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Executive construction organization design of the superstructure of South Canal Bridge

1. Basis for preparation

1. "Design Drawing of South Canal Bridge"

2. "Technical Specifications for Construction of Highway Bridges and Culverts"

2. Project Overview

1. Natural and geographical environment

The South Canal Bridge is located on the Beijing-Shanghai Highway From Qingxian County to Wuqiao Section, the central pile number of the main bridge is K64+036, crossing the South Canal. The South Canal is a third-level navigable river, and the terrain on both sides of the bridge is flat and hilly.

2. Design overview

The total length of the South Canal Bridge is 335 meters. The main bridge is a 3-hole prestressed continuous rigid frame (V-shaped pier) with a middle hole span of 60 meters. 35 meters on each side and 130 meters in length. The approach bridge at the north end is a 2-hole prestressed, simply supported and then continuous hollow slab, and the approach bridge at the south end is a 6-hole prestressed, simply supported and then continuous hollow slab. The whole bridge is located on a flat curve with a flat curve radius R=5500 meters from the center line of the road. The bridge has two horizontal bridges, each with a width of 13.5 meters, a gap of 1 meter in the middle, and a total width of 28 meters. The main bridge part uses No. 50 concrete, and the amount of concrete is 1205m3 per width

3. Hydrology and geological conditions

The design flow rate at the bridge location is 120 cubic meters/second, and the design is accordingly The water level is 13.5 meters (elevation of the Yellow Sea), which is also the highest navigable water level, with a navigation clearance of 7 meters and a navigation clear span of 50 meters.

The geological histogram at the bridge location shows that about 4 meters below the surface is yellow medium liquid limit clay or yellow sandy soil, loosely containing plant roots and wormholes. The bearing capacity is 180kpa. Below it is the second layer, which is about 3 meters thick. It is yellow-brown sub-sand soil, dense and hard plastic. The bearing capacity is 200kpa. The third layer is white silt sand, about 5 meters thick, with uniform particles and a horizontal layer. The water content is saturated and may liquefy, and the bearing capacity is 150 kpa. There are three layers of soil further down, which are basically silty clay, gray-yellow silt, containing quartz and feldspar. The structure is relatively dense and the bearing capacity is 180-200kpa.

3. Overall construction plan

The superstructure of the main bridge of the South Canal Bridge is a cast-in-situ prestressed continuous box structure. Since there is water in the main river, and in order to avoid the installation of too many temporary piers in the water, the main span support of the 60-meter main bridge adopts a pier-beam structure, and the built temporary piers in the water are used as the support pier foundation. The 65-type railway military The pier is used as the support pier, and the 64-type railway military beam is used as the support beam. The 35-meter-span bridge on both sides is located on a relatively flat terrain with no water, so full steel pipe racks are used as supports, and the supports are located on the treated foundation. Use the above construction plan to carry out the construction of the superstructure of the main bridge.

Since the bridge is on a flat curve, the span and beam height are also inconsistent. In order to increase the utilization rate of the formwork and improve the appearance quality of the beam concrete, the bottom form, outer form, and inner form are all assembled easily. The two sides of the laminated bamboo plywood are used as templates. The internal and external formwork frames adopt wooden frames.

According to the design requirements, we used integrated cast-in-place brackets to cast the 130-meter-long main bridge in two sections. First, the first section was poured with a length of 86 meters, which included a 60-meter middle hole and 13 side holes each. meters long, after the concrete reaches the design strength, the prestressed tendons are stretched, and then the remaining 22-meter-long beam sections on both sides are poured.

4. Main construction methods and process flow of the superstructure

The superstructure of the main bridge is a prestressed reinforced concrete box-shaped continuous beam, and the three spans are constructed by cast-in-place construction on supports.

1. Construction preparation

One month before the cast-in-place construction of the bracket, preparations for the superstructure construction should begin.

