Large-span simply-supported steel box girder incremental launching construction technology

Abstract

The invention provides a large-span simply-supported steel box girder incremental launching construction technology, and belongs to the technical field of steel box girder incremental launching construction.The construction technology comprises the following steps of temporary support structure and foundation construction, temporary support arrangement construction, steel box girder on-site hoisting, namely secondary assembling, steel box girder hoisting position adjustment and steel box girder bridge position construction. The steel box girder pushing construction comprises the steps of front and rear guide girder structure construction, pushing system technical parameter design, pushing route design, pushing equipment installation, pushing construction principle analysis, steel box girder pushing construction, pushing and deviation adjustment, anti-sliding measure setting, guide girder upsetting and girder falling. Pushing construction is adopted on site, no auxiliary pier is arranged in the middle of the steel box girder with the whole span of 70 m, equipment and manpower for arranging a large number of auxiliary piers are saved, the construction period is short, the cost is saved, meanwhile, bolting connection is adopted for the steel box girder and the cross beam on site, high-precision control is achieved, and the situation that the overturning moment is large in the maximum cantilever state in the pushing process is avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of incremental launching construction of steel box girders, and particularly to an incremental launching construction process for simply supported steel box girders with large spans. Background Art

[0002] At present, for straight-line steel box girders in China, the incremental launching type is mostly adopted, and the deviation correction control is simple. However, when spanning complex alignments, the hoisting process is mostly adopted, which has a great impact on traffic. Moreover, when spanning existing bridges, the hoisting difficulty is even greater. The self-weight of the steel box girder is large, resulting in large losses of the bottom plate of the steel box girder and greater damage to the painted topcoat. The main reason is that the frictional resistance between the bottom plate and the slideway is too large.

[0003] The existing incremental launching construction basically sets corresponding auxiliary support piers beside the piers. At present, for a simply supported steel box girder with a single span of 70 meters, and affected by natural conditions such as debris flow gullies under the bridge site, it is impossible to erect incremental launching auxiliary piers at the mid-span, and it is impossible to implement the conventional incremental launching process. Since the incremental launching span reaches 70 meters, the overturning moment is large in the maximum cantilever state during the incremental launching process, and the overall incremental launching construction is difficult. At the same time, there is a debris flow gully under the bridge site of the bridge, and due to the inability of large hoisting equipment to reach, the hoisting process cannot be adopted. The traditional incremental launching and assembling is directly carried out on the piers or auxiliary piers, so that the beam dropping height during incremental launching is not large. However, when it is impossible to assemble on the piers due to natural environment influence and can only be assembled on the roadbed, when the beam dropping height during incremental launching is very large, the beam dropping construction is difficult. Therefore, it is necessary to design an incremental launching construction process for simply supported steel box girders with large spans. Summary of the Invention

[0004] The purpose of the present invention is to provide an incremental launching construction process for simply supported steel box girders with large spans, and solve the technical problems that when the existing simply supported steel box girders with a single span of 70 meters cannot set auxiliary support piers and cannot assemble the box girder at the same horizontal plane of the piers, it causes difficult beam dropping construction and large overturning moment, resulting in difficult overall incremental launching construction.

[0005] In order to achieve the above purpose, the technical scheme adopted by the present invention is as follows:

[0006] An incremental launching construction process for simply supported steel box girders with large spans, the construction process includes the following steps:

[0007] Step 1: Construction of the temporary support structure and foundation;

[0008] Step 2: Construction of the temporary support layout;

[0009] Step 3: On-site hoisting of the steel box girder, that is, secondary assembly;

[0010] Step 4: Adjust the hoisting position of the steel box girder;

[0011] Step 5: Construction of the steel box girder at the bridge site;

[0012] Step 6: Jacking construction of the steel box girder, including the construction of front and rear guiding beam structures, the design of technical parameters of the jacking system, the design of the jacking route, the installation of jacking equipment, the analysis of the jacking construction principle, the jacking construction of the steel box girder, jacking and deviation adjustment, the setting of anti-slip measures, the guiding beam getting on the pier and the girder landing.

[0013] Further, the specific process of Step 1 is as follows: Step 1.1: Reassembling the support structure twice. The on-site second-assembly jig uses a structure supported by piers. First, set up the piers in the site. After the steel box girder transport vehicle arrives, directly hoist the steel box girder above the piers for secondary assembly. The main structure of the pier is a φ219×10 steel pipe, with a 12×240×240 cover plate set on it. An adjusting tooth plate is placed on the cover plate to adjust the overall elevation. A 12×400×400 steel plate is set below as the base, with bolt holes opened around it. Use anchor bolts to firmly connect the pier to the ground. The height of the pier is 1400 mm.

[0014] Step 1.2: Setting up the jacking support structure. The jacking support structure includes the temporary support in the assembly area, the jacking temporary support in the concrete beam erection area, and the jacking temporary support on both sides of the permanent piers.

[0015] The steel pipe columns of the temporary support are composed of 350×10 steel pipe columns. The jacking equipment is directly placed on the foundation. The jacking temporary support in the concrete beam erection area is composed of 350×10 steel pipe columns. The jacking equipment is directly placed at the position of the concrete beam surface on the column top. Affected by the cross slope of the precast beam deck, when installing the temporary pier, it is necessary to level the concrete on the concrete beam surface. The temporary piers in the concrete beam erection area are set at the top of the permanent piers of the concrete beam. The permanent piers and the two ends of the concrete beam on the pier top bear the fulcrum reaction force during the jacking process. The temporary piers are hoisted by a crane and directly installed on the embedded steel plate of the foundation and welded and fixed to the embedded steel plate.

[0016] The steel pipe columns of the jacking temporary support on both sides of the permanent piers are composed of 400×20 steel pipe columns. The jacking equipment is directly placed on the distribution beam at the top of the temporary pier. On the side with the precast beam, the jacking support is temporarily connected to the precast beam that has been installed to enhance its longitudinal stability.

[0017] Due to the large set value of the girder landing height, in order to increase the moment of inertia of the support section, add full-length stiffeners around the steel pipe to increase the support section to 620*620 mm and enhance its stability.

[0018] When the steel box girder lands, place 10 channel steels on the transverse connection system set on the jacking support as the skeleton, and place wooden planks above as a temporary construction platform. When the height of the support gradually decreases, the height of the transverse connection and the construction platform also decreases accordingly. Reinforcing bars and green nets are used as edge protection on both sides of the construction platform.

[0019] Step 1.3: Construction of the support foundation. The temporary support foundation is an enlarged reinforced concrete foundation with a plane size of 4m × 4m and a thickness of 1m. After ground treatment, the characteristic value of its bearing capacity shall not be less than 222.9 kPa.

[0020] 3. A jacking construction process for simply supported steel box girders with a large span according to claim 1, characterized in that: the specific process of step 2 is as follows:

[0021] Arrangement of the jacking temporary supports, which is divided into three parts: one is the jacking temporary support at the subgrade position; the second is the temporary support at the top of the concrete T-beam column, which is arranged at the tops of the 1# and 2# permanent piers; the third is the jacking temporary support at the completed bridge position, which is arranged at the tops of the 3# and 4# permanent piers.

[0022] Furthermore, the specific process of step 3 is as follows: after the transport vehicle enters the installation site from the construction access road, the truck crane lifts the steel box girder from the transport vehicle and then carries out the on-site installation work; the secondary assembly of the right span steel box girder and the lifting process of the steel box girder are as follows: step 3.1.1: the 100t truck crane is located at the right span small pile number side and lifts the right span WRA1 and WRA2 box girder segments; step 3.1.2: the 100t truck crane repositions and lifts the right span WRB1 and WRC1 segments and the cross section between boxes; step 3.1.3: the 100t truck crane repositions and sets up Set up the missing second-piece piers and re-measure the elevation, and hoist the right span WRB2 and WRC2; Step 3.1.4: The 100t truck crane re-positions and hoists the right span WRD1 and WRE1; Step 3.1.5: The 100t truck crane re-positions, sets up the missing second-piece piers and re-measures the elevation, and hoists the right span WRD2 and WRE2; Step 3.1.6: The 100t truck crane re-positions and hoists the right span WRF1; Step 3.1.7: The 100t truck crane re-positions and hoists the right span WRF2; Step 3.1.8: 1 100t truck crane repositions and hoists the right span WRG1 and WRG2; the left span steel box girder secondary assembly steel box girder hoisting process is as follows: Step 3.2.1: 100t truck crane is located at the small pile number side of the left span and hoists the left span WLA1; Step 3.2.2: 100t truck crane repositions and hoists the left span WLA2; Step 3.2.3: 100t truck crane repositions and hoists the left span WLB1 and WLC1; Step 3.2.4: 100t truck crane repositions, sets up the missing second assembly piers and remeasures the elevation, and hoists Left span WLB2, WLC2; Step 3.2.5: 100t truck crane repositions, hoisting left span WLD1, WLE1; Step 3.2.6: 100t truck crane repositions, erects the missing second-piece piers and remeasures the elevation, hoisting left span WLD2, WLE2; Step 3.2.7: 100t truck crane repositions, hoisting left span WLF1, WLG1; Step 3.2.8: 100t truck crane repositions, erects the missing second-piece piers and remeasures the elevation, hoisting left span WLF2, WLG2;

[0023] Guide beam installation process: After the steel box beam is assembled, piers are placed according to the ground sample line released in advance before the guide beam is hoisted. A 100t truck crane is used to hoist the guide beam. The hoisting process is as follows: Step 3.3.1: The 100t truck crane stands and hoists the D1 segments on both sides; Step 3.3.2: After the D1 segment is firmly connected to the column, the middle cross joint is hoisted; Step 3.3.3: Repeat the above steps to hoist the D2 segment and the middle cross joint; Step 3.3.4: Repeat the above steps to hoist the D3 segment and the middle cross joint; Step 3.3.5: Repeat the above steps to hoist the D4 segment and the middle cross joint.

[0024] Furthermore, the specific process of step 4 is:

[0025] Step 4.1: Determine the hoisting process of the steel box girder segments: (1) Check whether the crane's standing position is safe and accurate, and whether there are any potential hazards around; (2) Connect the wire rope and the lifting lug with a shackle, and connect the other end of the wire rope to the main hook; (3) Ensure that the wire rope is evenly stressed, and the angle between the wire rope and the girder segment is greater than 60°; (4) Before hoisting, tie 2 guy ropes to the girder segment to control the state of the girder segment in the air. After the hook is properly attached to the lifting lug of the steel box girder, the safety officer conducts an inspection and acceptance. After passing the inspection, the hoisting commander then commands the crane to lift the girder segment. When reaching the predetermined lifting height, which is more than 1 m above the top surface of the temporary support, the crane rotates the main boom to above the bridge position. Then, the hoisting commander commands the crane to slowly lower the hook to stop 10 cm above the top surface of the temporary support. Then, with reference to the previously laid out bottom edge line and center line of the steel box girder, the steel box girder is initially positioned, and then the crane continues to slowly lower the hook to the installation position to complete the precise positioning;

[0026] Step 4.2: Steel box girder positioning process: (1) Mark the center line and outer contour line of the girder segment on the transverse distribution beam of the support and on the ground; (2) After the steel girder segment is hoisted and in place, adjust the bottom elevation of the girder through the jack;

[0027] Step 4.3: Measurement and positioning for the steel box girder in place. After the steel box girder is temporarily in place, set up stoppers on both sides of the steel box girder to prevent the steel box girder from slipping and overturning. Fix it with positioning pins at the segmented interface of the steel box girder. The number of positioning pins and bolts is not less than 30% to prevent the displacement of the steel box girder segments. Then, conduct the initial tightening and final tightening of the high-strength bolts; (1) Positioning line. After the pre-assembly inspection is qualified, mark the transverse installation reference lines on both sides of the joint of the girder segment. When the girder segment is hoisted and in place, first conduct the docking of the transverse reference lines. Use a chain block and a jack to make the girder segment meet the in-place standard and the transverse reference lines coincide. After the steel girder is positioned by passing the pin through the bolt hole, insert the high-strength bolts;

[0028] Conduct the measurement for the steel box girder hoisting. The specific process is as follows: (1) During the installation process of the steel box girder, the project surveyors conduct full-process inspection; (2) Before the steel box girder is hoisted, the surveyors lay out the edge line and center line of the steel box girder on the ground in advance to facilitate the hoisting and positioning of the steel box girder. At the same time, check whether the elevation of the top of the concrete pier column is accurate. The top elevation is the bottom elevation of the steel box girder. If the error exceeds the specification requirements, adjust it in time to avoid delaying the steel box girder hoisting; (3) After each span of the steel box girder is hoisted, the surveyors conduct cross-measurement and setting out on the top plate of the installed steel box girder, and at the same time conduct elevation measurement to check whether the steel box girder is correctly installed in the horizontal and vertical directions. If the error exceeds the specification requirements, adjust it in time.

