Large circular cantilever steel structure support unloading construction method

Abstract

The application provides a large circular cantilever steel structure support unloading construction method, and belongs to the technical field of cantilever steel structure unloading. The method comprises the following steps: step 1: unloading of B type support in the stand area, A1 type support in the stand area and D type support in the triangular truss; step 2: unloading of C type support in the chord supported reticulated shell and A type support in the girdle truss; and step 3: unloading of the temporary connecting node, and completing the unloading construction. By controlling the unloading steps and sequence, stress concentration and uncontrollable deformation of the structure in the system conversion process can be minimized, so that the absolute safety of the main structure in the construction stage is ensured, and the design shape and internal force state are finally accurately realized. The step-by-step unloading guides the internal force of the structure to be smoothly transferred from the temporary support system to the permanent structure system, and the dynamic impact and mutation are avoided.

Description

Technical Field

[0001] This invention relates to the field of unloading technology for cantilevered steel structures, and more particularly to a method for unloading and constructing a large circular cantilevered steel structure support. Background Technology

[0002] With the development of modern engineering technology, large-span roof structures, cantilevered steel structures, and cable-stayed dome structures are widely used in architectural design, including exhibition halls, convention centers, and stadiums. These unique and complex structures present numerous challenges to construction. The construction process of large-span cantilevered structures and cable-stayed dome structures is complex, involving the interaction of multiple factors, such as deformation and displacement of the cantilever structure, welding deformation, unloading timing, and temporary support removal. These factors directly affect the safety of the structure and construction efficiency. The Ethiopian Grand Rotunda project is a complex spatial structure, comprising a large-span roof structure, a cantilevered steel structure, and a cable-stayed dome structure.

[0003] The unloading of the support structure is the dismantling process. During unloading, the entire structural system experiences continuous force changes, and the internal forces and force transmission between the members are complex. To ensure structural safety, maintain the design intent, and ensure that the internal forces of the structural members do not exceed the allowable stress, it is crucial to prevent damage caused by excessive internal forces in the support structure or the structural members. Only then can the structural system be reliably and steadily constructed.

[0004] During the installation of complex cable structures, temporary supports are typically installed internally to control deformation of internal components. However, after the roof is installed and the cable structure is tensioned, the supports are obstructed by the roof structure, making it inconvenient to directly remove the temporary supports with a crane. Furthermore, ordinary cranes cannot enter the structure for operation, and external hoisting is limited by distance and height, potentially resulting in insufficient boom length. Additionally, dismantling by cutting the supports into small segments would lead to extremely low construction efficiency, and the resulting fragmented temporary supports are difficult to reuse, causing significant material waste. Moreover, repeated cutting and dismantling require repeated hot work inside the structure, posing a significant safety hazard. Flames touching the cable structure could also affect its stress, causing quality issues. Therefore, a method for unloading and constructing large circular cantilevered steel structure supports needs to be designed. Summary of the Invention

[0005] The purpose of this invention is to provide a method for unloading and constructing large circular cantilevered steel structure supports, thereby solving the technical problems of low dismantling efficiency and excessive internal forces in the members during the dismantling process of existing complex cable structures, which can lead to damage.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for unloading and constructing a large circular cantilevered steel structure support, the method comprising the following steps: Step 1: Unload the Class B support frame in the grandstand area, the Class A1 support frame in the grandstand area, and the Class D support frame of the triangular truss. Step 2: Unloading of the C-type support for the cable-stayed reticulated shell and the A-type support for the ring truss; Step 3: Unload the temporary connection node to complete the unloading process.

[0007] Furthermore, the supports include Class A supports for cantilever trusses, Class A supports for ring trusses, Class B supports for grandstand areas, Class C supports for cable-stayed reticulated shells, and Class D supports for triangular trusses. Class A supports for cantilever trusses include A1 supports and A2 supports. Furthermore, in step 1, during the unloading of the A1 support in the grandstand area, since the A1 support is located in the grandstand structure area, to facilitate the installation of the grandstand structure, the two sets of A1 supports in the grandstand area are removed after the roof cantilever truss + ring truss are installed. Simulation analysis shows that the theoretical maximum downward deflection of the upper ring truss is 8.6mm. Unloading is carried out by synchronous flame cutting. The unloading process is as follows: a working platform is set up at the cutting point to prepare for cutting, a line is drawn at the cutting position and the maximum displacement is marked, and the two steel pipe support plates are simultaneously flame-cut by 15mm. Deformation and stress changes are monitored to confirm that the unloading is complete. Further, in step 1, during the unloading of the Class B supports in the grandstand area, after all the 11.9-meter triangular trusses have been installed, the Class B supports in the grandstand area are removed to complete the system transformation. The simulation analysis shows that the theoretical maximum downward deflection of the grandstand structure is 9mm. The unloading is carried out by synchronous flame cutting. The unloading process is as follows: a working platform is set up at the cutting point to prepare for cutting, a line is drawn at the cutting position and the maximum displacement is marked, and the 7 support teeth are simultaneously cut by flame for 15mm. The deformation and stress changes are monitored to confirm that the unloading is complete.

[0008] Furthermore, in step 1, during the unloading of the D-type support of the triangular truss, after all the triangular trusses on the 11.9-meter section were installed and the B-type support was removed, the D-type support was removed. Simulation analysis showed that the theoretical maximum downward deflection of the triangular truss was 10mm. The unloading was carried out using synchronous flame cutting. The unloading process was as follows: a working platform was set up at the cutting point to prepare for cutting; a line was drawn at the cutting position and the maximum displacement was marked; the support tooth plate was synchronously cut with flame for 15mm; deformation and stress changes were monitored; and the unloading was confirmed to be complete.

[0009] Furthermore, in step 2, through simulation calculation and analysis of the entire tensioning process, it is found that the roof chord support and ring truss support will have an upward displacement when the cable structure is tensioned, and can naturally detach and complete the unloading. The unloading process is as follows: the cable structure completes the first stage of tensioning, the connection weld between the support and the roof is removed, and the cable structure continues to be tensioned until the support separates from the structure.

