Anti-deviation assembling method and system for precise butt joint of steel bridge segment assembly

Abstract

The present application relates to the technical field of steel bridge segment assembly construction process, especially to a steel bridge segment assembly precision butt joint anti-deviation assembly method and system, comprising the following steps: butt joint end face flatness re-measurement and completion of the hoisting attitude preset of the to-be-installed segment; realization of the preliminary matching positioning of the segment axis and the elevation; offset of the butt joint deviation caused by the elastic rebound of the assembled beam segment; locking of the current precision butt joint state after the alignment accuracy meets the standard; division of the differentiated welding area and matching of the corresponding segmented welding sequence of each welding area; keeping the lock during the welding operation process to offset the progressive micro-slippage and micro-angle deviation caused by the asymmetric welding pulling; realization of the steel bridge segment non-accumulative deviation precision assembly after the segment ring seam welding forming and cooling to the specified temperature. The present application avoids the repeated operation of the end face defects in the traditional process being discovered after hoisting into position and needing to be hoisted and polished again, reduces the hoisting of a single segment by 1 to 2 times, and improves the uniformity of the end face gap.

Description

Technical Field

[0001] This invention relates to the field of prefabricated construction technology for steel bridge segments, and in particular to an anti-displacement assembly method and system for precise docking of prefabricated steel bridge segments. Background Technology

[0002] Segmental prefabricated construction of steel bridges is widely used in the construction of long-span steel box girder and steel truss bridges due to its advantages such as short construction period, less on-site work, and strong controllability of the completed bridge alignment. During construction, prefabricated steel bridge segments are transported to the construction site, and the main body of the bridge is formed by assembling them segment by segment through hoisting, alignment, temporary fixing, welding or bolting. The alignment accuracy throughout the assembly process directly determines the quality of the bridge alignment and the structural stability under stress.

[0003] Currently, the standard operating procedure for conventional steel bridge segment assembly construction in the industry is to first hoist the segments into place, then manually coordinate with machinery to finely adjust the alignment, complete the calibration of the axis and elevation, and then statically lock them before proceeding with the subsequent welding. This standardized process relies on static limiting and fixing to maintain the segment connection status and meet the basic accuracy requirements of conventional assembly construction.

[0004] However, under actual construction conditions, this traditional assembly process has obvious technical defects:

[0005] Firstly, the traditional assembly process involves a one-time fine adjustment followed by static locking. The process of hoisting, loading, and unloading the segments to be assembled can cause sudden changes in the support reaction force of the assembled beam segments, resulting in elastic deformation and rebound displacement of the beam body. This can easily lead to secondary deviations in the alignment of the finely adjusted beam, requiring repeated adjustments and corrections, resulting in poor construction efficiency and accuracy stability.

[0006] Secondly, traditional welding and assembly adopts a static shaping and continuous welding operation mode. The inherent flatness error of the prefabricated end face of the segment will lead to uneven joint gaps. Moreover, the traditional static locking process cannot dynamically offset the gradual micro-slippage and angular offset of the entire welding process, causing the deviation to accumulate step by step. This not only easily leads to excessive joint misalignment, but also increases the residual stress inside the beam, affecting the overall structural durability of the bridge.

[0007] Therefore, it is necessary to design a novel prefabricated anti-displacement assembly process for steel bridge segments. Summary of the Invention

[0008] To solve one of the aforementioned technical problems, the present invention employs the following technical solution: a method for precise assembly and anti-displacement of steel bridge segments, comprising the following steps:

[0009] S1. The flatness of the joint end face of the segment to be installed and the assembled beam segment is re-measured, and the gap distribution data of the joint end face recorded in the factory pre-assembly stage is retrieved to obtain the initial state parameters of the joint end face. Based on the initial state parameters, the hoisting posture preset of the segment to be installed is completed.

[0010] S2. Hoist the segment to be installed to the docking station, complete the initial alignment and apply the pre-limit, re-measure the gap distribution of the docking end face, and realize the initial matching and positioning of the segment axis and elevation.

[0011] S3. During the staged unloading process of the crane, the segment docking displacement and rotation angle are monitored in real time. Based on the monitoring results, the segment alignment is dynamically and finely adjusted to offset the docking deviation caused by the elastic rebound of the assembled beam segment.

[0012] S4. After the alignment accuracy meets the standard, apply multi-directional steady-state locking to the segment docking position to lock the current precise docking state;

[0013] S5. Divide the welding areas into different welding areas based on the differences in the gap distribution of the butt joint end faces, and match the segmented welding sequence corresponding to each welding area.

[0014] S6. Maintain locking constraints throughout the entire welding process and dynamically adjust the locking preload or welding parameters based on real-time displacement monitoring results to counteract the progressive micro-slippage and micro-rotation deviation caused by asymmetric welding tension.

[0015] S7. After the segment circumferential seam is welded and cooled to the specified temperature, the locking constraint is released to achieve precise assembly of the steel bridge segments without cumulative deviation.

[0016] Preferably, the preprocessing verification in S1 is performed according to the following steps:

[0017] Remove spatter, burrs, and rust from the mating surfaces;

[0018] Use a ruler and feeler gauge to measure the flatness of the mating end faces of the segment to be installed and the already assembled beam segment respectively. The flatness deviation within each meter length should not exceed 2mm, and record the flatness status of the end faces.

[0019] When the flatness deviation of the end face within each meter of length is greater than 2mm, the part of the end face that exceeds the tolerance shall be repaired by grinding. After grinding, the flatness deviation shall be re-measured until it is no greater than 2mm within each meter of length.

[0020] Retrieve the gap distribution data of the docking end faces recorded during the pre-assembly stage at the factory, including the maximum gap value, the minimum gap value, and the gap distribution location;

[0021] The preset offset of the hoisting posture of the segment to be installed is determined based on the end face flatness status and gap distribution data.

[0022] Preferably, the preliminary alignment described in S2 is performed according to the following steps: First, the segment to be installed approaches the pre-assembled beam segment at a speed not exceeding 0.5 m / min, and when the distance between the mating end faces reaches 50 mm, the speed is reduced to not exceeding 0.1 m / min; Second, a total station is used to monitor the segment's axial deviation and elevation deviation in real time; Third, when the axial deviation is not greater than 5 mm and the elevation deviation is not greater than 3 mm, a sliding pre-limit constraint with a gap is applied, allowing the segment to move relative to each other within a preset range; Fourth, a feeler gauge is used to re-measure the mating gap at equal intervals around the mating end faces, and the gap value and distribution position of each measurement point are recorded to complete the preliminary matching and positioning.

[0023] Preferably, the graded unloading and dynamic fine-tuning described in S3 are performed according to the following steps:

[0024] Before the crane unloads the load in stages, a temporary support bracket is installed at the front end of the assembled beam segment. A vertically adjustable support is set between the temporary support bracket and the bottom of the segment to be installed. A horizontally adjustable support is set on the side of the segment to be installed, and its reaction end is supported on the assembled beam segment or a temporary fixed structure. A longitudinally adjustable support is set between the process ear plate of the segment to be installed and the assembled beam segment, forming a multi-directional adjustable support with vertical, horizontal and longitudinal adjustment capabilities, so that the segment to be installed is jointly supported by the crane and the vertically adjustable support during the unloading process.

[0025] The crane load is monitored in real time by the crane weighing system. The crane load is divided into four levels of unloading in proportions of 30%, 30%, 20%, and 20%, and each level of unloading is left to stand still for no less than 30 seconds.

[0026] During each static settling period, displacement monitoring was used to collect the lateral displacement, longitudinal displacement, vertical displacement, and rotation angle of the docking end face at a frequency of not less than 1Hz.

