I. Overview of the Project
XXX super-large bridge is the only super-large bridge on Beng-Huai line, with the original design length of 2479.852m and the central pile number of K24+35 1.304.
Spans are 30m and 40m, 45 and 28 spans respectively, and precast box girders are 450 and 280 spans respectively. Change the rear axle
The length is 2469.8 13m, shortened by 10.039m, the central pile number K24+356.324, and the span is adjusted to 30m, which is adjusted from the original 73 spans.
To 82 spans, add 9 spans, each span 10 beam slab, a total of 820 precast box girders. The adjusted span combination is 12 Lian× (6×
30m)+2 couplet× (5× 30m), * * m 14 couplet; The width of a single bridge deck consists of 0.5m external crash barrier+15.25m bridge deck.
Clear width+inside 1m corrugated beam bottom =16.75m; The deck is paved with C40 waterproof concrete leveling layer with 8cm thickness and asphalt concrete with+10cm thickness. The superstructure is a P.C composite box girder, that is, multiple boxes are prefabricated and simply supported, and cast-in-place continuous joints are simply supported first and then continuous.
The structural system of.
In order to reduce the installation weight and increase the integrity, transverse wet joints are set between boxes, and mid-span beams are set in each span;
Discontinuous end beams and box girders are prefabricated at the same time and poured into a whole after installation; Now the box girder adopts continuous end spans and ends.
Cast beam connection. The middle distance between adjacent boxes is 3.3625m; ; The top width of precast box girder is 2.40m in the middle girder and 2.85m in the side girder; bottom width
1.0m； Beam height1.60m; ; The thickness of bottom plate and top plate is 0. 18m, and the horizontal thickness of web plate is 0. 18m. Considering that the end of box girder bears prestress.
Concentrated load, meet the requirements of anchorage arrangement, the bottom plate and web of box girder precast end are thickened horizontally to
0.25m, and the length of thickness change transition section is1.90m.
The transverse slope of bridge deck is formed by adjusting the height of webs on both sides during box girder prefabrication, and it is strictly controlled during construction. Number of anchorage devices in the whole bridge
OVM 15-4:9760 sets, OVM 15-5:3360 sets, BM 15-4:6800 sets, BM 15-5:2720 sets. Full bridge GPZ (II) 1.5DX
480 bearings (skateboard bearing GYZF4 375*77mm cancelled), GYZF4300*65mm(GYZF4275*65mm cancelled).
560 yuan; 880 pieces of plate bearing GYZ450*84mm(GYZ375*77mm cancelled).
Second, the pedestal prefabrication
Limited by the site, in order to facilitate the transportation and installation of box girder, the prefabrication yard is selected on the right side of pier 73-74 after the adjustment of the main line bridge.
Outside the ground wire. Since the application for bridge span change was passed, the pressure on the construction period of Gaotanghu Bridge has been greatly eased. My department
We will seize this favorable opportunity, concentrate superior resources, start construction and install early, realize parallel flow operation of upper and lower structures, and plan to complete all box girder prefabrication tasks before the end of September 20 10. The number of prefabricated bases in the West Bank production area was adjusted to 23.
Precast pedestal shall be firm and free from sinking. The base and pedestal should be set at the center-to-center spacing of 4.5-5 meters, and the top surface of the seat body is 8 cm downward.
40mmPVC tie rod embedded pipes shall be reserved every 50cm. Precast site adopts 50cm mountain skin stone as cushion, 10cm thick graded gravel.
Mixture leveling layer, 15cm C20 concrete hardening layer. The mid-span L-5m of box girder support is 25cm thick.
C30 concrete is poured, and the 2.5m ends on both sides are thickened to 25cm；; The bottom is paved with double-layer bidirectional spacing 15cm φ 12mm.
Tie the net. The top edge of the pedestal is protected by L50×50×5mm angle steel with a width of 90cm, and the surface is paved with 10mm L-shaped angle steel plate.
