Method for splicing ultra-large-span net rack floor

Abstract

The invention provides a super-large-span net rack floor splicing method, and belongs to the technical field of building construction.The method includes the steps that a three-dimensional stress monitoring device is arranged in the net rack splicing process to collect the stress distribution state of gusset plates in real time, and a single-ball-with-single-rod and single-ball-with-double-rod progressive splicing mode is adopted; when the stress concentration coefficient of the gusset plate is close to 75% of a material allowable value, prestress release adjustment is conducted immediately, meanwhile, a plumb bob instrument and a total station are used for continuously measuring the deviation value of the center of sphere position and conducting fine adjustment and resetting, and through a double real-time monitoring feedback mechanism of the stress state and the geometric position, the stress concentration coefficient of the gusset plate is measured; the stress accumulation in the whole splicing process is controlled to be below a safety threshold value, it is ensured that the offset of the axis of the rod piece and the overall deformation of the net rack meet the design requirements, and the technical problem that overall deformation exceeds the limit due to stress accumulation in the super-large-span net rack floor splicing process is solved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of building construction, and in particular relates to a method for assembling a super-large-span net rack floor. BACKGROUND

[0002] In the construction of a super-large-span net rack in an airport terminal, the traditional assembly method adopts a construction process of first assembling in whole and then hoisting in whole or segment hoisting and docking. The net rack structure is supported by a temporary support frame system, and after all the node assembly and welding are completed, the whole is unloaded, and a stable structure system is formed relying on the rigidity of the net rack. This method is widely used in the construction of small and medium-span net racks and is mature in technology. However, in the process of assembling a super-large-span net rack, the number of bars and nodes increases exponentially due to the increase in the span of the net rack. The stress of each node cannot be monitored in real time in the process of assembling by the traditional method, and the prestress generated when the bars are connected one by one accumulates in the structure. When the accumulated stress exceeds the bearing capacity of the node plate material, local stress concentration will be caused, which will further cause the welding seam to crack or the bar axis to deviate, and finally the overall deformation of the net rack will exceed the design allowable value, which will seriously affect the safety and use function of the structure. That is, there is a technical problem in the prior art that the overall deformation exceeds the limit due to stress accumulation in the process of assembling a super-large-span net rack floor. SUMMARY

[0003] Therefore, the present application provides a method for assembling a super-large-span net rack floor, which can solve the technical problem that the overall deformation exceeds the limit due to stress accumulation in the process of assembling a super-large-span net rack floor in the prior art.

[0004] The present application is implemented as follows: The present application provides a method for assembling a super-large-span net rack floor. A reference assembly grid is set in the floor assembly area. A total station is used to determine the design coordinate points of the ball centers of each lower chord. A three-way stress monitoring device is set at each design coordinate point of the ball center of the lower chord. A single-ball single-bar method is used to install the ball-bar units of the lower chord one by one, and a plumb instrument is used to measure the ball center deviation to adjust and reset the ball nodes. A single-ball double-bar method is used to install the upper chord balls and web bars, and the real-time stress data of the node plates of the three-way stress monitoring device are recorded. The stress concentration coefficient of the node plate is calculated and the prestress is released and adjusted. The node plate welding area is preheated in sections before welding and ultrasonic flaw detection. After the net rack is assembled, the bar axis deviation is measured and the axis is corrected by adding temporary support rods. The overall deformation of the assembled net rack is detected. The stress accumulation in the whole assembly process is controlled below the safety threshold through the dual real-time monitoring feedback mechanism of stress state and geometric position.

[0005] In the step of setting a reference assembly grid in the floor assembly area, the number of parallel assembly paths for multiple construction groups is calculated according to the total number of net rack nodes and the number of construction groups.

[0006] Among them, the calculation of the parallel assembly path of multiple construction groups adopts the graph coloring algorithm to color the vertex subsets so that adjacent vertices belong to different vertex subsets. The shortest Hamiltonian path algorithm is used to calculate the assembly order for each vertex subset.

[0007] In the calculation of the parallel assembly path of multiple construction groups, each edge is assigned a weight value to represent the assembly difficulty coefficient. The assembly difficulty coefficient is determined based on the height of the node position and the number of rods already installed around the node.

[0008] The assembly difficulty coefficient is determined by dividing the node height by the maximum height of the space frame and multiplying by 0.6, and then adding the number of installed members around the node divided by the total number of members designed for the node and multiplying by 0.4.

[0009] Among them, the triaxial stress monitoring device is a group of strain gauges installed in the three main stress directions of the node plate, which is used to collect the stress distribution of the node plate under the action of multi-directional tensile force in real time.

[0010] The lower chord club units are installed one by one using a single ball and single club method. After each lower chord club unit is installed, the deviation between the actual coordinate point of the lower chord ball center and the designed coordinate point of the lower chord ball center is measured using a plumb bob.

[0011] When the ball center deviation is less than 3mm, record the actual coordinates of the lower chord ball center and continue installing the next lower chord club unit. When the ball center deviation is greater than or equal to 3mm, perform fine-tuning and reset of the ball node until the ball center deviation is less than 3mm.

[0012] Among them, the ball node fine-tuning reset is achieved by adjusting the tightness of the bolts at the connection between the ball node and the member or by increasing the thickness of the adjusting shims, so that the actual coordinate point of the lower chord ball center returns to the design coordinate point of the lower chord ball center.

[0013] The upper ball and the web bar are installed using a single ball with two bars. A third web bar is used to form a triangular stable structure. The actual coordinates of the center of the upper ball are measured using a plumb bob.

[0014] The stress concentration factor of the gusset plate is the ratio of the maximum stress value of the gusset plate to the average stress value of the gusset plate. When the stress concentration factor of the gusset plate is less than 75% of the allowable stress concentration factor of the gusset plate material, the actual coordinate point of the upper chord ball center is recorded and the next upper chord ball bar unit is installed.

[0015] When the stress concentration factor of the gusset plate is greater than or equal to 75% of the allowable stress concentration factor of the gusset plate material, the prestress release adjustment of the members around the gusset plate is carried out until the stress concentration factor of the gusset plate is less than 75% of the allowable stress concentration factor of the gusset plate material.

[0016] The segmented preheating process divides the weld area of ​​the node plate into multiple preheating segments, and heats each segment to the preheating temperature value in sequence from the center of the weld to both sides, and then holds it at that temperature.

[0017] The preheating temperature value is determined by multiplying the carbon equivalent value of the node plate material by 450 and then adding the negative value of the ambient temperature value by 1.2, with the unit being °C.

[0018] After welding, ultrasonic testing is performed on the weld to obtain the depth of crack defects. When the depth of crack defects is less than or equal to 15% of the weld thickness, the weld qualification mark is recorded and welding of the next node plate continues.

[0019] The allowable value for the deviation of the design axis position is the upper limit of the allowable offset of the member axis determined according to the span of the space frame and the structural importance coefficient. For the space frame of an airport terminal with a super large span, it is taken as 0.2% of the span of the space frame.

[0020] This invention utilizes a triaxial stress monitoring device at the designed coordinate point of each lower chord sphere to collect real-time stress distribution data of the node plate. Combined with a progressive assembly method using single-sphere-with-single-rod and single-sphere-with-double-rod configurations, the stress concentration factor of the node plate is continuously monitored during assembly. When the stress concentration factor approaches 75% of the material's allowable stress concentration factor, prestress release adjustment is immediately implemented. This involves temporarily loosening surrounding member connections or adjusting the assembly sequence to redistribute excessive local stress to surrounding members, preventing excessive stress concentration at a single node. Simultaneously, a plumb bob and total station are used to measure the deviation between the actual coordinate point and the designed coordinate point of the sphere center at each assembly stage. When the deviation exceeds 3mm, the sphere node is immediately fine-tuned and reset. By adjusting the bolt tightness or increasing the thickness of the shims, the sphere center position is returned to the designed position, ensuring that the member axis offset is always controlled within the design allowable range. This ensures that stress accumulation is controlled below the safety threshold throughout the assembly process, guaranteeing that the overall deformation of the space frame meets design requirements. In summary, the present invention solves the technical problem mentioned in the background art of stress accumulation leading to excessive overall deformation during the assembly of ultra-large span space frame floors. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the space frame structure involved in the embodiment.

