A construction tool capable of lifting and unloading in one and sliding in all directions and a construction method

Abstract

A construction tool and construction method that can lift and unload in one and can slide in all directions, the construction tool comprises: two guide columns, a slide groove is arranged in the center of the opposite side along the height direction; a lifting beam, a guide part is arranged at both ends, and the two guide parts are arranged in the slide grooves of the two guide columns; a sliding area for temporary support or sliding of the sliding shoe is arranged in the middle of the top surface of the lifting beam, and a limit baffle is arranged around the sliding area; two jacks are symmetrically arranged on the inner side of the two guide columns. The construction tool of the present invention integrates lifting and unloading in one and can slide in all directions, which can greatly improve the flexibility of the unloading tool, accurately control the horizontal sliding amount, and can be paused at any time during the construction process.

Description

Technical Field

[0001] The invention relates to the field of steel structures, and in particular to a construction tool capable of integrated lifting and unloading and omnidirectional sliding, and a construction method. Background Art

[0002] In the current rapidly developing society, there are more and more large-span steel structure buildings. In the construction process of these large steel structures, jacking and unloading are needed to transfer the deadweight of the structure from the support frame to the steel structure itself. Due to the characteristics of the structural system of many steel structures, during the jacking and unloading process, they need to be jacked or unloaded for a large distance, or need to be unloaded for a large distance, and there will be large horizontal displacements during the jacking and unloading process. Therefore, each project will choose to release or not release these horizontal displacements in all directions or in some directions according to its own structural characteristics, so as to achieve the purpose of the final structure itself bearing the load.

[0003] However, the unloading tools used in most steel structure construction processes today still lack flexibility, that is, they cannot accurately control each unloading point during the unloading process, and cannot freely choose the release and adjustment of the temporary support in all directions at each unloading point, such as the sand box unloading method, the method of directly cutting off the temporary support with the assistance of a jack to achieve the purpose of unloading, etc. The sand box unloading method uses a construction method in which a sand box is placed at the bottom of the temporary support, and then the sand discharge hole is opened during the unloading stage. The sand in the sand box automatically flows out of the sand discharge hole under the deadweight of the structure, thereby causing the temporary support and the structure to slowly descend.

[0004] For example, a large-span steel structure unloading support sand box disclosed in Chinese patent CN204920277U can achieve the purpose of structural unloading and can effectively support the main structure, but it cannot accurately control the vertical unloading amount of the structure and the horizontal sliding amount of the temporary support, and thus cannot accurately control the vertical displacement of the main structure and the horizontal displacement in all directions during the unloading process. The unloading method of directly cutting off the temporary support refers to a construction method in which the temporary support of the structure is gradually flame-cut with the assistance of a jack so that the structure is gradually unloaded. This method makes the unloading amount of each step of the structure have a large uncertainty, that is, the unloading amount of each step depends entirely on the control of the flame cutting amount, and the horizontal sliding amount cannot be accurately controlled at all. These unloading tools and unloading methods have great limitations. If there are problems such as deviations in the installation of the steel module and large displacements during the unloading process, traditional unloading tools are difficult to handle. Summary of the invention

[0005] In view of the technical problems that it is impossible to accurately control each unloading point in the unloading process and it is impossible to freely choose the release and adjustment of the temporary support in all directions at each unloading point during the above-mentioned unloading process, the purpose of the present invention is to propose a construction tool and construction method that can integrate jacking and unloading and can slide in all directions, which can greatly improve the flexibility of the unloading tool, accurately control the horizontal sliding amount, and can be paused at any time during the construction process to deal with emergency problems.

[0006] To achieve the above object, the technical solution of the present invention is:

[0007] A construction tool with integrated jacking and unloading functions and capable of sliding in all directions, comprising: two guide columns, with slide grooves provided in the center of opposite sides along the height direction; a jacking beam, with guide parts provided at both ends, and the two guide parts are arranged in the slide grooves of the two guide columns; a sliding area for temporarily supporting a short column or a sliding shoe to slide is provided in the middle of the top surface of the jacking beam, and limit baffles are provided around the sliding area; two jacks are symmetrically arranged on the inner sides of the two guide columns.

[0008] Furthermore, it also includes a cushion block, which is arranged in the center between the two jacks, that is, located in the center below the jacking beam.

[0009] Preferably, a pad for adjusting height is also provided on the cushion block.

