Low-temperature welding and deformation control method for segmented installation of steel box arch bridge in plateau complex environment

Abstract

The invention relates to the technical field of welding construction, and particularly discloses a low-temperature welding and deformation control method for segmented installation of a steel box arch bridge in a plateau complex environment, which comprises the following steps of: starting preheating and windproof preparation when judging that the plateau complex environment temperature is lower than a first preset temperature threshold value or the environment wind speed is higher than a first preset wind speed threshold value; starting a layered symmetric welding process of the steel box arch bridge by adopting carbon dioxide gas shielded welding until the front requirement of corresponding layered symmetric welding is met, calculating welding deformation based on the three-dimensional coordinates of each steel box arch bridge section acquired in real time, starting corresponding correction measures when the welding deformation exceeds a preset threshold value, and stopping welding when the welding deformation exceeds the preset threshold value. Until a plurality of prefabricated sections of the steel box arch bridge are obtained; starting an arch bridge closure stage for a plurality of prefabricated sections of the steel box arch bridge, and performing cooling and deformation control operation on the arch bridge closure section by using a slow cooling process; low-temperature welding and deformation control of segmented installation of the steel box arch bridge in the plateau complex environment are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of welding construction, and in particular to a low-temperature welding and deformation control method for segmented installation of a steel box arch bridge in a complex plateau environment. Background Art

[0002] In modern bridge construction, steel-box arch bridges, with their advantages of high span capacity and aesthetic appeal, are widely used in various large-scale transportation infrastructure projects. In areas with complex terrain and large span requirements, steel-box arch bridges have become a preferred bridge type. However, the construction of steel-box arch bridges in the complex plateau environment presents numerous challenges. The environmental characteristics of plateau regions differ significantly from those of plains. Low temperatures can affect the properties of steel, reducing its toughness and weldability and increasing the risk of defects such as cracks during welding. Furthermore, complex meteorological conditions, such as high wind speeds, not only affect the stability of the welding arc, resulting in reduced weld quality, but can also accelerate weld cooling, further causing weld deformation. Furthermore, during the segmented installation of steel-box arch bridges, the welding quality and deformation control of each segment are directly related to the structural stability and safety of the entire bridge. Therefore, developing a low-temperature welding and deformation control method suitable for segmented steel-box arch bridge installation in the complex plateau environment is crucial. This approach is crucial for ensuring bridge construction quality and long-term stable operation. An increasing number of bridge projects are facing the challenges posed by the complex plateau environment. The development of advanced low-temperature welding and deformation control technologies can not only expand the application scope of steel box arch bridges in plateau areas and improve the technical level of bridge construction, but also provide valuable experience for engineering practices in related fields, and has broad development prospects.

[0003] However, when dealing with environmental conditions that are not conducive to welding, such as the complex environment of the plateau, the existing steel box arch bridge welding cannot reduce the impact of low temperature and strong wind on the welding quality. It is difficult to control the welding deformation generated during the welding process and the arch bridge closure stage. Ultimately, it is difficult to ensure the low-temperature welding quality and overall structural stability of the steel box arch bridge in the complex environment of the plateau.

[0004] Therefore, the present invention proposes a low-temperature welding and deformation control method for segmented installation of steel box arch bridges in complex plateau environments. Summary of the Invention

[0005] The present invention provides a low-temperature welding and deformation control method for the segmented installation of steel-box arch bridges in complex plateau environments. By real-time monitoring of the complex plateau environmental temperature and wind speed in the installation area, preheating and wind protection preparations are promptly initiated when environmental conditions are unfavorable, enabling welding operations to adapt to the harsh and changeable plateau environment and ensuring welding quality. After meeting the prerequisites, carbon dioxide gas shielded welding is used for layered, symmetrical welding. This process effectively reduces welding stress and deformation, improves the quality and stability of welded joints, and ensures the integrity and safety of the steel-box arch bridge structure. Simultaneously, welding deformation, including longitudinal shrinkage, transverse bending, and angular deformation, is precisely monitored to achieve comprehensive and accurate monitoring of welding deformation. Corrective measures are initiated when threshold values ​​are exceeded, resulting in multiple prefabricated segments, ensuring the dimensional accuracy and installation quality of the steel-box arch bridge segments. Subsequently, during the arch bridge closure stage, a slow cooling process is used to cool the closure segments and control deformation. This helps reduce temperature stress in the closure segments, mitigates deformation risks, further improves the stability and reliability of the overall steel-box arch bridge structure, and ensures the long-term safe operation of the steel-box arch bridge in complex plateau environments. This allows the bridge to effectively adapt to the complex plateau environment, ensure welding quality, precisely control deformation, and ensure the stability, safety, and reliability of the steel box arch bridge structure.

[0006] The present invention provides a low-temperature welding and deformation control method for segmented installation of a steel box arch bridge in a complex plateau environment, comprising:

[0007] Real-time collection of complex plateau environmental temperature and wind speed in the segmented installation area of ​​the steel box arch bridge;

[0008] When it is determined that the temperature of the complex plateau environment is lower than a first preset temperature threshold or the ambient wind speed is higher than a first preset wind speed threshold, preheating and windbreak preparation are started;

[0009] When the preheating and windproof preparations are started and the corresponding pre-conditions for layered symmetrical welding are met, the process of layered symmetrical welding of the steel box arch bridge using carbon dioxide gas shielded welding is started. At the same time, the welding deformation is calculated based on the three-dimensional coordinates of each steel box arch bridge segment collected in real time. When the welding deformation exceeds the corresponding dynamic threshold, the corresponding corrective measures are initiated until it is determined that the welding deformation is controlled within the corresponding dynamic threshold, and multiple prefabricated segments of the steel box arch bridge are obtained;

[0010] The arch closure stage was initiated for multiple prefabricated segments of a steel box arch bridge, and a slow cooling process was used to cool and control deformation of the closure segments, achieving low-temperature welding results for the segmented installation of the steel box arch bridge.

[0011] Among them, welding deformation includes longitudinal shrinkage deformation, transverse bending deformation, and angular deformation.

[0012] Preferably, preheating and windproofing preparations include:

[0013] An electric heating module is used to preheat the weld groove of a steel box arch bridge, controlling the temperature of the groove area to rise evenly to a second preset temperature threshold, and an infrared thermometer is used to monitor the temperature in real time;

[0014] Windproof preparation is achieved by using a movable windproof shed with a circulating fan inside the shed to maintain the internal wind speed not exceeding the second wind speed threshold.

[0015] Preferably, the welding deformation is calculated based on the three-dimensional coordinates of each steel box arch bridge segment acquired in real time, including:

[0016] The three-dimensional coordinates of each steel box arch bridge segment are collected in real time by laser trackers set at both ends and the midpoint of each steel box arch bridge segment;

[0017] The welding deformation is calculated based on the three-dimensional coordinates of each steel box arch bridge segment collected in real time.

[0018] Preferably, it also includes:

[0019] Generate a deformation trend curve based on the real-time calculated welding deformation, and calculate the real-time deformation growth rate of the deformation trend curve;

[0020] When the real-time deformation growth rate is greater than the preset growth rate threshold and the duration is greater than the preset time period threshold, a welding pause instruction is issued.

[0021] Preferably, the method for determining the corresponding dynamic threshold value of the welding deformation includes:

[0022] 1 plus the product of the temperature influence coefficient and the reference temperature minus the real-time ambient temperature, plus the product of the wind speed influence coefficient and the real-time ambient wind speed divided by the square of the reference wind speed, to obtain a first threshold correction coefficient;

[0023] determining a second threshold correction coefficient based on a real-time function value of a first-order derivative function of the welding deformation amount;

[0024] The product of the corresponding reference threshold value of the welding deformation amount, the first threshold correction coefficient, and the second threshold correction coefficient is used as the corresponding dynamic threshold value of the welding deformation amount.

[0025] Preferably, when the welding deformation exceeds the corresponding dynamic threshold, the corresponding corrective measures are initiated, including:

[0026] When the longitudinal shrinkage deformation or angular deformation of a single welding area exceeds the corresponding dynamic threshold, local heating correction is performed on the corresponding welding area based on the longitudinal shrinkage deformation correction parameter or the angular deformation correction parameter;

[0027] When the lateral bending deformation of a single welding area exceeds the corresponding dynamic threshold, a reverse force of a preset magnitude is applied to the corresponding welding area through a mechanical pushing device.

