1, the characteristics of urban bridge construction
Only by understanding the general construction characteristics of urban bridges can we design the best construction organization scheme. Therefore, before construction, we must carefully examine the drawings, conduct field visits, and understand the intention of the construction unit. Generally, urban bridge construction has the following characteristics:
(1) The construction scale is large, the area is large and the content is complex. Usually, an overpass project includes professional projects such as bridges (except the main bridge, including footbridges and approach bridges), roads, water supply and drainage (water supply, rainwater, sewage), electricity, communication, gas, street lamps, etc., with a large amount of work and great mutual influence. Therefore, it is necessary to make overall arrangements and coordinate with each other in the construction.
(2) Fully consider the traffic organization arrangement during the construction period, and try to avoid having a big impact on traffic and pedestrians. Construction is usually carried out by maintaining access roads or compressing existing motor vehicle lanes.
(3) Fully consider dismantling the original pipeline. Existing pipelines and new pipelines are densely distributed vertically and horizontally, so they must be considered comprehensively during construction, which will not affect the normal functions of existing pipelines.
(4) Overpasses often occupy a large area and have a narrow red line, so they often encounter demolition work.
(5) In order to minimize the impact on traffic and improve the surrounding environment, the construction period of urban bridges is generally tight, the quality target is high, and there are many working teams involved in the construction, which requires the project management department to do a lot of effective coordination and organization work.
(6) Effectively handle the relationship between night construction and noise pollution, and handle the relationship between civilized construction and project progress.
2. Consideration of overall arrangement of construction
2. Division and layout of1section
Principles of dividing construction sections: ① It is beneficial to the integrity of the structure, and expansion joints or settlement joints should be used as much as possible. Where there are changes in the plane, stubble will not affect the quality. (2) Segments should try to make the quantities of each segment roughly equal, so as to facilitate the smooth rhythm of construction organization and make the construction balanced. (3) The number of construction sections should be coordinated with the main construction procedures, and a process combination should be formed with leading construction as the main task. The number of process combinations should be equal to or less than the number of construction sections. (4) The size of the section should be suitable for the labor organization and there should be enough working faces. In the construction of urban interchange, there is usually enough labor, but there are often not many working faces at the same time.
According to the above principles, the geographical environment and engineering content of the overpass, and considering the distribution and characteristics of engineering quantity, the construction of each overpass is divided into 3 ~ 5 sections in parallel according to the professional nature and location. Although there are many teams involved, the construction period can be guaranteed.
The construction arrangement is based on the principle of underground first, above ground, and then general. First of all, you can build pile foundations or other types of foundations and pipe networks under the bridge. When constructing roads, half-width construction can be used to ensure smooth traffic, and retaining walls can be prefabricated first and then transported to the construction site for installation. The upper part of the construction bridge shall be prefabricated or cast-in-place according to the drawing requirements. Judging from the characteristics of urban bridge construction, the construction method of cast-in-place beam is often used at present.
2.2 Construction preparation
2.2. 1 water and electricity supply
In the construction of urban overpass, it is usually easier to connect water and electricity, but the principle of proximity and the secondary movement of water and electricity points should be considered. For power points, overhead lines should be overhead, and those directly buried should be directly buried. It must be noted that all distribution boxes and panels are equipped with leakage switches, and multi-level protection is implemented. All electricity consumption adopts three-phase five-wire system. Secondly, two or more 50kW generators and two waterwheels should be reserved to prevent water and power failure at the construction site.
Construction layout
The layout principle of urban overpass construction scheme: ① the principle of occupying less land and saving investment as much as possible, which is solved by using the scope of road red line; ②
Reasonable arrangement of materials, semi-finished products warehouse, equipment yard and prefabricated component factory to shorten the transportation distance; ③ Make full use of existing or proposed buildings and facilities to reduce the project cost of large temporary facilities; (4) It is beneficial to the work and life of employees and reduces commuting time; ⑤
Meet the requirements of labor protection, environmental protection, fire prevention and safety.
3, the construction schedule considerations
Once the bridge construction starts, it must be completed according to the established goals, otherwise it will bring great inconvenience to people's lives and affect the surrounding environment. When arranging the construction schedule, we must master the following principles:
(1) Give priority to projects that affect traffic and people's daily travel according to the time limit for completion and delivery. For example, in the construction of overpass, if a ramp meets the hospital gate, priority must be given to the construction of ramp. If the completion of the main bridge plays an important role in relieving traffic pressure, priority should be given to the construction conditions of the main bridge.
(2) Scientifically arrange the construction sequence, that is, underground first, above ground, leveling first and then construction. It is necessary to queue up for project establishment, highlight key points and overcome difficulties. For projects with long construction period, complex technology and difficult construction, such as public piers in bridge construction or beam construction with longitudinal and transverse prestress, early arrangements should be made and priority should be given.
