A linear control and deviation rectification method for steel truss bridge scattered assembly construction

Abstract

The application discloses a linear control and deviation rectification method for steel truss bridge scattered assembly construction, and relates to the technical field of bridge construction. The method realizes linear control and deviation rectification through stage measurement and welding. First, beam segment rough positioning and temporary fixing are performed, then main truss axial deviation, vertical deviation and vice truss shape position are controlled in three steps, each step is guided by measurement data to guide welding and retest, and positioning is supplemented by locking effect of a board. After that, high-strength bolts are used to replace punch nails, cross beams are installed in sequence and welding is completed, and finally crane constraints are released. The method ensures assembly accuracy through the cycle of "measurement, calculation, welding and retest". The application can provide data support for scattered assembly construction control of steel truss bridge in engineering by real-time guiding welding operation through measured data, and solves the problems of poor adaptability and insufficient precision of traditional methods.

Description

Technical Field

[0001] This invention relates to the field of bridge construction technology, and in particular to a method for alignment control and correction in the piecemeal construction of steel truss bridges. Background Technology

[0002] Steel truss bridges, as an important structural form in modern long-span bridge construction, are widely used in railway and highway engineering due to their advantages of light weight, high rigidity, and strong span capacity. Alignment, as a core control indicator for modern bridges, directly affects the structural safety performance, driving comfort, and long-term service performance of the bridge.

[0003] Currently, the commonly used alignment control method mainly consists of a series of processes, including setting the pre-camber through monitoring and calculation, manufacturing based on the dimensions of the members after compression compensation provided by the monitoring calculation, adjusting the matching degree of the truss segments by combining multi-segment continuous pre-assembly technology in the factory, and fine-tuning the lifting posture of the steel beams by the girder erection crane during construction. However, for steel truss bridges with on-site assembly and a large amount of welding work, the traditional method ignores the complex influences of welding deformation, assembly temperature gradient, and long-distance measurement errors, resulting in insufficient alignment control accuracy and difficulty in meeting the requirements of high-precision construction. Therefore, there is an urgent need for a refined alignment control and correction method to cope with the variability in actual construction. Summary of the Invention

[0004] The purpose of this invention is to provide a method for alignment control and correction during the assembly construction of steel truss bridges, aiming to solve or improve at least one of the above-mentioned technical problems.

[0005] To achieve the above objectives, the present invention provides the following solution:

[0006] A method for alignment control and correction during the piecemeal construction of a steel truss bridge includes:

[0007] Step S1: Use the girder erecting crane to adjust the spatial posture of the steel truss girder in the transverse and vertical directions for rough positioning, and use the steel strands to laterally pull and suppress the inward deformation of the lower chord node of the main truss. Finally, drive the punch nails into the bolt holes of the diagonal web members for temporary fixation.

[0008] Step S2: Measure the coordinates of the preset control points on the steel truss beam, calculate and obtain the measured axial offset values ​​of the upper chord node and the lower chord node of the main truss; determine and execute the first welding process based on the measured axial offset values ​​of each preset control point; after the first welding process is completed, remeasure the coordinates of the control points of the steel truss beam.

[0009] Step S3: Using the coordinate data obtained from the remeasurement in step S2, calculate and obtain the measured vertical deviation values ​​of the upper chord node and the lower chord node of the main truss; based on the measured vertical deviation values, determine and execute the second welding process; after the second welding process is completed, weld a positioning plate at the top plate of the main truss chord to lock the correction effect, and remeasure the coordinates of the control points of the steel truss beam.

[0010] Step S4: Using the coordinate data obtained from the remeasurement in Step S3, calculate and obtain the measured axial offset and measured vertical offset values ​​of the sub-truss node; based on the measured axial offset and measured vertical offset values, determine and execute the third welding process; after the third welding process is completed, remeasure the coordinates of the control points of the steel truss beam.

[0011] Step S5: Replace the punching pins with high-strength bolts to complete the fastening of the diagonal web members, and re-measure the coordinates of the control points of the steel truss beam;

[0012] Step S6: Following the order of constructing the railway crossbeams first and then the highway crossbeams, hoist the far end crossbeams of the railway and highway bridge decks and complete the weld construction of the connection between the crossbeams and the main truss, which is recorded as the fourth welding process.