[0028] Preferably, it also includes:

[0029] The force application point of the mechanical jacking device is located 200mm above the neutral axis of the arch rib section, and the thrust is controlled by a force sensor, with each adjustment amount ≤5kN.

[0030] Preferably, before starting the arch bridge closure stage for a plurality of prefabricated segments of a steel box arch bridge, the process includes:

[0031] Based on the finite element simulation method, the deformation law of multiple precast segments in the arch bridge closure stage was previewed to obtain the deformation law preview results;

[0032] The reserved expansion joint width and locking temperature window of the closure are set based on the deformation law preview results.

[0033] Preferably, the deformation law preview of multiple prefabricated segments at the closure stage of the arch bridge is performed based on the finite element simulation method to obtain the deformation law preview results, including:

[0034] A 3D mechanical model of multiple precast segments of an arch bridge during its closure phase was established using finite element simulation methods.

[0035] Based on the plateau environmental parameters and material parameters as well as the three-dimensional mechanical model, the data on the impact of temperature changes on the length of the arch bridge, the local shrinkage deformation data caused by heat conduction during the welding process, and the impact of the lateral bending of the arch bridge under strong wind loads on the accuracy of the joint are previewed as the deformation law preview results.

[0036] Preferably, the slow cooling process is used to cool the closure section of the arch bridge and control deformation, including:

[0037] While cooling the closure section of the arch bridge using a slow cooling process, a distributed sensor array is used to collect the axial stress, radial stress, and hoop stress of the preset weld zone in real time as the three-dimensional stress distribution of the preset weld zone.

[0038] Based on the three-dimensional stress distribution of the preset weld area, the three-dimensional stress difference and distance ratio of adjacent detection points in the distributed sensing array are calculated to obtain the three-dimensional stress gradient distribution of the preset weld area, and the high gradient area is screened out in the preset weld area based on the three-dimensional stress gradient threshold and the three-dimensional stress gradient distribution;

[0039] Calculating the ratio of the three-dimensional stress reduction value to the three-dimensional stress initial value at each detection point in the distributed sensing array within the latest preset period as the real-time stress relaxation rate of each detection point, and determining the stress release lag period of each detection point based on all the real-time stress relaxation rates collected at each detection point;

[0040] Based on the three-dimensional stress distribution of the preset weld area, the axial stress sequence, radial stress sequence and hoop stress sequence of the distributed sensing array are obtained, and the variance of the axial stress sequence, the variance of the radial stress sequence and the variance of the hoop stress sequence are calculated;

[0041] The ratio of the maximum value to the minimum value among the variance of the axial stress sequence, the variance of the radial stress sequence, and the variance of the hoop stress sequence is regarded as the three-dimensional stress coupling coefficient of the preset weld zone;

[0042] Based on the high gradient area and three-dimensional stress coupling coefficient in the preset weld area and the stress release lag period of each detection point, the current slow cooling process parameters are adjusted in real time to achieve deformation control.

[0043] The present invention offers the following advantages over existing technologies: by real-time monitoring of the complex plateau ambient temperature and wind speed, preheating and windbreak preparations can be initiated promptly when unfavorable environmental conditions occur, enabling welding operations to adapt to the harsh and variable plateau conditions and ensuring weld quality. After meeting pre-conditions, carbon dioxide gas shielded welding is used for layered, symmetrical welding. This process effectively reduces weld stress and deformation, improves the quality and stability of welded joints, and ensures the integrity and safety of the steel-box arch bridge structure. Welding deformation, including longitudinal shrinkage, transverse bending, and angular deformation, is precisely monitored, enabling comprehensive and accurate monitoring of weld deformation. Corrective measures are initiated when thresholds are exceeded, resulting in multiple prefabricated segments, ensuring the dimensional accuracy and installation quality of the steel-box arch bridge segments. Subsequently, during the arch bridge closure phase, a slow cooling process is used to cool the closure segments and control deformation. This helps reduce thermal stress and deformation risks in the closure segments, further improving the stability and reliability of the overall steel-box arch bridge structure and ensuring its long-term safe operation in the complex plateau environment. This effectively adapts to the complex plateau environment, ensures weld quality, precisely controls deformation, and ensures the stability, safety, and reliability of the steel-box arch bridge structure.

[0044] Other features and advantages of the present invention will be described in the following description, and in part will become apparent from the description, or will be understood by practicing the present invention. The purpose and other advantages of the present invention can be achieved and obtained through the structures specifically pointed out in this application document.

[0045] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0047] Figure 1This is a flow chart of a low-temperature welding and deformation control method for segmented installation of a steel box arch bridge in a complex plateau environment in an embodiment of the present invention;

[0048] Figure 2 This is a flow chart of preheating and windproof preparation in an embodiment of the present invention;

[0049] Figure 3 This is a flow chart of the welding deformation correction measures in an embodiment of the present invention. DETAILED DESCRIPTION

[0050] The preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0051] like Figure 1 As shown, the present invention provides an implementation method of a low-temperature welding and deformation control method for segmented installation of a steel box arch bridge in a complex plateau environment, comprising:

[0052] Temperature and humidity sensors, anemometers, and infrared thermometers were deployed in the steel box arch rib segment installation area to collect real-time data on the complex plateau environment temperature (accuracy ±0.5°C), ambient wind speed (sampling frequency 1Hz), and air humidity in the steel box arch bridge segment installation area.

[0053] When it is determined that the complex plateau environment temperature is lower than the first preset temperature threshold (5°C) or the ambient wind speed is higher than the first preset wind speed threshold (10m / s), preheating and windbreak preparation are initiated;

[0054] When the preheating and windproof preparations are started and the corresponding pre-conditions for layered symmetrical welding are met, the process of layered symmetrical welding of the steel box arch bridge using carbon dioxide gas shielded welding (determined based on the hexagonal cross-sectional characteristics of the steel box arch rib (inscribed circle diameter 2.2-4.0m)) is started. At the same time, the welding deformation is calculated based on the three-dimensional coordinates of each steel box arch bridge segment collected in real time. When the welding deformation exceeds the corresponding dynamic threshold, the corresponding corrective measures are initiated until it is determined that the welding deformation is controlled within the corresponding dynamic threshold, and multiple prefabricated segments of the steel box arch bridge are obtained;

[0055] The arch closure stage was initiated for multiple prefabricated segments of a steel box arch bridge, and a slow cooling process was used to cool and control deformation of the closure segments, achieving low-temperature welding results for the segmented installation of the steel box arch bridge.

[0056] Among them, welding deformation includes longitudinal shrinkage deformation, transverse bending deformation, and angular deformation.

[0057] In this embodiment, a 20 mm expansion joint is reserved during the arch rib closure stage and the ambient temperature is monitored. When the temperature stabilizes at 10-15°C, locking welding is performed, specifically including:

[0058] The process of first fixing with temporary bolts (spacing 300mm) and then welding is adopted, and the axis deviation of the joint is calibrated in real time by a total station (controlled within ±1mm);

[0059] After welding is completed, cover with electric heating blanket and slowly cool (cooling rate ≤ 5℃ / min) until the temperature drops to ambient temperature;

[0060] This embodiment also includes: a weld quality inspection step: 100% ultrasonic inspection of all welds (Level I qualification rate ≥ 95%), and additional radiographic inspection of the welds in the joint section to ensure that there are no defects such as lack of fusion and cracks.

[0061] In this embodiment, the initial parameters of the slow cooling process are as follows: the electric heating blanket covers an area of ​​1.5m on both sides of the joint section, and the power density is 200W / m 2 , which can be adjusted in 3 stages by the thermostat:

[0062] Stage 1 (0-1h): maintain temperature at 250°C;

[0063] The second stage (1-3h): reduce the temperature to 150℃ at 2℃ / min;

[0064] The third stage (3-6h): cool to ambient temperature at 1°C / min;

[0065] During the slow cooling process, the residual stress of the weld is monitored by strain gauges. When the stress peak is greater than 200 MPa, the holding time of the corresponding stage is extended.

[0066] In this embodiment, the steel box arch rib segment installation area refers to a specific site where the steel box arch rib segments are spliced ​​and assembled on site.

[0067] In this embodiment, the complex environmental temperature and environmental wind speed of the plateau: the complex environmental temperature of the plateau refers to the temperature conditions of the plateau area. For example, the annual average temperature in Gar County, Tibet is 0.35°C and the extreme low temperature is -36.6°C. The environmental wind speed refers to the wind conditions in the area. For example, there are 113 windy days in Gar County per year and the maximum wind speed is 23m / s.

