Large-span net rack jacking method under limited site condition

Abstract

The invention provides a method for jacking a large-span net rack under the condition of a limited site, which belongs to the technical field of building construction and comprises the following steps: firstly, determining the stress condition of the net rack and the position of a jacking point through finite element analysis, and drawing a spatial distribution diagram of the jacking point; and according to the distribution diagram, the net rack is deeply decomposed, and the production sequence of the components is determined. A jig frame is arranged on a floor, and parts are projected on the ground according to a net rack to assemble an initial structure. And then a jacking device and a reverse jacking device are installed on the floor, and jacking parameters are optimized through tests. Formal jacking is carried out according to the optimized parameters, and the support needs to be replaced every time jacking is carried out by one meter. Meanwhile, the net rack is kept stable through the cable rope, and the posture of the net rack is monitored in real time. And after the net rack is jacked in place, small hoisting equipment is used for carrying out high-altitude scattered splicing on components at the connecting positions of the periphery and the support, and overall installation is completed. And finally, the jacking device is removed, the whole net rack structure falls to the support, the large-span net rack is installed, and it is guaranteed that the net rack is jacked safely and reliably.

Description

Technical Field

[0001] The invention belongs to the technical field of building construction, and in particular relates to a method for lifting a large-span grid under a limited site condition. Background Art

[0002] As an efficient and beautiful spatial structure system, the large-span grid is widely used in large public buildings such as stadiums and airport terminals. Compared with the traditional beam-column structure, the grid structure has the advantages of large span, light weight and flexible shape, and can create an open and transparent interior space for the building. However, due to the complexity of the grid structure itself, its installation and construction has always been a technical problem.

[0003] Traditional grid installation methods usually adopt the method of full assembly or block hoisting. The full assembly method is to assemble the entire grid structure on the ground and then hoist it as a whole to the support position. This method has high requirements for the on-site construction environment and requires sufficient site space. The block hoisting method is to pre-divide the grid structure into several detachable units and hoist and install them in batches. This method can better adapt to the restricted conditions on site, but the connection between units and the control of overall spatial deformation are more difficult. In addition, both methods require the use of large lifting equipment, which not only has high construction costs, but also has high requirements for on-site roads, traffic conditions, etc. In other words, the existing methods are difficult to accurately determine the position of the lifting point and the size of the lifting force in a small space to ensure the force balance and overall stability of the grid during the lifting process. Summary of the invention

[0004] In view of this, the present invention provides a method for lifting a large-span grid under limited site conditions, which can solve the problem that the existing methods are difficult to accurately determine the lifting point position and the lifting force size in a small space to ensure the force balance and overall stability of the grid during the lifting process.

[0005] The present invention is achieved in that:

[0006] The present invention provides a method for lifting a large-span grid under limited site conditions, comprising the following steps:

[0007] S10, establishing a large-span grid model, and using finite element analysis, load combination analysis, and grid lifting safety equations to perform grid force analysis and calculation, determine the number and positions of jacking points, and obtain a spatial distribution diagram of the jacking points;

[0008] S20, according to the spatial distribution diagram of the jacking points, the grid drawings are further decomposed to determine the production sequence of grid components;

[0009] S30, setting a frame on the floor, performing ground assembly according to the projection positioning of the grid drawing, completing the overall assembly of the jacking area, and forming the initial structure of the grid;

[0010] S40, installing a jacking device on the floor according to the spatial distribution diagram of the jacking points, and setting a counter-jacking device on the floor below the corresponding position of the jacking device;

[0011] S50, testing the jacking device, and determining the jacking parameters through a jacking parameter optimization equation group;

[0012] S60, performing formal jacking according to the optimized jacking parameters, replacing the support and lifting section of the jacking device every time the jacking is lifted by one meter, until the initial structure of the grid is jacked to the designed elevation;

[0013] S70, during the formal jacking process, using cables and wind ropes to maintain the stability of the initial structure of the grid, and monitoring the spatial posture of the initial structure of the grid in real time;

[0014] S80, when the initial structure of the grid is lifted into place, small lifting equipment is used to assemble the grid components connected to the supports at high altitude to complete the overall structure of the grid;

[0015] S90, after the overall structure of the grid falls onto the support, the jacking device is unloaded and removed to complete the overall installation of the large-span grid.

[0016] On the basis of the above technical solution, the method for lifting a large-span grid under limited site conditions of the present invention can also be improved as follows:

[0017] The lifting parameter optimization equation group includes a lift calculation equation, a lifting speed calculation equation and a pressure-flow relationship equation.

[0018] The grid lifting safety equation group includes: static equilibrium equation, dynamic response equation, stability equation and stress distribution equation.

[0019] Furthermore, the static equilibrium equation is used to ensure the force balance of the grid during the jacking process, the input is the grid deadweight, wind load and jacking force, and the output is the displacement of each node of the grid.

[0020] Furthermore, the dynamic response equation is used to analyze the dynamic response of the grid during the jacking process, the input is the mass, stiffness and damping characteristics of the grid, and the output is the vibration frequency and amplitude of the grid.

[0021] Furthermore, the stability equation is used to evaluate the overall stability of the grid during the jacking process, the input is the geometric parameters and material properties of the grid, and the output is the critical buckling load of the grid.

[0022] Furthermore, the stress distribution equation is used to calculate the stress state of each component of the grid, the input is the internal force distribution of the grid, and the output is the stress level of each component.

[0023] Among them, the steps of using finite element analysis, load combination analysis and grid lifting safety equation group to perform grid stress analysis and calculation are as follows: first, a finite element model of the grid is established, then a load combination analysis is performed, and finally, a safety assessment is performed using the grid lifting safety equation group.

[0024] Furthermore, the lifting force calculation equation is used to calculate the required lifting force, the input is the mass of the grid, the lifting height and the lifting speed, and the output is the required lifting force;

[0025] The lifting speed calculation equation is used to determine the lifting speed, the input is the hydraulic pump flow and the hydraulic cylinder area, and the output is the lifting speed;

[0026] The pressure-flow relationship equation is used to optimize hydraulic system parameters, the input is the hydraulic pump power and the system pressure, and the output is the hydraulic pump flow.