[0010] Furthermore, in step 3, during the installation of the steel structure, in order to ensure installation efficiency, bolted connecting plates were used for temporary fixation at the structural docking positions. After welding was completed, these bolted joints were removed. The specific unloading process was as follows: welding the structural docking seam, removing the bolts and connecting plates, cutting the connecting plates and grinding them.

[0011] Furthermore, the above-mentioned solution also includes measures for handling abnormalities of the support frame, including deformation caused by overload, deformation caused by node failure, deformation caused by main body settlement, deformation of the component itself, and deformation caused by environmental factors. When deformation is caused by overload, remove excess material from the support and suspend hoisting operations. If it is a construction load, pouring must be stopped immediately. The already poured part should be supported by temporary supports to distribute the load. Temporary supports should be added around the deformed support to distribute the original load to the new support and reduce the stress on the deformed component. When deformation is caused by node failure, loose bolts should be retightened to the design value using a torque wrench. If the bolt is broken or stripped, replace it with a high-strength bolt of the same specification immediately and tighten the surrounding bolts to enhance the overall integrity. For welds that are not fully penetrated or have cracks, remove the defective part first and re-weld using low-hydrogen welding rods. After welding, use ultrasonic testing to check the quality. If the node plate is deformed, add stiffening ribs. If the pin is loose, fix it with wedges and spot weld it to prevent it from falling off. If the pin is bent, replace it with a new pin and apply grease to reduce wear. When deformation occurs due to main body settlement, the support is located at the top of the concrete column and the end of the beam. Timely detection is carried out during construction, and feedback is given to the general contractor as soon as possible. When a component deforms, additional supports are added. For horizontal supports with excessive deflection at mid-span, vertical columns are added at mid-span, rooted in a solid foundation at the bottom and tightened at the top with jacks. For columns that bend laterally, clamps and diagonal braces are used for reinforcement. Double C-shaped steel is wrapped around the bent section, and the gap between the steel plate and the column is filled with steel plate. Both ends are welded and fixed. At the same time, diagonal braces are added on both sides of the column at an angle of 45°-60° and connected to the surrounding stable structure. If a component cracks or undergoes plastic deformation, the failed component is removed directly and replaced with a new component of the same model. When deformation is caused by environmental factors, additional guy ropes are installed for high-altitude supports, with one end connected to the top of the support and the other end anchored to the ground anchor. The tension is adjusted according to the wind speed. In seasons with temperatures higher than the set temperature, sunshade cloths are used to cover the outdoor supports to reduce the temperature difference caused by sunlight. In cold winter regions, preheating measures are taken for welded joints to avoid low-temperature brittle fracture.

[0012] Furthermore, all stent unloading processes used a reverse dismantling method, the specific process of which is as follows: Step 3.1: After the cable structure tensioning is completed, unload the temporary support to detach the support from the roof structure, and set up a transfer trolley; Step 3.2: Remove the arc-shaped support at the top of the temporary support column to provide upper space for the subsequent overall lifting of the temporary support; Step 3.3: Remove the cantilevered portion of the distribution beam; Step 3.4: Install the lifting distribution beam and lifting hand chain hoist on the upper part of the roof; Step 3.5: Disconnect the lower part of the support and use a hand-operated hoist to lift the temporary support; Step 3.6: The transfer trolley moves under the temporary support; Step 3.7: Lower the temporary support and remove the connecting bolts of the lowest standard segment of the support. Secure the temporary support to the transfer trolley and lift the remaining upper support. Step 3.8: The transfer trolley moves a standard segment to the edge of the structure; Step 3.9: Use a truck crane to lift the standard section of the temporary support frame to the ground; Step 3.10: Repeat steps 1-9 of the disassembly process until all temporary support segments have been disassembled. The present invention, by adopting the above-described technical solution, has the following beneficial effects: (1) By controlling the unloading steps and sequence, this invention can minimize stress concentration and uncontrollable deformation of the structure during the system transformation process, thereby ensuring the absolute safety of the main structure during the construction stage and ultimately accurately realizing the design shape and internal force state. The step-by-step unloading guides the internal force of the structure to be transferred smoothly from the temporary support system to the permanent structure system, avoiding dynamic impact and sudden changes, and realizing a soft landing from the construction state to the design state. Each unloading stage is a monitoring window, and after each stage is completed, the structural deformation and stress data can be collected and analyzed to verify the calculation results and provide a decision basis for the next stage of unloading. Dynamic adjustments can be made when necessary, realizing information-based construction. (2) In confined spaces, the bracket dismantling method can facilitate the quick and easy removal of temporary brackets. If dismantling is done from top to bottom, without the assistance of large lifting equipment, the brackets can only be dismantled into individual parts, which are mainly done manually for dismantling, assembly, and transportation. This will prolong the operation time and reduce the secondary utilization rate of the brackets after dismantling, which violates the prefabricated design concept of temporary brackets. The bracket dismantling method described in this paper not only responds to the concept of prefabricated design and facilitates secondary utilization, but also reduces the operation time and improves work efficiency. In this method, the structure and power of the transport trolley can be improved. In this project, the power and braking of the transport trolley are provided by manpower. In the future, the structure of the trolley can be upgraded and modified by combining motors, mechanical structures, etc., to free up manpower and improve transportation efficiency and braking safety. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the Class A support structure of the present invention; Figure 2 This is a schematic diagram of the A-type support arrangement structure of the present invention; Figure 3 This is a schematic diagram of the Class B support structure of the present invention; Figure 4 This is a schematic diagram of the B-type support arrangement structure of the present invention; Figure 5 These are schematic diagrams of the C1 and C2 type support structures of this invention; Figure 6 This is a schematic diagram of the C-type support arrangement structure of the present invention; Figure 7 This is a schematic diagram of the triangular truss D-type support structure of the present invention; Figure 8 This is a schematic diagram of the triangular truss D-type support arrangement structure of the present invention; Figure 9 This is a schematic diagram of the E-type bracket structure for roof cantilever of the present invention; Figure 10 This is a schematic diagram of the E-type bracket arrangement structure for the eaves cantilever of the present invention; Figure 11 This is a schematic diagram of the rocker column clamp diagonal brace structure of the present invention; Figure 12 This is a flowchart of the unloading process for the A1 bracket in the grandstand area of ​​this invention; Figure 13 This is a schematic diagram of the unloading structure of the A1 support bracket in the grandstand area of ​​the present invention; Figure 14 This is a diagram showing the maximum downward deflection of the ring truss of the A1 support frame in the grandstand area of ​​this invention; Figure 15 This is a flowchart of the unloading process for the Class B stent of the present invention; Figure 16 This is a schematic diagram of the unloading structure of the type B bracket of the present invention; Figure 17 This is a diagram showing the maximum downward deflection of the Class B support grandstand structure of this invention; Figure 18 This is a schematic diagram of the Class B support structure for the grandstand area of ​​this invention; Figure 19 This is a flowchart of the unloading process for the D-type bracket of the present invention; Figure 20 This is a schematic diagram of the unloading structure of the D-type bracket of the present invention; Figure 21 This is a diagram showing the maximum downward deflection of the triangular truss of the D-type bracket of the present invention; Figure 22 This is a flowchart of the unloading process for the C-type cable-stayed grid shell support and the A-type ring truss support of the present invention; Figure 23 This is a flowchart of the temporary connection node unloading process of the present invention; Figure 24 This is a schematic diagram of the location of the temporary support in the confined space according to an embodiment of the present invention; Figure 25 This is a schematic diagram of the cross-sectional location of the temporary support structure in the confined space according to an embodiment of the present invention; Figure 26 This is a schematic diagram of the position of the hand chain hoist according to an embodiment of the present invention; Figure 27 This is a schematic diagram of the sliding trolley structure model according to an embodiment of the present invention; Figure 28 This is a schematic diagram of the dismantling process according to an embodiment of the present invention; Figure 29 This is a schematic diagram of the transport and fixation of the support segment according to an embodiment of the present invention; Figure 30 This is a schematic diagram of the standard section of the temporary support, the column base distribution beam, and the inter-segment bolting in an embodiment of the present invention; Figure 31 This is a plan view of the temporary support structure of type A in embodiment A of the present invention; Figure 32 This is an elevation layout diagram of a type A temporary support structure according to an embodiment of the present invention. Detailed Implementation To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and preferred embodiments. However, it should be noted that many details listed in the specification are merely to provide the reader with a thorough understanding of one or more aspects of the present invention, and these aspects of the invention can be implemented even without these specific details.