[0068] In this embodiment, after starting preheating and windproof preparation, the corresponding prerequisite requirements for layered symmetrical welding are met: the welding groove temperature is evenly increased to 100-150°C with a temperature difference of ≤10°C through the electric heating module, and the internal wind speed is maintained at no more than 3m / s by using a movable windproof shed. Only when these conditions are met can the prerequisite requirements for layered symmetrical welding be achieved.

[0069] In this embodiment, the three-dimensional temperature field gradient (unit: ° C / μm) of the weld cross section can also be collected by an infrared thermal imager to calculate the energy attenuation coefficient k from the center of the molten pool to the heat-affected zone (k = ΔT / Δx, ΔT is the temperature difference, Δx is the distance);

[0070] Energy concentration factor is defined as energy density in the molten pool area / energy density in the heat-affected zone. When the energy concentration factor is greater than 5, it is determined that the heat input distribution is uneven.

[0071] The quantitative relationship of stress initiation based on heat input gradient is specifically:

[0072] The first-order mapping is: initial thermal stress = 0.1 × deformation transfer coefficient + 50, fitted by 300 sets of experimental data);

[0073] The second-order mapping is: local stress peak = stress concentration factor × initial thermal stress;

[0074] The stress data collected by the fiber Bragg grating sensor is decomposed into instantaneous stress, stress growth rate, and stress acceleration rate. The instantaneous stress is the real-time stress value at a certain moment; the stress growth rate is the first-order derivative of the instantaneous stress with respect to time; and the stress acceleration rate is the second-order derivative of the stress growth rate with respect to time.

[0075] When the stress acceleration rate is greater than 0 and the stress growth rate is greater than 0.5, it is determined to be a stress acceleration accumulation state (which may trigger deformation tolerance within 10 minutes).

[0076] Deformation transfer coefficient is defined as: transverse bending deformation increment / local stress peak increment;

[0077] The deformation transfer coefficient is related to the number of welding layers: when welding the first layer, the deformation transfer coefficient = 0.02, that is, the material is initially stress sensitive; when welding the fifth layer, the deformation transfer coefficient = 0.005, that is, the stress gradually saturates;

[0078] Example: If the local stress peak increment during the third layer welding is 30 MPa and the deformation transfer coefficient is 0.01, then the predicted transverse bending deformation increment is 30 × 0.01 = 0.3, and the deviation from the measured value must be ≤ 0.05.

[0079] When the predicted deformation increment of the transverse bending deformation increment is close to 80% of the threshold, the heat input correction amount is reversely deduced and finally converted into the welding current correction amount ΔI = -0.5×energy attenuation coefficient.

[0080] In this embodiment, the welding deformation is calculated based on the real-time acquisition of the three-dimensional coordinates of each steel arch bridge segment. Laser trackers are set up at the ends and midpoint of the steel arch bridge segment to obtain the three-dimensional coordinates in real time. The segment deformation caused by welding is calculated based on these coordinates. Assuming the steel arch bridge segment is a regular rectangular parallelepiped, the laser tracker is used to obtain the initial three-dimensional coordinates of the ends and midpoint of the segment before welding begins. For example, the coordinates of one end are (x1, y1, z1), the coordinates of the other end are (x2, y2, z2), and the coordinates of the midpoint are (xm, ym, zm).

[0081] After welding for a period of time, the three-dimensional coordinates of these three points are measured again with a laser tracker, assuming that they become (x1', y1', z1'), (x2', y2', z2'), and (xm', ym', zm').

[0082] When calculating the longitudinal shrinkage deformation, if the segment is longitudinal along the x-axis, the longitudinal shrinkage deformation can be calculated by the change in the x-axis coordinates of the two end points, that is, |x2-x1|-|x2'-x1'|.

[0083] For transverse bending deformation, assuming the transverse direction is the y-axis, it can be calculated by comparing the change in the y-axis coordinate relationship between the midpoint and the two end points before and after welding. For example, the y-axis coordinate of the midpoint before welding is the average of the y-axis coordinates of the two end points, that is, ym = y1 + y2 / 2. After welding, if ym' = y1' + y2' / 2, the transverse bending deformation can be calculated based on the corresponding geometric relationship.

[0084] Angular deformation can be determined by analyzing the change in angle between different facets of a segment before and after welding. For example, assuming a facet of a segment is defined by its endpoints and midpoint, the normal vectors of this facet before and after welding can be calculated from the coordinates. The angular deformation can then be determined based on the change in angle between these normal vectors.

[0085] In this embodiment, multiple prefabricated segments of the steel box arch bridge are obtained until the welding deformation is determined to be controlled within the corresponding dynamic threshold: if the deformation during the welding process exceeds a preset standard such as longitudinal shrinkage > 3, measures are taken to adjust until the deformation meets the requirements, and then multiple prefabricated segments of the steel box arch bridge with satisfactory accuracy are obtained.

[0086] In this embodiment, the low-temperature welding result of the segmented installation of the steel box arch bridge is: the final result of a series of construction operations in a low-temperature environment of the plateau to ensure that the welding quality, structural deformation, etc. of the steel box arch bridge meet the design standards.

[0087] In this embodiment, the longitudinal shrinkage deformation refers to the shortening caused by the shrinkage of the weld during the welding of the steel box arch ribs along the length direction. For example, if it exceeds 3mm per meter, it needs to be corrected; the transverse bending deformation refers to the bending offset caused by the welding thermal stress in the vertical length direction. If the lateral offset exceeds 5mm per meter, it needs to be corrected; the angular deformation refers to the angle change caused by uneven heating on both sides of the welding area. If it exceeds 2°, it needs to be corrected.

[0088] like Figure 2 As shown in the figure, in order to create suitable conditions for layered symmetrical welding by preheating through electric heating modules and using movable windbreaks to prevent wind when the temperature or wind speed in complex plateau environments does not meet the requirements, preheating and windbreak preparations are proposed, including:

[0089] An electric heating module is used to preheat the weld groove of the steel box arch bridge, controlling the temperature of the groove area to rise evenly to the second preset temperature threshold (100-150°C with a temperature difference of ≤10°C), and an infrared thermometer is used to monitor the temperature in real time.

[0090] Windproof preparation is achieved by using a movable windproof shed (wind resistance level ≥ 12) with a circulating fan inside the shed to maintain the internal wind speed not exceeding the second wind speed threshold (3m / s).

[0091] In this embodiment, the movable windbreak includes:

[0092] Modular frame (made of Q355 steel, cross-section size 100mm×100mm), with hydraulic folding mechanism for quick erection (erectile time ≤30min);

[0093] The greenhouse temperature control system includes two sets of 50kW electric heaters (placed on both sides of the roof) and temperature feedback sensors (sampling points are 500mm apart). The PID controller maintains the temperature fluctuation within the greenhouse within 5°C.

[0094] Windproof curtain: Made of PVC coated cloth (thickness 0.8mm), the sides are sealed to the frame by magnetic strips, and the bottom counterweight (weight 50kg / m) ensures contact with the ground, with a drag coefficient of ≤0.3.

[0095] In this embodiment, the electric heating module is a device used to heat relevant parts of the steel box arch bridge. It is used to preheat the welding groove of the steel box arch bridge in a low-temperature environment on the plateau so that the temperature of the groove area is uniformly raised to a specified temperature.

[0096] In this embodiment, the welding groove of the steel box arch bridge is an area of ​​a specific geometric shape processed at the welding position of the steel box arch bridge segment before welding in order to ensure welding quality.

[0097] In this embodiment, real-time thermal insulation monitoring is performed using infrared thermometers: Infrared thermometers are used to continuously measure the temperature of areas requiring temperature control, such as the weld grooves of steel box arch bridges, to ensure that the temperature remains within the specified range. For example, during the preheating process, the temperature of the groove area is monitored in real time to ensure that it remains uniform and stable at 100-150°C with a temperature difference of ≤10°C. If the temperature does not meet the standard, the heating level can be adjusted promptly to ensure thermal insulation.

[0098] In this embodiment, the indoor circulation fan is a fan device installed in a movable windproof shed, which is used to circulate the air in the shed while assisting in maintaining uniform temperature in the shed and controlling the wind speed in the shed. For example, during the construction of the Deji Road to Xiangquan Road cross-river bridge, the indoor circulation fan is used to maintain the wind speed in the shed at no more than 3m / s.