(3) Adopt mechanized construction methods to improve the degree of assembly, such as prefabricated assembly in the construction of retaining wall of overpass approach; In road construction, from the base to the pavement, large-scale mechanized construction is often used.
(4) Adopt scientific network planning method to determine the most reasonable construction organization, create favorable conditions for working procedures, expand the working face and speed up the construction progress.
(5) Implement seasonal construction measures to ensure continuous construction. Such as water pump drainage for construction in rainy season and awning for concrete pouring.
(6) Fully balance manpower and material resources, compress the construction as much as possible, achieve balanced construction, avoid anticlimactic, and master the construction rhythm from beginning to end.
(7) The changing factors and unrealizability of urban bridge design should be fully considered. The construction of urban bridges often needs to be launched urgently, and the geological data, the location and design of underground pipelines are different. Once changed, the progress may be affected.
(8) Effective measures to ensure the progress can be realized should be considered. Such as organizational measures, technical measures and economic measures.
Steps and methods of compiling the general construction schedule;
(1) Calculate the engineering quantity. According to the approved project, roughly calculate the actual quantity of the unit project.
(2) Determine the construction period of each unit project according to the total construction period.
(3) Determine the commencement and completion time of each unit project and their relationship.
(4) Prepare the preliminary overall construction progress plan. According to the preliminary overall construction schedule, the construction period and cost of the network are optimized by computer. After the adjustment meets the requirements, a formal construction progress plan can be prepared.
4. Consideration of main construction methods
4. 1 principle
The construction method is the core content of the construction scheme and plays a decisive role in the implementation of the project. According to the basic requirements of the construction scheme, it is a tactical measure taken for the partial and sub-project of the bridge under specific construction conditions. Secondly, the construction method should be focused, and all projects that adopt new technologies and new processes and play a key role in the quality of this project, as well as projects in which workers are not skilled enough, should be detailed and specific. Not only the process and method of this operation, but also the quality requirements and technical measures to meet these requirements should be put forward. It is also necessary to foresee possible problems and propose ways to prevent and solve them. Conventional construction methods and skill items can be simplified appropriately.
To determine the construction method, we should consider the structure and stress characteristics of each part of the bridge, combine other projects in the field construction and the construction testing and equipment owned by the construction unit, and absorb successful construction methods and advanced technologies to achieve the purpose of rapid, economical and high-quality construction.
4.2 Traffic Organization
In the construction of urban bridges, priority must be given to the construction methods around traffic organization. At ordinary times, we can consider changing roads, hanging traffic signs and traffic lights at night to ensure that traffic is not greatly affected. Because the urban overpass is often the intersection of multiple intersections, there are many people and vehicles, so it is impossible to carry out closed construction. Therefore, priority should be given to the traffic flow in the main lane, and the traffic flow in the secondary trunk road should be closed to limit or change. Usually, in the construction of the main lane overpass bridge, two motor vehicle lanes and two pedestrian walkways are usually set up.
4.3 Foundation excavation or ground excavation
In the construction of urban overpass, whether it is earthwork excavation or foundation excavation (including bored piles), it is necessary to find out the exact location of underground pipelines before construction. Although the owner may provide the plane position and elevation of the relevant pipelines, the as-built drawings are often different from the actual ones due to the changes of urban underground pipelines. Therefore, it is necessary to measure with radar detector, and then dig carefully manually to confirm that there is no pipeline under this foundation or that there is pipeline deviation, and then use mechanical excavation. In construction, we often encounter the problems of time delay and compensation caused by digging underground pipelines. This is directly related to the hasty construction.
4.4 Selection of supports and templates
The appearance of urban bridges should be beautiful, both inside and outside, and the surface should be flawless, honeycomb-free and pockmarked, so special attention should be paid to the selection of formwork. For cylindrical piers, the formwork is usually assembled in place by assembled steel formwork, and the square symmetry is fixed by stay wires; When the column is too high, add a set of inclined cables in the middle to ensure the sag of the column. After formwork erection, concrete can be poured after inspectors check the verticality and diameter of pier. For square piers, if wooden formwork is used, the inner formwork is usually covered with iron sheet. For beams, the internal formwork generally adopts general-purpose board, but the external formwork is strictly required, and generally adopts 2 cm phenolic resin plywood. If there are obvious requirements for appearance, you should buy imported plates.
For the erection of cast-in-place beam support, foundation treatment should be carried out first. Urban bridges can generally use the existing pavement as the supporting foundation, but attention should be paid to tamping the surrounding backfill parts to prevent uneven settlement. Secondly, the turnover of scaffolding and formwork cannot be repeated too many times. The more times the bridge waits for the turnover of formwork and scaffolding, the longer the construction period. According to the calculated density size of the portal frame, wooden Fang is laid, so that the portal frame support is laid on the wooden Fang, the portal frame is erected to the transverse position of the beam bottom, the portal frame is fixed with steel pipes and fasteners, and the scissors are erected as designed. According to the design elevation and reserved settlement, the bottom formwork is provided with longitudinal and transverse wooden beams, the reserved traffic passage is made of I-beams, and then the phenolic resin plywood is laid.
