Steel box girder closure construction method for pier tower girder consolidation system

Abstract

The invention discloses a closure construction method for steel box girders of a pier tower girder consolidation system. The closure construction method is characterized in that a construction process comprises the steps of girder section installation, crane movement, stay cable tensioning, closure gap observation, closure section matching and cutting, transportation positioning and hoisting, single-side welding, elevation adjustment of a loose hoisting point, proper temperature opposite pulling, closure gap welding and temporary component and crane removal. The construction process comprises the steps of girder section installation, crane movement, stay cable tensioning, closure gap observation, closure section matching and cutting, transportation positioning and hoisting, single-side welding, elevation adjustment of a loose hoisting point, proper temperature opposite pulling, closure gap welding and temporary component and crane removal. According to the method, on the premise that the closure quality and safety of the steel box girder are guaranteed, the problem that the closure temperature is lower than the designed closure temperature is well solved, the construction efficiency is high, and economic benefits and social benefits are obvious; and after implementation, each index meets the design and specification requirements.

Description

Technical Field

[0001] The invention relates to a closure construction method for steel box beams of a pier-tower-beam consolidation system, in particular to a construction method for solving the problem of temperature being lower than a designed closure temperature by applying an extra tension force externally. Background Art

[0002] In the current construction of the middle span of a cable-stayed bridge, the conventional construction method is to place water tanks or counterweights on the cantilevers on both sides for counterweight leveling. The full floating or semi-floating system needs to use jacking to control the closure distance at a suitable temperature, and then use a rigid skeleton composed of a large number of steel sections to lock it, and finally weld both sides at the same time when closing. This construction method has a slow leveling speed, consumes a lot of steel, and the jacking process is not suitable for the pier tower beam consolidation system; the temperature requirement is high when locking, and construction can only be carried out when the design temperature is reached, the time period requirement is high, and the amount of closure welding is large, so the overall benefit is not good. Summary of the invention

[0003] Therefore, in order to solve the above-mentioned deficiencies, the present invention provides a method for the construction of steel box girder closure in a pier-tower-beam consolidation system; under the premise of ensuring the quality and safety of the steel box girder closure, the method well solves the problem that the closure temperature is lower than the designed closure temperature, the construction efficiency is fast, and the economic and social benefits are obvious; after implementation, all indicators meet the design and specification requirements.

[0004] The present invention is achieved by constructing a pier tower beam consolidation system steel box beam closure construction method, which is characterized by: the construction process is as follows: (1) Beam end installation: S16 beam section installation on the south bank and N16 beam section installation on the north bank.

[0005] (2) Simulation of moving the crane back and hanging the S16 cable on the south bank: After the S16 steel box girder is welded, the lifting point is released, the lower cross beam behind the crane is removed, and the bridge deck crane is moved back 3.1m and positioned next to the anchor plate of the S15 steel box girder. The rear anchor point is anchored next to the anchor plate of the S14 beam section, and the distance between the front support point and the rear anchor point is 15.5m. The scissor brace of the front column of the crane is removed, the inclined cable is passed through the middle of the crane, and the S16 inclined cable is installed to complete the tensioning.

[0006] (3) Simulation of moving the crane forward on the north bank, hanging the N16 cable and hoisting the F beam segment: After the welding of the N16 steel box girder is completed, the lifting point is released, the redundant parts of the lifting equipment are removed, and the bridge deck crane is moved forward 12.4m and positioned next to the anchor plate of the N16 steel box girder. The rear anchor point is anchored next to the anchor plate of the N15 beam segment. The distance between the front support point and the rear anchor point is 15.5m. The lower cross beam behind the crane is removed. Install the N16 inclined cable and complete the tensioning according to the previous process.

[0007] (4) Observation at the closure: When installing the S15 (N15) and S16 (N16) beam sections, joint measurements will be conducted on the bridge deck cross-section monitoring points on the south and north banks to facilitate timely adjustment of the axial deviation. Before closure, the structure will be subjected to multiple 48-hour temperature observations. Measurement frequency: once every 2 hours during the day and once every 1 hour at night; the measurement contents are as follows: ① The elevation of the three beam sections at the front end of the cantilever, the tower deviation and the length at the top and bottom of the joint.

[0008] ② Cable tensions of the first three pairs (tentative) of inclined cables.

[0009] ③Temperature field of cable-beam tower and atmospheric temperature.