[0027] When the lateral, longitudinal, or vertical displacement caused by a single-stage unloading exceeds 0.5 mm, or the angular deviation exceeds 0.1°, compensation and fine-tuning are performed using multi-directional adjustable supports: linear displacement is compensated according to the measured displacement in the opposite direction of the corresponding offset, and angular deviation is compensated according to the differential adjustment of the adjustable supports at the corresponding positions based on the angular direction; after compensation, monitoring is performed again to confirm that the displacement is controlled to be no greater than 0.5 mm and the angular deviation is controlled to be no greater than 0.1° before proceeding to the next stage of unloading;

[0028] After all four stages of unloading are completed, the crane is completely released from its hook. The docking displacement and rotation angle are monitored again. If the lateral, longitudinal, or vertical displacement is greater than 1 mm, or the rotation angle deviation is greater than 0.15°, final compensation and fine-tuning are performed until the docking accuracy meets the standard.

[0029] Preferably, in S2, a pre-biasing step is performed before applying the pre-limit constraint during the initial alignment process:

[0030] Before construction, based on the cross-sectional parameters, material elastic modulus, Poisson's ratio, density, cantilever length, boundary constraints, and crane support position and load of the pre-assembled beam segment, the existing finite element method is used to calculate the elastic rebound displacement at the end of the pre-assembled beam segment during the process of the crane changing from a fully loaded state to an unloaded state. The elastic rebound displacement is decomposed into lateral components, vertical components, longitudinal components, and rotational components.

[0031] During the initial alignment process, before applying pre-limit constraints, the segments to be installed are pre-biased by 80% to 95% of the lateral, vertical, and longitudinal components in the opposite direction of the springback displacement, and the angular component is deflected by 80% to 95% in the opposite direction of the springback rotation angle. The bias ratio and deflection ratio are determined based on the error range of finite element calculation, so that the residual deviation of segment docking after staged unloading is reduced by more than 80% compared with that without pre-biasing.

[0032] Preferably, the multi-directional steady-state locking in S4 is performed according to the following steps:

[0033] Longitudinal movement is limited by applying axial constraints to segments along the longitudinal direction of the bridge using adjustable constraint components.

[0034] Lateral constraints are applied along the transverse direction of the bridge by adjustable constraint members to limit lateral displacement;

[0035] Vertical settlement is limited by applying elevation constraints along the vertical direction using adjustable constraint components;

[0036] After all-directional constraints are applied, the axis deviation and elevation deviation are checked using a total station, and the misalignment of the butt joint is checked using a misalignment gauge to ensure that the axis deviation is no greater than 2mm, the elevation deviation is no greater than 2mm, and the misalignment of the butt joint is no greater than 1 / 10 of the plate thickness and no greater than 2mm. After the check is qualified, the welding process begins.

[0037] Preferably, the differentiated welding area division and welding sequence in S5 are performed according to the following steps:

[0038] Based on the gap distribution of the docking end face re-measured by S2, the arithmetic mean of the gap values ​​at each measurement point is taken to obtain the average gap value of the docking end face. The area with a gap greater than 1.2 times the average gap value is divided into the large gap area, the area with a gap less than 0.8 times the average gap value is divided into the small gap area, and the remaining area is divided into the normal gap area.

[0039] The 1.2 times and 0.8 times thresholds can be determined based on experience in controlling welding heat shrinkage deformation, and can be finely adjusted according to actual working conditions; when there is no large gap area or small gap area, all areas are treated as conventional gap areas.

[0040] If a small gap area exists, first fix the small gap area with tack welding. If there is no small gap area, fix it with tack welding evenly along the circumferential seam. The tack welding spacing is 300mm to 500mm, and the length of each tack welding segment is 50mm to 80mm.

[0041] First, weld the web butt weld; after the web welding is completed, weld the top plate and bottom plate butt weld. When welding the top plate and bottom plate, start the arc from the location of the large gap area of ​​the plate; if a plate does not have a large gap area, start the arc from the middle of the plate; weld the top plate and bottom plate synchronously with the same welding parameters and the same speed, and weld each plate symmetrically from the arc starting point along the weld to both sides.

[0042] The large gap area is welded in multiple layers and multiple passes, with each weld pass having a thickness of no more than 4mm.

[0043] Preferably, CO2 gas shielded welding is used in the large gap area, with a welding current of 220A to 260A, a welding voltage of 28V to 32V, and a welding speed of 30cm / min to 40cm / min; carbon dioxide gas shielded welding is used in the conventional gap area, with a welding current of 200A to 240A, a welding voltage of 26V to 30V, and a welding speed of 35cm / min to 45cm / min; carbon dioxide gas shielded welding is used in the small gap area, with a welding current of 180A to 220A, a welding voltage of 24V to 28V, and a welding speed of 40cm / min to 50cm / min; the interpass temperature is controlled within the range of 80℃ to 180℃ during welding in each area.

[0044] Preferably, the dynamic compensation of progressive micro-slippage and micro-rotation angle deviation in S6 is performed according to the following steps:

[0045] Throughout the welding process, displacement monitoring is used to continuously collect data on the lateral, longitudinal, vertical, and rotational displacements of the mating surfaces at a frequency of no less than 0.5 Hz.

[0046] When the cumulative lateral, longitudinal, or vertical displacement reaches 0.3mm, the welding in the current area is paused. The constraint preload is adjusted by using a multi-directional adjustable support to compensate for the offset, or the welding direction and sequence of the next weld pass are adjusted.

[0047] After offset compensation, welding continues. After each weld layer is completed, the misalignment, axis deviation, and elevation deviation are checked once.

[0048] When the cumulative angle deviation reaches 0.2°, the diagonal alternating welding method is used to suppress the further development of the angle, and the angle deviation that has been generated is gradually compensated by the reverse welding deformation of the subsequent weld.

[0049] Preferably, during all assembly operations from S1 to S7, the ambient temperature is controlled within the range of 5℃ to 35℃; when the ambient temperature is below 5℃, the docking area is preheated with an electric heating blanket at a temperature of 80℃ to 120℃, and the preheating range is not less than 100mm on both sides of the weld.

[0050] Alignment work can only be carried out when the temperature difference between the mating end faces of the segment to be installed and the already assembled beam segment is no greater than 10℃.

[0051] During fine-tuning alignment and welding forming operations, the ambient temperature change should not exceed ±5℃. If the ambient temperature change exceeds ±5℃, the operation should be suspended and the alignment accuracy should be rechecked. The operation can only continue after the accuracy is qualified. If the accuracy is not qualified, it should be readjusted until it meets the standard before continuing.

[0052] After the circumferential weld is completed, the locking constraint can be released only after the weld has cooled to ambient temperature.

[0053] The present invention also provides an anti-displacement assembly system for precise interlocking of steel bridge segments, the system being used to implement the above-mentioned method.

[0054] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0055] 1. Before the segment hoisting, the present invention uses a ruler and feeler gauge to measure the flatness of the docking end face point by point. Any deviation exceeding 2 mm within each meter of length is ground down. After grinding, the measurement is repeated until the standard is met. At the same time, the gap distribution data recorded in the factory pre-assembly stage is retrieved for hoisting posture preset. This avoids the repetitive work of end face defects being discovered only after hoisting and positioning, which requires re-hoisting and grinding in traditional processes. The rework hoisting of a single segment is reduced by 1 to 2 times, and the uniformity of the end face gap is improved.

[0056] 2. This invention installs a temporary support bracket at the front end of the assembled beam segment as a vertical support bearing foundation, and sets up adjustable supports in three directions: vertical, horizontal, and longitudinal. The crane load is unloaded in four levels: 30%, 30%, 20%, and 20%. When the displacement of a single level exceeds 0.5 mm or the rotation angle exceeds the threshold, it is immediately compensated by the corresponding support. After the compensation is confirmed, it proceeds to the next level. Compared with the traditional one-time hook release method, the instantaneous impact and deviation fluctuation during the unloading process are effectively reduced.