[0022] Figure 2 This is a parallel assembly path planning diagram for multiple construction groups in the embodiment.

[0023] Figure 3 This is a diagram illustrating the positioning and measurement process of the lower chord cue in the embodiment.

[0024] Figure 4 This is a monitoring diagram of the stress distribution at the upper chord ball node in the embodiment.

[0025] Figure 5 This is a diagram showing the overall deformation distribution of the space frame in the embodiment.

[0026] Figure 6 This is a schematic diagram of the positioning of the topspin cue.

[0027] Figure 7 This is a schematic diagram of the positioning of the bottom string club.

[0028] Figure 8 This is a schematic diagram of a hoisting setup consisting of a ball and a rod.

[0029] Figure 9 This is a schematic diagram of the hoisting of a two-pole configuration with a ball. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0031] This invention provides a method for assembling ultra-large span space frame floors, comprising the following steps:

[0032] S01. Set up an assembly reference grid in the floor assembly area, use a total station to measure the design coordinate points of the center of each lower chord sphere, set up a triaxial stress monitoring device at each design coordinate point of the center of each lower chord sphere, and mark the outer contour projection line of the sphere at the corresponding position on the floor. Calculate the parallel assembly path of multiple construction groups based on the total number of grid nodes and the number of construction groups.

[0033] S02. Install the lower chord club units one by one using a single ball and single club method. After installing each lower chord club unit, measure the deviation between the actual coordinate point of the lower chord ball center and the designed coordinate point of the lower chord ball center using a plumb bob. When the ball center deviation is 0mm to 3mm, record the actual coordinate point of the lower chord ball center and continue installing the next lower chord club unit. When the ball center deviation is greater than 3mm, perform ball node fine-tuning and reset until the ball center deviation is 0mm to 3mm.

[0034] S03. The upper chord ball and web member are installed using a single ball with two bars. A triangular stable structure is formed using the third web member. The actual coordinates of the center of the upper chord ball are measured using a plumb bob. The real-time stress data of the node plate of the triaxial stress monitoring device is recorded. The stress concentration factor of the node plate is calculated. When the stress concentration factor of the node plate is less than 75% of the allowable stress concentration factor of the node plate material, the actual coordinates of the center of the upper chord ball are recorded and the next upper chord ball and bar unit is installed. When the stress concentration factor of the node plate is greater than or equal to 75% of the allowable stress concentration factor of the node plate material, the prestress release adjustment of the bars around the node plate is performed until the stress concentration factor of the node plate is less than 75% of the allowable stress concentration factor of the node plate material.

[0035] S04. Before welding the node plate to the member, the weld area of ​​the node plate is preheated in sections. The preheating temperature is calculated based on the carbon equivalent of the node plate material and the ambient temperature. Welding is performed after heating to the preheating temperature. After welding, ultrasonic testing is performed on the weld to obtain the crack defect depth. When the crack defect depth is less than or equal to 15% of the weld thickness, the weld qualification mark is recorded and the next node plate welding continues. When the crack defect depth is greater than 15% of the weld thickness, repair welding is performed and the process returns to step S04 to perform ultrasonic testing again.

[0036] S05. After the space frame assembly is completed, use a total station to measure the actual coordinates of all lower chord ball centers and upper chord ball centers, calculate the offset of the member axis, and when the offset of the member axis is less than or equal to the allowable value of the design axis position deviation, record the space frame assembly qualification mark and proceed to step S06. When the offset of the member axis is greater than the allowable value of the design axis position deviation, the axis is corrected by adding temporary support rods and then return to step S02 to reinstall the lower chord ball unit.

[0037] S06. Perform overall deformation detection on the assembled space frame. Use a total station to measure the actual coordinates of key nodes of the space frame and calculate the overall deformation of the space frame. When the overall deformation of the space frame is less than or equal to the allowable value of the overall deformation of the space frame, the assembly is completed. When the overall deformation of the space frame is greater than the allowable value of the overall deformation of the space frame, return to step S02 and reinstall the lower chord ball bar unit.

[0038] The calculation steps for the parallel assembly path of multiple construction groups include: treating all nodes of the grid as a set of vertices in a graph, treating the assembly order constraints between adjacent nodes as a set of edges in the graph, assigning a weight value to each edge to represent the assembly difficulty coefficient, dividing the vertex set of the graph into multiple disjoint vertex subsets according to the number of construction groups, coloring the vertex subsets using a graph coloring algorithm so that adjacent vertices belong to different vertex subsets, and calculating the assembly order for each vertex subset using the shortest Hamiltonian path algorithm to obtain the parallel assembly path of multiple construction groups.

[0039] The assembly difficulty coefficient is determined based on the node height and the number of surrounding installed members using a formula. This formula is calculated by dividing the node height by the maximum height of the space frame, multiplying by 0.6, and then adding the number of surrounding installed members divided by the total number of designed members at the node, multiplied by 0.4. The triaxial stress monitoring device consists of strain gauges installed in the three main stress directions of the node plate, used to collect real-time stress distribution data under multiaxial member tension. The single-ball-with-single-rod method involves connecting only one member at a time when installing a lower chord ball node. Position correction is performed after a stable connection is formed between the member and the installed space frame structure. The ball center deviation is the spatial distance between the actual coordinates of the lower chord ball center and the designed coordinates. Ball node fine-tuning and resetting involves adjusting the bolt tightness at the connection between the ball node and the member or increasing the thickness of the shims to bring the actual coordinates of the lower chord ball center back to the designed coordinates. The single-ball-with-two-rod installation method involves connecting two rods simultaneously when installing one upper chord ball node, using a third web member to form a triangular stable structure. The gusset plate stress concentration factor is the ratio of the maximum stress value to the average stress value of the gusset plate, used to assess the degree of local stress concentration in the gusset plate. The allowable stress concentration factor for the gusset plate material is the upper limit of the allowable stress concentration factor for the gusset plate, determined based on the toughness index and safety factor of the gusset plate material.

[0040] The prestress release adjustment involves temporarily loosening some of the connections around the node plate or adjusting the installation sequence of the members to redistribute the excessive local stress at the node plate to the surrounding members. Segmented preheating treatment involves dividing the weld area of ​​the node plate into multiple preheating segments and heating each segment sequentially from the weld center outwards to the preheating temperature value, followed by heat preservation. The preheating temperature value is determined by a preheating temperature calculation formula, which is obtained by multiplying the carbon equivalent value of the node plate material by 450, adding the negative value of the ambient temperature, and multiplying by 1.2. The unit is °C. Crack defect depth is the maximum depth to which an internal crack extends inwards from the weld surface. Repair welding is a repair operation involving cleaning and re-welding the weld area with crack defects. Member axis offset is the spatial distance between the actual center axis of the member after assembly and the designed axis position. The allowable deviation of the design axis position is the upper limit of the allowable offset of the member axis determined based on the span of the space frame and the structural importance coefficient. For ultra-large span airport terminal space frames, it is taken as 0.2% of the space frame span. Temporary support rods are auxiliary rods temporarily added during the axis correction process to limit the offset of the member axis, and are removed after the correction is completed. Axis correction is an adjustment operation that gradually returns the actual center axis of the offset member to the design axis position by adding temporary support rods.