[0099] In this embodiment, the internal wind speed refers to the speed of air flow inside the movable windproof shed. For example, when welding a steel box arch bridge, the internal wind speed in the shed needs to be controlled to no more than 3m / s to ensure the stability of the welding arc and the welding quality.

[0100] In order to clarify the specific welding parameters and interlayer temperature control requirements during the layered symmetrical welding of steel box arch bridges using carbon dioxide gas shielded welding and ensure welding quality, the process of starting the layered symmetrical welding of steel box arch bridges using carbon dioxide gas shielded welding is proposed, including:

[0101] The first layer welding current is controlled at 180-220A, arc voltage at 28-32V, welding speed at 30-40cm / min, ensuring the penetration depth is ≥8mm. After each layer is welded, a temperature-controlled thermocouple is used to monitor the interlayer temperature. If the temperature is >200℃, welding is suspended and continued after natural cooling to 150-180℃.

[0102] For the T-joint connecting the arch rib diaphragm and the web, a symmetrical sequence of vertical welding followed by flat welding is adopted to reduce angular deformation.

[0103] In this embodiment, the welding sequence for the hexagonal arch rib is as follows:

[0104] The six webs of the arch rib section are welded in layers in a clockwise order of top → bottom → left → right → front → back. After each layer is welded, switch to a symmetrical position (for example, weld the first layer of the lower web immediately after the first layer of the upper web is completed);

[0105] The arc starting point and arc ending point of each layer of weld should be staggered by more than 50mm, and the arc pit should be filled with back welding method (length ≥ 10mm) when the arc is ended;

[0106] For the 30mm thick web butt weld, the welding is completed in 5 layers (the first layer thickness is 4-5mm, the middle layer is 5-6mm, and the surface layer is 3-4mm). After each layer is welded, the welding slag is cleaned with a wire brush and the weld formation is checked.

[0107] In this embodiment, the first layer welding current refers to the current intensity used for the first layer welding when the steel box arch bridge is subjected to layered symmetrical welding using carbon dioxide gas shielded welding, and the range is controlled within 180-220A.

[0108] In this embodiment, the arc voltage is the voltage across the arc during the welding process. In the carbon dioxide gas shielded welding layered symmetrical welding of this embodiment, the arc voltage is controlled at 28-32V.

[0109] In this embodiment, welding speed refers to the speed at which the welding electrode moves along the weld joint during the welding process. When welding a steel box arch bridge, the welding speed is set to 30-40 cm / min.

[0110] In this embodiment, penetration refers to the depth of the base material melted during the welding process. When welding the first layer of a steel box arch bridge, the penetration is required to be ≥8 mm.

[0111] In this embodiment, a thermocouple is used to monitor the interlayer temperature. A thermocouple is a temperature-sensing element that measures the interlayer temperature after each layer of symmetrical welding is completed. If the temperature exceeds 200°C, welding is suspended and resumed after the layer cools naturally to 150-180°C.

[0112] Alternatively, the dynamic interlayer temperature threshold can be determined using the following interlayer temperature dynamic control formula:

[0113]

[0114] Where, T inter is the upper limit of the current interlayer temperature (unit: °C); T base is the basic interlayer temperature (200℃); ΔT is the temperature correction (-50℃, used to adjust the upper limit according to the parameters); δ is the current weld thickness (unit: mm); δ0 is the reference weld thickness (30mm); θ is the groove angle; cos is the cosine function.

[0115] In order to accurately calculate the welding deformation by collecting three-dimensional coordinates with the help of a laser tracker set at a specific position of the steel box arch bridge segment, a method for calculating the welding deformation based on the three-dimensional coordinates of each steel box arch bridge segment collected in real time is proposed, including:

[0116] The three-dimensional coordinates of each steel box arch bridge segment were collected every 5 minutes by setting up three monitoring targets (diameter 50mm, reflectivity ≥90%) at both ends and the midpoint of each steel box arch bridge segment (accuracy ±0.1mm);

[0117] The welding deformation is calculated based on the three-dimensional coordinates of each steel box arch bridge segment acquired in real time.

[0118] In this embodiment, the steel box arch bridge segment refers to the part of the steel box arch bridge that is pre-fabricated in sections during the manufacturing process and subsequently transported to the construction site for splicing and installation.

[0119] In this embodiment, the three-dimensional coordinates of the steel box arch bridge segment are used to determine the coordinate values ​​of the steel box arch bridge segment in space, which are acquired in real time by setting laser trackers at both ends and the midpoint of each steel box arch bridge segment.

[0120] In order to generate a deformation trend curve and calculate the real-time deformation growth rate, a welding pause instruction can be issued in time when the growth rate is abnormal, thereby better controlling welding deformation. The following are also proposed:

[0121] Generate a deformation trend curve based on the real-time calculated welding deformation, and calculate the real-time deformation growth rate of the deformation trend curve;

[0122] When the real-time deformation growth rate exceeds the preset growth rate threshold (0.5 mm / min) for a period longer than the preset period threshold (three consecutive acquisitions), a welding pause instruction is issued.

[0123] In this embodiment, a deformation trend curve is generated based on the welding deformation calculated in real time: during the welding process of the steel box arch bridge, based on the welding deformation data obtained by real-time calculation of the three-dimensional coordinates of the steel box arch bridge segment, a curve is drawn with time or welding process as the horizontal axis and welding deformation as the vertical axis, which can intuitively show the trend of welding deformation changing with time or welding process.

[0124] In this embodiment, the real-time deformation growth rate of the deformation trend curve is calculated by analyzing the generated deformation trend curve to calculate the rate at which the deformation changes over time or during the welding process at a specific moment. For example, the real-time deformation growth rate can be obtained by observing the speed at which the welding deformation increases at consecutive time points.

[0125] In this embodiment, the duration of the real-time deformation growth rate exceeding a preset growth rate threshold is recorded. The preset growth rate threshold is a standard value set based on engineering experience and design requirements. When the calculated real-time deformation growth rate exceeds this threshold, the duration of this period is recorded. For example, during the welding of the steel box arch bridge from Deji Road to Xiangquan Road, if the real-time deformation growth rate exceeds the set value and persists for a certain period of time, it may indicate an abnormality in the welding process, requiring appropriate measures, such as issuing a welding pause instruction.

[0126] In order to consider the influence of plateau ambient temperature and wind speed on the mechanical properties of materials and improve the adaptability of the threshold value of welding deformation, a method for determining the corresponding dynamic threshold value of welding deformation is proposed, including:

[0127] The first threshold correction coefficient is obtained by adding the product of 1 plus the temperature influence coefficient (0.02 per degree Celsius, the material brittleness increases at low temperatures and the threshold value decreases) and (the reference temperature 20°C minus the real-time ambient temperature T), plus the product of the wind speed influence coefficient (0.01, when the wind speed increases, the wind load causes additional deformation, and the threshold value decreases) and (the real-time ambient wind speed v divided by the reference wind speed 3m / s) squared.

[0128] A second threshold correction coefficient is determined based on a real-time function value vd of a first-order derivative function of the welding deformation. For example, the second threshold correction coefficient is exp(-0.2*vd), where exp is a natural exponential function and a natural constant is 2.72.

[0129] The corresponding benchmark threshold of welding deformation (i.e., the threshold at normal temperature of 20°C and wind speed of 3m / s, the corresponding benchmark threshold of longitudinal shrinkage deformation is 3mm / m, the corresponding benchmark threshold of transverse bending deformation is 5mm of lateral offset per meter of length, and the corresponding benchmark threshold of angular deformation is 2°) multiplied by the first threshold correction coefficient and the second threshold correction coefficient is used as the corresponding dynamic threshold of welding deformation.

[0130] like Figure 3 As shown in the figure, in order to deal with different types of welding deformation exceeding the corresponding dynamic threshold, effective correction measures such as local heating correction or mechanical pushing are adopted to ensure that the welding deformation is controlled. It is proposed that when the welding deformation exceeds the corresponding dynamic threshold, the corresponding correction measures are initiated, including:

[0131] When the longitudinal shrinkage deformation or angular deformation of a single welding area exceeds the corresponding dynamic threshold, local heating correction is performed on the corresponding welding area based on the longitudinal shrinkage deformation correction parameters (i.e., heating temperature 250-300°C, holding time 5-10 minutes) or angular deformation correction parameters (i.e., using flame or electric heating to 250-300°C (holding time 5-10 minutes) for the out-of-tolerance area, using the material's thermoplasticity to release stress and restore angle accuracy);

[0132] When the lateral bending deformation of a single welding area exceeds the corresponding dynamic threshold, a reverse force of a preset magnitude (thrust force of 50-100kN) is applied to the corresponding welding area through a mechanical pushing device.