[0010] (5) Cutting of the joint section: After the cutting length of the joint section is determined, the cutting line is marked on the top and bottom plates of the steel box girder joint section using the original reference line, and the joint section is cut on site according to the cutting line using a semi-automatic flame cutting machine. Operators can only carry out the construction after training or technical briefing, and the construction must be carried out in accordance with the cutting process. During the cutting process, the operator must not leave the operation site and must always pay attention to the cutting situation.

[0011] (6) Lifting of the joint section: The cut F beam section of the joint section is transported to the bridge site. When the joint section is ready to enter the joint mouth, the lifting of the joint section begins.

[0012] (7) Joint mouth matching: ① Adjustment of the misalignment at the closure: The misalignment at the closure mainly refers to the axial deviation and elevation deviation. The misalignment is mainly controlled by joint measurement during the installation of the beam section before closure, and timely correction of each section is carried out, supplemented by the adjustment of the deviation at the closure. The elevation deviation is adjusted by cable force, and the tensioning jack is reserved at the tensioning end of the cable tower during closure. The axis deviation is adjusted by cross-pull of the chain hoist, and the elevation deviation is adjusted by fine-tuning the cable force.

[0013] ② Selection of weight for closure mouth: Weight for closure mouth is achieved by first welding the F beam section of the closure section to the S16 steel box beam on the south bank to form a whole, simulating counterweight, and then loosening the crane lifting point on the north bank to align the elevations of the north and south banks of the closure mouth.

[0014] After the No. 16 cable-stayed cables on the north and south banks were tensioned, the south bank was 6.9 cm higher than the north bank. After the F beam section was hoisted on the north bank, it would deflect 23 cm, a total of 30 cm. The effective space distance between the hoist and the crane was 1 m, which met the hoisting requirements. After welding the south bank side first, the F beam section was located on the south bank side, and then the hoisting point of the crane on the north bank was loosened to make the steel beams on both sides level.

[0015] ③ Adjustment of the weld width of the joint: After the joint elevation matches, install the tensioning device. The tensioning device is designed on the top and bottom plates, at the intersection of the two middle longitudinal webs and the transverse diaphragm. The tensioning device is arranged in 4 groups with a total of 8 tensioning points, and is composed of 8 13 φ15.2s steel strands and 8 200T jacks. During the tensioning, the same central control system is used for synchronous lifting to ensure that the force is as consistent as possible. The tensioning force is initially designed to be 800T. During the tensioning, the change of the weld width of the joint is observed synchronously, and the control is mainly based on the weld width and supplemented by the tensioning force. Because the tensioning device needs to be placed for a long time after the tensioning, a layer of insulating fireproof material is placed on the outside of the steel strand to prevent the steel strand from being damaged during the welding process of the weld. The tensioning device is only set as an additional external force. After the tensioning is completed, a temporary locking device is used to lock the joint, so that the locking device is used as the main force in subsequent work.

[0016] ④ Locking of the closure: The temporary locking of the closure uses 34 PSB1080 φ40mm fine-rolled threaded steel bars as tie rods, which are arranged on the top and bottom plates, with a total of 10 locations on one section, and can withstand a total tensile force of 1500T.

[0017] (8) Welding of the joint section: After the joint section is hoisted to the designed elevation, the F beam section and the S16 beam section are matched and locked before welding. Then the tension device is arranged, the elevation of the F beam section and the N16 beam section is adjusted, the tension force is applied at a suitable temperature, and the weld width is adjusted before locking and welding. The principle to be followed in the welding of the joint mouth is to polish the weld mouth in advance, quickly lock the two ring mouths, reserve time for welding as much as possible, and complete the necessary welds within a period of time when the temperature is relatively stable. The welding is carried out first on the longitudinal web, and the two longitudinal webs are welded simultaneously by two skilled welders. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Flow chart of mid-span closure; Figure 2-Figure 5 This is the construction flow chart for the middle span closure; Figure 6 Layout diagram of measuring points at the closure. DETAILED DESCRIPTION

[0020] The following will be combined with the attached Figure 1-Figure 6 The present invention is described in detail, and the technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] The present invention provides a method for the closure of steel box girders in a pier-tower-beam consolidation system by improving the method. The external tension is used to simulate the temperature drop gradient, so that the temperature stress generated after the subsequent bridge is heated up is offset by the external tension, so that it is consistent with the design temperature. By controlling the tension, the closure can be carried out under any low temperature conditions, thus breaking the traditional closure construction process of cable-stayed bridges and providing experience and technical reference for the closure of steel box girders in a pier-tower-beam consolidation system. Through the successful example of the closure process of adjusting the tension control in the closure project of the cable-stayed bridge in Sichuan Province, the construction technical measures and key points of attention of the process are introduced.

