1. General situation of the project: The separation interchange of Jianliu workshop is 6×40m ahead of schedule.

I. Overview of the Project

Jianliupu separated overpass is a 6×40m prestressed T-beam with a total length of 247. 16m, which is located on the left and right separation routes. According to the bridge design of left and right lines, cross Yunman Highway. The bridge is located on a horizontal curve, and the bridge on the curve is simplified as a straight bridge design. T-beams and piers are arranged radially along the route design line (route center line), and each prefabricated T-beam spans the standard length. Due to the influence of horizontal curve, the length of each beam in each hole is different from the standard length. According to each span curve, 40mT precast length and adjustment plate configuration table are provided. Adjust the radial distance between the pier abutment of the left and right lines and the route design line (route centerline) and the distance between the collision wall and the edge of the wing plate of the inner and outer beams respectively, so that the bridge carriageway meets the requirements of the route curve. T-beam prefabrication adopts adjustable formwork to make the transverse slope of wing plate conform to the superelevation change of the transverse slope of bridge deck. The whole bridge has ***60 T beams. For the prefabrication technology of T-beam, see Construction Technology of Prestressed T-beam Prefabricated by Post-tensioning Method.

Second, the construction scheme

1, prestressed T-beam precast pedestal

The abutment end of Liupu 6# separated overpass takes up a 400-meter-long and 20-meter-wide fill subgrade as the precast yard of the prestressed T-beam of the bridge. The pedestal requires its lower layer to have enough rigidity, and should be placed on a good foundation, and the settlement should not exceed 2mm. Mechanically level the site and lay a 20cm thick concrete hardening precast site. The beam foundation is processed and grown to be 4 1m, with a width of 60cm and a thickness of 30cm. The foundation has a width of 120cm and a thickness of 60cm, and there are 6 pedestals * * *. C25 concrete is poured, channel steel is embedded in the top surface, and a 3mm thick steel plate is laid on it as the beam bottom formwork, and the beam body is hoisted. The camber of 40mT beam pedestal is set downwards according to the quadratic parabola, and the maximum camber value in the middle span is tentatively set as 1cm, and both ends are 0, which is distributed according to the quadratic parabola ratio. The camber values of the remaining beams are determined according to the field test data of the first T-beam, and the line type of the beam top should be consistent with the beam bottom.

After the prestressed beam is tensioned, the middle part of the beam arches. In the process of prestressing, the mass of the whole beam gradually shifts from the uniformly distributed load on the bottom plate to the concentrated load supported at both ends. Therefore, the bottom plate and base of the beam end should be strengthened. The spacing between beam seats is 6m, which is convenient for prefabrication of reinforced concrete T-beams.

2. Installation of steel formwork

(1) T-beam formwork consists of side formwork and bottom formwork. The side formwork is segmented. Leveling screws are arranged at the fulcrum between each section and the ground, and transverse ribs and vertical stiffening ribs are arranged.

(2) After cleaning the template joints with acetone, apply FN-309 steel plate glue, and level with grinding wheel after 2 hours. Check the flatness of the template. After cleaning the template, apply release agent. Do not use waste engine oil instead of release agent. 1 set of middle plate and 0.5 set of side plates.

(3) Rubber pads (foam rubber thickness is 8 ~ 10 mm) or rubber strip should be set between the steel formwork and the base, and the rubber strip should have good elasticity to ensure the beam bottom formwork vibrates under the excitation of the side formwork to prevent slurry leakage. After the formwork is supported, the lower part is fixed with screws, the upper part is controlled with tie rods and fixed with steel wire tension. Template lap joint with 2mm thick double-sided tape seal.

(4) After the steel formwork is supported, its plane position, height, node, vertical and horizontal stability of connection, line type, etc. Should be inspected.

3, concrete pouring

(1), T-beam is C50 concrete, fine aggregate is medium-coarse sand with good grading, hard texture, clean particles, and the particle size meets the requirements. Coarse aggregate is clean and hard, with good grading of 0.5 ~ 2.5 cm gravel, and admixtures such as water reducer and early strength agent are appropriately added, which shall not exceed the specification requirements.

(2) Concrete mixing: concrete ingredients are mixed in the mixing station, and all kinds of weighing instruments should be kept accurate. Always check the water content of aggregate, the mixing time shall not be less than 2 ~ 3 minutes, and strictly control the slump of concrete.