[0133] In this embodiment, during the welding construction of a steel box arch bridge, when the lateral bending deformation of a single welding area exceeds the corresponding dynamic threshold, measures need to be taken to correct the deformation. At this time, a special mechanical pushing device is used. The device can apply a force in the opposite direction of the deformation to the welding area where the lateral bending deformation exceeds the threshold according to a predetermined force, so as to offset or reduce the lateral bending deformation and restore the welding area to a shape and position close to the design requirements. For example, in the construction of the steel box arch bridge from Deji Road to Xiangquan Road River Crossing Bridge, if the lateral bending deformation of a welding area exceeds the corresponding dynamic threshold of 5mm per meter, the mechanical pushing device will control the thrust through the force sensor at 200mm above the axis of the arch rib cross section, with each adjustment amount ≤5kN, and apply a preset size (such as 50-100kN) of reverse force to the welding area, thereby correcting the welding deformation and ensuring the structural accuracy and stability of the steel box arch bridge.

[0134] In order to clarify the force application point position of the mechanical pushing device, control the thrust and the adjustment amount each time through the force sensor, and accurately control the lateral bending deformation correction process, it is proposed to also include:

[0135] The force application point of the mechanical jacking device is located 200 mm above the neutral axis of the arch rib section, and the thrust is controlled by a force sensor (accuracy ±1 kN), and the adjustment amount each time is ≤5 kN.

[0136] In this embodiment, thrust is controlled by a force sensor. During the steel box arch bridge welding deformation correction process, a force sensor is installed on the mechanical thrust device. Its function is to accurately measure the thrust applied to the weld area by the mechanical thrust device in real time and feed this data back to the control system. Based on this feedback, the control system adjusts the thrust of the mechanical thrust device to ensure that the applied force meets the preset value, thus ensuring the accuracy and safety of the correction process.

[0137] In this embodiment, the adjustment amount of ≤5kN per time refers to the control of the thrust increase or decrease within 5kN when using the mechanical jacking device to correct deformation in the weld area of ​​the steel box arch bridge. This is to prevent excessive force changes from damaging the weld area or causing new deformation.

[0138] In order to reasonably set the reserved expansion joint width and locking temperature window of the closure mouth and improve the closure accuracy based on the finite element simulation to predict the deformation law before the arch bridge closure stage, it is proposed to start the arch bridge closure stage for multiple prefabricated segments of the steel box arch bridge, including:

[0139] Based on the finite element simulation method, the deformation law of multiple precast segments in the arch bridge closure stage was previewed to obtain the deformation law preview results;

[0140] Based on the deformation law preview results, the reserved expansion joint width (for example, 20 mm) and the locking temperature window (for example, 10-15°C) of the joint mouth are set.

[0141] In this embodiment, the steel box arch rib is composed of multiple prefabricated segments, and the closure is the last key step (connecting the segments at both ends of the arch rib into a whole). Due to the extreme temperature difference in the plateau environment (-36.6°C to room temperature), strong wind loads, and the thermal expansion and contraction characteristics of steel, the arch rib will deform (such as expansion and bending) during construction due to factors such as temperature changes, welding stress, and deadweight. Through finite element simulation technology, a three-dimensional mechanical model of the steel box arch rib can be established. By inputting plateau environmental parameters (temperature range, wind speed, material thermal expansion coefficient, etc.), the deformation law of the arch rib under different working conditions can be simulated: the effect of temperature changes on the length of the arch rib (for example, for every 10°C increase in temperature, the arch rib with a span of 85m may elongate by about 10mm); the local shrinkage deformation caused by heat conduction during welding is simulated (for example, the weld area may shrink by 2-3mm after cooling); and the impact of the lateral bending of the arch rib under strong wind load on the accuracy of the closure is analyzed. Through simulation, the deformation caused by different factors can be quantified, providing data support for the design of the closure mouth.

[0142] The closure is the gap between the arch ribs at the end of the joint. The expansion joint is reserved to provide a buffer for arch rib deformation, preventing excessive residual stress or structural damage caused by forced splicing. Based on the above finite element simulation results (predicted deformation patterns), the expansion joint reserved at the closure was optimized to 20mm. This is because: due to the large temperature differences on the plateau, the steel box arch ribs will contract at extremely low temperatures (such as -36.6°C) and elongate at high temperatures. A 20mm gap can accommodate the maximum expansion and contraction caused by temperature changes (simulation calculations show that the maximum temperature difference deformation of the 85m span arch ribs in this project is approximately 18mm, and a 20mm gap can cover this range). During welding, the weld will shrink and deform (approximately 2-3mm) as it cools. The reserved gap prevents the arch ribs from tightening or cracking due to this shrinkage. Considering lifting errors (such as slight offsets when the segments are connected), the 20mm gap provides an operational margin for on-site adjustments, ensuring precise connection of the segments.

[0143] The locking temperature refers to the ambient temperature during the joint welding. At this time, the arch rib segments are fixed and the welding is completed. When the temperature changes subsequently, the structure can expand and contract freely to avoid additional stress. The optimization basis for locking the temperature window (10-15°C) also comes from finite element simulation: simulation results show that the average annual temperature in the project area (Gar County, Tibet) is 0.35°C, but 10-15°C is the neutral temperature range for structural thermal expansion and contraction. After the joint is completed at this temperature, the increase in arch rib elongation during high summer temperatures and the decrease in contraction during low winter temperatures are basically balanced, which can minimize structural stress at extreme temperatures; if the joint is closed at too low a temperature (such as -10°C), the arch ribs will generate huge thrust due to thermal expansion during high summer temperatures, which may cause stress concentration at the arch foot nodes; if the joint is closed at too high a temperature (such as 25°C), the arch ribs will shrink at low winter temperatures, which may cause tensile cracking of the joint mouth weld; at 10-15°C, the welding performance of steel is more stable (weld toughness and strength compliance rate are high), and the wind speed is relatively low (strong winds on the plateau are mostly concentrated in low temperature periods), which can reduce the risk of wind-induced deformation during the welding process.

[0144] In this embodiment, before the closure of the steel box arch bridge, the deformation patterns of multiple prefabricated segments during the closure phase of the arch bridge were previewed using methods such as finite element simulation. Data results were obtained, such as the effect of temperature changes on the length of the arch bridge, local shrinkage deformation caused by welding heat conduction, and the effect of lateral bending under strong wind loads on closure accuracy, including:

[0145] First, determine the thermal expansion coefficient of the steel used in the steel box arch bridge, assuming it is α (unit: ° C). The initial length of the arch bridge is known to be L0 (for example, 85m).

[0146] Considering the temperature variation range in the area, it is assumed that the extreme low temperature Tmin is -30℃ and the extreme high temperature Tmax is 30℃.

[0147] According to the principle of thermal expansion and contraction, the elongation of the arch bridge when the temperature rises is:

[0148] ΔL1=L0×α×(Tmax-T0);

[0149] When the temperature drops, the arch bridge shortens by:

[0150] ΔL2=L0×α×(T0-Tmin);

[0151] Where T0 is the initial reference temperature (e.g., 0°C). The influence range of temperature change on the length of the arch bridge is calculated. For example, it is calculated that within such a temperature change range, the length of the arch bridge may vary between -15 mm and 18 mm.

[0152] By simulating the welding process, the power of the welding heat source, welding speed, and the thermophysical properties of the steel (such as specific heat capacity and thermal conductivity) were taken into account. Finite element simulation and other methods were used to preview the mechanical behavior of the arch bridge at different temperatures. Taking a steel box arch bridge as an example, the stress distribution and changes in the structure at different closure locking temperatures within the local temperature range were simulated. The results showed that when the locking temperature was between 10-15°C, the tensile and compressive stress distributions in the arch bridge structure were relatively balanced with seasonal temperature fluctuations, and local stress concentrations caused by temperature changes did not occur. For example, if the locking temperature was too low (such as 5°C), the expansion of the arch ribs during high summer temperatures would place excessive pressure on the arch foot, potentially causing structural instability. If the locking temperature was too high (such as 20°C), the contraction of the arch ribs during low winter temperatures would generate large tensile stresses in the closure section, which could easily lead to weld cracking.

