Method for controlling vortex-induced vibration of split steel box girder bridge

Abstract

The application provides a split steel box girder bridge vortex vibration control method, and relates to the technical field of bridge construction. The split steel box girder bridge vortex vibration control method comprises the following steps: providing a wind speed detection mechanism, a split steel box girder with a central slot, and a baffle mechanism arranged on the steel box girder and used for opening and closing the central slot; acquiring a real-time wind speed V 实 by using the wind speed detection mechanism; when V 实 is less than V 阈 , the baffle mechanism is closed to make the central slot closed; and when V 实 is greater than V 阈 , the baffle mechanism is opened to make the central slot ventilated.

Description

Technical Field

[0001] This invention relates to the field of bridge construction technology, and in particular to a method for controlling vortex-induced vibration in a split-type steel box girder bridge. Background Technology

[0002] Vortex-induced vibration (V-V) is a common wind-induced vibration phenomenon in bridges occurring at low wind speeds. This phenomenon occurs because the frequency of vortices formed by airflow around the bridge cross-section is the same as the structure's own frequency, causing resonance in the bridge. V-V has self-limiting amplitude properties and generally does not cause structural safety issues, but it can lead to construction safety problems and affect traffic safety and comfort after the bridge is completed. Therefore, its frequency should be minimized or its amplitude reduced in the design. Flutter is a divergent vibration involving single-degree-of-freedom torsional or bending-torsional coupling modes, generally occurring at high wind speeds. It is a dynamic instability phenomenon, and its occurrence should be strictly prevented in bridge design.

[0003] How to achieve bridge stability in both low and high wind speed conditions is an urgent problem to be solved. Summary of the Invention

[0004] The purpose of this invention is to provide a method for controlling vortex-induced vibration of a split box girder bridge, which can simultaneously meet the flutter prevention requirements, thereby solving the technical problem that existing methods for suppressing vibration in split box girders cannot simultaneously address both vortex-induced vibration control and flutter control.

[0005] This invention provides a method for controlling vortex-induced vibration of a split-type steel box girder bridge, comprising the following steps:

[0006] A wind speed detection mechanism, a split steel box girder with a central slot, and a partition mechanism disposed on the steel box girder for opening and closing the central slot are provided.

[0007] The real-time wind speed V is obtained using the aforementioned wind speed detection mechanism. 实 ;

[0008] When V 实 Less than V 阈 When the partition mechanism is closed, the central slot is sealed.

[0009] When V 实 Greater than V 阈 When the partition mechanism opens, it allows ventilation through the central slot, wherein the threshold wind speed V 阈 Below the critical flutter wind speed, above the vortex-induced vibration wind speed.

[0010] Furthermore, the wind speed detection mechanism includes a fan, a generator, and a voltage detection device, wherein the fan is connected to the generator and generates electricity by rotating the fan;

[0011] The generator is connected to the motor of the partition mechanism, and there is a control switch between the two. The control switch is used to control the partition mechanism to be in a closed state or an open state.

[0012] The voltage detection device is connected in parallel with the generator to detect the voltage U across the generator in real time. 实 Among them, U 阈 The voltage across the generator when the wind speed is between the threshold wind speed and the flutter wind speed;

[0013] When U 实 Less than U 阈 When the control switch is off, the partition mechanism is closed;

[0014] When U 实 Greater than U 阈 When the control switch is activated, the partition mechanism opens.

[0015] Furthermore, the partition mechanism includes a rotary drive module and partitions, and there are multiple partitions, which are distributed at equal intervals.

[0016] The rotation drive module is connected to the partition, and the rotation drive module drives the partition to rotate;

[0017] The multiple partitions can be rotated to the same plane to close the partition mechanism;

[0018] The multiple partitions can be rotated to be parallel to each other and have gaps between them, so that the partition mechanism can be opened.

[0019] Furthermore, the rotation drive module includes multiple motors, the number of which is the same as the number of partitions, and they are connected in a one-to-one correspondence.

[0020] Furthermore, the rotation drive module includes a motor and a linkage component, wherein the motor drives multiple partitions to move synchronously through the linkage component.