Its main content:

a. Conduct the mix ratio test of the beam concrete according to the process requirements;

b. Prepare materials according to the construction technical requirements, and carry out formwork Processing;

c. Overhaul and purchase the main machinery for beam construction;

d. Properly allocate the labor force, especially the personnel for each professional type of work; e . Technical cadres should be familiar with the drawings and carry out steel cutting and processing in advance

f. Provide pre-job training for superstructure construction personnel in the form of technical beams.

2. Bracket construction

① Structural form of the bracket

See the bracket design drawing for the mid-span and side span bracket forms of the main bridge.

The bracket mainly includes pier foundations, piers, beams, longitudinal beams and beams supporting the formwork. The pier foundation uses an enlarged concrete foundation, and the piers use steel pipe racks and 65-type railway military The piers and cross beams are made of shaped steel, and the longitudinal beams are made of shaped steel and 64-type railway military beams. Sectional steel is used as diagonal braces to connect the military beams of the 64-type railway laterally to enhance the integrity. Square timbers or steel sections are laid on the longitudinal beams to support the formwork.

② Force analysis and calculation

The bracket is designed as two structural systems: simply supported and continuous. The force analysis and calculation mainly consider the foundation bearing capacity, the internal force of the piers and longitudinal beams (Detailed calculation omitted).

The vertical load takes into account the beam section weight, formwork weight, longitudinal and horizontal beam weight, crowd and working load, etc., and the horizontal wind load is also considered.

③ Setting of pre-camber

The setting of pre-camber is closely related to the deformation of longitudinal beams. Both steel and military beams are rigid components. Since the support foundation is an enlarged concrete foundation, and the buttresses are also rigid military piers and steel pipe racks, their deformation is very small. Moreover, the joint deformation of the pad beam can be determined according to the "Specifications", so the military beam is a bracket longitudinal beam, and its camber is only the deflection of the pin hole and the elastic deformation of the bracket beam after being subjected to a maximum load. After the bracket beam is erected, the pin hole deflection has occurred. Elastic deformation can be calculated accurately, and the support using steel pipe racks as buttresses has very good integrity. The deformation can also be determined by combining theoretical calculations and empirical estimates to determine its subsidence. Therefore, during the construction process, the setting amount of pre-camber can be accurately set according to the calculated value.

3. Formwork construction

① Formwork design

Since the box-shaped continuous beam of this bridge is located on a horizontal curve, and is rigidly rotated to set the cross slope, at the same time the beam The constantly changing height brings difficulties to the formwork design. In addition, the bridge's construction period is tight, and the single-width formwork cannot be reused, so it is considered to be a one-time use during the design. The inner and outer formwork and bottom moldings are all made of large double-sided coated bamboo plywood. The formwork frames are all made of wooden frames. The cross slope of the box beams is adjusted with wooden wedges. See the formwork design drawing for details.

② Template production and installation

Ⅰ. Template production

a. When making the template, the outer frame and inner mold frame can be prefabricated on the ground in advance. All parts are fabricated and installed on-site on the bracket.

b. The dimensions of each rod should comply with the design requirements of the drawings.

c. Ensure the quality of the wood and do not use damaged or decayed wood.

Ⅱ. Template production and installation process: Place skids and longitudinal timbers → wooden wedges → cross timbers → detect vertical and horizontal elevations and measure the center line of the line → place a sample of the size of the beam bottom plate → lay the nail bottom template → tie the beam bottom plate Reinforcement → web reinforcement → place inner mold → tie roof reinforcement → pour concrete. Ⅲ. Technical requirements and precautions for formwork production and installation

a. Before making and installing the formwork, you must check again whether the center and elevation of the bracket meet the design requirements. Only after passing the inspection can the production and installation work be carried out.

b. The height adjustment of the wooden wedges at each point should be based on the pre-camber height provided for construction, with the midpoint of the beam span being the highest, and adjusted according to the quadratic parabola.

c. The thickness of the pads at each point is determined according to the design dimensions of the box beam cross slope, and further inspection and review should be carried out after placement.

d. After the crossbars are placed, in addition to being arranged at a center distance of 50cm, the center of the crossbars should be orthogonal to the center line of the line.

