A large gantry crane girder no excess construction control method

Abstract

A large gantry crane main beam without excess construction control method, the two ends of the main beam and the sub beam are divided to form two end beams and two sub beams, and then the two sub beams are sequentially divided to form a plurality of segmented beams with arbitrary lengths, the edges of the segmented beams need to be 300 mm away from adjacent large partition plates, a welding compensation amount is added to the upper panel, lower panel and web of each segmented beam, the plurality of segmented beams are spliced to form a sub beam, and then the sub beam is spliced to form a main beam, the main beam is subjected to a load test, after the final load test, the crane is kept empty, at this time, the camber value and the profile size of the main beam are measured and recorded. The turnover and construction time are reduced. The number of segments is reduced, the continuity of construction is improved, and the redundant process of manual cutting and research amount and on-site beveling required in the assembly stage of small segments is abandoned.

Description

Technical Field

[0001] This invention belongs to the field of design and construction of large gantry crane beams, specifically relating to a method for controlling the construction of large gantry crane main beams without margin. Background Technology

[0002] The current construction method for the main beam of large gantry cranes generally involves reserving 50-100mm of welding allowance for the panels and webs on both sides of each segment of the main beam. During construction, this allowance is added to both ends of the panels and webs of the main beam. This serves two purposes: first, to prevent structural shortening and twisting due to welding shrinkage and deformation; and second, to determine the length of each segment before overall assembly, thus controlling the overall length of the main beam. The construction sequence is as follows: (1) Cutting the webs and panels of the main beam, adding welding allowance to both ends, without cutting the bevels at the joints of the panels and webs to be joined with the connecting beam; (2) Welding the panels and webs of the small segments of the main beam to the transverse and longitudinal stiffening ribs of the structure, prefabricating single beams; (3) After pressing the beam, laying the upper panel of the main beam on the erected "recessed" fabrication jig, using the upper panel as the base plate, and fixing it, then proceeding with the reverse construction of the structure; (4) Marking and positioning the webs on the left and right sides of the panel, adding welding allowance to the sides of the webs. (3) Add supporting fixtures to prevent the web from tilting and bending during welding; (4) Weld the internal profiles and other accessories of the main beam, at which point the lower panel of the main beam has not yet been welded to the main beam; (5) Weld the lower panel of the main beam and weld the whole into a small segment; (6) According to the size requirements of the drawings, cut off the excess material on both sides of the small segment and cut the butt joint bevel at the interface between the panel and the web; (7) Repeat steps (1) to (6) and inspect the weld bevel of each segment; (8) Weld the main beam together, cut off the excess material, and inspect the overall closure joint.

[0003] The main drawbacks of the above methods are: complex welding procedures, difficulty in controlling welding deformation, and, compared to the crane involved in this patent, the need for manual cutting of 18 closure welds on a single main beam, with each weld section covering nearly 70m², and the requirement for on-site beveling by construction workers at the assembly site, increasing labor hours, energy consumption, cost control, and construction cycle. Therefore, a crane main beam construction method needs to be designed that can ensure construction continuity, improve welding quality, further reduce costs, and simultaneously improve work efficiency. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a method for controlling the construction of large gantry crane main beams without margin, aiming to improve manufacturing efficiency and effectively control welding deformation. The technical solution adopted is as follows: A method for controlling the construction of a large gantry crane main beam without margin is disclosed. The method is characterized in that the main beam consists of two identical sub-beams with an isosceles trapezoidal cross-section. Each sub-beam is composed of two webs, a top panel, and a bottom panel, forming a trapezoidal cross-section. Multiple reinforcing ribs are fixed to the webs and are continuously arranged along their length. Multiple large partitions are longitudinally inserted within the sub-beams, perpendicular to the top and bottom panels. Each partition consists of strip plates and support tubes. Four strip plates enclose an isosceles trapezoidal frame matching the sub-beam's cross-section. Multiple support tubes are fixed within the frame, forming multiple triangles that reinforce the frame from bottom to top. The two sub-beams are arranged laterally side-by-side with a gap between them. Their ends are welded together using square end plates to form a main beam with a square cross-section. The overall length of the main beam is 129m. The specific construction method is as follows: S1: Divide the main beam at both ends from the sub-beams to form two end beams and two sub-beams. Then divide the two sub-beams in sequence to form multiple segmented beams of arbitrary length. The edge of the segmented beam must be 300mm away from the adjacent large partition. Add welding compensation to the upper panel, lower panel and web of each segmented beam. The compensation value is 15mm. The segmented beam located in the middle of the sub-beam has compensation added on both sides, and the other segmented beams have compensation added on one side. Calculation formula: fa = main beam span * [0.9, 1.4] / 1000; The precast camber of the main beam = fa + the deflection due to the self-weight of the main beam + the camber correction value of the main beam; The precast camber of the main beam is obtained, and the remaining camber values ​​are evenly distributed. The camber value at the center span projection of the main beam and the track is set to 0mm.