[0021] Furthermore, the end of the partition is provided with a pivot; the split steel box girder is provided with a shaft hole for the pivot to pass through;

[0022] The linkage assembly includes multiple connecting rods and a cantilever beam. The number of connecting rods is the same as the number of partitions and they correspond one-to-one. One end of each connecting rod is connected to the pivot of the corresponding partition, and the other end of each connecting rod is connected to the cantilever beam.

[0023] The linkage component also includes a motor, which is connected to the rotating shaft of any of the partitions.

[0024] Furthermore, the linkage assembly includes a drive gear, a chain, and a driven gear. The drive gear is connected to the output shaft of the motor, the driven gear is connected to the rotating shaft of the partition, and both the drive gear and the driven gear are connected to the chain.

[0025] Furthermore, the partition mechanism includes a flexible plate, a roller body, and a motor. The motor is connected to the roller body and drives it to rotate. The flexible plate is connected to the side wall of the roller body and can be wound around the roller body.

[0026] The split steel box girder has guide grooves on both inner walls opposite to the central slot, and the flexible plate is slidably connected to the opposite sides within the guide grooves.

[0027] Furthermore, the partition mechanism includes a plate and a push-pull module, and the inner wall of the central slot of the split steel box girder has a telescopic groove; the telescopic groove is capable of accommodating the plate.

[0028] The push-pull module is connected to the plate body and is used to drive the plate body to slide into or out of the telescopic slide groove.

[0029] Furthermore, there are two plates and two push-pull modules. The two inner walls of the central slot of the split steel box girder are equipped with telescopic grooves. The two plates and the push-pull modules are located in the two telescopic grooves respectively, thereby realizing the movement of the two plates towards each other or away from each other.

[0030] The vortex-induced vibration control method for a split-type steel box girder bridge provided in this embodiment of the invention includes the following steps: providing a wind speed detection mechanism, a split-type steel box girder with a central slot, and a partition mechanism disposed on the steel box girder for opening and closing the central slot. The real-time wind speed V is obtained using the wind speed detection mechanism. 实 When V 实 Less than V 阈 When V is closed, the partition mechanism closes, sealing the central slot. The slot is in an airtight or near-airtight closed state, thereby preventing vortex generation at the slot and preventing vortex-induced vibration. 实 Greater than V 阈 When the central slot is open, the diaphragm mechanism is activated to allow ventilation. At this time, the central slot of the split steel box girder is fully ventilated, resulting in better flutter performance. Therefore, by changing the opening and closing state of the central slot according to the real-time wind speed, the closed and open states of the diaphragm mechanism at different wind speeds are used to control vortex-induced vibration and flutter respectively. Attached Figure Description

[0031] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0032] Figure 1 A schematic diagram of the split steel box girder in the vortex-induced vibration control method for split steel box girder bridges provided in this embodiment of the invention;

[0033] Figure 2 A diagram showing the power supply of the diaphragm mechanism in the vortex-induced vibration control method for a split-type steel box girder bridge provided in an embodiment of the present invention.

[0034] Figure 3 This is a schematic diagram of the first type of diaphragm mechanism in the vortex vibration control method for a split steel box girder bridge provided in an embodiment of the present invention;

[0035] Figure 4 for Figure 3 A magnified view of a portion of position A in the middle;

[0036] Figure 5 This is a schematic diagram of the second type of diaphragm mechanism in the vortex vibration control method for a split steel box girder bridge provided in an embodiment of the present invention;

[0037] Figure 6 This is a schematic diagram of the third type of diaphragm mechanism in the vortex vibration control method for a split steel box girder bridge provided in an embodiment of the present invention;

[0038] Figure 7 This is a schematic diagram of the fourth type of diaphragm mechanism in the vortex vibration control method for split steel box girder bridges provided in the embodiments of the present invention;

[0039] Figure 8 for Figure 7 A magnified view of a portion of position B in the middle;

[0040] Figure 9 This is a schematic diagram of the fifth type of diaphragm mechanism in the vortex vibration control method for split steel box girder bridges provided in the embodiments of the present invention.