[0013] Step S7: Complete the welding of the remaining main truss and secondary truss web plates and top and bottom plates, which is recorded as the fifth welding process;

[0014] Step S8: Release the restraints by releasing the hook of the girder erecting crane;

[0015] Step S9: Hoist and construct the weld connecting the remaining crossbeams to the main truss, which is recorded as the sixth welding process;

[0016] Step S10: After all welding processes are completed, the steel truss girder segment assembly construction is completed.

[0017] Optionally, the specific process of step S2 includes:

[0018] Step s201: Based on the measured axial offset value X of the upper chord node of the main truss A Determine welding procedure N1a; if -ε / 2≤X A If X ≤ ε / 2, and the axial deviation error of the upper chord node of the main truss is considered small, then the welding operation of the upper chord node of the main truss is symmetrical welding of AL1, AL2, AL3 and AL4; if X A If X > ε / 2, it is assumed that there is a large error in the axial deviation of the upper chord node of the main truss, indicating a tendency for inward contraction. Therefore, the welding operations for the upper chord node of the main truss should sequentially weld AL1, AL3, AL2, and AL4. AIf the deviation is less than -ε / 2, it is considered that there is a large error in the axial deviation of the main truss upper chord node, and the welding operations of the main truss upper chord node are performed sequentially: AL4, AL2, AL3, and AL1. Among them, AL1 is the outer layer weld of the outer web of the main truss upper chord; AL2 is the inner layer weld of the outer web of the main truss upper chord; AL3 is the inner layer weld of the inner web of the main truss upper chord; AL4 is the outer layer weld of the inner web of the main truss upper chord; ε is the axial deviation error control limit of the main truss and the secondary truss.

[0019] Step s202: Based on the measured axial offset value X of the lower chord node of the main truss B Determine welding procedure N1b; if -ε / 2≤X B If X ≤ ε / 2, and the axial deviation error of the lower chord node of the main truss is considered small, then the welding operations of the lower chord node of the main truss are symmetrical welding of BL1, BL2, BL3 and BL4; if X B If X > ε / 2, it is assumed that there is a large error in the axial deviation of the lower chord node of the main truss, indicating a tendency for inward contraction. Therefore, the welding operations for the lower chord node of the main truss should sequentially weld BL1, BL3, BL2, and BL4. B If the error is less than -ε / 2, it is assumed that there is a large error in the axial deviation of the lower chord node of the main truss, and then the welding operations of the lower chord node of the main truss are BL4, BL2, BL3 and BL1 respectively. Among them, BL1 is the outer layer weld of the outer web of the lower chord of the main truss; BL2 is the inner layer weld of the outer web of the lower chord of the main truss; BL3 is the inner layer weld of the inner web of the lower chord of the main truss; BL4 is the outer layer weld of the inner web of the lower chord of the main truss.

[0020] Optionally, the specific process of step S3 includes:

[0021] Step s301: Based on the measured vertical deviation value Y of the upper chord node of the main truss A Determine welding procedure N2a; if -δ / 2≤Y A If the elevation error of the upper chord node of the main truss is considered to be small (≤δ / 2), then the welding operation of the upper chord node of the main truss is symmetrical welding of AL5 and AL6; if Y A If the elevation of the upper chord node of the main truss is greater than δ / 2, indicating a large upward trend, then the welding operation of the upper chord node of the main truss should proceed by welding AL6 first, followed by AL5; if Y A <-δ / 2, indicating a large error in the elevation of the main truss upper chord node with a downward deflection trend, the welding operation of the main truss upper chord node shall first weld AL5, then weld AL6; where AL5 is the weld on the top plate of the main truss upper chord; AL6 is the weld on the bottom plate of the main truss upper chord; δ is the vertical deviation error control limit of the main truss and the secondary truss.

[0022] Step s302: Based on the measured vertical deviation value Y of the lower chord node of the main truss B Determine welding procedure N2b; if -δ / 2≤Y B If the elevation error of the lower chord node of the main truss is considered to be small (≤δ / 2), then the welding operation of the lower chord node of the main truss is symmetrical welding of BL5 and BL6; if YB If the elevation of the lower chord node of the main truss is greater than δ / 2, indicating a large upward trend, then the welding operation of the lower chord node of the main truss should proceed by welding BL6 first, followed by BL5; if Y B <-δ / 2, it is assumed that there is a large error in the elevation of the lower chord node of the main truss due to a downward deflection trend. Therefore, the welding operation of the lower chord node of the main truss should first weld BL5 and then weld BL6. Among them, BL5 is the weld of the top plate of the lower chord of the main truss, and BL6 is the weld of the bottom plate of the lower chord of the main truss.