[0153] Using heat conduction theory and numerical simulation methods, we calculated how the temperature distribution of the weld and its surrounding areas changes over time during welding. As the weld cools, it experiences localized shrinkage deformation. For example, simulations show that a weld of a specific length shrinks by approximately 2-3 mm after cooling.

[0154] Preliminary studies were conducted on the welding properties of steel at different temperatures, including metallurgical reactions during welding, crystallization of the weld metal, and changes in the properties of the heat-affected zone (HAZ). Experimental simulations revealed that at temperatures between 10 and 15°C, the toughness loss in the HAZ is minimal, and the strength and toughness of the weld metal are well matched. For example, welding in this temperature range results in a moderate hydrogen diffusion rate in the weld, effectively preventing hydrogen-induced cracking and ensuring the quality of the weld joint.

[0155] Determine the magnitude of the wind load acting on the arch bridge.

[0156] Rehearsals were conducted to assess the impact of local seasonal meteorological conditions on construction, such as wind speed and humidity. In the area where the steel box arch bridge is located, simulations showed that temperatures between 10°C and 15°C (71°F) provide relatively low wind speeds and stable humidity, which are conducive to high-altitude welding operations and the operation of construction equipment. For example, when the temperature drops below 10°C, strong winds increase, affecting the stability of the welding arc and increasing the risk to construction workers working at height. When the temperature rises above 15°C (91°F), humidity fluctuates significantly, potentially causing condensation on the steel surface and impacting welding quality.

[0157] Wind loads were applied to the mechanical model of a steel box arch bridge, and finite element analysis and other methods were used to determine the lateral bending deformation of the arch bridge under strong winds. For example, simulation results showed that at certain wind speeds, the lateral bending of the arch bridge could cause a 5-8 mm deviation in the closure position.

[0158] Based on these rehearsal results, the width of the expansion joint reserved for the closure was determined. Taking this data into account, temperature fluctuations could cause the arch bridge length to vary by -15mm to 18mm, welding shrinkage deformation could be approximately 2-3mm, and lateral bending under strong wind loads could cause the closure position to deviate by 5-8mm. To ensure the arch bridge can close smoothly under various adverse conditions, the reserved expansion joint width needs to be able to accommodate these deformations. Considering a safety margin of 2mm, the reserved expansion joint width W = 18 + 3 + 8 + 2 = 31mm.

[0159] Based on such preview results, 10-15℃ was set as the locking temperature window.

[0160] In this embodiment, risk intervention can also be performed in the following ways:

[0161] Breaking through the limitations of traditional geometric mapping, we build a macro-meso-micro three-level digital twin model to achieve real-time interaction in all dimensions of the physical field:

[0162] The macroscopic layer (structural scale) includes: constructing a 3D model of the entire steel box arch rib based on laser tracker (3 targets / segment) and millimeter-wave radar data, updating spatial coordinates in real time (accuracy ±0.1mm), and synchronously mapping macroscopic deformations such as longitudinal shrinkage and lateral bending;

[0163] Embed the plateau environmental parameter field (temperature, wind speed, air pressure), and every 1m 3 The space is given real-time environmental attributes (e.g., the -10°C area is marked in blue, and the 15m / s wind speed area is marked with a red arrow), which intuitively shows the impact of the environment on the structure.

[0164] The mesoscopic layer (weld seam scale) includes: using a high-resolution infrared thermal imager (pixel accuracy 0.5mm×0.5mm) to collect the temperature field of the weld area, generating a dynamic cloud map of the heat-affected zone in the model, and real-time marking of the molten pool boundary (temperature > 1538°C), the overheating zone (800-1538°C), and the normalizing zone (500-800°C). The area proportion of each zone is calculated (for example, an early warning is issued when the overheating zone proportion is >30%).

[0165] By integrating ultrasonic testing data, internal defects in the weld (such as lack of fusion and pores) are marked in the model, different defect types are distinguished by different colors (red = cracks, yellow = pores), and the equivalent diameter of the defect is automatically calculated (for example, pores ≥3mm trigger a rating upgrade).

[0166] The microscopic layer (material scale) includes: based on the data of the fiber Bragg grating strain sensor (sampling frequency 1 deformation transfer coefficient Hz), generating a stress distribution tensor diagram in the model, marking the direction and value of the maximum principal stress (e.g., tensile stress in the transverse bending area is highlighted when it is greater than 250MPa);

[0167] A simplified model of the material crystal structure is embedded to simulate the evolution of the microstructure (such as the austenite to ferrite transformation zone) according to the changes in the temperature field and stress field, and to predict the changes in the low-temperature toughness of the weld (such as early warning when the impact energy at -40°C is less than 47J).

[0168] Using the LSTM neural network and based on the deformation time series data (longitudinal contraction and lateral bending) of the past 10 minutes, it learns the nonlinear deformation law and outputs the basic prediction value for the next 5 minutes;

[0169] Based on the thermoelastic theory, the real-time welding current, interlayer temperature, and ambient wind speed are input, and the deformation is calculated by the formula (such as transverse bending amount = k×I 2 ×t / v, k is the material coefficient, I is the current, t is the welding time, v is the speed), output mechanism prediction value;

[0170] Retrieve cases in the historical database with similarity > 90% for environmental parameters + process parameters + structural type, and output analog prediction values.

[0171] When the LSTM prediction error is less than 5%, the weight is increased to 0.6; when the deviation between the physical mechanism model and the measured value is less than 3%, the weight is increased to 0.5;

[0172] The final prediction value = 0.6 × LSTM value + 0.3 × mechanism value + 0.1 × analogy value (dynamic update). When the prediction value exceeds 80% of the threshold (such as lateral bending reaches 4 mm / m), in addition to the early warning, pre-correction suggestions (such as reducing the welding speed by 2 cm / min in advance) are automatically pushed.

[0173] Based on 500+ plateau welding case data, the parameter-risk dynamic rule base is generated through the association rule mining algorithm (Apriori). Example:

[0174] Rule 1: Ambient temperature < -10°C, welding current > 220A, and strain acceleration > 0.3με / s will lead to cold crack risk (92% confidence level);

[0175] Rule 2: Wind speed > 12 m / s, interpass temperature < 150°C, and lateral bending > 5 mm / m will lead to the risk of uncontrolled welding deformation (confidence level 88%);

[0176] The rule base is automatically updated every time 100 new cases are accumulated, and old rules with a confidence level of less than 70% are eliminated.

[0177] When a high-risk weld zone is identified, the model automatically generates a parameter causal chain diagram:

[0178] Example: Wind speed suddenly increases to 14m / s → arc instability → current fluctuation (220→240A) → local temperature rises suddenly (250℃) → strain growth rate accelerates (0.4με / s) → lateral bending exceeds the threshold;

[0179] The contribution of each link is marked in the graph (for example, wind speed influence accounts for 60%, current fluctuation accounts for 30%), to assist welders in locating the root cause.

[0180] A graded intervention mechanism is triggered based on the identified risks:

[0181] Level 1 risk (warning): Push parameter adjustment suggestions (such as reducing the current to 200A and the wind speed to ≤8m / s);

[0182] Level 2 risk (alarm): Automatically cut off the welding power supply for 30 seconds, forcing the welder to confirm the adjustment and restart;

[0183] Level 3 risk (emergency): The windbreak shed control system is linked to automatically expand the shed width to 12m and start the booster fan, while notifying on-site technicians to come to the scene for disposal.

[0184] The historical working conditions are broken down into environmental fingerprints (24-hour variation curves of temperature, wind speed, and air pressure), process fingerprints (timing parameters of current, voltage, and speed), material fingerprints (batch test values ​​of yield strength and impact toughness), and deformation fingerprints (speed increase curves of longitudinal and transverse deformation). Each fingerprint is represented by a vector.

[0185] Using the cosine similarity algorithm, when the fingerprint similarity between the real-time working condition and the historical working condition is greater than 95%, they are determined to be the same working condition.

