Steel spring floating slab track structure

Abstract

The utility model discloses a steel spring floating slab track structure which comprises a base, a plurality of floating slab units are arranged at the top of the base and connected end to end, and each floating slab unit comprises floating slab end plates located at the two ends and a floating slab middle plate located between the two floating slab end plates. A wet joint is arranged between the floating slab end plate and the floating slab middle plate, and the end faces, facing the wet joint, of the floating slab end plate and the floating slab middle plate are designed to be concave and rough. The floating slab end plates and the floating slab middle plates are longitudinally connected through the wet joints to form the floating slab units, the adjacent floating slab units are connected through the second connecting pieces and the square shared vibration isolators, smoothness and coordination of adjacent slab bodies are effectively guaranteed, driving safety and stability are greatly improved, and the service life of the floating slab units is prolonged. And the service life of rail structure components such as the plate end fastener, the second connecting piece and the like is ensured.

Description

TECHNICAL FIELD

[0001] The utility model relates to the field of urban rail transit railway track structure, especially a steel spring floating slab track structure. BACKGROUND

[0002] The vibration reduction design of urban rail transit engineering is very crucial for improving ride comfort, reducing vibration and noise pollution, and protecting surrounding buildings and urban infrastructure. Effective vibration reduction design not only prolongs the service life of the track system, but also reduces maintenance costs and improves the overall performance of urban rail transit. Generally, the vibration reduction level is divided into three levels of medium vibration reduction, high vibration reduction and special vibration reduction according to the prediction of the environmental impact assessment. Among them, the special vibration reduction measure adopts a steel spring floating slab vibration reduction track with superior performance.

[0003] Currently, urban rail transit steel spring floating slabs generally use cast-in-place or prefabricated construction technology. The cast-in-place floating slab has complex structure, slow construction progress, large amount of on-site concrete pouring, difficult concrete cast-in-place quality control, high labor intensity, poor working environment, many cracks in the cast-in-place bed and difficult to control, difficult maintenance and many other disadvantages. Although the prefabricated floating slab greatly improves the quality of the slab and improves the construction speed, due to the limitation of tunnel construction space and lifting transportation, the length of the prefabricated floating slab unit is generally 3.6-6m, which is shorter than the 15-25m of the cast-in-place floating slab. The shorter length and smaller vibration mass reduce the vibration reduction effect. At the same time, the number of connecting hinges between the slabs is greatly increased, making the adjacent slab stiffness discontinuous. When the deformation difference is too large, the rail and the slab end fastener will bear a large stress, resulting in poor driving safety and stability, poor vibration reduction effect, short service life of the track structure, high maintenance cost and many other disadvantages.

[0004] There are some related patents on floating slab track structure in the field of urban rail transit. Patent CN203475237U discloses a lap joint type floating bed, in which the vertical load of the train is transmitted through the overhanging lap joint between the two adjacent floating slabs. The lap joint is fixed by bolts with upper and lower through holes. Under the action of a large train load, the bolts are prone to fatigue failure, which poses a safety hazard to driving. Patent CN113215863A discloses a prefabricated floating slab track structure and a limiting device. In this scheme, the adjacent floating slabs are fixed by the wave-shaped joints at the ends of the floating slabs. The limiting ability of the slab end is weak, which affects the driving safety and stability, and the adaptability to curved sections is poor.

[0005] Due to the existing floating slab track structure, the cast-in-place floating slab has the problems of slow construction progress, difficult engineering quality control, many cracks in the cast-in-place bed and difficult maintenance, and the precast floating slab can make up for the problems of the cast-in-place floating slab, but the stiffness of adjacent plates is discontinuous, the driving safety is poor, the vibration reduction effect is poor, and the service life of the track structure is short. Content of the utility model

[0006] In order to improve the problems of slow construction progress, difficult engineering quality control, many cracks in the cast-in-place bed and difficult maintenance of the cast-in-place floating slab, and the problems of discontinuous stiffness of adjacent plates, poor driving safety, poor vibration reduction effect and short service life of the track structure of the precast floating slab, the utility model provides a steel spring floating slab track structure.

