Automatic hooking and unhooking device and double-crane lifting device

Abstract

The utility model relates to an automatic hooking and unhooking device and a double-crane hoist, relates to the technical field of hoisting, can realize automatic hooking and unhooking of a crane hook, replaces traditional manual hooking and unhooking, reduces the labor intensity of operators, improves the safety, and is suitable for being applied to double-crane hoisting equipment. The utility model further designs an electric rotating device applied to double-machine lifting, the electric rotating device is characterized in that a driving mechanism provides rotating power, a transmission mechanism transmits rotating motion to a fork-shaped piece, a supporting mechanism carries out load bearing on the fork-shaped piece or a hook head, and the electric rotating device can be applied to double-machine lifting equipment. And the rotation control of the hoisted object hoisted by the two cranes is realized.

Description

[0001] This application is a divisional application of a utility model patent with the application number "202420147890.8", the application date of January 22, 2024, and the utility model name of "Electric Rotating Device". Technical Field

[0002] The utility model relates to the field of hoisting technology; specifically, the utility model relates to an automatic hook-on and hook-off device and double-crane lifting. Background Art

[0003] With the development and progress of manufacturing production technology, the volume and weight of manufactured equipment are gradually increasing. At present, the original lifting capacity of cranes in the production workshops of many enterprises cannot meet the production needs. Therefore, the method of using two cranes for lifting is adopted to solve this problem. As a result, special lifting tools for double-crane lifting have emerged. When using double-crane lifting, the hook hanging points of the two cranes are at both ends of the lifting tool, and the lifting tool cannot rotate. However, when the lifted object lands or is loaded onto a vehicle, it needs to be rotated and positioned. Therefore, the fork-shaped part or hook below the center of the lifting tool is usually made into a rotatable structure to facilitate the rotation and positioning of the lifted object when it lands or is loaded onto a vehicle. However, when using the above-mentioned lifting tool, the method of manual pushing and pulling is mostly adopted, which is laborious and unsafe. At the same time, the hook devices at both ends of the lifting tool are generally composed of shackles and strong rings, and manual operation is also required when hooking. Large-sized shackles and strong rings are large and heavy, and generally require 2 or more people to operate, and there are also problems of being laborious and unsafe. Summary of the Utility Model

[0004] The purpose of the utility model is to provide an automatic hook-on and hook-off device and double-crane lifting, which does not require manual hook-on and hook-off.

[0005] One of the purposes of the utility model is to provide an automatic hook-on and hook-off device, including:

[0006] A lifting lug plate provided with at least two positioning holes, two vertical plates arranged on the front and rear sides of the lifting lug plate, and a hanging shaft connected to the upper parts of the two vertical plates;

[0007] Connecting holes and sliding groove holes are symmetrically arranged at the lower parts of the two vertical plates. The sliding groove holes are arc grooves, and the center of the arc groove is the center of the connecting hole, and the radius is the same as the distance between the two positioning holes;

[0008] The first connecting shaft sequentially passes through the connecting hole of one vertical plate, a positioning hole of the lifting lug plate, and the connecting hole of the other vertical plate from one side, and the second connecting shaft sequentially passes through the sliding groove hole of one vertical plate, the other positioning hole of the lifting lug plate, and the sliding groove hole of the other vertical plate from one side.

[0009] Preferably, the positioning holes are arranged in the horizontal direction.

[0010] Preferably, the centers of the hanging shaft, the connecting hole, and the second connecting shaft form a non-obtuse triangle structure.

[0011] More preferably, the centers of the hanging shaft, the connecting hole, and the second connecting shaft form a right triangle structure or an isosceles triangle structure.

[0012] Preferably, the first connecting shaft and the second connecting shaft are a bolt and a nut.

[0013] The second object of the present invention is to provide a two-crane lifting, including the above automatic hanging and decoupling device.

[0014] Preferably, the two-crane lifting further includes a box girder, and the automatic hanging and decoupling device is arranged on both sides of the upper end surface of the box girder.

[0015] Preferably, the two-crane lifting further includes an electric rotating device.