(3) Transportation of concrete: The transportation capacity of concrete should meet the needs of concrete setting speed and pouring speed, so that the pouring work can be uninterrupted, and the uniformity and specified slump of concrete when transported to the pouring site can be maintained.

(4) Concrete pouring: Before pouring, the positions of supports, templates, steel bars and embedded parts shall be inspected and recorded, and pouring can be carried out only after meeting the design requirements. Debris, water and dirt on the steel bars in the formwork should be cleaned up. Template if there is a gap, should be tight. Concrete vibrating is mainly attached vibrating, supplemented by inserted vibrating. Attached vibrator adopts high-frequency fast external portable vibrator, which is started when pouring concrete. It is forbidden to empty vibration template. When pouring concrete at the lower part of the web, the vibrator at the corresponding position and the vibrator at the upper part should be started, so as to speed up the concrete entering the mold and prevent the cavity from forming. When the concrete completely enters the lower part of the web, stop starting the upper vibrator, and only start the lower vibrator until it is dense. The sign of compactness is that the concrete stops sinking, no longer bubbles, and the surface is smooth and full of slurry.

5], pouring panel concrete, using plug-in vibrating rod vibration, stop attaching vibrator. After each vibration, the vibrator should be slowly advanced during vibration to avoid collision between the vibrator and embedded parts such as formwork and reinforcement. When the concrete no longer sinks, the surface has been leveled, no bubbles emerge, and the concrete surface has been submerged, indicating that the concrete has been compacted and leveled by vibration. Finally, the surface of precast slab is roughened to facilitate the close combination of cast-in-place concrete and it.

[6], during concrete pouring, should be designated persons to check the stability of stents, templates, steel bars and embedded parts, etc., when found loose, deformation, displacement should be handled in time. Testers monitor the quality of concrete mixing in the whole process and in all directions, and find abnormal conditions such as uneven mixing, too large or too small slump, stone particle size and mixture ratio, and immediately take decisive measures to ensure the quality of concrete pouring. During concrete pouring, samples are randomly sampled according to the requirements of Trombus technical specification, and two groups of samples are made 1 ~ 2, which are cured under the same conditions as T-beam, providing reliable strength data for T-beam tensioning.

4, template removal

T-beam can only be dismantled when the compressive strength of concrete reaches more than 2.5MPa. When dismantling formwork, it should be dismantled in overlapping order according to the principle of supporting first and then dismantling first. Care should be taken to avoid damaging the concrete surface and concrete edges and corners by collision. Without the consent of on-site technicians and supervision engineers, the surface defects of concrete shall not be modified at will. After formwork removal, the formwork shall be repaired, cleaned, oiled and properly stored.

5. Maintenance

After the final set of concrete, assign special personnel to cover it with sacks or curing glue, and sprinkle water for curing. Keep in good health in strict accordance with the specification requirements, so as to ensure that the concrete surface is wet during keeping in good health. When curing the beam, it is necessary to place a sampling concrete specimen with the same conditions and temperature, and cure it with the beam under the same conditions, which will serve as the basis for prestress tensioning in the future.

6, the production and installation of prestressed reinforcement

(1), read the drawings carefully before binding reinforcement, and make a reasonable processing and installation plan.

⑵ Double-sided lap welding is adopted for the main reinforcement joints. The joint of reinforcement should not be set at the maximum stress of beam span, and the distance between welded joint and elbow should be greater than 10d. Other parts of the steel joints should be staggered. In any case, the number of joints in the same section shall not exceed 50% of the total area of steel bars in this section.

(3) Measures to ensure the thickness of the protective layer of steel bars: Fine stone concrete cushion blocks or special cushion blocks for buildings that are not lower than the strength of structural concrete shall be adopted to support the cushion layer evenly.

(4) The embedded steel bar and T-beam steel bar are connected by arc welding, and the position of embedded parts should be accurate. When precast beams, attention should be paid to the embedded positions of lap reinforcement, guardrail reinforcement and expansion joint reinforcement between embedded beams and slabs.

5], wire rod reinforced with straightening machine one-time blanking, straightening, derusting, steel bar must be derusting and decontamination before blanking.

[6], strictly control the reinforcement spacing comply with the design requirements, and binding firmly.