[0022] Features of the method: This method mainly adopts the construction technology of tension-controlled closure. Compared with the traditional technology, this technology has the following characteristics: (1) By welding first and then welding, the amount of welding at the same time during the joint closure can be reduced.

[0023] (2) By adjusting the release force under the crane, leveling can be achieved quickly without the need for counterweight facilities such as water tanks and sandbags.

[0024] (3) Apply a tensile force and set a temporary matching locking device, so that the joint can be closed under any low temperature conditions.

[0025] Scope of application: The cable-stayed bridge steel box girder closure project that meets the following points can be constructed using the tension-controlled closure process: (1) Projects where the closure temperature does not reach the design temperature.

[0026] (2) It is applicable to full floating, semi-floating and pier-tower-beam consolidation systems.

[0027] Process principle: Use external tension to simulate the gradient of temperature drop, so that when the bridge is subsequently heated up, the temperature stress generated is offset by the external tension, making it consistent with the design temperature.

[0028] The construction process and operation points of the present invention, the closure process of the steel box girder of the pier tower beam consolidation system is as follows Figure 1-Figure 5 ; (1) Beam end installation: S16 beam section installation on the south bank and N16 beam section installation on the north bank. Figure 2 As shown; (2) Simulation of moving the crane back and hanging the S16 cable on the south bank: After the S16 steel box girder is welded, the lifting point is released, the lower cross beam behind the crane is removed, and the bridge deck crane is moved back 3.1m and positioned next to the anchor plate of the S15 steel box girder. The rear anchor point is anchored next to the anchor plate of the S14 beam section, and the distance between the front support point and the rear anchor point is 15.5m. The scissor brace of the front column of the crane is removed, the inclined cable is passed through the middle of the crane, and the S16 inclined cable is installed to complete the tensioning.

[0029] (3) Simulation of moving the crane forward on the north bank, hanging the N16 cable and hoisting the F beam segment: After the welding of the N16 steel box beam is completed, the lifting point is released, the redundant parts of the lifting equipment are removed, and the bridge deck crane is moved forward 12.4m and positioned next to the anchor plate of the N16 steel box beam. The rear anchor point is anchored next to the anchor plate of the N15 beam segment. The distance between the front support point and the rear anchor point is 15.5m. The lower cross beam behind the crane is removed. Install the N16 inclined cable and complete the tensioning according to the previous process. Figure 3 shown.

[0030] (4) Observation at the closure: When installing the S15 (N15) and S16 (N16) beam sections, joint measurements will be conducted on the bridge deck cross-section monitoring points on the south and north banks to facilitate timely adjustment of the axial deviation. Before closure, the structure will be subjected to multiple 48-hour temperature observations. Measurement frequency: once every 2 hours during the day and once every 1 hour at night; the measurement contents are as follows: ① The elevation of the three beam sections at the front end of the cantilever, the tower deviation and the length at the top and bottom of the joint.

[0031] ② Cable tensions of the first three pairs (tentative) of inclined cables.

[0032] ③Temperature field of cable-beam tower and atmospheric temperature.

[0033] 14 observation points are arranged on the joint section and named according to the beam section number, such as S15-1 and N15-1, which respectively represent the No. 1 measuring point on the joint section of the S15 beam section and the N15 beam section.

[0034] The elevation of the 5 sections of beams at the front end of the cantilever is observed at points 2 and 7 on the cross diaphragm of the observation beam section.

[0035] The closure temperature and time period are determined by analyzing and fitting the observed data. In principle, the closure temperature should be selected to have a longer stable period. A longer stable period is convenient for locking the closure mouth, coding and other operations with sufficient time.

[0036] The installed beam sections at both ends of the joint mouth were observed multiple times under different temperature conditions, and the total length of the installed steel box beams at both ends of the joint mouth under various temperature conditions was obtained. The total length of the installed steel box beams at both ends of the joint mouth at the design temperature was calculated based on the above measurement values, and the length value of the steel box beam of the joint section at the design temperature was calculated. The manufacturing parameters of the joint section were calculated based on the observation results of temperature influence.