[0023] Optionally, the specific process of step S4 includes:

[0024] Step s401: Based on the measured axial offset value X of the secondary truss node C Determine welding procedure N31c; if -ε / 2≤X C If X ≤ ε / 2, and the axial deviation error of the secondary truss node is considered small, then the welding operation of the secondary truss node is symmetrical welding of CL1 and CL2; if X C If XC > ε / 2, it is considered that there is a large error in the axial deviation of the sub-truss node with a tendency to shrink inward. In this case, the welding operation of the sub-truss node should be performed by welding CL1 first, and then welding CL2. If XC < -ε / 2, it is considered that there is a large error in the axial deviation of the sub-truss node with a tendency to expand outward. In this case, the welding operation of the sub-truss node should be performed by welding CL2 first, and then welding CL1. CL1 is the outer web weld of the upper chord of the sub-truss, and CL2 is the inner web weld of the upper chord of the sub-truss.

[0025] Step s402: Based on the measured vertical deviation value Y of the secondary truss node C Determine welding procedure N32c; if -δ / 2≤Y C If the elevation error of the secondary truss node is ≤δ / 2, then the welding operation of the secondary truss node is symmetrical welding of CL3 and CL4; if Y C If the elevation of the secondary truss node is greater than δ / 2, indicating a large upward trend, then the welding operation of the secondary truss node should proceed by welding CL4 first, followed by CL3; if Y C If the elevation of the sub-truss node is considered to have a large error with a downward deflection tendency, then the welding operation of the sub-truss node should first weld CL3 and then weld CL4; where CL3 is the weld on the top plate of the upper chord of the sub-truss and CL4 is the weld on the bottom plate of the upper chord of the sub-truss.

[0026] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0027] This invention discloses a method for alignment control and correction during the assembly of steel truss bridges. The method involves phased measurement and welding to achieve alignment control and correction. First, the beam segments are roughly positioned and temporarily fixed. Then, the main truss axial deviation, vertical deviation, and secondary truss position are controlled in three steps. Each step is guided by measurement data and re-measured, supplemented by positioning plates for locking. Afterwards, high-strength bolts replace the drift pins, and the crossbeams are installed sequentially and welded. Finally, the crane constraints are released. This method uses a "measurement-calculation-welding-re-measurement" cycle to ensure assembly accuracy. This invention provides real-time guidance for welding operations using measured data, solving the problems of poor adaptability and insufficient accuracy of traditional methods, and providing data support for the control of assembly of steel truss bridges in engineering projects. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a flowchart illustrating the alignment control and correction method for the assembly and disassembly construction of steel truss bridges according to the present invention.

[0030] Figure 2 This is a diagram showing the control weld positions and numbering in this embodiment;

[0031] Figure 3 This is a schematic diagram of the coordinate error vector of the control points of the steel truss in this embodiment;

[0032] Figure 4 This is a structural schematic diagram of the steel truss beam segment in this embodiment;

[0033] Figure 5 This is a schematic diagram of the steel strand suspension point arrangement for the steel truss in this embodiment. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] The purpose of this invention is to provide a method for alignment control and correction during the assembly construction of steel truss bridges, aiming to solve or improve at least one of the above-mentioned technical problems.

[0036] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0037] like Figures 1-5 As shown, based on the main truss upper chord node A, main truss lower chord node B, secondary truss node C, and steel strand lifting point position D, this invention provides a method for alignment control and correction during the assembly construction of steel truss bridges, including:

[0038] Step S1: Use the girder erecting crane to adjust the spatial posture of the steel truss girder in the transverse and vertical directions for rough positioning, and use steel strands to laterally pull and suppress the inward deformation of the lower chord node B of the main truss. Finally, drive in the bolt holes of the diagonal web members to temporarily fix them.

[0039] Step S2: Measure the coordinates of the preset control points on the steel truss beam, calculate and obtain the measured axial offset values ​​of the upper chord node A and the lower chord node B of the main truss; determine and execute the first welding process (N1) based on the measured axial offset values ​​of the control points; after the first welding process (N1) is completed, remeasure the coordinates of the control points of the steel truss beam.