[0029] Furthermore, the specific process of Step 5 is as follows: Step 5.1: Bolt connection. The bolt connection at the bridge site includes the bolt connection between the steel box girder segments and the bolt connection between the cross beam and the steel box girder;

[0030] Installation of high-strength bolts: 1) After the steel beam is hoisted and in place, during the assembly by the support method, 25% of the drift pins shall be driven into each joint as required. During the assembly of the cantilever beam, 50% of the drift pins shall be driven into each joint as required, arranged alternately with the bolt holes. Then check whether all bolt holes can ensure the smooth and free passage of high-strength bolts, and clamp the gap between the connecting plates of the steel beam joints with no less than four ordinary bolts. Only after they are closely attached can high-strength bolts be installed. High-strength bolts shall not be used as temporary installation bolts during the installation process; 2) Before installing high-strength bolts, the appearance of the bolts shall be inspected. High-strength bolts with rust, damaged threads, wet surfaces, dust, sand, or changed surface conditions shall not be used. For high-strength bolts with changed surface conditions, they shall be sent back to the original manufacturer for re-surface treatment. After re-treatment, they shall be re-inspected according to the original supply requirements, and can be used only after passing the inspection; 3) When installing high-strength bolts, one washer shall be placed on each side of the bolt head and the nut. The chamfered sides of the washers shall face the bearing surfaces of the bolt head and the nut respectively, and the side with the mark on the nut shall face outwards; 4) The installation direction of high-strength bolts is specified as follows: For high-strength bolts on all main beam facades of the bridge, the nuts shall be installed on the outside of the joint plates; 5) When installing high-strength bolts, the bolts shall be smoothly inserted into the holes and shall not be forced in. A fixed number of positioning drift pins shall be driven first, and the bolts can be installed only after the hole positions are determined to coincide. If they cannot be freely inserted, they shall be trimmed with a reamer. The maximum diameter of the hole after trimming shall be less than 1.2 times the bolt diameter. When reaming the hole, in order to prevent iron filings from falling into the plate stack gap, all the bolts around shall be tightened before reaming so that the plate stack is closely attached and then reaming can be carried out. Gas cutting to enlarge the hole is strictly prohibited. If the bolts still cannot be freely inserted after reaming to 1.2 times the bolt diameter, the splicing plate shall be re-fitted; 6) The axes of the installed high-strength bolts shall be perpendicular to the surface of the joint plate. Otherwise, the reasons shall be found out and reinstalled;

[0031] (4) Tightening of high-strength bolts

[0032] 1) The tightening method of high-strength bolts for this bridge adopts the torque method, and the tightening of high-strength bolts is completed in two stages: initial tightening and final tightening;

[0033] Installation steps of high-strength bolts: (a) Install high-strength bolts corresponding to the bolt holes where neither drift pins nor ordinary bolts are driven in. The installation sequence spreads from the center of the node to the surrounding areas, and tighten them with a ring spanner; (b) Replace ordinary bolts with high-strength bolts one by one. The replacement sequence spreads from the center of the node to the surrounding areas, and tighten them simultaneously with a ring spanner; (c) Use a calibrated pre-tightening wrench to pre-tighten the high-strength bolts tightened with a ring spanner, which is 50% of the final tightening torque, and make pre-tightening marks. The tightening sequence spreads from the center of the node to the surrounding areas; (d) Withdraw the drift pins in batches, replace them with high-strength bolts, and perform pre-tightening, which is 50% of the final tightening torque, and make pre-tightening marks with a blue paint pen; (e) Perform final tightening on all pre-tightened high-strength bolts, which is 100% of the final tightening torque. The tightening sequence spreads from the center of the node to the surrounding areas, and at the same time make final tightening marks with red paint. Pre-tightening and final tightening should be completed within the same working day; (f) Within 4 hours to 24 hours after final tightening, randomly check the bolts tightened on the same day according to the specified quantity with a dial wrench, and at the same time make inspection marks with yellow paint; 3) Pre-tightening: After the high-strength bolts are installed in the bolt holes and checked to be correct, first tighten them with an ordinary manual ring spanner, and first use a calibrated electric wrench to tighten the bolts to 50% of the final tightening torque to complete pre-tightening; 4) For the pre-tightened high-strength bolts, a straight line should be immediately drawn on the nut, washer and plate surface with a blue marker pen to prevent repeated tightening, omission and facilitate inspection; 5) Final tightening: The final tightening torque value of each batch of high-strength bolts is determined by the following formula:

[0034] TC = K × PC × d

[0035] Where: TC is the final tightening torque value of the high-strength bolt, PC is the construction pre-tension value of the high-strength bolt, K is the average torque coefficient value of each batch of high-strength bolts, d is the nominal diameter of the high-strength bolt, and the average torque coefficient value K of the high-strength bolt in the formula is determined by tests; 6) The final tightening is completed by a calibrated electric torque wrench. For bolts in individual positions where electric tools cannot be used, a calibrated dial-type inspection wrench or a ringing manual wrench is used to complete the final tightening; 7) During the tightening process of the high-strength bolt, the bolt head and washer shall not rotate together with the nut. If it is found that the bolt and washer rotate, the high-strength bolt shall be replaced, and the operations of initial tightening and final tightening shall be repeated. The replaced high-strength bolts shall be returned to the warehouse and centrally returned to the factory for treatment. They can only be used after passing the acceptance. It is strictly prohibited to use them directly again; 8) When using the ringing manual wrench during the tightening process of the high-strength bolt, the force must be applied evenly, and no impact force shall be used. When starting the electric torque wrench, it must run continuously and smoothly until the electric wrench stops automatically to complete the tightening of a high-strength bolt. After the electric wrench stops automatically, it is strictly prohibited to start the electric wrench again to tighten the bolt to prevent over-tightening; 9) Whether in the initial tightening or final tightening stage, or when using different wrenches, generally, the tightening sequence from the center of the bolt group to the surrounding shall be followed. For special positions where this cannot be implemented, it can be reported to the chief engineer for research and handling; 10) During construction, the electric wrench shall use an independent power supply or a regulated power supply to reduce the voltage fluctuation and affect the stable output of the torque of the electric wrench; 11) If any abnormality or failure occurs during the use of various wrenches, the on-site construction personnel shall not handle it without authorization. Construction must be stopped immediately, and the wrench shall be handed over to the high-strength bolt test team for inspection and repair, and the fault situation shall be reported to formulate corresponding measures to handle the on-site bolts;

[0036] Step 5.2: Welding connection, including the butt weld between the cantilever top plate and the box girder top plate, the fillet welds between the cantilever web plate, bottom plate and the box girder web plate, and the butt welds between the steel bottom plate and the box girder top plate, cross beam top plate.

[0037] Further, the construction process of the front and rear guide beam structures in Step 6 is as follows: The guide beam and the tail beam are composed of 2 equal-height I-shaped solid web steel plate main girders. The longitudinal length of the guide beam is 45 m, the length of the tail beam is 10 m, and the height corresponds to the web plates on both sides of the steel box girder. The front end section of the guide beam is smaller, which is convenient for the guide beam to get on the pier. For the convenience of transportation and assembly, transverse connections and upper and lower plane connections composed of steel pipes are provided between the two main girders to form the whole guide beam. The root of the guide beam is reliably connected to the steel box girder, and the high-strength bolt connections of the guide beam are regularly inspected.

[0038] Further, the process of designing the technical parameters of the jacking system, designing the jacking route and installing the jacking equipment in Step 6 is as follows: Design of the technical parameters of the jacking system: The steel-concrete composite beam is located in the transition curve and circular curve sections. To adapt to the linear change of the horizontal curve and reduce the lateral deviation during the jacking process, the single-end jacking process is adopted, which can ensure the safety of the jacking process;

[0039] The incremental launching adopts the adaptive multi - point synchronous walking type incremental launching technology for the steel - concrete composite beam joints. During the incremental launching process, each jack realizes the functions of synchronous movement on both sides, synchronous movement of all points, single - point single - action and point - moving limit through the hydraulic pump station and the computer automatic control system. The maximum speed of the incremental launching technology is 5m / h. Since several support points are used for incremental launching, it has the characteristic that the temporary support is subjected to less horizontal force during the incremental launching process. Theoretically, it can achieve incremental launching without horizontal force. The incremental launching process is stable, the alignment is adjustable, the equipment is measurable and controllable, and an intelligent monitoring and detection system has been developed, which can monitor the stress, strain and video images of key points in real time. During the incremental launching process, each pump station is connected to 2 650t jacks, and the equipment is fixed to the bearing beam by setting limit plates around it;

[0040] Incremental launching route design: The steel box girder is assembled for the second time at the subgrade section 140m in front of the small - pile - number side of the bridge, and after the assembly is completed, it is incrementally launched from the Luding side to the Shimian side;

[0041] Installation of incremental launching equipment: The incremental launching adopts the adaptive multi - point synchronous walking type incremental launching technology. During the incremental launching process, each jack realizes the functions of synchronous movement on both sides, synchronous movement of several points, single - point single - action and point - moving limit through the hydraulic pump station and the computer automatic control system, and the incremental launching device is installed on the top of each temporary support pier;

[0042] The incremental launching device consists of a walking - type incremental launching jack, a hydraulic pump station and a computer control system;

[0043] (1) Walking - type incremental launching jack: For a single pusher of the walking - type jack, the horizontal pushing force is 60t, the stroke is 400mm, the vertical lifting force is 650t, the lifting stroke is 200mm, and the horizontal deviation - correcting pushing force is 60t, the stroke is 130mm. The mechanical system of the walking - type incremental launching equipment includes an upper sliding seat structure, a lifting support oil cylinder, a longitudinal incremental launching oil cylinder, a lateral adjustment oil cylinder and a base, and realizes intelligent incremental launching through computer control and hydraulic drive to meet the construction requirements;

[0044] By alternately performing the four steps of lifting, pushing, lowering and retracting, first lift the steel box girder as a whole, then push the translation oil cylinder forward for a stroke, then lower the steel box girder as a whole onto the vertical support structure, and the translation oil cylinder retracts to the end. After completing one - stroke incremental launching, continue the next cycle. Through the reciprocating incremental launching steps, finally, the steel box girder is incrementally launched to the designed position;

[0045] The mechanical structure of the jacking is installed on the longitudinal beam of the steel pipe column pier. When sliding, the entire walking jacking equipment remains stationary relative to the temporary pier. The sliding surface of the walking jacking equipment adopts a stainless steel plate and the contact surface with the MGE slide plate; the upper and lower parts of the jacking equipment are moved in the direction of the bridge through the oil cylinder. The thrust is the internal force of the equipment itself, which overcomes the horizontal thrust generated on the temporary pier during jacking due to the existing method. Through the control of the hydraulic system, it automatically adapts to the deformation of the jacking main bridge, making the jacking safer and more reliable; Hydraulic system: every 2 walking jacks are equipped with a hydraulic pump station, and the whole bridge has a total of 6 hydraulic pump stations; the computer control system includes a control system and an electronic control system.

[0046] Furthermore, the process of the jacking construction principle analysis in step 6 is: the equipment is installed in place, the jacking jack is raised, the deadweight of the beam is replaced by the pier to the jacking jack for support, the jacking cylinder is extended, the beam body is pushed forward a stroke, when the jacking cylinder is extended to lift the beam body, the correction cylinder is actuated to correct the beam body, the jacking cylinder is retracted, the beam body is replaced to the pier, the pushing jack is retracted, the pushing jack is returned to its original position, and a jacking stroke is completed.

[0047] Furthermore, the specific process of the steel box girder jacking construction in step 6 is as follows: the jacking process of the left span of the bridge is as follows: (1) Install temporary supports and jacking facilities according to the position of the design drawing; (2) Assemble and weld the 45-meter front steel guide beam, 70-meter steel beam and 10-meter tail beam; (3) Push forward for about 5 meters for trial jacking, and report and deal with any problems in a timely manner; (4) Push forward for about 209 meters to reach the designed mileage. During the jacking process, the guide beam is removed step by step, leaving only the last section of the steel guide beam and the tail beam; (5) The force system is converted, and the beam body is supported by the beam drop pier and the protection pier, preparing for the beam drop construction; (6) Each beam drop height is 20 mm as a round. After several rounds, the beam body falls to the designed elevation, the jacking and beam drop facilities are removed, and the jacking construction is completed;

[0048] The pushing process of the right span of the bridge is as follows: (1) Install temporary supports and pushing facilities according to the position in the design drawing; (2) Assemble and weld the 45-meter front steel guide beam, 70-meter steel beam and 10-meter tail beam; (3) Push forward for about 5 meters for trial pushing, and report and deal with any problems in a timely manner; (4) Push forward for about 198.2 meters to reach the designed mileage. During the pushing process, the guide beams are removed step by step, leaving only the last section of the steel guide beam and the tail beam; (5) The force system is converted, and the beam body is supported by the beam-dropping piers and protection piers, preparing for the beam-dropping construction; (6) Each beam-dropping height is 20 mm as one round. After several rounds, the beam body falls to the designed elevation, the pushing and beam-dropping facilities are removed, and the pushing construction is completed.

[0049] Furthermore, the process of pushing and offset adjustment, setting anti-slip measures, placing the guide beam on the pier and dropping the beam in step 6 is as follows:

[0050] Pushing and deviation adjustment: Before pushing, the construction process of the curved girder pushing must be simulated. According to the corresponding vertex positions of each temporary support top and the steel girder and the pushing step distance, set the pushing construction process control table, and carry out the actual construction of the pushing process according to the process control table; during the pushing process, the jacking force value is the main control and the elevation is the auxiliary. If the jacking force value displayed by the jacks at a certain pier exceeds the warning value, change the shimming height at the adjacent support points to reduce the force value of this pier, and ensure that the overall stress during the pushing process is within the control range;

[0051] Before each round of pushing, according to the monitoring instructions, clarify the change range of the vertical curve of the steel girder and the change range of the support reaction force during this round of pushing, clarify the thickness of the temporary shims at each support point, and equip several steel boxes on site for easy adjustment of the shimming thickness;

[0052] Since the steel girder is located in the transition curve and circular curve sections, when the steel-concrete composite girder is pushed, the pushing force is in the tangential direction of the curve. During the pushing process, there will be a deviation between the beam axis and the design axis in the plane. The following measures are taken to control the plane deviation:

[0053] (1) When debugging and using the pushing equipment, set the tolerance value of the position error in each direction of the pushing equipment to 5 mm, and control the synchronism error of each point within 5 mm;

[0054] (2) Ensure pushing synchronization. Before each pushing, carefully check the performance of the central control system and the pushing equipment at each pier position. During pushing, use computer centralized control for each pushing point to ensure synchronous operation of each pushing point, and pay attention to the change of the reaction force at each position and the displacement synchronization difference;

[0055] (3) Implement dynamic monitoring measures during pushing. Release the axis on the top of the temporary pushing piers. During the pushing process, use the method of hanging a plumb line to measure the feeding synchronization and the axis offset value. When the center line deviation is found, correct it in time. After each round of pushing of the steel-concrete composite girder, use a total station to measure the axis endpoints to determine whether there is an offset, and correct it in time once it occurs;

[0056] (4) During the pushing process of the steel girder, every 3 - 5 strokes, adjust and correct the deviation in time through the lateral jacks outside the movable pads. The axis deviation does not exceed 5 cm. When correcting the deviation, each support is corrected towards the center of the curve. If necessary, the pushing equipment at some support points can be laterally shifted;

[0057] (5) If the axis deviation is too large, stop the pushing construction, start the control system, input the center line deviation correction value of each point, start the adjustment cylinder, and adjust the center line deviation of the beam body within the allowable range;

[0058] Anti-slip measures: When the jacking direction is opposite to the longitudinal slope direction, the horizontal component force during downhill jacking needs to be considered. High-pressure asbestos boards are set on the contact surface between the movable cushion blocks and the steel beam to increase the friction force. The friction coefficient between steel plates is 0.15. During jacking and beam lowering, when the jacking slope is within 4%, the steel beam will not slide down by itself. When the jacking slope exceeds 1.5%, leveling steel plates need to be set on the top of the walking jack piers and support piers.