[0041] The key nodes of the space frame are the spherical nodes located at the mid-span, support, and maximum cantilever positions. The actual coordinates of the key nodes are the spatial coordinate values ​​obtained using a total station. The overall deformation of the space frame is the maximum spatial distance between the actual coordinates and the design coordinates of the key nodes. The allowable value for the overall deformation is the upper limit of the allowable deformation determined based on the space frame span and design deflection limits, taken as one-five-hundredth of the space frame span.

[0042] The specific implementation methods of the above steps are described in detail below.

[0043] The specific implementation of step S01 is as follows: First, an assembly reference grid system is established in the floor assembly area. This grid system uses the space frame nodes in the design drawings as reference points. A total station is used to perform three-dimensional spatial positioning measurements on the design coordinate points of each lower chord sphere center. The measurement accuracy should reach the millimeter level to ensure the accuracy of subsequent assembly. After completing the coordinate point measurement, a triaxial stress monitoring device is installed at each lower chord sphere center design coordinate point. This device consists of strain gauge groups installed in the three main force directions of the node plate. It can collect the stress distribution state of the node plate under the action of multi-directional member tension in real time. At the same time, the outer contour projection line of the sphere is marked at the corresponding position on the floor to facilitate the construction personnel to intuitively identify the installation position. Then, the parallel assembly path of multiple construction groups is calculated based on the total number of space frame nodes and the number of construction groups. This calculation process is implemented using a graph theory algorithm, treating all nodes of the space frame as graphs. The set of vertices is used to treat the assembly order constraints between adjacent nodes as the set of edges in a graph. Each edge is assigned a weight value to represent the assembly difficulty coefficient. This coefficient comprehensively considers the node's position height and the number of surrounding installed members. It is calculated by dividing the node's position height by the maximum height of the grid structure and multiplying by 0.6, and then adding the number of surrounding installed members divided by the total number of designed members for the node and multiplying by 0.4. Then, the vertex set is divided into multiple disjoint vertex subsets according to the number of construction groups. A graph coloring algorithm is used to color the vertex subsets so that adjacent vertices belong to different vertex subsets to avoid construction conflicts. Finally, the shortest Hamiltonian path algorithm is used for each vertex subset to calculate the assembly order and obtain the parallel assembly path for multiple construction groups. This algorithm can minimize the construction path length while ensuring the rationality of the assembly order, thereby improving the overall assembly efficiency.

[0044] The specific implementation of step S02 is as follows: The lower chord club units are installed one by one using a single-ball-single-rod method. This method involves connecting only one rod when installing each lower chord ball node. After a stable connection is formed between this rod and the installed space frame structure, position correction is performed. This method effectively controls the transmission of cumulative errors. After each lower chord club unit is installed, a plumb bob is immediately used to measure the actual coordinates of the lower chord ball center. The spatial distance between the measured actual coordinates and the design coordinates is calculated to obtain the ball center deviation. When the ball center deviation is within the range of 0mm to 3mm, it indicates... The installation position accuracy of this node meets the requirements. At this point, record the actual coordinate point data of the lower chord ball center and continue installing the next lower chord ball member. When the ball center deviation is greater than 3mm, a fine-tuning and resetting operation of the ball node is required. This operation is achieved by adjusting the tightness of the bolts at the connection between the ball node and the member or by increasing the thickness of the adjusting shims, so that the actual coordinate point of the lower chord ball center gradually returns to the design coordinate point position. The adjustment process requires repeated measurements until the ball center deviation meets the accuracy requirement of 0mm to 3mm. The purpose of this step is to ensure the geometric accuracy of the lower chord space frame to provide a reliable benchmark for the subsequent installation of the upper chord and web members.

[0045] The specific implementation of step S03 is as follows: The upper chord ball and web member are installed using a single-ball, double-rod method. This method involves connecting two members simultaneously when installing each upper chord ball node, using a third web member to form a triangular stable structure. This structure utilizes the geometric stability principle of a triangle, effectively resisting node displacement under multi-directional forces. During installation, the actual coordinates of the upper chord ball center are measured using a plumb bob to monitor node position accuracy. Simultaneously, the stress data of the node plate from the triaxial stress monitoring device is recorded in real time. Based on the collected stress data, the stress concentration factor of the node plate is calculated. This factor is the ratio of the maximum stress value to the average stress value of the node plate, used to assess the degree of local stress concentration in the node plate. When the stress concentration factor of the node plate is less than that of the node plate… When the allowable stress concentration factor of the material is 75%, it indicates that the stress distribution of the gusset plate is reasonable and has sufficient safety margin. At this time, the actual coordinate point of the upper chord ball center is recorded and the next upper chord ball bar unit is installed. When the stress concentration factor of the gusset plate is greater than or equal to 75% of the allowable stress concentration factor of the gusset plate material, it is necessary to adjust the prestress release of the members around the gusset plate. This adjustment is achieved by temporarily loosening the connection of some members around the gusset plate or adjusting the installation sequence of the members, so that the excessive local stress at the gusset plate is redistributed to the surrounding members. After the adjustment is completed, the stress concentration factor is re-tested until it meets the requirements. The purpose of this step is to control the stress state of the gusset plate while ensuring the geometric accuracy of the space frame, and to avoid the risk of fatigue failure caused by local stress concentration.

[0046] The specific implementation of step S04 is as follows: Before welding the node plate to the member, the weld area of ​​the node plate is preheated in sections. This process divides the weld area into multiple preheating sections, which are heated sequentially from the center of the weld to both sides. The preheating temperature is determined based on the carbon equivalent of the node plate material and the ambient temperature. It is calculated by multiplying the carbon equivalent of the node plate material by 450 and then adding the negative value of the ambient temperature by 1.2. This calculation relationship is based on the theory of metal welding performance. Materials with higher carbon equivalent are more prone to cold cracking during welding and require higher preheating temperatures to reduce the cooling rate. Lower ambient temperatures require higher preheating temperatures to compensate for heat loss. After heating to the preheating temperature, the temperature is held for a certain period of time to ensure uniform temperature distribution, and then... After welding, ultrasonic testing is performed on the weld to determine the depth of cracks. This test utilizes the principle that ultrasonic waves reflect when they encounter defects in the material. By analyzing the reflected wave signals, the location and depth of the defects are determined. When the crack depth is less than or equal to 15% of the weld thickness, the weld quality is considered acceptable. At this point, the weld quality mark is recorded, and welding continues to the next node plate. When the crack depth is greater than 15% of the weld thickness, repair welding is required. This repair operation involves cleaning the weld area with cracks and then re-welding. After repair, the process returns to this step to re-perform ultrasonic testing until it is acceptable. The purpose of this step is to ensure weld quality through reasonable preheating and testing measures, and to prevent welding defects from affecting the safety of the space frame structure.

[0047] The specific implementation of step S05 is as follows: After the space frame assembly is completed, a total station is used to measure the actual coordinates of all lower chord center points and upper chord center points. Based on the measurement data, the spatial distance between the actual center axis of the member and the design axis position, i.e., the member axis offset, is calculated. When the member axis offset is less than or equal to the allowable value of the design axis position deviation, it indicates that the geometric accuracy of the space frame meets the design requirements. At this time, the space frame assembly qualification mark is recorded and the process proceeds to step S06. For ultra-large span airport terminal space frames, the allowable value of the design axis position deviation is taken as two-thousandths of the space frame span. When the offset of a member's axis exceeds the allowable deviation of the designed axis position, it is necessary to correct the axis by adding temporary support rods. This correction operation involves adding temporary auxiliary support rods around the offset member and applying constraint force to the offset member by adjusting the length and angle of the support rods, so that the actual center axis of the offset member gradually returns to the designed axis position. After the correction is completed, the temporary support rods are removed, and then the process returns to step S02 to reinstall the lower chord ball-and-stick unit to eliminate accumulated errors. The purpose of this step is to ensure that the overall geometric accuracy of the space frame meets the design standards through comprehensive inspection and correction measures.