[0016] More preferably, the electric rotating device includes a driving mechanism, a transmission mechanism, a supporting mechanism, and a lifting member. The driving mechanism is a mechanical driving structure that provides rotational motion. The transmission mechanism is a structure that transmits the rotational motion to the lifting member. The lifting member is a fork-shaped member or a hook head.

[0017] The supporting mechanism includes two seat plates with central holes, a cross beam erected in the central holes of the two seat plates. The cross beam is fixedly connected to the lower end of a thrust bearing. The upper end of the thrust bearing is fixedly connected with a locking nut. The upper part of the lifting member passes through the cross beam, the thrust bearing, and the locking nut from bottom to top, and a thrust key is arranged between the locking nut and the lifting member.

[0018] Even more preferably, the structure of the thrust key is as follows: corresponding thrust grooves are opened on the upper surfaces of the locking nut and the lifting member respectively. A thrust plate is embedded in the two thrust grooves, and the thrust plate is fixedly connected to the locking nut and the lifting member through bolts.

[0019] Even more preferably, grooves are opened on the parts of the cross beam on both sides that penetrate outside the two seat plates. Two symmetrically arranged stop pieces are respectively connected to the outside of the two seat plates through bolts, and each stop piece has a part that is stuck into the groove.

[0020] Even more preferably, the transmission mechanism is a coupling combination, including a universal coupling.

[0021] Even more preferably, the transmission mechanism is fixedly connected to the top of the lifting member or the locking nut.

[0022] More preferably, the driving mechanism is a motor and a speed reducer connected in transmission, and the output shaft of the speed reducer is connected to the transmission mechanism.

[0023] More preferably, the box girder is provided with a first through hole penetrating from top to bottom and a second through hole penetrating from front to back. The driving mechanism is arranged above the box girder. The transmission mechanism and the lifting member extend downward through the first through hole, and the two seat plates of the supporting mechanism are respectively embedded in the second through holes on the front and rear sides of the box girder.

[0024] Further preferably, a horizontal pointer mechanism is arranged on the front end face and / or the rear end face of the box girder.

[0025] Compared with the prior art, the beneficial effects of the present utility model are as follows:

[0026] Through the design of the automatic hook-on and hook-off device, the present utility model is suitable for application in double-crane lifting. When the crane hook is lowered, translated, and lifted, the automatic hooking or unhooking operation between the hook and the hook-on and hook-off device can be realized, replacing the traditional manual hook-on and hook-off, reducing the labor intensity of the operators and improving the safety at the same time.

[0027] The present utility model also realizes the electric control rotation of the double-crane lifting through the structural design of the driving mechanism, the transmission mechanism, the supporting mechanism, and the fork-shaped member or the hook head. The driving mechanism provides rotational power, the transmission mechanism transmits rotation, and drives the fork-shaped member or the hook head to realize electric control rotation. And through the design of the supporting mechanism, the fork-shaped member or the hook head is supported for bearing, and with the cooperation of the thrust bearing and the thrust key, the electric rotation device can be stably supported in the box girder, and the transmission mechanism can smoothly drive the fork-shaped member or the hook head to rotate. That is, by controlling the start and stop of the motor, the electric control realizes the rotation of the lifting object mounted on the fork-shaped member or the hook head at the angle required for work. Description of the Drawings

[0028] Figure 1 Is a three-dimensional view of Embodiment 1 of the electric rotation device of the present utility model;

[0029] Figure 2 Is a three-dimensional schematic diagram of the electric rotation device of the present utility model applied in a double-crane lifting equipment;

[0030] Figure 3 In the present utility model Figure 1 Is an enlarged view of part A;

[0031] Figure 4 Is an exploded view of Embodiment 1 of the electric rotation device of the present utility model;

[0032] Figure 5Stereogram of the automatic hook hanging and detaching device in Embodiment 2 of the present utility model applied to a double-crane lifting device;

[0033] Figure 6 of the present utility model Figure 5 Exploded view of part of the automatic hook hanging and detaching device in;

[0034] Figure 7 In the present utility model Figure 6 Enlarged view of part B in.