[0041] Icons: 110 - Fan; 120 - Voltage relay (KV); 130 - Changeover switch; 140 - Generator; 200 - Split steel box girder; 300 - Partition mechanism; 510 - Partition; 520 - Motor;

[0042] 610 - Connecting rod; 620 - Cantilever beam;

[0043] 710 – Driving gear; 720 – Chain; 730 – Driven gear;

[0044] 810 – Flexible plate; 820 – Roller body; 830 – Guide chute;

[0045] 910-Plate body. Detailed Implementation

[0046] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0047] like Figure 1 As shown, the vortex-induced vibration control method for a split steel box girder bridge provided in this embodiment of the invention includes the following steps: providing a wind speed detection mechanism, a split steel box girder 200 with a central slot, and a partition mechanism 300 disposed on the steel box girder for opening and closing the central slot.

[0048] The split steel box girder 200 extends along the driving direction and has multiple central slots that vertically penetrate the split steel box girder 200. Each central slot has at least one baffle mechanism 300 inside. The baffle mechanism 300 can switch between a closed state and an open state. When in the closed state, the baffle mechanism 300 can close the central slot it is in, preventing vertical airflow. Conversely, when in the open state, airflow can pass vertically through the central slot.

[0049] The control method includes the following steps: acquiring real-time wind speed V using the wind speed detection mechanism. 实 A certain wind speed value between the flutter critical wind speed and the vortex vibration wind speed is selected as the threshold wind speed V. 阈 This threshold wind speed V 阈 It can be determined by the bridge management unit.

[0050] Wind speed testing equipment can be installed on or near bridges, or selected based on wind tunnel test results and operational management requirements. When V 实 Less than V 阈 When V is closed, the partition mechanism 300 closes to seal the central slot, placing the slot in an airtight or near-airtight closed state, thereby preventing vortex generation at the slot and preventing vortex-induced vibration. 实 Greater than V 阈 When the central slot is open, the diaphragm mechanism 300 is open to allow ventilation. At this time, the central slot of the split steel box girder 200 is in a fully ventilated state, resulting in better flutter performance. Therefore, by changing the opening and closing state of the central slot according to the real-time wind speed, the closed and open states of the diaphragm mechanism 300 at different wind speeds are used to control vortex-induced vibration and flutter respectively.

[0051] like Figure 2 As shown, the partition mechanism 300 is normally powered by an external source via cable. However, in severe weather conditions, such as strong winds or heavy rain, there is a risk of power outage. Therefore, to ensure the partition mechanism 300 can continue to operate normally under extreme weather conditions, this embodiment proposes a backup power supply scheme, which works perfectly in conjunction with the wind speed detection mechanism. Thus, the partition mechanism 300 has two power sources, which are switched by adjusting the transfer switch 130.

[0052] Specifically, the wind speed detection mechanism includes a fan 110, a generator 140, and a voltage detection device. The fan 110 is connected to the generator 140, and the rotation of the fan 110 drives the rotor inside the generator 140 to rotate and generate electricity. The electrical energy generated by the generator 140 can be used to drive the movement of the partition mechanism 300.

[0053] The voltage detection device is connected in parallel with the generator 140 and is used to detect the voltage U across the generator 140 in real time. 实 Among them, U 阈 U represents the voltage across generator 140 when the wind speed falls within the threshold wind speed between flutter and vortex speeds. This is because the higher the wind speed, the faster fan 110 rotates, and the greater the electrical energy generated by generator 140. 实 The larger it is, therefore, by detecting U 实 This can provide a different perspective on wind speed.

[0054] The generator 140 is connected to the motor of the partition mechanism 300, and a control switch is provided between them. This control switch controls the partition mechanism 300 to be in a closed or open state. Specifically, the control switch and voltage detection device can be formed by a voltage relay KV120, which is a voltage monitoring element and mainly includes four contacts. Contacts P1 and P2 are connected to the positive and negative terminals of the generator 140 to sense the voltage across the generator 140. When the voltage across P1 and P2 is greater than the threshold voltage U, contacts P3 and P4 close. Contact P3 is connected to the generator 140 via a wire, and contact P4 is connected to one end of the changeover switch 130 via a wire.

[0055] Under normal circumstances, when switching changeover switch 130 to circuit one, the partition mechanism 300 is powered by a centralized external power supply.