[0048] The specific implementation of step S06 is as follows: The overall deformation of the assembled space frame is detected. A total station is used to measure the actual coordinates of key nodes of the space frame. These key nodes include spherical nodes located at the mid-span, support, and maximum cantilever positions. These locations represent the areas of greatest deformation and most complex stress in the space frame structure. Based on the measurement data, the maximum spatial distance between the actual coordinates of the key nodes and the design coordinates is calculated, which represents the overall deformation of the space frame. When the overall deformation is less than or equal to the allowable value, it indicates that the overall stiffness of the space frame meets the requirements. At this point, the assembly is complete, and the entire space frame is ready for assembly. The allowable value for overall deformation is one-five-hundredth of the span of the space frame. This limit is based on the deflection control theory in structural mechanics to ensure that the deformation of the space frame under its own weight will not affect its functionality and structural safety. When the overall deformation of the space frame exceeds the allowable value, it indicates that the space frame has insufficient overall stiffness or excessive accumulation of local assembly errors. In this case, it is necessary to return to step S02 to reinstall the lower chord ball joint unit and eliminate the error source through systematic reassembly. The purpose of this step is to verify the assembly quality of the space frame through overall deformation detection to ensure that the space frame structure meets the design requirements for stiffness and deformation control.

[0049] It should be noted that the key technical ideas of this invention include graph theory-based parallel assembly path optimization for multiple construction groups, real-time stress monitoring and prestress release adjustment mechanism, and segmented preheating welding quality control method. These technical ideas work together to ensure the assembly accuracy and structural safety of ultra-large span space frames. First, the graph theory-based parallel assembly path optimization for multiple construction groups divides the space frame nodes into multiple regions that can be constructed in parallel through graph coloring algorithms and the shortest Hamiltonian path algorithm, and plans the optimal assembly sequence for each region. Compared with the traditional linear assembly method, this technology can significantly shorten the construction period and effectively avoid spatial conflicts between construction groups. At the same time, by designing the assembly difficulty coefficient weight, it prioritizes the assembly of nodes with lower difficulty, reducing construction risks. Second, the real-time stress monitoring and prestress release adjustment mechanism installs triaxial strain gauge groups at key nodes to collect the stress distribution state of the node plates in real time and calculate the stress concentration coefficient. When the stress concentration exceeds the safety threshold, the prestress release adjustment is performed in a timely manner. Compared with the traditional post-detection method, this technology can dynamically control the stress state during the assembly process, avoid fatigue failure caused by local stress concentration, and improve the long-term reliability of the space frame structure. Third, the segmented preheating welding quality control method quantitatively calculates the preheating temperature based on the material's carbon equivalent and ambient temperature, and adopts a segmented heating process from the center outwards. Compared to traditional empirical preheating methods, this technology can precisely control the temperature gradient, effectively reducing the tendency for cold cracking in welding. Combined with ultrasonic flaw detection, it forms a closed-loop quality control system. The synergistic effect of these three technical approaches lies in the fact that path optimization technology provides an efficient assembly framework, stress monitoring technology ensures the mechanical rationality of the assembly process, and welding quality control technology ensures the reliability of connection nodes. Together, they constitute a comprehensive control system from macroscopic organization to microscopic quality. Compared to the traditional method's independent control of each link, this invention achieves synergistic optimization of assembly efficiency, structural safety, and welding quality through multi-technology integration. It is particularly suitable for the construction of complex space frame structures with extremely high precision and reliability requirements, such as ultra-large span airport terminals.

[0050] It should be noted that this invention also solves the following technical problem: the problem of cold cracking defects easily occurring in welded node plates during the assembly of ultra-large span space frames. In the assembly of ultra-large span space frames, the connection between node plates and members requires welding for fixation. Due to the low ambient temperature at the airport terminal construction site and the high carbon equivalent of the node plate material, the weld area cools too quickly during welding, leading to the formation of hardened structures inside the weld. Under the combined action of welding residual stress and member prestress, cold cracking defects are easily formed. The cracks extending inward from the weld surface reduce the node connection strength, and in severe cases, lead to node failure. This invention employs segmented preheating treatment of the weld area of ​​the node plate. The preheating temperature is calculated based on the carbon equivalent of the node plate material and the ambient temperature. The weld area is heated segment by segment from the center outwards to the preheating temperature, and then held at that temperature before welding. This slows down the cooling rate of the weld and avoids the formation of hardened structures. Simultaneously, ultrasonic testing is immediately used after welding to determine the depth of crack defects. When the crack depth exceeds 15% of the weld thickness, repair welding is performed. Through quality control measures that combine preheating treatment and flaw detection, the problem of cold crack defects in welded node plates is effectively solved, ensuring the reliability of the node connection.

[0051] Specifically, the principle of this invention is as follows: The fundamental reason why this invention can solve the problem of deformation exceeding limits due to stress accumulation lies in the establishment of a dual real-time monitoring and feedback mechanism for stress state and geometric position during assembly. During the assembly of ultra-large span space frames, each installed member generates prestress at the connection node. This prestress is transmitted to surrounding members through the node plate and accumulates in the structure. When multiple members are connected at a certain node, the multi-directional tensile force borne by the node plate will cause stress concentration. If not adjusted in time, it will cause plastic deformation or even cracking, which will lead to the offset of the axis of all members connected to the node, ultimately causing the overall structural geometry to deviate from the design state. This invention uses a triaxial stress monitoring device to continuously collect strain data in the three main stress directions of the node plate during assembly, and calculates the stress concentration factor of the node plate. This factor reflects the ratio of the maximum stress to the average stress of the node plate. When this ratio approaches 75% of the allowable stress concentration factor of the material, it indicates that the node plate is about to enter a nonlinear stress state. At this time, the excessive stress is dispersed to the surrounding unsaturated nodes through prestress release adjustment to avoid single-point stress failure. At the same time, the spatial position accuracy of each node is ensured by real-time measurement and fine-tuning of the sphere center position deviation, preventing the accumulation and amplification of small deviations in large-span structures. The two measures work together to make the stress distribution uniform and the geometry controlled during assembly, thus effectively solving the technical problem of stress accumulation leading to excessive overall deformation.

[0052] The following provides a specific embodiment 1 of the present invention, and the specific implementation of each step in this embodiment 1 is described in detail below.

[0053] The specific implementation of step S01 is as follows: First, an assembly reference grid system is established in the floor assembly area. This grid system uses the space frame nodes in the design drawings as reference points. A total station is used to perform three-dimensional spatial positioning measurements on the design coordinate points of each lower chord sphere center. The measurement accuracy should reach the millimeter level to ensure the accuracy of subsequent assembly. After the coordinate point measurement is completed, a triaxial stress monitoring device is installed at each lower chord sphere center design coordinate point. This device consists of strain gauge groups installed in the three main force directions of the node plate. It can collect the stress distribution state of the node plate under the action of multi-directional member tension in real time. At the same time, the outer contour projection line of the sphere is marked at the corresponding position on the floor to facilitate the construction personnel to intuitively identify the installation position. Then, the parallel assembly path of multiple construction groups is calculated based on the total number of space frame nodes and the number of construction groups. This calculation process is implemented using graph theory algorithm. All nodes of the space frame are regarded as the set of vertices of the graph, and the assembly order constraints between adjacent nodes are regarded as the set of edges of the graph. Each edge is assigned a weight value to represent the assembly difficulty coefficient. The formula for the assembly difficulty coefficient is as follows:

[0054] ;

[0055] In the formula, For nodes With nodes The assembly difficulty coefficient between them is dimensionless; For nodes Position height, in units ; This represents the maximum height of the space frame, in units of... ; For nodes Number of poles already installed in the surrounding area, in units of poles; For nodes The total number of design members is expressed in units of "members"; 0.6 is the weighting coefficient for the height factor, which is dimensionless and reflects the difficulty of high-altitude operations; 0.4 is the weighting coefficient for the number of members factor, which is dimensionless and reflects the impact of structural constraints.