[0035] In the figure: 1, box girder; 2, lifting lug plate; 3, motor; 4, speed reducer; 5, machine base; 6, fork-shaped part; 61, pin shaft; 7, rigid coupling; 8, telescopic universal coupling; 9, cross beam; 91, groove; 10, seat plate; 11, stop piece; 12, thrust bearing; 13, lock nut; 14, thrust key; 141, thrust groove; 142, thrust plate; 15, pointer; 16, indicating plate; 17, positioning hole; 18, hanging shaft; 19, vertical plate; 20, connecting hole; 21, sliding groove hole; 22, first connecting shaft; 23, second connecting shaft. Specific embodiments

[0036] Next, the technical solutions in the embodiments of the present utility model will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present utility model. Obviously, the described embodiments are only a part of the embodiments of the present utility model, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present utility model without creative efforts shall fall within the protection scope of the present utility model.

[0037] It should be noted that in the description of the present utility model, the orientation or positional relationship indicated by the terms "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the accompanying drawings. It is only for the convenience of describing the present utility model and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. The "first", "second" and similar terms used in the description of the present utility model do not represent any order, quantity or importance, but are only used to distinguish different components, and therefore cannot be construed as a limitation to the present utility model.

[0038] In addition, it should be understood that for the convenience of description, the dimensions of the various components shown in the accompanying drawings are not drawn in actual proportional relationship. For example, the thickness or width of some layers may be exaggerated relative to other layers.

[0039] It should be noted that like reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined or described in one drawing, it will not require further detailed discussion and description in the description of the subsequent drawings.

[0040] Example 1

[0041] Figure 1 It is a three-dimensional diagram of the electric rotating device of the utility model.

[0042] The electric rotating device includes a driving mechanism, a transmission mechanism, a supporting mechanism and a fork 6. The driving mechanism is a mechanical driving structure that provides rotational motion, the transmission mechanism is a structure that transmits the rotational motion to the fork 6, and the supporting mechanism is a structure that the electric rotating device is installed on the hanging beam in actual application. When in use, the hanging object is hung on the fork 6, and the driving mechanism drives the hanging object to rotate, so that the hanging object rotates to a required angle.

[0043] In this embodiment, the electric rotating device is used in a double-machine lifting device as an example. Figures 1 to 4 As shown, specifically:

[0044] The twin-machine lifting equipment includes a box beam 1 with a hollow interior, and hook-and-unhook devices arranged at both sides of the upper end surface of the box beam 1, a common one being a lifting ear plate 2 as shown in the figure, which is used to connect the hook of the crane.

[0045] The box beam 1 is provided with a first through hole penetrating from top to bottom.

[0046] The driving mechanism uses a motor 3 and a reducer 4 in transmission connection, which are arranged above the box beam 1 and are installed on the upper end surface of the box beam 1 using a machine base 5. Of course, the mounting base of the reducer 4 can also be directly installed on the upper end surface of the box beam 1. In this embodiment, the machine base 5 is selected for installation, that is, the output shaft of the reducer 4 extends into the inside of the machine base 5, which can reduce the height of the box beam 1, partially raise the box beam 1 using the machine base 5, support the driving mechanism, and protect the transmission mechanism exposed above the box beam 1.

[0047] One end of the transmission mechanism is connected to the output shaft of the reducer 4, and the other end extends into the first through hole of the box beam 1 to connect to the top of the fork 6. The lower part of the fork 6 passes through the first through hole of the box beam 1 and is located below the box beam 1. The transmission mechanism includes a rigid coupling 7 and a telescopic universal coupling 8 connected to each other.

[0048] Specifically, the output shaft of the reducer 4 is connected to one end of the rigid coupling 7 , the other end of the rigid coupling 7 is connected to one end of the telescopic universal coupling 8 , and the other end of the telescopic universal coupling 8 is connected to the fork 6 .

[0049] The box girder 1 is provided with a second through hole from front to back, which penetrates the front end face and the rear end face of the box girder 1, and a seat plate 10 with a central hole is embedded at the second through hole. In this embodiment, two seat plates 10 are respectively connected to the front end face and the rear end face of the box girder 1 by bolts.

[0050] The support mechanism includes a cross beam 9, which is erected in the central holes of the two seat plates 10. Grooves 91 are provided on the parts of both sides of the cross beam 9 that penetrate outside the two seat plates 10. On the outside of each of the two seat plates 10, two symmetrically arranged stop pieces 11 are connected by bolts, and a part of each stop piece 11 is stuck into the groove 91 to limit the displacement of the cross beam 9. In this embodiment, the two seat plates 10 are flange plates.