[0014] The unloading construction method for a large circular cantilevered steel structure support system involves the on-site fabrication of a lattice-type temporary support system. The uprights are made of round tubular columns, while the horizontal and diagonal braces are composed of channel steel or steel pipes. After the support system is fabricated on-site according to the installation height and location, a 100t truck crane is used to install the temporary support system. Anchors are pre-embedded at the locations where the temporary support system needs to be installed, or expansion bolts are used for fixing to ensure the safety and stability of the temporary support system.

[0015] Temporary support frames can be divided into six categories according to their uses. Among them, categories A, B, C, D, and E are temporary load-bearing supports for structural hoisting, while sway column clamps are sway column stabilization measures.

[0016] Temporary scaffolding design and layout (1) Steel frame shear wall structure ring belt + cantilever truss Class A support Type A supports are used for hoisting trusses in steel frame shear wall structures, totaling 10 sets. Type A supports consist of 4m standard sections, with double-layered I20a I-beams at the top for distribution beams, and I36a beams at the bottom where there are no supports or insufficient load-bearing capacity. Specifically, A1 supports consist of 5 standard sections (4 sets), and A2 supports consist of 2 standard sections (6 sets). The standard section columns use Φ273×7.5 steel pipes, and the horizontal and diagonal braces use [8 channel steel]. A1 supports are installed on the floor slab within axis D and fixed with chemical anchors. A2 supports are installed on an 11.9m platform and fixed with fillet welds with a weld leg height of 8mm.

[0017] There are four groups of A1-type supports, each consisting of five standard sections. These sections are bolted together to form a prefabricated support structure, which facilitates installation, disassembly, and future reuse. There are six groups of A2-type supports, each consisting of two standard sections. The supports employ a four-limb assembly structure. The uprights are made of 273*7.5 steel pipe, and the horizontal and diagonal braces are made of [8 channel steel]. Double-layered I20a I-beam distribution beams are installed at the top, and double-layered I36a distribution beams are installed at unsupported locations at the bottom of the uprights.

[0018] (2) Class B support structure in the grandstand area The Class B scaffolding for the grandstand area is used for the installation of components in the 11.9m platform grandstand area. One set is installed in an arc-shaped arrangement. The uprights are made of Φ325×8 steel pipe, the diagonal support uprights are made of Φ159×6 steel pipe, the circumferential cross braces are made of [14b channel steel and 159×6 steel pipe, the diagonal braces are made of [14b channel steel, and the radial cross braces are made of Φ100×6 steel pipe. The diagonal braces are fixed at their bases with chemical anchors. Leveling beams are installed at the slopes, and the scaffolding is welded to the leveling beams, which are then fixed with chemical anchors.

[0019] The grandstand is designed as a suspended structure. To achieve this, a Class B support system is installed in the grandstand area for component installation, with one set arranged in an arc. The uprights are made of Φ325×8 steel pipe, the diagonal support uprights are made of Φ159×6 steel pipe, the circumferential cross braces are made of [14 channel steel and 159×6 steel pipe, the diagonal braces are made of [14 channel steel, and the radial cross braces are made of Φ100×6 steel pipe.

[0020] The diagonal bracing of the support frame is fixed to the structural beam of the B2 layer using chemical anchors. A concrete foundation is installed beneath the 325×8 steel pipe columns, with a pre-embedded steel plate welded to the top of the foundation.