After e, skids, longitudinal timbers, wooden wedges, and horizontal timbers are placed in place, iron nails should be used to lock the interconnected positions to prevent loosening.

f. The vertical and horizontal timbers can be made in full length. When extensions are needed, the joints must be at the position of the pads and wooden wedges.

g. Carefully measure the center line of the line and place a sample of the beam bottom dimensions to ensure the quality of the formwork installation.

h. The seams of the bamboo plywood panels of the template should be filled and smoothed with white lime putty after nailing. The remaining lime ballast outside the seams should be removed.

I. Before tying the steel bars, the surface of the bamboo rubber panel should be coated with release agent. Before pouring concrete, the construction waste on the panel should be removed and rinsed with water.

4. Construction of prestressed concrete box-shaped continuous beams

The main bridge is a prestressed concrete box-shaped continuous beam with a bridge length of 130 meters and a hole-span combination of 35+635 meters. The beams at both ends are 1.3 meters high, the mid-span beam is 1.3 meters high, the top beam of the pier is 2.5 meters high, the top and bottom widths are 13.5 meters, and the bottom plate is 7.5 meters wide. They are made of one-way prestressed, longitudinal beam continuous C50 concrete, and are constructed using the integrated cast-in-place method. , the construction process flow chart is shown below

Prestressed box-shaped continuous beam cast-in-situ construction process flow chart

Military beam assembly and formwork processing → Preparation work ← Temporary pier foundation construction ↓

Measure the elevation → Assemble the bracket ← Install the falling beam equipment ↓

Check the elevation → Install the bottom formwork ← Preset camber

Check

Binding and positioning steel bars

Cutting, braiding and numbering of steel strands

↓ Install the outer formwork ← Check the size, position and elevation ↓ → Binding bottom and web steel bars ↓ → Install corrugated pipes → Inspect joints↓ → Thread steel strands↓ Install inner formwork↓ Bind roof steel bars↓ Pour concrete in sections in sequence→ Make test pieces↓ Maintenance↓ Remove formwork↓

Tensioning

↓

Grouting

↓

Anchor sealing

↓

Removing the bracket

< p> ? Preparation work

Since the middle span of the main bridge is in the water, the trestle can be used to complete the temporary pier foundation construction of the support in advance according to the support design drawing. Complete the production of buttresses, assembly of military beams, and formwork processing and production.

? Erection of brackets

Use cranes on trestles and dry land to erect brackets according to the construction design drawings

? Install templates

First Install the bottom formwork, and then install the outer formwork. They are all hoisted by a crane. The bottom formwork is directly fixed with the square wood on the bracket. Wooden wedges are used to adjust the elevation of the bottom formwork. The outer formwork is hoisted in sections according to the numbers, and the side molds on both sides are blocked. The blocks are tightened with wooden wedges, and the elevation is adjusted with wooden wedges. Wooden wedges are also used to drop the formwork. A large amount of wooden wedges are used during construction. When installing the formwork, attention should be paid to the accuracy and stability of the position and elevation to ensure the overall dimensions of the structure. and beam body line. After installation, the formwork should be repaired in time and painted with release agent.

? Production and installation of steel skeleton

In order to speed up the construction progress, ordinary steel bars can be specially made under the bridge, and the bases can be segmented into skeletons or steel mesh pieces. The length is based on the length of the beam. Determined by body stress conditions and lifting capacity. In the process of making the skeleton, attention should be paid to the influence of the flat curve of the beam body. Place the prepared base plate skeleton and web frame into the bottom mold and the outer mold in sequence. After entering the mold, weld them section by section. Then install the inner mold section by section, and finally tie the roof steel bars.