[0010] Preferably, the guide column is a channel steel, a hot-rolled H-shaped steel or a welded H-shaped steel.

[0011] Preferably, the guide portion of the lifting beam is located at the center of both end surfaces of the lifting beam, and the width of the guide portion is smaller than the width of the lifting beam.

[0012] Preferably, the lifting beam is a beam of uniform cross-section or a beam of non-uniform cross-section.

[0013] Preferably, the lifting beam is an I-beam, a box beam or an H-beam, and a plurality of reinforcing ribs are provided on its side.

[0014] Preferably, the sliding area is coated with lubricating oil or grease, or a stainless steel plate is laid, or a low-friction engineering plastic is fixed to the bottom of the short column or the sliding shoe.

[0015] Preferably, a scale is provided on the side of the guide column for real-time observation of whether the two sides of the lifting beam are level, and can be used to real-time observation of the lifting and unloading distance of the lifting beam.

[0016] Preferably, the limit baffle is welded or bolted to the top surface of the lifting beam.

[0017] In the construction tooling of the present invention:

[0018] The bottom of the jacking beam of the present invention is provided with two jacks and a pad, and the pad can be composed of plates of different thicknesses or other pads of smaller thicknesses, and pads of different thicknesses can be flexibly composed. The jack and the pad alternately bear the vertical load transmitted by the jacking beam, that is, during the jacking and unloading process, the jack bears the load, and when the jacking and unloading are paused or ended, or when the jack reaches the maximum stroke, the pad bears the load.

[0019] When the lifting and unloading distance exceeds the single maximum stroke of the jack, it is necessary to flexibly arrange pads at the bottom of the jack. For example, during the unloading process, when the unloading distance exceeds the single maximum stroke of the jack, it is necessary to arrange pads at the bottom of the jack before the formal unloading to ensure that when the jack reaches the maximum stroke, the pads can be removed to obtain unloading space again; during the jacking process, if the jacking distance exceeds the single maximum stroke of the jack, it is necessary to add pads of a certain thickness at the bottom of the jack each time the jack reaches the maximum stroke to ensure that the jack can still obtain sufficient lifting space.

[0020] The guide column is a chute structure, which limits the vertical sliding of the lifting beam in the chute. At the same time, the guide column can also bear the horizontal load from the lifting beam. The guide column can be flexibly made of channel steel, hot-rolled H-shaped steel or welded H-shaped steel.

[0021] The lifting beam mainly bears the load of the main structure, which is transmitted through temporary support short columns or sliding shoes. The shape of the beam can be a uniform cross-section beam, such as a box beam, H-beam, etc., or it can be transformed into a non-uniform cross-section beam according to specific requirements. For example, when the temporary support short columns or sliding shoes require a large horizontal sliding distance during the lifting and unloading process, the width of the upper flange of the lifting beam can be widened.

[0022] In order to prevent the lifting beam from tipping over during vertical sliding, the clearance between each flange corner of the lifting beam and the guide column should be controlled within a relatively small distance. In actual operation, plugs can also be welded or bolted to control the clearance between the lifting beam and the inner side of the guide column slot to ensure that the lifting beam can smoothly transfer the force to the guide column when subjected to horizontal force, and the lifting beam itself will not tip over.

[0023] A sliding area is provided at the top of the jacking beam, and the size of this area needs to be determined according to the amount of sliding of the temporary support short column or the sliding shoe during the jacking and unloading process of the structure. The bottom of the temporary support short column or the sliding shoe of the structure acts on the sliding area, and the structure support can slide horizontally in the sliding area during the jacking and unloading process. If it is in the non-jacking or unloading stage, the temporary support short column or the sliding shoe of the structure needs to be fixed to limit its horizontal sliding, then it is only necessary to fill the pad between the temporary support short column or the sliding shoe and the limit baffle. In actual operation, in order to reduce the sliding friction, you can also choose to apply lubricating oil or grease in the sliding area, or lay a stainless steel plate, or fix low-friction engineering plastics at the bottom of the short column or the sliding shoe according to the actual situation.