[0186] When the deviation between the real-time deformation curve and the historical curve is greater than 20%, multi-dimensional traceability is initiated:

[0187] Material dimension: retrieve the mechanical property report of the current batch of steel and compare it with the historical batches (for example, if the yield strength deviation is greater than 5%, it will be marked as a material factor);

[0188] Environmental dimension: Analyze the sudden change points of real-time environmental parameters (e.g., wind speed increases from 5m / s to 15m / s within 10 minutes) and calculate the impact on deformation (e.g., Δbend = 0.8mm / m);

[0189] Process dimension: Inverse the deviation of welding parameters (such as the actual current is 15A higher than the historical average), simulate the deformation after correcting the parameters through digital twin simulation, and output the optimal parameter adjustment plan (such as reducing the current to the historical average).

[0190] In order to establish a three-dimensional mechanical model, preview various data that affect the closure accuracy based on the plateau environment and material parameters, obtain deformation law preview results, and provide a scientific basis for the closure stage, it is proposed to preview the deformation laws of multiple prefabricated segments in the arch bridge closure stage based on the finite element simulation method. The deformation law preview results obtained include:

[0191] A 3D mechanical model of multiple precast segments of an arch bridge during its closure phase was established using finite element simulation methods.

[0192] Based on the plateau environmental parameters and material parameters as well as the three-dimensional mechanical model, the data on the impact of temperature changes on the length of the arch bridge, the local shrinkage deformation data caused by heat conduction during the welding process, and the impact of the lateral bending of the arch bridge under strong wind loads on the accuracy of the joint are previewed as the deformation law preview results.

[0193] In this embodiment, a three-dimensional mechanical model of multiple precast segments during the closure phase of an arch bridge is established based on the finite element simulation method: the finite element simulation method is a numerical analysis technique that discretizes a complex engineering structure into a finite number of units and solves their mechanical response through a computer program. During the closure phase of a steel box arch bridge, this method is used to establish a three-dimensional mechanical model for multiple precast segments. This means that a three-dimensional virtual model is constructed in the computer based on the actual geometric shape, size, and connection method between each precast segment. The model will assign corresponding mechanical properties to each material, such as elastic modulus, Poisson's ratio, etc.

[0194] In this embodiment, the data on the impact of temperature changes on the length of the arch bridge are previewed: the environmental parameters such as the temperature change range in the plateau area and the material parameters such as the thermal expansion coefficient of the steel box arch bridge material are combined and input into the established three-dimensional mechanical model. The model is used to simulate the length changes of the steel box arch bridge due to thermal expansion and contraction under different temperature conditions. For example, in the area where the Deji Road to Xiangquan Road river crossing bridge is located, taking into account the extreme temperature difference in the plateau area (-36.6℃ to room temperature), the model preview shows that for every 10℃ increase in temperature, the arch rib of an 85m span may elongate by about 10mm. These data are of great guiding significance for determining the width of the expansion joint reserved for the closure and the selection of the timing of the closure construction.

[0195] Data on local shrinkage and deformation caused by heat conduction during welding: Based on welding process parameters and material parameters such as the steel's thermophysical properties, the heat transfer and distribution during welding are simulated in a 3D mechanical model. Because the high temperature during welding causes local expansion of the steel and subsequent contraction upon cooling, model pre-training can provide data on local shrinkage and deformation caused by heat conduction during welding. For example, the simulated weld area may shrink by 2-3mm after cooling. This data helps to estimate and control welding deformation before closure, allowing for proactive measures to minimize the impact of welding deformation on closure accuracy.

[0196] Data on the impact of lateral bending of arch bridges under strong wind loads on closure accuracy: Based on environmental parameters such as wind speed and direction in the plateau region, strong wind loads were applied to a 3D mechanical model. This simulated the lateral bending deformation of a steel box arch bridge under strong winds, thereby pre-testing the impact of lateral bending on closure accuracy. For example, the analysis determined that strong winds could cause a certain degree of lateral deflection of the arch ribs. Understanding the specific impact of this deflection on closure accuracy provided a basis for implementing appropriate wind-resistant measures and ensuring closure accuracy during closure construction.

[0197] In order to effectively control the deformation of the closure section by real-time monitoring the residual stress of the weld and adjusting the slow cooling process parameters when cooling the closure section of the arch bridge using the slow cooling process, it is proposed to use the slow cooling process to cool the closure section of the arch bridge and control the deformation, including:

[0198] During the cooling operation of the arch bridge closure section using the slow cooling process, the weld residual stress is monitored in real time. Based on the real-time monitored weld residual stress, the current slow cooling process parameters are adjusted in real time to achieve deformation control. Specifically, the following are performed:

[0199] The distributed sensor array is used to collect the axial stress, radial stress, and hoop stress of the preset weld area in real time as the three-dimensional stress distribution of the preset weld area. That is, in the preset weld area (the weld of the joint section and the range of 100-300mm on both sides), the fiber Bragg grating sensor array is arranged at a spacing of 50mm to simultaneously collect stress in three directions:

[0200] Axial stress: stress along the longitudinal direction of the steel box arch rib (in the direction of the weld length);

[0201] Radial stress: stress perpendicular to the weld surface (pointing from the weld center to the outside);

[0202] Hoop stress: stress along the circumference of the steel box section (around the weld).

[0203] The three-dimensional stress values ​​of each detection point are recorded in real time at a frequency of 1 Hz to form a stress data set covering the entire preset weld area (e.g., 21 detection points × 3 directions = 63 real-time stress values).

[0204] Based on the three-dimensional stress distribution of the preset weld area, the three-dimensional stress difference and distance ratio of adjacent detection points in the distributed sensing array are calculated to obtain the three-dimensional stress gradient distribution of the preset weld area. Specifically, for two adjacent detection points (with a spacing of 50 mm), the stress difference Δσ in the axial, radial, and circumferential directions is calculated respectively. The stress difference and distance ratio are then calculated: gradient value = Δσ / 50 mm (unit: MPa / mm), to obtain the gradient distribution in the three directions.

[0205] Example: If the axial stress difference between adjacent points is 30 MPa, then the axial gradient = 30 MPa / 50 mm = 0.6 MPa / mm.

[0206] Based on the three-dimensional stress gradient threshold and three-dimensional stress gradient distribution, high-gradient areas are screened out in the preset weld area, that is, the three-dimensional stress gradient threshold (such as 2MPa / mm) is set; when any direction of the axial / radial / circumferential gradient in a certain area exceeds the threshold, it is marked as a high-gradient area (the stress in this area changes dramatically and cracks are prone to occur).

[0207] The ratio of the 3D stress reduction value to the initial 3D stress value at each detection point in the distributed sensing array within the latest preset time period is calculated as the real-time stress relaxation rate of each detection point. This means that for each detection point, the initial 3D stress value (starting point of the time period) and the current value (end point of the time period) within the latest preset time period (e.g., 1 hour) are taken.

[0208] Calculate the ratio of the stress reduction value to the initial value: stress relaxation rate = (initial value - current value) / initial value × 100%. For example, if the axial stress decreases from 250 MPa to 230 MPa, the stress relaxation rate = (250 - 230) / 250 = 8%.

[0209] Based on all the real-time stress relaxation rates of each detection point that have been collected, the stress release lag period of each detection point is determined, that is, all the real-time relaxation rates of the detection point are collected (such as calculated once every 10 minutes, a total of 6 values ​​in 1 hour); when the relaxation rates of three consecutive time periods are all less than 5% (preset threshold), the time period is determined to be a stress release lag period (the stress release speed is too slow).

[0210] Based on the three-dimensional stress distribution of the preset weld area, the axial stress sequence, radial stress sequence and hoop stress sequence of the distributed sensing array are obtained, and the variance of the axial stress sequence, the variance of the radial stress sequence and the variance of the hoop stress sequence are calculated respectively;

[0211] The ratio of the maximum value to the minimum value of the variance of the axial stress sequence, the variance of the radial stress sequence, and the variance of the hoop stress sequence is taken as the three-dimensional stress coupling coefficient of the preset weld area. For example: Var1 = 300, Var2 = 150, Var3 = 100, then the coupling coefficient = 300 / 100 = 3 (indicating that the axial stress distribution is far more uneven than the hoop stress distribution). When the three-dimensional coupling coefficient is greater than 1.5, it indicates that the stress distribution is unbalanced (directional control is required).