[0037] If the actual temperature is inconsistent with the design reference temperature, the length of the joint section must also take into account the temperature correction. The calculation formula for the length of the joint section is: In the formula, L x is the cutting length; LS is the design length, which is taken as 4.4m; Lt is the temperature influence (if the actual closure temperature is greater than the design reference temperature, it is a positive value, otherwise it is a negative value); L y The compression deformation of the joint section from the installation of the joint section to the stability of the completed bridge can be calculated and analyzed by the full bridge construction control theory; L c is the error in the total length of the installed beam section in the middle span (if the actual beam length is greater than the designed beam length, a positive value is taken; otherwise, a negative value is taken). L h is the weld width; L d It is the push adjustment amount.

[0038] (5) Cutting of the joint section: After the cutting length of the joint section is determined, the cutting line is marked on the top and bottom plates of the steel box girder joint section using the original reference line, and the joint section is cut on site according to the cutting line using a semi-automatic flame cutting machine. Operators can only carry out the construction after training or technical briefing, and the construction must be carried out in accordance with the cutting process. During the cutting process, the operator must not leave the operation site and must always pay attention to the cutting situation.

[0039] ① Clean the steel plate before cutting, especially the oil stains on the surface of the steel plate; at the same time, check whether the equipment is operating normally before construction, check whether the cutting torch is vertical to the steel plate being cut, if not, adjust it vertically; check whether various gas sources are sufficient, whether the gas path is unobstructed, whether there is any leakage, and deal with problems in time if found.

[0040] ② Matters needing attention in cutting surface quality. When the oxygen pressure is too high, the incision is too wide, the surface of the incision is rough, and oxygen is wasted; when it is too low, the iron oxide cannot be blown off, and the slag of the incision is easy to stick together and difficult to remove. Therefore, the size of the cutting oxygen pressure should be properly controlled. To control the cutting speed, the slag and sparks fly vertically downward; when the cutting speed is too fast, a large amount of back drag is produced, it is not easy to cut through, the sparks fly backward, and even cause the iron slag to fly upward, which is easy to cause tempering; when the cutting speed is too slow, the edges and corners on both sides of the steel plate melt, and the plate is prone to excessive deformation. Whether the speed of gas cutting is appropriate can be judged and flexibly controlled by observing the flow of slag and listening to the sound produced during cutting. To keep it clean, there should be no iron oxide slag splashes sticking to the nozzle, especially the inner hole of the cutting nozzle should be kept smooth. Careful care and regular maintenance of equipment are important conditions for improving cutting quality and efficiency.

[0041] ③After cutting, the cutting edge should be polished and cleaned in time to remove slag and other debris. The quality of the parts on the cutting edge should meet the requirements of the specification. The allowable deviation of the precision cutting edge is ±2.0mm; the allowable deviation of the manual cutting edge is ±3.0mm. The hardness of the cutting surface shall not exceed HV350; the cutting surface shall not have cracks or other defects that may endanger the performance of the permanent structure, and the arc part shall be polished evenly.

[0042] (6) Lifting of the joint section: The F beam section of the joint section that has been cut is transported to the bridge site. When the joint section is ready to enter the joint mouth, the lifting of the joint section begins. Since the joint mouth is located outside the main channel, it is necessary to report to the maritime department before lifting, and there is no need to ban navigation. Figure 4 shown.

[0043] (7) Joint mouth matching: ① Adjustment of the misalignment at the closure: The misalignment at the closure mainly refers to the axial deviation and elevation deviation. The misalignment is mainly controlled by joint measurement during the installation of the beam section before closure, and timely correction of each section is carried out, supplemented by the adjustment of the deviation at the closure. The elevation deviation is adjusted by cable force, and the tensioning jack is reserved at the tensioning end of the cable tower during closure. The axis deviation is adjusted by cross-pull of the chain hoist, and the elevation deviation is adjusted by fine-tuning the cable force.

[0044] ② Selection of weight for closure mouth: Weight for closure mouth is achieved by first welding the F beam section of the closure section to the S16 steel box beam on the south bank to form a whole, simulating counterweight, and then loosening the crane lifting point on the north bank to align the elevations of the north and south banks of the closure mouth.

[0045] After the No. 16 cable-stayed cables on the north and south banks were tensioned, the south bank was 6.9 cm higher than the north bank. After the F beam section was hoisted on the north bank, it would deflect 23 cm, a total of 30 cm. The effective space distance between the hoist and the crane was 1 m, which met the hoisting requirements. After welding the south bank side first, the F beam section was located on the south bank side, and then the hoisting point of the crane on the north bank was loosened to make the steel beams on both sides level.

