Attitude control device and method in unbalanced swivel process of cable-stayed swivel bridge

Abstract

The invention belongs to the technical field of swivel bridge construction, and particularly relates to a posture control device and method in the unbalanced swivel process of a cable-stayed swivel bridge. Comprising a round slide way which is arranged between an upper rotating body and a lower rotating body. The number of the sliding assemblies is eight, the sliding assemblies are evenly arranged on the sliding ways, and each sliding assembly comprises a supporting foot walking plate arranged below the beam body; the sliding steel base plate is arranged in the advancing direction of the bottom of the supporting foot walking plate; and the polyfluortetraethylene plate is arranged between the slide way and the sliding steel base plate. According to the invention, the attitude of the bridge in the turning process can be completely controlled, the problems existing in the conventional operation mode can be overcome, and the stable turning of the bridge can be realized with the minimum cost and the simplest operation mode.

Description

Technical Field

[0001] The invention belongs to the technical field of rotating bridge construction, and in particular relates to a posture control device and method for an unbalanced rotating process of a cable-stayed rotating bridge. Background Art

[0002] The original intention of the design of the rotating bridge is to be able to cross the structure in the shortest time and reduce the impact of the construction process on nearby facilities. The inclination of the bridge during the rotation process must be strictly controlled to ensure the clearance height between the rotating beam section and the existing structure under the bridge. The construction methods commonly used to control the clearance height under the bridge during the rotation process of similar rotating bridges are: ① Control the balance state of the rotating bridge, accurately measure the unbalanced weight of the bridge before the rotation, accurately calculate the counterweight tonnage and counterweight position of the bridge, and use the counterweight to achieve a completely balanced rotation state for the bridge that could have been rotated unbalanced, so as to achieve a smooth rotation of the bridge and avoid tilting. ② Temporarily dismantle the structures under the bridge that may collide due to the tilt of the bridge or lower the height of the structures, increase the clearance height during the rotation process, improve the safety and reliability of the rotation, and prevent the bridge from colliding with the structures under the beam after the bridge deflects once the upper structure tilts during the rotation process. ③ Adjust the tilt direction of the rotating bridge. Before the rotation, the rotating bridge is tilted to the opposite side where the clearance height of the rotation needs to be strictly controlled by using a jack at the bottom of the turntable. In this way, the beam section on the side where the clearance height needs to be controlled is lifted as a whole, and the clearance height of the bridge is effectively guaranteed, avoiding collision with the structure under the beam during the rotation of the bridge. The conventional method is relatively intuitive, and this is also the first method we think of when we need to control the posture of the bridge during the rotation process, but there are also many disadvantages. ① In order to achieve a completely balanced rotation of the bridge, the weight of the counterweight is relatively large, and both loading and unloading are time-consuming and labor-intensive; and although the balance state is achieved in theory, this method cannot be guaranteed 100%. The situation during the rotation process is ever-changing, and it may still tilt due to other reasons during the rotation process. ② If the structure at the bottom of the rotating bridge is removed, it seems to be more effective, but not all structures can be removed, and if the clearance height of the rotation is guaranteed by removing the building, the design intention of the rotating bridge is lost. ③ Adjust the rotating bridge as a whole to the opposite side where the clearance height needs to be strictly controlled by jacking. Past experience shows that this method is feasible to a certain extent, but it also has certain risks. Although the bridge as a whole has been adjusted to the opposite side before the rotation, it may still tilt in the opposite direction due to other reasons during the rotation process. Although the probability is relatively small, this possibility still exists; even if the rotation is successfully completed by adjusting the direction before the rotation, the bridge posture needs to be adjusted by jacking after the rotation. Summary of the invention

[0003] In order to be able to fully control the posture of the bridge during rotation, overcome the disadvantages of conventional operation methods, and achieve smooth rotation of the bridge with minimal cost and simplest operation methods, the present invention provides a posture control device and method for the unbalanced rotation process of a cable-stayed rotating bridge.