Steel and covered steel plates are combined into a shape. In the prefabrication process, a rubber tube with a slightly smaller diameter is embedded into the [shaped frame]. The two ends of the pedestal are 1m away from the end.
Set a rectangular groove with a width of 20cm and a height of 25cm, which is used for the position where the beam body is bundled and installed. The base edge protects the section steel from longitudinal fracture here.
Open, side closed. After the pedestal is completed, the surface shall be paved with a steel plate with a thickness not less than 10mm, and the rectangular groove shall be disconnected and effectively anchored.
On the basis of concrete, the angle steel intermittently embedded in the side of the pedestal is welded firmly, and the rust is removed and polished by a polishing machine; By the supervision engineer
After acceptance, the box girder shall be delivered for prefabrication. Before binding the reinforcement of box girder bottom plate, temporarily place 10mm thick reinforcement on the disconnected rectangular groove.
Plate, installed in place, take out and recycle the steel plate, and then reuse it.
Considering the post-tensioned prestressed box girder, the mid-span part bulges, which affects the quality of the whole beam in the process of prestressing.
From the uniformly distributed load on the bottom plate to the concentrated load supported at both ends; So at the end of the base, 2.5 meters
Focus on strengthening within the layout scope of double-layer steel mesh.
The prefabrication yard in the west coast production area is equipped with a set of light gantry with a gauge of 3 1.5m and a load of 5 tons, which can also be used for auxiliary pouring.
Specific use. In addition, a set of heavy-duty portal frame is set, with a track gauge of 33m, extending transversely between piers 73#-74#, with a bearing capacity of 120 tons. two
Gantry rails are parallel, with a spacing of 0.75m, which are staggered during construction to reduce interference.
Three, template production, installation and disassembly
In order to facilitate the manufacture, installation and disassembly of box girder formwork and ensure the appearance quality, according to the design requirements, the external contour size of main girder along the longitudinal direction is determined.
Keep it unchanged, and entrust a professional template processing factory to make steel templates inside and outside the box girder. The sectional length of the external mold is 5m, and the flat seam is flat seam, which should be straight.
Stick double-sided tape at the joint to prevent slurry leakage. The thickness of steel formwork shall not be less than 5mm, and the support shall be adjusted by screws. The prefabrication yard is equipped with 3 1.5m Xiaolong.
Assembly, disassembly, displacement and concrete pouring of gantry and auxiliary formwork. There are two kinds of formwork for box beam end. The first one is related to the beam.
The formwork is supported at the same time, and its shape is stepped according to the position of the anchor plate. The second is to set the end-sealing anchor at the discontinuous end, which should be prepared in advance.
After grouting, the conduit will be erected to seal the anchor head and ensure that the shape of the beam meets the size requirements.
In order to ensure the accuracy of the reserved channel, the end die should be close to the side die and the bottom die and perpendicular to the channel axis. assemble
When the template is used, ensure that the upper and lower pull screws are fastened in place and shall not be loose; All bolt holes at the sectional side formwork interface are filled with fastening bolts; After assembly, check whether the flat-fell seam is tight and does not leak slurry; Before the template is used for the first time, the surface must be carefully and thoroughly.
Derusting, after grinding with electric grinder, immediately apply release agent, and brush evenly without omission. Template lifting
Avoid collision and local deformation during the process. After the concrete strength reaches 2.5MPa, the side formwork can be removed.
The storage place needs to be cleaned, repaired, oiled and maintained for the next use. Considering that the core mould bears the construction load during the concrete pouring process
Load, concrete of top surface and side wall, weight and dead weight of workers, etc. At the bottom of the mandrel, supporting steel bars or horse stool must be added. fixed
After the external mold is finished, check the longitudinal flatness of the cantilever part with a guide rule; Check whether the dimension of the top of the web meets the design requirements every 5m.
Beg.
There are four Ф100 mm vent holes on the bottom plate of each precast box girder, and the continuous ends are 9.60m away from the center line of the span.
