Pre-assembly method of steel pipe arch site

The semi-finished steel pipe arch assembly units processed through the factory and put into the construction site mainly include: single dumbbell-shaped main arch pipe, webs (and oblique webs), cross braces, cross bracings, baffles, arched foot connecting plates, etc. . After entering the market, these unit components should be stacked in accordance with the assembly order, and they should be pre-assembled and installed one by one.

1, pre-assemble pedestal production

The site is pre-punched by the horizontal group plan construction. The layout of the pre-assembled pedestal is based on the control parameters after the coordinates are converted from the design drawings. The main arch pipe pre-assembled the pedestal longitudinally to make two adjacent segments at the same time. Cross struts (X-shaped struts) A group of pre-patch pedestals are arranged, first to make horizontal struts, and then to reform the X struts.

The bench is a bench base. Five horizontal bars are set within a length of 25 m. The width of the seat is 80 cm. The seat length of the steel pipe port is 12.5 m. The length of the middle bar of each section is 7.0 m. The pedestal is made of 7.5-milliliter chipping stone and the surface is leveled with grout to measure the stake. The pedestal is buried 10 to 30 cm deep in the ground, requiring a dense and stable foundation. The top of the pedestal is 50 cm above the ground and is horizontal. During construction, pre-embedded steel plates (positions according to measurement and stakeout, 500 mm × 600 mm × 12 mm steel plates), supporting frames for the tire frame, and spare anchor rings were prepared as required.

2, tire frame production

Make a solid, rigid frame on the pre-assembled pedestal. According to the size of the construction sample and set aside work adjustment space, horizontal support rods, vertical positioning pillars and stability limit for the pre-assembled members shall be made of steel plates (thickness 10 to 16 mm) and profiled steel (180 to 220, 100 to 160). Bit braces. Theodolite and level gauges are used to control the horizontal and vertical accuracy of the tire frame.

3, the main arch pipe positioning

The interface of the main arch pipe is projected on the pedestal by using the theodolites according to the conversion coordinates. The site gantry crane is used to hoist the main arch pipe into two segments. At the two ends of the main arch tube with excess length, the interface ring stitch line was released. By adjusting the positioning, the horizontal spacing of the tube axis of the two segments is the design coordinate value. The plane of the upper and lower centerlines of the individual segments is perpendicular to the horizontal bottom line of the tire frame, and it coincides with the interface projection line on the interface of the interface between the ring and the pedestal. . After precise positioning, use a limit strut to fix the tire on the tire frame, and then repeat it with the instrument. After the geometrical accuracy control is passed, cut off the length of the port length (the length should be determined by considering the influence of welding), lay the groove and smooth it to ensure smooth welding.

4, on-site pre-spliced welding

The prepared joint support rods were accurately welded near the port of the main arch pipe, approximately 30 cm from the interface, and had sufficient rigidity to maintain the docking geometry of the main arch pipe ports. The welding of the abdominal rods is done in the order from bottom to top, then in the order of the straight web members and the oblique web members. When welding, symmetrical and staggered sections are used to reverse the order. During the group fight, the size error of the steel pipe arches was strictly monitored.

Due to the difficulty of on-site welding overhead welding, in order to ensure the quality of the weld, after the completion of the flat welding and vertical welding of the entire section, the gantry crane is used to turn over the pre-assembled section as a whole, and then weld the other side of the weld. In the construction before turning over, it is necessary to pay attention to the manual welding of the top weld as required, and the first group should be welded to the partition. During turning, it should be gentle and gentle, and the necessary support or pull rope should be set to prevent impact and concentration. Force. Before turning on the flat welding of the original overhead welding, the main control dimensions of the section of the steel pipe arch are inspected to prevent deformation.

The pre-assembled installation section shall be welded on the ground before hoisting all kinds of lifting aids, set cross-positions and measurement control marks, and install welding access channels.

5. Neighboring standard installation section to interface ground treatment

In order to reduce the workload and construction difficulty of accurate alignment of air butt welding, pre-assembled installation sections must be ground pre-connected to the interface and necessary technical processing. Because the steel pipe arch will encounter various factors during the production process, the ellipticity error of the main arch pipe exists objectively, and the elliptical shape of the interface between two adjacent segments is inconsistent. When the construction is docked, the mutual misalignment between the interface steel plates (pipe walls) is common, and the misalignment values are generally 1 to 5 mm or even more than 20 mm. For this purpose, the two steel pipe arches on each set of pedestals at the pre-spelling site shall be pre-connected to complete rounds before lifting, and corresponding to each other, clamps and markings shall be set up, so that each of the four steel pipes and the eight interface steel pipe faces The docking misalignment error is limited to ±1 mm. When lifting, the adjacent section is dismantled and then the installation section is lifted, and then the rear installation section is shifted to the position of the original tire frame where the section has been hoisted, and then a new section of pre-assembly is performed. Here, with the advancing of the segment, the size of the main arch pipe segment also changes, and the position of the upper limit strut of the tire frame also needs to be adjusted accordingly.

6, air welding

The bridge steel pipe arch is welded and arched into segments. This puts forward high technical requirements for the manufacture of steel pipe arches, on-site pre-assembly and aerial butt welding, and cable lifting-holding system, which increases the difficulty of the entire installation process and greatly prolongs the installation period. After the steel pipe arch installation segment is placed in place by cable hoisting, the steel bar (or steel plate) is positioned using a preset interface for initial positioning. According to the linear control instructions of the theodolite and the leveling instrument (or total station), the cable crane and the laterally stabilized wind cable are used. The chain block hoist adjusts it vertically, horizontally, vertically and rotationally, so that the two interfaces are matched. For out-of-roundness errors and small center-to-center distance errors, steel clips can be used to shape the air, and if necessary, jacks can be used. For joints with large deformation or misalignment that exceed the specified requirements, steel linings (or pre-manufactured spare steel pipe hoops) shall be used for strengthening treatment to ensure the quality of arching.

7, horizontal support (X-shaped support) field pre-spelling

Cross struts (X-shaped struts) The approach cell elements are made by assembling a gantry monolith by means of welding by a site gantry crane assembly and installed by a cable crane. The pre-spelling construction process for the site is: cross struts (X-shaped struts) universal pedestal and tire frame production, stake out marking, chord hoisting and positioning, strut pipe group fight positioning, welding, testing, lifting and moving, the next unit pre spell.