[0021] (3) Cable-stayed reticulated shell Class C support During the installation of cable-stayed grid shells, the shell sections deform significantly before forming an integral structure. Therefore, temporary supports are required during hoisting to reduce deformation and improve installation accuracy. Type C supports are used for hoisting cable-stayed grid shell segments, totaling 26 sets, including 19 sets of Type C1 supports and 7 sets of Type C2 supports.

[0022] For Class C1 scaffolding, each standard section is 4 meters long. The uprights are made of Φ159×6 or Φ100×6 steel pipes, the horizontal and diagonal braces are made of [8 channel steel, and the top distribution beam is made of double-layered I20a I-beams. For Class C2 scaffolding, the uprights are made of Φ159×6 steel pipes, the horizontal and diagonal braces are made of [8 channel steel, and the top distribution beam is made of double-layered I20a I-beams. The bottom end plate of the scaffolding is welded to the steel beam using fillet welds with a weld leg height of 8mm.

[0023] Class C supports are used for hoisting cable-stayed shell segments, totaling 26 sets, including 19 sets of Class C1 supports and 7 sets of Class C2 supports.

[0024] C1 type scaffolding consists of 4m standard sections, which are connected by bolts to form a prefabricated scaffolding structure. This prefabricated structure facilitates installation, dismantling, and subsequent reuse. The uprights use Φ159×6 (load-bearing columns) and Φ100×6 steel pipes (stabilizing columns), while the horizontal and diagonal braces use [8 channel steel. The top cantilever beams use double-splitting I20a I-beams. The large-spacing chord-supported radial steel pipes are symmetrically cantilevered from the top beams, ensuring safety while reducing the amount of scaffolding required and lowering construction costs.

[0025] The C2 type support column uses Φ159×6 steel pipe, the horizontal and diagonal braces use [8] channel steel, and the top distribution beam uses double-jointed I20a I-beams. A sealing plate is installed at the bottom of the support and welded to the ring beam and radial beam.

[0026] (4) Triangular truss type D support The triangular truss D-type supports are used to support the 11.9m platform triangular truss panels. There are four sets of supports in total: three sets of D1 type and one set of D2 type. Two sets of D1 type supports are for inversion. The uprights are made of Φ273 × 7.5 steel pipe, the diagonal support uprights are made of Φ159 × 6 steel pipe, the circumferential cross braces are made of [14b channel steel and 159 × 6 steel pipe, the diagonal braces are made of [14b channel steel, and the radial cross braces are made of Φ100 × 6 steel pipe.

[0027] The Class D triangular truss brackets are used to support the installation of the 11.9m platform triangular truss panels, improving installation efficiency and ensuring installation accuracy. There are four bracket sets in total: three Class D1 and one Class D2. The uprights are made of Φ273×7.5 steel pipe, the diagonal support uprights are made of Φ159×6 steel pipe, the circumferential cross braces are made of [14b channel steel and 159×6 steel pipe, the diagonal braces are made of [14b channel steel, and the radial cross braces are made of Φ100×6 steel pipe.

[0028] (5) E-class brackets for roof cantilever The E-class cantilever brackets are used for supporting cantilevered installations on the eaves, with a total of twelve sets of brackets for interchange. The columns are made of Φ273×7.5 steel pipe, the horizontal and diagonal braces are made of [8 channel steel, and the diagonal supports are made of [14b channel steel). A support plate is installed at the top of the columns.

[0029] To ensure installation accuracy, Class E brackets are used for support during the cantilevered installation of the eaves. A total of twelve Class E brackets are installed, and they are reversed during installation to reduce construction costs. The uprights are made of Φ273×7.5 steel pipe, the horizontal bracing is made of [8 channel steel, and the cross braces are made of Φ100×6 steel pipe.

[0030] (6) Swaying column clamp diagonal brace The clamps and diagonal braces are used for radial support adjustment during the installation of the swaying column. A total of 45 sets are required, with 20 sets manufactured for reverse use. The lateral circumferential support uses

[14] channel steel. Clamps are installed at a height of 3m on the swaying column. The clamps are made of 10mm thick steel plates, and the diagonal braces are Φ100×6 steel pipes. The adjusting struts are custom-made, using matching Φ80 steel pipes with an effective wall thickness of 10mm.

[0031] The adjustable clamp struts are used for radial support adjustment during the installation of the sway column. A total of 45 sets are required, with 20 sets manufactured for reverse use. The circumferential support uses

[14] channel steel. Clamps are installed at a height of 3m on the sway column. The clamps are made of 10mm thick steel plate, with a 10mm rubber pad between the clamp and the steel pipe. The diagonal brace is a Φ100×6 steel pipe. The adjustable strut diameter is 80mm, and the effective wall thickness is 10mm. The sway column clamps can be adjusted in real time to improve the verticality of the sway column via adjusting the screw, improving installation efficiency and reducing construction costs. The uninstallation method is as follows: (1) Unloading of Class B and A1 supports in the grandstand area 1) A1 support frame in the grandstand area Since the A1 support frame in the grandstand area is located within the grandstand structure, to facilitate the installation of the grandstand structure, the two sets of A1 supports in the grandstand area were removed immediately after the roof cantilever truss + ring truss were installed. At this point, the theoretical maximum downward deflection of the upper ring truss was 8.6mm. Unloading was performed using synchronous flame cutting, and the unloading steps are as follows: Figure 12 As shown, the structural diagram is as follows Figure 13 As shown.

[0032] 2) Class B stent unloading After the installation of all 11.9-meter triangular trusses was completed, the Class B supports in the grandstand area were removed, completing the system conversion. The theoretical maximum downward deflection of the grandstand structure is 9mm. Unloading was carried out using synchronous flame cutting. The unloading steps are as follows: Figure 15 As shown in the diagram, the structural schematic is as follows: Figure 16-18 As shown.

[0033] 3) Class D stent unloading After all the 11.9-meter triangular trusses were installed and the B-type supports were removed, the D-type supports were also removed. The theoretical maximum downward deflection of the triangular trusses was 10mm. Unloading was performed using synchronous flame cutting, and the unloading steps were as follows: Figure 19 As shown, the specific structure is as follows: Figure 20-21As shown.