7. Fabrication, tensioning and anchoring of prestressed tendons of T-beam

(1), reserved channel

The side span of circular steel beam pipeline is φ87mm, and the middle span is φ77mm corrugated pipe. The size and position of the reserved holes for prestressed tendons should be correct, the holes should be smooth, and the embedded steel plates at the ends should be perpendicular to the center of the reserved holes. The pipeline is fixed and installed with positioning steel bars, so that it can be firmly fixed at the design position in the formwork, and there will be no displacement during concrete pouring.

The connecting pipe at the bellows joint should be of the same kind with larger diameter, and its length should be 5 ~ 7 times of the inner diameter of the connecting pipe. When connecting, the angle change of the joint and the rotation or displacement of the pipeline during concrete pouring should be avoided, and the joint should be tightly wrapped to prevent cement slurry from infiltrating. During installation, welding sparks are strictly prohibited from falling on the bellows. Pay attention to check the bellows for cracks. If there are cracks, wrap them with tape paper in time. In order to prevent the difficulty of beam penetration caused by slurry leakage of corrugated pipes, it is necessary to thread steel strands or put a hard plastic pipe with a wall thickness of 1cm and an outer diameter of 2 ~ 3 mm smaller than that of corrugated pipes in each corrugated pipe. Immediately after concrete pouring, pull out the plastic pipe and thread the steel strand in time.

Bellows should be provided with grouting holes, and if necessary, exhaust holes should be provided at the highest point and drainage holes should be provided at the lowest point. Grouting pipes, exhaust pipes and drainage pipes shall be standard pipes with a minimum inner diameter of 20mm or suitable plastic pipes. Metal or plastic structural fasteners shall be used for connection with the pipes, and the length shall be enough to lead out the structure from the pipes. After the pipeline is installed in the formwork, the end of the pipeline should be covered to prevent water or other sundries from entering.

2, prestressed reinforcement installation

Prestressed steel strand shall conform to the current national technical specifications, with factory certificate and quality specification. After the prestressed steel strand enters the site, it should be strictly inspected, and three groups should be selected from each batch for surface quality, diameter deviation and mechanical properties test.

Pre-stressed tendon blanking: according to the distance from the anchorage at T-beam end to the tensioning beam end, the length of tool anchor, the exposed length of steel strand at anchorage end and the length of tensioning jack required at tensioning end, the blanking size of pre-stressed tendon is determined. When blanking, use a grinder to cut, and arc cutting is not allowed.

Prestressed tendons can be inserted into pipes before or after concrete pouring. This bridge adopts the method of inserting beams after concrete pouring. For steel strands, all the steel strands in a steel beam can be bundled into the pipeline or inserted into the pipeline one by one. Before crossing the beam, check the anchor pad and channel. Anchor pad should be located accurately, the channel should be smooth, and there should be no water and other sundries.

(3), tensioning

Before prestressing tendons are applied, the members shall be inspected, and the appearance and size shall meet the requirements of quality standards. When tensioning, the concrete strength of members shall meet the design requirements and shall not be less than 90% of the design strength. The tensioning sequence of steel beams is N4-N3-N2-N 1, and both ends of prestressed tendons are tensioned at the same time. Tension equipment jack: YDC2500, with a stroke of 200mm. Anchorages: OVM 15-7, OVM 15-8, OVM15-9; Oil pump: ZB4-500 oil pump matched with jack. The tensioning procedure of prestressed tendons is: 0-10% Δ con (marked with elongation value)-20% Δ con-Δ con (measured with elongation value after 2 minutes of loading), and Δ con is the tension control stress. Stress and strain are used to control tension.

Tensioning operation flow: Before the steel strand is tensioned, the metering mechanism must check the jack and oil pressure gauge and issue a report. The number of each beam should match the corresponding anchorage, the clamps should be put away, and the steel strand should pass through the center of the jack. When the prestress of steel strand reaches 10%δcon during tensioning, stop oil supply. After checking whether the clamp is in good condition, draw a line to mark it as the starting point for retracting the measuring tool clamp.

After the above work is completed, the jack cylinder is filled with oil and the steel strand is tensioned. The tension value is mainly based on the reading of oil pressure gauge, and checked by the elongation value of prestressed steel strand. The actual tensile elongation and theoretical elongation are controlled within 6%. When the oil pressure reaches the tensioning tonnage, close the oil circuit of the master cylinder and keep it for 2 minutes, and measure the elongation of the steel strand for inspection. After 2 minutes, if the oil pressure drops slightly, it must be replenished to the designed tonnage oil pressure value, and the jack limit plate is locked with clips, and recorded in time. The total number of broken and slippery wires in the whole beam shall not exceed 1% of the total number of steel wires.