[0057] 3. This invention continuously collects lateral, longitudinal, and vertical displacement and rotation data at a frequency of no less than 0.5 Hz throughout the welding process. When the cumulative displacement reaches 0.3 mm, the welding of the current area is immediately paused. Compensation is achieved by adjusting the preload of the multi-directional adjustable support or changing the welding direction and sequence of the next weld pass. After each weld pass is completed, the misalignment, axis deviation, and elevation deviation are checked. When the cumulative rotation angle reaches the threshold, a diagonal alternating welding method is used to generate reverse welding deformation for self-compensation. Compared with the traditional post-weld measurement method, the welding deformation deviation rate is reduced, avoiding the quality risks of uncorrectable deviations after weld solidification. Detailed Implementation

[0058] The embodiments of the technical solution of the present invention are described in detail below. These embodiments are only used to more clearly illustrate the technical solution of the present invention, and are therefore merely examples and should not be used to limit the scope of protection of the present invention.

[0059] To solve one of the aforementioned technical problems, the present invention provides a method for precise assembly and anti-displacement of steel bridge segments, comprising the following steps:

[0060] S1. The flatness of the joint end face of the segment to be installed and the assembled beam segment is re-measured, and the gap distribution data of the joint end face recorded in the factory pre-assembly stage is retrieved to obtain the initial state parameters of the joint end face. Based on the initial state parameters, the hoisting posture preset of the segment to be installed is completed.

[0061] S2. Hoist the segment to be installed to the docking station, complete the initial alignment and apply the pre-limit, re-measure the gap distribution of the docking end face, and realize the initial matching and positioning of the segment axis and elevation.

[0062] S3. During the staged unloading process of the crane, the segment docking displacement and rotation angle are monitored in real time. Based on the monitoring results, the segment alignment is dynamically and finely adjusted to offset the docking deviation caused by the elastic rebound of the assembled beam segment.

[0063] S4. After the alignment accuracy meets the standard, apply multi-directional steady-state locking to the segment docking position to lock the current precise docking state;

[0064] S5. Divide the welding areas into different welding areas based on the differences in the gap distribution of the butt joint end faces, and match the segmented welding sequence corresponding to each welding area.

[0065] S6. Maintain locking constraints throughout the entire welding process and dynamically adjust the locking preload or welding parameters based on real-time displacement monitoring results to counteract the progressive micro-slippage and micro-rotation deviation caused by asymmetric welding tension.

[0066] S7. After the segment circumferential seam is welded and cooled to the specified temperature, the locking constraint is released to achieve precise assembly of the steel bridge segments without cumulative deviation.

[0067] Specifically, this solution integrates anti-deviation control throughout the entire process, from pre-setting the hoisting attitude to releasing constraints after welding and cooling. Before deviation occurs, the solution predicts offset through attitude pre-setting; during deviation occurrence, it synchronously cancels it out through real-time monitoring and dynamic fine-tuning; and before deviation solidifies, it provides rigid constraints through multi-directional steady-state locking, thus achieving the control effect of eliminating deviation in its nascent stage. This solution constructs a three-level anti-deviation closed loop: pre-offset prediction, real-time unloading compensation, and dynamic welding suppression. The three levels correspond to different development stages of elastic rebound deviation. The first level uses finite element calculation to pre-offset 80% to 95% of the rebound amount; the second level compensates for the remaining 5% to 20% deviation in real-time during unloading; and the third level dynamically suppresses micro-slippage and micro-rotation caused by thermal shrinkage during welding. The three closed loops are interconnected and progressively enhance each other, ensuring that deviation does not accumulate and amplify at any stage.

[0068] This solution incorporates elastic rebound deviation and welding heat shrinkage deviation into a unified displacement-rotation dual-dimensional control system. Existing technologies typically only control the two linear displacement dimensions of axis and elevation, ignoring the impact of rotation deviation on misaligned joints. This solution, however, simultaneously monitors and compensates for four parameters: lateral displacement, longitudinal displacement, vertical displacement, and rotation, achieving comprehensive control of four key degrees of freedom in the six degrees of freedom of space and eliminating the hidden danger of misaligned joints caused by rotation deviation.

[0069] Regarding the implementation boundary of the dynamic fine-tuning segment alignment state in step S3, it should be clarified that the fine-tuning is carried out during the staged unloading of the crane and before the segment is completely unhooked. The fine-tuning power comes from the multi-directional adjustable support, and the fine-tuning amplitude is controlled within 0.5 mm per stage. It is a micro-precise adjustment, rather than a large-scale realignment.

[0070] Preferably, the preprocessing verification in S1 is performed according to the following steps:

[0071] Remove spatter, burrs, and rust from the mating surfaces;

[0072] Use a ruler and feeler gauge to measure the flatness of the mating end faces of the segment to be installed and the already assembled beam segment respectively. The flatness deviation within each meter length should not exceed 2mm, and record the flatness status of the end faces.

[0073] When the flatness deviation of the end face within each meter of length is greater than 2mm, the part of the end face that exceeds the tolerance shall be repaired by grinding. After grinding, the flatness deviation shall be re-measured until it is no greater than 2mm within each meter of length.

[0074] Retrieve the gap distribution data of the docking end faces recorded during the pre-assembly stage at the factory, including the maximum gap value, the minimum gap value, and the gap distribution location;

[0075] The preset offset of the hoisting posture of the segment to be installed is determined based on the end face flatness status and gap distribution data.

[0076] Specifically, the end-face pre-processing verification and hoisting posture preset methods in this solution are designed to complete the end-face quality inspection and hoisting posture preset before the segment hoisting is in place. This eliminates the impact of microscopic defects on the subsequent assembly accuracy from the very beginning, while providing accurate input parameters for the subsequent pre-offset process. This solution moves end-face quality control forward to before hoisting, enabling early detection and handling of end-face defects. Factory pre-assembly gap data is directly converted into input parameters for on-site hoisting posture preset. The gap distribution data recorded during the factory pre-assembly stage contains the actual matching state of the two segment end faces. This data does not change during transportation and hoisting, and its direct use for on-site hoisting posture preset avoids errors and time consumption from repeated on-site measurements, achieving seamless integration between factory data and on-site processes. Excessive flatness tolerances on the end face can lead to excessively large or small gaps after welding. Excessively large gaps result in increased welding shrinkage and segment misalignment, while excessively small gaps may cause incomplete penetration or additional stress due to forced tightening. This solution eliminates flatness tolerances by grinding before hoisting, ensuring controllable uniformity of subsequent gap distribution. A flatness benchmark of 2 mm per meter is used as the inspection standard for end face quality. This eliminates the impact of microscopic unevenness on the uniformity of the joint gap from the outset. This benchmark is stricter than the conventional requirements for steel structure end face flatness in national standards. By raising the inspection standard, the difficulty of controlling subsequent welding deformation is reduced, achieving the technical effect of simplifying subsequent processes by controlling quality at the outset. Regarding the specific meaning of determining the preset offset amount of the hoisting posture of the segment to be installed based on the end face flatness status and gap distribution data, it needs to be clarified that the offset amount includes two aspects: first, the fine adjustment amount of the segment's lateral and longitudinal posture based on the unevenness of the gap distribution, so that the side with larger gaps can obtain an increased assembly gap in advance; second, the fine adjustment amount of the segment's tilt angle based on the end face flatness status, so that areas with poor end face flatness can obtain relaxed fitting conditions during docking.

