1. 1 project introduction
* * * * The extra-large bridge crosses Huainan, and at DK 125+696.332 (Huainan goes up around K5+84 1.46), portal piers and simply supported beams are adopted to bypass the upstream. The pier is supported by Bailey beam and steel pipe pile. The clearance of the pier is 9.5m, the beam span is 22.3m, the height of the support from the rail surface during construction is 6.8m, and the minimum distance between the steel pipe pile and the center of the line is 6.8m, which can meet the boundary requirements.
The contents of pier construction include: bored pile construction, relocation and temporary protection of existing pipelines, protection of steel sheet piles, hoisting of Bailey beams of steel pipe columns, formwork pouring concrete, etc.
2 door pier column construction
Two rows of bowl-shaped scaffolding are used outside the pier, with a step distance of 60? , scaffolding height requirements than pier template 30? , and build a working platform and protective railings on it, and it is required to hang a double-layer dense mesh safety net on the protective railings as an anti-throwing net. Erect scaffolding in strict accordance with the requirements, including scissors, sweeping poles, protective railings and action platforms.
The pier formwork adopts steel formwork, and the formwork is assembled on site by combining 35t crane with manual transportation. Template joints and tie rods are installed in line with the requirements, and full-time quality inspectors are sent to check and accept, and pier concrete can be poured only after they are qualified.
After the formwork assembly is completed, the cable wind rope must be pulled away from the existing line to prevent the formwork from overturning and falling to the existing line during concrete pouring.
In addition to the embedded parts according to the design requirements, after the bridge pier formwork is installed qualified, embedded steel plates are connected to the embedded steel pipe columns on the side of the bridge pier and the front facing the existing line, and the size of the steel plates is 200mm×200mm× 10mm, and the embedded steel bars are welded with the bridge pier steel bars.
The pier concrete is transported by tanker, and the concrete pump is used for one-time pouring, leaving no construction joints. In the process of concrete pouring, an experienced tamping hand shall be sent to vibrate, and formwork monitoring personnel shall be arranged to observe the deformation of the formwork to ensure the quality of concrete construction. The concrete pouring speed shall not exceed 1.0m per hour.
3 Gantry installation
3. 1 Installation of steel pipe pier
The steel pipe column is manually installed by 35t truck crane. After the steel pipe column is accurately hoisted in place, the steel pipe column and the embedded steel plate of the bearing platform are connected with high-strength bolts and fully welded. L75×75×8 is adopted between steel pipe columns. Angle steel is connected into a whole and connected with embedded steel plates on three sides of the pier at the same time.
3.2 beam installation
Before hoisting, the I45a I-beam is welded into a whole, the steel plate at the top of the steel pipe column is ejected to the exact position of the beam with paint, and it is manually installed with a 35t truck crane.
3.3 Bailey beam acceptance, trial assembly and trial hoisting
Bailey beams are assembled by three rows of steel bars 32 1 Bailey beams, and the spacing between Bailey beams is 22.5? , using standard steel bar connection.
After Bailey beam comes into play, the Engineering Department, Quality Assurance Department and ministry of materials and equipment shall organize acceptance one by one. Distortion shall not be used, and the bolt connection shall be adjusted, reinforced or replaced if it is unreliable. Corroded Bailey beams should be removed, and those with serious corrosion should not be used. Those with cracks and falling off should be welded and reinforced. After the Bailey beam is qualified, it will be tested at the assembly site, and the Bailey beam with poor test results will not be used.
3.4 Bailey beam support preloading and observation
In order to reduce the influence on the existing line, Bailey beam support is pre-pressed outside the site to eliminate the inelastic deformation of the whole support. After the preloading site is leveled and compacted, the clear pouring distance is the same as that of each pier beam, with a width of 0.45m (the same as that of the beam) and a height of 50? The pressure test beam adopts strip foundation, and the upper part is assembled and connected with Bailey beam. After the support is completed, the square timber and bottom formwork are directly laid for pressure test of the support, and the inelastic deformation and elastic deformation of the support are mastered through pressure test, so as to guide the construction.
3.5 Bailey beam installation
3.5. 1 Bailey beam hoisting
Bailey beam hoisting should be carried out under the condition of "blocking point" in business line. Before hoisting, connect all components of Bailey beam. The supporting connection structure includes diagonal braces, support frames, wind-resistant tie rods, beam clamps, truss bolts, chord bolts, diagonal braces and other components. Before hoisting the Bailey beam, determine the exact position of the Bailey beam on the cross beam, and immediately connect and fix the Bailey beam with the cross beam with a U-clip after it is in place. The whole hoisting process is carried out according to the parameters determined by trial hoisting.