[0024] The construction method of the construction tooling capable of jacking and unloading in one body and being able to slide in all directions of the present invention comprises the following steps:

[0025] a) Lifting operation

[0026] First, put in the jack and level the jacking beam. If the temporary supporting short column or the sliding shoe of the structure needs to slide horizontally, adjust the number of plugs set between the short column or the sliding shoe and the limit baffle in the sliding area of ​​the top surface of the jacking beam;

[0027] Then start the jacks on both sides to lift the jacking beam synchronously until the jacking beam reaches the designed elevation or the jack reaches the maximum stroke; when the jack is about to reach the maximum stroke and the jacking beam has not reached the designed elevation, stop lifting, increase the number of pads at the pad, so that there is only a gap of no more than 5mm between the jacking beam and the pad, and then drop the jack to transfer the vertical load of the jacking beam to the pad;

[0028] Then add pads under the jacks on both sides, restart the jacks, and start the next stroke of jacking; and so on until the jacking reaches the designed elevation;

[0029] b) Uninstallation operation

[0030] First, put the jack in. At this time, the bottom of the jack should be padded with a pad of sufficient thickness according to the pre-calculated pads. The jacking beam should be leveled. If the structural support needs to slide horizontally, adjust the plug plate in the sliding area on the top surface of the jacking beam.

[0031] Then start the jacks on both sides to lift the jacking beam to a distance no more than 5mm, and then remove the pad on the middle pad; then simultaneously unload the jacks on both sides until the jacking beam is unloaded to the designed elevation.

[0032] Preferably, a scale is provided on the side of the guide column; when leveling the lifting beam, the lower flanges at both ends of the lifting beam are aligned with the scale of the scale to observe in real time whether the two sides of the lifting beam are level, and the lifting and unloading distances of the lifting beam are observed in real time.

[0033] Preferably, when the total unloading distance is greater than the distance of one stroke of the jack, before the unloading operation, a number of pads are added to the bottom of the jacks on both sides, and the total thickness of these pads should be equal to or greater than the total unloading distance minus the distance of one stroke of the jack; during the unloading operation, when the unloading distance reaches within 10 mm from the maximum stroke of the jack but has not yet been unloaded to the designed elevation, a pad is added at the middle pad so that the pad contacts the lower surface of the lower flange of the jacking beam or the net distance between the two is less than 10 mm, and then the jack is continued to be unloaded so that the load is transferred to the middle pad, and then the pad at the bottom of the jack is extracted, and then the jack is started, and the jacks on both sides are simultaneously pushed to the jacking beam, so that the load is transferred to the jacks on both sides again; then the middle pad is extracted, and then the jacks on both sides are simultaneously unloaded to start the next stroke of unloading; and so on until the unloading is completed.

[0034] In actual operation, horizontal slip of the structure occurs during the jacking or unloading process.

[0035] The lifting operation is:

[0036] First, put in the jack and level the jacking beam so that the lower surface of the lower flange at both ends of the jacking beam is aligned with the same elevation scale on the scale; if the temporary support short column or sliding shoe of the structure needs to slide horizontally, release the constraint in the sliding area, that is, remove the plugging plate between the temporary support short column or sliding shoe and the limit baffle; then start the jacks on both sides so that the jacking beam is lifted synchronously until the jacking beam reaches the design elevation or the jack reaches the maximum stroke; when the jack is about to reach the maximum stroke and the jacking beam has not reached the design elevation, stop lifting, increase the number of pads at the pad, so that there is only a gap of no more than 5mm between the jacking beam and the pad, and then drop the jack so that the vertical load of the jacking beam is transferred to the pad; then add pads under the jacks on both sides, restart the jacks, and start the jacking of the next stroke; and so on until the jacking reaches the design elevation.

[0037] The uninstallation operation is:

[0038] First, put in the jack. At this time, the bottom of the jack should be padded with a pad of sufficient thickness according to the pre-calculated pads. The jacking beam is leveled so that the lower surface of the lower flange at both ends of the jacking beam is aligned with the same elevation scale of the scale. If the temporary support short column or sliding shoe of the structure needs to slide horizontally, release the constraint in the sliding area, that is, remove the plug between the temporary support short column or sliding shoe and the limit baffle. Then start the jacks on both sides, lift the jacking beam by no more than 5mm, and then remove the pad on the pad. Then synchronize Unload the jacks on both sides until the jacking beam is unloaded to the designed elevation or is about to reach the jack stroke; if the jack is about to reach the maximum stroke and is not unloaded to the designed elevation, transfer the jack load to the middle pad, then extract the pad at the bottom of the jack, start the jack again, and push the jacks on both sides to the jacking beam simultaneously, so that the load is transferred to the jacks on both sides again; then extract the middle pad, and then unload the jacks on both sides simultaneously, and start the next stroke unloading; and so on until the unloading is completed.

