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

Abstract

The present application relates to the technical field of welding construction, and discloses a low-temperature welding and deformation control method for segmented installation of a steel box arch bridge in a complex highland environment, comprising: when it is determined that the temperature of the complex highland environment is less than a first preset temperature threshold or the environmental wind speed is greater than a first preset wind speed threshold, preheating and windproof preparation are started, until the preconditions for corresponding layered symmetrical welding are met, then the process of layered symmetrical welding of the steel box arch bridge using carbon dioxide gas shielded welding is started, and the welding deformation is calculated based on the real-time collected three-dimensional coordinates of each steel box arch bridge segment, when the welding deformation exceeds a preset threshold, corresponding correction measures are started, until a plurality of prefabricated segments of the steel box arch bridge are obtained; the arch bridge closure stage of the plurality of prefabricated segments of the steel box arch bridge is started, and the slow cooling process is used for temperature reduction and deformation control operation of the arch bridge closure segment; low-temperature welding and deformation control for segmented installation of a steel box arch bridge in a complex highland environment are realized.

Description

Technical Field

[0001] This invention relates to the field of welding construction technology, and in particular to a method for low-temperature welding and deformation control of segmented installation of steel box arch bridges in complex high-altitude environments. Background Technology

[0002] In the field of modern bridge construction, steel box arch bridges are widely used in various large-scale transportation infrastructure projects due to their advantages such as strong span capacity and beautiful appearance. Especially in areas with complex terrain and large span requirements, steel box arch bridges have become one of the preferred bridge types. However, the construction of steel box arch bridges in complex high-altitude environments faces numerous severe challenges. The environmental characteristics of high-altitude areas differ significantly from those of plains areas. On the one hand, low temperatures affect the properties of steel, reducing its toughness and weldability, and increasing the risk of defects such as cracks during welding. On the other hand, complex meteorological conditions, such as high wind speeds, not only affect the stability of the welding arc, leading to a decline in welding quality, but may also accelerate the cooling rate of the weld, further causing welding deformation. Furthermore, during the segmented installation of steel box arch bridges, the welding quality and deformation control of each segment directly affect the structural stability and safety of the entire bridge. Therefore, researching a low-temperature welding and deformation control method suitable for the segmented installation of steel box arch bridges in complex high-altitude environments is crucial, as it has undeniable significance for ensuring bridge construction quality and long-term stable operation. An increasing number of bridge projects need to address the challenges posed by the complex high-altitude environment. Developing 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, existing steel box arch bridge welding methods cannot reduce the impact of low temperatures and strong winds on welding quality when dealing with unfavorable welding conditions such as complex high-altitude environments. They also have difficulty controlling welding deformation during the welding process and the arch bridge closure stage, ultimately making it difficult to guarantee the low-temperature welding quality and overall structural stability of steel box arch bridges in complex high-altitude environments.

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

[0005] This invention provides a low-temperature welding and deformation control method for segmented installation of steel box girder arch bridges in complex high-altitude environments. By real-time acquisition of temperature and wind speed data from the installation area, preheating and windproofing are promptly initiated when environmental conditions are unfavorable, enabling welding work to adapt to the harsh and variable conditions of high-altitude regions and ensuring welding quality. After meeting the preconditions, layered symmetrical welding is performed using carbon dioxide gas shielded 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 girder arch bridge structure. Simultaneously, welding deformation, including longitudinal shrinkage, transverse bending, and angular deformation, is precisely monitored, achieving comprehensive and accurate monitoring of welding deformation. When thresholds are exceeded, corrective measures are initiated to obtain multiple prefabricated segments, ensuring the dimensional accuracy and installation quality of the steel box girder arch bridge segments. Subsequently, during the arch bridge closure stage, a slow cooling process is used to cool and control deformation of the closure segment, helping to reduce temperature stress in the closure segment, lower deformation risks, and further improve the overall stability and reliability of the steel box girder arch bridge structure, ensuring its long-term safe operation in complex high-altitude environments. This effectively adapts to the complex environment of the plateau, ensures welding quality, precisely controls deformation, and ensures the stability, safety, and reliability of the steel box arch bridge structure.

[0006] This invention provides a low-temperature welding and deformation control method for segmented installation of steel box arch bridges in complex high-altitude environments, including:

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

[0008] When it is determined that the temperature in the complex plateau environment is lower than the first preset temperature threshold or the ambient wind speed is greater than the first preset wind speed threshold, preheating and wind protection preparations are initiated.

[0009] When the preheating and windproofing preparations are completed and the corresponding requirements for layered symmetrical welding are met, the layered symmetrical welding process of the steel box arch bridge using carbon dioxide gas shielded welding is initiated. 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 correction measures are initiated until it is determined that the welding deformation is controlled within the corresponding dynamic threshold, thus obtaining multiple prefabricated segments of the steel box arch bridge.

[0010] The arch bridge closure stage was initiated for multiple prefabricated segments of the steel box arch bridge, and the closure segment of the arch bridge was cooled and deformed using a slow cooling process to obtain low-temperature welding results for the segmented installation of the steel box arch bridge.

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

[0012] Preferred preheating and windproofing preparations include:

[0013] An electric heating module is used to preheat the welding bevel of the steel box arch bridge, control the temperature of the bevel area to rise uniformly to the second preset temperature threshold, and monitor the heat preservation in real time using an infrared thermometer.

[0014] A movable windproof shed, which maintains the internal wind speed below the second wind speed threshold using an internal circulating fan, is used to prepare for wind protection.

[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 segment.

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

[0018] Preferred options also include:

[0019] A deformation trend curve is generated based on the real-time calculated welding deformation, and the real-time deformation growth rate of the deformation trend curve is calculated.

[0020] When the duration of the real-time deformation growth rate exceeding the preset growth rate threshold exceeds the preset time period threshold, a welding pause command is issued.

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

[0022] 1. Add the product of the temperature influence coefficient and the reference temperature minus the real-time ambient temperature, and add 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 the first threshold correction coefficient.

[0023] The second threshold correction coefficient is determined based on the real-time function value of the first derivative function of the welding deformation.

[0024] The product of the corresponding baseline threshold for welding deformation and the first threshold correction coefficient and the second threshold correction coefficient is used as the corresponding dynamic threshold for welding deformation.