[0046] ③ Adjustment of the weld width of the joint: After the joint elevation matches, install the tensioning device. The tensioning device is designed on the top and bottom plates, at the intersection of the two middle longitudinal webs and the transverse diaphragm. The tensioning device is arranged in 4 groups with a total of 8 tensioning points, and is composed of 8 13 φ15.2s steel strands and 8 200T jacks. During the tensioning, the same central control system is used for synchronous lifting to ensure that the force is as consistent as possible. The tensioning force is initially designed to be 800T. During the tensioning, the change of the weld width of the joint is observed synchronously, and the control is mainly based on the weld width and supplemented by the tensioning force. Because the tensioning device needs to be placed for a long time after the tensioning, a layer of insulating fireproof material is placed on the outside of the steel strand to prevent the steel strand from being damaged during the welding process of the weld. The tensioning device is only set as an additional external force. After the tensioning is completed, a temporary locking device is used to lock the joint, so that the locking device is used as the main force in subsequent work.

[0047] ④ Locking of the closure: The temporary locking of the closure uses 34 PSB1080 φ40mm fine-rolled threaded steel bars as tie rods, which are arranged on the top and bottom plates, with a total of 10 locations on one section, and can withstand a total tensile force of 1500T.

[0048] (8) Welding of the joint section: After the joint section is hoisted to the designed elevation, match the F beam section and the S16 beam section, lock them and then weld them. Then arrange the tensioning device, adjust the elevation of the F beam section and the N16 beam section, apply the tensioning force at the appropriate temperature, adjust the weld width and then lock and weld. The principle to be followed in the joint welding is to polish the weld in advance, quickly lock the two rings, reserve as much time as possible for welding, and complete the necessary welds within a period of time when the temperature is relatively stable. The welding shall give priority to the longitudinal web, and the two longitudinal webs shall be welded simultaneously by two skilled welders. Figure 5 shown.

[0049] Figure 2-Figure 5 The flow chart of the mid-span closure construction is as follows: Step 1: 1. Installation of S16 beam section on the south bank and N16 beam section on the north bank; Step 2: 2. The crane on the south bank is moved back 3.1m (the rear lower beam is removed), and the No. S16 inclined cable on the south bank is hung and tensioned; 3. The crane on the north bank adjusts the hoisting device and moves forward 12.4m. The rear lower crossbeam is removed, and the No. N16 cable on the north bank is hung and tensioned; Step 3: 4. Continuous observation for 48 hours, once every 2 hours during the day and once every 1 hour at night (14 measuring points of N16 / S16, 8 on the top plate and 6 on the bottom plate); 5. Provide matching and cutting data according to the joint test data monitoring, complete matching and cutting in Chongqing or on-site and transport to the destination; 6. Complete the hoisting posture adjustment of the F beam section according to the monitoring instructions and lift the F beam section (the estimated seam width is 8cm); Step 4: 7. Match the south bank joint, weld the longitudinal web, girth weld, and install U-rib stiffeners or patching sections; 8. Release the force at the crane lifting point and level the north bank joint; 9. Install the tensioning device and wait for the optimal closure temperature; 10. Apply pulling force to complete temporary matching and locking; 11. Weld the longitudinal web, remaining welds and U-rib patching sections to complete the jointing construction; 12. All cranes in the middle span were removed, and the cable tension in the area affected by the closure was adjusted to meet the conditions for auxiliary construction. The transformation of the closure system of the entire bridge was completed.

[0050] The benefit analysis is reflected in the construction period and economic effect: compared with the traditional sandbag or water tank counterweight, the direct use of no additional counterweight method, using the steel box girder's own weight as a leveling measure, directly saves 3 days of construction period, with high precision and high efficiency; the use of a quick locking joint device, compared with the traditional large-scale steel welding locking, directly saves 2 days of construction period, and the temperature can be controlled at any time, which is convenient and fast; the entire construction method reduces the use of steel, saves counterweights and transportation equipment, reduces manpower and material resources, directly saves construction costs of 3.26 million yuan, and safety and quality are effectively guaranteed.

[0051] Social effect: After using this method, the problem of joint closure under low temperature conditions is effectively solved. The joint closure of steel box girders is of excellent quality and has strong operability, saving construction costs, achieving good social benefits, and can be applied to other types of bridges. This method has been well received by owners, designers, and supervision companies during the joint closure construction. This method has played a positive role in enriching and developing the construction technology of similar bridges and has broad application prospects.