[0056] The parameter acquisition method is as follows: The vertical coordinates of the node are obtained by measuring with a total station. Obtain the maximum vertical dimension of the space frame from the design drawings; The number of members connected to the node is counted in real time during the assembly process; The total number of members that should be connected to this node is determined from the design drawings; empirically, this is between 8 and 12. Then, based on the number of construction teams, the vertex set is divided into multiple disjoint vertex subsets. A graph coloring algorithm is used to color these subsets so that adjacent vertices belong to different subsets to avoid construction conflicts. Finally, the shortest Hamiltonian path algorithm is used for each subset to calculate the assembly order and obtain the parallel assembly path for multiple construction teams. The objective function of the shortest Hamiltonian path algorithm is expressed as follows:

[0057] ;

[0058] In the formula, The total length of the construction path is dimensionless. This represents the total number of nodes in the vertex subset, expressed in units of nodes. For the first in the path The number of nodes visited; For nodes With nodes The assembly difficulty coefficient between them is dimensionless; This represents the node access sequence number. The algorithm solves this using dynamic programming. The minimum node access order can minimize the construction path length while ensuring the rationality of the assembly sequence, thereby improving the overall assembly efficiency.

[0059] The specific implementation of step S02 is as follows: The lower chord club units are installed one by one using a single-ball-single-rod method. This method involves connecting only one rod when installing each lower chord ball node. After a stable connection is formed between this rod and the installed space frame structure, position correction is performed. This method effectively controls the transmission of cumulative errors. After each lower chord club unit is installed, a plumb bob is immediately used to measure the actual coordinates of the lower chord ball center. The spatial distance between the measured actual coordinates and the design coordinates is calculated to obtain the ball center deviation. The formula for the ball center deviation is as follows:

[0060] ;

[0061] In the formula, The deviation of the ball's center is expressed in units of . ; , , These are the three-dimensional coordinate components of the actual coordinate point of the lower chord sphere's center, in units of... ; , , The three-dimensional coordinate components of the design coordinate point at the center of the lower chord sphere are given, in units of . .

[0062] The parameter acquisition method is as follows: , , The three-dimensional coordinates of the ball's center were recorded after measuring the actual position of the lower string using a plumb bob. , , Find the three-dimensional coordinates of the design position of the lower chord ball center from the design drawings. When the ball center deviation is between 0 and 3... When the position is within the specified range, it indicates that the installation accuracy of the node meets the requirements. At this point, record the actual coordinates of the lower chord ball center and continue installing the next lower chord club unit. When the ball center deviation is greater than 3... At this time, a fine-tuning and resetting operation of the ball node is required. This operation is achieved by adjusting the tightness of the bolts at the connection between the ball node and the member or by increasing the thickness of the adjusting shims, so that the actual coordinate point of the lower chord ball center gradually returns to the design coordinate point position. The adjustment process requires repeated measurement until the ball center deviation meets the requirements. The purpose of this step is to ensure the geometric accuracy of the lower chord space frame to provide a reliable benchmark for the subsequent installation of the upper chord and web members.

[0063] The specific implementation of step S03 is as follows: The upper chord ball and web member are installed using a single-ball, double-rod method. This method involves connecting two members simultaneously when installing each upper chord ball node, using a third web member to form a triangular stable structure. This structure utilizes the geometric stability principle of a triangle, effectively resisting node displacement under multi-directional forces. During installation, the actual coordinates of the upper chord ball center are measured using a plumb bob to monitor node position accuracy. Simultaneously, the stress data of the node plate from the triaxial stress monitoring device is recorded in real time. Based on the collected stress data, the stress concentration factor of the node plate is calculated. The formula for the stress concentration factor of the node plate is as follows:

[0064] ;

[0065] In the formula, is the stress concentration factor of the gusset plate, which is dimensionless; This represents the maximum stress value of the gusset plate, in units of... ; The average stress value of the gusset plate, in units of .

[0066] The parameter acquisition method is as follows: The calculation formula is In the formula The elastic modulus of the gusset plate material, in units of 1. The value is usually taken as , The maximum value among the strain data in the three directions collected by the triaxial stress monitoring device is dimensionless. The calculation formula is In the formula , , These are dimensionless strain values ​​collected by the triaxial stress monitoring device in the three main stress directions. When the stress concentration factor of the gusset plate is less than 75% of the allowable stress concentration factor of the gusset plate material, it indicates that the stress distribution of the gusset plate is reasonable and has sufficient safety margin. At this time, the actual coordinate point of the upper chord ball center is recorded and the next upper chord ball bar unit is installed. The allowable stress concentration factor of the gusset plate material is determined according to the toughness index and safety factor of the gusset plate material, with an empirical value of 2.5 to 3.5. When the stress concentration factor of the gusset plate is greater than or equal to 75% of the allowable stress concentration factor of the gusset plate material, it is necessary to adjust the prestress release of the members around the gusset plate. This adjustment is achieved by temporarily loosening the connection of some members around the gusset plate or adjusting the installation sequence of the members, so that the excessive local stress at the gusset plate is redistributed to the surrounding members. After the adjustment is completed, the stress concentration factor is re-tested until the requirements are met. The purpose of this step is to control the stress state of the gusset plate while ensuring the geometric accuracy of the space frame, and to avoid the risk of fatigue failure caused by local stress concentration.

[0067] The specific implementation of step S04 is as follows: before welding the node plate to the member, the weld area of ​​the node plate is preheated in sections. This process divides the weld area into multiple preheating sections, which are heated section by section from the center of the weld to both sides. The preheating temperature is determined based on the carbon equivalent of the node plate material and the ambient temperature. The formula for the preheating temperature is expressed as follows:

[0068] ;

[0069] In the formula, This is the preheating temperature value, in °C. The carbon equivalent of the gusset plate material is dimensionless. 450 is the ambient temperature, in °C; 450 is the carbon equivalent amplification factor, in °C, reflecting the degree of influence of carbon equivalent on preheating temperature; 1.2 is the ambient temperature compensation factor, dimensionless, reflecting the influence of ambient temperature on heat loss.

[0070] The parameter acquisition method is as follows: The calculation formula is In the formula , , , , , , These represent the mass percentages of carbon, manganese, chromium, molybdenum, vanadium, nickel, and copper in the gusset plate material, expressed as %. This information is obtained from a material inspection report. This formula is the carbon equivalent calculation formula recommended by the International Institute of Welding. The value ranges from 0.4 to 0.6; The temperature was measured at the welding site using a thermometer. The calculation formula is based on the theory of weldability of metallic materials. Materials with higher carbon equivalent are more prone to cold cracking during welding, requiring higher preheating temperatures to reduce cooling rates. Lower ambient temperatures necessitate even higher preheating temperatures to compensate for heat loss. After heating to the preheating temperature, the temperature is held for a certain period to ensure uniform temperature distribution before welding. After welding, ultrasonic testing is performed on the weld to determine the crack depth. When the crack depth is less than or equal to 15% of the weld thickness, the weld quality is considered acceptable. At this point, the weld qualification mark is recorded, and welding continues to the next node plate. When the crack depth exceeds 15% of the weld thickness, repair welding is required. This repair involves cleaning the affected weld area and re-welding. After repair, the process returns to this step for repeated ultrasonic testing until the weld is deemed acceptable. The purpose of this step is to ensure weld quality through reasonable preheating and testing measures, preventing welding defects from affecting the safety of the space frame structure.