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

[0026] When the longitudinal shrinkage deformation or angular deformation of a single weld area exceeds the corresponding dynamic threshold, the corresponding weld area is locally heated and corrected based on the longitudinal shrinkage deformation correction parameter or angular deformation correction parameter.

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

[0028] Preferred options also include:

[0029] The mechanical jacking device applies force at a point 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 initiating the arch bridge closure stage for multiple precast segments of the steel box arch bridge, the following steps are included:

[0031] The deformation law of multiple prefabricated segments during the closure stage of the arch bridge was pre-simulated using the finite element method, and the deformation law pre-simulation results were obtained.

[0032] Based on the results of the deformation law simulation, the width of the reserved expansion joint at the closure point and the locking temperature window are set.

[0033] Preferably, the deformation patterns of multiple precast segments during the arch bridge closure stage are pre-simulated using the finite element method, and the pre-simulation results of the deformation patterns are obtained, including:

[0034] A three-dimensional mechanical model of multiple prefabricated segments during the closure stage of the arch bridge was established based on the finite element simulation method.

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

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

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

[0038] The three-dimensional stress gradient distribution of the preset weld area is obtained by calculating the three-dimensional stress difference and distance ratio between adjacent detection points in the distributed sensing array based on the three-dimensional stress distribution of the preset weld area, and high gradient areas are screened out in the preset weld area based on the three-dimensional stress gradient threshold and the three-dimensional stress gradient distribution.

[0039] The ratio of the three-dimensional stress reduction value to the initial three-dimensional stress value of each detection point in the latest preset time period is calculated as the real-time stress relaxation rate of each detection point, and the stress release lag period of each detection point is determined based on all the real-time stress relaxation rates of each detection point that have been collected.

[0040] Based on the three-dimensional stress distribution of the pre-defined weld zone, the axial stress sequence, radial stress sequence, and circumferential stress sequence of the distributed sensing array are obtained, and the variances of the axial stress sequence, radial stress sequence, and circumferential stress sequence are calculated.

[0041] The ratio of the maximum to the minimum value among the variances of the axial stress sequence, the radial stress sequence, and the circumferential stress sequence is used as the three-dimensional stress coupling coefficient of the preset weld zone.

[0042] Deformation control is achieved by adjusting the current slow cooling process parameters in real time based on the high gradient zone and three-dimensional stress coupling coefficient in the preset weld zone and the stress release lag period at each detection point.

[0043] The beneficial effects of this invention compared to existing technologies are as follows: By real-time acquisition of temperature and wind speed in the complex high-altitude environment of the installation area, preheating and windproofing preparations are promptly initiated when environmental conditions are unfavorable, enabling welding work to adapt to the harsh and variable environmental conditions of the high-altitude region and ensuring welding quality. After meeting the pre-requisites, layered symmetrical welding is performed using carbon dioxide gas shielded welding. This process effectively reduces welding stress and deformation, improves the quality and stability of the 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, achieving comprehensive and accurate monitoring of welding deformation. When thresholds are exceeded, corrective measures are initiated to obtain 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 and control deformation of the closure segment, helping to reduce temperature stress in the closure segment, lower the risk of deformation, and further improve the overall stability and reliability of the steel box arch bridge structure, ensuring its long-term safe operation in the complex high-altitude environment. Thus, it effectively adapts to the complex high-altitude environment, ensures welding quality, precisely controls deformation, and ensures the structural stability, safety, and reliability of the steel box arch bridge.

[0044] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in this application.

[0045] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0046] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0047] Figure 1This is a flowchart of a low-temperature welding and deformation control method for segmented installation of a steel box arch bridge in a complex plateau environment, as described in this embodiment of the invention.

[0048] Figure 2 This is a flowchart of the preheating and windproofing preparation process in an embodiment of the present invention;

[0049] Figure 3 This is a flowchart illustrating the welding deformation correction measures in an embodiment of the present invention. Detailed Implementation

[0050] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0051] like Figure 1 As shown, this invention provides an implementation method for low-temperature welding and deformation control of segmented installation of steel box arch bridges in complex high-altitude environments, including:

[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 temperature (accuracy ±0.5℃), ambient wind speed (sampling frequency 1Hz), and air humidity in the complex plateau environment of the steel box arch bridge segment installation area.

[0053] When it is determined that the temperature in the complex plateau environment is less than the first preset temperature threshold (5℃) or the ambient wind speed is greater than the first preset wind speed threshold (10m / s), preheating and wind protection preparations are initiated.

[0054] Once the preheating and windproofing preparations are completed and the corresponding requirements for layered symmetrical welding are met, the layered symmetrical welding process 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 ribs (inscribed circle diameter 2.2-4.0m)) is initiated. Simultaneously, the welding deformation is calculated based on the real-time collected three-dimensional coordinates of each steel box arch bridge segment. When the welding deformation exceeds the corresponding dynamic threshold, corresponding correction measures are initiated until it is determined that the welding deformation is controlled within the corresponding dynamic threshold, thus obtaining multiple prefabricated segments of the steel box arch bridge.

[0055] The arch bridge closure stage was initiated for multiple prefabricated segments of the steel box arch bridge, and the closure segment of the arch bridge was cooled and deformed using a slow cooling process to obtain low-temperature welding results for the segmented installation of the steel box arch bridge.

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

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

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

[0059] After welding, cover with an electric heating blanket for slow cooling (cooling rate ≤5℃ / min) until the temperature drops to ambient temperature;

[0060] This embodiment also includes: a weld quality inspection step: 100% ultrasonic testing of all welds (Level I pass rate ≥ 95%), and additional radiographic testing of the welds in the closure section to ensure that there are no defects such as incomplete fusion or 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 each side of the closure section, with a power density of 200W / m². 2 The temperature can be adjusted in three stages using a thermostat:

[0062] Phase 1 (0-1h): Maintain temperature at 250℃;

[0063] Second stage (1-3h): Reduce to 150℃ at a rate of 2℃ / min;

[0064] Third stage (3-6h): Reduce to ambient temperature at a rate of 1℃ / min;

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

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

[0067] In this embodiment, the complex environment temperature and wind speed of the plateau are defined as follows: The complex environment temperature of the plateau refers to the air temperature conditions of the plateau region. For example, the average annual temperature in Gar County, Tibet is 0.35℃ and the extreme low temperature is -36.6℃. The wind speed refers to the wind conditions in the region. For example, Gar County has an average of 113 days of strong winds per year and the maximum wind speed is 23m / s.