[0027] Specifically, the step S10 specifically includes: first, using computer-aided design (CAD) software to establish a three-dimensional geometric model of a large-span grid, the model should include various components of the grid, such as main chords, webs and diagonal bars, and accurately describe the cross-sectional dimensions, material properties and node connection relationships of the components. Then, the finite element analysis method is used to perform a force analysis on the grid model, including establishing a finite element model, determining various load combinations, and using finite element software to solve the internal force distribution, displacement response and stress state of the grid under various loads. In addition, it is also necessary to establish a grid lifting safety equation group to analyze and evaluate the stress state of the grid during the jacking process, including static equilibrium equations, dynamic response equations, stability equations and stress distribution equations. Through the above analysis and calculation, the key parameters in the grid jacking process, such as the number and position of jacking points, can be determined, providing a basis for subsequent jacking construction.

[0028] Specifically, the step S20 specifically includes: first, according to the spatial distribution diagram of the lifting points obtained in step S10, determine the initial assembly area of ​​the grid and the path of the staged lifting. Combined with the structural characteristics of the grid and the construction process requirements, the grid drawings are further decomposed to divide the grid units that can be manufactured independently. Determine the production order of each grid unit, and give priority to those components that are in the initial lifting position and bear greater forces to ensure the overall stability of the grid. For each grid unit, analyze the production order of its internal components, and try to adopt the principle of making easy-to-install components first and then making complex components to improve production efficiency. Finally, compile the overall production sequence table of grid components to provide guidance for subsequent production operations.

[0029] Specifically, the step S30 specifically includes: setting up a temporary support structure, i.e., a tire frame, on the floor where the grid is to be installed. The tire frame should be a steel pipe or steel truss structure, and its height should be able to meet the requirements of the grid lifting. Using the plane projection of the grid drawing, the positioning marks of each grid component are made on the tire frame. According to the manufacturing sequence determined in step S20, the grid components are assembled on the ground according to the marks. During the ground assembly process, the size of each component must be strictly controlled to ensure that they can be assembled accurately, and temporary fixing measures must be taken to ensure that the assembled grid units will not be deformed due to gravity and other effects. After all grid components are assembled on the ground according to the design sequence, the initial structure of the grid can be formed. At this time, the entire grid structure is temporarily erected on the tire frame and has not yet been lifted.

[0030] Specifically, the step S40 specifically includes: according to the spatial distribution diagram of the jacking points obtained in step S10, the position of the jacking device is reasonably arranged on the floor, and the hydraulic jack is selected as the main jacking device, and its number and bearing capacity should match the initial structure of the grid and the stress state during the jacking process. On the floor below each jacking point, a counter-jacking device corresponding to the jacking device is set, and the counter-jacking device can be a reinforced concrete reinforcement plate or a steel plate, and its bearing capacity should be greater than the maximum reaction force during the jacking process. Reliable connection measures should be adopted between the jacking device and the counter-jacking device to ensure that no displacement or falling off occurs during the jacking process. In order to ensure the stability of the overall structure of the grid, fixed support points are appropriately set around the jacking area, and steel cables or steel supports are used to constrain the initial structure of the grid.

[0031] Specifically, the step S50 specifically includes: determining the key parameters required for jacking of the grid, such as jacking force, jacking speed and system pressure, through experimental measurement and parameter fitting according to the jacking force calculation equation, the jacking speed calculation equation and the pressure-flow relationship equation.

[0032] Furthermore, the lifting force calculation equation is specifically expressed as follows:

[0033] F=mg+μv+k1h+k2v 2 +ε F ;

[0034] Where F is the required lifting force (N); m is the mass of the grid (kg); g is the acceleration due to gravity (m / s 2 ), take 9.8; μ is the friction coefficient, ranging from 0.1 to 0.3; v is the lifting speed (m / s); h is the lifting height (m); k1 is the height correlation coefficient (N / m), determined by experiment; k2 is the speed correlation coefficient (N·s 2 / m 2 ), determined by experiment; εF is the error term (N).

[0035] The lifting speed calculation equation is specifically expressed as follows:

[0036]

[0037] Where, v is the lifting speed (m / s); Q is the hydraulic pump flow (m 3 / s); A is the hydraulic cylinder area (m 2 ); k3 is the pulsation coefficient, ranging from 0.01-0.05; ω is the pulsation frequency (rad / s), determined by experiment; t is time (s); ε v is the error term (m / s).

[0038] The pressure-flow relationship equation is specifically expressed as follows:

[0039]

[0040] Where Q is the hydraulic pump flow rate (m 3 / s); P is the hydraulic pump power (W); p is the system pressure (Pa); k4 is the pressure correlation coefficient (m ( 5 / 2)·s ( -1)·N ( -1 / 2)), determined by experiment; ε Q is the error term (m 3 / s).

[0041] The static equilibrium equation is specifically expressed as follows:

[0042]

[0043] Where n is the number of grid nodes; F i is the lifting force of the ith node (N); W i is the self-weight of the ith node (N); L i is the wind load at the ith node (N); ε S is the error term (N).

[0044] The dynamic response equation is specifically expressed as follows:

[0045]

[0046] Where M is the mass matrix (kg); C is the damping matrix (N·s / m); K is the stiffness matrix (N / m); u is the displacement vector (m); F(t) is the time-varying external force vector (N); ε D is the error term (N).

[0047] The stability equation is specifically expressed as follows:

[0048]

[0049] Where P cr is the critical buckling load (N); E is the elastic modulus (Pa); I is the section inertia moment (m 4 ); K is the effective length coefficient, ranging from 0.5-2.0; L is the length of the component (m); A is the cross-sectional area (m 2 ); k5 is the area correlation coefficient (N / m 2 ), determined by experiment; k6 is the moment of inertia correlation coefficient (N / m ( 10 / 3)), determined by experiment; ε P is the error term (N).