[0007] The steel spring floating slab track structure provided by the utility model adopts the following technical scheme:

[0008] A steel spring floating slab track structure, comprising a base, a plurality of floating slab units are arranged on the top of the base, the plurality of floating slab units are connected end to end, each floating slab unit comprises floating slab end plates at both ends and a floating slab middle plate between the two floating slab end plates, a wet joint is arranged between the floating slab end plates and the floating slab middle plate, and the end faces of the floating slab end plates and the floating slab middle plate towards the wet joint are designed as concave rough surfaces.

[0009] Further, the end faces of the floating slab end plates and the floating slab middle plate towards the wet joint are fixedly connected with first connecting pieces for ensuring successful lapping of the floating slab end plates and the floating slab middle plate.

[0010] Further, the first connecting pieces comprise exposed steel bars, and the exposed steel bars are arranged in an interlaced complementary mode of long steel bars and short steel bars.

[0011] Further, a plate joint is arranged between every two floating slab units, and every two floating slab units are connected through square shared vibration isolators and second connecting pieces.

[0012] Further, the floating slab end plates and the floating slab middle plate are both pre-buried with RFID chips.

[0013] Further, inspection holes are arranged at the centers of the connecting ends of the floating slab end plates and the floating slab middle plate, and inspection cover plates are arranged above the inspection holes.

[0014] Further, lifting sleeve pipes are pre-buried in the side faces of the floating slab end plates and the floating slab middle plate.

[0015] Further, circular vibration isolators are arranged on the two sides of the floating slab end plates and the floating slab middle plate.

[0016] Further, the floating plate end plate and the floating plate middle plate are further embedded with sealing strip mounting sleeves on both sides, and the sealing strip mounting sleeves are located outside the circular vibration isolator.

[0017] Further, the floating plate unit is provided with grounding terminals at one end close to the plate joint, and two adjacent grounding terminals are connected through connecting steel cables.

[0018] In summary, the utility model has at least one of the following beneficial technical effects:

[0019] 1. The utility model minimizes the weak link of the plate joint and the number of shear hinges as the principle, and the floating plate end plate and the floating plate middle plate are connected longitudinally through wet joints to form a floating plate unit, and adjacent floating plate units are connected through shear hinges and square shared vibration isolators, which effectively ensures the smoothness and coordination of adjacent plate bodies, greatly improves the driving safety and stability, and ensures the service life of the plate end fastener shear hinge and other track structure components. The plate end of the floating plate end plate and the floating plate middle plate is provided with an inspection hole, which reduces the weight of the track structure to some extent, saves the engineering cost, is mainly used for checking whether there is foreign matter in the floating plate and the central ditch, and the plate body is provided with an inspection cover plate mounting space to ensure the flatness of the plate surface and facilitate subsequent inspection by the maintenance personnel.

[0020] 2. The floating plate of the utility model is a factory prefabricated structure, which is more convenient for production, manufacturing, stacking, transportation and on-site assembly, and an RFID chip is embedded during factory prefabrication, the chip contains track manufacturing information, line mileage information and the like, and information management of the floating plate track can be realized.

[0021] 3. The utility model adopts prefabricated floating short plate assembly to form a long plate type, a plurality of short plates are connected into an assembly type floating plate unit through cast-in-place wet joints, the vibration mass is increased, the overall vibration reduction effect of the floating plate system is improved, and compared with other cast-in-place floating plate structures, the construction efficiency and engineering quality are better under the same vibration reduction effect.

[0022] 4. The joint end face of the floating plate end plate and the floating plate middle plate is designed with a careful concave section and rough interface, which strengthens the mechanical interlocking force of the section and the bonding force between the new and old concrete. This design not only improves the bending resistance of the wet joint position, but also effectively enhances the overall stability of the floating plate unit structure, ensures the safety and durability of the structure. The rough treatment of the joint interface can be achieved by the slow-setting water flushing method or the chiseling method. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a schematic diagram of the overall structure of the steel spring floating plate track structure of the utility model embodiment;

[0024] Figure 2 is an exploded view of the steel spring floating plate track structure of the utility model embodiment.