[0039] The present invention does not require the use of fire during the entire use process and is easy to operate, thereby greatly reducing potential safety hazards during the jacking and unloading processes.

[0040] The present invention can accurately control the vertical displacement and horizontal displacement of each unloading point, which can greatly ensure the construction accuracy and ensure that the structure after construction conforms to the force system and force concept of the structural design.

[0041] The present invention can freely select the direction of horizontal release of the sliding shoe during the jacking and unloading process, that is, no matter the sliding shoe can only slide in the radial direction, or can only slide in the circumferential direction, or can only slide radially in the field direction but not radially out of the field direction, or can only slide circumferentially to the right but not to the left, or allows simultaneous circumferential and radial sliding, etc., the present invention can make corresponding precise control.

[0042] The present invention can accurately adjust the positioning accuracy during the structural installation process, that is, during the steel structure installation process, when the structural conditions for jacking and unloading are not yet met, the positioning accuracy of each lifting module can be adjusted by the present invention, thereby greatly ensuring the accuracy of subsequent installation.

[0043] The present invention can pause the jacking and unloading process at any time to deal with emergency situations occurring during the jacking and unloading process, thereby greatly improving the safety during the construction process.

[0044] Compared with other traditional unloading methods, the present invention has the following beneficial effects:

[0045] Compared with the traditional unloading method, the present invention can accurately control the vertical slip amount and horizontal slip amount of each unloading point, greatly improving the construction accuracy.

[0046] Compared with the traditional unloading method, the present invention can accurately and flexibly control the sliding direction of the sliding shoe, thereby greatly improving the accuracy of the lifting and unloading process.

[0047] Compared with the traditional unloading method, the present invention can achieve multiple uses. It can not only meet the requirements of precise lifting and unloading, but also can achieve precise regulation of each lifting unit during the structural installation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 It is a three-dimensional diagram of an embodiment of the construction tooling of the present invention.

[0049] Figure 2 It is a front view of an embodiment of the construction tooling of the present invention. DETAILED DESCRIPTION

[0050] See also Figure 1 , Figure 2 The construction tooling with integrated lifting and unloading and omnidirectional sliding function of the present invention comprises:

[0051] Two guide columns 1, 1', the center of the opposite side faces thereof are provided with slide grooves 11, 11' along the height direction;

[0052] The lifting beam 2 has guide parts 21 and 22 at both ends, and the two guide parts 21 and 22 are arranged in the slide grooves 11 and 11' of the two guide columns 1 and 1'; a sliding area 23 for temporary support or sliding of the sliding shoe 100 is provided in the middle of the top surface of the lifting beam 2, and a limit baffle 24 is arranged around the sliding area 23;

[0053] The two jacks 3, 3' are symmetrically arranged on the inner sides of the two guide pillars 1, 1' respectively.

[0054] Furthermore, the construction tool is further provided with a cushion block 4 , which is arranged at the center between the two jacks 3 , 3 ′, that is, located at the center below the jacking beam 2 .

[0055] Preferably, a pad 5 for adjusting height is further provided on the cushion block 4 .

[0056] Preferably, the guide column 1 is a channel steel, a hot-rolled H-shaped steel or a welded H-shaped steel.

[0057] Preferably, the guide parts 21 , 22 of the lifting beam 2 are located in the center of both end surfaces of the lifting beam 2 , and the width of the guide parts 21 , 22 is smaller than the width of the lifting beam 2 .

[0058] Preferably, the lifting beam 2 is a beam with a uniform cross-section or a beam with a non-uniform cross-section.

[0059] Preferably, the lifting beam 2 is an I-beam, a box beam or an H-beam, and a plurality of reinforcing ribs are provided on its side.

[0060] Preferably, the sliding area 23 is coated with lubricating oil or grease, or is paved with a stainless steel plate, or a low-friction engineering plastic is fixed to the bottom of the short column or the sliding shoe.

[0061] Preferably, a scale 6 is adhered to the side of the guide column 2 .

[0062] Preferably, the limit baffle 24 is welded or bolted to the top surface of the lifting beam 2 .

[0063] The tooling of the present invention is mainly operated for lifting and unloading during use.