[0051] A thrust bearing 12 is arranged above the cross beam 9. The lower end face of the thrust bearing 12 is fixed to the upper end face of the cross beam 9, and a locking nut 13 is fixedly connected to the upper end face of the thrust bearing 12. When rotating, the locking nut 13 drives the upper end face of the thrust bearing 12 to rotate, while the cross beam 9 does not rotate.

[0052] The upper part of the fork-shaped member 6 sequentially passes through the cross beam 9, the thrust bearing 12 and the locking nut 13 from bottom to top, and a thrust key 14 is arranged between the locking nut 13 and the fork-shaped member 6 to support the fork-shaped member 6 by the locking nut 13, that is, the weight of the lifted object is borne by the cross beam 9.

[0053] The setting method of the thrust key 14 in this embodiment is as follows: Corresponding thrust grooves 141 are provided on the upper surfaces of the locking nut 13 and the fork-shaped member 6 respectively. A thrust plate 142 is embedded in the thrust groove 141, and the thrust plate 142 is fixedly connected to the locking nut 13 and the fork-shaped member 6 by bolts. The other end of the telescopic universal coupling 8 is connected to the top of the fork-shaped member 6 (in actual implementation, the other end of the telescopic universal coupling 8 can also be connected to the locking nut 13). In this way, when the motor 3 is started, the coupling unit transmits the rotary motion to the locking nut 13 through the thrust key 14, and the locking nut 13 drives the fork-shaped member 6 to rotate.

[0054] A pin shaft 61 is arranged at the lower end of the fork-shaped member 6, and the pin shaft 61 is used for hanging the lifted object.

[0055] In this embodiment, the rigid coupling 7 is located in the machine base 5, and the central axis of the rigid coupling 7 coincides with the central axis of the machine base 5.

[0056] In this embodiment, a horizontal indicating mechanism is further provided on the box girder 1, specifically:

[0057] A horizontal pointer mechanism is provided on the front end face and / or the rear end face of the box girder 1. The horizontal pointer mechanism includes a pointer 15 and an indicating board 16. The upper part of the pointer 15 is rotatably connected to the front end face and / or the rear end face. Depending on the action of gravity, the arrow always points vertically downward. An indicating board 16 is provided at the position corresponding to the arrow on the front end face. Different states are represented by partitions. When the box girder 1 is balanced, that is, the area of the indicating board 16 corresponding to when the pointer 15 is vertically downward is the balance area. On-site operators can intuitively see whether the box girder 1 is tilted through the cooperation of the pointer 15 and the indicating board 16, and can determine the tilt degree of the box girder 1 through the position of the indicating board 16 pointed by the pointer 15.

[0058] In this embodiment, a cable storage frame and an electric control box are provided on the upper end face of the box girder 1. The cable storage frame is used to place cables, and the electric control box is further controlled through a controller (or remote controller) to control this equipment.

[0059] In this embodiment, the fork-shaped member 6 is described. In actual application, the fork-shaped member 6 can also be replaced by a hook head. The structure of the tail of the hook head can be designed as the top of the fork-shaped member 6 to achieve the same effect. An electric rotary hook head can also be used as an electric rotary device in double-crane lifting.

[0060] Embodiment 2

[0061] This specific implementation manner also provides an automatic hook-on and hook-off device, which can be applied to double-crane lifting equipment. The following introduces the automatic hook-on and hook-off device of the double-crane lifting equipment applied to the above-mentioned electric rotary device, that is, as Figures 5 - 6 shown, changing the ordinary hook-on and hook-off used in the previous Embodiment 1 into a new style. An automatic hook-on and hook-off device is provided on the lifting lug plate 2 for connecting the crane hook.

[0062] At least two positioning holes 17 are provided on the lifting lug plate 2, preferably several positioning holes 17 are arranged in the horizontal direction.

[0063] The automatic hook-on and hook-off device includes two vertical plates 19 provided on the front and rear sides of the lifting lug plate 2 and a hanging shaft 18 connected to the upper parts of the two vertical plates 19 for hanging the hook, etc.