[0059] The guiding beam onto the pier: During the jacking process, due to the self-weight of the structure, the front end of the guiding beam will deflect downward. To facilitate the guiding beam onto the pier, a 1.5m long "eagle beak" with a 1m height difference is set at the front end of the guiding beam;

[0060] The specific steps for getting onto the pier are as follows:

[0061] The first step is to place cushion blocks under the walking jacks; the second step is for the walking jacks to move forward one stroke until the position of the "eagle beak" at the front end of the guiding beam reaches the position of the cushion blocks, and then level the cushion blocks; the third step is to alternately lift the device for getting onto the pier between the walking jacks and the cushion blocks until the bottom plate of the guiding beam is higher than the walking jacks; the fourth step is to remove the cushion blocks placed under the walking jacks and the walking jacks return; the fifth step is for the walking jacks to push forward until the bottom of the front end of the guiding beam is supported on the cushion blocks; the sixth step is for the walking jacks to return; the seventh step is for the walking jacks to push forward until the end of the steel beam is supported on the cushion blocks, completing the process of getting onto the pier; Lowering the beam: The construction process for lowering the beam is: Construction preparation → Remove the jacking equipment → Install the top beam steel supports and jacks → Jack up with the jacks → Place the beam on the temporary steel supports → Remove the brackets → Lower the beam construction → Precise alignment → Fix the bearing and the beam bottom → Construction completed;

[0062] The specific process is as follows:

[0063] Step 1: After the steel beam is jacked in place, use the walking jacks to lift the beam and tightly pad between the beam and the pier on the cushion blocks, and disconnect between the walking jacks and the beam bottom to prepare for the beam lowering construction; Step 2: Remove the walking jacks and replace them with beam lowering jacks and support cushion blocks, place them on the longitudinal beams, conduct the force system conversion, and use the jacking support cushion blocks and the beam lowering jacks to replace each other for beam lowering until the beam reaches the top of the longitudinal beams; Step 3: Place the beam lowering jacks on the beam lowering piers, remove the longitudinal and transverse distribution beams, conduct the force system conversion, use the support piers and the beam lowering jacks to replace each other, and lower the beam by 100mm per round until the beam reaches the top surface position of the concrete beam in the adjacent span; Step 4: Remove the remaining front and rear guiding beams, continue to lower the beam, use the support piers and the beam lowering jacks to replace each other, and lower the beam by 100mm per round until the beam reaches the top surface position of the bearing; Step 5: Adjust the elevation dimensions of the beam in the front, rear, left, and right directions to meet the requirements of the design drawings; Fix the bearing and the beam body. After the external prestressing construction is completed, fix the bearing and the beam body to complete the beam lowering construction;

[0064] Arrangement of supports for beam dropping: Each pier of the beam body is provided with 4 steel supports, among which 2 are steel supports for beam dropping and 2 are temporary supports. The steel supports are welded with steel plates with a wall thickness of 16 mm, the diameter of the steel supports is 406 mm, and the heights are 400 mm, 200 mm, and 100 mm respectively, which can meet the requirements of beam dropping. To ensure the stability of the steel supports, the steel supports are connected by bolts.

[0065] Due to the adoption of the above technical solutions, the present invention has the following beneficial effects:

[0066] In the present invention, jacking construction is adopted on site, and no auxiliary piers are arranged in the middle of the 70 - m steel box girder of the whole span, saving a large amount of equipment and manpower for setting auxiliary piers, with a short construction period and cost savings. At the same time, the steel box girder and the cross - beam are connected by bolt connection on site, achieving high - precision control, avoiding the situation of large overturning moment under the maximum cantilever state during the jacking process, and realizing a beam - dropping height exceeding the existing beam - dropping height through the beam - dropping method, which is a technological innovation. Description of the Drawings

[0067] Figure 1 It is a schematic diagram of the two - piece pier structure of Wangjiagou Bridge in the embodiment of the present invention;

[0068] Figure 2 It is a structural diagram of the jacking temporary support in the assembly area of Wangjiagou Bridge in the embodiment of the present invention;

[0069] Figure 3 It is a structural diagram of the jacking temporary support in the concrete beam erection area of Wangjiagou Bridge in the embodiment of the present invention;

[0070] Figure 4 It is a structural diagram of the jacking temporary support on both sides of the permanent pier of Wangjiagou Bridge in the embodiment of the present invention;

[0071] Figure 5 It is a schematic diagram of the temporary support structure of Wangjiagou Bridge in the embodiment of the present invention;

[0072] Figure 6 It is a jacking flow chart of the left - hand span of Wangjiagou Bridge in the embodiment of the present invention. Detailed Embodiment

[0080] To make the objectives, technical solutions and advantages of the present invention more clear and understandable, the following preferred embodiments are given with reference to the accompanying drawings for further detailed description of the present invention. However, it should be noted that many details listed in the specification are only for enabling the reader to have a thorough understanding of one or more aspects of the present invention, and these aspects of the present invention can be implemented even without these specific details.

[0081] A construction technology for launching a simply supported steel box girder with a large span, the technology comprising the following steps:

[0082] Step 1: Temporary supports and foundations, secondary assembly of the support structure

[0083] The on-site secondary assembly jigs are in the form of structures supported by piers. First, piers are erected on the site. After the steel box girder transport vehicle arrives, the steel box girder is directly hoisted above the piers for secondary assembly. The main structure of the piers is a φ219×10 steel pipe, with a 12×240×240 cover plate arranged above, and adjusting tooth plates are placed on the cover plate to adjust the overall elevation. A 12×400×400 steel plate is arranged below as the base, with bolt holes opened around, and anchor bolts are used to firmly connect the piers to the ground. The height of the piers is 1400 mm, and the pier structure is as Figure 1 shown.

[0084] Launching support structure: (1) The temporary support in the assembly area, the temporary support steel pipe columns are composed of 350×10 steel pipe columns, and the launching equipment is directly placed on the foundation. The temporary support structure is as Figure 2 shown. (2) The launching temporary support in the concrete beam erection area, the temporary support steel pipe columns are composed of 350×10 steel pipe columns, and the launching equipment is directly placed at the position of the concrete beam surface on the top of the columns. The temporary support structure is as Figure 3 shown. Affected by the cross slope of the precast beam deck, when installing the temporary piers, concrete must be used for leveling on the concrete beam surface. The temporary piers in the concrete beam erection area are arranged at the top of the permanent piers of the concrete beam, and the permanent piers and both ends of the concrete beam on the pier top bear the support reaction force during the launching process. The temporary piers are hoisted by a crane and directly installed on the embedded steel plates of the foundation and welded and fixed to the embedded steel plates.

[0085] (3) The launching temporary supports on both sides of the permanent piers, the temporary support steel pipe columns of the launching temporary supports on both sides of the permanent piers are composed of 400×20 steel pipe columns, and the launching equipment is directly placed on the distribution beams on the top of the temporary piers. On the side with the precast beam, the launching support is temporarily connected to the precast beam that has been installed to enhance its longitudinal stability. The temporary support structure is as Figure 4As shown. Due to the large height of the dropped beam, in order to increase the moment of inertia of the bracket section, full-length reinforcement is added around the steel pipe to increase the bracket section to 620*620mm to enhance stability. When the steel box beam is dropped, 10 channel steels are set up on the transverse connection system set on the top push bracket as a skeleton, and a wooden springboard is placed on top as a temporary construction platform. When the height of the bracket is gradually reduced, the transverse connection and the height of the construction platform also decrease. Steel bars and green nets are used on both sides of the construction platform as edge protection.

[0086] Support foundation: temporary support foundation is a reinforced concrete enlarged foundation with a plane size of 4m×4m and a thickness of 1m. After foundation treatment, its bearing capacity characteristic value should not be less than 222.9kPa.

[0087] Step 2: Temporary support layout, push temporary support layout, divided into three parts: one is the push temporary support at the roadbed position; the second is the temporary support at the top of the concrete T-beam column, arranged on the top of the 1# and 2# permanent piers; the third is the push temporary support at the completed bridge position, arranged on the top of the 3# and 4# permanent piers.

[0088] Step 3: On-site hoisting of steel box girders (secondary assembly), construction preparation: (1) Before construction, carefully read the drawings, hoisting plan, and carefully understand the on-site conditions, so as to have a clear idea before setting up temporary supports. (2) Before construction personnel enter the site, they must undergo three-level safety education and corresponding assessments. Only those who pass the assessment can go through the on-site entry procedures and start work, and receive safety education and training once a week. (3) The responsible persons at all levels will conduct technical and safety technical briefings for the installers and users according to the plan.

[0089] Step 4: Construction process: (1) According to the temporary support layout, use the total station to release the temporary support foundation coordinates, tie the steel bars, set up the formwork and correct the foundation concrete; (2) Make the temporary support on site according to the temporary support construction drawings; (3) Hoist the temporary support and connect the support base with the embedded steel plate; (4) Measure the support elevation, determine the support tooth plate height, and use the total station to re-measure the tooth plate elevation; (5) Hoist the beam section;

[0090] Preparation before hoisting: (1) Process preparation. According to the on-site installation and construction conditions, formulate the corresponding connection process as the on-site construction guidance process document. (2) Personnel preparation. In order to ensure the on-site construction quality and construction period requirements, a sufficient number of construction personnel are equipped. The construction personnel in key areas are assessed for their skills. Only those who meet the requirements can enter the site for construction. The construction personnel in other areas are selected from those with strong sense of responsibility. (3) Equipment preparation. Equip with sufficient types and quantities of construction equipment. The equipment is identified before leaving the factory to ensure the construction quality and normal use of the equipment to meet the construction requirements. (4) Inspection and trial lifting before hoisting. 1) Before hoisting, the normal operation of the crane must be ensured through maintenance, and the wire rope must be checked to ensure that it is safe and reliable to ensure smooth hoisting. 2) Before hoisting, check the site and check whether there are any wires above the hoisting area that do not meet the hoisting safety distance. If there are any problems, negotiate with the relevant parties in advance. 3) Before hoisting, check whether the connections of various parts of the temporary support are reliable. 4) Before lifting the beam section, a trial lifting of the beam section should be carried out. Before the trial lifting, check whether the connection between the lifting lug and the beam section meets the lifting requirements, and whether the wire rope and the pin passing through the lifting lug are firm. After checking that everything is correct, fix the wire rope on the crane hook, start the crane slowly, and slowly lift the box beam. During the lifting, observe the stability and overturning of the crane. If any problems are found, stop and check in time. When the beam is lifted to a height of 20cm from the ground, the crane will pause for 10 minutes to observe whether the box beam is stable and check whether the crane is stable. After it is stable, the commander will blow the whistle to command and slowly lower the box beam. After the trial lifting, the overall trial lifting record will be archived.

[0091] Steel box girder hoisting process: After the transport vehicle enters the installation site from the construction access road, the truck crane lifts the steel box girder from the transport vehicle and then carries out on-site installation work. (1) Secondary assembly of the right span steel box girder The steel box girder hoisting process is as follows: Step 3.1.1: The 100t truck crane is located on the right span small pile side and hoists the right span WRA1 and WRA2 box girder segments. Step 3.1.2: The 100t truck crane repositions and hoists the right span WRB1 and WRC1 segments and the crossbar between boxes. Step 3.1.3: The 100t truck crane repositions, sets up the missing secondary assembly piers and remeasures the elevation, and hoists the right span WRB2 and WRC2. Step 3.1.4: The 100t truck crane repositions and hoists the right span WRD1 and WRE1. Step 3.1.5: The 100t truck crane repositions, sets up the missing second piers and remeasures the elevation, and hoists the right span WRD2 and WRE2. Step 3.1.6: The 100t truck crane repositions, and hoists the right span WRF1. Step 3.1.7: The 100t truck crane repositions, and hoists the right span WRF2. Step 3.1.8: The 100t truck crane repositions, and hoists the right span WRG1 and WRG2.

[0092] The lifting process of the steel box girder for secondary assembly of the left span is as follows: Step 3.2.1: The 100t truck crane is located at the small pile number side of the left span and lifts the left span WLA1. Step 3.2.2: The 100t truck crane repositions and lifts the left span WLA2. Step 3.2.3: The 100t truck crane repositions and lifts the left span WLB1 and WLC1. Step 3.2.4: The 100t truck crane repositions, sets up the missing second-assembly piers and remeasures the elevation, and lifts the left span WLB2 and WLC2. Step 3.2.5: The 100t truck crane repositions and lifts the left span WLD1 and WLE1. Step 3.2.6: The 100t truck crane repositions, sets up the missing second-assembly piers and remeasures the elevation, and lifts the left span WLD2 and WLE2. Step 3.2.7: The 100t truck crane repositions and hoists the left span WLF1 and WLG1. Step 3.2.8: The 100t truck crane repositions, sets up the missing second piers and remeasures the elevation, and hoists the left span WLF2 and WLG2;

[0093] Guide beam installation process: After the steel box beam is assembled, the piers are placed according to the pre-placed ground sample line before the guide beam is hoisted. A 100t truck crane is used to hoist the guide beam. The hoisting process is as follows: Step 3.3.1: The 100t truck crane stands and hoists the D1 segments on both sides. Step 3.3.2: After the D1 segment is firmly connected to the column, the middle cross joint is hoisted. Step 3.3.3: Repeat the above steps to hoist the D2 segment and the middle cross joint. Step 3.3.4: Repeat the above steps to hoist the D3 segment and the middle cross joint. Step 3.3.5: Repeat the above steps to hoist the D4 segment and the middle cross joint.