[0052] Application example: Luzhou Shenbicheng Yangtze River Bridge, constructed by Sichuan Highway and Bridge Construction Group Co., Ltd., is located between Baisha Town and Daqiao Town in Hejiang County. The south bank of the bridge is connected to G353 (formerly S308), and the north bank is connected to S438. It crosses the Yangtze River in a north-south direction and is the main crossing channel in Hejiang County. This project is a double-tower, single-column, central parallel cable-plane hybrid beam cable-stayed bridge with a main span of 520m. The main bridge span is arranged as 44.2+56+59.8+520+59.8+56+44.2m, with a steel box girder in the middle span and a cast-in-place concrete box girder in the side span. The consolidation system of piers, towers and beams is adopted. The main pier has no support, and two auxiliary piers are set on each of the two side spans. 720 and 640 expansion joints are set at the junction piers and abutments. The middle span of the main bridge of Shenbicheng Yangtze River Bridge adopts a flat steel box girder, which is a flat streamlined section with a wind nozzle. The top width of the beam is 27.5m (excluding the wind nozzle), the bottom plate width is 17.2m, the beam height is 3.5m, and the wind nozzle length is 1.5m. Two middle longitudinal webs are set in the box girder with a spacing of 2.29m. The inclined cable is anchored on the inner side of the middle longitudinal web. The steel box girder of the whole bridge is divided into 9 types, A, A1, B, B1, C, C1, D, E, and F, with a total of 35 beam sections. Among them, E is a steel-concrete combined section; D is a beam section adjacent to the steel-concrete combined section; A, A1, B, B1, C, C1 are standard beam sections; F is a mid-span closure section. The standard segment length of the main beam is 15.5m, the maximum height of the bottom of the steel box girder from the river surface is 60m (dry season), the net weight of the E segment is 244T, and the maximum net weight segment is the C segment 330T. Using a new steel box girder closure construction technology, construction began on December 27, 2022, the hoisting operation was completed on January 4, 2023, and the locking was completed on January 6, 2023, with a construction period of 11 days.

[0053] After using this method, the problem of steel box girder closure under low temperature conditions is effectively overcome, the closure welding time is greatly shortened, and the construction cost is saved.

[0054] Practice has proved that this construction method is highly operational, has great application prospects in the field of cable-stayed bridge closure construction, and has outstanding social and economic benefits.

[0055] Brief description of the method content: External tension is used to simulate the gradient of temperature drop, so that the temperature stress generated after the subsequent bridge temperature rises is offset by the external tension, making it consistent with the design temperature. By controlling the tension size, the closure can be carried out under any low temperature conditions, thus breaking the traditional closure construction process of cable-stayed bridges and providing experience and technical reference for the closure of steel box girders in the pier-tower-beam consolidation system.

[0056] Shenbicheng Yangtze River Bridge in Luzhou City is located between Baisha Town and Daqiao Town in Hejiang County. The south bank of the bridge is connected to G353 (formerly S308) and the north bank is connected to S438. It crosses the Yangtze River in a north-south direction. It is a double-tower, single-column, central parallel cable-plane hybrid beam cable-stayed bridge with a main span of 520m.

[0057] The middle span of the main bridge of Shenbicheng Yangtze River Bridge adopts a flat steel box girder, which is a flat streamlined section with a wind nozzle. The top width of the beam is 27.5m (excluding the wind nozzle), the bottom plate width is 17.2m, the beam height is 3.5m, and the wind nozzle length is 1.5m. Two middle longitudinal webs are set in the box girder with a spacing of 2.29m. The inclined cable is anchored on the inner side of the middle longitudinal web. The steel box girder of the whole bridge is divided into 9 types, A, A1, B, B1, C, C1, D, E, and F, with a total of 35 beam sections. Among them, E is a steel-concrete combined section; D is a beam section adjacent to the steel-concrete combined section; A, A1, B, B1, C, C1 are standard beam sections; F is a mid-span closure section. The standard segment length of the main beam is 15.5m, the maximum height of the bottom of the steel box girder from the river surface is 60m (dry season), the net weight of the E segment is 244T, and the maximum net weight segment is the C segment 330T.