[0064] A connecting hole 20 and a sliding groove hole 21 are symmetrically provided at the lower parts of the two vertical plates 19. The sliding groove hole 21 is an arc groove, and the center of the arc is the center of the connecting hole 20, and the radius is the same as the distance between the two positioning holes 17.

[0065] The first connecting shaft 22 passes through the connecting hole 20 of a vertical plate 19, a positioning hole 17 of the lifting lug plate 2, and the connecting hole 20 of the other vertical plate 19 in sequence from one side. The second connecting shaft 23 passes through the sliding groove hole 21 of a vertical plate 19, another positioning hole 17 of the lifting lug plate 2, and the sliding groove hole 21 of the other vertical plate 19 in sequence from one side. In this embodiment, the two connecting shafts selected are bolts and nuts, that is, the bolt passes through the corresponding holes in sequence and is tightened and fixed with nuts.

[0066] When the electric rotating device is lowered and not under force, the vertical plate 19 of the automatic hook hanging and releasing device slides downward, the second connecting shaft 23 abuts against the top surface of the sliding groove, and the vertical plate 19 is in an inclined state, so that automatic unhooking can be realized. This is the initial state of the vertical plate 19. A hook pin shaft is provided between the upper ends of the two vertical plates 19.

[0067] In this way, when there is no hook lifting the automatic hook hanging and releasing device, the two vertical plates 19 are in a lowered state, that is, the second connecting shaft 23 is located at the upper position of the sliding groove hole 21; when the hook is lowered to the horizontal lower position of the hanging shaft 18, control the hook to translate so that the hook tip hooks into the hanging shaft 18, and then lift the hook. In this way, the hook hooks the hanging shaft 18 and pulls up the two vertical plates 19. In this way, the lower part of the second connecting shaft 23 abuts against the upper part of the sliding groove hole 21. In this way, only the lowering, horizontal translation, and vertical lifting of the hook in the vertical direction are required to realize automatic hooking. Similarly, reverse operation can realize automatic hook hanging and releasing.

[0068] In this embodiment, it can be seen that the connecting hole 20 is located inside, the sliding groove hole 21 is located outside, and the two positioning holes 17 on the lifting lug plate 2 are arranged horizontally. With such an arrangement, when there is no hook hanging on the hanging shaft 18, the vertical plate 19 is in a state of inclining outward, which is beneficial for the hook to automatically hook the hanging shaft 18 from the outside.

[0069] It should be noted that in actual implementation, the automatic hook hanging and releasing device can be arranged in reverse, that is, the connecting hole 20 is located outside and the sliding groove hole 21 is located inside. In this way, in the unhooking state, the vertical plate 19 is in an inclined state inward, and when lifted, the vertical plate 19 rotates outward until the second connecting shaft 23 abuts against the lower part of the sliding groove hole 21.

[0070] It should be noted that when the hook hooks into the hanging shaft 18, it can translate from the outside to the inside or from the inside to the outside.

[0071] It should be noted that, when viewed from the front or the rear, the centers of the hanging shaft 18, the connecting hole 20, and the second connecting shaft 23 preferably form an acute / right triangle structure. In this embodiment, it is an approximate right triangle structure. When lifting, the line connecting the centers of the hanging shaft 18 and the second connecting shaft 23 is a right side. In this way, the pulling force of the lifting hook, the automatic hook-on / hook-off device, and the pulling force of the lower fork-shaped member 6 are in the same direction. Of course, an isosceles triangle can also be formed among the three. The upper two sides are the isosceles sides. In this way, the pulling force of the lifting hook can be evenly distributed to the lower first connecting shaft 22 and the second connecting shaft 23.

[0072] Combined with the above embodiments of the present invention, during the working process of the electric rotating device, the lifting hooks of two cranes are respectively hung on the automatic hook-on / hook-off devices on both sides of the upper end surface of the box girder 1. The lifted object is hung at the fork-shaped member 6. The box girder 1 is lifted by the two cranes, that is, the lifted object is lifted. The reducer 4 is driven to rotate by the motor, the rigid coupling 7 is driven to rotate by the reducer 4, the telescopic universal coupling 8 is driven to rotate by the rigid coupling 7, the fork-shaped member 6 is driven to rotate by the telescopic universal coupling 8, and the lifted object is driven to rotate by the fork-shaped member 6 for angle adjustment until the correct position, and then the two cranes lower the lifted object.