[0040] Step S3: Using the coordinate data obtained from the remeasurement in step S2, calculate and obtain the measured vertical deviation values ​​of the upper chord node A and the lower chord node B of the main truss; based on the measured vertical deviation values ​​of the control points, determine and execute the second welding process (N2); after the second welding process (N2) is completed, weld a positioning plate at the top plate of the main truss chord to lock the deviation correction effect, and remeasure the coordinates of the control points of the steel truss beam.

[0041] Step S4: Using the coordinate data obtained from the remeasurement in step S3, calculate and obtain the measured axial offset and vertical offset values ​​of the sub-truss node C; based on the measured axial offset and vertical offset values ​​of the control point, determine and execute the third welding process (N3); after the third welding process (N3) is completed, remeasure the coordinates of the control point of the steel truss beam.

[0042] Step S5: Replace the punch pins with high-strength bolts to complete the fastening of the diagonal web members, and re-measure the coordinates of the control points of the steel truss beam.

[0043] Step S6: Hoist the far end crossbeams of the railway and highway bridge decks and complete the weld construction of the connection between the crossbeams and the main truss. The railway crossbeams should be constructed first, followed by the highway crossbeams. This is recorded as welding procedure N4.

[0044] Step S7: Complete the welding of the remaining main truss and secondary truss web plates and top and bottom plates, which is recorded as welding operation N5.

[0045] Step S8: Release the restraints by releasing the hook of the girder erecting crane.

[0046] Step S9: Hoist and construct the weld connecting the remaining crossbeams to the main truss, denoted as welding process N6.

[0047] Step S10: Complete the assembly of steel truss girder segments.

[0048] As a specific implementation method, step S2 is specifically implemented as follows:

[0049] Step s201: Based on the measured axial offset value X of the upper chord node A of the main truss A Determine welding procedure N1a. If -ε / 2 ≤ X A If ≤ε / 2, and the axial deviation error of the main truss upper chord node A is considered small, then the welding operation of the main truss upper chord node A should be symmetrical welding of the outer layer weld AL1 of the outer web of the main truss upper chord, the inner layer weld AL2 of the outer web of the main truss upper chord, the inner layer weld AL3 of the inner web of the main truss upper chord, and the outer layer weld AL4 of the inner web of the main truss upper chord; if X A If the deviation of the main truss upper chord node A is greater than ε / 2, and a large error is considered to exist with an inward tendency, then the welding operation of the main truss upper chord node A should be performed sequentially: outer layer weld AL1 on the outer web of the main truss upper chord, inner layer weld AL3 on the inner web of the main truss upper chord, inner layer weld AL2 on the outer web of the main truss upper chord, and outer layer weld AL4 on the inner web of the main truss upper chord; if X A If the error is considered to be a large error with an outward expansion tendency at the axis of the upper chord node A of the main truss, then the welding operation of the upper chord node A of the main truss should be carried out in the following order: the outer layer weld of the inner web of the upper chord of the main truss AL4, the inner layer weld of the outer web of the upper chord of the main truss AL2, the inner layer weld of the inner web of the upper chord of the main truss AL3, and the outer layer weld of the outer web of the upper chord of the main truss AL1.

[0050] Step s202: Based on the measured axial offset value X of the lower chord node B of the main truss B Determine welding procedure N1b. If -ε / 2 ≤ X B If ≤ε / 2, and the axial deviation error of the lower chord node B of the main truss is considered small, then the welding operation of the lower chord node B of the main truss should be symmetrical welding of the outer layer weld BL1 of the outer web of the lower chord of the main truss, the inner layer weld BL2 of the outer web of the lower chord of the main truss, the inner layer weld BL3 of the inner web of the lower chord of the main truss, and the outer layer weld BL4 of the inner web of the lower chord of the main truss; if X B If X > ε / 2, and considering a large error indicating a tendency for inward shrinkage at the B-axis of the lower chord of the main truss, then the welding operation at the B-axis of the lower chord of the main truss should sequentially weld the outer layer weld BL1 of the outer web of the lower chord of the main truss, the inner layer weld BL3 of the inner web of the lower chord of the main truss, the inner layer weld BL2 of the outer web of the lower chord of the main truss, and the outer layer weld BL4 of the inner web of the lower chord of the main truss; if X BIf the deviation of the lower chord node B of the main truss is considered to be a large error with an outward expansion trend, then the welding operation of the lower chord node B of the main truss should be carried out in the following order: the outer layer weld of the inner web of the lower chord of the main truss BL4, the inner layer weld of the outer web of the lower chord of the main truss BL2, the inner layer weld of the inner web of the lower chord of the main truss BL3, and the outer layer weld of the outer web of the lower chord of the main truss BL1.