Relevant regulations:

(1), before tensioning the steel strand, the beam should be thoroughly inspected. If there is any defect, it must be approved by the supervision engineer in advance, repaired well and reach the design strength. The residual mortar of the pressure pad and the expanded part of the anchoring pipeline should be carved out at the root, otherwise it shall not be tensioned.

(2), high pressure oil gauge, jack can be used only after inspection, and shall not exceed the validity period.

(3), each span tensioning must have someone who's in charge to fill in the tensioning records in time.

(4), jack are not allowed to overload, shall not exceed the prescribed travel; When transferring the oil pump, the oil gauge must be removed and transferred.

⑤ When tensioning steel strand, both sides must be slowly filled with oil to tension the jack master cylinder, and the elongation at both ends should be basically the same. It is forbidden to tighten one end. If the design has special provisions, it can be handled according to the design documents.

Inspection of tensile elongation value:

The tensile elongation value shall be measured with a ruler with a measuring accuracy not exceeding 65438 0 mm. Under the initial stress, the exposed length of the oil cylinder shall be measured, and under the corresponding graded load, the exposed length of the oil cylinder shall be measured. In the case of intermediate anchorage, the initial load in the second stage should be the final load in the previous stage, and the measured elongation value from initial stress to final stress can be obtained by superposition of multi-stage elongation values. Measured elongation △L=△L 1+△L2-A-B-C

△ l1-the measured elongation value from initial stress to maximum tensile force, including the total elongation of multi-section tension and tension at both ends;

△L2- calculated elongation value lower than initial stress. 20% Δ con minus10% Δ con (initial stress) can be used as the measured elongation value;

A- the shrinkage of prestressed reinforcement in the process of tensioning refers to the shrinkage value of tool anchor when both ends are tensioned;

B -- the tensile elongation value of prestressed steel bar in jack with working length;

C- the elastic compression value of members is generally not considered for small spans, and the design shall prevail for large spans.

(4), hole grouting

Hole grouting should use cement slurry, which can be mixed with appropriate amount of fine sand. All materials shall meet the following requirements:

Ordinary portland cement is used as the cement, the strength grade of cement is 42.5, and clear water is used as the water. The strength of cement slurry is not less than 40Mpa, and the technical requirements of cement slurry are as follows: the water cement ratio is 0.4 ~ 0.45, which can be reduced to 0.35 after adding a proper amount of water reducing agent, and the bleeding rate of cement slurry should not exceed 3% at most. After stirring for 3 hours, the bleeding rate should be controlled at 2%, and the consistency of cement slurry should be controlled between 14 ~ 18s.

Before grouting, the channel should be cleaned. When necessary, the corrugated pipe should be cleaned to remove the oil pollution that may be caused by harmful substances in the pipeline channel. Neutral detergent or soap solution which has no corrosive effect on prestressed tendons and pipelines can be used for cleaning after being diluted with water. After flushing, all the accumulated water in the channel should be blown out by compressed air without oil. And observe whether there is string hole, if there is string hole, several holes should be grouted at the same time.

The time from mixing cement slurry to tunnel entrance depends on the air temperature, and generally ranges from 30 to 45 minutes. Cement slurry should be continuously stirred before use and during pressure injection. It is not allowed to increase the fluidity of cement slurry by adding water because of its reduced fluidity due to delayed use.

Grouting sequence should be injected into the lower channel first. Grouting shall be carried out slowly and evenly without interruption. Piston grouting pump is used for grouting, and the maximum grouting pressure is 0.5 ~ 0.7 MPa. Grouting should reach the other end full of slurry, and should reach the exhaust hole to discharge cement slurry with the same consistency as specified; In order to ensure that the pipeline is filled with cement slurry, a stable period of not less than 0.5Mpa should be maintained after the slurry outlet is closed, and the stable period should not be less than 2min. After the cement slurry has solidified 10 minutes, the slurry stop nozzle can be removed.