[0004] The present invention adopts the following technical scheme: a posture control device for an unbalanced rotation process of a cable-stayed rotating bridge, comprising: The slideway is circular and arranged on the top surface of the lower support platform and connected with the lower support platform as a whole; Sliding components, 8 sliding components are provided, the projection center line of the sliding component coincides with the center line of the slideway, and is connected to the upper turntable as a whole, and the sliding component includes: The support foot is anchored in the upper turntable and rotates with the upper turntable, and the bottom of the support foot is fixed with a support foot walking board; A sliding steel pad, which is arranged at the bottom of the foot support walkway on the elevation side of the rotating beam and is placed on the slideway, and its moving direction is consistent with the rotation direction of the bridge; A polytetrafluoroethylene plate is arranged between the slideway and the sliding steel pad or other support footboards without the sliding steel pad, and is fastened to the forward end of the support footboard.

[0005] In some embodiments, the bottom of the sliding steel pad in the forward direction is cut into a groove, and a stiffening plate is arranged above the forward direction of the sliding steel pad.

[0006] In some embodiments, the total thickness of the sliding steel pad + polytetrafluoroethylene plate is t, t=h×d / L, where the cantilever length of the rotating bridge is L, the distance between the support leg and the center of the rotation is d, and the height of the cantilever beam end needs to be controlled to be h during the rotation process.

[0007] A construction method of a posture control device for an unbalanced rotation process of a cable-stayed rotating bridge, comprising: S1: Prepare for rotation construction; S2: Conduct a trial rotation to detect in real time whether there are any abnormalities in the key stress-bearing parts. If any problems are found, stop the trial rotation in time. Rotation construction can only be carried out after the problems are completely eliminated. S3: Perform formal rotation; S4: After the rotation is completed, the rotation position monitoring and the rotation bridge posture adjustment are carried out.

[0008] Step S1 includes: S11: The construction of the rotating box girder is completed, and the floating objects and easily falling objects on the bridge deck are cleared, and it is confirmed whether the steel bars at the ends of the beams hinder the rotation; S12: Ball joint preparation: remove the sand box, remove the sand box between the upper and lower turntables, clean up all the garbage on the slide, and use high-pressure water to wash to ensure the top surface of the slide is clean; S13: Slide preparation: 1) Slide cleaning: Clean the slide surface and remove rust from the ring steel plate, and use high-pressure air to clean the reserved gap between the slide and the support foot; 2) Slideway inspection: Check the smoothness of the slideway; check the reserved gap between the slideway and the support leg; check the path that the support leg passes through within the rotation range, and perform an appearance inspection on the support leg to see if there is any damage; 3) Install the medium: Place a PTFE slide plate under the support foot with the PTFE side facing down, and apply lubricating oil on the slide to reduce friction.

[0009] Step S2 includes: S21: Release the temporary consolidation of the beam; S22: beam body starts; S23: Turn to 3° during trial run; S24: jog 1°, perform 5 10s jogs, 5 5s jogs, and 5 3s jogs respectively. The measurement personnel measure the arc length displacement of the beam end after each jog and record the relevant data. If the displacement of the beam end is irregular and the discreteness is large after several jogs, perform more jogs; S25: After the inching operation is completed and recorded, the bridge is rotated to a predetermined trial rotation angle of 5 degrees; S26: Temporary consolidation of beam.

[0010] Step S3 includes: S31: Perform horizontal rotation, observe the angle of the rotating body, and report to the on-site person in charge every 5°; when the last 5° is reached, report to the on-site commander every 1°; when the center axis of the two ends of the bridge deck is within 2m before closure, the staff at the monitoring point will start to report the monitoring data to the control console in countdown, reporting every 10cm; within 30cm, report every 1cm; S32: When the rotating structure approaches the designed position, the system "pauses". To prevent the structure from over-rotating, the power system changes from "manual" state to jog operation after the inertial operation ends. Each time the jog operation is performed, the surveyor measures and reports the current status data of the axis once, and the cycle is repeated until the axis of the structure is accurately in place; S33: Positioning. After the swivel is in place, accurately adjust the tilt position of the swivel, and use wedges to wedge and fix between the support walking board and the slideway. Each support walking board is equipped with 4 wedges to prevent the beam from swinging under the action of external force.