[0077] Preferably, the preliminary alignment described in S2 is performed according to the following steps: First, the segment to be installed approaches the pre-assembled beam segment at a speed not exceeding 0.5 m / min, and when the distance between the mating end faces reaches 50 mm, the speed is reduced to not exceeding 0.1 m / min; Second, a total station is used to monitor the segment's axial deviation and elevation deviation in real time; Third, when the axial deviation is not greater than 5 mm and the elevation deviation is not greater than 3 mm, a sliding pre-limit constraint with a gap is applied, allowing the segment to move relative to each other within a preset range; Fourth, a feeler gauge is used to re-measure the mating gap at equal intervals around the mating end faces, and the gap value and distribution position of each measurement point are recorded to complete the preliminary matching and positioning.

[0078] Specifically, this solution ensures the safety of hoisting large-tonnage steel bridge segments while achieving high-precision initial positioning of the segments, and at the same time reserves sufficient operating space for dynamic fine-tuning in the subsequent stage of unloading. Through the coordination of four steps—stage deceleration, real-time monitoring, pre-limiting with gaps, and gap re-measurement—it achieves a balance between safe positioning and adjustability.

[0079] The progressive positioning method, employing a 50mm interval triggering two-stage deceleration, minimizes the impact of positioning large-tonnage segments. Existing technologies typically only set a single positioning speed, which can easily lead to collisions due to crane braking lag when the end faces are close together. This solution reduces the speed from 0.5 meters per minute to 0.1 meters per minute when the end face interval is 50mm, providing ample reaction time for crane operators and the automatic control system. Simultaneously, the low-speed positioning reduces the swing amplitude of the crane wire rope, improving positioning accuracy. This solution utilizes a gapped, sliding pre-limiting mechanism, allowing segments to slide freely within a preset range. This limits large-amplitude segment movement to ensure construction safety while reserving operational space for dynamic fine-tuning during the unloading phase, achieving a harmonious balance between constraint and adjustability. Immediately after the pre-limiting, the gap is re-measured, and the actual gap data on site is used as the direct basis for subsequent zonal welding. This achieves real-time linkage between measurement data and process parameters. The gap data of the factory pre-assembly may change slightly after transportation and hoisting. On-site re-measurement can obtain the most realistic gap distribution state. These data are directly input into the subsequent zonal welding process as the basis for area division, ensuring accurate matching between welding process parameters and actual gap state.

[0080] Regarding the specific implementation of the sliding pre-limit constraint with gap, it should be clarified that the constraint is usually achieved by installing temporary connecting plates with elongated holes on both sides of the top and bottom plates of the segment. The plates are connected to the segment by bolts. The length of the elongated hole is the range within which the segment can slide relative to each other. This range is generally set to 5 mm to 20 mm, and the specific value is determined according to the segment weight and the expected fine-tuning amount.

[0081] Preferably, the graded unloading and dynamic fine-tuning described in S3 are performed according to the following steps:

[0082] Before the crane unloads the load in stages, a temporary support bracket is installed at the front end of the assembled beam segment. A vertically adjustable support is set between the temporary support bracket and the bottom of the segment to be installed. A horizontally adjustable support is set on the side of the segment to be installed, and its reaction end is supported on the assembled beam segment or a temporary fixed structure. A longitudinally adjustable support is set between the process ear plate of the segment to be installed and the assembled beam segment, forming a multi-directional adjustable support with vertical, horizontal and longitudinal adjustment capabilities, so that the segment to be installed is jointly supported by the crane and the vertically adjustable support during the unloading process.

[0083] The crane load is monitored in real time by the crane weighing system. The crane load is divided into four levels of unloading in proportions of 30%, 30%, 20%, and 20%, and each level of unloading is left to stand still for no less than 30 seconds.

[0084] During each static settling period, displacement monitoring was used to collect the lateral displacement, longitudinal displacement, vertical displacement, and rotation angle of the docking end face at a frequency of not less than 1Hz.

[0085] When the lateral, longitudinal, or vertical displacement caused by a single-stage unloading exceeds 0.5 mm, or the angular deviation exceeds 0.1°, compensation and fine-tuning are performed using multi-directional adjustable supports: linear displacement is compensated according to the measured displacement in the opposite direction of the corresponding offset, and angular deviation is compensated according to the differential adjustment of the adjustable supports at the corresponding positions based on the angular direction; after compensation, monitoring is performed again to confirm that the displacement is controlled to be no greater than 0.5 mm and the angular deviation is controlled to be no greater than 0.1° before proceeding to the next stage of unloading;

[0086] After all four stages of unloading are completed, the crane is completely released from its hook. The docking displacement and rotation angle are monitored again. If the lateral, longitudinal, or vertical displacement is greater than 1 mm, or the rotation angle deviation is greater than 0.15°, final compensation and fine-tuning are performed until the docking accuracy meets the standard.

[0087] Specifically, this solution addresses the issue of connection deviations caused by the elastic rebound of assembled beam segments during the unloading process of the crane in the cantilever assembly of steel bridges. It achieves this through a coordinated approach involving five stages: temporary support brackets, four-stage unloading, real-time displacement and rotation monitoring, equal-amount compensation fine-tuning, and final compensation. A non-uniform four-stage unloading sequence of 30%-30%-20%-20% is employed. The first two stages, with their large unloading proportions, correspond to the period of rapid deformation change, while the latter two stages, with their smaller unloading proportions, correspond to the period of stable deformation. This achieves a match between the unloading rate and the structural deformation rate. In this non-uniform sequence, the first two stages involve large unloading volumes, but each stage is followed by sufficient resting and compensation time. The latter two stages involve smaller unloading volumes for precise fine-tuning, enabling refined control of the unloading process.

[0088] During operation, temporary support brackets are used as the load-bearing foundation for vertical support as needed, solving the space problem of no direct load-bearing surface at the bottom of the segment to be installed under cantilever assembly conditions. Since the segment to be installed is located in front of the front end of the already assembled beam segment in cantilever assembly, its bottom is suspended, and conventional jacks cannot be directly set up. This solution provides a stable load-bearing foundation for vertical adjustable support by installing a forward-extending temporary support bracket at the front end of the already assembled beam segment. The cantilever length of the bracket is determined according to the width of the segment bottom plate to ensure that the vertical support acts within the effective load-bearing area of ​​the segment bottom plate.

[0089] This scheme measures and compensates for the incremental deviation caused by each unloading stage immediately. This is a minor adjustment within the elastic range of the structure and will not introduce additional stress.

[0090] The lateral support reaction end is designed to be either a pre-assembled beam segment or a temporary fixed structure to adapt to the support requirements under different construction site conditions. When the pre-assembled beam segment has sufficient lateral stiffness and bearing area, the lateral support reaction end is directly supported on the pre-assembled beam segment. When the pre-assembled beam segment is not suitable for bearing load or there is a temporary support on site, the reaction end is supported on a temporary fixed structure. This flexible design ensures that the lateral support can obtain stable reaction force under various working conditions.

[0091] Regarding the specific implementation method for compensating for angular deviation based on the direction of the angular movement using differentiated adjustment amounts of adjustable supports at corresponding positions, it is important to clarify the following: Angular deviation around the longitudinal axis of the bridge is compensated for by differentiated jacking amounts of the vertically adjustable supports on both sides of the segment, with one side jacking more and the other side jacking less or retracting; angular deviation around the transverse axis is compensated for by differentiated adjustment amounts of the vertical supports at the front and rear positions of the segment; angular deviation around the vertical axis is compensated for by differentiated pushing amounts of the longitudinally adjustable supports on both sides. The magnitude of the differentiated adjustment amount can be calculated using conventional mathematical and geometric relationships based on the angular deviation value and the support spacing, ensuring that the angular deviation falls back within the threshold after compensation.