[0051] As a specific implementation method, step S3 is specifically implemented as follows:

[0052] Step s301: Based on the measured vertical deviation value Y of the upper chord node A of the main truss A Determine welding procedure N2a. If -δ / 2 ≤ Y A If the elevation error of the upper chord node A of the main truss is considered to be small (≤δ / 2), then the welding operation of the upper chord node A of the main truss should be symmetrical welding of the top plate weld AL5 and the bottom plate weld AL6 of the upper chord of the main truss; if Y A If Y > δ / 2, it is considered that there is a large error in the elevation of the upper chord node A of the main truss, indicating an upward trend. Therefore, the welding operation of the upper chord node A of the main truss should first weld the bottom plate weld AL6 of the upper chord of the main truss, and then weld the top plate weld AL5 of the upper chord of the main truss. A If the elevation of the upper chord node A of the main truss is considered to have a large error due to a downward deflection trend, then the welding operation of the upper chord node A of the main truss should first weld the top plate weld AL5 of the upper chord of the main truss, and then weld the bottom plate weld AL6 of the upper chord of the main truss.

[0053] Step s302: Based on the measured vertical deviation value Y of the lower chord node B of the main truss B Determine welding procedure N2b. If -δ / 2 ≤ Y B If the elevation error of the lower chord node B of the main truss is considered to be small (≤δ / 2), then the welding operation of the lower chord node B of the main truss should be symmetrical welding of the top plate weld BL5 and the bottom plate weld BL6 of the lower chord of the main truss; if Y B If the elevation of the lower chord node B of the main truss is considered to have a large upward tilting error, then the welding operation of the lower chord node B should first weld the bottom plate weld BL6 of the lower chord of the main truss, and then weld the top plate weld BL5 of the lower chord of the main truss; if Y B If the elevation of the lower chord node B of the main truss is considered to have a large error due to a downward deflection trend, then the welding operation of the lower chord node B of the main truss should first weld the top plate weld BL5 of the lower chord of the main truss, and then weld the bottom plate weld BL6 of the lower chord of the main truss.

[0054] As a specific implementation method, step S4 is specifically implemented as follows:

[0055] Step s401: Based on the measured axial offset value X of the secondary truss node C C Determine welding procedure N31c. If -ε / 2 ≤ X CIf ≤ε / 2, and the axial deviation error of the secondary truss node C is considered small, then the welding operation of the secondary truss node C should be symmetrical welding of the outer web weld CL1 of the upper chord of the secondary truss and the inner web weld CL2 of the upper chord of the secondary truss; if X C If X > ε / 2, and it is considered that there is a large error with an inward tendency in the axis deviation of the secondary truss node C, then the welding operation of the secondary truss node C should first weld the outer web weld CL1 of the upper chord of the secondary truss, and then weld the inner web weld CL2 of the upper chord of the secondary truss; if X C If the deviation of the sub-truss node C is considered to be a large error with an outward expansion tendency, then the welding operation of the sub-truss node C should first weld the inner web plate CL2 of the upper chord of the sub-truss, and then weld the outer web plate CL1 of the upper chord of the sub-truss.

[0056] Step s402: Based on the measured vertical deviation value Y of the secondary truss node C C Determine welding procedure N32c. If -δ / 2≤Y C If the elevation error of the secondary truss node C is considered to be small (≤δ / 2), then the welding operation of the secondary truss node C should be symmetrical welding of the top plate weld CL3 of the upper chord of the secondary truss and the bottom plate weld CL4 of the upper chord of the secondary truss; if Y C If the elevation of the secondary truss node C is considered to have a large upward tilting error, then the welding operation at the secondary truss node C should first weld the bottom plate weld CL4 of the upper chord of the secondary truss, and then weld the top plate weld CL3 of the upper chord of the secondary truss; if Y C If the elevation of the sub-truss node C is considered to have a large error with a downward deflection trend, then the welding operation of the sub-truss node C should first weld the top plate weld CL3 of the sub-truss upper chord, and then weld the bottom plate weld CL4 of the sub-truss upper chord.