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

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

[0070] The energy concentration factor is defined as the energy density of the molten pool region divided by the energy density of the heat-affected zone. When the energy concentration factor is greater than 5, it is considered that the heat input distribution is uneven.

[0071] Establishing a quantitative relationship for stress initiation based on thermal input gradient specifically includes:

[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 value = stress concentration factor × initial thermal stress;

[0074] The stress data acquired by the fiber Bragg grating sensor is decomposed into instantaneous stress, stress rate of increase, and stress acceleration rate. Instantaneous stress is the real-time stress value at a certain moment; stress rate of increase is the first derivative of instantaneous stress with respect to time; and stress acceleration rate is the second derivative of stress rate of increase 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 state of accelerated stress accumulation (deformation deviation may be triggered within 10 minutes).

[0076] Define deformation transfer coefficient = lateral bending deformation increment / local stress peak increment;

[0077] The deformation transfer coefficient is related to the number of welding layers: the deformation transfer coefficient is 0.02 when welding the first layer, which means the material is sensitive to initial stress; the deformation transfer coefficient is 0.005 when welding the fifth layer, which means 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 transverse bending deformation is close to 80% of the threshold, the heat input correction is derived in reverse, and finally converted into the welding current correction 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 box arch bridge segment: Laser trackers are installed at both ends and the midpoint of each steel box arch bridge segment to acquire the three-dimensional coordinates in real time. The segment deformation caused by welding is calculated based on these coordinates. Assuming the steel box arch bridge segment is a regular cuboid shape, the initial three-dimensional coordinates of both ends and the midpoint of the segment are acquired using laser trackers before welding begins. For example, one end's coordinates are (x1, y1, z1), the other end's coordinates are (x2, y2, z2), and the midpoint's coordinates are (xm, ym, zm).

[0081] After welding for a period of time, the three-dimensional coordinates of the three points are measured again using a laser tracker, assuming 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 of the x-axis coordinates of the two endpoints, i.e., |x2-x1|-|x2'-x1'|.

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

[0084] Angular deformation can be determined by analyzing the changes in the angles between different surfaces of a segment before and after welding. For example, assuming a surface of a segment is determined by its two endpoints and midpoint, the normal vector of this surface before and after welding can be calculated using coordinates, and then the angular deformation can be obtained based on the change in the angle between the normal vectors.

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

[0086] In this embodiment, the low-temperature welding results of the segmented installation of the steel box arch bridge are: the final result of a series of construction operations in a high-altitude low-temperature environment that ensures the welding quality and structural deformation of the steel box arch bridge meet the design standards.

[0087] In this embodiment, the longitudinal shrinkage deformation refers to the amount of shortening caused by weld shrinkage along the length direction during the welding of the steel box arch rib. For example, if it exceeds 3mm per meter, it needs to be corrected. The transverse bending deformation refers to the amount of bending offset caused by 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 amount of 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 order to create suitable conditions for layered symmetrical welding by preheating with an electric heating module and using a movable windproof canopy for wind protection in complex high-altitude environments where temperature or wind speed does not meet requirements, preheating and wind protection preparations are proposed, including:

[0089] An electric heating module is used to preheat the weld bevel of the steel box arch bridge, and the temperature of the bevel area is controlled to rise uniformly to the second preset temperature threshold (100-150℃ and temperature difference ≤10℃), and the heat preservation is monitored in real time by an infrared thermometer.

[0090] A movable windproof shed (wind resistance level ≥ 12) is used to maintain the internal wind speed at no more than the second wind speed threshold (3m / s) by using an internal circulating fan to achieve wind protection preparation.

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

[0092] The modular frame (made of Q355 steel, with a cross-sectional size of 100mm×100mm) can be quickly assembled via a hydraulic folding mechanism (assembly time ≤30min);

[0093] The greenhouse temperature control system includes two sets of 50kW electric heating elements (arranged on both sides of the greenhouse roof) and a temperature feedback sensor (sampling point spacing 500mm). The system uses a PID controller to maintain the greenhouse temperature fluctuation ≤5℃.

[0094] Windproof curtain: Made of polyvinyl chloride coated fabric (0.8mm thick), the sides are sealed to the frame by magnetic strips, and the bottom counterweight (50kg / m) ensures that it is in close contact with the ground, with a wind resistance coefficient ≤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 weld bevel of the steel box arch bridge in low-temperature environments at high altitudes, ensuring the bevel area temperature rises uniformly to the specified temperature.

[0096] In this embodiment, the welding bevel of the steel box arch bridge is a specific geometric shape area processed at the part to be welded before welding the steel box arch bridge segment in order to ensure the welding quality.

[0097] In this embodiment, the insulation is monitored in real time using an infrared thermometer: the infrared thermometer is used to continuously measure the temperature of parts requiring temperature control, such as the welding bevel of the steel box arch bridge, to ensure that the temperature is maintained within the specified range. For example, during the preheating process, the temperature of the bevel area is monitored in real time to ensure that it is uniform and stable at 100-150℃ with a temperature difference ≤10℃. If the temperature does not meet the standard, the heating can be adjusted in time to achieve insulation.

[0098] In this embodiment, the circulating fan inside the shed is a fan device installed inside the movable windproof shed. Its function is to circulate the air inside the shed, while also helping to maintain a uniform temperature inside the shed and control the wind speed inside the shed. For example, during the construction of the Deji Road to Xiangquan Road cross-river bridge, the circulating fan inside the shed was used to maintain the wind speed inside the shed to no more than 3m / s.

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

[0100] To clarify the specific welding parameters and interpass temperature control requirements during the layered symmetrical welding process of the steel box arch bridge using CO2 gas shielded welding, and to ensure welding quality, this paper proposes the process for initiating the layered symmetrical welding of the steel box arch bridge using CO2 gas shielded welding, including:

[0101] The welding current for the first layer is controlled at 180-220A, the arc voltage at 28-32V, and the welding speed at 30-40cm / min, ensuring a penetration depth of ≥8mm. After each layer is welded, a temperature-controlled thermocouple is used to monitor the interlayer temperature. If the temperature is >200℃, welding is paused and resumed 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 horizontal 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 a clockwise order of top → bottom → left → right → front → back. After each layer is welded, the sections are switched to a symmetrical position (e.g., after the first layer of the upper web is finished, the first layer of the lower web is welded immediately).