[0092] Preferably, in S2, a pre-biasing step is performed before applying the pre-limit constraint during the initial alignment process:

[0093] Before construction, based on the cross-sectional parameters, material elastic modulus, Poisson's ratio, density, cantilever length, boundary constraints, and crane support position and load of the pre-assembled beam segment, the existing finite element method is used to calculate the elastic rebound displacement at the end of the pre-assembled beam segment during the process of the crane changing from a fully loaded state to an unloaded state. The elastic rebound displacement is decomposed into lateral components, vertical components, longitudinal components, and rotational components.

[0094] During the initial alignment process, before applying pre-limit constraints, the segments to be installed are pre-biased by 80% to 95% of the lateral, vertical, and longitudinal components in the opposite direction of the springback displacement, and the angular component is deflected by 80% to 95% in the opposite direction of the springback rotation angle. The bias ratio and deflection ratio are determined based on the error range of finite element calculation, so that the residual deviation of segment docking after staged unloading is reduced by more than 80% compared with that without pre-biasing.

[0095] Specifically, the segment pre-offset and pre-deflection method in this scheme, based on existing finite element error models, pre-places segments at offset positions opposite to the rebound direction based on theoretical calculations before crane unloading. This ensures that the segments automatically return to their target alignment positions after unloading and rebound, thereby reducing the amount of deviation that needs to be compensated in real time during the unloading stage. This scheme achieves predictive active cancellation of elastic rebound deviation through three stages: finite element error model prediction, four-component decomposition, and under-proportional pre-offset. It adopts an 80%-95% under-offset method instead of 100% full compensation, reserving a 5%-20% deviation margin for real-time fine-tuning during the unloading stage. This avoids reverse deviation caused by overcompensation. The 5%-20% deviation margin ensures that even if the calculated value is too large, overcompensation will not occur. The residual positive deviation is precisely eliminated by real-time fine-tuning during the unloading stage, achieving optimal coordination between theoretical prediction and real-time correction. The elastic rebound displacement is decomposed into four independent components: lateral, vertical, longitudinal, and angular, and each component is pre-biased to achieve separate control of the six degrees of freedom deviation in space. In existing technologies, even if pre-biasing is considered, only vertical displacement is usually considered, completely ignoring lateral, longitudinal, and angular deviations. However, the rebound at the cantilever end of the assembled beam segment is actually a spatial deformation, containing three linear displacement components and one angular component. The magnitude and direction of each component are different. This scheme calculates and pre-biases the four components separately to ensure that the deviation in each direction is specifically and predictively offset, avoiding the loss of control over deviations in other directions caused by single-component control.

[0096] Using the existing finite element calculation error range as the basis for determining the pre-bias ratio, the uncertainty of theoretical calculation is transformed into a quantifiable range of process parameters, resolving the conflict between calculation accuracy and construction reliability. This scheme sets the lower limit of the pre-bias ratio at 80% (corresponding to a maximum calculation error of 20%) and the upper limit at 95% (corresponding to a minimum calculation error of 5%). During construction, an appropriate ratio is selected within this range based on the accuracy of the finite element model of the specific project, thereby achieving quantitative control of calculation uncertainty.

[0097] Regarding the timing and method of pre-offsetting the segments to be installed in the opposite direction of the springback displacement, it should be clarified that this pre-offsetting is completed during the initial alignment process, before the application of pre-limit constraints. At this time, the segments are still fully supported by the crane, and the position adjustment is achieved through the fine-movement operation of the crane. The offset amount is a millimeter-level micro-adjustment, which does not affect the basic positioning state of the segments. Immediately after the pre-offsetting is completed, a sliding pre-limit constraint with a gap is applied to lock the segments in the pre-offset position, and then the staged unloading process begins.

[0098] Preferably, the multi-directional steady-state locking in S4 is performed according to the following steps:

[0099] Longitudinal movement is limited by applying axial constraints to segments along the longitudinal direction of the bridge using adjustable constraint components.

[0100] Lateral constraints are applied along the transverse direction of the bridge by adjustable constraint members to limit lateral displacement;

[0101] Vertical settlement is limited by applying elevation constraints along the vertical direction using adjustable constraint components;

[0102] After all-directional constraints are applied, the axis deviation and elevation deviation are checked using a total station, and the misalignment of the butt joint is checked using a misalignment gauge to ensure that the axis deviation is no greater than 2mm, the elevation deviation is no greater than 2mm, and the misalignment of the butt joint is no greater than 1 / 10 of the plate thickness and no greater than 2mm. After the check is qualified, the welding process begins.

[0103] Specifically, after the staged unloading and dynamic fine-tuning are completed and the segment alignment accuracy meets the standard, this scheme applies stable and reliable multi-directional constraints to the segments, precisely locking them in the target position. This provides a stable reference for subsequent welding operations and prevents accidental displacement of the segments during welding. Adjustable constraint components are used to apply three-dimensional independent constraints, and three parameters are checked after constraint to achieve a balance between the stability, adjustability, and accuracy of locking.

[0104] A locking method employing independent constraints in three directions—axial, lateral, and elevation—is used. These constraints do not interfere with each other, avoiding excessive or insufficient constraints caused by a single comprehensive constraint. The constraints in each direction are applied independently: the longitudinal constraint only restricts longitudinal movement without affecting lateral or vertical movement; the lateral constraint only restricts lateral offset without affecting longitudinal or vertical movement; and the vertical constraint only restricts vertical settlement without affecting longitudinal or lateral movement. The application sequence and preload of each constraint can be independently controlled, preventing mutual interference between constraints. A dual control standard of proportional and absolute values ​​is used: thin plates are controlled at one-tenth of the plate thickness (e.g., within 1 mm for a 10 mm thick plate), and thick plates are controlled at an absolute value of 2 mm (e.g., within 2 mm for a 40 mm thick plate), achieving scientific and rational control of edge misalignment under different plate thickness conditions.

[0105] This plan requires that the axis and elevation be checked immediately after the constraints are applied using a total station, and the misalignment be checked using a misalignment gauge. Welding can only proceed after all three parameters meet the requirements, ensuring that the positional accuracy after locking meets the requirements.

[0106] Regarding the specific form of the adjustable constraint component, it should be clarified that the component includes, but is not limited to, temporary constraint devices that can precisely adjust the preload, such as screw jacks, hydraulic jacks, steel tie rods with adjusting nuts, and wedge-shaped pads. One end of the constraint component acts on the segment to be installed, and the other end acts on the assembled beam segment or temporary fixed structure. The amount of constraint preload is adjusted by rotating the nut or telescopic jack.

[0107] The restraint components can only be removed after welding is completed and the components have cooled to ambient temperature. The removal sequence is to remove the vertical restraints first, then the horizontal restraints, and finally the longitudinal restraints to avoid sudden displacement of the segments during the removal process.

[0108] Preferably, the differentiated welding area division and welding sequence in S5 are performed according to the following steps:

[0109] Based on the gap distribution of the docking end face re-measured by S2, the arithmetic mean of the gap values ​​at each measurement point is taken to obtain the average gap value of the docking end face. The area with a gap greater than 1.2 times the average gap value is divided into the large gap area, the area with a gap less than 0.8 times the average gap value is divided into the small gap area, and the remaining area is divided into the normal gap area.

[0110] The 1.2 times and 0.8 times thresholds can be determined based on experience in controlling welding heat shrinkage deformation, and can be finely adjusted according to actual working conditions; when there is no large gap area or small gap area, all areas are treated as conventional gap areas.

[0111] If a small gap area exists, first fix the small gap area with tack welding. If there is no small gap area, fix it with tack welding evenly along the circumferential seam. The tack welding spacing is 300mm to 500mm, and the length of each tack welding segment is 50mm to 80mm.

[0112] First, weld the web butt weld; after the web welding is completed, weld the top plate and bottom plate butt weld. When welding the top plate and bottom plate, start the arc from the location of the large gap area of ​​the plate; if a plate does not have a large gap area, start the arc from the middle of the plate; weld the top plate and bottom plate synchronously with the same welding parameters and the same speed, and weld each plate symmetrically from the arc starting point along the weld to both sides.