[0050] The stress distribution equation is specifically expressed as follows:

[0051]

[0052] Where σ is stress (Pa); N is axial force (N); A is cross-sectional area (m 2 );M y ,M z are the bending moments in the y and z directions (N·m); I y ,I z are the section inertia moments in the y and z directions (m^4); y and z are the coordinates on the section (m); τ is the shear stress (Pa); k7 is the shear stress influence coefficient, ranging from 0.1-0.3; ε σ is the error term (Pa).

[0053] The parameter acquisition method is:

[0054] k1 and k2 are obtained by experimental methods, including step 1: measuring the lifting force at different lifting heights and speeds; step 2: using the least squares method to fit the k1 and k2 values. k3 and ω are obtained by experimental methods, including step 1: measuring the flow fluctuation of the hydraulic system under different working conditions; step 2: obtaining the main pulsation frequency ω and the amplitude coefficient k3 through Fourier analysis. k4 is obtained by experimental methods, including step 1: measuring the flow of the hydraulic pump at different system pressures; step 2: using the least squares method to fit the k4 value. k5 and k6 are obtained by finite element analysis, including step 1: establishing component models with different section parameters; step 2: performing buckling analysis and fitting to obtain k5 and k6 values.

[0055] Specifically, the step S60 specifically includes: according to the optimized lifting parameters determined in step S50, the hydraulic lifting device is started to lift the initial structure of the grid. During the lifting process, the parameters such as the lifting force, lifting speed and system pressure should be monitored in real time and compared with the optimized parameters. If necessary, the lifting speed or system pressure should be adjusted to ensure the safety and stability of the lifting process. For every 1 meter of lifting height, the hydraulic jack should be replaced, that is, the original support point should be replaced to a higher place to ensure that the grid structure is in a state of force balance during the entire lifting process. During the lifting process, a segmented lifting method should also be adopted. After the grid is lifted to a certain height, the lifting is suspended and the structure is checked. After confirming that there is no abnormality, the lifting is continued until the initial structure of the grid is completely lifted to the designed elevation.

[0056] Specifically, the step S70 specifically includes: installing steel cable wind ropes at appropriate positions around the initial structure of the grid. The steel cable wind ropes should be made of high-strength steel wire ropes, and their number and arrangement should meet the stability constraint requirements of the grid structure. One end of the steel cable wind rope is reliably connected to the grid structure, and the other end is fixed to the floor structure or temporary support device. During the jacking process of the grid, the spatial position and deformation state of the grid structure should be monitored in real time. If the monitoring data shows that the grid structure has obvious offset or deformation, measures should be taken immediately to adjust the steel cable tension or local jacking force to adjust the grid structure to the designed position. The monitoring and adjustment of the grid structure should be carried out throughout the entire jacking process to ensure that the grid maintains good overall stability during the jacking process.

[0057] Specifically, the step S80 specifically includes: after the initial structure of the grid is lifted into place and fixed, a small tower crane or other high-altitude working equipment is used to perform high-altitude loose assembly operations at the connection points of the grid around the support. During the high-altitude loose assembly process, the positioning and connection quality of the components should be strictly controlled to ensure the stability of the overall structure of the grid. For the components connected to the support, reliable connection methods such as high-strength bolts or welding should be used. During the high-altitude loose assembly operation, strict safety protection measures should be taken, such as using safety belts, setting up warning areas, etc., to ensure the personal safety of the operators. After all components are installed, the entire grid structure should be fully inspected to ensure that the connection of each component is reliable and the overall deformation meets the design requirements.

[0058] Specifically, the step S90 specifically includes: after the overall structure of the grid falls to the support, a comprehensive inspection shall be conducted on the grid components and their connection with the support to ensure that the grid structure meets the design requirements. After the inspection is correct, the hydraulic jacking device is unloaded and removed. First, the hydraulic system is turned off, and the pressure in the hydraulic cylinder is slowly released to ensure that the grid structure does not fall suddenly. The hydraulic cylinder and its supporting device are removed, and the site is cleaned up. The anti-jacking device, such as reinforced concrete reinforcement plate or steel plate, should also be removed. Finally, the entire grid structure is finally inspected and accepted, focusing on the connection quality, overall deformation and stress state of the grid components to ensure that the structure is safe and reliable.

[0059] Compared with the prior art, the method for lifting a large-span grid under limited site conditions provided by the present invention has the following beneficial effects:

[0060] 1. It can effectively control the stress state of the grid during the lifting process. By establishing a finite element model, the grid structure is accurately analyzed for stress, and the reasonable lifting point position and lifting force are determined to ensure that the grid maintains a balanced force during the entire lifting process, avoiding deformation or damage caused by excessive stress on local components.

[0061] 2. It can effectively control the geometric deformation of the grid during the lifting process. During the lifting process, steel cables and wind ropes are used to constrain the grid structure, monitor the spatial position and deformation state of the grid in real time, and adjust the lifting parameters or local support force in time to ensure that the overall deformation of the grid meets the design requirements.

[0062] 3. It can ensure the connection quality of each component of the grid during the high-altitude assembly process. Small lifting equipment is used to carry out high-altitude assembly in sections, and strict safety protection measures are taken to ensure the quality of operators and construction, thereby ensuring the safety and reliability of the overall structure of the grid.

[0063] 4. It can better adapt to the narrow construction site environment. The present invention adopts the jacking method to install the grid, avoiding the use of large lifting equipment, and has low requirements for on-site roads and traffic conditions, which is conducive to the smooth implementation of construction work under limited site conditions.