[0105] The starting and ending points of each weld layer are staggered by more than 50mm. When ending the arc, the arc crater is filled by back welding (length ≥ 10mm).

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

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

[0108] In this embodiment, the arc voltage is the voltage at both ends of the arc during the welding process. In the layered symmetrical welding of carbon dioxide gas shielded welding in 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 welding 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, the penetration depth refers to the depth to which the base material melts during the welding process. When welding the first layer of the steel box arch bridge, the penetration depth is required to be ≥8mm.

[0111] In this embodiment, a temperature-controlled thermocouple is used to monitor the interlayer temperature. The temperature-controlled thermocouple is a temperature sensing element used to measure the interlayer temperature after each layer of the steel box arch bridge has been symmetrically welded. If the temperature exceeds 200°C, welding is paused and allowed to cool naturally to 150-180°C before resuming.

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

[0113]

[0114] In the formula, T inter This represents the current upper limit of interlayer temperature (unit: °C); T base ΔT is the base interpass 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 bevel angle; cos is the cosine function.

[0115] To accurately calculate welding deformation by acquiring three-dimensional coordinates using laser trackers positioned at specific locations on steel box girder arch bridge segments, a method for calculating welding deformation based on the real-time acquired three-dimensional coordinates of each steel box girder arch bridge segment is proposed, including:

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

[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 prefabricated in sections during the manufacturing process and then 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 coordinate values ​​used to determine the spatial position of the steel box arch bridge segment, which are collected in real time by setting up laser trackers at both ends and the midpoint of each steel box arch bridge segment.

[0120] To better control welding deformation by generating deformation trend curves and calculating the real-time deformation growth rate, and issuing timely welding pause commands when the growth rate is abnormal, the following additional measures are proposed:

[0121] A deformation trend curve is generated based on the real-time calculated welding deformation, and the real-time deformation growth rate of the deformation trend curve is calculated.

[0122] If the duration of the real-time deformation growth rate being greater than the preset growth rate threshold (0.5 mm / min) is greater than the preset time period threshold (3 consecutive acquisitions), a welding pause command will be issued.

[0123] In this embodiment, a deformation trend curve is generated based on the real-time calculated welding deformation: During the welding process of the steel box arch bridge, the welding deformation data obtained in real time through the three-dimensional coordinates of the steel box arch bridge segments are plotted with time or welding progress as the horizontal axis and welding deformation as the vertical axis to intuitively show the trend of welding deformation with time or welding progress.

[0124] In this embodiment, the real-time deformation growth rate of the deformation trend curve is calculated: the generated deformation trend curve is analyzed to calculate the rate at which the deformation changes with time or welding progress at a certain moment. For example, at consecutive time points, the rate of increase in welding deformation is observed to obtain the real-time deformation growth rate.

[0125] In this embodiment, the duration during which the real-time deformation growth rate exceeds a preset growth rate threshold is defined as follows: 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 of the Deji Road to Xiangquan Road cross-river bridge, if the real-time deformation growth rate exceeds the set value and continues for a certain period of time, it may indicate an abnormality in the welding process, requiring corresponding measures such as issuing a welding pause command.

[0126] To account for the influence of high-altitude environmental temperature and wind speed on the mechanical properties of materials and improve the adaptability of the welding deformation threshold, a method for determining the corresponding dynamic threshold of welding deformation is proposed, including:

[0127] 1. Add the product of the temperature influence coefficient (0.02 per degree Celsius, the material brittleness increases at low temperatures and the threshold decreases) and (reference temperature 20℃ minus real-time ambient temperature T), and add the product of the wind speed influence coefficient (0.01, wind load causes additional deformation when wind speed increases and the threshold decreases) and (real-time ambient wind speed v divided by reference wind speed 3m / s) to obtain the first threshold correction coefficient;

[0128] The second threshold correction coefficient is determined based on the real-time function value vd of the first 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 the natural constant is 2.72.

[0129] The product of the corresponding reference threshold for welding deformation (i.e., the threshold at room temperature of 20℃ and wind speed of 3m / s, the corresponding reference threshold for longitudinal shrinkage deformation is 3mm / m, the corresponding reference threshold for transverse bending deformation is 5mm of lateral offset per meter length, and the corresponding reference threshold for angular deformation is 2°) and the first threshold correction coefficient and the second threshold correction coefficient is taken as the corresponding dynamic threshold for welding deformation.

[0130] like Figure 3 As shown, in order to address 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 welding deformation is controlled. It is proposed that when the welding deformation exceeds the corresponding dynamic threshold, corresponding correction measures be initiated, including:

[0131] When the longitudinal shrinkage deformation or angular deformation of a single weld area exceeds the corresponding dynamic threshold, the corresponding weld area is locally heated and corrected based on the longitudinal shrinkage deformation correction parameters (heating temperature 250-300℃, holding time 5-10min) or the angular deformation correction parameters (using flame or electric heating to 250-300℃ (holding time 5-10min) to release stress and restore angular accuracy in the out-of-tolerance area, utilizing the thermoplasticity of the material).

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

[0133] In this embodiment, during the welding construction of a steel box arch bridge, when the lateral bending deformation of a single welded area exceeds the corresponding dynamic threshold, measures must be taken to correct the deformation. A specialized mechanical jacking device is used at this time. This device applies a force opposite to the direction of deformation to the welded area experiencing lateral bending deformation exceeding the threshold, according to a pre-set magnitude, thereby counteracting or reducing the lateral bending deformation and restoring the welded area to a shape and position close to the design requirements. For example, in the construction of the steel box arch bridge across the river from Deji Road to Xiangquan Road, if the lateral bending deformation of a certain welded area exceeds the corresponding dynamic threshold of 5mm per meter, the mechanical jacking device will apply a pre-set magnitude (e.g., 50-100kN) of reverse force to the welded area at 200mm above the neutral axis of the arch rib section, controlled by a force sensor. Each adjustment is ≤5kN, and the force is controlled to correct the welding deformation, ensuring the structural accuracy and stability of the steel box arch bridge.

[0134] To clarify the application point of the mechanical jacking device, control the thrust and adjustment amount through force sensors, and precisely control the lateral bending deformation correction process, the following additional measures are proposed:

[0135] The mechanical jacking device applies force at a point 200mm above the neutral axis of the arch rib section, and controls the thrust through a force sensor (accuracy ±1kN), with each adjustment amount ≤5kN.