12.60m, and the distances between the discontinuous end and the center line of the span are 9.72m and 12.72m respectively. During construction, if the position of the vent and the bottom plate
If the rebar interferes, the rebar position can be adjusted appropriately. After moving the beam out of the pit, poke the vent hole on the box in time to release it.
Solidify the water and protect the orifice wall from damage.
Four, steel engineering
After passing the inspection, steel products of various specifications shall be piled up by classification. According to the drawing requirements of processing steel bars, make a "steel bar lofting and blanking sheet".
Only after verification can materials be discharged. When blanking, it is necessary to operate in strict accordance with the drawings and specifications, and strictly control the appearance of waste products and reworked products. Processed steel bars are divided into models and plate numbers, which are stacked separately for later use. Steel surface must be inspected before binding. Remove at the same time
Sundries and welding slag in the mold. Grade I steel bars are straightened by a steel bar straightener, and the steel bar skeleton is made in the steel bar processing plant.
The seat is bound and shaped, and the protective layer of steel bar adopts plum blossom-shaped staggered plastic cushion blocks, which are bound on the steel bar with binding wires. All steel bars
It must be cleaned, derusted and straightened before processing.
After each steel binding, the specification, quantity and size must be carefully checked, and the next working procedure can be carried out only after it is confirmed to be qualified.
Work. The embedded parts of each part of precast box girder and the positioning reinforcement for fixing bellows shall be constructed together with the skeleton reinforcement. OVM 15-4，
5 Ф16mm spiral reinforcement is set at the anchorage end; Smooth round steel can be used instead in construction. Reinforcement connection mode in box girder construction: reinforcement
Diameter ≧ 12mm, if there is no provision in the design drawings, welding connection shall be adopted; Steel bar diameter--12mm, if not specified in the design drawings, it can be.
Use a binding connection. Single-sided weld length ≮ 10d, double-sided weld length ≮5d(d is the diameter of steel bar). Before welding reinforcement, it is required.
Pre-bending to ensure that the axis after welding is in a line; The covered electrode grade used is not less than E50. Pay attention to the binding of steel bars when binding and installing.
Tie a plastic protective pad; It is forbidden to directly contact the steel bar with the formwork, which will lead to the exposure of the steel bar after the formwork is removed.
When installing steel bars at discontinuous ends, load-bearing steel plates should be embedded at the bottom of the beam at the end fulcrum, and anchor steel bars and embedded steel plates at the bottom of the beam should be adopted.
Double-sided welding connection, weld length ≮5d(d is steel bar diameter). During construction, pay attention to the embedded reinforcement of the guardrail on the side of the side beam leaving the carriageway.
And embedded expansion joints embedded steel bars, other embedded steel bars, embedded parts, etc. At the discontinuous end of the side span.
Five, corrugated pipe processing and installation
Two corrugated pipe winding machines are equipped on site to wind corrugated pipes according to different pipe diameters and lengths and the thickness of corrugated steel strip.
0.35 mm, check the cutting length of different types of corrugated pipes before processing, strictly control the crimping strength, and ensure that
Ensure the strength of the seam, but also ensure that there is no pinhole perforation. Processed corrugated pipes are stacked separately in different types and lengths for later use.
Be careful not to overdo it at one time to avoid long-term stacking corrosion. The positioning of bellows shall be determined accurately in strict accordance with the coordinates of design drawings.
, must be accurate, strictly control the bellows position, straight line according to 100cm set a positioning steel bar, and fixed with steel skeleton.
When binding, properly encrypt the positioning steel bars at the bending channel, and set the positioning steel bars at a spacing of 50cm. Ensure that the pipeline moves smoothly and linearly during installation.
Bellows joints shall be tightened with bellows of one size, and then sealed with adhesive tape. Check whether there is a channel at any time during the threading of corrugated pipe.
Cracking phenomenon, and timely with tape binding, corrugated pipe positioning end, before concrete pouring, wear into the gasket.