[0212] Based on the high gradient area and three-dimensional stress coupling coefficient in the preset weld area and the stress release delay period of each detection point, the current slow cooling process parameters are adjusted in real time to achieve deformation control. For example:

[0213] In the high gradient area, increase the heating power of the corresponding temperature control area (such as from 200W / m 2 Increased to 250W / m 2 ), while reducing the power in adjacent areas and guiding stress diffusion through temperature gradient;

[0214] When the coupling coefficient is greater than 1.5, the holding time of the area corresponding to the high variance direction (such as the axial direction) is extended (30 minutes for every 0.5 increase) to promote stress redistribution;

[0215] Reduce the cooling rate during the stagnation period (e.g., from 1°C / min to 0.5°C / min) to provide sufficient time for stress release.

[0216] The following slow cooling rate dynamic adjustment formula can also be used to achieve dynamic adjustment of the slow cooling rate:

[0217]

[0218] Where r(T,σ) is the current slow cooling rate (unit: °C / min); r0 is the reference slow cooling rate (2 °C / min); exp is the natural exponential function with the value of e being 2.72; k σis the stress sensitivity coefficient (0.5, dimensionless); σ is the real-time monitored weld residual stress (unit: MPa); σ0 is the allowable residual stress threshold (200 MPa); T is the current weld temperature (unit: ℃); T0 is the reference temperature (250℃).

[0219] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the present invention and its equivalents, the present invention is intended to include these modifications and variations.

Claims

1. Low-temperature welding and deformation control method for segmented installation of steel box arch bridges in complex plateau environments, characterized by: include: Real-time collection of complex plateau environmental temperature and wind speed in the segmented installation area of ​​the steel box arch bridge; When it is determined that the temperature of the complex plateau environment is lower than a first preset temperature threshold or the ambient wind speed is higher than a first preset wind speed threshold, preheating and windbreak preparation are started; When the preheating and windproof preparations are started and the corresponding pre-conditions for layered symmetrical welding are met, the process of layered symmetrical welding of the steel box arch bridge using carbon dioxide gas shielded welding is started. At the same time, the welding deformation is calculated based on the three-dimensional coordinates of each steel box arch bridge segment collected in real time. When the welding deformation exceeds the corresponding dynamic threshold, the corresponding corrective measures are initiated until it is determined that the welding deformation is controlled within the corresponding dynamic threshold, and multiple prefabricated segments of the steel box arch bridge are obtained; The arch closure stage was initiated for multiple prefabricated segments of a steel box arch bridge, and a slow cooling process was used to cool and control deformation of the closure segments, achieving low-temperature welding results for the segmented installation of the steel box arch bridge. Among them, welding deformation includes longitudinal shrinkage deformation, transverse bending deformation, and angular deformation.

2. The low-temperature welding and deformation control method for segmented installation of steel box arch bridges in complex plateau environments according to claim 1 is characterized in that: Warming up and preparing for windbreaks, including: An electric heating module is used to preheat the weld groove of a steel box arch bridge, controlling the temperature of the groove area to rise evenly to a second preset temperature threshold, and an infrared thermometer is used to monitor the temperature in real time; Windproof preparation is achieved by using a movable windproof shed with a circulating fan inside the shed to maintain the internal wind speed not exceeding the second wind speed threshold.

3. The low-temperature welding and deformation control method for segmented installation of steel box arch bridges in complex plateau environments according to claim 1 is characterized in that: Calculate welding deformation based on the real-time collected 3D coordinates of each steel box arch bridge segment, including: The three-dimensional coordinates of each steel box arch bridge segment are collected in real time by laser trackers set at both ends and the midpoint of each steel box arch bridge segment; The welding deformation is calculated based on the three-dimensional coordinates of each steel box arch bridge segment collected in real time.

4. The low-temperature welding and deformation control method for segmented installation of steel box arch bridges in complex plateau environments according to claim 3 is characterized in that: Also includes: Generate a deformation trend curve based on the real-time calculated welding deformation, and calculate the real-time deformation growth rate of the deformation trend curve; When the real-time deformation growth rate is greater than the preset growth rate threshold and the duration is greater than the preset time period threshold, a welding pause instruction is issued.

5. The low-temperature welding and deformation control method for segmented installation of steel box arch bridges in complex plateau environments according to claim 1 is characterized in that: The method for determining the corresponding dynamic threshold value of welding deformation includes: 1 plus the product of the temperature influence coefficient and the reference temperature minus the real-time ambient temperature, plus the product of the wind speed influence coefficient and the real-time ambient wind speed divided by the square of the reference wind speed, to obtain a first threshold correction coefficient; determining a second threshold correction coefficient based on a real-time function value of a first-order derivative function of the welding deformation amount; The product of the corresponding reference threshold value of the welding deformation amount, the first threshold correction coefficient, and the second threshold correction coefficient is used as the corresponding dynamic threshold value of the welding deformation amount.

6. The low-temperature welding and deformation control method for segmented installation of steel box arch bridges in complex plateau environments according to claim 1 is characterized in that: When the welding deformation exceeds the corresponding dynamic threshold, the corresponding corrective measures are initiated, including: When the longitudinal shrinkage deformation or angular deformation of a single welding area exceeds the corresponding dynamic threshold, local heating correction is performed on the corresponding welding area based on the longitudinal shrinkage deformation correction parameter or the angular deformation correction parameter; When the lateral bending deformation of a single welding area exceeds the corresponding dynamic threshold, a reverse force of a preset magnitude is applied to the corresponding welding area through a mechanical pushing device.

7. The low-temperature welding and deformation control method for segmented installation of steel box arch bridges in complex plateau environments according to claim 6 is characterized in that: Also includes: The force application point of the mechanical jacking device is located 200mm above the neutral axis of the arch rib section, and the thrust is controlled by a force sensor, with each adjustment amount ≤5kN.

8. The low-temperature welding and deformation control method for segmented installation of steel box arch bridges in complex plateau environments according to claim 1 is characterized in that: Before starting the arch closure phase for multiple precast segments of a steel box arch bridge, the following steps were performed: Based on the finite element simulation method, the deformation law of multiple precast segments in the arch bridge closure stage was previewed to obtain the deformation law preview results; The reserved expansion joint width and locking temperature window of the closure are set based on the deformation law preview results.

9. The low-temperature welding and deformation control method for segmented installation of steel box arch bridges in complex plateau environments according to claim 8 is characterized in that: Based on the finite element simulation method, the deformation law of multiple precast segments in the arch bridge closure stage was previewed, and the deformation law preview results were obtained, including: A 3D mechanical model of multiple precast segments of an arch bridge during its closure phase was established using finite element simulation methods. Based on the plateau environmental parameters and material parameters as well as the three-dimensional mechanical model, the data on the impact of temperature changes on the length of the arch bridge, the local shrinkage deformation data caused by heat conduction during the welding process, and the impact of the lateral bending of the arch bridge under strong wind loads on the accuracy of the joint are previewed as the deformation law preview results.

10. The low-temperature welding and deformation control method for segmented installation of steel box arch bridges in complex plateau environments according to claim 1 is characterized in that: The slow cooling process is used to cool down and control deformation of the closure section of the arch bridge, including: While cooling the closure section of the arch bridge using a slow cooling process, a distributed sensor array is used to collect the axial stress, radial stress, and hoop stress of the preset weld zone in real time as the three-dimensional stress distribution of the preset weld zone. Based on the three-dimensional stress distribution of the preset weld area, the three-dimensional stress difference and distance ratio of adjacent detection points in the distributed sensing array are calculated to obtain the three-dimensional stress gradient distribution of the preset weld area, and the high gradient area is screened out in the preset weld area based on the three-dimensional stress gradient threshold and the three-dimensional stress gradient distribution; Calculating the ratio of the three-dimensional stress reduction value to the three-dimensional stress initial value at each detection point in the distributed sensing array within the latest preset period as the real-time stress relaxation rate of each detection point, and determining the stress release lag period of each detection point based on all the real-time stress relaxation rates collected at each detection point; Based on the three-dimensional stress distribution of the preset weld area, the axial stress sequence, radial stress sequence and hoop stress sequence of the distributed sensing array are obtained, and the variance of the axial stress sequence, the variance of the radial stress sequence and the variance of the hoop stress sequence are calculated; The ratio of the maximum value to the minimum value among the variance of the axial stress sequence, the variance of the radial stress sequence, and the variance of the hoop stress sequence is regarded as the three-dimensional stress coupling coefficient of the preset weld zone; Based on the high gradient area and three-dimensional stress coupling coefficient in the preset weld area and the stress release lag period of each detection point, the current slow cooling process parameters are adjusted in real time to achieve deformation control.

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