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

[0137] In this embodiment, the adjustment amount is ≤5kN: this means that when using a mechanical jacking device to correct the deformation of the welded area of ​​the steel box arch bridge, the magnitude of each increase or decrease in thrust is controlled within 5kN. This is to prevent excessive changes in thrust from damaging the welded area or causing new deformations.

[0138] To improve closure accuracy by pre-evolving the deformation patterns based on finite element simulation before the arch bridge closure stage, and thus rationally setting the width of the reserved expansion joint and the locking temperature window at the closure opening, a method is proposed for initiating the arch bridge closure stage before the closure of multiple precast segments of the steel box arch bridge, including:

[0139] The deformation law of multiple prefabricated segments during the closure stage of the arch bridge was pre-simulated using the finite element method, and the deformation law pre-simulation results were obtained.

[0140] Based on the results of the deformation law simulation, the width of the reserved expansion joint at the closure joint (e.g., 20mm) and the locking temperature window (e.g., 10-15℃) are set.

[0141] In this embodiment, the steel box arch rib is assembled from multiple prefabricated segments, with closure being the final crucial step (connecting the segments at both ends of the arch rib into a whole). Due to the extreme temperature differences (-36.6℃ to normal temperature), strong wind loads, and the thermal expansion and contraction characteristics of steel in the high-altitude environment, the arch rib will deform (e.g., expansion and contraction, bending) during construction due to factors such as temperature changes, welding stress, and its own weight. Using finite element simulation technology, a three-dimensional mechanical model of the steel box arch rib can be established. High-altitude environmental parameters (temperature range, wind speed, material thermal expansion coefficient, etc.) can be input to simulate the deformation patterns of the arch rib under different working conditions: the impact of temperature changes on the arch rib length can be simulated (e.g., for every 10℃ increase in temperature, an 85m span arch rib may elongate by approximately 10mm); local shrinkage deformation caused by heat conduction during welding can be simulated (e.g., the weld area may shrink by 2-3mm after cooling); and the impact of lateral bending of the arch rib under strong wind loads on the closure accuracy can be analyzed. Simulation can quantify the deformation caused by different factors, providing data support for the design of the closure joint.

[0142] The closure joint is the final seam where the arch ribs are joined. The purpose of reserving an expansion joint is to provide buffer space for arch rib deformation, preventing excessive residual stress or structural damage caused by forced splicing. Based on the finite element simulation results (pre-simulated deformation patterns), the expansion joint at the closure joint is optimized to 20mm. The reasons are as follows: High-altitude areas have large temperature differences; the steel box arch ribs will shrink at extreme low temperatures (e.g., -36.6℃) 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 rib in this project is approximately 18mm, and a 20mm gap can cover this range); during welding, the weld will shrink (approximately 2-3mm) upon cooling, and the reserved gap can prevent the arch ribs from tightening or cracking due to shrinkage; considering hoisting errors (such as slight offsets during segment docking), the 20mm gap provides operational margin for on-site adjustments, ensuring precise segment docking.

[0143] Locking temperature refers to the ambient temperature during the closure welding. At this time, the arch rib segment is fixed and the welding is completed. The structure can freely expand and contract when the temperature changes subsequently, avoiding the generation of additional stress. The optimization basis for locking the temperature window (10-15℃) also comes from finite element simulation: the simulation results show that the average annual temperature in the area where the project is located (Gar County, Tibet) is 0.35℃, but 10-15℃ is the neutral temperature range for thermal expansion and contraction of the structure. After the closure is completed at this temperature, the increase in the elongation of the arch rib during the high temperature in summer and the decrease in the shrinkage during the low temperature in winter are basically balanced, which can minimize the structural stress under extreme temperatures. If the closure is completed at too low a temperature (such as -10℃), the arch rib will generate huge thrust due to thermal expansion during the high temperature in summer, which may lead to stress concentration at the arch foot node. If the closure is completed at too high a temperature (such as 25℃), the shrinkage of the arch rib during the low temperature in winter may cause the weld at the closure joint to crack due to tension. At 10-15℃, the welding performance of steel is more stable (the weld toughness and strength meet the standards) and the wind speed is lower (strong winds in the plateau are mostly concentrated in the low temperature period), which can reduce the risk of wind-induced deformation during the welding process.

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

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

[0146] Considering the temperature variation range in this region, we assume 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 as the temperature rises is:

[0148] ΔL1=L0×α×(Tmax-T0);

[0149] As the temperature decreases, the arch bridge shortens by:

[0150] ΔL2=L0×α×(T0-Tmin);

[0151] Where T0 is the initial reference temperature (e.g., 0℃). The range of influence 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 change between -15mm and 18mm.

[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) are considered. Finite element simulation and other methods are used to pre-simulate the mechanical behavior of the arch bridge at different temperatures. Taking a steel box arch bridge as an example, the stress distribution and changes of the structure under different closure locking temperatures within the range of local temperature variations are simulated. The results show that when the locking temperature is between 10-15℃, the tensile and compressive stress distribution of the arch bridge structure is relatively balanced with seasonal temperature fluctuations, and there is no local stress concentration phenomenon caused by temperature changes. For example, if the locking temperature is too low (e.g., 5℃), the expansion of the arch ribs in the high temperatures of summer will cause excessive pressure on the arch foot, which may lead to structural instability; if the locking temperature is too high (e.g., 20℃), the contraction of the arch ribs in the low temperatures of winter will generate large tensile stress in the closure section, which is prone to weld cracking.

[0153] Based on heat conduction theory and numerical simulation methods, the temperature distribution of the weld and its surrounding area during welding was calculated over time. As the weld cools, local shrinkage deformation occurs. For example, simulation calculations show that a weld of a specific length will shrink by approximately 2-3 mm after cooling.

[0154] A preliminary study was conducted to investigate the weldability of steel at different temperatures, including metallurgical reactions during welding, the crystallization process of the weld metal, and the performance changes in the heat-affected zone. Experimental simulations revealed that at 10-15℃, the toughness loss in the weld heat-affected zone of steel was minimal, and the strength and toughness of the weld metal were well-matched. For example, welding within this temperature range resulted in a moderate hydrogen diffusion rate in the weld, effectively preventing hydrogen-induced cracking and ensuring the quality of the welded joint.