[0011] Step S33 also includes: After the rotating body is in place, tighten the iron wedges in the forward direction of the support legs and check whether there are any omissions. After completion, weld and fix them. When over-rotation is found during re-measurement due to rotational inertia or measurement error, the force couple boosting system composed of jacks can be used to push the support legs and the board in the opposite direction to make the rotating body rotate back to the designed position.

[0012] Step S4 includes: S41: Linear measurement, adjustment of lateral inclination, lateral and longitudinal deviation of the axis, locking of the pads between the upper and lower plates, plane positioning, etc., the swivel structure is precisely positioned and the structure is constrained and fixed; S42: Elevation adjustment is carried out by using a jack between the upper and lower platforms. After precise adjustment, the elevation error is controlled within 1 cm. S43: There are 8 pairs of sliding components on the turntable of the swivel. Iron wedges are used to fix the gap between the bottom surface of the welded steel plate at the bottom of the foot support and the 35mm stainless steel plate on the slideway. In addition, the embedded steel bars of the upper and lower turntables are welded to ensure that the structure is precisely positioned without slight deviation. S44: Carry out the sealing concrete pouring construction to complete the turntable structure consolidation in the shortest time. After the turntable is in place, clean the upper surface of the lower turntable, weld the reserved steel bars, and set up the mold to pour the sealing concrete so that the upper turntable and the lower turntable are connected as one.

[0013] Compared with the prior art, the purpose of the present invention is to use a simple tool that can control the posture of the bridge during rotation 100%, overcome the drawbacks of conventional operation methods, and achieve smooth rotation of the bridge with the lowest cost and the simplest operation method. At the same time, this tool is simple to manufacture, low cost, and can be recycled. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a structural schematic diagram of the posture control device during the unbalanced rotation process of the cable-stayed rotating bridge; Figure 2 It is a schematic diagram of the sliding component structure; In the figure, 1- slideway, 2- foot support walking board, 3- sliding steel pad, 4- polytetrafluoroethylene plate. DETAILED DESCRIPTION

[0015] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0016] like Figure 1 ,2 As shown, a posture control device for an unbalanced rotation process of a cable-stayed rotating bridge comprises: The slideway 1 is circular and arranged on the top surface of the lower support platform and connected with the lower support platform as a whole; The sliding assembly, whose projection center line coincides with the center line of the slideway, is connected to the upper turntable as a whole. The sliding assembly includes: Support legs, 8 of which are evenly arranged and anchored in the upper turntable, rotating with the upper turntable; A foot support walking board 2, the foot support walking board is located at the bottom of the foot support and is fixed together with the foot support; A sliding steel pad 3, which is arranged at the bottom of the foot support walkway on the side where the elevation of the rotating beam needs to be strictly controlled, and is placed on the slideway, and its moving direction is consistent with the rotation direction of the bridge; A polytetrafluoroethylene plate 4 is arranged between the slideway and the sliding steel pad or other foot support walking boards that are not provided with the sliding steel pad, and is fastened to the forward end of the foot support walking board with a wire.

[0017] The bottom of the sliding steel pad 3 in the forward direction is cut into a groove, and a stiffening plate is arranged above the sliding steel pad 3 in the forward direction.

[0018] The total thickness of the sliding steel pad 3 + polytetrafluoroethylene plate 4 is t, t=h×d / L, where it is assumed that the cantilever length of the rotating bridge is L, the radius of the slideway axis is d, and the height of the cantilever beam end needs to be controlled to be h during the rotation process.

[0019] Assuming that the cantilever length of the rotating bridge is L, the distance between the support leg and the center of rotation is d, the height of the cantilever beam end that needs to be controlled during the rotation process is h, and the support height that the support leg needs to support is t. Then, through t=h*d / L, the support height t=22mm is calculated, and the thickness of the polytetrafluoroethylene plate at the bottom of the support leg is 4mm, so t=18mm steel plate is used to make the sliding steel pad at the bottom of the support leg.

[0020] This sliding steel pad is made of t=18mm steel plate and t=30mm steel plate by welding, and a groove is cut at the bottom of the sliding steel pad in the forward direction. The manufactured sliding steel pad is placed between the bottom of the support foot board and the polytetrafluoroethylene plate at the top of the slideway, forming a tool that can both play a supporting role and slide with the support foot.