[0058] First, install the beam section before the joint section of the south and north banks; move the crane on the south bank back 3.1m, hang the S16 cable on the south bank and tension it; adjust the hoist on the north bank, move forward 12.4m, hang the N16 cable on the north bank and tension it; observe continuously for 48 hours, every 2 hours during the day and every 1 hour at night (14 measuring points of N16 / S16, 8 top plates and 6 bottom plates); give the matching data according to the joint measurement data monitoring, complete the matching in Chongqing or on-site and transport it to the site; According to the monitoring instructions, the lifting posture of the F beam section is adjusted and the F beam section is lifted; the south bank joint mouth is matched, the longitudinal web and circumferential welds are welded, and the U-rib stiffener or patching section is installed; the force is released at the crane lifting point to wait for the optimal jointing temperature; the tension is applied to complete the temporary matching and locking; the longitudinal web, the remaining welds and the U-rib patching section are welded to complete the jointing construction; all cranes in the middle span are removed, the cable tension of the inclined cables in the jointing-affected area is adjusted, and the conditions for ancillary construction are met, and the transformation of the whole bridge jointing system is completed.

[0059] The innovation of the present invention is: 1. Use a crane for leveling, which is faster and does not require water tank sandbags for counterweights.

[0060] 2. Use high-quality rolled threaded steel for temporary locking, eliminating the need to use a large amount of steel sections and reducing construction costs.

[0061] 3. By adjusting the external pulling force, locking can be performed under any low temperature conditions to reach the designed closure temperature.

[0062] Technical level and technical difficulty (including comparison with similar technical levels at home and abroad): The new pier-tower-beam consolidation system steel box girder closure construction method mainly uses a tensioning device to adjust the tensioning force to simulate the optimal closure temperature. The tensioning device is designed on the top and bottom plates, at the intersection of the two middle longitudinal webs and the transverse diaphragm, and is composed of steel strands and jacks. The tensioning device is only set as an additional external force. After the tensioning is completed, a temporary locking device is used to lock the closure mouth, so that the locking device will bear the force in subsequent work.

[0063] In addition, the method also uses the method of moving the crane and adjusting the lifting force to quickly level the two cantilever ends. When closing the joint, the counterweights on both sides are welded to the higher end by the closing section, and then the lifting point is loosened to allow the closing section to be used as a counterweight, so that the two sides are balanced and the work efficiency is high.

[0064] The construction technology of cable-stayed bridge steel box girder closure is basically the conventional closure method at home and abroad, and the jacking is used to control the length of the closure section. In the pier-tower-beam consolidation system, the jacking process cannot be used. This project is the first to use the additional tension method in the closure of the steel box girder of the pier-tower-beam consolidation system to simulate the temperature drop gradient, control the weld width, use steel strands and jacks, and make tensioning convenient; and the closure counterweight is used by first welding and then releasing the force from the crane, so that the closure section can be used as a counterweight, and the leveling speed is fast, and no other counterweight facilities are required. The efficiency of this closure process is significantly improved, and it is very valuable for promotion.

[0065] After using this method, the problem of steel box girder closure under low temperature conditions is effectively solved. The tensioning process is applicable to various cable-stayed bridge systems and is widely used. The quality and safety can be fully guaranteed, and the construction cost is also saved. This method does not need to rely on the jacking process, which increases the applicability and economy.

[0066] With the continuous development of my country's transportation industry, bridge projects are still being built in large quantities, and the scale of projects is constantly expanding. Cable-stayed bridge steel box girder closure will be widely used. The promotion and use of this method under similar bridge types will achieve good time efficiency and economic benefits.