[0056] When extreme weather occurs and the external power supply is switched, switch changeover switch 130 is switched to circuit two, when V 实 Less than V 阈 At that time, the voltage generated by generator 140 is lower than the control threshold, i.e., U 实 Less than U 阈With contacts P3 and P4 of voltage relay KV120 open, motor 520 of partition mechanism 300 does not drive partition 510 to move. Partition 510 remains closed to suppress vortex-induced vibration of the split steel box girder 200 bridge.

[0057] When V 实 >V 阈 At that time, the voltage generated by generator 140 is higher than the control threshold, i.e., U 实 Greater than U 阈 When contacts P3 and P4 of voltage relay KV120 are closed, the external power source for motor 520 of partition mechanism 300 is generator 140. Motor 520 drives partition 510 to move. After partition 510 is fully open, a locking device is triggered, which keeps partition 510 open. At this time, the flutter of the split steel box girder 200 bridge can be controlled.

[0058] The partition mechanism 300 includes a rotation drive module and partitions 510. There are multiple partitions 510, which are evenly spaced. The rotation drive module is connected to the partitions 510, and the rotation drive module drives the partitions 510 to rotate. The multiple partitions 510 can rotate to the same plane to close the partition mechanism 300. The multiple partitions 510 can rotate to be parallel to each other and have gaps between them to open the partition mechanism 300.

[0059] In this embodiment, the partition mechanism 300 contains multiple partitions 510, which are evenly spaced and have equal width and length. The length direction of each partition 510 is perpendicular to the travel direction. When a partition 510 is rotated to be parallel to the horizontal plane, it forms a complete surface that closes the slot. Conversely, when a partition 510 is rotated to be parallel to the vertical plane, the gap between two adjacent partitions 510 allows for ventilation.

[0060] The partition mechanism 300 provided in this embodiment has various types. The design principle is that the rotation drive module can control the partition 510 to open or close, and the open state of the partition 510 will not block the wind coming from the transverse bridge (the partition 510 does not face the wind), that is, it will not change the aerodynamic shape of the original split beam structure.

[0061] like Figure 3 and Figure 4As shown, in the first embodiment, the rotation drive module includes multiple motors 520, the number of which is the same as the number of partitions 510, and they are connected one-to-one. Each partition 510 has a motor 520 at both ends, capable of rotating around its longitudinal central axis. The motors 520 are fixedly connected to the movable central partition 510 via connecting shafts; each motor 520 is mounted on the straight web plate within the slot of the box girder (or it can be placed inside the box girder with holes drilled in the straight web plate, through which the connecting shaft passes). In the closed state, the distance between adjacent partitions 510 is 0-0.1m, which can be flexibly selected according to the thickness of the partition 510. The motors 520 can drive the partitions 510 to rotate, with the rotation axis being the central axis along the length of the partition 510 (transverse bridge direction), and the control angle for the rotation of the partition 510 is 0-90°.

[0062] In addition to using a motor 520 to drive the partition 510 to rotate, the partition 510 can also be driven to move by hydraulic means.

[0063] The rotation drive module includes a motor 520 and a linkage component. The motor 520 drives multiple partitions 510 to move synchronously through the linkage component. Unlike the first solution, synchronous movement can be achieved with fewer motors 520, saving costs.

[0064] In the second solution provided in this embodiment:

[0065] like Figure 5 As shown, the end of the partition 510 is provided with a rotating shaft; the split steel box girder 200 is provided with a shaft hole for the rotating shaft to pass through; the linkage assembly includes multiple connecting rods 610 and a cantilever beam 620, the number of connecting rods 610 is the same as the number of partitions 510, and they correspond one-to-one, one end of the connecting rod 610 is connected to the rotating shaft of the corresponding partition 510, and the other end of the connecting rod 610 is connected to the cantilever beam 620; the linkage assembly also includes a motor 520, which is connected to the rotating shaft of any partition 510. Assuming that initially, the partition 510 is in the closed state, the control motor 520 is started, and the partition 510 connected to the motor 520 begins to rotate. The connecting rod 610 connected to the partition 510 rotates simultaneously. Since the connecting rod 610 is connected to the cantilever beam 620, the rotation of a single connecting rod 610 drives all the connecting rods 610 in the entire linkage mechanism to rotate simultaneously. The rotation of each connecting rod 610 drives the partition 510 connected to the corresponding connecting rod 610 to rotate. That is, the motor 520 can realize the linkage action of other partitions 510 by changing the opening degree of one partition 510.