[0021] This sliding steel pad is welded from 4 500×800×18mm steel plates and 4 150×150×30mm triangular steel plates. The above steel plates are welded together according to the designed shape, and the corresponding positions are specially processed to form a sliding steel pad that can slide with the swivel support leg.

[0022] The steel plate should be cut with a plasma cutting machine to ensure that the steel plate is flat and free of deformation after cutting, and there should be no distortion, etc., and there should be no burrs on the cut edge of the steel plate. After the t=18mm steel plate is cut, a 10×20mm groove is cut on the single side in the width direction as the sliding groove of the sliding steel pad; the triangular stiffener should have a 10×10mm groove on both sides of the bevel as the weld of the steel plate welding fillet weld, mainly to improve the welding quality.

[0023] Determine the support leg that needs to strictly control the downward deflection of the beam during the rotation process, lay a polytetrafluoroethylene slide plate that is 30cm wider than the sliding steel pad on each side on the slideway in the forward direction of the rotation support leg, and then place the manufactured sliding steel pad on the polytetrafluoroethylene plate, push it into the bottom of the support leg together, and place it in the center of the bottom of the support leg. In this way, during the rotation process, the polytetrafluoroethylene slide plate and the sliding steel pad will move forward together on the slideway under the thrust of the support leg walking board.

[0024] After the rotation is completed, use a jack to place it on the slideway, lift the turntable until the sliding steel pad is no longer under pressure, then pull out the sliding steel pad and polytetrafluoroethylene plate at the bottom of the support leg, and they can be recycled later.

[0025] A construction method of a posture control device for an unbalanced rotation process of a cable-stayed rotating bridge, comprising: S1: Prepare for rotation construction; Step S1 includes: S11: The construction of the rotating box girder is completed. Check that there are no light floating objects or objects that are easy to fall on the bridge deck, and confirm whether the steel bars at the ends of the beams hinder the rotation; S12: Ball joint preparation: remove the sand box, remove the sand box between the upper and lower turntables, clean the dry sand between the slideway and the support legs, and use high-pressure water to rinse after removal to ensure cleanliness; S13: Slide preparation: 1) Slide cleaning: Clean the slide surface and remove rust from the ring steel plate, and use high-pressure air to clean the reserved gap between the slide and the support foot; 2) Slideway inspection: Check the smoothness of the slideway; check the reserved gap between the slideway and the support leg; check the path that the support leg passes through within the rotation range, and perform an appearance inspection on the support leg to see if there is any damage; 3) Install the medium: Place a PTFE slide plate under the support foot with the PTFE side facing down, and apply lubricating oil on the slide to reduce friction.

[0026] S2: Conduct a trial rotation to detect in real time whether there are any abnormalities in the key stress-bearing parts. If any problems are found, stop the trial rotation in time. Rotation construction can only be carried out after the problems are completely eliminated. Step S2 includes: S21: Release the temporary consolidation of the beam; S22: beam body starts; S23: Turn to 3° during trial rotation; S24: jog 1°, perform 5 10s jogs, 5 5s jogs, and 5 3s jogs respectively. The measurement personnel measure the arc length displacement of the beam end after each jog and record the relevant data. If the displacement of the beam end is irregular and the discreteness is large after several jogs, perform more jogs; S25: After the inching operation is completed and recorded, the bridge is rotated to a predetermined trial rotation angle of 5 degrees; S26: Temporary consolidation of beam.

[0027] S3: Perform formal rotation; Step S3 includes: S31: Perform horizontal rotation, observe the angle of the rotating body, and report to the on-site person in charge every 5°; when the last 5° is reached, report to the on-site commander every 1°; when the center axis of the two ends of the bridge deck is within 2m before closure, the staff at the monitoring point will start to report the monitoring data to the control console in countdown, reporting every 10cm; within 30cm, report every 1cm; S32: When the rotating structure approaches the designed position, the system "pauses". To prevent the structure from over-rotating, the power system changes from "manual" state to jog operation after the inertial operation ends. Each time the jog operation is performed, the surveyor measures and reports the current status data of the axis once, and the cycle is repeated until the axis of the structure is accurately in place; S33: Positioning. After the swivel is in place, accurately adjust the tilt position of the swivel, and use wedges to wedge and fix between the support walking board and the slideway. Each support walking board is equipped with 4 wedges to prevent the beam from swinging under the action of external force.