[0025] Figure 3 is a floating plate end plate schematic view of the steel spring floating plate track structure of the embodiment of the utility model;

[0026] Figure 4 is a floating plate middle plate schematic view of the steel spring floating plate track structure of the embodiment of the utility model;

[0027] Figure 5 is a plate joint place side surface structure schematic view of the steel spring floating plate track structure of the embodiment of the utility model;

[0028] Figure 6 is a wet joint place exposed reinforcing bar schematic view of the steel spring floating plate track structure of the embodiment of the utility model;

[0029] Figure 7 is a plate joint place front surface structure schematic view of the steel spring floating plate track structure of the embodiment of the utility model;

[0030] Figure 8 is a steel spring floating plate track structure and ordinary integral track bed transition section schematic view of the embodiment of the utility model;

[0031] Figure 9 is a steel spring floating plate track structure and medium damping track bed transition section schematic view of the embodiment of the utility model;

[0032] Figure 10 is a steel spring floating plate track structure and high damping track bed transition section schematic view of the embodiment of the utility model.

[0033] Reference signs: 1, rail; 2, fastener; 3, rail bearing platform; 4, floating plate end plate; 5, floating plate middle plate; 6, exposed reinforcing bar; 7, wet joint; 8, round vibration isolator; 9, upper shear hinge; 10, square shared vibration isolator; 11, inspection cover plate; 12, hoisting sleeve; 13, sealing strip mounting sleeve; 14, grounding terminal; 15, connecting steel cable; 16, base. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical scheme and advantages of the utility model more clearly, the following will be further described in detail by combining with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the utility model, and are not used to limit the utility model. In addition, the technical features involved in each embodiment of the utility model described below can be combined with each other as long as they do not conflict with each other.

[0035] In the description of the utility model, it is understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the utility model and simplifying the description, and therefore cannot be understood as indicating or implying that the devices or elements indicated must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the utility model.

[0036] In addition, the terms "first" and "second" are only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features.

[0037] In the utility model, unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connecting", "fixing" and the like should be understood in a broad sense, for example, can be fixedly connected, or can be detachably connected, or can be integrated; can be mechanically connected, or can be electrically connected; can be directly connected, or can be indirectly connected through an intermediate medium; can be the internal communication of two elements or the interaction relationship of two elements, unless otherwise explicitly limited. For ordinary skilled persons in the art, the specific meaning of the above terms in the utility model can be understood according to the specific circumstances.

[0038] In the utility model, unless otherwise explicitly specified and limited, the first feature "on" or "under" the second feature can be that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, the first feature "above", "over" and "on" the second feature can be that the first feature is directly above or obliquely above the second feature, or only indicates that the horizontal height of the first feature is higher than that of the second feature. The first feature "under", "below" and "under" the second feature can be that the first feature is directly below or obliquely below the second feature, or only indicates that the horizontal height of the first feature is less than that of the second feature.

[0039] The following will be described in detail with reference to the accompanying drawings Figures 1-10 The utility model will be further described in detail.

[0040] The utility model embodiment discloses a steel spring floating slab track structure. Figures 1-10, the steel spring floating slab track structure mainly comprises a rail 1, a fastener 2, a rail bearing platform 3, a floating slab end plate 4, a floating slab middle plate 5, exposed steel bars 6, a wet joint 7, a circular vibration isolator 8, a second connecting piece, a square shared vibration isolator 10, an inspection cover plate 11, a hoisting sleeve 12, a sealing strip mounting sleeve 13, a grounding terminal 14, a connecting steel cable 15, a base 16 and the like. The base 16 is provided with a plurality of floating slab units at the top, the floating slab units are connected in a head-to-tail manner, each floating slab unit comprises the floating slab end plates 4 at two ends and the floating slab middle plate 5 between the two floating slab end plates 4, the wet joint 7 is arranged between the floating slab end plates 4 and the floating slab middle plate 5, and the end faces of the floating slab end plates 4 and the floating slab middle plate 5 towards the wet joint 7 are designed as concave rough surfaces, which can increase the mechanical interlocking force of the cross section, the bonding force of the new and old concrete and ensure the bending resistance of the position of the wet joint 7. The rough treatment of the joint interface can adopt a retarding water flushing method or a chiseling method.