[0066] In the third solution provided in this embodiment:

[0067] like Figure 6As shown, the linkage assembly includes a drive gear 710, a chain 720, and a driven gear 730. The drive gear 710 is connected to the output shaft of the motor 520, and the driven gear 730 is connected to the rotating shaft of the partition 510. Both the drive gear 710 and the driven gear 730 are connected to the chain 720. The motor 520 remains stationary. The drive gear 710 on the motor 520 drives the chain 720 to rotate, and the chain 720 drives each driven gear 730 to rotate, thereby causing the partitions 510 to switch states.

[0068] In the fourth solution provided in this embodiment:

[0069] like Figure 7 and Figure 8 As shown, the partition mechanism 300 includes a flexible plate 810, a roller 820, and a motor 520. The flexible plate 810 can be formed by splicing together multiple partitions 510 with stops, and adjacent partitions 510 are hinged. The flexible plate 810 is connected to the side wall of the roller 820 and can be wound around the roller 820. Both the roller 820 and the motor 520 are fixed to the steel box girder. The motor 520 is connected to the roller 820 and drives its rotation, realizing the winding and unwinding of the flexible plate 810. The split steel box girder 200 has guide grooves 830 on both inner walls opposite to the central slot, and the opposite sides of the flexible plate 810 are slidably connected within the guide grooves 830. The difference from the above implementation scheme is that in this scheme, the individual partitions 510 are spliced ​​into a whole, and only one motor 520 drives the entire partition 510 to slide on the guide groove 830 and roll it up onto the roller 820 (similar to a garage roller shutter). In order to balance the rigidity and flexibility of the overall plate 910 (the rigidity is to maintain the strength of the partition 510, and the flexibility is to facilitate the winding of the partition 510), the individual partitions 510 themselves can be made of rigid materials, and the individual partitions 510 are connected by flexible materials (flexible materials such as steel wire ropes can also be used for series traction). The motor 520 and the roller 820 can be placed inside a sealed box to ensure the stability and durability of the drive system.

[0070] In the fifth solution provided in this embodiment:

[0071] like Figure 9As shown, the partition mechanism 300 includes a plate 910 and a push-pull module. The plate 910 is a solid plate. The inner wall of the central slot of the split steel box girder 200 has a telescopic groove. In the sliding direction, the length of the plate 910 is greater than or equal to the length of the telescopic groove. The telescopic groove can accommodate the plate 910, meaning the plate 910 can completely enter and slide out of the telescopic groove, thus closing the slot. The push-pull module is connected to the plate 910 and is used to drive the plate 910 into or out of the telescopic groove. The push-pull module can be a lead screw module, a rack and pinion module, or a linear drive module such as a cylinder.

[0072] Furthermore, there are two of each of the plate 910 and the push-pull module. The two inner walls of the central slot of the split steel box girder 200 are provided with the telescopic sliding groove. The two plates 910 and the push-pull module are located in the two telescopic sliding grooves respectively, forming a double door shape, thereby realizing that the two plates 910 can move towards each other or away from each other, which can reduce the movement stroke of the plates 910 and shorten the opening and closing switching time of the slot.