[0064] In summary, the large-span grid jacking method proposed in the present invention effectively solves key technical problems such as force balance, geometric deformation control and high-altitude splicing quality during the grid jacking process by establishing an accurate grid structure model, determining optimized jacking parameters, taking effective jacking control measures, and real-time monitoring of the grid structure status. It greatly improves the safety and reliability of the installation of large-span grid structures and solves the problem that the existing methods are difficult to achieve in accurately determining the jacking point position and the jacking force in a small space to ensure the force balance and overall stability of the grid during the jacking process. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] Figure 1 A flow chart of the method provided by the present invention;

[0066] Figure 2 This is a schematic diagram of ground scattered puzzle in the embodiment;

[0067] Figure 3 This is a schematic diagram of the jacking point in place in the embodiment;

[0068] Figure 4 This is a schematic diagram of the jacking process in the embodiment;

[0069] Figure 5 This is a schematic diagram of lifting into place in the embodiment;

[0070] Figure 6 It is a schematic diagram of scattered puzzles around the four sides in the embodiment;

[0071] Figure 7 It is a schematic diagram of unloading the jacking device in the embodiment. DETAILED DESCRIPTION

[0072] In order to make the purpose, technical solution and advantages of the embodiments of the present invention more clear, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0073] like Figure 1 As shown, it is a flow chart of a method for lifting a large-span grid under limited site conditions provided by the present invention. The method comprises the following steps:

[0074] S10, establishing a large-span grid model, and using finite element analysis, load combination analysis, and grid lifting safety equations to perform grid force analysis and calculation, determine the number and location of jacking points, and obtain a spatial distribution diagram of the jacking points;

[0075] S20. According to the spatial distribution diagram of the jacking points, the grid drawings are further decomposed to determine the production sequence of the grid components;

[0076] S30, setting up a frame on the floor, performing ground assembly according to the projection positioning of the grid drawing, completing the overall assembly of the jacking area, and forming the initial structure of the grid;

[0077] S40, according to the spatial distribution diagram of the jacking points, installing a jacking device on the floor, and setting an anti-jacking device on the floor below the corresponding position of the jacking device;

[0078] S50, testing the jacking device, and determining the jacking parameters through a jacking parameter optimization equation group;

[0079] S60, performing formal jacking according to the optimized jacking parameters, replacing the support and lifting section of the jacking device every one meter of jacking, until the initial structure of the grid is jacked to the designed elevation;

[0080] S70, during the formal jacking process, using the wind ropes to maintain the stability of the initial structure of the grid, and monitoring the spatial posture of the initial structure of the grid in real time;

[0081] S80, when the initial structure of the grid is lifted into place, small lifting equipment is used to assemble the grid components connected to the supports at high altitude to complete the overall structure of the grid;

[0082] S90. After the overall structure of the grid falls onto the support, the jacking device is unloaded and removed to complete the overall installation of the large-span grid.

[0083] The specific implementation methods of the above steps are described in detail below:

[0084] Step S10: Establish a large-span grid model, and use finite element analysis, load combination analysis, and grid lifting safety equations to perform grid force analysis and calculation, determine the number and location of jacking points, and obtain a spatial distribution diagram of the jacking points. The specific implementation method is as follows:

[0085] First, a three-dimensional geometric model of the long-span grid is established using computer-aided design (CAD) software. The model should include various components of the grid, such as the main chord, web and diagonal bars, and accurately describe the cross-sectional dimensions, material properties and node connection relationships of the components.

[0086] Then, the finite element analysis method is used to analyze the stress of the grid model. Specifically, the following steps are included: 1) According to the actual use environment and load conditions of the grid, a finite element model of the grid is established, including the unit type, mesh division and boundary conditions of the grid components. 2) According to the requirements of the specification, the various loads on the grid, such as deadweight, live load, wind load, etc., are determined, and different load combinations are used for calculation and analysis. 3) Finite element software is used to solve the internal force distribution, displacement response and stress state of the grid under various loads.

[0087] In addition, it is necessary to establish a grid lifting safety equation group to analyze and evaluate the stress state of the grid during the lifting process. The grid lifting safety equation group includes the following contents:

[0088] Static equilibrium equation Used to ensure the force balance of the grid during the lifting process, where F i is the lifting force of the ith node, W i is the self-weight of the ith node, L i is the wind load at the ith node, ε S is the error term.

[0089] Dynamic response equation It is used to analyze the dynamic response of the grid during the lifting process, where M is the mass matrix, C is the damping matrix, K is the stiffness matrix, u is the displacement vector, F(t) is the time-varying external force vector, ε D is the error term.

[0090] Stability equation It is used to evaluate the overall stability of the grid during the lifting process, where P cr is the critical buckling load, E is the elastic modulus, I is the section inertia moment, K is the effective length factor, L is the member length, A is the cross-sectional area, k5 and k6 are empirical coefficients, ε P is the error term.

[0091] Stress distribution equation Used to calculate the stress state of each member of the grid, where σ is stress, N is axial force, M y and M z are the bending moments in the y and z directions, I y and I z are the section inertia moments in the y and z directions, y and z are the coordinates on the section, τ is the shear stress, k7 is the empirical coefficient, ε σ is the error term.

[0092] Through the above analysis and calculation, the key parameters in the jacking process of the grid, such as the number and location of jacking points, can be determined, providing a basis for subsequent jacking construction.

[0093] Step S20: According to the spatial distribution diagram of the lifting points, the grid drawings are further decomposed to determine the production sequence of grid components. The specific implementation method is as follows:

[0094] According to the spatial distribution diagram of the lifting points obtained in step S10, the initial assembly area of ​​the grid and the path of the staged lifting are determined.

[0095] In combination with the structural characteristics of the grid and the construction process requirements, the grid drawings are further decomposed to divide the grid units that can be manufactured independently.

[0096] Determine the production order of each grid unit, giving priority to those components that are in the initial jacking position and bear greater stress, so as to ensure the overall stability of the grid.

[0097] For each grid unit, the production order of its internal components is analyzed, and the principle of making easy-to-install components first and then complex components is adopted as much as possible to improve production efficiency.

[0098] Prepare the overall manufacturing sequence table of grid components to provide guidance for subsequent production operations.

[0099] The above steps can effectively determine the optimal production sequence of grid components and lay the foundation for subsequent on-site installation and construction.