[0041] Further, the end faces of the floating slab end plates 4 and the floating slab middle plate 5 towards the wet joint 7 are fixed with the first connecting piece, the first connecting piece comprises the exposed steel bars 6, and the exposed steel bars 6 adopt long-short steel bar staggered complementary arrangement. A plate joint is arranged between every two floating slab units, and every two floating slab units are connected through the square shared vibration isolator 10 and the second connecting piece, and the second connecting piece is an upper shear hinge 9. The floating slab end plates 4 and the floating slab middle plate 5 are arranged with two layers of ordinary steel bars in an up-down manner, and the steel bars are arranged in a reinforcing manner at the circular vibration isolator 8, the longitudinal bars in the plate are inclined at a certain angle and exposed to form the long-short staggered exposed steel bars 6, so as to ensure the successful complementary lapping of the two short plate units. The exposed steel bars 6 at the wet joint 7 adopt the long-short steel bar staggered complementary arrangement as a preferred scheme, in addition to which sleeve connection, tension locking piece connection and the like can also be adopted.

[0042] In specific implementation, the floating slab end plate 4 is 3445mm long, 2600mm wide and 340mm high, the side close to the plate joint is reserved with an upper shear hinge 9 interface, a square shared vibration isolator 10 interface and an inspection cover plate 11 mounting interface, the other side is reserved with an inspection cover plate 11 mounting interface and staggered exposed steel bars 6 at the wet joint 7 end, wherein the plate joint end is provided with square shared vibration isolator 10 mounting spaces which are symmetrical along the center line of the line, and the specific size is 270mm long, 350mm wide and 100mm high; the middle plate 5 is 3320mm long, 2600mm wide and 340mm high, and the two sides of the plate are reserved with an inspection cover plate 11 mounting interface and staggered exposed steel bars 6, and the floating slab end plate 4 and the floating slab middle plate 5 are transported to the construction site for installation and laying after being prefabricated in the factory.

[0043] More specifically, since the track in urban rail transit often adopts direct current, it is easy to cause direct current leakage and electrochemical corrosion. In order to meet the insulation performance requirements of urban rail transit, the floating slab structure with bearing rail platform 3 type is adopted, and eight pairs of bearing rail platforms 3 are arranged on the floating slab end plate 4 and the floating slab middle plate 5. The fastener 2 adopts the type of fastener corresponding to the floating slab end plate 4 and the floating slab middle plate 5, and the fastener spacing is 600mm. In a floating slab unit, the wet joint 7 between the adjacent floating slab end plate 4 and the floating slab middle plate 5 is 280mm wide, and UHPC ultra-high performance concrete is used as the pouring material, and the concrete grade is C80.

[0044] Further, the floating slab end plate 4 and the floating slab middle plate 5 are pre-buried with RFID chips, which contain track manufacturing information, line mileage information, etc., and can realize the informatization management of the floating slab track.

[0045] Further, the floating slab end plate 4 and the floating slab middle plate 5 are provided with an inner sleeve of a built-in circular vibration isolator 8, the longitudinal arrangement spacing of the circular vibration isolator 8 is twice the fastener 2 spacing 1200mm, the transverse arrangement spacing is 1860mm, a total of three pairs are arranged, and the whole is located on the outside of the steel rail 1, facilitating later maintenance and repair. The floating slab unit is provided with a 30mm plate joint, and is connected through a square shared vibration isolator 10 and an upper shear hinge 9, so that the "broken" stiffness is continuous, ensuring the smooth and coordinated deformation of adjacent long plate units, effectively improving the driving safety and stability, and further ensuring the overall stability of the structure through the connection of the floating slab end plate 4 and the floating slab middle plate 5 by the wet joint 7, and meeting the special damping requirements of rail transit.

[0046] Further, the upper shear hinge 9 between the floating slab units is connected to the plate body through six anchor bolts, mainly arranged on the upper plate surface outside the steel rail 1, and the key structure of the shear hinge is exposed and visible, improving the intuitiveness and operability of maintenance and monitoring, which is beneficial to the timely and effective maintenance of the engineering department.