? Install prestressed pipes and run steel strands

The main bridge is designed to be a full-length longitudinal prestressed bundle, connected with a coupler in the middle, using a 15.24mm diameter high Low strength low-relaxation steel strand, standard tensile strength R y b =1860Mpa, σk =1302Mpa, each bundle of steel strands is in two forms: 9--7φ5mm and 12--7φ5mm steel strands. The corrugated pipe is made into holes. When tying the web steel bars, place the corrugated pipe according to the designed position. Use the positioning mesh to fix the corrugated pipe. After checking the position is accurate, the positioning mesh and the steel frame are spot welded. The distance between the positioning mesh and the mesh should not be greater than 50cm.

The steel strands are threaded from one end to the other by a combination of manual threading and winch threading.

? Install the inner mold

After the bottom mold and web steel bars are tied, install the inner mold in sequence according to the number. ? Binding roof steel bars

? Pouring concrete

The concrete number of the prestressed box-shaped continuous beam of the main bridge is designed to be C50. It is uniformly mixed at the concrete mixing station and the concrete is pumped. of pouring.

Concrete pouring is carried out in sections and in layers. The beam section is divided into the first section, which is 86 meters long. It includes a 60-meter middle hole and a 13-meter side hole each. After the concrete reaches the design strength, it will be prestressed and tensioned, and then the remaining 22 meters on both sides will be poured. Beam section. The order of pouring is from both sides to the middle.

According to the "Technical Specifications for Construction of Highway Bridges and Culverts" and the "Construction Manual of Highway Bridges and Culverts", when continuous beam concrete is poured on the supports, the piers and supports will produce uneven settlement. In order to prevent cracks from occurring at the piers, this bridge adopts the method of setting working joints.

The beam body at the top of the pier is relatively high, and string tubes are set up for pouring. Concrete for other beam sections can be directly put into the mold. Before pouring concrete, a technical explanation must be made to the vibrator, and the location of the corrugated pipe must be explained to strictly prevent The vibrator rod directly contacts the corrugated pipe, and the steel strand must be pumped in time during the concrete pouring process to prevent the pipe from being blocked.

The key points of construction are as follows:

a. The bottom formwork, outer formwork and inner formwork are continuous and not segmented.

b. The bottom plate and web steel bars are continuous and not broken. The roof steel bars are disconnected

c. Each section requires one injection molding.

d. When pouring the bottom slab concrete at the top of the pier, open a skylight on the top plate to facilitate the direct

entry of the concrete into the bottom slab.

e. Use a plug-in vibrator to vibrate. When vibrating the bottom plate, work inside the box and pay attention

to the vibrating quality.

f. Control the speed of concrete entering the mold and reduce the impact force as much as possible

g. After all concrete pouring, clean the site and strengthen health care work to ensure health care

Quality and health maintenance time are generally not less than 7 days.

? Health care

? Tensioning

a. Preparation work

Before tensioning, the jack and oil gauge must be calibrated , perform

inspection on steel strands and anchors.

b. Tension construction

When the concrete strength reaches 100%, tension the prestressed tendons. The tensioning method is symmetrical at both ends

. The tensioning sequence is first bottom and then up, first both sides and then the middle. The steel tendon tensioning adopts a two-control method, that is, prestressing is used to control the tensioning. , the elongation is used as a reference,

to check each other. The tensioning procedure is as follows:

0→ 10%σk (initial tensioning) → 100%σk (load holding for 5 minutes) → anchoring

The tensioning process flow is as shown in the figure

Beam concrete strength inspection, tensioning equipment inspection→ Preparation work←

Inspection and processing of concrete under anchor pad↓ Communication equipment preparation, tensioning equipment installation