[0094] Adjustment of steel box girder hoisting position and hoisting precautions:

[0095] The method of lifting the steel box girder section is as follows: (1) Check whether the crane position is safe and accurate, and whether there are any dangerous sources around. (2) Connect the wire rope and the lifting lug with a shackle, and connect the other end of the wire rope to the main hook. (3) Ensure that the wire rope is evenly stressed and the angle between the wire rope and the beam section is greater than 60°. (4) Before lifting, tie two cable wind ropes on the beam section to control the state of the beam section in the air. After the hook and the steel box girder lifting lug are hung, the safety officer will inspect and accept it. After it passes the inspection, the lifting commander will command the crane to slowly lift the beam section. When the predetermined lifting height is reached (more than 1m above the top surface of the temporary support), the crane slowly rotates the main arm to the air above the bridge position, and the lifting commander commands the crane to slowly drop the hook to lift the beam section to about 10cm above the top surface of the temporary support and stop. Then, refer to the edge line and center line of the steel box girder bottom plate released in advance to preliminarily position the steel box girder, and then the crane will continue to slowly drop the hook to the installation position to complete precise positioning.

[0096] Steel box girder positioning method: (1) Mark the center line and outer contour line of the beam segment on the transverse distribution beam of the support and on the ground. (2) After the steel beam segment is hoisted in place, adjust the elevation of the beam bottom through the jack. Steel box girder in-place measurement and positioning measures: After the steel box girder is temporarily in place, set stoppers on both sides of the steel box girder to prevent the steel box girder from slipping and overturning. Fix it with positioning pins at the segmented interface of the steel box girder. The number of positioning pins and bolts shall not be less than 30% to prevent the displacement of the steel box girder segments. Then carry out the initial tightening and final tightening of the high-strength bolts. (1) Positioning line. After the pre-assembly inspection is qualified, mark the transverse installation reference line on both sides of the beam segment joint. When the beam segment is hoisted in place, first carry out the docking of the transverse reference line. Use equipment such as chain blocks and jacks to make the beam segment meet the in-place standard and the transverse reference line coincide. After the steel beam is positioned by passing the dowel pin through the bolt hole, insert the high-strength bolts. Measuring method for steel box girder hoisting: (1) During the installation process of the steel box girder, the project surveyors conduct full-process inspection. (2) Before the steel box girder is hoisted, the surveyors shall release the side line and center line of the steel box girder on the ground in advance to facilitate the hoisting and positioning of the steel box girder; at the same time, check whether the elevation of the top of the concrete pier column (i.e., the elevation of the steel box girder bottom plate) is accurate. If the error exceeds the specification requirements, adjust it in time to avoid delaying the hoisting of the steel box girder. (3) After each span of the steel box girder is hoisted, the surveyors conduct cross-measurement and setting out on the top plate of the installed steel box girder, and at the same time conduct elevation measurement to check whether the steel box girder is installed correctly in the plane direction and vertical direction. If the error exceeds the specification requirements, adjust it in time.

[0097] Matters needing attention in steel box girder hoisting: (1) When hoisting the steel beam, special tools must be used to avoid twisting and deformation of the steel beam. When hoisting the steel beam, the standing point, boom length, hoisting angle and operating pressure of the crane shall be determined according to factors such as the weight of the component, the hoisting distance and the actual situation of the construction site. (2) During the process of hoisting the steel beam in place, the signals shall be clear and the command shall be unified. During hoisting, prevent the steel beam segments from colliding, and it is not allowed to temporarily place the steel beam segments on uneven sites.

[0098] Step 5: Steel box girder bridge construction, bolt connection (1) Construction content, bridge bolt connection includes bolt connection between steel box girder segments and bolt connection between cross beam and steel box girder. (2) Preparation before construction, 1) The project chief engineer shall conduct technical briefing for all construction personnel involved, explain in detail the process and key points of high-strength bolt tightening, clarify the respective responsibilities of all construction personnel involved, and the matters that should be paid attention to during the construction process, organize the participating construction personnel to study and train, familiarize themselves with the regulations of construction technology, and master the use of various wrenches and operating procedures. 2) Establish a high-strength bolt test team and complete relevant test and inspection work, including: site acceptance of high-strength bolts, construction process test report, site re-inspection of plate friction coefficient, adjustment of construction tool calibration system, adjustment of various wrenches, determination of various construction record forms, etc. 3) Before construction, the friction surface of the steel beam node should be carefully checked. The friction plate surface of the node should be kept clean and dry. Remove oil stains and dirt that may reduce the friction coefficient of the plate surface. Remove the flash, burrs and other attachments on the edge of the hole and the plate edge. For the dirt in the hole or on the plate surface, use a fine copper wire brush and a clean cotton cloth to clean it. For the oily places, use a clean cotton cloth dipped in acetone to clean it. The on-site technicians are responsible for checking the friction surface during pre-assembly and installation. Only after passing the inspection can the high-strength bolts be installed. 4) If the friction surface is exposed to the atmosphere for more than 6 months, it is necessary to check whether the friction surface has any effect or reduces the anti-friction coefficient. If there are doubts, tests must be carried out. The deteriorated friction surface must be reprocessed according to the design requirements. 5) The steel beam joint plate surface should be kept flat and intact. If the spliced ​​plate surface is deformed during installation and transportation, it must be repaired and leveled before assembly; if the friction surface is damaged, it should be reprocessed according to the design requirements before erection. 6) Before the on-site tightening team assembles, the on-site technicians should use a whiteboard pen to mark the use area lines of high-strength bolts of different specifications at the assembly site according to the pre-puzzle map, and indicate the specifications and quantities respectively to facilitate the installation of the bolt construction personnel, but the marking lines must not invade the range of the high-strength bolt washers. 7) Understand the weather conditions of the day in advance, and stop the high-strength bolt construction if it rains or snows. If there are signs of bad weather (such as rain or snow) suddenly, stop the installation of high-strength bolts immediately. If time is urgent, send the high-strength bolts to the temporary warehouse on the construction site to prevent the bolts from getting wet.

[0099] (3) Installation of High-strength Bolts 1) After the steel beam is hoisted and in place, during the assembly by the bracket method, 25% of the drift pins shall be driven into each joint as required. When assembling the cantilever beam, 50% of the drift pins shall be driven into each joint as required, arranged alternately with the bolt holes. Then check whether all bolt holes can ensure the smooth and free passage of high-strength bolts (if not, report to the supervisor engineer and on-site supervisor, and then study and handle according to the specific situation). Use no less than four ordinary bolts to clamp the gap between the connecting plates of the steel beam joints. Only after they are closely attached can high-strength bolts be installed. (If the close attachment of the plate surfaces cannot be ensured, high-strength bolts cannot be installed. Report to the supervisor engineer and on-site supervisor, and then study and handle according to the specific situation). High-strength bolts shall not be used as temporary installation bolts during the installation process. 2) Before installing high-strength bolts, the appearance of the bolts shall be inspected. High-strength bolts with rust, damaged threads, wet surfaces, or dust, sand, and changed surface conditions shall not be used. For high-strength bolts with changed surface conditions, they shall be sent back to the original manufacturer for re-surface treatment. After re-treatment, they shall be re-inspected according to the original supply requirements, and can be used only after passing the inspection. 3) When installing high-strength bolts, one washer shall be placed on each side of the bolt head and nut; the chamfered side of the washer shall face the bearing surfaces of the bolt head and nut respectively; the side with the mark on the nut shall face outwards. 4) For the convenience of construction and the aesthetics of the whole bridge, the following regulations are made for the installation direction of high-strength bolts: (a) For high-strength bolts on the vertical surfaces of all main girders of the bridge, their nuts shall be installed on the outside of the joint plates; (b) For high-strength bolts in individual parts where the nut position cannot meet the above requirements, the project chief engineer can be consulted to determine its direction. The penetration direction shall be based on the principles of facilitating the screwing, being beautiful and generous, and being consistent throughout the bridge. 5) When installing high-strength bolts, the bolts shall be smoothly inserted into the holes and shall not be forced in. A certain number of positioning drift pins shall be driven first, and the bolts can be installed only after the vacant positions coincide. If they cannot be freely inserted, the hole shall be trimmed with a reamer. The maximum diameter of the hole after trimming shall be less than 1.2 times the bolt diameter. When trimming the hole, in order to prevent iron filings from falling into the plate stack gap, all the surrounding bolts shall be tightened before reaming so that the plate stack is closely attached and then reaming can be carried out. Gas cutting to enlarge the hole is strictly prohibited. If the bolt still cannot be freely inserted after reaming to 1.2 times the bolt diameter, the splicing plate shall be re-fitted. 6) The axis of the installed high-strength bolts is perpendicular to the surface of the joint plate. Otherwise, the reason shall be found out and reinstalled. (4) Tightening of High-strength Bolts 1) The tightening method of high-strength bolts for this bridge adopts the torque method (controlled only by the torque method), that is, on the basis of a series of process tests, the tightening of high-strength bolts is completed in two stages: initial tightening and final tightening.

[0100] Installation steps of high-strength bolts: (a) Install high-strength bolts corresponding to the bolt holes where neither drift pins nor ordinary bolts are installed. The installation sequence spreads from the center of the joint to the surrounding areas, and tighten them with a plum blossom wrench. (b) Replace ordinary bolts with high-strength bolts one by one. The replacement sequence spreads from the center of the joint to the surrounding areas, and tighten them simultaneously with a plum blossom wrench. (c) Use a calibrated initial tightening wrench to perform initial tightening (50% of the final tightening torque) on the high-strength bolts tightened with a plum blossom wrench, and make initial tightening marks. The tightening sequence spreads from the center of the joint to the surrounding areas. (d) Withdraw drift pins in batches, replace them with high-strength bolts, and perform initial tightening (50% of the final tightening torque), and make initial tightening marks with a blue paint pen. (e) Perform final tightening (100% of the final tightening torque) on all high-strength bolts after initial tightening. The tightening sequence spreads from the center of the joint to the surrounding areas, and at the same time, make final tightening marks with red paint. Generally, initial tightening and final tightening should be completed within the same working day. (f) Within 4 hours to 24 hours after final tightening, randomly check the bolts tightened on the same day according to the specified quantity with a dial wrench, and make inspection marks with yellow paint at the same time. 3) Initial tightening: After the high-strength bolts are installed in the bolt holes and checked to be correct, first perform general tightening with an ordinary plum blossom manual wrench, and then use a calibrated electric wrench to tighten the bolts to 50% of the final tightening torque to complete the initial tightening. 4) For the high-strength bolts after initial tightening, a straight line should be immediately drawn on the nut, washer, and plate surface with a blue board pen to prevent repeated tightening, omission, and facilitate inspection. 5) Final tightening: The final tightening torque values of each batch of high-strength bolts are determined by the following formula:

[0101] TC = K × PC × d

[0102] Where: TC—the final tightening torque value of high-strength bolts (N·m); PC—the construction pre-tension value of high-strength bolts (kN); K—the average torque coefficient value of high-strength bolts in each batch; d—the nominal diameter of high-strength bolts (mm). The average torque coefficient value K of high-strength bolts in the formula is determined by tests. 6) The final tightening is completed by a calibrated electric torque wrench. For bolts in individual positions where electric tools cannot be used, a calibrated dial-type inspection wrench or a clicking manual wrench is used to complete the final tightening. 7) During the tightening process of high-strength bolts, the bolt head and washer shall not rotate together with the nut. If it is found that the bolt and washer rotate, the high-strength bolt shall be replaced and the operations of initial tightening and final tightening shall be repeated. The replaced high-strength bolts shall be returned to the warehouse and centrally returned to the factory for treatment. They can only be used after passing the acceptance. It is strictly prohibited to directly use them again. 8) When using a clicking manual wrench during the tightening process of high-strength bolts, the force must be applied evenly and no impact force shall be used; when starting an electric torque wrench, it must run continuously and smoothly until the electric wrench stops automatically, completing the tightening of a high-strength bolt. After the electric wrench stops automatically, it is strictly prohibited to start the electric wrench again to tighten the bolt to prevent over-tightening. 9) Whether in the initial tightening or final tightening stage, or when using different wrenches, generally the tightening sequence from the center of the bolt group to the surrounding shall be followed. For special positions where this cannot be implemented, it can be reported to the chief engineer for research and handling. 10) During construction, the electric wrench shall use an independent power supply or a regulated power supply to reduce the voltage fluctuation and affect the stable output of the torque of the electric wrench. 11) If any abnormality or failure occurs during the use of various wrenches, the on-site construction personnel shall not handle it without permission. Construction must be stopped immediately, and the wrench shall be handed over to the high-strength bolt test team for inspection and repair, and the failure situation shall be reported to formulate corresponding measures to handle the on-site bolts.