[0005] S2: Determine the web curve of each segment beam according to the formula Y=fa*(122000-X)X / 61000², where Y is the camber value of the main beam at the calculation point; X is the distance from the calculation point to the starting point of the span. Add 1mm welding shrinkage for every 1m of length of web, upper and lower panels along the length of the segment beam, and strictly check the outer dimensions of the steel plate after cutting. The allowable deviation of the length dimension is ±2mm, the allowable deviation of the width dimension is ±1mm, the diagonal is <3mm, the allowable straightness of 3m length is <3mm, the camber value matches the actual line shape ≤2mm, and K-type butt bevels are opened on the edges of the web and panel.

[0006] S3: Use a level to level the jig, place the web plate on the jig, and fix a metal pad on the lower surface of the thinner part of the web plate according to the thickness data of the web plate in the drawing. Ensure that the web plate is laid flat and the assembly surface is level. With the main web plate as the base plate, the web plate that is first placed on the jig for welding is the main web plate, and the web plate that is welded later is the secondary web plate. Draw the center position line of the main web plate on the jig, and then draw the upper panel on the jig one by one according to its inner width center line, web plate assembly center line, partition assembly center line, and partition width center line.

[0007] After the drawings are completed, assembly and positioning welding are performed. The segmented beams are welded in the following order: main web plate to large diaphragm, upper panel to main web plate and secondary web plate, secondary web plate to large diaphragm, and lower panel to main web plate and secondary web plate. The web plate and upper and lower panels are welded using automatic welding. 4.8mm diameter welding material is used for the root pass, fill pass and cover pass. The welding current is 500~550A, the welding voltage is 28~32V and the welding speed is 400~600mm / min for the root pass. The welding current is 600~700A, the welding voltage is 32~36V and the welding speed is 400~600mm / min for the fill pass and cover pass. The large diaphragm, web plate and stiffeners are welded using gas shielded welding.

[0008] To prevent asymmetrical deformation during corner welding, the welding sequence should be symmetrical from the middle outwards.

[0009] S4: 24 hours after the splice seam and corner seam welding is completed, UT flaw detection and dimensional measurement shall be carried out on each segment beam and end beam. The quality of UT flaw detection shall not be lower than the Class 1 requirement in JB / T 10559. For suspicious parts, MT flaw detection shall be carried out. The quality of MT flaw detection shall not be lower than the Class I requirement specified in JB / T 6061.

[0010] Use a total station to measure the diagonal of the cross section, the diagonal of the longitudinal section, the horizontal skewness of the top and bottom panels, the horizontal height difference at the same section, the twist of the segmented beam, the verticality of the web, the waviness of the web, the horizontal curvature of the beam, and its length. Compare the measured values ​​with the data on the drawings to see if there are any excessive deviations. If there are excessive deviations, the dimensions of the segmented beam should be corrected to ensure that the measured values ​​are within the allowable deviation range. The deviation of the diagonal of the cross section of the segmented beam should not exceed 4mm, and the deviation of the diagonal of the longitudinal section of the segmented beam should not exceed 5mm.