Flushing tunnel tensioning Labor organization ↓

Alignment of anchors, tunnels and jacks

↓

Initial tension ← Measure elongation ↓

Tension to controlled tonnage ← Measure elongation value ↓

Anchorage

↓

Channel grouting

↓

< p> Anchor sealing

⑴ Grouting

Grouting should be carried out in time after tensioning. Because the pipeline is long, two grouting machines are used to grout from both ends to the middle at the same time. Set a slurry outlet (exhaust) at the top beam of the pier until the cement slurry with the same consistency as the specified consistency is discharged from the slurry outlet. When grouting, attention should be paid to:

a. The water-cement ratio should be controlled at 0.4-0.5, the consistency should be controlled between 14-18s, and the maximum water rate should not exceed 4%.

b. The maximum grouting pressure can be controlled at 0.5-0.7μpa, and there should be a certain pressure stabilization time after the grout is discharged from the grout outlet.

c. Before grouting, the holes must be rinsed clean, and then the accumulated water must be discharged with air compressor blowing. d. Grouting should be carried out slowly and evenly without pauses in the middle. The grouting should be completed in one go. If a failure occurs and the shutdown time is long, the cement slurry that has been pressed in should be flushed out and cleaned. e. During grouting, test pieces should be taken from each shift and the construction records should be filled in. ⑵ Seal the anchors

⑶ Remove the formwork and brackets

The outer formwork can be removed after the beam concrete reaches 80% of the design strength. Use wooden wedges to drop the formwork, and the brackets will be tensioned and grouted. After dismantling, wooden wedges were also used to unload. The dismantling sequence should be carried out in the order of two side spans first, then the middle span, and the disassembly should be completed in cycles from the middle span to the support. It should be small at the beginning and gradually increase in size later. It should be symmetrically and evenly removed in the longitudinal direction and simultaneously in the transverse direction. It should be removed at the same time. Have a dedicated person use instruments to observe whether there are any abnormal changes in the beam body and make records.

5. Construction Guarantee Measures 1. Technical Guarantee Measures

① Strengthen the functions of the technical management system led by the project chief engineer. The project department consists of chief engineer, construction technology department, quality inspection department, planning and finance department, materials and equipment department and other functional departments. The technical management system is responsible for joint review of design documents, design change management, technical disclosure, measurement and assessment, Prepare commencement report, prepare implementation construction organization plan and construction calculation quota management. It also regulates and controls the construction process, examines and approves the performance standards of materials and semi-finished products, and manages construction technical files, so that the entire project construction process can be operated under effective control of design documents, technical standards, and construction specifications.

② Engineers with experience in bridge construction are transferred from the bureau to form a working group, responsible for scientific and technological research on construction technical problems, discussion of construction technical plans and proposing construction technical measures to solve technical problems that arise during construction.

③ Earnestly carry out technical briefings and strengthen construction technology training. Provide written technical briefings and major engineering operations to the construction team. Technical training must be organized and workers must hold certificates to work.

④ Do a good job in the technical management of the construction site, and equip the construction team with technical, measurement and quality inspection personnel to be responsible for the technical management of the construction team. The project department should strengthen the guidance and inspection and supervision of on-site construction technology Guarantee measures.

⑤ Strengthen cooperation and collaboration with construction units, supervision units, design units and other relevant units. If design changes occur during the construction process, report them in a timely manner and strive to obtain guidance from the owner, supervision unit, and design unit. 2. Quality assurance measures

① The project department and construction team shall establish a comprehensive quality management network headed by the first manager and a technical management network headed by the chief engineer, and hire an expert group as technical consultants.

② Implement a hierarchical quality management system and take responsibility at every level. The project department has a quality inspection department, with a dedicated person responsible for the quality of the project in this contract section. The construction team has a full-time quality inspection engineer, who is responsible for the quality of the sub-projects undertaken by the construction team; quality inspection personnel at all levels have rich construction experience and professional and technical titles. Technical personnel who are familiar with specifications and drawings and work rigorously are in charge.