[0103] Construction quality inspection of high-strength bolts, (1) Relevant regulations for construction quality inspection of high-strength bolts: The construction quality inspection of high-strength bolts shall be organized by specialized test and inspection personnel, with the cooperation of construction personnel, and completed within 4 - 24 hours after the final tightening of the high-strength bolts. For the initial tightening inspection, use a small hammer weighing about 0.3 kg to tap each nut one by one, and at the same time press one side of the opposite edge of the nut with your finger. If your finger feels that the nut vibrates too much or is loose, it means that the bolt is under-tightened or missed tightening, and it needs to be re-tightened. Or use the method of marking to confirm the initial tightening, that is, use three different colors of paint, blue, red, and white, to mark the different states of the bolts for the three states of initial tightening, final tightening, and inspection respectively. (2) Relevant regulations for the final tightening inspection personnel of high-strength bolts: The final tightening inspection shall be carried out with a calibrated torque inspection wrench, and its accuracy error must be less than 3% of the torque value used by the wrench. 1) Before using the torque inspection wrench for inspection, first visually inspect the scribing misalignment when the initial tightening is completed to determine whether there is any missed tightening during the final tightening and whether the washer or bolt rotates. If the scribing does not move, it means that the bolt is missed tightened. If the misalignment is too large, it may mean that the bolt is over-tightened or the washer slips, and it should be inspected key points. (Note: Visual inspection is to further ensure the quality of the tightening.) 2) The final tightening torque inspection is carried out by the tight-clamping method, that is, for the high-strength bolts that have been finally tightened, use a pointer-type dial inspection wrench to tighten the nut along the tightening direction. The inspector evenly applies force to the wrench handle to make the torque indication increase evenly and the pointer rotate smoothly. When the pointer stops, it means that the torque value has caused the nut to rotate slightly, and this torque value is the final tightening inspection torque value of the bolt. 3) Before the tight-clamping inspection, first draw a thin line on the nut and washer to monitor the rotation of the nut. To prevent the bolt head from rotating with the nut during the inspection, causing misjudgment, the inspector should pay attention to observation and bring a tool for fixing the movement. 4) The on-site inspection torque value should be within 0.9 - 1.1 Tch, where the tight-clamping inspection torque Tch is the inspection torque of the high-strength bolt, which is determined by the test. If it exceeds, the final tightening inspection torque value of the bolt is unqualified. 5) For each node of the high-strength bolts, the inspection quantity is 5% of the total number of bolt groups at this node, but not less than two sets. 6) For unqualified nodes, the unqualified quantity shall not exceed 20% of the total number of spot checks, otherwise continue to conduct spot checks until 80% of the cumulative bolt groups are reached. Then re-tighten the under-tightened bolts, and replace and re-tighten the over-tightened bolts. 7) The high-strength bolts inserted into the joint plate on the same day on site must be initially tightened and finally tightened on the same day. The high-strength bolts after final tightening must be inspected on the same day and marked. For unqualified ones, opinions on treatment must be put forward in a timely manner, and records and visas should be done well.

[0104] Welding connection ① Construction content The welding operations at the bridge site include: (1) butt welds between the cantilever top plate and the box girder top plate; (2) fillet welds between the cantilever web, bottom plate and the box girder web; (3) butt welds between the steel bottom plate and the box girder top plate, cross beam top plate. ② Construction preparation (1) Determine the operation area, material storage area and living area according to the on-site environment, site and construction conditions. Ensure the safe arrival of construction equipment, materials and construction equipment. (2) The quality of welding-related materials must meet the requirements, and the inspection methods and frequencies comply with relevant regulations. Before use, they must be re-inspected by a third-party testing agency to ensure qualified results. (3) Prepare safety guarantee facilities for steel beam construction, temporary working platforms, welding wind and rain protection facilities, and safety protection facilities for high-altitude operations according to construction requirements. (4) Check whether the markings of longitudinal and transverse reference control points meet the requirements, and protect the markings and the on-site butt weld areas. (5) Formulate rules and regulations such as job responsibility systems, safety systems, and power supply systems at the construction site. ③ Welding construction process Use backing plates to adjust the weld width, level the welds, control the misalignment of plates <1mm, and control the installation spacing of backing plates within the range of 200-300mm. Before using backing plates to level the welds, grind the weld edges and the areas 50mm on both sides of the weld edges to a metallic luster in advance. If the welded joints are to be welded overnight, the weld edge areas need to be re-ground to a metallic luster; use as few backing plates as possible to reduce the amount of grinding of the backing feet. When local assembly is difficult due to severe deformation, flame heating and external force can be combined to level the weld edges, but the heating temperature should be controlled at 600-800°C. Water cooling and hammering are strictly prohibited. When removing temporary matching parts and backing plates at the construction site, pay attention to using the process of flame cutting and air gouging, and do not hammer to avoid damaging the base metal; during cutting, the flame is strictly prohibited from touching the flat surface to ensure a remaining height of 3-5mm after cutting, and then use a grinder to grind it smoothly to be flush with the plate surface. After adjusting the weld width and flatness, the butt welds of the top plate are welded with CO2 gas shielded welding for the root pass and submerged arc automatic welding for the cover pass, and the fillet welds are welded with CO2 gas shielded welding for the root pass, filling and cover pass. During welding operations, welding parameters must be strictly controlled to ensure welding quality. ④ Welding protection measures When performing gas shielded welding, when the wind speed exceeds 2m / s, windshields, wind hoods or other wind protection measures should be set up. Heavy objects are used to press the canvas tightly on the outside of the windproof cloth to prevent the CO2 shielding gas from being blown away by the strong wind and affecting the welding quality. Thermometers, hygrometers and anemometers are set up at the construction site to detect the on-site working environment at any time. 1) Welding wind and rain protection measures For the welding operation area outside the steel beam, use angle steel, mobile wheels and canvas to make a movable canvas enclosure to form an operation area without wind convection. 2) Rain and snow weather During rain and snow weather, construction is stopped. If it is really necessary to rush the construction due to progress requirements, in addition to local heating and wind protection, the entire weld must be protected by effective canvas (or colored strip cloth) during welding.

[0105] Prestress tensioning. After the box girders of this project are installed in place and the welding is completed, prestress tensioning is carried out. The prestressed steel tendons of the 70m steel box girders in this project are divided into N1, N2, and N3. During tensioning, double-end symmetric tensioning is adopted. The tensioning sequence is N1 - N2 - N3, and 7*15.2 epoxy-sprayed unbonded steel strands are used.

[0106] According to the Construction Technology Code for Highway Bridges and Culverts, the tensioning procedure for the N1 tendon is 0 - 25% - 50% - 100% - constant pressure for 5 minutes, and the tensioning procedures for the N2 and N3 tendons are 0 - 15% - 30% - 100% - constant pressure for 5 minutes.

[0107] (1) Preliminary preparation

[0108] Before the prestressed tendons are tensioned, ensure that the steel box girders are installed in place and the welding is completed. The jacks and sensors used for tensioning should be calibrated and used in sets. The calibration should be carried out regularly by a legally authorized metrological technical institution. When calibrating, the running direction of the jack should be consistent with the actual tensioning working state. When any of the following situations occurs, recalibration should be carried out: a The service time exceeds 6 months; b The number of tensioning times exceeds 300; c Abnormal situations occur to the jack or pressure gauge during use; d After the jack is repaired or replacement parts are installed.

[0109] (2) Installation of the anchor plate and jack

[0110] Installation sequence: Install the bearing plate → Install the anchor plate → Install the limiting plate → Install the jack in place → Install the tool anchor → Install the tool clamping pieces. Before installing the anchor, the mortar and grout adhered to the surface of the steel strand should be removed with a wire brush. The anti-rust oil on the surface of the anchor plate does not need to be removed, but the tapered hole must be kept clean and free of dirt such as soil and sand grains.

[0111] When installing the anchor, attention should be paid to the centering of the working anchor ring or anchor plate, and the clamping pieces should be evenly tightened and exposed uniformly. When installing the jack, attention should be paid to the alignment of the hole positions of the tool anchor on its piston and the hole positions of the working anchor at the end of the component. It is strictly prohibited for the steel strands to cross in the through-hole of the jack to avoid accidents such as broken wires during tensioning. For the clamping pieces of the tool anchor, attention should be paid to keeping them clean and in good lubrication state. Before the new tool anchor clamping pieces are used for the first time, lubricating grease should be applied to the back of the clamping pieces. After every 5 - 10 uses, the baffle plate on the tool anchor should be removed together with the clamping pieces, and a new layer of lubricating grease should be applied to the tapered hole of the anchor plate to prevent the clamping pieces from being stuck when withdrawing the wedge.

[0112] (3) Tensioning of the steel strands. The 70 steel box girder uses 7*15.2 epoxy-sprayed unbonded steel strands. According to the design drawings, the tension control stress for each prestressed tendon is 1265 KN, and the steel strand control stress for the 70 box girder is 8855 KN.

[0113] ①Set the tensioning formula. a Install the supporting host computer software (prestressed intelligent control system data management software) folder on the computer and connect it to the remote control. If the connection fails, drivers are required. b After successful connection, open the software, click the "New" button in the instrument formula parameter setting interface, and enter the calibration equation coefficients of the jack, bridge number, duct number, and the data required for tensioning. After completion, select the formula to be downloaded and then click "Download to Device". After completion, query whether the formula is successfully downloaded in the "Tensioning Test" on the remote control main interface. c Turn on the power button on the remote control. Parameters can also be modified in the "Tensioning Test" on the main interface. Click [OK] to enter and input the password to modify the bridge number, duct number, and the designed tension value, theoretical elongation value, and tensioning times of the steel strand to be tensioned and other tensioning process parameters. d After input is completed, click [OK] "Start Test", and it will prompt "Maximum oil pressure of the oil gauge", which can check the actual oil pressure during operation to prevent operation errors. Then click OK to connect the remote control to the device. After successful connection, tensioning can be carried out. ②The remote control selects the tensioning formula to start tensioning. a Select the beam and duct number to be tensioned in the "Tensioning Test" of the remote control. b After entering, if the tensioning data is correct, wait until the jack is installed, power on the pump station, click the "Tensioning Test" interface on the remote control, and press the [OK] button to enter the main tensioning interface. Click the [Auto] button on the remote control to start tensioning.

[0114] ③ Tensioning process: a. Click the automatic button to enter the first tensioning control stage. The first tensioning control stage is to bring the steel strands from the relaxed state to the stressed state, eliminate the measurement error of the elongation value, and make the forces on each steel strand in the same bundle tend to be consistent. The system automatically controls the tensioning force value to reach the target value and enters the load-holding timing stage. The automatic pressure compensation controls the tensioning force to be maintained within the range of ±1% of the target value. After the load-holding is completed, the system automatically records the actual tensioning force and the elongation value of the oil cylinder. b. After the load-holding timing of the first stage is completed, enter the second tensioning control stage. The system automatically controls the pressure increase speed, raises the pressure smoothly, and automatically balances the elongation values of the oil cylinders at both ends of the same bundle of prestressed steel strands. The automatic control of the tensioning force value reaches the target value and enters the load-holding timing stage. The automatic pressure compensation controls the tensioning force to be maintained within the range of ±1% of the target value. After the load-holding is completed, the system automatically records the actual tensioning force and the elongation value of the oil cylinder. c. After the load-holding timing of the second stage is completed, enter the third tensioning control stage. The system automatically controls the oil pump to continue tensioning, controls the pressure increase speed, raises the pressure smoothly, and automatically balances the elongation values of the oil cylinders at both ends of the same bundle of prestressed steel strands. When the tensioning force is close to 90%σcon, the pressure increase speed is automatically slowed down for precise control until it reaches 100%σcon. The control of the tensioning force value reaches the target value and enters the load-holding timing stage. The automatic pressure compensation controls the tensioning force to be maintained within the range of ±1% of the target value. After the load-holding is completed, the system automatically records the actual tensioning force and the elongation value of the oil cylinder. After the 5-minute load-holding timing is completed, "Stop" or "Pause" is displayed. d. During the load-holding stage, when the tensioning force reaches 100%σcon, statically hold the load (5 min), automatically compensate for pressure, and control the tensioning force to be maintained within the range of 100%σcon±1%. After the load-holding is completed, the system automatically records the elongation value of the oil cylinder. e. When the load-holding time is up, press the anchor button to wait for the tensioning force, and the oil pressure drops to "0". f. After the anchoring is completed, press the jack retraction control button to retract the jack (pay attention to whether the tensioning force and the oil pressure value are normal during the retraction process). After the retraction is completed, remove the tool anchor and the jack, and use a stone pen to mark the steel strand at a position 2 - 3 cm from the end of the wedge. Observe for 24 hours and measure again to determine whether there is any wire slippage or wire breakage. g. Continue to select the second and third groups of steel bundles for tensioning, and the operation sequence is the same.

[0115] ④ Export, view, and report output of the tensioning result data: a. The tensioning data can be exported through the SD card or directly connected to the computer through the upper computer software "Prestressed Intelligent Control System Data Management Software" supporting the tensioning equipment. b. In the "Prestressed Intelligent Control System Data Management Software", the detailed information of this tensioning record can be viewed by double-clicking. c. For data export, directly click "Data Query", enter the corresponding beam number point, and click the report output at the lower right corner to output the tensioning reports of all ducts under this beam slab.

[0116] (5) The theoretical elongation of the steel strand is calculated as follows:

[0117] The average tensioning force is calculated using the formula:

[0118] Pp = P[1 - e^(-(kx + uθ))] / (kx + uθ)

[0119] Pp——Average tensile force of prestressed tendons (N); P——Tensile force at the tensioning end of prestressed tendons (N); x——Length from the tensioning end to the calculated section (m); θ——Coefficient of influence of local deviation per meter of the duct on friction, and the reference value can be taken as 0.0015; u——Friction coefficient between the prestressed tendon and the duct wall, and the reference value can be taken as 0.155.