[0011] S5: Draw a baseline on the closure site. On the closure site, according to the position of each segment beam, start from the mid-span segment beam to place the support frame and adjust the horizontal data value. The horizontal data value adjustment is based on the camber.

[0012] S6: When connecting segmented beams, take the middle segmented beam of the sub-beam as the reference and place the segmented beams on both sides in sequence. After placing two segments of the same cross section, adjust and align them according to the ground survey line. Use a level to check the camber, vertical deviation of the web, horizontal deviation of the upper panel, horizontal bending, twisting, center distance between adjacent segmented beams, and diagonal to ensure that they meet the requirements of the ground survey line. After the above values ​​are verified to be qualified, use tooling plates to seal the upper and lower panels of the two adjacent segments. Align the segmented beams with the center line of the ground survey and assemble and weld them as a whole to form the sub-beam.

[0013] S7: After the segmented beams are joined, all closure positions of each segmented beam shall be inspected for defects. The welds shall be subjected to ultrasonic and radiographic inspection. The butt welds shall be subjected to ultrasonic inspection covering 100% of the weld length. The quality shall not be lower than the Class 1 standard of GB11345-B inspection. For important butt welds, 10% of the total weld length shall be selected for radiographic inspection. The quality shall not be lower than the Class II standard specified in GB / T3323. At least one radiograph shall be taken for each tension weld.

[0014] S8: After the sub-beam dimensions are determined, measure the dimensions of the sub-beam closure joint. Then, cut and bevel the upper, lower, and web plates of the end beam. The installation method of the end beam is the same as that of the sub-beam segments. After the end beam is independently welded, connect the end beam to the sub-beam. At this time, make a K-shaped bevel on the edge of the end beam and leave a 2mm butt weld to complete the overall closure of the main beam and record the finished dimensions.

[0015] S9: Conduct a load test on the main beam. After passing the final load test, keep the crane unloaded. At this time, measure and record the camber value and dimensions of the main beam.

[0016] Furthermore, the above-mentioned method for controlling the construction of a large gantry crane main beam without margin involves dividing the sub-beams into segments based on the lifting capacity of the construction site, with each segmented beam being within the lifting capacity range.

[0017] Furthermore, in the above-mentioned method for controlling the construction of a large gantry crane main beam without margin, the web, upper panel, and lower panel of the main beam are cut using a plasma CNC cutting machine with a cutting accuracy of <0.2mm.

[0018] Furthermore, in step S3, during the positioning welding, gas shielded welding is used to first weld the fillet weld between the main web plate and the large diaphragm plate. Then, the segment beam is rotated 90° clockwise and placed on the jig with the upper panel as the base plate. Then, automatic welding is used to weld the fillet weld between the upper panel and the main web plate of the segment beam. After the upper panel and the main web plate are welded, the segment beam is rotated 90° clockwise and placed on the jig with the secondary web plate as the base plate. Gas shielded welding is used to weld the fillet weld between the secondary web plate and the large diaphragm plate. Automatic welding is used to weld the fillet weld between the secondary web plate and the lower panel, and the fillet weld between the lower panel and the main web plate.

[0019] Furthermore, in step S7 of the above-mentioned method for controlling the construction of a large gantry crane main beam without margin, the tooling stack plates are selected with the same thickness as the main beam structure, with basic thicknesses of 10, 14, and 20 mm.

[0020] Furthermore, the above-mentioned method for controlling the construction of a large gantry crane main beam without margin further utilizes an automatic submerged arc welding wire trolley, model MZ-ZK-1000, with a welding speed of 0.2~1.5m / min and a wire feeding speed of 0.3~3m / min.

[0021] Furthermore, in step S6, the ground survey baseline includes: the center line of the main beam track, the longitudinal center line of the main beam, the center line of the trolley track, the center line of the main beam span, the transverse center line of the end beam, the longitudinal center line of the end beam, and the segment end line.