[0028] After the rotating body is in place, tighten the iron wedges in the forward direction of the support legs and check whether there are any omissions. After completion, weld and fix them. When over-rotation is found during re-measurement due to rotational inertia or measurement error, the force couple boosting system composed of jacks can be used to push the support legs and the board in the opposite direction to make the rotating body rotate back to the designed position.

[0029] S4: After the rotation is completed, the rotation position monitoring is carried out.

[0030] Step S4 includes: S41: Linear measurement, adjustment of lateral inclination, lateral and longitudinal deviation of the axis, locking of the pads between the upper and lower plates, plane positioning, etc., the swivel structure is precisely positioned and the structure is constrained and fixed; S42: Elevation adjustment is carried out by using a jack between the upper and lower platforms. After precise adjustment, the elevation error is controlled within 1 cm. S43: There are 8 pairs of sliding components on the turntable of the swivel. Iron wedges are used to fix the gap between the bottom surface of the welded steel plate at the bottom of the foot support and the 35mm stainless steel plate on the slideway. In addition, the embedded steel bars of the upper and lower turntables are welded to ensure that the structure is precisely positioned without slight deviation. S44: Carry out the sealing concrete pouring construction to complete the turntable structure consolidation in the shortest time. After the turntable is in place, clean the upper surface of the lower turntable, weld the reserved steel bars, and set up the mold to pour the sealing concrete so that the upper turntable and the lower turntable are connected as one.

[0031] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements 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 device for controlling the posture of an unbalanced rotation process of a cable-stayed rotating bridge, characterized in that: include: A slideway (1), the slideway (1) is circular, arranged on the top surface of the lower support platform, and connected to the lower support platform as a whole; Sliding components, wherein 8 sliding components are provided, the projected midline of the sliding components coincides with the midline of the slideway (1), and is connected to the upper turntable as a whole, and the sliding components include: A support leg (2), wherein the support leg (2) is anchored in the upper turntable and rotates together with the upper turntable, and a support foot walking board is fixed at the bottom of the support leg (2); A sliding steel pad (3), the sliding steel pad (3) being arranged at the bottom of the foot support walkway on the elevation side of the rotating beam and placed on the slideway (1), and its moving direction is consistent with the rotation direction of the bridge; A polytetrafluoroethylene plate (4) is arranged between the slideway (1) and the sliding steel pad (3) or other support walking boards that are not provided with the sliding steel pad (3), and is fastened to the forward end of the support walking board.

2. The device for controlling the posture of an unbalanced rotation process of a cable-stayed rotating bridge according to claim 1 is characterized in that: The bottom of the sliding steel pad (3) in the forward direction is cut into a groove, and a stiffening plate is arranged above the sliding steel pad (3) in the forward direction.

3. The device for controlling the posture of an unbalanced rotation process of a cable-stayed rotating bridge according to claim 1 is characterized in that: The total thickness of the sliding steel pad (3) + polytetrafluoroethylene plate (4) is t, t=h×d / L, wherein the cantilever length of the rotating bridge is L, the distance between the support leg (2) and the center of the rotating body is d, and the height of the cantilever beam end needs to be controlled to be h during the rotation process.

4. A construction method of the unbalanced rotation process posture control device of the cable-stayed rotating bridge according to claim 1, characterized in that: include: S1: Prepare for rotation construction; S2: Conduct a trial rotation to detect in real time whether there are any abnormalities in the key stress-bearing parts. If any problems are found, stop the trial rotation in time. Rotation construction can only be carried out after the problems are completely eliminated. S3: Perform formal rotation; S4: After the rotation is completed, the rotation position monitoring and the rotation bridge posture adjustment are carried out.