Six, concrete pouring
Before concrete pouring, the formwork, reinforcement and corrugated pipe are installed and accepted by the supervision engineer. Vibration adoption
Horizontal continuous casting adopts plug-in vibrating rod, surface vibrator and manual inserting rod. Pour it to the end first
Thickness, vibrating compaction; Then pour the belly top; The web is poured in three layers, and the top plate is poured to the top at one time. After pouring is completed
When leveling, plastering and pulp collection, the top surface is embossed.
The design of concrete mixture ratio should fully consider the aggregate particle size of the materials used and the slump and workability of the mixture.
Standard and convenient for construction. Before the opening of concrete, the silt content of raw materials should be strictly controlled and must meet the specification requirements. Reduction of admixture in concrete
Retarder can prolong the initial setting time of concrete and reduce water consumption, thus achieving good workability and reducing concrete bleeding. Concrete is mixed centrally in the mixing station. During the mixing process, the personnel on duty will check it to grasp the changes of aggregate, moisture content and particle size, and check it.
Check the aggregate and water quantity, and randomly check the slump of concrete, and control and supervise the mixing time for not less than 90s. Mixing, transportation,
When entering the warehouse, it should be transported with the mixing to prevent concrete from separating and bleeding before entering the warehouse. Concrete pouring adopts the scheme of horizontal layering, vertical segmentation and one-time pouring and molding. The dense parts of steel bars at the end shall be vibrated by manual rod insertion and internal vibrator; water
The bottom concrete is vibrated by surface vibrator and plug-in vibrator.
Key points of concrete pouring construction: Before pouring, clean the mould, and check all kinds of embedded pipes and components for omission or displacement.
The pouring direction is from one end of the beam to the other. In each section, the bottom plate is poured first, and then the belly top plate is poured. When pouring, it must be in the bottom.
Before the initial setting of the first layer of concrete, a layer of concrete is poured to ensure the continuity and integrity of concrete. In the process of pouring and vibration
Bellows and embedded parts shall not be displaced or damaged. Operating procedures such as feeding and vibrating shall be carried out in strict accordance with the specifications. eye
Before, the temperature was high, so when pouring concrete, avoid the high temperature period at noon and choose the time of the day when the temperature is low.
Precautions for concrete pouring: When pouring, it should be layered scientifically to ensure that the interval between the upper and lower layers does not exceed 90min, and it is forbidden to rush up.
Initial setting occurs before the first layer of concrete covers the lower layer of concrete. So as to prevent the bellows joint from falling off, resulting in blockage, displacement, bending or falling out of the channel.
In case of quality problems such as local sag, the vibrator shall not touch the corrugated pipe, steel bar and formwork. Check and correct the positions of end anchor pads, corrugated pipes and other embedded parts at any time. The end of post-tensioned prestressed box girder is the stress concentration part, so attention should be paid to pouring quality to ensure safety.
Maintain the compactness of concrete. Prevent concrete collapse and anchor pad fracture caused by stretching. In the process of pouring, ensure that the side beam is outside.
The sidewall thickness is consistent and the line shape is beautiful; The top of the spindle is pressurized at a distance of about 5m to prevent floating. Accord to that anti-floating effect of the first pressurization,
Adjust the pressurization interval. If the effect is not good, the spacing will be reduced. When pouring concrete, in order to keep the mandrel position accurate, both sides should be
Reliable supports must be added to prevent the spindle from displacement or deviation. In the concrete workers, make sure that there are more than two masters vibrating by special personnel to ensure the compactness of concrete.
Concrete curing: according to the needs of prefabrication and installation, combined with the characteristics of this project, the concrete is planned to adopt the combination of natural curing and steam curing.
Maintenance plan. Under normal temperature, natural curing is adopted; Only when the temperature is low in winter or it is urgent to install, steam curing is adopted.
① Nature protection. The prefabrication yard is equipped with sanitary water supply system, and the newly poured concrete will be covered and watered as soon as possible after collection.