[0067] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for closure construction of steel box beams in a pier-tower-beam consolidation system, characterized in that: The construction process is as follows; (1) Beam end installation: installation of S16 beam section on the south bank and installation of N16 beam section on the north bank; (2) Simulation of moving the crane backward and hanging the S16 cable on the south bank: After the S16 steel box girder is welded, the lifting point is released, the rear lower crossbeam of the crane is removed, and the bridge deck crane is moved back 3.1m and positioned next to the anchor plate of the S15 steel box girder. The rear anchor point is anchored next to the anchor plate of the S14 beam section, and the distance between the front support point and the rear anchor point is 15.5m; the scissor brace of the front column of the crane is removed, the inclined cable is passed through the middle of the crane, and the S16 inclined cable is installed to complete the tensioning; (3) Simulation of moving the crane forward on the north bank, hanging the N16 cable and hoisting the F beam segment: After the welding of the N16 steel box girder is completed, the lifting point is released, the redundant parts of the lifting equipment are removed, and the bridge deck crane is moved forward 12.4m and positioned next to the anchor plate of the N16 steel box girder. The rear anchor point is anchored next to the anchor plate of the N15 beam segment. The distance between the front support point and the rear anchor point is 15.5m. The lower crossbeam behind the crane is removed; the N16 inclined cable is installed and tensioned according to the previous process; (4) Observation at the closure: When the S15 (N15) and S16 (N16) beam sections are installed, joint measurements will be conducted at the monitoring points on the bridge deck cross sections on the south and north banks to facilitate timely adjustment of the axial deviation. Before closure, the structure will be subjected to multiple 48-hour temperature observations. The measurement frequency is once every 2 hours during the day and once every hour at night. The measurement contents are as follows: ① The elevation of the three sections of beams at the front end of the cantilever, the tower deviation and the length of the top and bottom of the joint; ② Cable forces of the first three pairs (tentative) of inclined cables; ③ Temperature field of cable-beam tower and atmospheric temperature; (5) Cutting of the joint section: After the cutting length of the joint section is determined, the cutting line is marked on the top and bottom plates of the steel box girder joint section using the original reference line, and the joint section is cut on site according to the cutting line using a semi-automatic flame cutting machine; operators can only carry out the construction after training or technical briefing, and the construction must be carried out in accordance with the cutting process; during the cutting process, the operator must not leave the operation site and must always pay attention to the cutting situation; (6) Lifting of the closure section: transport the cut F beam section of the closure section to the bridge site, and start lifting the closure section when the closure section is ready to enter the closure mouth; (7) Joint mouth matching: ① Adjustment of the misalignment at the closure: The misalignment at the closure mainly refers to the axial deviation and elevation deviation. The misalignment is mainly controlled by joint measurement during the installation of the beam section before closure, and timely correction of each section is carried out, supplemented by adjusting the deviation at the closure. The elevation deviation is adjusted by cable force, and the tensioning jack is reserved at the tensioning end of the cable tower during closure. The axis deviation is adjusted by cross-pull of chain hoists, and the elevation deviation is adjusted by fine-tuning the cable force. ② Selection of closure weight: The closure weight is first welded to the closure section F beam section and the S16 steel box beam on the south bank to form a whole, simulate the counterweight, and then loosen the crane lifting point on the north bank to align the elevations of the north and south banks of the closure; After the No. 16 cable-stayed cables on the north and south banks were tensioned, the south bank was 6.9 cm higher than the north bank. After the F beam section was hoisted on the north bank, it would deflect 23 cm, a total of 30 cm. The effective space distance between the hoist and the crane was 1 m, which met the hoisting requirements. After welding the south bank side first, the F beam section was located on the south bank side, and then the hoisting point of the crane on the north bank was loosened to make the steel beams on both sides level. ③ Adjustment of the weld width of the joint: After the joint elevation is matched, install the tensioning device; the tensioning device is designed on the top and bottom plates, at the intersection of the two middle longitudinal webs and the transverse diaphragm; the tensioning device is arranged in 4 groups with a total of 8 tensioning points, using 8 13 φ15.2s steel strands and 8 200T jacks. During the tensioning, the same central control system is used for synchronous lifting to ensure consistent force. The tensioning force is initially designed to be 800T; During the pulling process, the change in the weld width of the joint is observed simultaneously, and the control is mainly based on the weld width and supplemented by the pulling force. Because the pulling device needs to be placed for a long time after pulling, a layer of insulating fireproof material is placed on the outside of the steel strand to prevent damage to the steel strand during the welding process; The pulling device is only set as an additional external force. After the pulling is completed, a temporary locking device is used to lock the joint mouth, so that the locking device is used as the main force in subsequent work; ④ Closure locking: The temporary locking of the closure uses 34 PSB1080 φ40mm finely rolled threaded steel bars as tie rods, which are arranged on the top and bottom plates, with a total of 10 locations on one section, with a total resistance of 1500T tension; (8) Welding of the joint section: After the joint section is hoisted to the designed elevation, the F beam section and the S16 beam section are matched and locked before welding. Then the tensioning device is arranged, the elevation of the F beam section and the N16 beam section is adjusted, the tensioning force is applied at an appropriate temperature, and the weld width is adjusted before locking and welding. The principle to be followed in the welding of the joint mouth is to polish the weld mouth in advance, quickly lock the two ring mouths, reserve time for welding as much as possible, and complete the necessary welds within a period of relatively stable temperature. The welding is carried out preferentially on the longitudinal web, and the two longitudinal webs are welded simultaneously by two skilled welders.

Images