[0057] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0058] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for alignment control and correction during the piecemeal construction of a steel truss bridge, characterized in that, include: Step S1: Use the girder erecting crane to adjust the spatial posture of the steel truss girder in the transverse and vertical directions for rough positioning, and use the steel strands to laterally pull and suppress the inward deformation of the lower chord node of the main truss. Finally, drive the punch nails into the bolt holes of the diagonal web members for temporary fixation. Step S2: Measure the coordinates of the preset control points on the steel truss beam, calculate and obtain the measured axial offset values ​​of the upper chord node and the lower chord node of the main truss; determine and execute the first welding process based on the measured axial offset values ​​of each preset control point; after the first welding process is completed, remeasure the coordinates of the control points of the steel truss beam. Step S3: Using the coordinate data obtained from the remeasurement in Step S2, calculate and obtain the measured vertical deviation values ​​of the upper chord node and the lower chord node of the main truss; based on the measured vertical deviation values, determine and execute the second welding process; after the second welding process is completed, weld a positioning plate at the top plate of the main truss chord to lock the correction effect, and remeasure the coordinates of the control points of the steel truss beam. Step S4: Using the coordinate data obtained from the remeasurement in Step S3, calculate and obtain the measured axial offset and measured vertical offset values ​​of the sub-truss node; based on the measured axial offset and measured vertical offset values, determine and execute the third welding process; after the third welding process is completed, remeasure the coordinates of the control points of the steel truss beam. Step S5: Replace the punching pins with high-strength bolts to complete the fastening of the diagonal web members, and re-measure the coordinates of the control points of the steel truss beam; Step S6: Following the order of constructing the railway crossbeams first and then the highway crossbeams, hoist the far end crossbeams of the railway and highway bridge decks and complete the weld construction of the connection between the crossbeams and the main truss, which is recorded as the fourth welding process. Step S7: Complete the welding of the remaining main truss and secondary truss web plates and top and bottom plates, which is recorded as the fifth welding process; Step S8: Release the restraints by releasing the hook of the girder erecting crane; Step S9: Hoist and construct the weld connecting the remaining crossbeams to the main truss, which is recorded as the sixth welding process; Step S10: After all welding processes are completed, the steel truss girder segment assembly construction is completed.

2. The method for alignment control and correction during the piecemeal construction of steel truss bridges according to claim 1, characterized in that, The specific process of step S2 includes: Step s201: Based on the measured axial offset value X of the upper chord node of the main truss A Determine welding procedure N1a; if -ε / 2≤X A If X ≤ ε / 2, and the axial deviation error of the upper chord node of the main truss is considered small, then the welding operation of the upper chord node of the main truss is symmetrical welding of AL1, AL2, AL3 and AL4; if X A If X > ε / 2, it is assumed that there is a large error in the axial deviation of the upper chord node of the main truss, indicating a tendency for inward contraction. Therefore, the welding operations for the upper chord node of the main truss should sequentially weld AL1, AL3, AL2, and AL4. A If the deviation is less than -ε / 2, it is considered that there is a large error in the axial deviation of the main truss upper chord node, and the welding operations of the main truss upper chord node are performed sequentially: AL4, AL2, AL3, and AL1. Among them, AL1 is the outer layer weld of the outer web of the main truss upper chord; AL2 is the inner layer weld of the outer web of the main truss upper chord; AL3 is the inner layer weld of the inner web of the main truss upper chord; AL4 is the outer layer weld of the inner web of the main truss upper chord; ε is the axial deviation error control limit of the main truss and the secondary truss. Step s202: Based on the measured axial offset value X of the lower chord node of the main truss B Determine welding procedure N1b; if -ε / 2≤X B If X ≤ ε / 2, and the axial deviation error of the lower chord node of the main truss is considered small, then the welding operations for the lower chord node of the main truss are symmetrical welding of BL1, BL2, BL3 and BL4; if X B If X > ε / 2, it is assumed that there is a large error in the axial deviation of the lower chord node of the main truss, indicating a tendency for inward contraction. Therefore, the welding operations for the lower chord node of the main truss should sequentially weld BL1, BL3, BL2, and BL4. B If the error is less than -ε / 2, it is assumed that there is a large error in the axial deviation of the lower chord node of the main truss, and then the welding operations of the lower chord node of the main truss are BL4, BL2, BL3 and BL1 respectively. Among them, BL1 is the outer layer weld of the outer web of the lower chord of the main truss; BL2 is the inner layer weld of the outer web of the lower chord of the main truss; BL3 is the inner layer weld of the inner web of the lower chord of the main truss; BL4 is the outer layer weld of the inner web of the lower chord of the main truss.