[0113] The large gap area is welded in multiple layers and multiple passes, with each weld pass having a thickness of no more than 4mm.

[0114] Specifically, this solution achieves proactive control of welding deformation through the systematic coordination of six steps: zoning, tack welding, web plate welding first, determining the arc initiation point plate by plate from top to bottom, symmetrical welding, and multi-layer multi-pass welding.

[0115] This scheme employs a relative threshold, using the actual measured arithmetic mean gap as a benchmark. Gaps greater than 1.2 times the average are classified as large gap zones, and gaps less than 0.8 times the average are classified as small gap zones. This relative zoning method automatically adapts to different design gap conditions, accurately reflecting the relative unevenness of gap distribution regardless of the design gap size. First, tack welding is performed in the small gap zone. The small gap zone has a small filler volume and minimal shrinkage, resulting in stable tack weld quality and reduced cracking. After establishing several stable tack weld points in the small gap zone, the segment position is essentially fixed. The shrinkage force generated during subsequent welding in the large gap zone is constrained by the tack weld points in the small gap zone, preventing overall segment displacement. Each plate is independently judged: if a large gap zone exists, the arc starts from the large gap zone; if no large gap zone exists, the arc starts from the mid-span, ensuring that the arc starting point of each plate matches the actual gap distribution of that plate. By employing thin-layer multi-pass welding with each layer not exceeding 4 mm, the filling amount of the large gap area is distributed to multiple thin weld passes. The heat input and shrinkage of each weld pass are relatively small, and the shrinkage of the previous weld pass has basically stabilized before the subsequent weld passes are applied, effectively suppressing the concentrated shrinkage deformation of the large gap area.

[0116] Regarding the specific implementation method of symmetrically welding each plate from the arc initiation point along the weld to both sides, it should be clarified that the welding of each plate (top plate or bottom plate) requires two welders working together. They simultaneously weld from the arc initiation point towards both ends of the weld. Both welders use the same welding parameters and maintain the same welding speed to ensure a symmetrical balance of heat input and shrinkage on both sides of the weld, thereby offsetting welding deformation. The welding of the top and bottom plates is carried out simultaneously, meaning a total of four welders work at the same time (two for the top plate and two for the bottom plate), achieving symmetrical welding in four directions: up / down, left / right.

[0117] When there are fewer than four welders on site, a diagonal alternation sequence can be adopted, first welding one half of the top plate, then the corresponding half of the bottom plate, then the other half of the top plate, and finally the other half of the bottom plate, to ensure symmetrical deformation.

[0118] Preferably, CO2 gas shielded welding is used in the large gap area, with a welding current of 220A to 260A, a welding voltage of 28V to 32V, and a welding speed of 30cm / min to 40cm / min; carbon dioxide gas shielded welding is used in the conventional gap area, with a welding current of 200A to 240A, a welding voltage of 26V to 30V, and a welding speed of 35cm / min to 45cm / min; carbon dioxide gas shielded welding is used in the small gap area, with a welding current of 180A to 220A, a welding voltage of 24V to 28V, and a welding speed of 40cm / min to 50cm / min; the interpass temperature is controlled within the range of 80℃ to 180℃ during welding in each area.

[0119] Specifically, this scheme matches different parameter combinations to the three regions to achieve precise matching between welding parameters and gap conditions. The large gap region requires a larger deposition rate to fill the gap; using a high current of 220-260 amps improves deposition efficiency, while a low welding speed of 30-40 cm / min ensures full penetration at the root of the large gap. The small gap region, with its smaller gap and less need for extensive filling, uses a lower current of 180-220 amps to prevent burn-through of the thin plate, while a high welding speed of 40-50 cm / min reduces heat input, avoiding overheating in the small gap region that leads to grain coarsening and increased deformation. The conventional gap region uses intermediate parameters between the two, achieving a continuous and gradual transition of parameters across the three regions.

[0120] In addition, this scheme controls both upper and lower limits. The lower limit of 80℃ ensures that the interpass temperature of the weld is not lower than the preheating temperature, avoiding the risk of cold cracking. The upper limit of 180℃ strictly controls the highest temperature of the heat-affected zone of the weld, inhibits the growth of austenite grains, and ensures the impact toughness of the weld joint. At the same time, the lower interpass temperature also reduces the peak value of the welding thermal cycle and reduces the overall welding deformation.

[0121] The current ranges for the large gap zone are 220-260 amps, the normal zone is 200-240 amps, and the small gap zone is 180-220 amps. There is a 20-amp overlap transition zone between the current ranges of the three zones. The voltage and speed also have an overlap transition zone. This gradual design ensures that the welding parameters do not change abruptly at the junction of different zones. The weld penetration, weld width, and reinforcement height transition smoothly at the junction, avoiding uneven mechanical properties and stress concentration of the joint caused by abrupt parameter changes.

[0122] Regarding the specific selection principles for welding parameters in each region, it is important to clarify that: within the parameter range for each region, the specific values ​​should be determined comprehensively based on the plate thickness, welding wire diameter, groove type, and welding position. For thicker plates, the upper limit of the parameters should be used to ensure penetration; for thinner plates, the lower limit should be used to prevent burn-through. For flat welding positions (the upper surfaces of the top and bottom plates), a larger current can be used; for vertical welding positions (web plates), a smaller current and reduced speed should be used. The gas flow rate for CO2 gas shielded welding should be uniformly controlled at 15-25 liters per minute. A solid welding wire with a diameter of 1.2 mm should be used, and the wire type should match the base material (e.g., ER50-6 welding wire for Q345q steel).

[0123] Preferably, the dynamic compensation of progressive micro-slippage and micro-rotation angle deviation in S6 is performed according to the following steps:

[0124] Throughout the welding process, displacement monitoring is used to continuously collect data on the lateral, longitudinal, vertical, and rotational displacements of the mating surfaces at a frequency of no less than 0.5 Hz.

[0125] When the cumulative lateral, longitudinal, or vertical displacement reaches 0.3mm, the welding in the current area is paused. The constraint preload is adjusted by using a multi-directional adjustable support to compensate for the offset, or the welding direction and sequence of the next weld pass are adjusted.

[0126] After offset compensation, welding continues. After each weld layer is completed, the misalignment, axis deviation, and elevation deviation are checked once.

[0127] When the cumulative angle deviation reaches 0.2°, the diagonal alternating welding method is used to suppress the further development of the angle, and the angle deviation that has been generated is gradually compensated by the reverse welding deformation of the subsequent weld.

[0128] Specifically, this solution integrates deviation control into the entire welding process, achieving real-time dynamic control of welding deformation through four stages: continuous monitoring, threshold-triggered pause compensation, layer-by-layer verification, and alternating corner-to-corner compensation.

[0129] The deviation during the unloading stage is elastic deformation, which can be fully recovered through support and fine-tuning. The threshold can be appropriately relaxed to 0.5 mm. However, the deviation during the welding stage is plastic deformation caused by weld solidification shrinkage. Once the weld is fully solidified, it cannot be recovered through support and fine-tuning. Compensation must be carried out at a high temperature before the weld is fully solidified. The compensation window is very narrow. Therefore, the threshold is set to a more stringent 0.3 mm to ensure that compensation is carried out when the deviation is still small and the weld is still in a plastic state, thereby improving the effectiveness of compensation.

[0130] During welding, when the displacement reaches 0.3 mm, welding in the current area should be stopped immediately. At this time, the weld metal is still in a high-temperature state (interpass temperature 80-180℃ or higher) and has a certain plastic deformation capacity. By adjusting the constraint preload of the multi-directional adjustable support (such as increasing the support thrust in the opposite direction of the offset or decreasing the constraint preload in the offset direction), the segment can be slightly moved back to the target position before the weld solidifies. Welding can then continue, and the weld solidifies in the correct position, avoiding the problem of uncorrectable deviations after solidification.