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for controlling vortex-induced vibration in a split-type steel box girder bridge, characterized in that, Including the following steps: Provided a wind speed detection mechanism, a split steel box girder (200) with a central slot, and a partition mechanism (300) disposed on the steel box girder for opening and closing the central slot. The real-time wind speed V is obtained using the aforementioned wind speed detection mechanism. 实 ; When V 实 Less than V 阈 When the partition mechanism (300) is closed, the central slot is closed; When V 实 Greater than V 阈 At that time, the partition mechanism (300) opens to allow ventilation in the central slot, wherein V 阈 The threshold wind speed; the threshold wind speed V 阈 Below the critical flutter speed, above the vortex-induced vibration speed; The wind speed detection mechanism includes a fan (110), a generator (140), and a voltage detection device. The fan (110) is connected to the generator, and the fan (110) generates electricity by rotating. The generator (140) is connected to the motor of the partition mechanism (300), and there is a control switch between the two. The control switch is used to control the partition mechanism (300) to be in a closed state or an open state. The voltage detection device is connected in parallel with the generator (140) and is used to detect the voltage U across the generator (140) in real time. 实 Among them, U 阈 The voltage across the generator (140) is the value when the wind speed is between the threshold wind speed of flutter and vortex vibration. When U 实 Less than U 阈 When the control switch is turned off, the partition mechanism (300) is closed; When U 实 Greater than U 阈 When the control switch is connected, the partition mechanism (300) opens.

2. The method for controlling vortex-induced vibration of a split-type steel box girder bridge according to claim 1, characterized in that, The partition mechanism (300) includes a rotary drive module and partitions (510), and there are multiple partitions (510) distributed at equal intervals. The rotation drive module is connected to the partition (510), and the rotation drive module drives the partition (510) to rotate; The plurality of said partitions (510) can be rotated to the same plane to close the partition mechanism (300); The plurality of said partitions (510) can be rotated to be parallel to each other and with gaps between them, so that the partition mechanism (300) can be opened.

3. The method for controlling vortex-induced vibration of a split-type steel box girder bridge according to claim 2, characterized in that, The rotation drive module includes multiple motors (520), the number of which is the same as the number of partitions (510), and they are connected in a one-to-one correspondence.

4. The method for controlling vortex-induced vibration of a split-type steel box girder bridge according to claim 3, characterized in that, The rotation drive module includes a motor (520) and a linkage component. The motor (520) drives multiple partitions (510) to move synchronously through the linkage component.

5. The method for controlling vortex-induced vibration of a split-type steel box girder bridge according to claim 4, characterized in that, The end of the partition (510) is provided with a rotating shaft; the split steel box girder (200) is provided with a shaft hole for the rotating shaft to pass through; The linkage assembly includes multiple connecting rods (610) and a cantilever beam (620). The number of connecting rods (610) is the same as the number of partitions (510) and they correspond one-to-one. One end of each connecting rod (610) is connected to the pivot of the corresponding partition (510), and the other end of each connecting rod (610) is connected to the cantilever beam (620). The linkage component also includes a motor (520), which is connected to the shaft of any of the partitions (510).

6. The method for controlling vortex-induced vibration of a split-type steel box girder bridge according to claim 4, characterized in that, The linkage assembly includes a drive gear (710), a chain (720), and a driven gear (730). The drive gear (710) is connected to the output shaft of the motor (520), and the driven gear (730) is connected to the rotating shaft of the partition (510). Both the drive gear (710) and the driven gear (730) are connected to the chain (720).

7. The method for controlling vortex-induced vibration of a split-type steel box girder bridge according to claim 1, characterized in that, The partition mechanism (300) includes a flexible plate (810), a roller (820) and a motor (520). The motor (520) is connected to the roller (820) and drives it to rotate. The flexible plate (810) is connected to the side wall of the roller (820) and can be wound around the roller (820). The split steel box girder (200) has guide grooves (830) on both inner walls opposite to the central slot, and the flexible plate (810) is slidably connected to the opposite sides of the guide grooves (830).

8. The method for controlling vortex-induced vibration of a split-type steel box girder bridge according to claim 1, characterized in that, The partition mechanism (300) includes a plate (910) and a push-pull module. The inner wall of the central slot of the split steel box girder (200) has a telescopic groove; the telescopic groove can accommodate the plate (910). The push-pull module is connected to the plate (910) and is used to drive the plate (910) to slide into or out of the telescopic groove.

9. The method for controlling vortex-induced vibration of a split-type steel box girder bridge according to claim 8, characterized in that, The number of the plate (910) and the push-pull module are both two. The two inner walls of the central slot of the split steel box girder (200) are equipped with the telescopic sliding groove. The two plates (910) and the push-pull module are located in the two telescopic sliding grooves respectively, so as to realize the two plates (910) moving towards each other or away from each other.

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