[0034] (2) Unloading of C-type support for cable-stayed reticulated shell + A-type support for ring truss Through simulation calculation and analysis of the entire tensioning process, it is found that the roof chord support and ring truss support will have an upward displacement during the tensioning of the cable structure, which can be naturally released and unloaded. The unloading steps are shown in Figure 22.

[0035] (3) Temporary connection node unloading During steel structure installation, to ensure installation efficiency, bolted connection plates were used for temporary fixation at the structural joints. These bolted joints were removed after welding was completed. The unloading steps are as follows: Figure 23 As shown.

[0036] Preparations before uninstallation include the following steps: (1) Verify the plane control network and elevation control network, and conduct a preliminary survey to serve as the benchmark for observing structural deformation and displacement during the unloading process.

[0037] (2) Measure and record the initial elevation of the unloading monitoring point before unloading.

[0038] (3) Set up a safety warning line in the unloading area and put up safety warning signs.

[0039] (4) Inspect the unloading area for potential hazards of falling objects from height.

[0040] (5) Inspect the construction operation platform to ensure safety.

[0041] (6) Before unloading, complete the document verification and signing procedures. (7) Before the formal unloading, a comprehensive inspection should be carried out on the equipment, measures, main structure, etc.

[0042] (8) Before demolition, conduct simulation training to explain the operating procedures to all personnel involved in the construction, and conduct technical, quality and safety briefings, and complete the signing procedures.

[0043] During unloading, the unloading operation primarily uses the vertical displacement of the triangular truss as the control method, with the support reaction force as an auxiliary method. Specifically, the unloading of Class B and Class D supports is considered complete when the supporting jaw plate is completely detached. Before unloading, monitoring points for support unloading are set at the same elevation as the inclined columns above the supporting jaw plate. During unloading, the displacement changes of all monitoring points are observed simultaneously and compared with the calculated values. A warning value is set: if the displacement change exceeds the calculated value by more than 5mm, unloading should be stopped immediately, and the cause analyzed and resolved before continuing. One manager and two unloading operators are assigned to each support point. Before unloading, the commander is notified, and a comprehensive inspection of each unloading point is conducted under the commander's direction. Unloading can only begin if there are no problems. Unloading operations must ensure synchronization of all support points and cutting must be performed strictly according to the required dimensions. Before unloading Class B and Class D supports, the connection of each support point must be carefully checked. At this time, the steel structure should be kept in a free state without any additional constraints, and special attention should be paid to ensuring that there are no fixed connections between the support system and the grandstand structure. After each unloading, measurements should be taken at each monitoring point and recorded. If cracks are found in the weld seams of the member nodes or excessive displacement during the unloading process, unloading should be stopped immediately, and rectification measures should be discussed with the steel structure subcontractor, general contractor, supervisor, design and construction units.

[0044] Uninstallation security measures include the following: (1) Establish a safety management team on site to take charge of safety activities, assign full-time safety officers, and strictly implement the safety duty system. During unloading, assign full-time safety officers to be responsible for the safety inspection of the structure, supporting towers, and unloading operation points. Report any safety hazards in a timely manner, stop unloading, and take corresponding measures immediately.

[0045] (2) During unloading, in order to prevent confusion in organization and command, it is necessary to understand the distribution of operators and the details of operation, and strengthen communication.

[0046] (3) When unloading, you must obey the unified command, ensure synchronization, and strictly cut according to the cutting size.

[0047] (4) Conduct safety training for operators before unloading. (5) Before unloading, debris on the structure and debris in the unloading operation area must be cleaned up. During the unloading process, no other work shall be carried out on or off the structure.

[0048] (6) During the unloading process, the coordinating and monitoring personnel should observe at all times to ensure that the workers are in sync. If a problem occurs at one point, the workers at other points should stop unloading.

[0049] (7) Ensure safe passages are in place. In case of an accident, immediately organize personnel to evacuate the unloading area.

[0050] (8) Monitoring and operation are difficult in rainy weather and there are safety hazards. Therefore, unloading operations are avoided in rainy weather and unloading is carried out during the day.

[0051] Support frame abnormal handling measures 1. Deformation caused by exceeding load limits Emergency unloading: Remove excess materials from the supports and suspend hoisting operations; if it is a construction load (such as pouring concrete), pouring must be stopped immediately, and the already poured portion should be supported by temporary supports to share the load.

[0052] Load transfer: Temporary supports (jacks) are added around the deformable support to distribute the original load to the new support and reduce the stress on the deformable component.

[0053] 2. Deformation caused by node failure Bolt joints: For loose bolts, tighten them again with a torque wrench according to the design value; if the bolt is broken or stripped, replace it with a high-strength bolt of the same specification immediately, and tighten the surrounding bolts to enhance the overall integrity.

[0054] Welding joints: For welds that are not fully penetrated or have cracks, remove the defective parts first, and re-weld using low-hydrogen welding rods (E5015). After welding, use ultrasonic testing to check the quality. If the node plate is deformed, add stiffening ribs (weld L100×8 angle steel to both sides of the node plate).

[0055] Pin joint: If the pin is loose, fix it with a wedge and spot weld it to prevent it from falling off; if the pin is bent, replace it with a new pin and apply grease to reduce wear.

[0056] 3. Deformation caused by main structure settlement The supports are mainly located at the top of concrete columns and the ends of beams. During construction, timely inspections are conducted, and feedback is provided to the general contractor immediately.

[0057] 4. Deformation of the component itself (such as bending and buckling) Additional support: For horizontal supports (such as beams) with excessive deflection at mid-span, add vertical columns (such as φ219×8 steel pipes) at mid-span, rooted at the bottom in a solid foundation, and tightened at the top with jacks (pre-loaded with 10% of the design load).