[0022] The beneficial effects of this invention are: 1. This method simplifies the process by rationally allocating the number of main beam segments based on the manufacturer's production capacity, enabling better construction and transportation, and reducing turnaround and construction time. The reduced number of segments also improves the continuity of construction.

[0023] 2. The welding compensation amount at the joint of the small segments and the welding shrinkage amount of the structural components have been increased, thereby eliminating the redundant processes of manual cutting and grinding and on-site beveling required during the assembly stage of the small segments.

[0024] 3. In the segmented group stage, the side plate is used as the base plate for construction, which can reduce the original standard value of lateral bending of the main beam ≤20mm to ≤10mm, reducing the amount of work required for post-weld straightening.

[0025] 4. Using a horizontal jig makes it easier to assemble small sections. The original main beam construction plan used the upper panel as the base plate for construction, which required welding a large number of partitions or piers at the bottom and building them into the shape of the main beam arch, increasing manpower and consuming a large amount of welding materials and tooling materials.

[0026] 5. Reduced energy consumption and rework waste: The pre-cut bevel of the joint during the material preparation stage greatly reduces the uncontrollability of manual on-site beveling, improves the flaw detection pass rate, and thus eliminates a lot of waste (labor costs, energy, materials, site, lifting machinery, etc. for rework), saving a lot of expenses. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the main beam structure rotated 90° from top view and divided into segments; Figure 2 This is a schematic diagram of the cross-sectional structure of the sub-beam; Figure 3 This is a schematic diagram of a segmented beam placed on a jig; Figure 4 This is a schematic diagram of the diagonal dimensions of the cross section of the main beam in the method of this invention; Figure 5 This is a schematic diagram of the diagonal dimensions of the longitudinal section of the main beam in the method of this invention; Among them, 1-web plate, 2-strip plate, 3-support tube, 4-frame, 5-upper panel, 6-lower panel. Detailed Implementation

[0028] The invention will be further described with reference to the accompanying drawings.

[0029] A 350t double-girder gantry crane has a main girder span design requirement of 122m ± 25mm and an overall main girder length of 129m. Figure 1 As shown, the main beam consists of two identical sub-beams. The cross-section of the sub-beam is an isosceles trapezoid. It is composed of a front web, a rear web, an upper panel, and a lower panel, forming a trapezoidal sub-beam. Multiple reinforcing ribs are fixed on the web, and these reinforcing ribs are continuously arranged along the length of the web.

[0030] like Figure 2 As shown, the large partition consists of strip plates and supporting pipes. Four strip plates enclose an isosceles trapezoidal frame that matches the cross-section of the sub-beam. Multiple supporting pipes are fixed inside the frame, forming multiple triangles that reinforce the frame from bottom to top. Multiple large partitions are interspersed at equal intervals inside the sub-beams, with the partitions positioned longitudinally within the sub-beams. Two sub-beams are arranged laterally side-by-side, with a gap between them. Their ends are welded together using square end plates to form a main beam with a square cross-section. The overall length of the main beam is 129m.

[0031] The specific operational steps of a method for controlling the construction of a large gantry crane main beam without margin are as follows: S1: Divide the two ends of the main beam from the sub-beams to form two end beams and two sub-beams. Then, divide the two sub-beams sequentially to form multiple segmented beams of arbitrary length, such as... Figure 1As shown, each segment beam is labeled. The edge of the segment beam must be 300mm away from the adjacent large partition. Welding compensation is added to the upper panel, lower panel and web of each segment beam. The compensation value is 15mm. The segment beam located in the middle of the sub-beam has compensation added on both sides, and the other segment beams have compensation added on one side.

[0032] Calculation formula: fa = main beam span * [0.9, 1.4] / 1000.

[0033] The precast camber of the main beam = fa + deflection due to the self-weight of the main beam + correction value for the camber of the main beam.

[0034] According to the drawings, the main beam span is 122000mm, [0.9,1.4] takes the value of 1.4, and fa is 170mm. The self-weight deflection of the main beam is 136mm, and the camber correction value of the main beam is 44mm. Therefore, the precast camber of the main beam is 170mm + 136mm + 44mm.