③ Set quality excellence goals, with a pass rate of 100% for sub-projects and an excellent rate of unit projects

above 85%.

④ Conscientiously implement technical specifications, obey the work instructions of the supervision engineer, and ensure the satisfaction of the supervision engineer.

⑤ Carry out quality management activities for all employees and establish a quality responsibility system. Check the construction technology and the quality of raw materials.

⑥ Strengthen measurement and testing work. Adhere to the process quality self-inspection system. After each process is completed, a process self-inspection should be carried out. If the previous process is not qualified, the next process is not allowed to be constructed. After the self-inspection is passed, the supervision engineer will be reported to the supervision engineer for inspection and identification.

⑦ Carry out QC activities, select fine decoration formwork technology, steel frame hoisting technology, continuous beam cast-in-place and prestressed technology as excellence research topics, implement on-the-job training, carry out QC competition activities during construction, and overcome technical difficulties , ensuring quality success the first time.

⑧ The project department organizes project quality inspections on a monthly basis and strictly implements the right of quality veto during work inspection and pricing.

3. Safety Guarantee Measures

① During construction, the principles of “safety first, prevention first” and “adhere to production must be managed safety” were implemented. The project department established The "Safety Production Management Committee" is headed by a paid manager and is equipped with a full-time safety production cadre responsible for daily safety production work. The construction team accordingly established a "safety production leading group" with part-time safety production cadres. ② Before the start of the project, according to the characteristics of the project and the topography, geology, hydrology, meteorology and other data of the construction site, corresponding safety technical measures should be formulated while preparing the construction organization design. ③ Those who participate in construction must receive safety technical education, improve their awareness of production safety, be familiar with and abide by various safety operating procedures for this type of work, and undergo regular safety technical assessments. Only those who pass the test are allowed to work.

④ Set safety production goals, strictly control safety accidents, and eliminate major casualties.

Control the minor injury rate below 1‰.

⑤ Civilized construction. The construction site should be kept tidy, materials and equipment should be stacked in an orderly manner, and construction roads and drainage ditches should be clear. Hang various eye-catching safety production slogans on the construction site and erect safe operation regulations signs next to various machines. Regularly carry out production safety knowledge competitions.

⑥ Operators must wear protective equipment as required before taking up their duties.

⑦ The living and production houses, concrete mixing stations, and temporary houses at the construction site should be fire-proof, flood-proof, and theft-proof.

⑧ Organize a safety production inspection at least once a month, immediately propose and implement corrective measures if potential accident hazards are discovered, and adhere to the "three no-goes" principle for those who cause safety accidents due to violations, that is: if the cause of the accident is not known, Don’t let it go if you find out; don’t let it go if the responsible person doesn’t understand it well; don’t let it go if there are no corrective measures.

⑨ After entering the beam construction, all operations are at high altitude. Therefore, safety education must be strengthened for construction workers. Workers must strictly follow safety operating procedures to carry out construction and beware of illegal operations. ⑩ Those who have made significant contributions to safety production work will be praised and rewarded, and those who repeatedly violate regulations will be severely educated and punished. 6. Construction period arrangement of the beam part

The construction period arrangement of the main bridge superstructure is based on the premise of ensuring the total construction period, and taking into account the effects of rain and climate, and maximizes the use of support materials and formwork. Each construction cycle lasts for 90 days, and ancillary facilities are interspersed. The total construction period arrangement is shown in the "Superstructure Construction Period Schedule"

Superstructure Construction Period Schedule

7. Workforce Plan

When entering the beam construction, the labor force is relatively concentrated. During the period, according to the construction schedule, reasonable allocation of labor is a necessary condition for the smooth progress of the project. The construction of the superstructure is arranged in three shifts. Each support group is equipped with a professional construction team. Each team of bridge workers needs to be equipped with 120 people.

8. List of main machines and materials used in beam construction

(1) Main machines and tools

(2) Main materials

9 , Attached pictures