[0058] Component reinforcement: For columns that bend laterally, "clamping + diagonal bracing" is used for reinforcement: double C-shaped steel is wrapped around the bent section (the gap between the steel plate and the column is filled with steel plate), and the two ends are welded and fixed; at the same time, diagonal bracing (angle 45°-60°) is added on both sides of the column body and connected to the surrounding stable structure.

[0059] Replacement of components: If a component is cracked or plastically deformed, remove the failed component directly and replace it with a new component of the same model (the cross-sectional dimensions and material must be checked before installation).

[0060] 5. Deformation caused by environmental factors Wind-resistant reinforcement: For high-altitude supports, add guy ropes (4 ropes per support, symmetrically arranged), one end connected to the top of the support, and the other end anchored to the ground anchor (pull-out force ≥100kN), and adjust the tension according to the wind speed (tighten when the wind speed is >10m / s).

[0061] Temperature difference control: During the hot season, cover the outdoor supports with shade cloth to reduce the temperature difference caused by sunlight; in cold winter regions, take preheating measures for the welded joints (preheating temperature ≥150℃) to avoid low-temperature brittle fracture.

[0062] The detailed uninstallation process uses a reverse removal method, and the specific process is as follows: Step 1: Design and manufacture prefabricated temporary supports and transfer trolleys according to requirements. The temporary supports adopt a prefabricated structure, manufactured in standard sections of 4 meters each. The columns between standard sections are connected by flanges and M16 bolts. Bolt holes are opened at the ends of the diagonal bracing channel steel, which are then bolted to the column connecting plates using M16 bolts. The columns are made of steel pipes, the horizontal and diagonal braces are made of channel steel, and the top distribution beams are made of double-span I20a I-beams. The bottom end plate of the supports is welded to the steel beams using fillet welds with a weld leg height of 8mm.

[0063] like Figures 31-32 As shown, the support structure adopts a prefabricated design, taking into account structural form, connection method, and versatility. Taking the ring truss temporary support as an example, the required heights are approximately 20.4m and 8.5m respectively. Considering the common divisor of heights and ease of installation, 4m was ultimately selected as the standard height, a four-column structure with a column spacing of 1.5m, and bolted connections between sections for easy assembly and disassembly. According to the height classification, A1 type consists of 5 standard sections, and A2 type consists of 2 standard sections. The remaining height is adjusted by the top I20a distribution beam and adjusting pipe. The standard section columns are Φ273×7.5, and the horizontal and diagonal braces are [8 channel steel. For locations without bottom support or where the support position has insufficient bearing capacity, I36a distribution beams are installed to change the support position to meet the support requirements. Simulation calculations were performed on the support structure, and the maximum deflection was found to be approximately 1mm < 2000 / 400 = 5mm, and the maximum stress ratio of the members was 0.77, meeting the specifications.

[0064] The steel frame of the transfer trolley is welded from I-beams. The upper part of the frame is covered with 6mm steel plates, and the lower part of the frame is equipped with 4 sets of universal wheels. Each set consists of 2 two-inch universal brake wheels arranged side by side. Multiple fastening lugs are installed on the outside of the frame, which can be used to fasten disassembled temporary support sections to the trolley via steel wire ropes or aramid ropes.

[0065] Step 2: Install temporary supports and roof structure according to the design drawings. This step is not a key technical point of this application and will not be described in detail.

[0066] Step 3: After the cable structure tensioning is completed, unload the temporary supports, allowing them to detach from the roof structure. The specific process for unloading and detaching the temporary supports from the roof is as follows: Step 1: During the tensioning process of the cable-stayed roof structure, there will be upward displacement. After tensioning is completed, observe whether the arc-shaped support at the top of the temporary support automatically separates from the roof structure.

[0067] Step 2: If there are still unseparated supports, they should be unloaded using a tiered synchronous unloading method, with synchronous flame cutting unloading performed at 15mm intervals.

[0068] Step 3: Once a gap appears between the temporary support and the roof structure, and after monitoring confirms no sagging, the unloading is complete.

[0069] Step 4: Remove the curved support at the top of the temporary support column. Removing the curved support at the top of the temporary support column provides upper space for the subsequent overall lifting of the temporary support.

[0070] Step 5: Remove the cantilevered portion of the distribution beam. The cantilevered distribution beam is designed to support both sides of the roof structure and reduce the amount of temporary supports. During removal, this part of the structure is too long and may collide with the surrounding cable structure. Therefore, it should be cut into smaller parts before removal.

[0071] Step 6: Install the lifting distribution beam and lifting hand chain hoist on the upper part of the roof. The lifting distribution beam is installed on the upper part of the roof. The distribution beam uses double-section I20a I-beams. A U-shaped base plate is installed at the bottom of the distribution beam to connect with the roof pipe, and a lifting lug plate is installed at the top to facilitate the fixing of the lifting hand chain hoist. Furthermore, during later dismantling, the distribution beam is located above the roof structure without obstruction and can be directly moved by crane.

[0072] Step 7: Disconnect the lower connection of the support frame and use a hand-operated hoist to lift the temporary support frame. After dismantling the lower connection of the temporary support frame, use a lifting hand-operated hoist to lift the entire support frame. To ensure stability during the lifting process, a lifting hand-operated hoist should be installed above each steel pipe column, and the lifting operation should be carried out simultaneously. The lifting height should not be too high, exceeding the height of the transfer trolley by 50mm. At the same time, when lifting, observe whether the lifting device and structure are operating normally when it is 50mm away from the bottom surface. Only after confirming that there are no problems can the formal lifting begin.

[0073] Step 8: The transfer trolley drives under the temporary support.

[0074] Step 9: Lower the temporary support and remove the connecting bolts of the lowest standard segment of the support.

[0075] Step 10: Secure the temporary support to the transfer trolley and lift the remaining upper support. The standard section bolts should only be removed after the temporary support has been stably lowered onto the trolley. Immediately after removal, secure the disassembled temporary support section to the trolley using wire rope or aramid rope. Use a targeted wire rope for securing to ensure safe and stable transport. Only after securing is complete can the remaining upper temporary support be lifted using a lifting hand-operated hoist.