[0120] Calculation of theoretical elongation value:

[0121] δL = PpL / AyEy

[0122] The calculation formula for the elongation value △L (mm) of prestress tensioning is as follows:

[0123] △L = △L2 + △L1

[0124] △L1——Measured elongation value (mm) from the initial tension to the maximum tensile stress; △L2——Calculated elongation value (mm) at the initial tension, and the elongation value of the adjacent level can be adopted. The theoretical single-end elongation of N1 bundle is 21.7 cm, the theoretical single-end elongation of N2 bundle is 15.1 cm, and the theoretical single-end elongation of N3 bundle is 8.5 cm. (4) Key points for prestress tensioning control: 1) During tensioning, pay attention to observing the working states of the jacks at both ends and the working state of the anchor plate in a timely manner, and adjust immediately when problems are found. 2) The accuracy of the maximum control stress of the prestressed tendons should be ±1.5%. 3) During tensioning, control by the tensile force and check the elongation. The error should be within ±6%. If the actual elongation during tensioning exceeds the allowable range, analyze the reasons and solve the problems before continuing the tensioning. 4) The tensioning of the steel bundles is carried out symmetrically at both ends simultaneously, and the tensioning sequence shall be carried out according to the requirements. The sequence is: first upper then lower, first middle then both sides, and it should be symmetrical about the vertical axis of the component section. 5) When cutting the steel strands, a working length should be reserved. The working length of the 70m steel box girder is 50 cm. 6) The jacks and sensors used for tensioning should be calibrated and used in sets. The calibration should be carried out regularly by a legally authorized metrological technical institution. When calibrating, the running direction of the jack should be consistent with the actual tensioning working state. When any of the following situations occurs, calibration should be carried out again: a. The service time exceeds 6 months; b. The number of tensioning times exceeds 300 times; c. Abnormal situations occur to the jack or pressure gauge during use; d. After the jack is repaired or its accessories are replaced. (5) Safety guarantee measures for prestress tensioning: a. Before using the winch during the installation of prestressed steel strands, its safety and reliability should be detected to prevent safety accidents such as electric shock and mechanical damage; b. During the prestress tensioning process, construction personnel are strictly prohibited from staying inside the steel box girder, and the controller should be moved outside the top plate of the steel box girder for control.

[0125] In Step 6, the process of designing the technical parameters of the jacking system, designing the jacking route, and installing the jacking equipment is as follows: Design of the technical parameters of the jacking system: The steel-concrete composite beam is located in the transition curve and circular curve sections. To adapt to the linear change of the horizontal curve and reduce the lateral deviation during jacking, the single-end jacking process is adopted, which can ensure the safety of the jacking process;

[0126] The jacking adopts the self-adaptive multi-point walking jacking process for the steel-concrete composite beam joints. During the jacking process, each jack realizes the functions of synchronous jacking on both sides, synchronous jacking at all points, single-point single-action, and point-motion limit through the hydraulic pump station and computer automatic control system. The maximum jacking speed of the jacking technology is 5 m / h. Since multi-point jacking is adopted, the temporary support is subject to less horizontal force during the jacking process. In theory, jacking without horizontal force can be achieved. The jacking process is stable, the alignment is adjustable, the equipment is measurable and controllable, and an intelligent monitoring and detection system has been developed, which can monitor the stress, strain, and video images of key points in real time. During the jacking process, each pump station is connected to 2 650t jacks, and the equipment is fixed to the bearing beam by setting limit plates around;

[0127] Design of the jacking route: The steel box girder is assembled for the second time at the subgrade section 140 m in front of the small pile number side of the bridge, and after the assembly is completed, it is jacked from the Luding side to the Shimian side;

[0128] Installation of the jacking equipment: The jacking adopts the self-adaptive multi-point synchronous walking jacking process. During the jacking process, each jack realizes the functions of synchronous jacking on both sides, synchronous jacking at multiple points, single-point single-action, and point-motion limit through the hydraulic pump station and computer automatic control system, and the jacking device is installed on the top of each temporary support pier;

[0129] The jacking device consists of a walking jacking jack, a hydraulic pump station, and a computer control system;

[0130] (1) The walking jacking jack, the horizontal jacking force of a single jacking actuator of the walking jack is 60t, the stroke is 400mm, the vertical jacking force is 650t, the jacking stroke is 200mm, the jacking force of the lateral deviation correction jack is 60t, and the stroke is 130mm. The mechanical system of the walking jacking equipment includes an upper sliding seat structure, a jacking support oil cylinder, a longitudinal jacking oil cylinder, a lateral adjustment oil cylinder, and a base, which is intelligently jacked through computer control and hydraulic drive to meet the construction requirements;

[0131] By alternately performing the four steps of jacking, pushing, lowering, and retracting, first lift the steel box girder as a whole, then push the translation oil cylinder forward for one stroke, then lower the steel box girder as a whole onto the vertical support structure, and the translation oil cylinder of the jacking retracts to the end to complete one stroke of jacking, and continue the next cycle. Through the reciprocating jacking steps, the steel box girder is finally jacked to the designed position;

[0132] The mechanical structure of the jacking is installed on the longitudinal beam of the steel pipe column pier. When sliding, the entire walking jacking equipment remains stationary relative to the temporary pier. The sliding surface of the walking jacking equipment adopts a stainless steel plate and the contact surface with the MGE slide plate; the upper and lower parts of the jacking equipment are moved in the direction of the bridge through the oil cylinder. The thrust is the internal force of the equipment itself, which overcomes the horizontal thrust generated on the temporary pier during jacking due to the existing method. Through the control of the hydraulic system, it automatically adapts to the deformation of the jacking main bridge, making the jacking safer and more reliable; Hydraulic system: every 2 walking jacks are equipped with a hydraulic pump station, and the whole bridge has a total of 6 hydraulic pump stations; the computer control system includes a control system and an electronic control system.

[0133] The process of the jacking construction principle analysis in step 6 is: the equipment is installed in place, the jacking jack is raised, the deadweight of the beam is replaced by the pier to the jacking jack for support, the jacking cylinder is extended, the beam body is pushed forward a stroke, when the jacking cylinder is extended to lift the beam body, the correction cylinder is actuated to correct the beam body, the jacking cylinder is retracted, the beam body is replaced to the pier, the pushing jack is retracted, the pushing jack is returned to its original position, and a jacking stroke is completed.

[0134] The specific process of the steel box girder top-pushing construction in step 6 is as follows: Figure 5 As shown in the figure, the process of pushing the left span of the bridge is as follows: (1) Install temporary supports and pushing facilities according to the position of the design drawing; (2) Assemble and weld the 45-meter front steel guide beam, 70-meter steel beam and 10-meter tail beam; (3) Push forward about 5 meters for trial pushing, and report and deal with any problems in a timely manner; (4) Push forward about 209 meters to reach the designed mileage. During the pushing process, the guide beams are removed step by step, leaving only the last section of the steel guide beam and the tail beam; (5) The force system is converted, and the beam body is supported by the beam-dropping piers and protection piers, preparing for the beam-dropping construction; (6) Each beam-dropping height is 20 mm. After several rounds, the beam body is dropped to the designed elevation, the pushing and beam-dropping facilities are removed, and the pushing construction is completed;

[0135] The pushing process of the right span of the bridge is as follows: (1) Install temporary supports and pushing facilities according to the position in the design drawing; (2) Assemble and weld the 45-meter front steel guide beam, 70-meter steel beam and 10-meter tail beam; (3) Push forward for about 5 meters for trial pushing, and report and deal with any problems in a timely manner; (4) Push forward for about 198.2 meters to reach the designed mileage. During the pushing process, the guide beams are removed step by step, leaving only the last section of the steel guide beam and the tail beam; (5) The force system is converted, and the beam body is supported by the beam-dropping piers and protection piers, preparing for the beam-dropping construction; (6) Each beam-dropping height is 20 mm as one round. After several rounds, the beam body falls to the designed elevation, the pushing and beam-dropping facilities are removed, and the pushing construction is completed.

[0136] In Step 6, the processes of jacking and deviation adjustment, setting anti-slip measures, guiding beam ascending onto the pier, and beam lowering are as follows: Jacking and deviation adjustment: Before jacking, the construction process of the curved beam jacking must be simulated. According to the corresponding vertex positions of each temporary support top and the steel beam and the jacking step distance, a jacking construction process control table is set up, and the actual construction of the jacking process is carried out according to the process control table. During the jacking process, the jacking force value is the main control and the elevation is the auxiliary. If the jacking force value displayed by the jacks at a certain pier exceeds the warning value, change the shimming height at the adjacent support points to reduce the force value of this pier and ensure that the overall stress during the jacking process is within the control range. Before each round of jacking, according to the monitoring instructions, clarify the change range of the vertical curve of the steel beam and the change range of the support reaction force during this round of jacking, clarify the thickness of the temporary shims at each support point, and equip several steel boxes on site for easy adjustment of the shimming thickness;

[0137] Since the steel beam is located in the transition curve and circular curve sections, when the steel-concrete composite beam is jacked, the jacking force is in the tangential direction of the curve. During the jacking process, there will be a deviation between the beam axis and the design axis in the plane. The following measures are taken for plane deviation control: (1) When debugging and using the jacking equipment, set the tolerance of the position error in each direction of the jacking equipment to 5 mm, and control the synchronization error of each point within 5 mm; (2) Ensure jacking synchronization. Before each jacking, carefully check the performance of the central control system and the jacking equipment at each pier position. During jacking, use computer centralized control for each jacking point to ensure synchronous operation of each jacking point, and pay attention to the change of the reaction force at each position and the displacement synchronization difference; (3) Implement dynamic monitoring measures during jacking. Release the axis on the top of the jacking temporary pier, and use the method of hanging a plumb line to measure the feeding synchronization and axis offset value during the jacking process. When the center line deviation is found, correct it in time. After each round of jacking of the steel-concrete composite beam, use a total station to measure the axis endpoints to determine whether there is any deviation, and correct it in time once it occurs; (4) During the jacking process of the steel beam, every 3 - 5 jacking strokes, adjust and correct the deviation in time through the transverse jacks outside the movable shims. The axis deviation does not exceed 5 cm. When correcting the deviation, each support is corrected towards the center of the curve. If necessary, the jacking equipment at some support points can be laterally moved; (5) If the axis deviation is too large, stop the jacking construction, start the control system, input the center line deviation correction value of each point, start the adjustment cylinder, and adjust the center line deviation of the beam body to within the allowable range; Anti-slip measures: When the jacking direction is opposite to the longitudinal slope direction, the horizontal component force during downhill needs to be considered during jacking. Set high-pressure asbestos boards on the contact surface between the movable shims and the steel beam to increase the friction force. The friction coefficient between steel plates is 0.15. During jacking and beam lowering, when the jacking slope is within 4%, the steel beam itself will not slide. When the jacking slope exceeds 1.5%, it is necessary to set platform leveling steel plates on the top of the walking jack piers and the support piers; Guiding beam ascending onto the pier: During the jacking process, due to the self-weight of the structure, the front end of the guiding beam will deflect downward. To facilitate the guiding beam ascending onto the pier, a 1.5 m long and 1 m high beak with a height difference is set at the front end of the guiding beam;

[0138] The specific steps of pier placement are as follows: first, the walking top places pads on the pads; second, the walking top moves forward a stroke, from the eagle beak position at the front end of the guide beam to the pad position, and the pad is leveled; third, the walking top and the pad are used alternately to raise the pier device, until the bottom plate of the guide beam is higher than the walking jack; fourth, the pad on the walking top is removed, and the walking top returns; fifth, the walking top pushes forward, until the bottom of the front end of the guide beam is supported on the pad; sixth, the walking top returns; seventh, the walking top pushes forward, until the end of the steel beam is supported on the pad, and the pier is completed; beam drop: the beam drop construction process is: construction preparation → removal of the pushing equipment → installation of the top beam steel support and jack → jacking → beam drop on the temporary steel support → removal of the bracket → beam drop construction → precise alignment → support and beam bottom consolidation → construction completed;

[0139] like Figure 6 As shown, the specific process is as follows: Step 1: After the steel beam is pushed into place, use the walking jack to lift the beam, tighten the beam and the pier on the pad, separate the walking top from the bottom of the beam, and prepare for the beam drop construction; Step 2: Remove the walking top, replace it with the beam drop jack and support pad, place it on the longitudinal beam, and convert the force system. Use the pushing support pad and the beam drop jack to replace each other to drop the beam to the top of the longitudinal beam; Step 3: Place the beam drop jack on the beam drop pier, remove the longitudinal and transverse distribution beams, and carry out force System conversion, using the support piers and beam-dropping jacks to replace each other, dropping the beams 100mm each time, and dropping the beams to the top surface of the adjacent span concrete beams; Step 4: Remove the remaining front and rear guide beams, continue to drop the beams, using the support piers and beam-dropping jacks to replace each other, dropping the beams 100mm each time, and dropping the beams to the top surface of the supports; Step 5: Adjust the front, back, left, and right elevation dimensions of the beam body to meet the requirements of the design drawings; The supports and the beam body are consolidated, and after the external prestressing construction is completed, the supports and the beam body are consolidated to complete the beam drop construction;

[0140] Arrangement of beam drop support: Each pier of the beam body is equipped with 4 steel supports, 2 of which are beam drop steel supports and 2 are temporary supports. The steel supports are welded with 16mm thick steel plates. The diameter of the steel supports is 406mm, and the heights are 400mm, 200mm, and 100mm respectively. They can meet the needs of beam drop. In order to ensure the stability of the steel supports, bolts are used to connect the steel supports.

[0141] During the pushing process, the jacking force value is the main control parameter and the elevation is the secondary parameter. If the force value shown by the jacks at a certain pier exceeds the warning value, the height of the shims at the adjacent supports is changed to reduce the force value at this pier, ensuring that the overall stress during the pushing process is within the control range. Before each round of pushing, according to the monitoring instructions, clarify the change range of the vertical curve (i.e., the elevation change value) of the steel beam and the change range of the support reaction force during this round of pushing, and clarify the thickness of the temporary shims at each support. Since the steel beam is located in the transition curve and circular curve sections, when the steel-concrete composite beam is pushed, the jacking force is in the tangent direction of the curve, and there will be a deviation between the beam axis and the design axis in the plane during the pushing process. Therefore, it is necessary to synchronously control the plane deviation.

[0142] During the pushing process, due to the self-weight of the structure, the front end of the pilot truss will deflect downward. To facilitate the pilot truss to move onto the pier, an eagle beak with a height difference of 1 m is set within a length of 1.5 m at the front end of the pilot truss. Overall synchronous beam lowering construction method: After the temporary supports are installed, the jacks of the outer beam lowering supports return oil, and the temporary supports bear the weight of the beam body. The operators on the pier replace the upper shims of the beam lowering supports with combined steel shims of different thicknesses according to the falling height of the beam body; then the jacks are pressurized to lift the beam body so that the beam body is separated from the temporary supports. The operators on the pier remove the upper shims of the temporary supports and replace them with combined steel shims of different thicknesses. Finally, the jacks of the beam lowering supports return oil, and the beam body falls back onto the temporary supports, ending one cycle of beam lowering.