[0100] Step S30: Set up a frame on the floor, assemble the frame on the ground according to the projection positioning of the grid drawing, complete the overall assembly of the jacking area, and form the initial structure of the grid. The specific implementation method is as follows:

[0101] A temporary support structure, i.e. a cradle, is set up on the floor where the grid is to be installed. The cradle should be a steel pipe or steel truss structure, and its height should be able to meet the requirements of the grid jacking, generally 5-10 meters.

[0102] Using the plane projection of the grid drawing, the positioning marks of the grid components are made on the tire frame. According to the manufacturing sequence determined in step S20, the grid components are assembled on the ground according to the marks.

[0103] During the ground assembly process, the dimensions of each component must be strictly controlled to ensure that they can be assembled accurately. At the same time, temporary fixing measures are taken to ensure that the assembled grid units will not be deformed due to gravity and other effects.

[0104] After all the grid components are assembled on the ground according to the design sequence, the initial structure of the grid can be formed. At this time, the entire grid structure is temporarily erected on the tire frame and has not yet been lifted.

[0105] Through the above steps, the initial assembly of the grid can be completed efficiently, laying the foundation for subsequent jacking operations.

[0106] Step S40: According to the spatial distribution diagram of the jacking points, a jacking device is installed on the floor, and an anti-jacking device is set on the floor below the corresponding position of the jacking device. The specific implementation method is as follows:

[0107] According to the spatial distribution diagram of the jacking points obtained in step S10, the positions of the jacking devices are reasonably arranged on the floor. The number and arrangement of the jacking devices should match the initial structure of the grid and the stress state during the jacking process.

[0108] Hydraulic jacks are selected as the main lifting devices. The hydraulic jacks should have sufficient lifting stroke and load-bearing capacity to meet the needs of grid lifting. The selection of lifting devices should be determined based on factors such as grid weight and lifting height.

[0109] On the floor slab below each jacking point, an anti-jacking device corresponding to the jacking device is set. The anti-jacking device can be a reinforced concrete reinforced plate or a steel plate, and its bearing capacity should be greater than the maximum reaction force during the jacking process.

[0110] Reliable connection measures, such as welding or bolt connection, should be adopted between the jacking device and the counter-jacking device to ensure that no displacement or falling off occurs during the jacking process.

[0111] In order to ensure the stability of the overall structure of the grid, fixed support points are appropriately set around the jacking area, and steel cables or steel supports are used to constrain the initial structure of the grid.

[0112] Through the above measures, the force balance and overall stability of the grid during the jacking process can be ensured, laying a good foundation for subsequent jacking operations.

[0113] Step S50: Test the lifting device and determine the lifting parameters through the lifting parameter optimization equation group. The specific implementation is as follows:

[0114] Lifting force calculation equation (F = mg + μv + k1h + k2v 2 +ε F ): This equation is used to calculate the force required for lifting the grid, where F is the required lifting force, m is the mass of the grid, g is the acceleration of gravity, μ is the friction coefficient, v is the lifting speed, h is the lifting height, k1 and k2 are empirical coefficients, ε F is the error term. The lifting force under different working conditions is measured experimentally, and the values ​​of k1 and k2 are obtained by fitting using the least squares method.

[0115] Lifting speed calculation equation This equation is used to determine the lifting speed, where v is the lifting speed, Q is the hydraulic pump flow, A is the hydraulic cylinder area, k3 is the pulsation coefficient, ω is the pulsation frequency, t is the time, and ε v is the error term. By measuring the flow fluctuation of the hydraulic system under different working conditions, the main pulsation frequency ω and pulsation coefficient k3 are obtained by Fourier analysis.

[0116] Pressure-Flow Relationship Equation This equation is used to optimize the hydraulic system parameters, where Q is the hydraulic pump flow, P is the hydraulic pump power, p is the system pressure, k4 is the empirical coefficient, ε Q is the error term. The value of k4 is obtained by measuring the hydraulic pump flow rate at different system pressures and fitting using the least squares method.

[0117] Through the above-mentioned tests and parameter optimization process, the hydraulic system parameters required for jacking of the grid, such as jacking force, jacking speed and system pressure, can be determined, providing a basis for the subsequent formal jacking operation.

[0118] Step S60: According to the optimized lifting parameters, formal lifting is carried out, and the lifting device is replaced with a lifting section every time the lifting is one meter, until the initial structure of the grid is lifted to the designed elevation. The specific implementation method is as follows:

[0119] According to the optimized lifting parameters determined in step S50, the hydraulic lifting device is started to start lifting the initial structure of the grid.

[0120] During the jacking process, parameters such as the jacking force, jacking speed and system pressure should be monitored in real time and compared with the optimized parameters. If necessary, the jacking speed or system pressure should be adjusted to ensure the safety and stability of the jacking process.

[0121] The hydraulic jack should be replaced and lifted every time the height is raised by 1 meter, that is, the original support point should be moved to a higher place to ensure that the grid structure is in a state of force balance during the entire lifting process.

[0122] During the lifting process, the lifting method should be adopted in sections, that is, after lifting the grid to a certain height, the lifting should be stopped and the structure should be checked, and the lifting should be continued after confirming that there is no abnormality. This kind of section lifting is conducive to controlling the deformation and stress state of the grid structure.

[0123] Until the initial structure of the grid is fully lifted to the designed elevation, the entire lifting process is completed. At this point, the grid structure is basically in place and ready to enter the next step of loose assembly installation.

[0124] By precisely controlling the lifting parameters and taking measures such as segmented lifting and replacement lifting, the overall stability of the grid and the safety of the stress state of the components during the lifting process can be ensured.

[0125] Step S70: During the formal lifting process, the stability of the initial structure of the grid is maintained by using the guy ropes, and the spatial posture of the initial structure of the grid is monitored in real time. The specific implementation is as follows:

[0126] Steel cables and wind ropes are installed at appropriate locations around the initial structure of the grid. High-strength steel wire ropes should be used for the steel cables and their quantity and arrangement should meet the stability constraint requirements of the grid structure.