During grouting and within 48 hours after grouting, the temperature of the structure shall not be lower than 5℃. When the temperature is higher than 35℃, grouting should be carried out at night. After grouting, the compactness of grouting should be checked in time, and if it is not dense, it should be handled and corrected in time; During grouting, not less than 3 groups of specimens shall be taken from each working class, cured for 28d, and their compressive strength shall be checked as the basis for evaluating the quality of cement slurry.

8, moving beam, stacking

Before moving the beam, mark the beam number and production date at both ends of the beam. Because this kind of beam is long and heavy (lifting weight of middle beam 1 19.4T, side beam114t; Mid-span center beam 120T, and mid-span side beam 1 13.8T) have poor lateral stiffness. The hanging beam is transported by gantry crane rail, and the bottom of the beam is bound with bags.

The beam storage site should be leveled and compacted, without water accumulation. The drainage system should be well arranged around the site to prevent the foundation from sinking, and the concrete platform for beam storage should be built with C25 concrete. The fulcrum of beam storage is on the theoretical support line of T-beam and supported by sleepers. When the T-beam is stored, support or other effective measures shall be taken to maintain the stability of the T-beam. The storage time of T-beam shall not exceed 90 days, otherwise too long time will produce excessive pre-camber.

Third, safety measures

1, the project department set up a safety production leading group, and set up a safety inspection department. Each team has 1 full-time safety officer, and each team has 1 part-time safety officer. Implement regular and irregular inspection, education and daily publicity system, so that all employees entering this project have basic knowledge and skills of safety production, attach importance to safety work ideologically, and consciously implement safety technical regulations. Do a good job in entrance education, clearly mark, carefully prevent and check regularly.

2, special staff must pass the exam and show certificates. You must wear a safety helmet when entering the construction site. It is forbidden to wear slippers, high heels and operate barefoot.

3, construction machinery should be kept clean, should have protective grounding, zero leakage protection device. The rotating parts or flash parts of the machine should be equipped with protective covers and baffles.

4. When the steel strand is tensioned, set the security alert range, and the site should be clearly marked, and it is strictly forbidden for people who have nothing to do with work to enter.

5. Before using high-pressure tubing, pressure test shall be conducted, and unqualified tubing shall not be used. The safety valve on the oil pump should be adjusted to automatically open under the maximum working oil pressure. When the oil pump is not operating normally, stop immediately for inspection, and do not twist the screws of various parts of the oil pump or jack at will under pressure.

6. The oil pressure gauge must be installed firmly and buckled completely. The high-pressure tubing used between the oil pump and the jack, together with various joints of the oil circuit, must be complete and tight, and the oil circuit should be smooth. It is not allowed to leak oil for more than 5 minutes under the maximum working oil pressure. If it is damaged, it should be repaired and replaced in time.

7. When tensioning, people are not allowed to stand behind the jack, and high-pressure oil pipes are not allowed to be trampled. The elongation value should be measured on the side. When the tensioning equipment is found to have abnormal operation sound, it should be stopped immediately for inspection and maintenance.

8, anchorage, fixture should be properly kept by designated personnel, to avoid corrosion, pollution, mechanical damage or loss. After the final tensioning, the anchorage should be treated with antirust and waterproof, and 88 1-I waterproof coating can be used and diluted with banana oil.

Four, personnel, machinery, materials comes into play

Manager 1 technician 1

Quality inspector 1 tester 1

Three drivers and two electricians.

Vibrator 6 Reinforcement Worker 10

Repairman 1 General Worker 15

Two prestressed tensioning devices and two electric welding machines.

2 steel bar straightening machines and 2 steel bar cutting machines.

1 concrete mixing station, equipped with 8 internal vibrators.

1 generator, 2 concrete transport vehicles.

Gantry crane 1 30 additional vibrator.

Setting steel mold (middle mold) 1 set of setting steel mold (side plate) 0.5 sets.

Three Gorges brand cement 1 189T steel bar 5374 17T

Bellows 9449 steel strand 86975T

480 sets of medium coarse sand 1202m3 anchorage devices.

Gravel (5-25)mm 17 13m3 admixture 9486kg.

Fan Nanchun, head of construction, Han Zhenjiang and Zhao, technical directors, head of test, head of quality inspection and head of safety, Wang and Jinchuan Li.

Verb (abbreviation of verb) construction progress plan

The commencement date of this project is 65438+February 2005 15, and the completion date is April 30, 2006. The prefabrication of T-beam of this bridge was completed in 137 days.