[0047] Further, the floating slab end plate 4 and the floating slab middle plate 5 are provided with inspection holes at the ends, which facilitate the engineering department to check whether there are foreign matters in the floating slab and the central water channel to affect the damping effect of the floating slab system, and the plate body is provided with an installation space for an inspection cover plate 11, and the inspection cover plate 11 is installed, with specific dimensions of 710mm in length, 380mm in width and 20mm in height, which can ensure the flatness of the inspection cover plate 11 and facilitate the walking of the engineering inspection personnel. The inner wall of the inspection hole is provided with a lateral shear hinge installation condition along the longitudinal direction of the line, and the integrity of the joint position is improved by installing a shear hinge on the side wall of the inspection hole.

[0048] Further, the floating slab end plate 4 and the floating slab middle plate 5 are provided with lifting sleeve pipes 12 pre-buried on the side for subsequent construction and adjustment; and sealing strip installation sleeves 13 are pre-buried on the side of the plate for facilitating the subsequent construction and installation of the sealing strip.

[0049] Further, the track overall structure adopts a floating slab unit long plate structure type, a plate joint is arranged between adjacent floating slab units, the grounding terminal 14 is arranged at the plate joint position of the adjacent floating slab units, one grounding terminal 14 is arranged on each of the left and right sides of the plate joint, and the two adjacent grounding terminals 14 are connected through the connecting steel cable 15. The urban rail transit track pipeline can pass through the plate joint / plate for track passing, the track passing in the plate avoids the outer sleeve of the circular vibration isolator 8 and is arranged in the middle of the two rail supporting tables 3. The track system drainage can be longitudinally drained through the central water channel of the base 16.

[0050] The construction of the utility model comprises the following steps: step one, construction preparation: the construction preparation work comprises internal and external preparation. The internal preparation mainly comprises checking construction drawings, communicating and answering questions in the drawings and design, calculating and checking construction materials and auxiliary materials, technical disclosure and the like; the external preparation comprises handing over and cleaning the operation site, arranging water and electricity for construction, determining a material transportation scheme, measuring and setting a track measurement network and the like; gantry crane running track laying: 24kg / m steel rails are used as running tracks, the running tracks are fixed on the bottom or side wall of the civil structure by using specially-made height-adjustable steel piers; first, the steel pier bottom plate is fixed on the tunnel bottom plate, then the height of the steel pier is adjusted to a determined position, and the upper plate of the steel pier is fastened and connected with the running track by using bolts;

[0051] Step two, steel bar binding of the floating slab base 16: the steel bars of the base 16 after incoming inspection and processing are discharged through the track row opening and transported to the operation surface, and the steel bar net is bound on site;

[0052] Step three, concrete pouring of the floating slab base 16: first, it is ensured that the formwork is firmly installed and the inside is clean; then, the uniformly mixed concrete according to the proportion is stirred and transported to the pouring site; in the pouring process, the speed is controlled, the concrete is uniformly poured and vibrated to remove air bubbles and excess water; before initial setting, the surface is polished and finished to eliminate unevenness; after pouring is completed, timely maintenance is carried out to keep the concrete wet until the design strength is reached;

[0053] Step four, base 16 re-measurement treatment: after the concrete reaches the specified strength, the base 16 is accurately re-measured in terms of plane position, elevation and levelness by using high-precision measuring instruments, and timely adjustment and treatment are carried out according to the results to ensure that the base is flat and stable and meets the design requirements;

[0054] Step five, prefabricated floating slab production, transportation and laying: the prefabricated floating slab is produced in the factory mainly through a strict process control procedure such as mold preparation, placing vibration isolator outer sleeve, binding steel bar drainage welding, concrete pouring and maintenance, the prefabricated slab is transported to the track laying base, the gantry crane provided by the track laying base hoists the slab from the discharging opening to the flat car, the track car runs to the laying site, and the track laying gantry crane hoists the slab to the operation surface;

[0055] Step six, install the sealing strip: the sealing strip is firmly installed on the floating plate end plate 4 and the floating plate middle plate 5, effectively preventing debris from entering the floating plate during subsequent construction processes;