3. The method for alignment control and correction during the piecemeal construction of steel truss bridges according to claim 1, characterized in that, The specific process of step S3 includes: Step s301: Based on the measured vertical deviation value Y of the upper chord node of the main truss A Determine welding procedure N2a; if -δ / 2≤Y A If the elevation error of the upper chord node of the main truss is considered to be small (≤δ / 2), then the welding operation of the upper chord node of the main truss is symmetrical welding of AL5 and AL6; if Y A If the elevation of the upper chord node of the main truss is greater than δ / 2, indicating a large upward trend, then the welding operation of the upper chord node of the main truss should proceed by welding AL6 first, followed by AL5; if Y A <-δ / 2, indicating a large error in the elevation of the main truss upper chord node with a downward deflection trend, the welding operation of the main truss upper chord node shall first weld AL5, then weld AL6; where AL5 is the weld on the top plate of the main truss upper chord; AL6 is the weld on the bottom plate of the main truss upper chord; δ is the vertical deviation error control limit of the main truss and the secondary truss. Step s302: Based on the measured vertical deviation value Y of the lower chord node of the main truss B Determine welding procedure N2b; if -δ / 2≤Y B If the elevation error of the lower chord node of the main truss is considered to be small (≤δ / 2), then the welding operation of the lower chord node of the main truss is symmetrical welding of BL5 and BL6; if Y B If the elevation of the lower chord node of the main truss is greater than δ / 2, indicating a large upward trend, then the welding operation of the lower chord node of the main truss should proceed by welding BL6 first, followed by BL5; if Y B <-δ / 2, it is assumed that there is a large error in the elevation of the lower chord node of the main truss due to a downward deflection trend. Therefore, the welding operation of the lower chord node of the main truss should first weld BL5 and then weld BL6. Among them, BL5 is the weld of the top plate of the lower chord of the main truss, and BL6 is the weld of the bottom plate of the lower chord of the main truss.

4. The method for alignment control and correction during the piecemeal construction of steel truss bridges according to claim 1, characterized in that, The specific process of step S4 includes: Step s401: Based on the measured axial offset value X of the secondary truss node C Determine welding procedure N31c; if -ε / 2≤X C If X ≤ ε / 2, and the axial deviation error of the secondary truss node is considered small, then the welding operation of the secondary truss node is symmetrical welding of CL1 and CL2; if X C If XC > ε / 2, it is considered that there is a large error in the axial deviation of the sub-truss node with a tendency to shrink inward. In this case, the welding operation of the sub-truss node should be performed by welding CL1 first, and then welding CL2. If XC < -ε / 2, it is considered that there is a large error in the axial deviation of the sub-truss node with a tendency to expand outward. In this case, the welding operation of the sub-truss node should be performed by welding CL2 first, and then welding CL1. CL1 is the outer web weld of the upper chord of the sub-truss, and CL2 is the inner web weld of the upper chord of the sub-truss. Step s402: Based on the measured vertical deviation value Y of the secondary truss node C Determine welding procedure N32c; if -δ / 2≤Y C If the elevation error of the secondary truss node is ≤δ / 2, then the welding operation of the secondary truss node is symmetrical welding of CL3 and CL4; if Y C If the elevation of the secondary truss node is greater than δ / 2, indicating a large upward trend, then the welding operation of the secondary truss node should proceed by welding CL4 first, followed by CL3; if Y C If the elevation of the sub-truss node is considered to have a large error due to a downward deflection trend, then the welding operation of the sub-truss node should first weld CL3 and then weld CL4; where CL3 is the weld on the top plate of the upper chord of the sub-truss and CL4 is the weld on the bottom plate of the upper chord of the sub-truss.

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