[0127] One end of the steel cable wind rope is reliably connected to the grid structure, and the other end is fixed to the floor structure or temporary support device. By adjusting the tension of the steel cable, the plane displacement and inclination angle of the grid structure during the jacking process can be controlled.

[0128] During the jacking process of the grid, the spatial position and deformation state of the grid structure should be monitored in real time, such as by using equipment such as a total station or camera, and compared and analyzed with the design requirements.

[0129] If the monitoring data shows that the grid structure has obvious deviation or deformation, measures should be taken immediately to adjust the tension of the steel cables or the local lifting force to adjust the grid structure to the designed position.

[0130] Monitoring and adjustment of the grid structure should be carried out throughout the entire jacking process to ensure that the grid maintains good overall stability during the jacking process.

[0131] Through the above measures, the spatial position and deformation of the grid during the jacking process can be effectively controlled to avoid serious consequences caused by structural instability.

[0132] Step S80: After the initial structure of the grid is lifted into place, a small lifting device is used to assemble the grid components connected to the supports at high altitude to complete the overall structure of the grid. The specific implementation method is as follows:

[0133] After the initial structure of the grid is lifted into place and fixed, a small tower crane or other aerial work equipment is used to carry out high-altitude loose assembly work around the grid where it is connected to the supports.

[0134] During the high-altitude assembly process, the positioning and connection quality of the components should be strictly controlled to ensure the stability of the overall structure of the grid. For the components connected to the support, reliable connection methods such as high-strength bolts or welding should be used.

[0135] During high-altitude assembly operations, strict safety protection measures should be taken, such as using safety belts, setting up warning areas, etc., to ensure the personal safety of operators.

[0136] For some key components that are subject to greater forces or have more complex connections, they can be prefabricated and debugged on the ground in advance and then hoisted to high altitudes to improve construction efficiency and quality.

[0137] As the surrounding components are installed one after another, the overall structure of the grid is gradually formed. After all components are installed, the entire grid structure should be fully inspected to ensure that the connections of each component are reliable and the overall deformation meets the design requirements.

[0138] Through the above steps, the final assembly of the overall grid structure can be completed efficiently under the premise of ensuring construction safety, laying the foundation for subsequent use and acceptance.

[0139] Step S90: After the overall structure of the grid falls to the support, the lifting device is unloaded and removed to complete the overall installation of the large-span grid. The specific implementation method is as follows:

[0140] After the overall grid structure falls onto the support, a comprehensive inspection shall be carried out on all grid components and their connections with the support to ensure that the grid structure meets the design requirements.

[0141] After checking that everything is correct, unload and remove the hydraulic jacking device. First, turn off the hydraulic system and slowly release the pressure in the hydraulic cylinder to ensure that the grid structure will not fall suddenly.

[0142] Remove the hydraulic cylinder and its supporting device, and clean up the site. Anti-top devices, such as reinforced concrete reinforcement plates or steel plates, should also be removed.

[0143] Finally, the entire grid structure is subject to final inspection, with a focus on checking the connection quality, overall deformation and stress state of each grid component to ensure that the structure is safe and reliable.

[0144] Through the above steps, the safety of the large-span grid lifting process can be ensured, and the final installation of the overall grid structure can be completed, providing good prerequisites for subsequent use.

[0145] In summary, the large-span jacking method proposed in the present invention can ensure the overall stability and safety of the truss during the jacking process by establishing an accurate finite element model, determining key jacking parameters, taking effective jacking measures, and real-time monitoring and adjusting the truss structure status.

[0146] Specifically, the principle of the present invention is:

[0147] 1. Grid structure analysis and jacking point determination

[0148] Firstly, the finite element analysis method is used to establish a three-dimensional geometric model of the long-span grid. The model should accurately describe the geometric dimensions, material properties and node connection relationships of each grid component.

[0149] Then, according to the actual use environment and load conditions of the grid, the grid model is subjected to force analysis and calculation, including: determining the various loads on the grid, such as deadweight, live load and wind load, etc.; using finite element software to solve the internal force distribution, displacement response and stress state of the grid under various loads.

[0150] In addition, it is necessary to establish a set of safety equations for truss lifting, including static equilibrium equations, dynamic response equations, stability equations and stress distribution equations, to analyze and evaluate the stress state of the truss during the lifting process.

[0151] Through the above analysis and calculation, the key parameters in the jacking process of the grid can be determined, such as the number, position and size of the jacking force of the jacking points, providing a basis for subsequent jacking construction.

[0152] 2. Prefabrication and initial construction of grid structure

[0153] According to the determined distribution of lifting points, the grid drawings are further decomposed to determine the manufacturing sequence of each unit of the grid. This can improve production efficiency and lay the foundation for the initial construction of the grid.

[0154] A temporary support structure (cradle) is set up on the floor. According to the plane projection of the grid drawings, the grid components are positioned on the cradle and assembled on the ground to form the initial structure of the grid. Figure 2 At this time, the entire grid structure is temporarily erected on the tire frame and has not yet been lifted.

[0155] 3. Lifting device layout and parameter optimization

[0156] According to the jacking point position determined in step 1, the hydraulic jacking device is reasonably arranged on the floor. In order to ensure the force balance and stability of the grid during the jacking process, a corresponding anti-jacking device is required to be set on the floor below each jacking point, and the two are fixed together by a reliable connection method.

[0157] Then, through experimental testing, the key parameters required for the jacking of the grid, such as jacking force, jacking speed and system pressure, are determined. Specifically, the values ​​of various empirical coefficients are obtained by measuring and fitting parameters using the jacking force calculation equation, jacking speed calculation equation and pressure-flow relationship equation, so as to determine the optimized jacking parameters, such as Figure 3 shown.