[0071] The specific implementation of step S05 is as follows: After the space frame assembly is completed, a total station is used to measure the actual coordinates of all lower chord center points and upper chord center points. Based on the measurement data, the spatial distance between the actual center axis of the member and the design axis position, i.e., the member axis offset, is calculated. The calculation of the member axis offset requires first determining the spatial position of the actual center axis of the member and the design axis. The formula for the member axis offset is expressed as follows:

[0072] ;

[0073] In the formula, This represents the offset of the member's axis, in units of... ; , , These are the three-dimensional coordinate components of the actual coordinates of end point 1 of the member, in units of... ; , , These are the three-dimensional coordinate components of the design coordinates of end point 1 of the member, in units of... ; , , These are the three-dimensional coordinate components of the actual coordinates of the end point 2 of the member, in units of... ; , , These are the three-dimensional coordinate components of the design coordinates of end point 2 of the member, in units of... ;2 is the average coefficient, which is dimensionless.

[0074] The parameter acquisition method is as follows: the actual coordinates of end points 1 and 2 of the member are obtained by measuring the actual coordinate points of the corresponding sphere centers using a total station; the design coordinates of end points 1 and 2 of the member are obtained from the design drawings. When the offset of the member axis is less than or equal to the allowable value of the design axis position deviation, it indicates that the geometric accuracy of the space frame meets the design requirements. At this time, the space frame assembly qualification mark is recorded and the process proceeds to step S06. The formula for calculating the allowable value of the design axis position deviation is... In the formula The allowable deviation of the design axis position is given in units of , The span of the space frame is expressed in units of 1 / 2000. 500 is a control coefficient, dimensionless, reflecting the accuracy requirements of the ultra-large span airport terminal space frame. When the offset of the member axis exceeds the allowable value of the design axis position deviation, it is necessary to correct the axis by adding temporary support rods. This correction operation involves adding temporary auxiliary support rods around the offset member and applying constraint force to the offset member by adjusting the length and angle of the support rods, so that the actual center axis of the offset member gradually returns to the design axis position. After the correction is completed, the temporary support rods are removed, and then the process returns to step S02 to reinstall the lower chord ball-and-stick unit to eliminate the accumulated error. The purpose of this step is to ensure that the overall geometric accuracy of the space frame meets the design standards through comprehensive inspection and correction measures.

[0075] The specific implementation of step S06 is as follows: The overall deformation of the assembled space frame is detected. A total station is used to measure the actual coordinates of key nodes of the space frame. These key nodes include spherical nodes located at the mid-span, support, and maximum cantilever positions of the space frame. These locations are the areas with the greatest deformation and most complex stress in the space frame structure. Based on the measurement data, the maximum spatial distance between the actual coordinates of the key nodes and the design coordinates is calculated, which is the overall deformation of the space frame. The formula for the overall deformation of the space frame is as follows:

[0076] ;

[0077] In the formula, The value represents the overall deformation of the space frame, expressed in units of... ; This represents the total number of critical nodes, expressed in units. , , The first The three-dimensional coordinate components of the actual coordinates of each key node, in units of ; , , The first The three-dimensional coordinate components of the design coordinate points of each key node are shown in units of . ; The key node number; This indicates the operation of finding the maximum value.

[0078] The parameter acquisition methods are as follows: the actual coordinates of key nodes are obtained through total station measurement, and the design coordinates of key nodes are obtained by querying the design drawings. The value is determined based on the space frame structure, with an empirical value of 15-30. When the overall deformation of the space frame is less than or equal to the allowable value, it indicates that the overall stiffness of the space frame meets the requirements, and assembly is completed at this point. The formula for calculating the allowable value of the overall deformation of the space frame is as follows: In the formula This represents the allowable value for the overall deformation of the space frame, in units of... , The span of the space frame is expressed in units of 1 / 2000. 500 is the deflection control coefficient, which is dimensionless. This limit is based on the deflection control theory in structural mechanics to ensure that the deformation of the space frame under its own weight will not affect its functionality and structural safety. When the overall deformation of the space frame exceeds the allowable value, it indicates that the space frame has insufficient overall stiffness or excessive accumulation of local assembly errors. At this time, it is necessary to return to step S02 to reinstall the lower chord ball joint unit and eliminate the error source through systematic reassembly. The purpose of this step is to verify the assembly quality of the space frame through overall deformation detection and ensure that the space frame structure meets the design stiffness and deformation control requirements.

[0079] It needs to be explained that the assembly difficulty coefficient formula comprehensively considers two key factors: the height of the node location and the number of installed members. Through normalization, parameters with different dimensions are transformed into dimensionless weights. The height factor, with a weight of 0.6, reflects the increased difficulty of high-altitude operations, while the number of installed members, with a weight of 0.4, reflects the impact of structural constraints on subsequent installation. This formula can quantitatively assess the assembly complexity of different nodes, providing a scientific path planning basis for parallel operations by multiple construction teams, avoiding construction conflicts and improving overall efficiency. The sphere center deviation formula uses a three-dimensional Euclidean distance calculation method, which can accurately reflect the degree of deviation between the actual and designed positions of the node. By setting a range of 0 to 3... The deviation control threshold ensures the high precision requirements of the space frame assembly and effectively prevents the impact of cumulative errors on the overall structural quality. The stress concentration factor formula for gusset plates quantitatively assesses the uniformity of stress distribution by the ratio of maximum stress to average stress. A coefficient close to 1 indicates uniform stress distribution, while a coefficient much greater than 1 indicates significant stress concentration. By setting a control threshold of 75% allowable stress concentration factor, a clear trigger condition is provided for prestress release adjustment, effectively avoiding the risk of fatigue failure caused by excessive local stress and ensuring the long-term safety of the space frame structure. The preheating temperature formula is established based on the influence of carbon equivalent on welding crack sensitivity and the influence of ambient temperature on heat loss. Using a carbon equivalent amplification factor of 450℃ and an ambient temperature compensation factor of 1.2, a suitable preheating temperature range is determined. This formula can dynamically adjust preheating parameters according to material properties and construction conditions, effectively reducing the probability of welding cold cracks and improving the reliability of weld quality. The formula for member axis offset evaluates the positional accuracy of the entire member by calculating the average deviation between its two endpoints. This method takes into account the characteristics of the member as a linear component and can accurately reflect the spatial offset of the member's central axis, providing a quantitative basis for axis correction operations. The formula for overall space frame deformation evaluates the overall deformation state of the space frame by taking the maximum value of the deviation of all key nodes. This method focuses on the location of the largest deformation in the structure and can effectively identify problems such as insufficient space frame stiffness or accumulated assembly errors. By setting a control threshold of 1 / 500 of the span, it ensures that the deformation of ultra-large span space frames under their own weight meets the requirements of functional use and structural safety, providing a reliable guarantee for the high-quality assembly of airport terminal space frames.

[0080] It should be noted that the variables involved in this embodiment are explained in detail in Table 1.

[0081] Table 1. Variable Explanation Table

[0082]

[0083] To better understand and implement this invention, the following is a specific application scenario of the invention, Example 2: The space frame of a large airport terminal involves, as follows: Figure 1 As shown, the technical team first set up an assembly reference grid in the floor assembly area and used a Leica TS60 total station to determine the design coordinates of each lower chord sphere center. The lower chord sphere nodes were arranged according to an 8m × 8m grid, and technicians measured the design coordinates of each of the 512 lower chord sphere centers one by one, controlling the measurement accuracy within ±1mm. Figure 7As shown, the lower chord ball joint is connected to the lower chord member via bolted flanges. Each connection joint is equipped with adjusting shims for fine-tuning the ball center position, ensuring that the deviation between the actual coordinates and the design coordinates of the ball center is controlled within the allowable range. A triaxial stress monitoring device is installed at each lower chord ball center design coordinate point. This device consists of three strain gauges, respectively arranged at 0°, 120°, and 240° on the node plate, to monitor the stress distribution of the node plate under multiaxial member tension in real time. Technicians mark the outer contour projection line of the ball with red marking lines at corresponding positions on the floor surface. The projection line diameter is 600mm, consistent with the design ball joint outer diameter.