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

[0156] The simulation simulated the impact of local seasonal weather conditions on construction, such as wind speed and humidity. In the area where the steel box arch bridge is located, the simulation showed that at 10-15℃, wind speeds were relatively low and humidity conditions were relatively stable, which was favorable for high-altitude welding operations and the operation of construction equipment. For example, when the temperature is below 10℃, strong winds increase, affecting not only the stability of the welding arc but also increasing the danger for construction workers working at heights; when the temperature is above 15℃, humidity fluctuates significantly, which may cause condensation on the steel surface, affecting welding quality.

[0157] By applying wind loads to a mechanical model of a steel box arch bridge and using methods such as finite element analysis, the lateral bending deformation of the arch bridge under strong winds was determined. For example, simulation results show that at this wind speed, the lateral bending of the arch bridge may cause a deviation of 5-8 mm at the closure position.

[0158] Based on these preliminary results, the width of the expansion joint reserved at the closure point was determined. Considering the above data, temperature changes could cause the arch bridge length to change by -15mm to 18mm, welding shrinkage deformation would be approximately 2-3mm, and lateral bending under strong wind loads could lead to a 5-8mm deviation in the closure position. To ensure the arch bridge can be successfully closed under various adverse conditions, the width of the reserved expansion joint needs to accommodate these deformations. Considering a certain safety margin, assuming a safety margin of 2mm, the width of the reserved expansion joint at the closure point is W = 18 + 3 + 8 + 2 = 31mm.

[0159] Based on these preliminary results, 10-15℃ was set as the lockout temperature window.

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

[0161] Breaking through the limitations of traditional geometric mapping, a three-level digital twin model (macro-meso-micro) is constructed to achieve real-time interaction of physical fields across all dimensions.

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

[0163] Embedded plateau environmental parameter field (temperature, wind speed, air pressure), in the model every 1m 3 The space is given real-time environmental attributes (e.g., the -10℃ 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 scale) includes: acquiring the temperature field of the weld area using a high-resolution infrared thermal imager (pixel accuracy 0.5mm×0.5mm), generating a dynamic cloud map of the heat-affected zone in the model, marking the molten pool boundary (temperature > 1538℃), overheated zone (800-1538℃), and normalizing zone (500-800℃) in real time, and calculating the area ratio of each region (e.g., an early warning is issued when the overheated zone ratio > 30%).

[0165] By integrating ultrasonic flaw detection data, internal defects in the weld (such as lack of fusion and porosity) are marked in the model. Different colors are used to distinguish the defect types (red = crack, yellow = porosity), and the equivalent diameter of the defect is automatically calculated (e.g., porosity ≥3mm triggers rating upgrade).

[0166] The micro-layer (material scale) includes: generating a stress distribution tensor map in the model based on data from fiber optic strain sensors (sampling frequency 1, deformation transfer coefficient Hz), and marking the direction and value of the maximum principal stress (e.g., highlighting when the tensile stress in the transverse bending region is >250MPa).

[0167] A simplified model of the embedded material crystal structure is used to simulate the evolution of the microstructure (such as the austenite to ferrite transformation region) based on changes in temperature and stress fields, and to predict changes in the low-temperature toughness of the weld (such as early warning when the impact energy at -40℃ is <47J).

[0168] Using an LSTM neural network and based on the deformation time series data (longitudinal contraction and lateral bending) from the past 10 minutes, the nonlinear deformation pattern is learned, and the basic prediction value for the next 5 minutes is output.

[0169] Based on the thermo-elastic-plastic theory, real-time welding current, interpass temperature, and ambient wind speed are input, and the deformation (e.g., transverse bending = k × I) is calculated using formulas. 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 from the historical database where the similarity of environmental parameters, process parameters, and structural type is greater than 90%, and output the analogy prediction value.

[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 predicted value = 0.6 × LSTM value + 0.3 × mechanism value + 0.1 × analog value (dynamically updated). When the predicted value exceeds 80% of the threshold (e.g., lateral bending reaches 4 mm / m), in addition to the warning, a pre-correction suggestion is automatically pushed (e.g., reduce the welding speed by 2 cm / min in advance).

[0173] Based on data from over 500 high-altitude welding cases, a parameter-risk dynamic rule base was generated using the Apriori association rule mining algorithm. Example:

[0174] Rule 1: Ambient temperature < -10℃ and welding current > 220A and strain rate increase > 0.3με / s will lead to cold cracking risk (92% confidence level);

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

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

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

[0178] Example: Wind speed suddenly increases to 14 m / s → electric arc becomes unstable → current fluctuates (220 → 240 A) → local temperature rises sharply (250 ℃) → strain rate increases rapidly (0.4 με / s) → lateral bending exceeds threshold;

[0179] The graph indicates the contribution of each factor (e.g., wind speed accounts for 60%, current fluctuation accounts for 30%), which is the fundamental reason for assisting the welder in positioning.

[0180] Based on the identified risk-triggered tiered intervention mechanism:

[0181] Level 1 Risk (Warning): Push parameter adjustment suggestions (such as reducing current to 200A, wind speed to ≤8m / s);

[0182] Level 2 Risk (Alarm): Automatically cuts off welding power for 30 seconds, forces welder to confirm adjustments, and then restarts;

[0183] Level 3 Risk (Emergency): The windbreak control system will be activated, automatically expanding the width of the shed to 12m and starting the pressurized fan. At the same time, on-site technical personnel will be notified to handle the situation.

[0184] Historical operating conditions are decomposed into environmental fingerprints (24-hour variation curves of temperature, wind speed, and air pressure), process fingerprints (time-series parameters of current, voltage, and speed), material fingerprints (batch test values ​​of yield strength and impact toughness), and deformation fingerprints (growth rate curves of longitudinal / transverse deformation). Each fingerprint is represented by a vector.

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

[0186] When the deviation between the real-time deformation curve and the historical curve exceeds 20%, multi-dimensional source tracing is initiated:

[0187] Material dimension: Retrieve the mechanical property report of the current batch of steel and compare it with historical batches (e.g., if the yield strength deviation is >5%, mark it as a material factor);

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

[0189] Process dimension: Invert the deviation of welding parameters (e.g., the actual current is 15A higher than the historical average), correct the deformation after the parameters are corrected by digital twin simulation, and output the optimal parameter adjustment scheme (e.g., the current is reduced to the historical average).