[0056] Step seven, install the vibration isolator: lift the floating plate, install the square shared vibration isolator 10 and the circular vibration isolator 8, ensure that the vibration isolator is placed in the correct position and direction; use a special hydraulic jack to individually lift each floating plate from the base to the designed height;

[0057] Step eight, erect the wet joint 7 and pour the concrete: accurately set the formwork between the adjacent floating plate end plate 4 and the floating plate middle plate 5, ensure that the position and size of the wet joint 7 are accurate, then pour the concrete, strictly control the quality and pouring speed of the concrete, ensure that the concrete uniformly fills the formwork space, and achieve the designed density and strength;

[0058] Step nine, install the rail 1 fastener 2 and the sealing strip, ensure that the sealing strip is flat, firm and gapless; install the second connecting piece: install the second connecting piece on the adjacent floating plate end plate 4 with bolts, ensure that the installation is firm and reliable; track fine adjustment: adjust the elevation, center line and longitudinal position of the track through the fine adjustment device.

[0059] The utility model discloses a weak link and shear hinge quantity are as the principle of reducing the board joint as far as possible, and the floating plate end plate and the floating plate middle plate are longitudinally connected through the wet joint and form the floating plate unit, and the adjacent floating plate unit is connected through the shear hinge and the square shared vibration isolator, effectively ensure the smoothness and the coordination of the deformation of the adjacent plate body, greatly improve the driving safety and the stability, guarantee the life of the plate end fastener shear hinge and other track structure parts. The plate end of the floating plate end plate and the floating plate middle plate is equipped with an inspection hole, which reduces the weight of the track structure to some extent, saves the engineering cost, is mainly used for the inspection of whether there is foreign matter into the floating plate and the center ditch, and the plate body is equipped with an inspection cover plate installation space, guarantees the flatness of the plate surface, and is convenient for subsequent maintenance personnel to inspect.

[0060] The above are the preferred embodiments of the utility model, and do not limit the protection scope of the utility model, so: all equivalent changes made according to the structure, shape and principle of the utility model should be covered in the protection scope of the utility model.

Claims

1. A steel spring floating slab track structure comprising a subgrade, characterized in that, The base top is provided with a plurality of floating slab units connected end to end, each floating slab unit comprising floating slab end plates at both ends and a floating slab middle plate between the two floating slab end plates, a wet joint being provided between the floating slab end plates and the floating slab middle plate, and the end faces of the floating slab end plates and the floating slab middle plate towards the wet joint being designed as concave and rough surfaces.

2. A steel spring floating slab track structure according to claim 1, characterized in that: First connecting members are fixed to the end faces of the floating slab end plates and the floating slab middle plate towards the wet joint, for ensuring successful lapping of the floating slab end plates and the floating slab middle plate.

3. A steel spring floating slab track structure according to claim 2, characterized in that: The first connecting members comprise exposed steel bars, which are arranged in an interlaced complementary manner with long and short steel bars.

4. A steel spring floating slab track structure according to claim 1, characterized in that: A slab joint is provided between every two floating slab units, and the two floating slab units are connected through square shared vibration isolators and second connecting members.

5. A steel spring floating slab track structure according to claim 1, characterized in that: The floating slab end plates and the floating slab middle plate are both pre-buried with RFID chips.

6. A steel spring floating slab track structure according to claim 1, characterized in that: A check hole is provided at the center of the connecting end of the floating slab end plates and the floating slab middle plate, and a check cover plate is provided above the check hole.

7. A steel spring floating slab track structure as claimed in claim 1, wherein: Hoisting sleeve pipes are pre-buried on the side faces of the floating slab end plates and the floating slab middle plate.

8. A steel spring floating slab track structure according to claim 1, characterized in that: Round vibration isolators are provided on both sides of the floating slab end plates and the floating slab middle plate.

9. A steel spring floating slab track structure according to claim 8, characterized in that: Sealing strip mounting sleeve pipes are also pre-buried on both sides of the floating slab end plates and the floating slab middle plate, and the sealing strip mounting sleeve pipes are located outside the round vibration isolators.

10. A steel spring floating slab track structure according to claim 4, characterized in that: Ground terminals are provided at one end of the floating slab units close to the slab joint, and adjacent two ground terminals are connected through connecting steel cables.

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