[0076] Step 11: The transfer trolley moves a standard segment to the edge of the structure. The trolley is moved 1.5 meters from the edge of the cantilever structure for easy crane lifting and unloading. However, to ensure safety during the lifting and unloading process, the trolley must be secured to the swaying columns on both sides of the structure using steel wire ropes or aramid ropes to stabilize the trolley. Simultaneously, simulation calculations and analyses of the cantilever structure are required, and these analyses are verified to ensure that the structural stress meets the usage requirements.

[0077] Step 12: Use a truck crane to lift the standard section of the temporary support to the ground.

[0078] Step 13: Repeat the above disassembly process until all temporary support segments have been disassembled.

[0079] like Figure 24-25 As shown, for temporary supports with sufficient construction space, after unloading, they can be dismantled section by section from top to bottom using a truck crane or crawler crane, with the process flow being the reverse of the installation process. However, for the aforementioned ring truss type A temporary supports, dismantling should be carried out after the roof installation is completed and the cable structure tensioning is finished. At this time, the supports are located inside the overall structure of the large rotunda. Figure 24 As shown, due to the complex roof structure and dense components, conventional methods, such as direct crane dismantling, lack construction space and necessitate manual dismantling into components for transport. This reduces efficiency and contradicts the design principles of prefabricated scaffolding. However, there is space between the roof structure and the 11.9m platform, with approximately 7m spacing between the sway columns. Considering the dimensions of the prefabricated scaffolding, an innovative reverse dismantling method was proposed. This method involves dismantling the scaffolding from bottom to top, with a designed unloading device to transport temporary scaffolding segments to the outer edge of the 11.9m platform. A truck crane is then used to lower the temporary scaffolding, completing the dismantling process.

[0080] like Figure 26 As shown, the unloading equipment includes a lifting device (manual chain hoist) and a transport device (sliding trolley). The heaviest temporary support dismantled using the reverse dismantling method is approximately 3.5t, so two 3t manual chain hoists are used for lifting. The manual chain hoists are fixed to the lower chord of the ring truss, and four 20mm thick steel plates are welded to the lower chord, with two plates at each hoist position.

[0081] like Figure 27As shown, the design of the sliding trolley mainly considers load-bearing capacity and external dimensions. However, due to space constraints, the lifting height of the entire temporary support is only between 200mm and 300mm. Therefore, controlling the height of the sliding trolley to below 200mm can meet the usage requirements.

[0082] Considering the temporary support column spacing is 1.5m, and to meet requirements for load-bearing capacity, support binding and fixing, and usable height, the final dimensions of the sliding trolley are designed to be 2420mm × 1850mm × 186mm. It uses four sets of swivel casters, each set consisting of two 2-inch swivel brake wheels arranged side-by-side, forming the overall frame of the sliding trolley with I-beams. A 6mm steel plate is laid on top, and perforated stiffening plates are installed on both sides to facilitate binding and fixing of the support during transportation. The overall frame consists of two 2400mm long HW100×100×6×8mm H-beam longitudinal beams and five 1730mm long HW100×100×6×8mm HW100×100×6×8mm H-beam crossbeams. The eight swivel casters are installed at the intersections of the longitudinal and crossbeams, except at the middle crossbeam. Five 10mm perforated steel plates are installed on the outer side of each of the two longitudinal beams, flush with the crossbeams. A single 2-inch swivel brake wheel can bear 300kg, so the theoretical load capacity of the sliding steer trolley is 2400kg. The trolley itself weighs 440kg. Therefore, the maximum load of the sliding steer trolley is controlled below 1800kg, and the heaviest support segment is 1500kg, which can meet the requirements for use.

[0083] like Figures 28-29 As shown, after the temporary support was secured with a hand-operated hoist, the base of the support was cut close to the 11.9m platform floor. Then, the entire support was lifted upwards by 200mm-300mm using the hand-operated hoist. The sliding trolley was moved to the bottom of the support, and the support was slowly lowered onto the sliding trolley, secured with four 8mm abrasion-resistant aramid ropes. The bolts connecting the bottom section to the previous section were loosened. The upper section of the support was lifted using a hand-operated hoist, ensuring it was free from the lower section, and then the lower section was transported to approximately 1.5m outside the sway column using the sliding trolley. Finally, a truck crane was used to lift the support section to the ground. The cantilever bearing capacity of the 11.9m platform is relatively small, so a simulation was conducted. Under no load, the cantilever deflects by 16.8mm, and after the support is transported to the cantilever position, it deflects by 17.75mm. The displacement caused by the load of the support and the transport trolley is approximately 0.95mm < 5800 / 400 = 14.5mm, and the stress of the cantilever steel beam is 30.6MPa < 305MPa, both of which meet the requirements.

[0084] Matters not covered in this invention are common knowledge.

[0085] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for unloading and constructing a large circular cantilevered steel structure support, characterized in that: The method includes the following steps: Step 1: Unload the Class B support frame in the grandstand area, the Class A1 support frame in the grandstand area, and the Class D support frame of the triangular truss. Step 2: Unloading of the C-type support for the cable-stayed reticulated shell and the A-type support for the ring truss; Step 3: Unload the temporary connection node to complete the unloading process.

2. The unloading construction method for a large circular cantilevered steel structure support according to claim 1, characterized in that: The supports include Class A supports for cantilever trusses, Class A supports for ring trusses, Class B supports for grandstand areas, Class C supports for cable-stayed reticulated shells, and Class D supports for triangular trusses. Class A supports for cantilever trusses include A1 supports and A2 supports.

3. The unloading construction method for a large circular cantilevered steel structure support according to claim 1, characterized in that: In step 1, during the unloading of the A1 support in the grandstand area, since the A1 support is located in the grandstand structure area, to facilitate the installation of the grandstand structure, the two sets of A1 supports in the grandstand area were removed after the roof cantilever truss + ring truss were installed. Simulation analysis showed that the theoretical maximum downward deflection of the upper ring truss was 8.6mm. Unloading was carried out using synchronous flame cutting. The unloading process was as follows: a working platform was set up at the cutting point to prepare for cutting, a line was drawn at the cutting position and the maximum displacement was marked, and the two steel pipe support plates were simultaneously flame-cut 15mm. Deformation and stress changes were monitored, and the unloading was confirmed to be complete.