[0158] 4. Sectional lifting and monitoring of grid structure

[0159] According to the optimized lifting parameters, the initial structure of the grid is lifted in sections. During the lifting process, key parameters such as lifting force, lifting speed and system pressure should be monitored in real time and compared with the optimized parameters. If necessary, the lifting speed or system pressure should be adjusted to ensure the safety and stability of the lifting process.

[0160] At the same time, steel cable wind ropes are installed at appropriate positions around the initial structure of the grid. By adjusting the tension of the steel cable, the plane displacement and tilt angle of the grid during the lifting process can be effectively controlled to ensure that the overall geometric deformation meets the requirements. The spatial position and deformation state of the grid are monitored in real time, and adjustment measures are taken in time, such as Figure 4 shown.

[0161] After the initial structure of the grid is lifted to the designed elevation, Figure 5 As shown, small lifting equipment is then used to assemble the grid components connected to the supports at high altitude. Figure 6 As shown, the final installation of the overall grid structure is completed. Figure 7 shown.

[0162] In summary, the large-span grid jacking method proposed in the present invention fully considers key factors such as the stress state of the grid during the jacking process, the geometric deformation characteristics and the high-altitude splicing quality, and effectively solves the problems existing in the prior art by establishing an accurate grid structure model, determining optimized jacking parameters, taking effective jacking control measures, and real-time monitoring of the grid structure status, providing a reliable technical solution for the efficient installation of similar large-span grid structures.

[0163] The following is an example of a specific application scenario of the present invention: A new construction project of a gymnasium adopts a large-span grid structure with a span of 150 meters and a coverage area of ​​about 12,000 square meters. Since the gymnasium is located in the city center, surrounded by dense buildings and a small construction site, it is impossible to use the traditional full assembly or block lifting method to install the grid. Therefore, the project adopts the large-span grid lifting method proposed in the present invention, which comprehensively solves the key technical problems in the grid installation process and ensures the construction quality and safety of the project.

[0164] Grid structure analysis and jacking point determination

[0165] First, the project team used computer-aided design (CAD) software to establish a three-dimensional geometric model of the long-span grid. The grid consists of main chords, webs and diagonal bars. The main chords are made of Φ550×30mm thick-walled steel pipes, and the webs and diagonal bars are made of Φ325×16mm medium-thick steel pipes. The material of each component of the grid is Q345 steel, with an elastic modulus of 2.06×10^11Pa and a yield strength of 345MPa.

[0166] Then, the finite element analysis software was used to calculate the stress of the grid model. According to relevant specifications, load conditions such as grid deadweight, live load (4kN / m2) and design wind load (0.9kN / m2) were considered. Through finite element analysis, the internal force distribution, displacement response and stress state of the grid under various loads were obtained.

[0167] At the same time, a safety equation group for lifting the grid was established to evaluate the force balance, dynamic response, overall stability and stress distribution during the lifting process. According to calculations, the critical buckling load of the grid structure during the lifting process is 128kN and the maximum stress is 215MPa, which meets the requirements for safe use of the structure.

[0168] According to the above analysis results, 16 key lifting points in the jacking process of the grid are determined, and their spatial distribution is shown in Table 1. Among them, one lifting point is set at each of the four corners of the grid and three lifting points are set in the middle to ensure the force balance of the grid during the jacking process.

[0169] Table 1 Spatial distribution of jacking points of grid

[0170] Lifting point number X coordinate (m) Y coordinate (m) Z coordinate (m) 1 0 0 5.0 2 75 0 5.0 3 150 0 5.0 4 150 75 5.0 5 75 75 5.0 6 0 75 5.0 7 37.5 37.5 5.0 8 112.5 37.5 5.0 9 150 37.5 5.0 10 75 37.5 5.0 11 0 37.5 5.0 12 37.5 0 5.0 13 112.5 0 5.0 14 150 75 5.0 15 75 75 5.0 16 0 75 5.0

[0171] Prefabrication and initial construction of grid structure: According to the distribution of jacking points determined in step 1, the grid production drawings are further decomposed and the manufacturing sequence of each unit of the grid is reasonably arranged. First, the main components located in the initial jacking area, such as the main chord and some key web members and diagonal members, are manufactured, and then other components are manufactured. This not only improves the production efficiency, but also helps to ensure the overall stability of the initial structure of the grid.

[0172] At the construction site, a steel pipe support structure is set up as a temporary frame on the floor where the grid is to be installed. The height of the frame is 8 meters, which can meet the needs of subsequent grid lifting. Then, according to the plane projection of the grid drawing, the positioning marks of each grid component are made on the frame. According to the manufacturing sequence determined in step 1, the grid units are assembled on the ground. During the assembly process, temporary supports are used to fix the assembled grid units to ensure that they will not deform due to their own weight.

[0173] Finally, the initial structure of the grid was completed by splicing it on the ground, and the entire grid structure was temporarily erected on an 8-meter-high frame.

[0174] Lifting device layout and parameter optimization: According to the 16 jacking point locations determined in step 1, a corresponding number of hydraulic jacks are arranged on the floor as jacking devices. A corresponding anti-jacking device is also set on the floor slab below each jacking point, using a reinforced concrete reinforcement plate with a thickness of 300 mm. The jacking device and the anti-jacking device are connected together by high-strength bolts to ensure that they will not be displaced or fall off during the jacking process.

[0175] In order to determine the optimized lifting parameters, the project team conducted experimental tests on the hydraulic system. First, the lifting force required by the grid structure was measured under different lifting heights and speeds, and the formula F = mg + μv + k1h + k2v was used to calculate the lifting force. 2 +ε F After fitting analysis, we obtained k1 = 800 N / m and k2 = 120 N·s 2 / m 2 .

[0176] Secondly, the flow fluctuation of the hydraulic system under different working conditions was measured, and the main pulsation frequency ω=2π×0.5rad / s and pulsation coefficient k3=0.03 ​​were obtained through Fourier analysis. Furthermore, the flow of the hydraulic pump was measured under different system pressures, and the formula was used to calculate the flow rate of the hydraulic pump. After fitting, we obtained k4 = 3.6 × 10 -7 m 5 / 2 ·s -1 ·N -1 / 2.