[0064] Lifting operation:

[0065] 1) Two jacks are lifted at the same time for a certain distance;

[0066] Turn on the oil pump, open the jack regulating valve, and adjust the reversing valve to the rising position; during this process, the regulating valves of the two jacks must be controlled well to ensure that the jacks on both sides rise synchronously, slowly, and at a uniform speed;

[0067] Level the jacking beam so that the lower flanges at both ends of the jacking beam are aligned with the same elevation scale on the ruler.

[0068] 2) Insert one or more pads on the top surface of the pad under the jacking beam to increase the thickness of the existing pad and ensure a small clearance between the bottom of the jacking beam and the pad;

[0069] 3) Continue to lift the two jacks a certain distance;

[0070] 4) Insert the pad under the jacking beam again to reduce the distance between the bottom of the jacking beam and the pad;

[0071] 5) Repeat steps 3) and 4) until the jacking reaches the designed elevation or the jack approaches the maximum stroke;

[0072] If the design elevation is reached, the lifting operation is completed. If the jack is close to the maximum stroke but has not reached the design elevation, further lifting is required, and the following steps are continued;

[0073] 6) Drop the jack;

[0074] Lower the jack until the jacking beam changes from being supported by the jack to being supported by the pad at the bottom, and the jack stroke returns to zero;

[0075] 7) Insert pads into the bottom of the jacks on both sides until a small gap is maintained between the top of the jack and the bottom of the jacking beam;

[0076] 8) Lift the jack again and repeat steps 3 to 5) until it reaches the designed elevation.

[0077] Uninstallation operation:

[0078] 1) Two jacks are used to lift the beam at a small distance at the same time. The purpose of this step is to transfer the vertical force on the lifting beam from the pad at the bottom to the jack, so that the pad under the lifting beam can be smoothly removed, so that the lifting beam has space for unloading. It is also to level the lifting beam so that the lower surface of the lower flange at both ends of the lifting beam is aligned with the same elevation scale of the scale.

[0079] 2) Remove the pad under the jacking beam;

[0080] In this step, only the pad with smaller thickness is removed. The main purpose is to control the unloading amount in each step, so as to achieve the purpose of synchronous, slow and uniform unloading.

[0081] 3) Both jacks are unloaded simultaneously until the bottom of the jacking beam approaches the top of the pad;

[0082] After this step of unloading, the force of the lifting beam still acts on the jack, but it still maintains a small clearance from the bottom pad to ensure safety;

[0083] 4) Remove a certain thickness of pad from the pad;

[0084] 5) The two jacks are unloaded again simultaneously until the bottom of the jacking beam approaches the top of the pad;

[0085] 6) Repeat steps 4) and 5) until the load is unloaded to the designed elevation, or the jack stroke is close to zero;

[0086] If the load has been unloaded to the designed elevation, the unloading operation is completed; if the jack stroke is close to zero and the unloading purpose has not been achieved, continue with the following steps;

[0087] 7) Continue to unload the jack and transfer the load of the jacking beam to the pad;

[0088] 8) Remove the pad at the bottom of the jack, then raise the jack without load until it contacts the lifting beam, and then continue to lift the jack a small distance to transfer the load of the lifting beam to the jacks on both sides;

[0089] 9) Repeat steps 4), 5), and 6) until the uninstallation is complete.

Claims

1. A construction tool with integrated lifting and unloading and omnidirectional sliding, characterized by: include: Two guide columns, with a slide groove provided in the center of the opposite side along the height direction; A lifting beam, with guide parts at both ends, the two guide parts are arranged in the slide grooves of the two guide columns; a sliding area for temporarily supporting short columns or sliding shoes is provided in the middle of the top surface of the lifting beam, and limit baffles are arranged around the sliding area; Two jacks are symmetrically arranged on the inner sides of the two guide columns.

2. The construction tooling with integrated lifting and unloading and omnidirectional sliding function as claimed in claim 1 is characterized in that: It also includes a cushion block, which is arranged in the center between the two jacks, that is, located in the center under the jacking beam.

3. The construction tooling with integrated lifting and unloading and omnidirectional sliding function as claimed in claim 2 is characterized in that: The cushion block is also provided with a cushion plate for adjusting height.

4. The construction tooling with integrated lifting and unloading and omnidirectional sliding function as claimed in claim 1 is characterized in that: The guide column is a channel steel, a hot-rolled H-shaped steel or a welded H-shaped steel.