3.6 Installation of bottom formwork for capping beam
After the Bailey beam is hoisted and fixed, I32 I-beams are placed perpendicular to the Bailey direction with a spacing of 75cm. The square timber of 15cm× 10cm is laid on the upper part of I-beam, and the square timber is covered with bamboo veneer. Then place a layer of 15cm× 10cm square timber on the bamboo veneer as the transverse rib of the capping beam bottom formwork with a spacing of 30cm, then install the bamboo veneer of the capping beam bottom formwork (thickness 1.8cm) on it, and immediately set up the upper steel pipe protective railing and dense mesh safety net. Laying bamboo plywood between the outer side of the capping beam bottom die and the railing as a construction operation platform. The elastic deformation of supporting preloading should be considered in the leveling and installation of bottom die.
3.7 steel processing and installation and prestressed steel installation
Steel bars are made into semi-finished products in the steel bar processing shed, and are transported manually or hoisted to the bottom formwork of the capping beam for binding and installation.
Install corrugated pipe and its positioning reinforcement, anchorage and anchoring reinforcement in strict accordance with the design drawings, and install prestressed steel strand on the left side of the line.
3.8 Side formwork installation
Due to the construction across the existing line, in order to reduce the dead weight and make the assembly simple, convenient and fast, high-quality bamboo veneer is selected for the side formwork of the capping beam. Vertical bars are set every 30cm outside the side formwork, and double drawstrings are set every 90cm outside the vertical bars. The vertical ribs are made of 15× 10cm square timber, and the straps are made of 2 [2] [12.6 cm channel steel with φ25mm tie rods, and the outside of the straps are welded with 10×65438+.
3.9 Concrete pouring and prestressed construction
3.9. 1 Concrete pouring and prestress construction technology
Concrete should be pumped horizontally and symmetrically in layers, and the thickness of each layer of concrete should be controlled at 30 ~ 40 cm. The order of concrete pouring is: first low, then high, then outside, then inside, and concrete is poured symmetrically at one time. After initial setting of concrete pouring, cover it with geotextile to keep moisture, and spray curing water with sprayer.
Prestressed tensioning construction can only be carried out after the concrete strength of capping beam reaches 90% of the design and the age is not less than 7 days. Tension in strict accordance with the order of design drawings, using integral tensioning method. After tensioning, hole grouting must be carried out within 24 hours.
3. 10 support removal
The design of portal support fully considers the influence of support removal on railway operation. In order to facilitate the removal of the top formwork, adjust the elevation of the top formwork with a sand box, so that the formwork can be removed easily. When dismantling the capping beam template, there should be a special person to direct it, and it is forbidden to throw it around. Materials such as square wood, bamboo veneer, steel mesh, dense mesh, channel steel and I32a I-beam are removed, transported manually from east to west to the working platform outside the existing fence for centralized stacking, and finally shipped out from the south. During the removal of the support, apply to the station every day to block the Huainan bypass line 180 minutes.
Because the Bailey beam is under the cover beam, in order to avoid the problem that the two groups of electric hoists may not work synchronously, the manual hoists are slowly pulled out. Firstly, the end of I-beam distribution beam is welded with the channel steel bracket, then the I-beam is derusted and coated with lubricating oil, and then both sides are pulled out simultaneously. During the operation, both parties shall assign special personnel to command and monitor the longitudinal inclination of Bailey beam.
After the Bailey beam is pulled out from the bottom of the capping beam, it is slowly hoisted out with a 200t crane. The Bailey beam is hoisted out of the "blocking point" construction, and the process and requirements for hoisting out of the existing line area are the same as those for Bailey beam hoisting.
I-beams are lifted by two cranes at both ends at the same time. After landing slowly, lift the capping beam out manually, and then lift it out of the working face with a crane.
For the three steel pipe columns outside the capping beam, they are all distributed outside the capping beam. After the upper end is fixed with a crane, it is disconnected from the embedded parts and directly hoisted away. For the steel pipe column in the middle of the capping beam, the steel pipe and pier ring should be wrapped together with steel wire rope before dismantling to prevent the steel pipe from dumping into the existing line and endangering the safety of the existing line. Fix the top of the column with inverted chain, loosen the connecting bolt on one side, slowly remove the steel pipe from the capping beam, then slowly put down the column and transport it out with a 50t crane.
4 emergency plan and preventive measures for blockade construction
4. 1 Strictly check the construction scheme, and disclose the key construction scheme and corresponding safety measures to each construction worker, so that everyone knows their work contents and responsibilities.
4.2 The Safety and Quality Department works closely with the Engineering Department to integrate the construction scheme and safety assurance measures, so as to keep pace and closely connect.
4.3 Check whether all safety measures are put in place. Those that are not implemented as required must be rectified immediately, and the blockade construction can be carried out only after the safety measures are in place. To cause mass casualties, we must quickly organize the rescue work for the wounded.
4.4 The "Eight Prevention" measures to prevent labor safety are not in place, resulting in personal injury.
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