[0190] To establish a three-dimensional mechanical model, based on plateau environment and material parameters, and to pre-simulate various data affecting the closure accuracy, thereby obtaining deformation law prediction results and providing a scientific basis for the closure stage, this paper proposes to use the finite element simulation method to pre-simulate the deformation laws of multiple precast segments during the arch bridge closure stage, obtaining deformation law prediction results, including:

[0191] A three-dimensional mechanical model of multiple prefabricated segments during the closure stage of the arch bridge was established based on the finite element simulation method.

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

[0193] In this embodiment, a three-dimensional mechanical model of multiple prefabricated segments for the arch bridge closure stage is established based on the finite element method (FEM). The FEM is a numerical analysis technique that discretizes complex engineering structures into a finite number of elements and solves for their mechanical responses using computer programs. During the closure stage of the steel box arch bridge, a three-dimensional mechanical model is established for multiple prefabricated segments using this method. This means that a three-dimensional virtual model is constructed in the computer for each prefabricated segment according to its actual geometry, dimensions, and connection methods. The model assigns corresponding mechanical properties to the materials of each part, such as elastic modulus and Poisson's ratio.

[0194] In this embodiment, data on the impact of temperature changes on the length of the arch bridge were simulated: environmental parameters such as the temperature variation range in the plateau region, and material parameters such as the thermal expansion coefficient of the steel box arch bridge material, were input into the established three-dimensional mechanical model. The model was 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 cross-river bridge is located, considering the extreme temperature difference in the plateau region (-36.6℃ to normal temperature), the model simulation showed that for every 10℃ increase in temperature, the arch rib with an 85m span might elongate by about 10mm. This data is of great guiding significance for determining the width of the expansion joint reserved at the closure point and the selection of the timing of the closure construction.

[0195] Data on localized shrinkage deformation caused by heat conduction during welding: Based on welding process parameters and material parameters such as the thermophysical properties of the steel, the heat transfer and distribution during welding are simulated in a three-dimensional mechanical model. Since the high temperature during welding causes localized thermal expansion of the steel, followed by contraction upon cooling, model simulations can yield data on localized shrinkage deformation caused by heat conduction during welding. For example, the simulation may show a 2-3mm shrinkage in the weld area after cooling. This data helps to predict and control welding deformation before closure, allowing for proactive measures to reduce 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 plateau regions, strong wind loads are applied to a three-dimensional mechanical model. The lateral bending deformation of the steel box arch bridge under strong winds is simulated, thus predicting the impact of lateral bending on closure accuracy. For example, the analysis shows that strong winds may cause a certain degree of lateral displacement of the arch ribs, and understanding the specific impact of this displacement on closure accuracy provides a basis for taking appropriate wind-resistant measures and ensuring closure accuracy during the closure construction.

[0197] To effectively control the deformation of the closure segment of an arch bridge by real-time monitoring of residual weld stress and adjustment of slow cooling process parameters during the cooling process, a method for cooling and deformation control of the closure segment using a slow cooling process is proposed, including:

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

[0199] The axial, radial, and circumferential stresses in the pre-designed weld zone are collected in real time using a distributed sensor array to obtain the three-dimensional stress distribution of the pre-designed weld zone. This involves arranging fiber optic grating sensor arrays at 50mm intervals in the pre-designed weld zone (the weld of the closure section and a range of 100-300mm on both sides) to simultaneously collect stresses in three directions.

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

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

[0202] Circumferential stress: The stress along the perimeter 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 1Hz to form a stress dataset covering the entire preset weld area (e.g., 21 detection points × 3 directions = 63 real-time stress values).

[0204] The three-dimensional stress gradient distribution of the preset weld seam area is obtained by calculating the three-dimensional stress difference and distance ratio between adjacent detection points in the distributed sensor array based on the three-dimensional stress distribution of the preset weld seam area. This involves calculating the axial, radial, and circumferential stress differences Δσ for two adjacent detection points (50mm apart); then calculating the stress difference and distance ratio: gradient value = Δσ / 50mm (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 the three-dimensional stress gradient distribution, high gradient areas are selected in the preset weld area. This is achieved by setting a three-dimensional stress gradient threshold (e.g., 2 MPa / mm). When the axial / radial / circumferential gradient of a certain area exceeds the threshold in any direction, it is marked as a high gradient area (the stress in this area changes drastically and is prone to cracking).

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

[0208] Calculate the ratio of stress reduction to initial value: Stress relaxation rate = (initial value - current value) / initial value × 100%. Example: When 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 collected for each detection point, the stress release lag period for each detection point is determined. This involves collecting all the real-time relaxation rates for that detection point (e.g., calculating once every 10 minutes, for a total of 6 values ​​per hour). When the relaxation rate for 3 consecutive periods is less than 5% (preset threshold), that period is determined to be a stress release lag period (stress release speed is too slow).

[0210] Based on the three-dimensional stress distribution of the pre-set weld zone, the axial stress sequence, radial stress sequence, and circumferential stress sequence of the distributed sensing array are obtained, and the variances of the axial stress sequence, radial stress sequence, and circumferential stress sequence are calculated respectively.

[0211] The ratio of the maximum to the minimum value among the variances of the axial stress sequence, the radial stress sequence, and the circumferential stress sequence is used as the three-dimensional stress coupling coefficient for the preset weld zone. For example, if Var1 = 300, Var2 = 150, and Var3 = 100, then the coupling coefficient = 300 / 100 = 3 (indicating that the axial stress distribution is far less uniform than the circumferential one). When the three-dimensional coupling coefficient is greater than 1.5, it indicates that the stress distribution is uneven (requiring directional control).

[0212] Deformation control is achieved by adjusting the current slow cooling process parameters in real time based on the high gradient zone and three-dimensional stress coupling coefficient in the preset weld zone, as well as the stress release lag period at each detection point. For example:

[0213] In the high gradient zone, increase the heating power of the corresponding temperature control zone (e.g., from 200W / m). 2 Increased to 250W / m 2 At the same time, it reduces the power in adjacent areas and guides stress diffusion through temperature gradient;

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

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

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

[0217]