[0143] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A large-span simply supported steel box girder top-pushing construction process, characterized in that: The construction process comprises the following steps: Step 1: Temporary support structure and foundation construction; Step 2: Temporary support layout and construction; Step 3: On-site hoisting of steel box beams, i.e. secondary assembly; Step 4: Adjust the hoisting position of the steel box girder; Step 5: Construction of steel box girder bridge site; Step 6: Top-pushing construction of steel box girders, including the construction of front and rear guide beam structures, design of technical parameters of the top-pushing system, design of the top-pushing route, installation of top-pushing equipment, analysis of the top-pushing construction principle, top-pushing construction of steel box girders, top-pushing and offset adjustment, setting of anti-slip measures, guide beam pier installation and beam drop.

2. The long-span simply supported steel box girder top-pushing construction process according to claim 1 is characterized in that: The specific process of step 1 is: Step 1.1: Secondary assembly of the support structure The secondary assembly cradle on site adopts the structural form of pier support. The pier is set up in the site first. After the steel box girder transport vehicle arrives, the steel box girder is directly hoisted to the top of the pier for secondary assembly. The main structure of the pier is φ219×10 steel pipe, with a 12×240×240 cover plate on the top, and an adjusting tooth plate is placed on the cover plate to adjust the overall elevation. A 12×400×400 steel plate is set as the base below, with bolt holes opened around it. Anchor bolts are used to firmly connect the pier to the ground. The height of the pier is 1400mm; Step 1.2: Setting up the jacking support structure, which includes temporary supports in the assembly area, temporary jacking supports in the concrete beam erection area, and temporary jacking supports on both sides of the permanent pier; The steel pipe columns of the temporary support are composed of 350×10 steel pipe columns. The jacking equipment is placed directly on the foundation. The temporary jacking support in the concrete beam erection area is composed of 350×10 steel pipe columns. The jacking equipment is placed directly on the concrete beam surface at the top of the column. Affected by the transverse slope of the prefabricated beam bridge deck, concrete must be used for leveling on the concrete beam surface during the installation of the temporary pier. The temporary piers in the concrete beam erection area are set at the top of the permanent piers of the concrete beam. The permanent piers and the two ends of the concrete beam at the top of the pier bear the fulcrum reaction force during the jacking process. The temporary piers are hoisted by a crane and directly installed on the embedded steel plate of the foundation and fixed by welding to the embedded steel plate. The steel pipe columns of the temporary supports on both sides of the permanent pier are composed of 400×20 steel pipe columns. The pushing equipment is directly placed on the distribution beam on the top of the temporary pier. On the side with the prefabricated beam, the pushing support is temporarily connected to the installed prefabricated beam to enhance the longitudinal stability. Due to the large set value of the beam drop height, in order to increase the moment of inertia of the bracket section, full-length reinforcement is added around the steel pipe to increase the bracket section to 620*620mm to enhance the stability; When the steel box girder is dropped, 10 channel steels are set up on the transverse connection system set on the top push bracket as the skeleton, and a wooden springboard is placed on top as a temporary construction platform. When the height of the bracket is gradually lowered, the height of the transverse connection and the construction platform also decreases. Steel bars and green nets are used on both sides of the construction platform as edge protection; Step 1.3: Construction of support foundation. The temporary support foundation is a reinforced concrete enlarged foundation with a plane size of 4m×4m and a thickness of 1m. After foundation treatment, its bearing capacity characteristic value should not be less than 222.9kPa.

3. The long-span simply supported steel box girder top-pushing construction process according to claim 1 is characterized in that: The specific process of step 2 is: The layout of the top-pushing temporary support is divided into three parts: the first is the top-pushing temporary support at the roadbed position; the second is the temporary support at the top of the concrete T-beam column, which is arranged on the top of the 1# and 2# permanent piers; the third is the top-pushing temporary support at the completed bridge position, which is arranged on the top of the 3# and 4# permanent piers.

4. The long-span simply supported steel box girder top-pushing construction process according to claim 1 is characterized in that: The specific process of step 3 is: After the transport vehicle enters the installation site from the construction access road, the truck crane lifts the steel box girder from the transport vehicle and then carries out on-site installation work; The hoisting process of the secondary assembly steel box girder of the right steel box girder is as follows: Step 3.1.1: The 100t truck crane station is located at the small pile number side of the right span to hoist the right span WRA1 and WRA2 box girder segments; Step 3.1.2: The 100t truck crane repositions and hoists the right span WRB1, WRC1 segments and the crossbar between boxes; Step 3.1.3: The 100t truck crane repositions, sets up the missing second pier and remeasures the elevation, and hoists the right span WRB2 and WRC2; Step 3.1.4: The 100t truck crane repositions and hoists the right span WRD1 and WRE1; Step 3.1.5: The 100t truck crane repositions, sets up the missing second pier and remeasures the elevation, and hoists the right span WRD2 and WRE2; Step 3.1.6: The 100t truck crane repositions and hoists the right span WRF1; Step 3.1.7: The 100t truck crane repositions and hoists the right span WRF2; Step 3.1.8: The 100t truck crane repositions and hoists the right span WRG1 and WRG2; The hoisting process of the secondary assembly steel box girder of the left steel box girder is as follows: Step 3.2.1: The 100t truck crane station is located at the small pile number side of the left span, and the left span WLA1 is hoisted; Step 3.2.2: The 100t truck crane repositions and hoists the left span WLA2; Step 3.2.3: The 100t truck crane repositions and hoists the left span WLB1 and WLC1; Step 3.2.4: The 100t truck crane repositions, sets up the missing second pier and remeasures the elevation, and hoists the left span WLB2 and WLC2; Step 3.2.5: The 100t truck crane repositions and hoists the left span WLD1 and WLE1; Step 3.2.6: The 100t truck crane repositions, sets up the missing second pier and remeasures the elevation, and hoists the left span WLD2 and WLE2; Step 3.2.7: The 100t truck crane repositions and hoists the left span WLF1 and WLG1; Step 3.2.8: The 100t truck crane repositions, sets up the missing second pier and remeasures the elevation, and hoists the left span WLF2 and WLG2; The installation process of the guide beam is as follows: After the steel box beam is assembled, the piers are placed according to the ground sample line laid out in advance before the guide beam is hoisted. A 100t truck crane is used to hoist the guide beam. The hoisting process is as follows: Step 3.3.1: Use a 100t truck crane to hoist the D1 segments on both sides; Step 3.3.2: After the D1 segment is firmly connected to the column, hoist the middle cross-connection; Step 3.3.3: Repeat the above steps to hoist the D2 segment and the middle cross joint; Step 3.3.4: Repeat the above steps to hoist the D3 segment and the middle cross joint; Step 3.3.5: Repeat the above steps to hoist the D4 segment and the middle cross joint.

5. The long-span simply supported steel box girder top-pushing construction process according to claim 1 is characterized in that: The specific process of step 4 is: Step 4.1: Determine the lifting process of steel box girder sections: (1) Check whether the crane station is safe and accurate, and whether there are any dangerous sources around; (2) Connect the wire rope to the lifting lug with a shackle, and connect the other end of the wire rope to the main hook; (3) Ensure that the wire rope is evenly stressed and the angle between the wire rope and the beam section is greater than 60°; (4) Before lifting, two cables are tied to the beam section to control the state of the beam section in the air. After the hook is hung on the lifting lug of the steel box beam, the safety officer will inspect and accept it. After passing the inspection, the lifting commander will command the crane to lift the beam section. When the predetermined lifting height is reached, it will exceed the top surface of the temporary support by more than 1m. After the crane rotates the main arm to the air above the bridge position, the lifting commander will command the crane to slowly drop the hook to lift the beam section to 10cm from the top surface of the temporary support and stop. Then, refer to the edge line and center line of the bottom plate of the steel box beam released in advance to preliminarily position the steel box beam, and then the crane will continue to slowly drop the hook to the installation position to complete the precise positioning; Step 4.2: Steel box girder positioning process: (1) The bracket horizontally distributes the beam and the ground position, and marks the center line and outer contour line of the beam section; (2) After the steel beam segment is hoisted into place, adjust the bottom elevation of the beam by using the jack height; Step 4.3: Measurement and positioning of steel box girder After the steel box girder is temporarily in place, blocks are set on both sides of the steel box girder to prevent the steel box girder from sliding and overturning. The steel box girder is fixed at the segment interface with positioning pins. The number of positioning pins and bolts is not less than 30% to prevent the displacement of the steel box girder segment. Then, the high-strength bolts are initially tightened and finally tightened. (1) Positioning line: after the pre-assembly inspection is passed, the transverse installation reference line is marked on both sides of the beam segment seam. When the beam segment is hoisted into place, the transverse reference line is first connected. The chain and jack are used to make the beam segment reach the positioning standard and the transverse reference line coincide. The pin is passed through the bolt hole to position the steel beam, and then the high-strength bolt is inserted; The specific process of measuring the hoisting of steel box beam is as follows: (1) During the installation of the steel box girder, the project surveyors conduct full-process inspection; (2) Before the steel box girder is hoisted, the surveying personnel shall lay out the edge line and center line of the steel box girder on the ground in advance to facilitate the hoisting and positioning of the steel box girder. At the same time, they shall check whether the top elevation of the concrete pier is accurate. The top elevation is the elevation of the bottom plate of the steel box girder. If the error exceeds the specification requirements, timely adjustments shall be made to avoid delaying the hoisting of the steel box girder. (3) After each span of the steel box girder is hoisted, the surveying personnel will conduct cross measurement and layout of the installed steel box girder top plate, and at the same time perform elevation measurement to verify whether the plane direction and vertical direction of the steel box girder are installed correctly. If the error exceeds the specification requirements, timely adjustments will be made.

6. The long-span simply supported steel box girder top-pushing construction process according to claim 1 is characterized in that: The specific process of step 5 is: Step 5.1: Bolt connection: the bolt connection at the bridge position includes bolt connection between steel box girder segments and bolt connection between the cross beam and the steel box girder; Installation of high-strength bolts: 1) After the steel beam is hoisted in place, when assembling by the bracket method, each joint should be driven with 25% of the nails as required, and when assembling the cantilever beam, each joint should be driven with 50% of the nails as required, arranged alternately with the bolt holes, and then check whether all bolt holes can ensure that the high bolts can pass smoothly and freely, and use no less than four ordinary bolts to clamp the gap between the connecting plate surfaces of the steel beam node. Only after they are tightly attached can high-strength bolts be installed. High-strength bolts shall not be used as temporary installation bolts during the installation process; 2) Before installing high-strength bolts, the appearance of the bolts should be inspected. High-strength bolts with rust, damaged threads, damp surfaces, dust, sand, or changes in surface conditions should not be used. High-strength bolts with changed surface conditions should be sent back to the original manufacturer for re-surface treatment. After re-treatment, they should be re-inspected according to the original supply requirements and can only be used after passing the inspection; 3) When installing high-strength bolts, there is a washer on each side of the bolt head and the nut. The chamfered side of the washer faces the bolt head and the nut support surface respectively, and the marked side of the nut faces outward; 4) The installation direction of high-strength bolts is stipulated as follows: the nuts of high-strength bolts on all main beam facades of the bridge shall be installed on the outside of the node plate; 5) When installing high-strength bolts, the bolts should be inserted into the holes smoothly and should not be knocked in by force. A fixed number of positioning pins should be punched first to ensure that the gaps overlap before installing the bolts. If they cannot be inserted freely, use a reamer to trim the holes. The maximum diameter of the holes after trimming should be less than 1.2 times the bolt diameter. When trimming the holes, in order to prevent iron filings from falling into the gaps between the plates, all the bolts around should be tightened before trimming the holes, so that the plates are closely attached before trimming. It is strictly forbidden to use gas cutting to expand the holes. If the bolts cannot be inserted freely after the holes are trimmed to 1.2 times the bolt diameter, the splicing plates should be re-assembled. 6) The axis of the installed high-strength bolts should be perpendicular to the surface of the node plate. Otherwise, find out the reason and reinstall; (4) Tightening of high-strength bolts 1) The high-strength bolts of this bridge are tightened using the torque method, which is divided into two stages: initial tightening and final tightening. High-strength bolt installation steps: (a) Install high-strength bolts corresponding to the bolt holes that have neither punches nor ordinary bolts installed. The installation sequence is from the center of the node to the surrounding area, and tighten them with a plum wrench; (b) Replace ordinary bolts with high-strength bolts one by one, starting from the center of the node and moving toward the surrounding areas, and tighten them simultaneously with a plum wrench; (c) Use a calibrated initial tightening wrench to perform initial tightening on the high-strength bolts that have been tightened with a box spanner, i.e. 50% of the final tightening torque, and make initial tightening marks. The tightening sequence is spread from the center of the node to the surrounding areas; (d) Remove the punches in batches, replace them with high-strength bolts, and perform initial tightening, which is 50% of the final tightening torque, and mark the initial tightening with a blue paint pen; (e) All high-strength bolts that have been initially tightened shall be tightened to a final torque of 100%. The tightening sequence shall be from the center of the node to the surrounding areas. At the same time, the final tightening mark shall be made with red paint. The initial tightening and final tightening shall be completed on the same working day. (f) Within 24 hours after the final tightening, the bolts tightened on that day shall be checked according to the specified quantity using a dial wrench and marked with yellow paint; 3) Initial tightening: After the high-strength bolts are installed into the bolt holes and checked to be correct, tighten them with an ordinary plum-shaped manual wrench first, and then use a calibrated electric wrench to tighten the bolts to 50% of the final tightening torque to complete the initial tightening; 4) For high-strength bolts that have been initially tightened, a straight line should be immediately drawn on the nut, washer and plate surface with a blue marker to prevent repeated tightening, omissions and facilitate inspection; 5) Final tightening: The final tightening torque value of each batch of high-strength bolts is determined by the following formula: TC=K×PC×d In the formula: TC is the final tightening torque value of the high-strength bolt, PC is the construction pre-tension value of the high-strength bolt, K is the average value of the torque coefficient of each batch of high-strength bolts, d is the nominal diameter of the high-strength bolt, and the average value K of the torque coefficient of the high-strength bolt in the formula is determined by the test; 6) Final tightening is completed by a calibrated electric torque wrench. For bolts in some parts where electric tools cannot be used, a calibrated dial inspection wrench or a manual wrench with a sound is used to complete the final tightening; 7) During the tightening process of high-strength bolts, the bolt head and washer shall not rotate with the nut. If the bolt or washer is found to rotate, the high-strength bolt shall be replaced and the initial tightening and final tightening operations shall be repeated. The replaced high-strength bolts shall be returned to the warehouse and sent back to the factory for centralized processing. They can only be used after passing the acceptance inspection. It is strictly forbidden to use them directly again; 8) When tightening high-strength bolts, the use of manual torque wrenches must be uniform, and impact force must not be used. When the electric torque wrench is started, it must be operated continuously and smoothly until the electric wrench stops automatically. After the electric wrench stops automatically, it is strictly forbidden to start the electric wrench again to tighten the bolt to prevent over-tightening; 9) Whether in the initial tightening or final tightening stage, or when using different wrenches, the tightening sequence should generally be from the center of the bolt group to the surrounding area. If this cannot be followed for special parts, report to the chief engineer for further processing; 10) During construction, the electric wrench should use an independent power supply or a voltage-stabilized power supply to reduce voltage fluctuations that affect the output stability of the electric wrench torque; 11) If any abnormality or failure occurs during the use of various wrenches, on-site construction personnel shall not handle them without authorization, and must immediately stop construction, hand over the wrench to the high-strength bolt test team for inspection and repair, and report the failure so that corresponding measures can be formulated to deal with the on-site bolts; Step 5.2: Welding connection, including the butt weld between the cantilever top plate and the box beam top plate, the fillet weld between the cantilever web plate, the bottom plate and the box beam web plate, and the butt weld between the steel bottom plate and the box beam top plate and the cross beam top plate.