[0131] When the rotation angle deviation reaches 0.02°, it indicates that the segment has undergone slight torsion. At this time, it may be difficult to accurately compensate for the rotation angle by simply relying on support adjustment. This solution adopts a diagonal alternating welding method, welding alternately at the diagonal positions of the segment, and using the reverse torsional moment generated by the shrinkage of the weld at the diagonal position to offset the generated rotation angle. This method of compensating for welding deformation with welding deformation itself does not require additional external force intervention and will not introduce additional stress into the structure, thus achieving self-compensation of deformation.

[0132] This solution immediately checks three parameters after each weld layer is completed, which can accurately grasp the deformation contribution of each weld layer. When a weld layer causes an abnormal increase in deformation, the welding parameters or sequence of the next layer can be adjusted in time, so as to achieve fine control of deformation layer by layer.

[0133] Regarding the specific meaning of adjusting the welding direction and sequence of the next weld pass, it is important to clarify that when the displacement deviation reaches a threshold, in addition to adjusting the constraint preload, compensation can also be achieved by adjusting the process of subsequent weld passes. Specifically, this includes: changing the arc starting point of the next weld pass to the side opposite to the deviation direction, causing the shrinkage force of that weld pass to be biased towards the opposite direction of the deviation; adjusting the welding sequence of the weld passes, welding the weld in the opposite direction of the deviation first, using its shrinkage force to pull the segment back; increasing the welding current or decreasing the welding speed of the weld pass in the opposite direction of the deviation, increasing the shrinkage on that side. These process adjustments, used in conjunction with the constraint preload adjustment, can achieve more precise deformation compensation.

[0134] Preferably, during all assembly operations from S1 to S7, the ambient temperature is controlled within the range of 5℃ to 35℃; when the ambient temperature is below 5℃, the docking area is preheated with an electric heating blanket at a temperature of 80℃ to 120℃, and the preheating range is not less than 100mm on both sides of the weld.

[0135] Alignment work can only be carried out when the temperature difference between the mating end faces of the segment to be installed and the already assembled beam segment is no greater than 10℃.

[0136] During fine-tuning alignment and welding forming operations, the ambient temperature change should not exceed ±5℃. If the ambient temperature change exceeds ±5℃, the operation should be suspended and the alignment accuracy should be rechecked. The operation can only continue after the accuracy is qualified. If the accuracy is not qualified, it should be readjusted until it meets the standard before continuing.

[0137] After the circumferential weld is completed, the locking constraint can be released only after the weld has cooled to ambient temperature.

[0138] Specifically, this solution simultaneously manages four dimensions: ambient temperature is controlled between 5-35℃ to ensure the mechanical properties of the steel and the stability of the welding process; the end-face temperature difference is no greater than 10℃ to ensure consistent thermal expansion and contraction between the two sections; the temperature change rate is no more than ±5℃ to ensure a stable structural temperature field during operation; and cooling to ambient temperature after welding removes the constraints to ensure complete post-weld shrinkage. Using an end-face temperature difference of no more than 10℃ as the inspection standard for alignment, this solution eliminates the risk of temperature difference deformation after butt welding caused by inconsistent temperatures between the two sections from the outset. If the two sections have different temperatures (e.g., one section is exposed to sunlight and has a higher temperature, while the other is in the shade and has a lower temperature), the section with the higher temperature will experience greater shrinkage after cooling, leading to relative displacement and misalignment at the butt joint. This temperature difference deformation cannot be corrected after welding. This solution measures the end-face temperatures of the two sections before alignment; if the temperature difference exceeds 10℃, alignment is not allowed. It is necessary to wait for temperature equalization or use heating / cooling measures to reduce the temperature difference to within 10℃, thus eliminating the potential for temperature difference deformation from the outset.

[0139] Fine-tuning and welding operations are limited to periods where the ambient temperature variation does not exceed ±5℃. This avoids interference with assembly accuracy caused by structural thermal expansion and contraction due to temperature fluctuations. Steel bridge segments are large, and a 5℃ temperature change can cause expansion and contraction of several millimeters (e.g., for a 10-meter segment, the expansion and contraction due to a 5℃ temperature difference = 10 × 1.2 × 10⁻⁻⁻⁴). 5 (×5=0.6 mm) If fine-tuning and alignment are completed at a high temperature, the temperature will drop during welding, and segment shrinkage will cause alignment deviation. This solution requires fine-tuning and welding to be completed within a period when the temperature change does not exceed ±5℃ (usually selected during the stable temperature period from night to early morning) to ensure that the structural temperature field is basically stable throughout the entire process from fine-tuning to welding completion, and to eliminate the accuracy interference caused by temperature fluctuations.

[0140] After welding, the weld will shrink and deform as it cools from high temperature to ambient temperature. If the locking constraint is released before the weld has completely cooled, the shrinkage deformation will change freely in an unconstrained state, causing the segment position to shift. This solution requires that the constraint be released after cooling to ambient temperature. At this time, the post-weld shrinkage has been completed, the segment is kept in the correct position under the locking constraint, and no significant temperature deformation will occur after the constraint is released.

[0141] Regarding the specific implementation method for controlling the ambient temperature within the range of 5-35℃, it should be clarified that this temperature range refers to the ambient air temperature of the assembly operation area. When the ambient temperature is below 5℃, in addition to using electric heating blankets to preheat the welding area, wind and rain protection measures should be taken to ensure that the local temperature of the welding area meets the requirements. When the ambient temperature is above 35℃, work should be avoided under direct sunlight; shading measures can be used, or work can be carried out during the cooler hours of the morning or evening. When using electric heating blankets for preheating, the heating blankets should be evenly covered within a 100mm range on both sides of the weld. Thermocouples or temperature measuring pens should be used to monitor the preheating temperature, ensuring that the temperature of the entire preheating area reaches a uniform 80-120℃. Welding should begin immediately after preheating to prevent the preheating temperature from dropping.

[0142] The present invention also provides an anti-displacement assembly system for precise interlocking of steel bridge segments, the system being used to implement the above-mentioned method.

[0143] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention. For those skilled in the art, any alternative improvements or transformations made to the implementation of the present invention fall within the protection scope of the present invention.

[0144] Any aspects of this invention not described in detail are well-known to those skilled in the art.

Claims

1. A method for anti-displacement assembly of steel bridge segments with precise interlocking, characterized in that, Includes the following steps: S1. The flatness of the joint end face of the segment to be installed and the assembled beam segment is re-measured, and the gap distribution data of the joint end face recorded in the factory pre-assembly stage is retrieved to obtain the initial state parameters of the joint end face. Based on the initial state parameters, the hoisting posture preset of the segment to be installed is completed. S2. Hoist the segment to be installed to the docking station, complete the initial alignment and apply the pre-limit, re-measure the gap distribution of the docking end face, and realize the initial matching and positioning of the segment axis and elevation. S3. During the staged unloading process of the crane, the segment docking displacement and rotation angle are monitored in real time. Based on the monitoring results, the segment alignment is dynamically and finely adjusted to offset the docking deviation caused by the elastic rebound of the assembled beam segment. S4. After the alignment accuracy meets the standard, apply multi-directional steady-state locking to the segment docking position to lock the current precise docking state; S5. Divide the welding areas into different welding areas based on the differences in the gap distribution of the butt joint end faces, and match the segmented welding sequence corresponding to each welding area. S6. Maintain locking constraints throughout the entire welding process and dynamically adjust the locking preload or welding parameters based on real-time displacement monitoring results to counteract the progressive micro-slippage and micro-rotation deviation caused by asymmetric welding tension. S7. After the segment circumferential seam is welded and cooled to the specified temperature, the locking constraint is released to achieve precise assembly of the steel bridge segments without cumulative deviation.