[0035] The precast camber of the main beam is 350mm, and the remaining camber values ​​are evenly distributed. The camber value at the center span projection of the main beam and the track is set to 0mm.

[0036] S2: Determine the web curve of each segment beam according to the formula Y=fa*(122000-X)X / 61000², where Y is the camber value of the main beam at the calculation point; X is the distance from the calculation point to the starting point of the span. Add 1mm welding shrinkage allowance for every 1m of length of the web, upper panel, and lower panel along the length direction of the segment beam, and strictly check the external dimensions of the steel plate after cutting. The allowable deviation of the length dimension is ±2mm, the allowable deviation of the width dimension is ±1mm, the diagonal is <3mm, the allowable straightness of 3m length is <3mm, the camber value matches the actual line shape ≤2mm, and K-type butt bevels are opened on the edges of the web and panel.

[0037] S3: Use a level to level the jig. According to the varying web thicknesses shown in the drawings, place strip-shaped metal pads (i.e., tooling plates of varying thicknesses) on the platform at the corresponding positions for web assembly. Weld them in place to ensure the web is laid flat and the assembly surface is level. Figure 3 As shown, the main web plate is the base plate. The web plate that is first placed on the jig and welded is the main web plate. The web plate that is welded later in the process is the secondary web plate. The center position line of the main web plate is drawn on the jig. Then, the upper panel is drawn on the jig according to its inner width center line, web plate assembly center line, partition assembly center line, and partition width center line.

[0038] After the drawing is completed, the assembly and positioning welding is carried out. The segmented beams are welded in the following order: main web plate to large diaphragm, upper panel to main web plate and secondary web plate, secondary web plate to large diaphragm, and lower panel to main web plate and secondary web plate. The web plate and the upper and lower panels are welded by automatic welding, and the large diaphragm and the web plate are welded by gas shielded welding. The welding current, voltage, and weld temperature are controlled.

[0039] To prevent asymmetrical deformation, the welding sequence in the above processes is symmetrical, starting from the middle and working outwards to both sides.

[0040] S4: 24 hours after welding is completed, flaw detection and dimensional measurement are performed on each segment beam and end beam. like Figure 4 , 5 As shown, a total station was used to measure the dimensions of the cross-section diagonals D11 and D12 of the segmented beam, and the longitudinal section diagonals D21 and D22 of the segmented beam. The horizontal skewness of the upper and lower panels, the horizontal height difference of the same section, the twist of the segmented beam, the verticality of the web, the waviness of the web, the horizontal curvature of the beam, and the length were also measured. The deviation of diagonals D11 and D12 should not exceed 4 mm, and the deviation of diagonals D21 and D22 should not exceed 5 m.

[0041] S5: Perform ultrasonic and radiographic testing on the welds. For butt welds, perform ultrasonic testing on 100% of the weld length. The quality should not be lower than the Class 1 standard of GB11345-B. For important butt welds, 10% of the total weld length should be sampled for radiographic testing. The quality should not be lower than the Class II standard specified in GB / T3323. For tension welds, take at least one radiograph for each weld.

[0042] S6: First, draw the ground sample reference lines, which include: the center line of the main trolley track, the longitudinal center line of the main beam, the center line of the trolley track, the center line of the main beam span, the transverse center line of the end beam, the longitudinal center line of the end beam, and the segment end lines. To ensure the quality of the assembly, the horizontal tread and ground sample layout need to be checked. The accuracy control of the ground sample layout is as follows: ① Segment ground sample dimension line accuracy: ≤1mm; ② Segment ground sample diagonal difference: ≤1mm; ③ Assembly ground sample dimension line accuracy: ≤1mm; ④ Assembly ground sample diagonal accuracy: ≤2mm.

[0043] On the closure site, according to the position of each segment beam, starting from the mid-span segment beam, the pads are placed and the horizontal data values ​​are adjusted. The horizontal data values ​​are adjusted with reference to the camber.