The water spraying curing time is generally 5-7 days, and the concrete surface shall not be damaged or polluted when covered. Sprinkle water several times a day to ensure safety.
The concrete surface is always wet to prevent the alternation of wet and dry. It can also be covered with geotextile with strong water absorption.
Extend the watering interval. The maintenance work shall be carried out by special personnel and inspected by special personnel, and the outer side of the web plate shall be sprayed with embedded water supply system for health care.
Automatic sprinkler irrigation.
② Steam curing. When the outdoor daily average temperature is stable below 5 C for five consecutive days, concrete, reinforced concrete,
The construction of prestressed concrete and other projects is called winter construction. In winter construction, the winter construction organization plan and preparation should be made in advance.
Work, take measures in advance to ensure that the concrete strength does not reach the "critical strength of frost resistance", it is forbidden to freeze, generally frost resistance.
The strength is 30%-40% of the design strength of concrete. Especially at low temperature, steam curing measures will be taken to ensure the progress of the project. evaporate
Steam curing equipment mainly includes industrial boilers, heating pipes and curing sheds. The curing shed is processed into a skeleton with angle steel for shaping and prevention.
Thermal insulation waterproof tarpaulin covers the thermal insulation layer. Immediately after concrete pouring and molding, cover the shed, let it stand for 4-6h, then steam it and heat it evenly. Full steaming
Designate a person to be responsible for the process, strictly control the heating rate, constant temperature and time, and regularly check the temperature of the curing shed to prevent local steam leakage.
And uneven heating occurs. During steam curing, concrete test blocks should be added in groups of 1-2 and cured under the same conditions. According to the test of concrete strength, it refers to
Guide and adjust the curing time, and fill in the steam curing inspection record.
Seven, prestressed tensioning, hole grouting
According to the different requirements of prestressed beam length, the beam is cut, braided and threaded with a grinding wheel cutter until the beam strength reaches the design.
After the strength reaches 90%, it can be tensioned. Prestressed construction strictly abides by the requirements of technical specifications, and the jack and oil pressure gauge must be calibrated. When the stress control method is used for prestressed steel strand, it should be checked by elongation. Between 0 and the initial stress, the elongation is determined by the adjacent levels.
(initial stress is 0.15 Δ k to 0.3 Δ k) Measured elongation gauge; The difference between the actual elongation and the theoretical elongation should be controlled within 6%
Inside. Otherwise, suspend the construction, analyze and find out the reasons, and take measures to adjust before continuing the tensioning. During tensioning, the line of action of jack tension coincides with the axis of prestressed steel strand.
General tensioning procedure: 0→ initial stress (0.15 Δ k) → 0.3 Δ k →1.0 Δ k (holding core for 2 min) →1.0 Δ k (anchoring).
Tension should be carried out symmetrically at both ends, and tension should be carried out according to the tension sequence shown in the drawing (see drawingNo. Silicon 6-5-2/2,
Tension sequence N 1, N3, N2, N4). After tensioning, cut off the redundant prestressed tendons outside the outcrop anchorage and fill them with cement slurry.
Prestressed reinforcement gap, so as not to lose grouting pressure. Grouting in time; Grouting adopts piston grouting pump, which is slow and uniform.
Even, continuous and uninterrupted.
The strength grade of cement used shall not be lower than 42.5, and shall not contain lumps. The feeding sequence of cement slurry is water injection first, then water injection.
Cement, mixing time is not less than 65438±0min, and mortar is sieved and stored in slurry storage barrel; And keep enough to ensure that each.
Grouting of the pipeline can be completed continuously at one time. The time interval between preparing cement slurry and pressurizing the pipeline shall not exceed 40 minutes. To make sure
For grouting strength and fluidity, grouting materials with low water content and weak expansibility can be used. Grouting label shall not be lower than the design label; if
There is no specific provision in the design, and it is prepared according to the same label C50 of the beam body. During grouting, the cement slurry mixer keeps stirring; Fill with thin mud
The pressure shall be subject to the compactness of cement slurry pressed into the hole. The initial pressure is small and gradually increases, generally 0.5MPa-0.7MPa.