[0177] Based on the above test results, the optimized lifting parameters are determined as follows: lifting force F = 4200kN, lifting speed v = 0.015m / s, system working pressure p = 28MPa. These parameters can ensure the force balance and overall stability of the grid during the lifting process.

[0178] Segmented lifting and monitoring of the grid structure: Based on the optimized lifting parameters mentioned above, the project team began to lift the initial structure of the grid in segments. First, 16 hydraulic jacks were started to lift the grid as a whole at the same lifting speed and force. During this process, the lifting force, lifting speed and system pressure of each lifting point were monitored in real time and compared with the optimized parameters. When the actual parameters of a certain detection point deviated from the optimized value by more than 5%, the lifting force or speed of that point was adjusted immediately to ensure the safety of the entire lifting process.

[0179] At the same time, 16 steel cables and wind ropes were set up around the initial structure of the grid. One end of these steel cables and wind ropes is reliably connected to the grid structure, and the other end is fixed to the surrounding floor structure. By adjusting the tension of the steel cables, the plane displacement and tilt angle of the grid during the jacking process can be effectively controlled. In addition, the project team also used a total station to monitor the spatial position and deformation of the grid structure in real time. Once abnormal deformation is found, measures are immediately taken to adjust the tension of the steel cables or the local jacking force.

[0180] After 5 days of segmented lifting, the initial structure of the grid was successfully lifted to the designed elevation of 8 meters. During this process, monitoring data showed that the maximum displacement of the grid structure was 32mm and the maximum stress was 185MPa, both meeting the design requirements.

[0181] High-altitude assembly and final installation of the grid: After the initial structure of the grid was lifted into place, the project team used a 10-ton tower crane to assemble the grid components connected to the supports on all sides. During the high-altitude operation, the workers wore safety helmets and safety belts, and warning signs were set up in the operation area to ensure construction safety.

[0182] Through high-altitude assembly, the connecting components of the grid around the support were put in place one by one, and the entire grid structure was finally installed. After testing, the connection quality of the grid components was good, and the overall deformation met the design requirements. Finally, the jacking device was dismantled to complete the overall installation of the large-span grid.

[0183] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for lifting a large-span grid under limited site conditions, characterized in that: The following steps are involved: S10, establishing a large-span grid model, and using finite element analysis, load combination analysis, and grid lifting safety equations to perform grid force analysis and calculation, determine the number and positions of jacking points, and obtain a spatial distribution diagram of the jacking points; S20, according to the spatial distribution diagram of the jacking points, the grid drawings are further decomposed to determine the production sequence of grid components; S30, setting a frame on the floor, performing ground assembly according to the projection positioning of the grid drawing, completing the overall assembly of the jacking area, and forming the initial structure of the grid; S40, installing a jacking device on the floor according to the spatial distribution diagram of the jacking points, and setting a counter-jacking device on the floor below the corresponding position of the jacking device; S50, testing the jacking device, and determining the jacking parameters through a jacking parameter optimization equation group; S60, performing formal jacking according to the optimized jacking parameters, replacing the support and lifting section of the jacking device every time the jacking is lifted by one meter, until the initial structure of the grid is jacked to the designed elevation; S70, during the formal jacking process, using cables and wind ropes to maintain the stability of the initial structure of the grid, and monitoring the spatial posture of the initial structure of the grid in real time; S80, when the initial structure of the grid is lifted into place, small lifting equipment is used to assemble the grid components connected to the supports at high altitude to complete the overall structure of the grid; S90, after the overall structure of the grid falls onto the support, the jacking device is unloaded and removed to complete the overall installation of the large-span grid.

2. The method for lifting a large-span grid under limited site conditions according to claim 1, characterized in that: The lifting parameter optimization equation group includes a lift calculation equation, a lifting speed calculation equation and a pressure-flow relationship equation.

3. The method for lifting a large-span grid under limited site conditions according to claim 1, characterized in that: The grid lifting safety equation group includes: static balance equation, dynamic response equation, stability equation and stress distribution equation.

4. The method for lifting a large-span grid under limited site conditions according to claim 3 is characterized in that: The static balance equation is used to ensure the force balance of the grid during the lifting process. The input is the grid deadweight, wind load and lifting force, and the output is the displacement of each node of the grid.

5. The method for lifting a large-span grid under limited site conditions according to claim 3 is characterized in that: The dynamic response equation is used to analyze the dynamic response of the grid during the jacking process, the input is the mass, stiffness and damping characteristics of the grid, and the output is the vibration frequency and amplitude of the grid.

6. The method for lifting a large-span grid under limited site conditions according to claim 3 is characterized in that: The stability equation is used to evaluate the overall stability of the grid during the jacking process, the input is the geometric parameters and material properties of the grid, and the output is the critical buckling load of the grid.

7. The method for lifting a large-span grid under limited site conditions according to claim 3 is characterized in that: The stress distribution equation is used to calculate the stress state of each component of the grid, the input is the internal force distribution of the grid, and the output is the stress level of each component.

8. The method for lifting a large-span grid under limited site conditions according to claim 1 is characterized in that: The steps of using finite element analysis, load combination analysis and grid lifting safety equation group to perform grid stress analysis and calculation are as follows: first, a finite element model of the grid is established, then a load combination analysis is performed, and finally, a safety assessment is performed using the grid lifting safety equation group.

9. The method for lifting a large-span grid under limited site conditions according to claim 2, characterized in that: The lifting force calculation equation is used to calculate the required lifting force, the input is the grid mass, lifting height and lifting speed, and the output is the required lifting force; The lifting speed calculation equation is used to determine the lifting speed, the input is the hydraulic pump flow and the hydraulic cylinder area, and the output is the lifting speed; The pressure-flow relationship equation is used to optimize hydraulic system parameters, the input is the hydraulic pump power and the system pressure, and the output is the hydraulic pump flow.

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