[0044] S7: When connecting segmented beams, take the middle segmented beam of the sub-beam as the reference and place the segmented beams on both sides in sequence. After placing two segments of the same cross section, adjust and align them according to the ground survey line. Use a level to check the camber, vertical deviation of the web, horizontal deviation of the upper panel, horizontal bending, twisting, center distance between adjacent segmented beams, and diagonal to ensure that they meet the requirements of the ground survey line. After the above values ​​are verified to be qualified, use tooling plates to seal the upper and lower panels of the two adjacent segments. Align the segmented beams with the center line of the ground survey and assemble and weld them as a whole to form the sub-beam.

[0045] S8: After the sub-beam dimensions are determined, measure the dimensions of the sub-beam closure joint. Then, cut and bevel the upper, lower, and web plates of the end beam. The installation method of the end beam is the same as that of the sub-beam segments. After the end beam is installed, connect the end beam to the sub-beam. Make a K-shaped bevel on the edge of the end beam and leave a 2mm butt weld. Erect the end beam in groups and finally complete the overall closure of the main beam and record the finished dimensions.

[0046] S9: Conduct a load test on the main beam. After passing the final load test, keep the crane unloaded. At this time, measure and record the camber value and dimensions of the main beam.

[0047] To ensure the welding quality of the panels, we eliminated the uncertainties of manual welding and used automatic welding as much as possible to improve the welding quality. We selected the existing automatic submerged arc welding wire carriage (model MZ-ZK-1000), with a welding speed of 0.2~1.5m / min and a wire feeding speed of 0.3~3m / min.

[0048] The tooling stack plates are selected with the same thickness as the main beam structure, with basic thicknesses of 10, 14, and 20 mm.

[0049] The main beam steel plate and profiles are made of Q355C.

[0050] Regarding the above steps: 1. Strictly ensure the levelness of the tire tread and the dimensional accuracy of each process; 2. When automatically welding plates, a retaining plate needs to be installed at the start and end points of the automatic welding. The retaining plate and the steel plate should have the same automatic welding bevel to ensure full penetration and prevent welding defects. 3. During hoisting operations, steel pipes and channel steel with sufficient structural strength should be used to reinforce the openings of the main beam structure to prevent damage to the structural dimensions during hoisting operations; 4. Welding: Welding shall be carried out in strict accordance with the WPS welding process requirements and in the corresponding sequence.

[0051] Before welding, the weld bead needs to be preheated at a temperature of ≥10℃. This temperature should be monitored in real time using an industrial temperature gun. If the ambient temperature allows, this step can be omitted. 5. Flaw detection: Perform UT and RT flaw detection as required.

[0052] For butt joints and T-joints of important metal structural components that are marked as having full penetration on drawings, non-destructive testing (NDT) shall be performed post-weld. Radiographic testing shall meet Level II of GB3323, and ultrasonic testing shall meet Level B-I of GB11345. Radiographic testing (RT) shall cover at least 10% of the total length, and ultrasonic testing (UT) shall cover 100% of the entire length. For full penetration fillet welds, at least 50% of the total weld length shall be sampled for ultrasonic testing, and the quality shall be no lower than Level 2 of JB / T10559. Suspected areas shall be further subjected to magnetic particle testing, and the defect level shall be no lower than Level I of JB / T6061.