2. The anti-displacement assembly method according to claim 1, characterized in that, The preprocessing verification described in S1 is performed according to the following steps: Remove spatter, burrs, and rust from the mating surfaces; Use a ruler and feeler gauge to measure the flatness of the mating end faces of the segment to be installed and the already assembled beam segment respectively. The flatness deviation within each meter length should not exceed 2mm, and record the flatness status of the end faces. When the flatness deviation of the end face within each meter of length is greater than 2mm, the part of the end face that exceeds the tolerance shall be repaired by grinding. After grinding, the flatness deviation shall be re-measured until it is no greater than 2mm within each meter of length. Retrieve the gap distribution data of the docking end faces recorded during the pre-assembly stage at the factory, including the maximum gap value, minimum gap value, and gap distribution location; The preset offset of the hoisting posture of the segment to be installed is determined based on the end face flatness status and gap distribution data.

3. The anti-displacement assembly method according to claim 1, characterized in that, The preliminary alignment described in S2 is performed as follows: First, the segment to be installed approaches the pre-assembled beam segment at a speed not exceeding 0.5 m / min, and when the distance between the mating end faces reaches 50 mm, the speed is reduced to not exceeding 0.1 m / min; Second, a total station is used to monitor the segment's axial deviation and elevation deviation in real time; Third, when the axial deviation is not greater than 5 mm and the elevation deviation is not greater than 3 mm, a sliding pre-limit constraint with a gap is applied, allowing the segment to move relative to each other within a preset range; Fourth, a feeler gauge is used to re-measure the mating gap at equal intervals around the mating end faces, and the gap value and distribution of each measurement point are recorded to complete the preliminary matching and positioning.

4. The anti-displacement assembly method according to claim 1, characterized in that, The graded unloading and dynamic fine-tuning described in S3 are performed according to the following steps: Before the crane unloads the load in stages, a temporary support bracket is installed at the front end of the assembled beam segment. A vertically adjustable support is set between the temporary support bracket and the bottom of the segment to be installed. A horizontally adjustable support is set on the side of the segment to be installed, and its reaction end is supported on the assembled beam segment or a temporary fixed structure. A longitudinally adjustable support is set between the process ear plate of the segment to be installed and the assembled beam segment, forming a multi-directional adjustable support with vertical, horizontal and longitudinal adjustment capabilities, so that the segment to be installed is jointly supported by the crane and the vertically adjustable support during the unloading process. The crane load is monitored in real time by the crane weighing system. The crane load is divided into four levels of unloading in proportions of 30%, 30%, 20%, and 20%, and each level of unloading is left to stand still for no less than 30 seconds. During each static settling period, displacement monitoring was used to collect the lateral displacement, longitudinal displacement, vertical displacement, and rotation angle of the docking end face at a frequency of not less than 1Hz. When the lateral, longitudinal, or vertical displacement caused by a single-stage unloading exceeds 0.5 mm, or the angular deviation exceeds 0.1°, compensation and fine-tuning are performed using multi-directional adjustable supports: linear displacement is compensated according to the measured displacement in the opposite direction of the corresponding offset, and angular deviation is compensated according to the differential adjustment of the adjustable supports at the corresponding positions based on the angular direction; after compensation, monitoring is performed again to confirm that the displacement is controlled to be no greater than 0.5 mm and the angular deviation is controlled to be no greater than 0.1° before proceeding to the next stage of unloading; After all four stages of unloading are completed, the crane is completely released from its hook. The docking displacement and rotation angle are monitored again. If the lateral, longitudinal, or vertical displacement is greater than 1 mm, or the rotation angle deviation is greater than 0.15°, final compensation and fine-tuning are performed until the docking accuracy meets the standard.

5. The anti-displacement assembly method according to claim 3, characterized in that, In S2, a pre-biasing process is performed before applying the pre-limit constraint during the initial alignment process: Before construction, based on the cross-sectional parameters, material elastic modulus, Poisson's ratio, density, cantilever length, boundary constraints, and crane support position and load of the pre-assembled beam segment, the existing finite element method is used to calculate the elastic rebound displacement at the end of the pre-assembled beam segment during the process of the crane changing from a fully loaded state to an unloaded state. The elastic rebound displacement is decomposed into lateral components, vertical components, longitudinal components, and rotational components. During the initial alignment process, before applying pre-limit constraints, the segments to be installed are pre-biased by 80% to 95% of the lateral, vertical, and longitudinal components in the opposite direction of the springback displacement, and the angular component is deflected by 80% to 95% in the opposite direction of the springback rotation angle. The bias ratio and deflection ratio are determined based on the error range of finite element calculation, so that the residual deviation of segment docking after staged unloading is reduced by more than 80% compared with that without pre-biasing.

6. The anti-displacement assembly method according to claim 1, characterized in that, The multi-directional steady-state locking described in S4 is performed according to the following steps: Longitudinal movement is limited by applying axial constraints to the segments along the longitudinal direction of the bridge using adjustable constraint components. Lateral constraints are applied along the transverse direction of the bridge by adjustable constraint members to limit lateral displacement; Vertical settlement is limited by applying elevation constraints along the vertical direction using adjustable constraint components; After all-directional constraints are applied, the axis deviation and elevation deviation are checked using a total station, and the misalignment of the butt joint is checked using a misalignment gauge to ensure that the axis deviation is no greater than 2mm, the elevation deviation is no greater than 2mm, and the misalignment of the butt joint is no greater than 1 / 10 of the plate thickness and no greater than 2mm. After the check is qualified, the welding process begins.

7. The anti-displacement assembly method according to claim 1, characterized in that, The differentiated welding area division and welding sequence described in S5 shall be carried out according to the following steps: Based on the gap distribution of the docking end face re-measured by S2, the arithmetic mean of the gap values ​​at each measurement point is taken to obtain the average gap value of the docking end face. The area with a gap greater than 1.2 times the average gap value is divided into the large gap area, the area with a gap less than 0.8 times the average gap value is divided into the small gap area, and the remaining area is divided into the normal gap area. When there are no large or small gap areas, all areas are treated as regular gap areas. If a small gap area exists, first fix the small gap area with tack welding. If there is no small gap area, fix it with tack welding evenly along the circumferential seam. The tack welding spacing is 300mm to 500mm, and the length of each tack welding segment is 50mm to 80mm. First, weld the web butt joint. After the web is welded, weld the top and bottom plates butt joint. When welding the top and bottom plates, start the arc from the location of the largest gap area of ​​the plate. If a plate does not have a large gap area, start the arc from the middle of the plate. The top and bottom plates are welded synchronously with the same welding parameters and the same speed. Each plate is welded symmetrically from the arc starting point along the weld to both sides. The large gap area is welded in multiple layers and multiple passes, with each weld pass having a thickness of no more than 4mm.

8. The anti-displacement assembly method according to claim 7, characterized in that: For large gap zones, CO2 gas shielded welding is used with a welding current of 220A–260A, a welding voltage of 28V–32V, and a welding speed of 30cm / min–40cm / min. For regular gap zones, carbon dioxide gas shielded welding is used with a welding current of 200A–240A, a welding voltage of 26V–30V, and a welding speed of 35cm / min–45cm / min. For small gap zones, carbon dioxide gas shielded welding is used with a welding current of 180A–220A, a welding voltage of 24V–28V, and a welding speed of 40cm / min–50cm / min. The interpass temperature is controlled within the range of 80℃–180℃ during welding in each zone.

9. A prefabricated, precision-jointed anti-displacement assembly system for steel bridge segments, characterized in that: The system is used to implement the method according to any one of claims 1-8.