[0218] In the formula, r(T,σ) is the current slow cooling rate (unit: ℃ / min); r0 is the baseline slow cooling rate (2℃ / min); exp is a function of the natural exponential function with e taking the value of 2.72; k σσ is the stress sensitivity coefficient (0.5, dimensionless); σ is the real-time monitored residual stress of the weld (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 can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of this invention and its equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for low-temperature welding and deformation control of segmented installation of a steel box arch bridge in a high-altitude complex environment, characterized in that, The method comprises the following steps: Real-time acquisition of temperature and wind speed in complex highland environment in the steel box arch bridge segment installation area; When it is determined that the temperature in the complex highland environment is less than the first preset temperature threshold or the wind speed is greater than the first preset wind speed threshold, the preheating and windproof preparation is started; When the preheating and windproof preparation reaches the preconditions of corresponding hierarchical symmetrical welding, the hierarchical symmetrical welding process of the steel box arch bridge using carbon dioxide gas shielded welding is started, and the welding deformation is calculated based on the real-time acquisition of the three-dimensional coordinates of each steel box arch bridge segment. When the welding deformation exceeds the corresponding dynamic threshold, the corresponding correction measures are started until the welding deformation is controlled within the corresponding dynamic threshold, and the multiple prefabricated segments of the steel box arch bridge are obtained; The arch bridge closure stage of the multiple prefabricated segments of the steel box arch bridge is started, and the cooling process is used for temperature reduction and deformation control operation of the arch bridge closure segment, so that the low-temperature welding result of the steel box arch bridge segment installation is obtained. The 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 a steel box arch bridge in a high-altitude complex environment according to claim 1, characterized in that, The preheating and windproof preparation comprises the following steps: The steel box arch bridge welding groove is preheated by using an electric heating module, the temperature of the groove area is uniformly raised to the second preset temperature threshold, and the infrared temperature measuring instrument is used for real-time monitoring of the temperature. The movable windproof shed is used for windproof preparation by maintaining the internal wind speed of the shed within the second wind speed threshold.

3. The low-temperature welding and deformation control method for segmented installation of a steel box arch bridge in a high-altitude complex environment according to claim 1, characterized in that, The three-dimensional coordinates of each steel box arch bridge segment are acquired by using a laser tracker arranged at the two ends and the midpoint of each steel box arch bridge segment. The welding deformation is calculated based on the real-time acquisition of the three-dimensional coordinates of each steel box arch bridge segment. The method further comprises the following steps:

4. The low-temperature welding and deformation control method for segmented installation of a steel box arch bridge in a high-altitude complex environment according to claim 3, characterized in that, A deformation trend curve is generated based on the real-time calculated welding deformation, and the real-time deformation rate of the deformation trend curve is calculated. When the real-time deformation rate is greater than the preset rate threshold for a duration greater than the preset duration threshold, a welding suspension instruction is issued. The determination method of the corresponding dynamic threshold of the welding deformation comprises the following steps:

5. The low-temperature welding and deformation control method for segmented installation of a steel box arch bridge in a high-altitude complex environment according to claim 1, characterized in that, 1. The first threshold correction coefficient is obtained by adding the product of the temperature influence coefficient and the reference temperature minus the real-time environment temperature, and adding the product of the wind speed influence coefficient and the real-time environment wind speed divided by the square of the reference wind speed. The second threshold correction coefficient is determined based on the real-time function value of the first derivative function of the welding deformation. The product of the corresponding reference threshold of the welding deformation and the first threshold correction coefficient and the second threshold correction coefficient is taken as the corresponding dynamic threshold of the welding deformation. When the welding deformation exceeds the corresponding dynamic threshold, the corresponding correction measures are started, which comprises the following steps:

6. The low-temperature welding and deformation control method for segmented installation of a steel box arch bridge in a high-altitude complex environment according to claim 1, characterized in that, When the longitudinal shrinkage deformation or the 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 transverse bending deformation of a single welding area exceeds the corresponding dynamic threshold, a mechanical pushing device is used to apply a preset size of reverse force to the corresponding welding area. The method further comprises the following steps:

7. The low-temperature welding and deformation control method for segmented installation of a steel box arch bridge in a high-altitude complex environment according to claim 6, characterized in that, The force point of the mechanical pushing device is located 200 mm above the neutral axis of the arch rib section, the pushing force is controlled by a force sensor, and the adjustment amount is less than or equal to 5 kN each time. ​ 8. The low-temperature welding and deformation control method for segmented installation of a steel box arch bridge in a high-altitude complex environment according to claim 1, characterized in that, Before starting the closure stage of the multiple prefabricated segments of the steel box arch bridge, comprising: Based on the finite element simulation method, the deformation law of the multiple prefabricated segments of the arch bridge in the closure stage is preplayed, and the deformation law preplay result is obtained; Based on the deformation law preplay result, the closure gap width and locking temperature window are set.

9. The low-temperature welding and deformation control method for segmented installation of a steel box arch bridge in a high-altitude complex environment according to claim 8, characterized in that, Based on the finite element simulation method, the deformation law of the multiple prefabricated segments of the arch bridge in the closure stage is preplayed, and the deformation law preplay result is obtained, comprising: Based on the finite element simulation method, a three-dimensional mechanical model of the multiple prefabricated segments of the arch bridge in the closure stage is established; Based on the plateau environment parameters and material parameters and the three-dimensional mechanical model, the influence data of temperature change on the length of the arch bridge, the local shrinkage deformation data caused by heat conduction in the welding process, and the influence data of lateral bending of the arch bridge under strong wind load on the closure accuracy are preplayed as the deformation law preplay result.

10. The low-temperature welding and deformation control method for segmented installation of a steel box arch bridge in a high-altitude complex environment according to claim 1, characterized in that, The cooling and deformation control operation of the arch bridge closure segment by using the slow cooling process, comprising: During the cooling operation of the arch bridge closure segment by using the slow cooling process, the axial stress, radial stress and hoop stress of the preset weld zone are simultaneously collected by the distributed sensing array as the three-dimensional stress distribution of the preset weld zone; Based on the three-dimensional stress distribution of the preset weld zone, the three-dimensional stress difference value 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 zone, and the high gradient area in the preset weld zone is screened based on the three-dimensional stress gradient threshold and the three-dimensional stress gradient distribution; The ratio of the three-dimensional stress reduction value of each detection point in the distributed sensing array to the three-dimensional stress initial value in the latest preset time period is calculated as the real-time stress relaxation rate of each detection point, and the stress release lag period of each detection point is determined based on all the collected real-time stress relaxation rates of each detection point; Based on the three-dimensional stress distribution of the preset weld zone, 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 in 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 zone; Based on the high gradient area in the preset weld zone and the three-dimensional stress coupling coefficient and the stress release lag period of each detection point, the current slow cooling process parameters are adjusted in real time to realize deformation control.

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