Claims

1. A method for controlling the construction of a large gantry crane main beam without margin, characterized in that, The main beam consists of two identical sub-beams with an isosceles trapezoidal cross-section. Each sub-beam is composed of two webs, a top panel, and a bottom panel, forming a trapezoidal cross-section. Multiple reinforcing ribs are fixed to the webs and are continuously arranged along the length of the webs. Multiple large partitions are longitudinally inserted inside the sub-beams, perpendicular to the top and bottom panels. Each large partition consists of strip plates and support tubes. Four strip plates enclose an isosceles trapezoidal frame that matches the cross-section of the sub-beams. Multiple support tubes are fixed inside the frame, forming multiple triangles that reinforce the frame from bottom to top. The two sub-beams are arranged side by side laterally with a gap between them. Their ends are welded together by square end plates to form a main beam with a square cross-section. The overall length of the main beam is 129m. The specific construction method is as follows: S1: Divide the main beam at both ends from the sub-beams to form two end beams and two sub-beams. Then divide the two sub-beams in sequence to form multiple segmented beams of arbitrary length. The edge of the segmented beam must be 300mm away from the adjacent large partition. Add welding compensation to the upper panel, lower panel and web of each segmented beam. The compensation value is 15mm. The segmented beam located in the middle of the sub-beam has compensation added on both sides, and the other segmented beams have compensation added on one side. Calculation formula: fa = main beam span * [0.9, 1.4] / 1000; The precast camber of the main beam = fa + the deflection due to the self-weight of the main beam + the camber correction value of the main beam; The precast camber of the main beam is obtained, and the remaining camber values ​​are evenly distributed. The camber value at the center span projection of the main beam and the track is set to 0mm. S2: Determine the web curve of each segment beam according to the formula Y=fa*(122000-X)X / 61000², where Y is the camber value of the main beam at the calculation point; X is the distance from the calculation point to the starting point of the span. Add 1mm welding shrinkage for every 1m of length of web, upper and lower panels along the length of segment beam, and strictly check the external dimensions of the steel plate after cutting. The allowable deviation of length dimension is ±2mm, the allowable deviation of width dimension is ±1mm, the diagonal is <3mm, the allowable straightness of 3m length is <3mm, the camber value matches the actual line shape ≤2mm, and K-type butt bevels are opened on the edges of web and panel. S3: Use a level to level the jig, place the web plate on the jig, and fix a metal pad on the lower surface of the thinner part of the web plate according to the thickness data of the web plate in the drawing. Ensure that the web plate is laid flat and the assembly surface is level. With the main web plate as the base plate, the web plate that is first placed on the jig for welding is the main web plate, and the web plate that is welded later is the secondary web plate. Draw the center position line of the main web plate on the jig, and then draw the upper panel on the jig one by one according to its inner width center line, web plate assembly center line, partition assembly center line, and partition width center line. After the drawings are completed, assembly and positioning welding are performed. The segmented beams are welded in the following order: main web plate to large diaphragm, upper panel to main web plate and secondary web plate, secondary web plate to large diaphragm, and lower panel to main web plate and secondary web plate. The web plate and the upper and lower panels are welded using automatic welding. 4.8mm diameter welding material is used for the root pass, fill pass and cover pass. The welding current is 500~550A, the welding voltage is 28~32V and the welding speed is 400~600mm / min for the root pass. The welding current is 600~700A, the welding voltage is 32~36V and the welding speed is 400~600mm / min for the fill pass and cover pass. The large diaphragm, web plate and stiffeners are welded using gas shielded welding. To prevent asymmetrical deformation during corner welding, the welding sequence should be symmetrical from the middle outwards. S4: 24 hours after the splice seam and corner seam welding is completed, UT flaw detection and dimensional measurement shall be carried out on each segment beam and end beam. The quality of UT flaw detection shall not be lower than the Class 1 requirement in JB / T 10559. For suspicious parts, MT flaw detection shall be carried out. The quality of MT flaw detection shall not be lower than the Class I requirement specified in JB / T 6061. Use a total station to measure the diagonal of the cross-section, the diagonal of the longitudinal section, the horizontal skewness of the top and bottom panels, the horizontal height difference at the same section, the twist of the segmented beam, the verticality of the web, the waviness of the web, the horizontal curvature of the beam, and its length. Compare the measured values ​​with the data on the drawings to see if there are any excessive deviations. If there are excessive deviations, the dimensions of the segmented beam should be corrected to ensure that the measured values ​​are within the allowable deviation range. The deviation of the diagonal of the cross-section of the segmented beam should not exceed 4mm, and the deviation of the diagonal of the longitudinal section of the segmented beam should not exceed 5mm. S5: Draw the baseline of the ground pattern on the closure site. On the closure ground pattern, according to the position of each segment beam, start from the mid-span segment beam to place the support frame and adjust the horizontal data value. The adjustment of the horizontal data value is based on the camber. S6: After the segmented beams are joined, all closure positions of each segmented beam shall be inspected for defects. The welds shall be subjected to ultrasonic and radiographic inspection. The butt welds shall be subjected to ultrasonic inspection for 100% of the weld length. The quality shall not be lower than the Class 1 standard of GB11345-B inspection. For important butt welds, 10% of the total weld length shall be selected for radiographic inspection. The quality shall not be lower than the Class II standard specified in GB / T3323. At least one radiograph shall be taken for each tension weld. S7: When connecting segmented beams, take the middle segmented beam of the sub-beam as the reference and place the segmented beams on both sides in sequence. After placing two segments of the same cross section, adjust and align them according to the ground pattern line. Use a level to check the camber, vertical deviation of the web, horizontal deviation of the upper panel, horizontal bending, twisting, center distance between adjacent segmented beams, and diagonal to meet the requirements of the ground pattern line. After the above values ​​are qualified, use tooling plates to seal the upper and lower panels of the two adjacent segments. Align the segmented beams with the center line of the ground pattern and assemble and weld them as a whole to form the sub-beam. S8: After the sub-beam dimensions are formed, measure the dimensions of the sub-beam closure joint. Then, cut and bevel the upper panel, lower panel, and web of the end beam. The installation method of the end beam is the same as that of the segmented beam. After the end beam is welded independently, connect the end beam to the sub-beam. At this time, make a K-shaped bevel on the edge of the end beam and leave a 2mm butt weld to complete the overall closure of the main beam and record the finished dimensions. S9: Conduct a load test on the main beam. After passing the final load test, keep the crane unloaded. At this time, measure and record the camber value and dimensions of the main beam.

