight of the steel box girder through the reasonable distribution of multiple sliding track devices. The support frame 11 of the support component 1 provides a stable foundation for the whole. The I-shaped structure and high-strength material of the track beam 21 ensure its load-bearing capacity and stability. The splicing component 22 connects multiple track beams 21 into an arc track, which facilitates the rotation of the steel box girder. The special rollers 232 of the sliding component 23 and the setting of the friction-reducing component 24 reduce the sliding resistance, making the rotation of the steel box girder smoother. The reinforcement component 3 adjusts the angle of the reinforcement rod 31 to make the friction plate 32 in close contact with the steel box girder, preventing the steel box girder from separating from the sliding seat 231, which greatly improves the stability and safety of the steel box girder rotation construction.

[0039] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A slide structure for steel box girder swivel construction across an existing line, characterized by: The system includes multiple sliding devices, which are spaced apart along the length of the steel box girder. Each sliding device includes a support assembly (1) and a sliding assembly (2). The sliding assembly (2) includes multiple track beams (21) and multiple sliding members (23). The track beams (21) are connected to form an arc-shaped track for rotating the steel box girder. The arc-shaped track is connected to the top of the support assembly (1). The sliding members (23) are spaced apart along the length of the track beams (21). Each sliding member (23) includes a sliding seat (231) and four rollers (232). The sliding seat (231) is slidably connected to the top of the track beams (21) along the length of the track beams (21). (231) The top is connected to the steel box girder, and the traction device pulls the steel box girder to rotate. The bottom of the sliding seat (231) is provided with a receiving groove (2312) for the top of the track beam (21) to be accommodated. The receiving groove (2312) passes through the sliding seat (231) along the length direction of the track beam (21). The four rollers (232) are divided into two groups. The two groups of rollers (232) are located on the inner and outer sides of the arc track. The rollers (232) are rotatably connected to the sliding seat (231). The rollers (232) can slide on the arc track. The arrangement of the four rollers (232) needs to be trapezoidal. The center distance between the two rollers (232) on the outer side of the arc track is larger.

2. The sliding track structure for rotating a steel box girder across an existing railway line according to claim 1, characterized in that: The sliding assembly (2) also includes a plurality of friction-reducing components (24), each of which corresponds to one of the sliding seats (231). The friction-reducing components (24) are located in the receiving groove (2312). The friction-reducing components (24) are MGE plates. The friction-reducing components (24) are located between the sliding seats (231) and the track beam (21). The friction-reducing components (24) are fixed to the sliding seats (231).

3. The sliding track structure for rotating a steel box girder across an existing railway line according to claim 1, characterized in that: The sliding device also includes multiple reinforcing components (3). At least one of the reinforcing components (3) is provided on each of the sliding seats (231). The reinforcing component (3) includes two reinforcing rods (31) and two friction plates (32). The two reinforcing rods (31) are located on the inner and outer sides of the arc track. The reinforcing rods (31) are inclined from the bottom of the sliding seat (231) to the top of the sliding seat (231) towards the side away from the sliding seat (231). The lower end of the reinforcing rod (31) is connected to the sliding seat (231). The friction plates (32) correspond one-to-one with the reinforcing rods (31). The friction plates (32) are located at the higher end of the reinforcing rods (31). The friction plates (32) are located on the side where the two reinforcing rods (31) are close to each other. The side of the friction plates (32) close to the reinforcing rods (31) is connected to the reinforcing rods (31). The friction plates (32) are in contact with the bottom of the steel box girder.

4. The sliding track structure for rotating a steel box girder across an existing railway line according to claim 3, characterized in that: The reinforcement component (3) also includes two reinforcement members (33). The lower end of the reinforcement rod (31) is hinged to the sliding seat (231). The reinforcement members (33) correspond one-to-one with the reinforcement rod (31). The reinforcement member (33) is a hydraulic cylinder. The hydraulic cylinder is set perpendicular to the top of the sliding seat (231) from the bottom to the top of the sliding seat (231). The cylinder body of the hydraulic cylinder is connected to the sliding seat (231). The piston rod of the hydraulic cylinder is hinged to the middle of the reinforcement rod (31).

5. The sliding track structure for rotating a steel box girder across an existing railway line according to claim 3, characterized in that: The friction plate (32) is hinged to the reinforcing rod (31) on the side near the reinforcing rod (31).

6. The slide structure for the steel box girder swivel construction across the existing line according to claim 2, characterized in that: A fixing plate (213) is fixed to the top of the track beam (21), and the friction reducing component (24) is located between the sliding seat (231) and the fixing plate (213).

7. The sliding track structure for rotating a steel box girder across an existing railway line according to claim 1, characterized in that: The sliding assembly (2) also includes multiple splicing components (22), with one splicing component (22) between two adjacent track beams (21). The splicing component (22) includes a splicing plate (221) and at least two fixing bolts (222). The longitudinal section of the splicing plate (221) is consistent with the longitudinal section of the track beam (21). Each end of the splicing plate (221) has a splicing groove (2211) for the track beam (21) to be inserted. Both ends of the track beam (21) have a fitting groove (212). When the track beam (21) is inserted into the track beam, a fitting groove (212) is provided at both ends. When the splicing plate (221) is connected to the track beam (21), the fitting groove (212) fits into the splicing plate (221), the periphery of the splicing plate (221) is flush with the periphery of the track beam (21), the two fixing bolts (222) are distributed along the length of the track beam (21), the fixing bolts (222) are sequentially inserted into the splicing plate (221) and the track beam (21), and the fixing bolts (222) are sequentially threaded into the splicing plate (221) and the track beam (21).

8. The sliding track structure for rotating a steel box girder across an existing railway line according to claim 1, characterized in that: The top of the sliding seat (231) is fixed with an anti-slip pad (2311) that contacts the bottom of the steel box girder.

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