5. The construction method of the unbalanced rotation process posture control device of the cable-stayed rotating bridge according to claim 4 is characterized in that: The step S1 comprises: S11: The construction of the rotating box girder is completed. Check that there are no light floating objects or objects that are easy to fall on the bridge deck, and confirm whether the steel bars at the ends of the beams hinder the rotation; S12: Ball joint preparation: remove the sand box, remove the sand box between the upper and lower turntables, clean the dry sand between the slideway and the support legs, and use high-pressure water to rinse after removal to ensure cleanliness; S13: Slide preparation: 1) Slide cleaning: Clean the slide surface and remove rust from the ring steel plate, and use high-pressure air to clean the reserved gap between the slide and the support foot; 2) Slideway inspection: Check the smoothness of the slideway; check the reserved gap between the slideway and the support leg; check the path that the support leg passes through within the rotation range, and perform an appearance inspection on the support leg to see if there is any damage; 3) Install the medium: Place a PTFE slide plate under the support foot with the PTFE side facing down, and apply lubricating oil on the slide to reduce friction.

6. The construction method of the unbalanced rotation process posture control device of the cable-stayed rotating bridge according to claim 4 is characterized in that: The step S2 comprises: S21: Release the temporary consolidation of the beam; S22: beam body starts; S23: Turn to 3° during trial rotation; S24: jog 1°, perform 5 10s jogs, 5 5s jogs, and 5 3s jogs respectively. The measurement personnel measure the arc length displacement of the beam end after each jog and record the relevant data. If the displacement of the beam end is irregular and the discreteness is large after several jogs, perform more jogs; S25: After the inching operation is completed and recorded, the bridge is rotated to a predetermined trial rotation angle of 5 degrees; S26: Temporary consolidation of beam.

7. The construction method of the unbalanced rotation process posture control device of the cable-stayed rotating bridge according to claim 4 is characterized in that: The step S3 comprises: S31: Perform horizontal rotation, observe the angle of the rotating body, and report to the on-site person in charge every 5°; when the last 5° is reached, report to the on-site commander every 1°; when the center axis of the two ends of the bridge deck is within 2m before closure, the staff at the monitoring point will start to report the monitoring data to the control console in countdown, reporting every 10cm; within 30cm, report every 1cm; S32: When the rotating structure approaches the designed position, the system "pauses". To prevent the structure from over-rotating, the power system changes from "manual" state to jog operation after the inertial operation ends. Each time the jog operation is performed, the surveyor measures and reports the current status data of the axis once, and the cycle is repeated until the axis of the structure is accurately in place; S33: Positioning. After the swivel is in place, accurately adjust the tilt position of the swivel, and use wedges to wedge and fix between the support walking board and the slideway. Each support walking board is equipped with 4 wedges to prevent the beam from swinging under the action of external force.

8. The construction method of the unbalanced rotation process posture control device of the cable-stayed rotating bridge according to claim 4 is characterized in that: The step S33 further comprises: After the rotating body is in place, tighten the iron wedges in the forward direction of the support legs and check whether there are any omissions. After completion, weld and fix them. When over-rotation is found during re-measurement due to rotational inertia or measurement error, the force couple boosting system composed of jacks can be used to push the support legs and the board in the opposite direction to make the rotating body rotate back to the designed position.

9. The construction method of the unbalanced rotation process posture control device of the cable-stayed rotating bridge according to claim 4 is characterized in that: The step S4 comprises: S41: Linear measurement, adjustment of lateral inclination, lateral and longitudinal deviation of the axis, locking of the pads between the upper and lower plates, plane positioning, etc., the swivel structure is precisely positioned and the structure is constrained and fixed; S42: Elevation adjustment is carried out by using a jack between the upper and lower platforms. After precise adjustment, the elevation error is controlled within 1 cm. S43: There are 8 pairs of sliding components on the turntable of the swivel. Iron wedges are used to fix the gap between the bottom surface of the welded steel plate at the bottom of the foot support and the 35mm stainless steel plate on the slideway. In addition, the embedded steel bars of the upper and lower turntables are welded to ensure that the structure is precisely positioned without slight deviation. S44: Carry out the sealing concrete pouring construction to complete the turntable structure consolidation in the shortest time. After the turntable is in place, clean the upper surface of the lower turntable, weld the reserved steel bars, and set up the mold to pour the sealing concrete so that the upper turntable and the lower turntable are connected as one.

Images