2. The method for controlling the construction of a large gantry crane main beam without margin as described in claim 1, characterized in that, The sub-beams are divided into sections according to the hoisting capacity of the construction site, and the divided sections must be within the hoisting capacity.

3. The method for controlling the construction of a large gantry crane main beam with no margin as described in claim 1, characterized in that, The web, upper panel, and lower panel of the main beam are cut using a plasma CNC cutting machine with a cutting accuracy of <0.2mm.

4. The method for controlling the construction of a large gantry crane main beam without margin as described in claim 1, characterized in that, In step S3, during tack welding, gas shielded welding is used to first weld the fillet weld between the main web plate and the large diaphragm. Then, the segment beam is rotated 90° clockwise and placed on the jig with the upper panel as the base plate. Then, automatic welding is used to weld the fillet weld between the upper panel and the main web plate of the segment beam. After the upper panel and the main web plate are welded, the segment beam is rotated 90° clockwise and placed on the jig with the secondary web plate as the base plate. Gas shielded welding is used to weld the fillet weld between the secondary web plate and the large diaphragm. Automatic welding is used to weld the fillet weld between the secondary web plate and the lower panel, and the fillet weld between the lower panel and the main web plate.

5. The method for controlling the construction of a large gantry crane main beam with no margin as described in claim 1, characterized in that, In step S7, the tooling stack plate is selected with the same thickness as the main beam structure, with basic thicknesses of 10, 14, and 20 mm.

6. The method for controlling the construction of a large gantry crane main beam without margin as described in claim 1, characterized in that, The automatic welding uses an automatic submerged arc welding wire carriage, model MZ-ZK-1000, with a welding speed of 0.2~1.5m / min and a wire feeding speed of 0.3~3m / min.

7. The method for controlling the construction of a large gantry crane main beam without margin as described in claim 1, characterized in that, In step S6, the ground sample baseline includes: the center line of the main track, the longitudinal center line of the main beam, the center line of the trolley track, the center line of the main beam span, the transverse center line of the end beam, the longitudinal center line of the end beam, and the segment end line.

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