[0084] Based on the total number of 992 space frame nodes and 4 construction teams, the technical team calculated parallel assembly paths for multiple construction teams. All space frame nodes were considered as the set of vertices in a graph, and the assembly order constraints between adjacent nodes were considered as the set of edges. Technicians assigned a weight value to each edge to represent the assembly difficulty coefficient, which was determined based on the node's height and the number of surrounding members already installed. For a lower chord node with a height of 6m, the assembly difficulty coefficient was 0.2; for an upper chord node with a height of 18m, the assembly difficulty coefficient was 0.6. A graph coloring algorithm was used to divide the vertex set into 4 disjoint subsets, each containing approximately 248 nodes, ensuring that adjacent vertices belonged to different subsets. The shortest Hamiltonian path algorithm was used to calculate the assembly order for each subset, ultimately obtaining 4 parallel assembly paths, such as... Figure 2 As shown, the assembly paths of each construction group do not interfere with each other.

[0085] The technical team began installing the bottom chord club units one by one using a single ball and single club method. For example... Figure 8 As shown, the single-ball-with-single-rod hoisting method employs a double-hook hoisting device. The main hook hoists the ball node, and the auxiliary hook hoists the rod, ensuring the stability of the ball node and rod in the air. The first construction team started from the first lower chord ball node at the southwest corner of the space frame, hoisting a ball node weighing 85kg and a rod weighing 42kg. Technicians first hoisted the ball node into place and connected it to the installed reference space frame structure via a lower chord rod. The connecting bolts were M24 high-strength bolts with an initial tightening torque of 200N·m. After the connection was stable, technicians used a Trimble DiNi03 precision plumb bob to measure the actual coordinates of the lower chord ball center, with a measurement accuracy of ±0.5mm. The measured deviation of the ball center at the first node was 1.8mm, within the allowable range of 0mm to 3mm. Technicians recorded the actual coordinates of the lower chord ball center and continued installing the next lower chord ball rod unit.

[0086] During the installation of the 15th lower chord ball joint, a plumb bob measurement showed a ball center deviation of 4.2 mm, exceeding the 3 mm limit. Technicians immediately performed a fine-tuning and resetting operation on the ball joint. By adjusting the tightness of the bolts connecting the ball joint to the member, the initial tightening torque was reduced from 200 N·m to 180 N·m. Simultaneously, a 2 mm thick adjusting shim was added to the connecting flange. After fine-tuning and re-measuring, the ball center deviation was reduced to 2.6 mm, meeting the requirements. Technicians recorded the adjustment data for this joint and continued with subsequent installations. Figure 3 As shown, during the positioning process of the lower chord club, the plumb bob is always aligned with the design coordinate point of the ball's center, and the deviation of the ball's center is monitored in real time.

[0087] After 72 hours of continuous construction, the four construction teams completed the installation of all 512 lower chord ball joints. The technical team then began installing the upper chord balls and web members using a single ball with two struts. The first upper chord ball joint was located in the middle of the space frame, at a height of 18m. Technicians used an 80t crawler crane to hoist the upper chord ball into place, simultaneously connecting two web members, each 12.7m long, forming a 45° angle with the lower chord ball. After connecting the two web members, the structure was still unstable, so technicians immediately installed a third web member to form a stable triangular structure. Figure 6 As shown, the upper chord ball joint forms a stable spatial triangular pyramid structure with the lower chord ball through three web members. Each web member is connected with M24 high-strength bolts to ensure connection strength. After the three web members are connected, the actual coordinates of the upper chord ball center are measured using a plumb bob, yielding coordinates of (64.2m, 64.1m, 18.0m), which deviates from the design coordinates of (64.0m, 64.0m, 18.0m) by 0.28m.

[0088] Simultaneously, a triaxial stress monitoring device records real-time stress data for the gusset plate. The gusset plate is made of Q345B steel with a yield strength of 345 MPa. The strain gauge readings are 820 με at 0°, 780 με at 120°, and 760 με at 240°. Based on the strain-stress relationship and an elastic modulus of 206 GPa, the calculated stresses are 169 MPa at 0°, 161 MPa at 120°, and 157 MPa at 240°. The average stress of the gusset plate is 162 MPa, the maximum stress is 169 MPa, and the stress concentration factor is 1.04. The allowable stress concentration factor for this gusset plate material is determined based on the material's toughness index and a safety factor of 2.0, resulting in a value of 1.73. The current stress concentration factor of 1.04 is less than 75% of the allowable value of 1.73 (1.30), meeting the requirements. Technicians record the actual coordinates of the top chord ball center and continue installing the next top chord club unit.

[0089] During the installation of the 28th top-chord ball joint, the triaxial stress monitoring device displayed an anomaly. The stress in the 0° direction reached 246 MPa, the stress in the 120° direction was 168 MPa, the stress in the 240° direction was 172 MPa, the average stress in the gusset plate was 195 MPa, and the stress concentration factor of the gusset plate was 1.26, approaching the allowable value of 1.30. Technicians determined that the tensile force distribution in the surrounding members was uneven and decided to perform prestress release adjustments. Figure 9 As shown, in the two-rod, one-ball hoisting method, the upper chord ball joint connects two web members simultaneously via a hoisting beam. The two members are connected to the ball joint via flexible slings to ensure relative stability during hoisting. Technicians temporarily loosened the bolts connecting the two members in the 0° direction of the node plate, reducing the bolt torque from 200 N·m to 100 N·m. Simultaneously, the installation sequence of adjacent members was adjusted, installing the members in the 120° and 240° directions first, and finally the member in the 0° direction. After adjustment, the stress distribution was remeasured. The stress in the 0° direction decreased to 198 MPa, the stress in the 120° direction was 185 MPa, the stress in the 240° direction was 188 MPa, the average stress of the node plate was 190 MPa, and the stress concentration factor decreased to 1.04, meeting the requirements.

[0090] After the top chord spheres and web members were installed, the technical team began welding the gusset plates to the member connections. The gusset plates for this space frame are 20mm thick, with V-grooved welds of 16mm thickness. Before welding, the technicians preheated the weld areas of the gusset plates in sections. Each weld is approximately 800mm long, divided into four preheating sections, each 200mm long. The preheating sequence proceeded from the weld center outwards: the first section was 200mm from the weld center, the second and third sections were 200mm each on either side of the center, and the fourth section was 100mm from each end of the weld.

[0091] The gusset plate material is Q345B steel with a carbon equivalent of 0.42%. The ambient temperature on the day of construction was -8℃. According to the preheating temperature calculation formula, the preheating temperature is 0.42×450+(-8)×(-1.2)=198.6℃. Technicians used an electric heating blanket to heat the weld area, and an infrared thermometer monitored the temperature in real time. After heating to 200℃, the temperature was maintained for 10 minutes. After preheating, the welder used CO2... Gas shielded welding was performed at a welding current of 280A, a welding voltage of 32V, and a welding speed of 300mm / min. After welding, the material was allowed to cool naturally to ambient temperature.

[0092] After the weld cooled, technicians used an ultrasonic flaw detector to inspect it. The detector had a frequency of 5MHz, a probe diameter of 20mm, and a scanning speed of 150mm / s. The first weld inspection revealed a crack defect inside the weld, located at a depth of 8mm and with a depth of 3.2mm. The weld thickness was 16mm, and the crack defect depth accounted for 20% of the weld thickness, exceeding the 15% limit. Technicians immediately performed a repair weld, first cleaning the cracked area with an angle grinder to remove the defective portion to a depth of 5mm. After cleaning, the weld was reheated to 200℃ and the repair weld was performed using the same welding parameters as the initial weld. After the repair weld was completed, ultrasonic flaw detection was performed again, and the results showed no internal crack defects, indicating that the weld quality was acceptable.