7. The long-span simply supported steel box girder top-pushing construction process according to claim 1 is characterized by: The process of constructing the front and rear guide beam structures in step 6 is as follows: The guide beam and tail beam are composed of two I-shaped solid web steel plate main beams of equal height. The longitudinal length of the guide beam is 45m, and the length of the tail beam is 10m. The height is consistent with the webs on both sides of the steel box beam. The front section of the guide beam is small, which is convenient for the guide beam to be put on the pier. For the convenience of transportation and assembly, the two main beams are connected horizontally by steel pipes and the upper and lower plane connections are set to form the entire guide beam as a whole. The root of the guide beam is reliably connected to the steel box beam, and the high-strength bolt connection of the guide beam is regularly checked.

8. The long-span simply supported steel box girder top-pushing construction process according to claim 1 is characterized by: The process of designing the technical parameters of the jacking system, designing the jacking route and installing the jacking equipment in step 6 is as follows: Technical parameter design of the jacking system: The steel-concrete composite beam is located in the transition curve and circular curve sections. In order to adapt to the linear changes of the flat curve and reduce the plane deviation during the jacking process, the single-end jacking process is adopted to ensure the safety of the jacking process; The jacking process adopts the self-adaptive walking-type jacking process of several points at the nodes of the steel-concrete composite beam. During the jacking process, each jack realizes the synchronization of both sides, synchronization of all points, single-point single movement and inching limit functions through the hydraulic pump station and computer automatic control system. The maximum speed of the jacking technology is 5m / h. Due to the use of several fulcrums for jacking, the temporary support is subjected to small horizontal force during the jacking process. In theory, jacking without horizontal force can be achieved. The jacking process is smooth, the linear shape is adjustable, the equipment is measurable and controllable, and an intelligent monitoring and detection system has been developed, which can monitor the video images of stress, strain and key points in real time. During the jacking process, each pump station is connected to 2 650t jacks, and the connection between the equipment and the cushion beam is fixed with limit plates set around. Pushing route design: The steel box girder is assembled twice at the roadbed section 140m in front of the small pile number side of the bridge. After the assembly is completed, it is pushed from the Luding side to the Shimian side; Installation of jacking equipment: The jacking adopts the adaptive multi-point synchronous walking jacking process. During the jacking process, each jack realizes the synchronization of both sides, synchronization of several points, single-point single movement and inching limit functions through the hydraulic pump station and computer automatic control system, and the jacking device is installed on the top of each temporary support pier; The jacking device is composed of a walking jack, a hydraulic pump station, and a computer control system; (1) Walking jacking jack: The horizontal thrust of a single walking jack is 60t, with a stroke of 400mm, the vertical lifting force is 650t, with a lifting stroke of 200mm, and the lateral correction jacking force is 60t, with a stroke of 130mm. The mechanical system of the walking jacking equipment includes an upper sliding seat structure, a lifting support cylinder, a longitudinal pushing cylinder, a lateral adjustment cylinder and a base. It is intelligently pushed through computer control and hydraulic drive to meet construction requirements. The four steps of jacking, pushing, lowering and shrinking are performed alternately. First, the steel box girder is lifted up as a whole, and then the jacking and translation cylinder is pushed forward for a stroke. After that, the steel box girder is lowered as a whole and placed on the vertical support structure. The jacking and translation cylinder is then retracted to the bottom to complete a jacking stroke, and then the next cycle is continued. Through the reciprocating jacking steps, the steel box girder is finally pushed to the designed position. The jacking mechanical structure is installed on the longitudinal beam of the steel pipe column pier. When sliding, the entire walking jacking equipment does not move relative to the temporary pier. The sliding surface of the walking jacking equipment adopts a stainless steel plate and the contact surface with the MGE slide plate; The upper and lower parts of the jacking equipment are moved in the direction of the bridge through the oil cylinder. The thrust is the internal force of the equipment itself, which overcomes the horizontal thrust on the temporary piers caused by the existing jacking method. Through the control of the hydraulic system, it automatically adapts to the deformation of the jacking main bridge, making the jacking safer and more reliable. Hydraulic system: one hydraulic pump station for every two walking jacks, a total of six hydraulic pump stations for the entire bridge; The computer control system includes the control system and the electronic control system.

9. The long-span simply supported steel box girder top-pushing construction process according to claim 1 is characterized by: The process of analyzing the principle of top-pushing construction in step 6 is as follows: The equipment is installed in place, the jacking jack is raised, the deadweight of the beam is replaced by the pier to the jacking jack for support, the jacking cylinder is extended, the beam body is pushed forward a stroke, when the jacking cylinder is extended to lift the beam body, the correction cylinder is actuated to correct the beam body, the jacking cylinder is retracted, the beam body is replaced to the pier, the pushing jack is retracted, the pushing jack is returned to its original position, and one jacking stroke is completed.

10. The long-span simply supported steel box girder top-pushing construction process according to claim 1 is characterized in that: The specific process of the steel box girder top-pushing construction in step 6 is: The process of pushing the left side of the bridge is as follows: (1) Install temporary supports and jacking facilities according to the positions in the design drawings; (2) Assemble and weld the 45-meter front steel guide beam, 70-meter steel beam and 10-meter tail beam; (3) Push forward for about 5 meters to test push. If any problems are found, report and handle them in a timely manner; (4) Push forward about 209 meters to reach the designed mileage. During the pushing process, the guide beams are removed step by step, leaving only the last section of the steel guide beam and the tail beam; (5) The force system is converted, and the beam body is supported by the beam-dropping piers and protection piers, preparing for the beam-dropping construction; (6) Each beam drop height is 20 mm, and after several rounds, the beam is dropped to the designed height, and the jacking and beam dropping facilities are removed, and the jacking construction is completed; The process of pushing the right side of the bridge is as follows: (1) Install temporary supports and jacking facilities according to the positions in the design drawings; (2) Assemble and weld the 45-meter front steel guide beam, 70-meter steel beam and 10-meter tail beam; (3) Push forward for about 5 meters to test push. If any problems are found, report and handle them in a timely manner; (4) Push forward about 198.2 meters to reach the designed mileage. During the pushing process, the guide beams are removed step by step, leaving only the last section of the steel guide beam and the tail beam; (5) The force system is converted, and the beam body is supported by the beam-dropping piers and protection piers, preparing for the beam-dropping construction; (6) Each round of beam lowering is 20 mm high. After several rounds, the beam falls to the designed height, the jacking and beam lowering facilities are removed, and the jacking construction is completed.

11. The long-span simply supported steel box girder top-pushing construction process according to claim 1 is characterized in that: The process of pushing and offset adjustment, setting anti-slip measures, placing the guide beam on the pier and dropping the beam in step 6 is as follows: Pushing and offset adjustment: Before pushing, the construction process of the curved beam must be simulated. According to the top position and pushing step distance corresponding to each temporary support top and steel beam, the pushing construction process control table is set, and the actual construction of the pushing process is carried out according to the process control table; During the jacking process, the lifting force is the main control and the elevation is the auxiliary control. If the force value displayed by the jack of a certain pier exceeds the warning value, the height of the support pad at the adjacent support point is changed to reduce the force value of the pier to ensure that the overall stress during the jacking process is within the control range; Before each round of pushing, according to the monitoring instructions, the vertical curve change range of the steel beam and the change range of the support reaction force of the pushing round are determined, the thickness of the temporary support at each support is determined, and several steel boxes are equipped on site to facilitate the adjustment of the support thickness; Since the steel beam is located on a transition curve or circular curve, when the steel-concrete composite beam is pushed, the pushing force is in the tangent direction of the curve. During the pushing process, the beam axis and the design axis will deviate on the plane. The following measures are taken to control the plane deviation: (1) When debugging and using the jacking equipment, set the tolerance value of the position error of the jacking equipment in each direction to 5mm, so that the synchronization error of each point is controlled within 5mm; (2) Ensure the synchronization of jacking. Before each jacking, the performance of the central control system and the jacking equipment at each pier position should be carefully checked. During jacking, each jacking point should be centrally controlled by computer to ensure the synchronization of each jacking point, and pay attention to the reaction force changes and displacement synchronization differences at each position; (3) Implement dynamic monitoring measures during jacking, release the axis on the top of the temporary pier, and use the method of hanging plumb line to measure the synchronization of the footage and the axis deviation value during jacking. When the centerline is found to be deviated, correct it in time. After each round of jacking of the steel-concrete composite beam, use the total station to measure the axis endpoints to determine whether deviation occurs. If deviation occurs, correct it in time; (4) During the steel beam jacking process, every 3 to 5 jacking strokes, the horizontal jack on the outside of the movable pad shall be used to adjust and correct the deviation in time. The axis deviation shall not exceed 5 cm. When correcting the deviation, each fulcrum shall be corrected toward the center of the curve. If necessary, the jacking equipment at some fulcrums may be moved horizontally; (5) If the axis deviation is too large, the jacking construction should be stopped, the control system should be started, the centerline deviation correction value of each point should be input, the adjustment cylinder should be started, and the centerline deviation of the beam should be adjusted to the allowable range; Anti-slip measures: The pushing direction is opposite to the longitudinal slope direction. The horizontal component of downhill force needs to be considered during pushing. A high-pressure asbestos plate is set on the contact surface between the movable pad and the steel beam to increase the friction. The friction coefficient between the steel plates is 0.

15. When pushing and dropping the beam, the pushing slope is within 4%, and the steel beam itself will not slide down. When the pushing slope exceeds 1.5%, it is necessary to set a leveling steel plate on the top of the walking jack pier and the supporting pier. Guide beam on the pier: During the jacking process, the front end of the guide beam will bend downward due to the deadweight of the structure. To facilitate the guide beam on the pier, a 1.5m long and 1m high beak is set at the front end of the guide beam; The specific steps for going up the pier are as follows: Step one, step onto the top pad; The second step is to move the stepper forward a stroke to the position of the pad at the front end of the guide beam, and to level the pad; In the third step, the upper pier device is alternately raised between the walking top and the pad until the bottom plate of the guide beam is higher than the walking jack; Step 4: Remove the pad on the top of the step and return the top of the step; Step 5: Push the stepper forward until the bottom of the front end of the guide beam is supported on the pad; Step 6: Walk back from the top; Step 7: Push the top forward until the end of the steel beam is supported on the pad to complete the pier. Beam dropping: The construction process of beam dropping is: construction preparation → dismantling the jacking equipment → installing the top beam steel support and jack → lifting with jack → dropping the beam on the temporary steel support → dismantling the bracket → beam dropping construction → precise alignment → consolidation of the support and the bottom of the beam → completion of construction; The specific process is as follows: Step 1: After the steel beam is pushed into place, use the walking jack to lift the beam, tighten the beam and the pier on the pad, separate the walking jack from the bottom of the beam, and prepare for the beam drop construction; Step 2: Remove the walking top, replace it with the beam-dropping jack and support pad, place it on the longitudinal beam, convert the force system, and use the top-pushing support pad and the beam-dropping jack to replace each other to drop the beam to the top of the longitudinal beam; Step 3: Place the beam-dropping jack on the beam-dropping pier, remove the longitudinal and transverse distribution beams, convert the force system, and use the supporting piers and beam-dropping jacks to replace each other, dropping the beams 100mm each time to the top surface of the adjacent span concrete beams; Step 4: Remove the remaining front and rear guide beams, continue to drop the beams, use the support piers and the beam-dropping jacks to replace each other, drop the beams 100mm each time, and drop the beams to the top surface of the support; Step 5: Adjust the front, back, left, and right elevations of the beam to meet the requirements of the design drawings; consolidate the support and the beam, and after the external prestressing construction is completed, consolidate the support and the beam to complete the beam drop construction; Falling beam support arrangement: Each pier of the beam body is equipped with 4 steel supports, 2 of which are beam-dropping steel supports and 2 are temporary supports. The steel supports are welded with 16mm thick steel plates. The diameter of the steel supports is 406mm, and the heights are 400mm, 200mm, and 100mm respectively. They can meet the needs of beam-dropping. In order to ensure the stability of the steel supports, bolts are used to connect the steel supports.

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