4. The unloading construction method for a large circular cantilevered steel structure support according to claim 1, characterized in that: In step 1, during the unloading of the Class B supports in the grandstand area, after all the 11.9-meter triangular trusses have been installed, the Class B supports in the grandstand area are removed to complete the system transformation. The simulation analysis shows that the theoretical maximum downward deflection of the grandstand structure is 9mm. The unloading is carried out by synchronous flame cutting. The unloading process is as follows: a working platform is set up at the cutting point to prepare for cutting. A line is drawn at the cutting position and the maximum displacement is marked. The 7 support teeth are simultaneously flame-cut by 15mm. Deformation and stress changes are monitored to confirm that the unloading is complete.

5. The unloading construction method for a large circular cantilevered steel structure support according to claim 1, characterized in that: In step 1, during the unloading of the triangular truss D-type support, after all the triangular trusses on the 11.9-meter section have been installed and the B-type support has been removed, the D-type support is removed. Simulation analysis shows that the theoretical maximum downward deflection of the triangular truss is 10mm. Unloading is carried out using synchronous flame cutting. The unloading process is as follows: a working platform is set up at the cutting point to prepare for cutting; a line is drawn at the cutting position and the maximum displacement is marked; the support tooth plate is synchronously cut with flame for 15mm; deformation and stress changes are monitored; and the unloading is confirmed to be complete.

6. The unloading construction method for a large circular cantilevered steel structure support according to claim 1, characterized in that: In step 2, through simulation calculation and analysis of the entire tensioning process, it is found that the roof chord support and ring truss support will have an upward displacement when the cable structure is tensioned, and can be unloaded naturally. The unloading process is as follows: the cable structure completes the first stage of tensioning, the connection weld between the support and the roof is removed, and the cable structure continues to be tensioned until the support is separated from the structure.

7. The unloading construction method for a large circular cantilevered steel structure support according to claim 1, characterized in that: In step 3, during the steel structure installation, bolted connecting plates were used for temporary fixation at the structural docking positions to ensure installation efficiency. After welding, these bolted joints were removed. The specific unloading process is as follows: welding the structural docking seam, removing the bolts and connecting plates, cutting the connecting plates and grinding them.

8. The unloading construction method for a large circular cantilevered steel structure support according to claim 1, characterized in that: It also includes measures for handling abnormalities in the support frame, including deformation caused by overload, deformation caused by node failure, deformation caused by main body settlement, deformation of the component itself, and deformation caused by environmental factors. When deformation is caused by overload, remove excess material from the support and suspend hoisting operations. If it is a construction load, pouring must be stopped immediately. The already poured part should be supported by temporary supports to distribute the load. Temporary supports should be added around the deformed support to distribute the original load to the new support and reduce the stress on the deformed component. When deformation is caused by node failure, loose bolts should be retightened to the design value using a torque wrench. If the bolt is broken or stripped, replace it with a high-strength bolt of the same specification immediately and tighten the surrounding bolts to enhance the overall integrity. For welds that are not fully penetrated or have cracks, remove the defective part first and re-weld using low-hydrogen welding rods. After welding, use ultrasonic testing to check the quality. If the node plate is deformed, add stiffening ribs. If the pin is loose, fix it with wedges and spot weld it to prevent it from falling off. If the pin is bent, replace it with a new pin and apply grease to reduce wear. When deformation occurs due to main body settlement, the support is located at the top of the concrete column and the end of the beam. Timely detection is carried out during construction, and feedback is given to the general contractor as soon as possible. When a component deforms, additional supports are added. For horizontal supports with excessive deflection at mid-span, vertical columns are added at mid-span, rooted in a solid foundation at the bottom and tightened at the top with jacks. For columns that bend laterally, clamps and diagonal braces are used for reinforcement. Double C-shaped steel is wrapped around the bent section, and the gap between the steel plate and the column is filled with steel plate. Both ends are welded and fixed. At the same time, diagonal braces are added on both sides of the column at an angle of 45°-60° and connected to the surrounding stable structure. If a component cracks or undergoes plastic deformation, the failed component is removed directly and replaced with a new component of the same model. When deformation is caused by environmental factors, additional guy ropes are installed for high-altitude supports, with one end connected to the top of the support and the other end anchored to the ground anchor. The tension is adjusted according to the wind speed. In seasons with temperatures higher than the set temperature, sunshade cloths are used to cover the outdoor supports to reduce the temperature difference caused by sunlight. In cold winter regions, preheating measures are taken for welded joints to avoid low-temperature brittle fracture.

9. The unloading construction method for a large circular cantilever steel structure support according to claim 1, characterized in that: All stents were removed using a reverse dismantling method, the specific process of which is as follows: Step 3.1: After the cable structure tensioning is completed, unload the temporary support to detach the support from the roof structure, and set up a transfer trolley; Step 3.2: Remove the arc-shaped support at the top of the temporary support column to provide upper space for the subsequent overall lifting of the temporary support; Step 3.3: Remove the cantilevered portion of the distribution beam; Step 3.4: Install the lifting distribution beam and lifting hand chain hoist on the upper part of the roof; Step 3.5: Disconnect the lower part of the support and use a hand-operated hoist to lift the temporary support; Step 3.6: The transfer trolley moves under the temporary support; Step 3.7: Lower the temporary support and remove the connecting bolts of the lowest standard segment of the support. Secure the temporary support to the transfer trolley and lift the remaining upper support. Step 3.8: The transfer trolley moves a standard segment to the edge of the structure; Step 3.9: Use a truck crane to lift the standard section of the temporary support frame to the ground; Step 3.10: Repeat steps 1-9 of the disassembly process until all temporary support segments have been disassembled.

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