[0093] After 96 hours of construction, all 480 upper chord spherical nodes and 2856 members were installed and welded. The technical team used a total station to measure the actual coordinates of the center points of all lower and upper chord spheres, measuring a total of 992 node coordinates. Technicians compared the actual coordinates with the design coordinates to calculate the axial offset of the members. The maximum axial offset of the lower chord was 186mm, the maximum axial offset of the upper chord was 198mm, and the maximum axial offset of the web members was 172mm. The allowable deviation of the design axial position is two-thousandths of the 128m span of the space frame, i.e., 256mm. All member axial offsets were less than 256mm, meeting the design requirements. Technicians recorded the space frame assembly as qualified and proceeded to the overall deformation detection stage.

[0094] The technical team conducted overall deformation testing on the assembled space frame. The space frame has 44 key nodes, including 12 at mid-span, 24 at supports, and 8 at the maximum cantilever location. Technicians used a total station to measure the actual coordinates of each of these key nodes. The designed coordinates for the mid-span nodes were (64.0m, 64.0m, 18.0m), while the actual measured coordinates were (64.0m, 64.0m, 17.78m), with a vertical deviation of 220mm. The designed coordinates for the support nodes were (0.0m, 64.0m, 6.0m), while the actual measured coordinates were (0.0m, 64.0m, 5.82m), with a vertical deviation of 180mm. The design coordinates of the maximum cantilever position node are (128.0m, 64.0m, 12.0m), and the actual measured coordinates are (128.0m, 64.0m, 11.76m), with a vertical deviation of 240mm.

[0095] Technicians calculated the overall deformation of the space frame, which is the maximum spatial distance between the actual coordinates of key nodes and the design coordinates. The calculation showed that the maximum deformation occurred at the maximum cantilever position, with a value of 240mm. The allowable value for the overall deformation of the space frame is one-five-hundredth of the space frame span of 128m, or 256mm. The current maximum deformation of 240mm is less than the allowable value of 256mm, meeting the design requirements. The technical team marked the completion of the space frame floor assembly work. The entire assembly process took 168 hours, and both construction accuracy and efficiency met the expected goals.

[0096] To more intuitively display the key data during the construction process, the technical team compiled monitoring data on the center deviation of some nodes, as shown in Table 2.

[0097] Table 2. Monitoring data on the center deviation of typical lower chord ball joints.

[0098]

[0099] The technical team also compiled some stress monitoring data for the upper chord ball joints, as shown in Table 3.

[0100] Table 3. Monitoring data of stress concentration factor for typical upper chord spherical nodes.

[0101]

[0102] The weld quality inspection data are shown in Table 4.

[0103] Table 4. Ultrasonic testing data for typical welds

[0104]

[0105] This invention represents a significant technological advancement over traditional space frame assembly methods. Traditional methods typically employ empirical sequential assembly, lacking scientific path planning, leading to interference between multiple construction teams and low construction efficiency. This invention transforms the assembly path optimization problem into a graph coloring and shortest Hamiltonian path problem using graph theory algorithms, enabling automatic calculation of parallel assembly paths for multiple construction teams. This eliminates spatial conflicts between teams and significantly improves construction efficiency. Traditional methods often rely on workers' visual judgment of positional deviations during spherical node installation, making accuracy difficult to guarantee. This invention introduces a plumb bob to measure the spherical center deviation in real time and sets a clear deviation control standard of 0mm to 3mm. Timely fine-tuning and resetting operations ensure the installation accuracy of each node, laying the foundation for the overall geometric accuracy of the space frame.

[0106] Traditional methods lack stress state monitoring before welding gusset plates, often discovering stress concentration issues only after welding is complete, leading to high rework rates. This invention uses a triaxial stress monitoring device to collect the stress distribution of the gusset plate in real time and adjusts the prestress release according to the stress concentration coefficient, avoiding the risk of gusset plate cracking caused by stress concentration and improving structural safety. Traditional methods typically use empirical or fixed values ​​for welding preheating temperature, failing to consider the influence of material carbon equivalent and ambient temperature, easily leading to cold cracking in the weld. This invention establishes a preheating temperature calculation formula, dynamically determining the preheating temperature based on the carbon equivalent of the gusset plate material and ambient temperature, effectively reducing the probability of cold cracking in the weld.

[0107] Traditional methods only perform spot checks after the space frame is assembled, making it difficult to fully grasp the overall deformation status. This invention requires measuring the coordinates of all nodes, calculating the axial offset of members and the overall deformation of the space frame, and setting clear allowable standards. Through a systematic inspection and correction process, the overall geometric accuracy and structural performance of the space frame are ensured. These technological improvements, from path planning, precision control, stress monitoring, welding processes to quality inspection, form a complete technical system, providing a scientific and reliable construction method for the floor assembly of ultra-large span space frames.

[0108] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for assembling ultra-large span space frame floors, characterized in that, An assembly reference grid was set up in the floor assembly area. The design coordinates of the center of each lower chord sphere were determined using a total station. A triaxial stress monitoring device was set up at each design coordinate point of the center of the lower chord sphere. The lower chord ball and rod units were installed one by one using a single ball with a single rod. The ball center deviation was measured with a plumb bob and the ball nodes were fine-tuned and reset. The upper chord spheres and web members were installed using a single ball with a double rod. The real-time stress data of the node plates of the triaxial stress monitoring device were recorded. The stress concentration factor of the node plates was calculated and the prestress was released and adjusted. The weld area of ​​the node plates was preheated in sections before welding and ultrasonic testing was performed. After the space frame was assembled, the axial offset of the members was measured and the axial offset was corrected by adding temporary support rods. The overall deformation of the assembled space frame was detected. Through a dual real-time monitoring and feedback mechanism of stress state and geometric position, the stress accumulation during the entire assembly process was controlled below the safety threshold.

2. The method according to claim 1, characterized in that, In the step of setting up the assembly reference grid in the floor assembly area, the parallel assembly path of multiple construction groups is calculated based on the total number of grid nodes and the number of construction groups.

3. The method according to claim 2, characterized in that, The calculation of the parallel assembly path for multiple construction groups adopts a graph coloring algorithm to color the vertex subsets so that adjacent vertices belong to different vertex subsets. For each vertex subset, the shortest Hamiltonian path algorithm is used to calculate the assembly order.

4. The method according to claim 3, characterized in that, In the calculation of the parallel assembly path of multiple construction groups, each edge is assigned a weight value to represent the assembly difficulty coefficient. The assembly difficulty coefficient is determined based on the height of the node position and the number of rods already installed around the node.

5. The method according to claim 4, characterized in that, The assembly difficulty coefficient is determined by dividing the node height by the maximum height of the space frame and multiplying by 0.6, and then adding the number of installed members around the node divided by the total number of members designed for the node and multiplying by 0.

4.

6. The method according to claim 5, characterized in that, The triaxial stress monitoring device is a group of strain gauges installed in the three main stress directions of the node plate, used to collect the stress distribution of the node plate under the action of multiaxial tensile force in real time.

7. The method according to claim 6, characterized in that, The lower chord club units are installed one by one using a single ball and single club method. After each lower chord club unit is installed, the deviation between the actual coordinate point of the lower chord ball center and the designed coordinate point of the lower chord ball center is measured using a plumb bob.

8. The method according to claim 7, characterized in that, When the ball center deviation is less than 3mm, record the actual coordinates of the lower chord ball center and continue installing the next lower chord club unit. When the ball center deviation is greater than or equal to 3mm, perform fine-tuning and reset of the ball node until the ball center deviation is less than 3mm.

9. The method according to claim 8, characterized in that, The ball joint fine-tuning reset is achieved by adjusting the tightness of the bolts connecting the ball joint to the member or by increasing the thickness of the adjusting shims, so that the actual coordinate point of the lower chord ball center returns to the design coordinate point of the lower chord ball center.

10. The method according to claim 9, characterized in that, The top ball and the web bar are installed using a single ball with two bars. A third web bar forms a triangular stable structure. The actual coordinates of the top ball's center are measured using a plumb bob.

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