[0073] Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principle and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. An automatic hook-on and hook-off device, characterized in that, The device includes a lug plate provided with at least two positioning holes, two vertical plates arranged on the front and rear sides of the lug plate, and a hanging shaft connected to the upper parts of the two vertical plates; Two connecting holes and chute holes are symmetrically arranged at the lower parts of the two vertical plates. The chute holes are arc-shaped grooves, the center of the arc-shaped groove is the center of the connecting hole, and the radius is the same as the distance between the two positioning holes; The first connecting shaft sequentially penetrates the connecting hole of one vertical plate, a positioning hole of the lug plate, and the connecting hole of the other vertical plate from one side, and the second connecting shaft sequentially penetrates the chute hole of one vertical plate, the other positioning hole of the lug plate, and the chute hole of the other vertical plate from one side.

2. The automatic hook-on and hook-off device according to claim 1, wherein, The positioning holes are arranged in the horizontal direction.

3. The automatic hook-on / hook-off device according to claim 1, wherein The centers of the hanging shaft, the connecting hole, and the second connecting shaft form a non-obtuse triangle structure.

4. The automatic hook-on and hook-off device according to claim 3, characterized in that, The centers of the hanging shaft, the connecting hole, and the second connecting shaft form a right triangle structure or an isosceles triangle structure.

5. The automatic hook-on and hook-off device according to claim 1, characterized in that, The first connecting shaft and the second connecting shaft are bolts and nuts.

6. A two-crane hoisting method, characterized in that, An automatic hanging and decoupling device according to any one of claims 1 to 5 is included.

7. The twin-crane lifting according to claim 6, wherein, The double-crane lifting also includes a box girder, and the automatic hanging and decoupling device is arranged at both sides of the upper end surface of the box girder.

8. The twin-crane lifting according to claim 6, characterized in that, The double-crane lifting also includes an electric rotating device. The electric rotating device includes a driving mechanism, a transmission mechanism, a supporting mechanism, and a lifting member. The driving mechanism is a mechanical driving structure that provides rotational motion. The transmission mechanism is a structure that transmits rotational motion to the lifting member. The lifting member is a fork-shaped member or a hook head; The supporting mechanism includes two seat plates with central holes, a cross beam installed in the central holes of the two seat plates. The cross beam is fixedly connected to the lower end of a thrust bearing. The upper end of the thrust bearing is fixedly connected with a locking nut. The upper part of the lifting member sequentially passes through the cross beam, the thrust bearing, and the locking nut from bottom to top, and a thrust key is arranged between the locking nut and the lifting member.

9. The twin-crane lifting according to claim 8, wherein, The electric rotating device also has one or more of the following technical features: A. The structure of the thrust key is that corresponding thrust grooves are opened on the upper surfaces of the locking nut and the lifting member respectively. A thrust plate is embedded in the two thrust grooves, and the thrust plate is fixedly connected to the locking nut and the lifting member through bolts; B. Grooves are opened on the parts of the two sides of the cross beam that penetrate outside the two seat plates. Two symmetrically arranged stop pieces are respectively connected to the outside of the two seat plates through bolts, and each stop piece has a part stuck in the groove; C. The transmission mechanism is a coupling combination, including a universal coupling; D. The transmission mechanism is fixedly connected to the top of the lifting member or the locking nut; E. The driving mechanism is a motor and a reducer connected in transmission, and the output shaft of the reducer is connected to the transmission mechanism.

10. The twin-crane lifting according to claim 8, wherein, The double-crane lifting also includes a box girder, the automatic hook hanging and disengaging device is arranged on both sides of the upper end surface of the box girder, the box girder is provided with a first through hole penetrating from top to bottom and a second through hole penetrating from front to back, the driving mechanism is arranged above the box girder, the transmission mechanism and the lifting member extend downward through the first through hole, and the two seat plates of the support mechanism are respectively embedded in the second through holes on the front and rear sides of the box girder.

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