5. The construction tooling with integrated lifting and unloading and omnidirectional sliding function as claimed in claim 1 is characterized in that: The lifting beam is a beam with a uniform cross section or a beam with a non-uniform cross section.

6. The construction tooling with integrated lifting and unloading and omnidirectional sliding function as claimed in claim 1 or 5, characterized in that: The guide part of the lifting beam is located at the center of the two end surfaces of the lifting beam, and the width of the guide part is smaller than the width of the lifting beam.

7. The construction tooling with integrated lifting and unloading functions and capable of all-round sliding movement as claimed in claim 1 or 5, characterized in that: The jacking beam is an I-beam, a box beam or an H-shaped steel, and a plurality of reinforcing plates are arranged on its side.

8. The construction tooling with integrated lifting and unloading functions and capable of all-round sliding movement as claimed in claim 6, characterized in that: The jacking beam is an I-beam, a box beam or an H-shaped steel, and a plurality of reinforcing plates are arranged on its side.

9. The construction tooling with integrated lifting and unloading functions and capable of all-round sliding movement as claimed in claim 1 or 4, characterized in that: A scale is arranged on the side of the guide column.

10. The construction tool with integrated lifting and unloading function and omnidirectional sliding function as claimed in claim 1, characterized in that: The sliding area is coated with lubricating oil or grease, or a stainless steel plate is laid, or low-friction engineering plastic is fixed to the bottom of the short column or the sliding shoe.

11. The construction tool with integrated lifting and unloading function and omnidirectional sliding function as claimed in claim 1, characterized in that: The limit baffle is welded or bolted to the top surface of the lifting beam.

12. The construction method of the construction tooling with integrated lifting and unloading and omnidirectional sliding as claimed in claim 1, characterized in that: The steps include: a) Lifting operation First, put in the jack and level the jacking beam. If the temporary supporting short column or the sliding shoe of the structure needs to slide horizontally, adjust the number of plugs set between the short column or the sliding shoe and the limit baffle in the sliding area of ​​the top surface of the jacking beam; Then start the jacks on both sides to lift the jacking beam synchronously until the jacking beam reaches the designed elevation or the jack reaches the maximum stroke; when the jack is about to reach the maximum stroke and the jacking beam has not reached the designed elevation, stop lifting, increase the number of pads at the pad, so that there is only a gap of no more than 5mm between the jacking beam and the pad, and then drop the jack to transfer the vertical load of the jacking beam to the pad; Then add pads under the jacks on both sides, restart the jacks, and start the next stroke of jacking; and so on until the jacking reaches the designed elevation; b) Uninstallation operation First, put the jack in. At this time, the bottom of the jack should be padded with a pad of sufficient thickness according to the pre-calculated pads. The jacking beam should be leveled. If the structural support needs to slide horizontally, adjust the plug plate in the sliding area on the top surface of the jacking beam. Then start the jacks on both sides to lift the jacking beam to a distance no more than 5mm, and then remove the pad on the middle pad; then simultaneously unload the jacks on both sides until the jacking beam is unloaded to the designed elevation.

13. The construction method of the construction tooling with integrated lifting and unloading and omnidirectional sliding as claimed in claim 12, characterized in that: A scale is provided on the side of the guide column; when leveling the lifting beam, the lower flanges at both ends of the lifting beam are aligned with the scale of the scale to observe in real time whether the two sides of the lifting beam are level, and the lifting and unloading distances of the lifting beam are observed in real time.

14. The construction method of the construction tooling with integrated lifting and unloading and omnidirectional sliding as claimed in claim 12, characterized in that: When the total unloading distance is greater than the distance of one stroke of the jack, before the unloading operation, several pads are added to the bottom of the jacks on both sides. The total thickness of these pads should be equal to or greater than the total unloading distance minus the distance of one stroke of the jack; during the unloading operation, when the unloading distance reaches within 10mm of the maximum stroke of the jack but has not yet been unloaded to the designed elevation, a pad is added at the middle pad so that the pad contacts the lower surface of the lower flange of the jacking beam or the net distance between the two is less than 10mm, and then the jack is continued to be unloaded so that the load is transferred to the middle pad, and then the pad at the bottom of the jack is extracted, and then the jack is started, and the jacks on both sides are simultaneously pushed to the jacking beam, so that the load is transferred to the jacks on both sides again; then the middle pad is extracted, and then the jacks on both sides are simultaneously unloaded, and the unloading of the next stroke is started; and so on until the unloading is completed.

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