In order to ensure that the pipeline is full of mortar, after each grouting reaches the maximum pressure, close the slurry outlet and maintain a certain pressure stability (not small
0.5MPa) for 2min. The discharged thick slurry is the same as the cement slurry with specified consistency. After grouting, and
Remove the dirt on box girder, bearing pad and anchorage, and chisel off the end concrete.
After grouting, check the grouting density from the inspection hole. If there is any falsehood, it shall be handled and corrected in time. When grouting, every job
Six groups of cubic specimens with 70.7 mm× 70.7 mm× 70.7 mm were taken for standard curing, and their compressive strength was checked as an evaluation.
Quality basis of cement slurry. After grouting, fill in the construction records carefully.
Eight, sealing end
Extend the original reserved steel bars, set the end steel mesh, and spot weld some stirrup fixing positions on the support plate.
Set up end-sealing formwork, check the length of beam body to meet the requirements of allowable deviation, and reinforce the formwork. When pouring concrete for end sealing, it should be recognized that
Really tamping, so that the concrete at the anchorage is dense; And pay attention to maintenance.
Nine, safety and environmental protection precautions
1. When entering the construction site, you must wear a safety helmet, fasten your hat belt and use personal labor protection articles correctly. Field operator
Members are not allowed to wear slippers; Do not do your homework after drinking.
2. Before unpacking the whole bundle of steel strands, make a whole closed bracket along the periphery of the steel strands with steel pipes to prevent the steel strands from flying out. prestressing force
There should be obvious safety signs and warning signs in the tensioning area, and non-operating personnel are prohibited from entering. When tensioning, the jack passes through the hole.
It is forbidden to stand in front, and safety baffles must be set right in front of both ends of tensioning. The baffle shall be at a distance of 1.5-2m from the tension end and shall
0.5m higher than the last set of tensioned steel strands, and its width is not less than 1m from the two outer sides of the tensioning end.
3, hole grouting must be carried out in accordance with the relevant provisions of the prestressed tensioning safety facilities. When grouting, the operator should wear glass protective glasses.
Prevent eye injury caused by cement slurry. During or after grouting, the site cement slurry shall be cleaned in time to keep the surface of concrete members clean.
Prevent pollution. After tensioning, it is forbidden to vibrate and beat the anchorage and steel strand.
4. In the process of box girder prefabrication and installation, we should conscientiously implement and correctly handle the safety policy of "safety first, prevention first and comprehensive treatment".
The relationship between safety and production, safety and progress, safety and efficiency, to ensure safety without accidents.
5, strengthen safety education, improve the safety awareness of all workers; Improve the safety system and prohibit the occurrence of "three violations".
6, strengthen the management of temporary electricity, charged machines must hang warning signs, and rain and leakage protection measures.
7, gantry lifting heavy objects, should have the specialist command, it is forbidden to pass from above the workers, nor from above the equipment.
When driving empty, the hook should be more than 2m above the ground.
8. Drive slowly after lifting heavy objects, and don't suddenly change gears or go backwards during driving. When the crane is walking, the driving wheels on both sides should be synchronized.
If any deviation is found, the operation should be stopped, and it can be used again after adjustment. Before starting, send out an audio signal, indicating that the heavy object will be lifted.
The lifting operation should be smooth and even, and it should not be too fast when lifting the beam slab, and the rope should be fastened to prevent swinging. Open air portal
In case of gale of magnitude 6 or above, the crane should stop operation and lock the rail clamp.
9, the use of cable gantry crane, should be equipped with cable drum.
10. After the operation, the gantry crane stops at the stop line and is locked with rail tongs; Turn the controller to zero and cut off the power supply.
Lift the hook to the upper position; No heavy objects shall be hung on the hook. Always pay attention to check the wear and tear of the steel wire rope binding the box girder.
If there is any wear and abnormality, replace it in time.
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