4.5 concrete construction
Due to the limitation of the site and the influence of concrete mixing on the surrounding residents, commercial concrete should be considered in the construction of urban overpass. In Shenzhen, it has been stipulated that commercial concrete should be used in projects with concrete volume greater than 20m3. Concrete pouring shall be considered according to the following procedures: ① Before concrete pouring, check whether the mixture ratio matches the grade of bridge concrete, whether the personnel are in place and whether the machinery and equipment are in good condition, and inform the pouring personnel of the pouring method and operation essentials. (2) Concrete shall be transported by tank truck, transported by pump truck, and continuously vibrated by internal vibrator. ③
Concrete is poured from low end to high end, and it is poured by sections and layers. Taking the box girder as an example, the box girder should be cut evenly from the side formwork on both sides and rammed into the inner box. Because the inner box is generally wide (the upper plate of the inner box is 50cm temporarily unsealed), it can be cut from the top of the inner box, and there should be someone who is responsible for tamping in the inner box, so that the concrete in the inner box is compacted and leveled, and then the upper plate of the inner box is sealed after plastering. When pouring bridge deck concrete, the length of segments should be adjusted according to the pouring speed, so as to avoid that the inner box concrete is too thick or the initial setting time is too long and the joints are not good.
4.6 Construction of Bridge Deck System
The later the urban overpass is built, the tighter the construction period is, so the quality of the bridge deck system often goes wrong in the later period, which must be paid attention to.
(1) Construction of railings and crash barriers: Most railings are ordered by concrete manufacturers and transported to the construction site for installation. During installation, lofting should be carried out according to the design installation size, and the basement should be leveled with hard mortar according to the design elevation, then the railings should be installed one by one, the mortar should be filled after correction, and the handrail floor should be installed in time. After correction, steel bars shall be bound and concrete shall be poured. Template installation requirements are firm, ensuring straight lines, arcs and smooth surfaces.
The key to the construction of anti-collision guardrail is to leave expansion joints at the pier top and bridge span, disconnect steel bars and fix expansion joint templates with foam. Usually, the crash barrier is cast-in-situ formed by steel formwork at the construction site, and the protection of embedded parts should be paid attention to before forming.
(2) Bridge deck construction: The urban overpass adopts concrete bridge deck and asphalt bridge deck.
In principle, the construction of concrete bridge deck shall be carried out according to the construction method of concrete pavement, but attention should be paid to the accurate position of steel mesh to prevent the movement of personnel and small vehicles from causing the steel mesh to sink during construction. Secondly, after the strength meets the design requirements, traffic must be opened to prevent cracks in the bridge deck concrete.
The construction of asphalt bridge deck shall be carried out according to the construction method of asphalt pavement in principle, but attention should be paid to the contact between asphalt surface and bridge concrete. First, the bottom surface should be clean and rough. Second, the rubber layer oil should be sprinkled. Third, ensure the paving thickness of asphalt pavement.
(3) Installation of expansion joints: After all the embedded parts of expansion joints are installed according to the design, they should be installed at a relatively low temperature, and the installation should be carried out in strict accordance with the instructions to ensure the installation quality.
5, the construction organization framework
It should be emphasized that the coordination department is mainly responsible for assisting government departments to do a good job in land acquisition, demolition, tree removal, pipeline relocation, protection and compensation of relevant public utility management units.
6. Measures to ensure the construction period and environmental protection
6. 1 Measures to ensure the construction period
(1) Take planning management as the leading factor, and set up full-time planning engineers to be fully responsible for project planning management. First of all, it is necessary to determine the total project schedule and sub-schedule, that is, to establish the unit project construction schedule until the project operation plan task list.
(2) Establish control measures ① Determine the progress coordination system, hold a regular meeting of the project on a fixed day every week, hold a meeting every day, study the daily progress of the project and new problems, give timely feedback and implement dynamic management; (2) Analyze the interference and risk factors that affect the realization of the progress goal, such as the influence of demolition, traffic, typhoon and rainstorm. ③ Fully consider design change factors. The phenomenon of repeated changes in the design of urban overpasses is common, which will directly affect the progress. After the design change, the progress will be adjusted in time according to the situation, and the total progress will remain unchanged; ④
Take economic measures, use special funds for special purposes, never misappropriate them, and implement the reward and punishment system for project progress; ⑤ adopt simple and feasible technical measures to speed up or delay the progress, not to pursue profits unilaterally, but also to pay attention to social benefits.
(3) Ensure personnel and mechanical equipment, small machinery and professional equipment. On-site equipment shall not be transferred at will, and mechanical equipment shall be overhauled in advance to maintain good working conditions.
(4) Material supply should be timely, appropriate, quality and quantity guaranteed.
6.2 Environmental protection measures
(1) Strengthen civilized construction, carefully plan the construction site, and arrange the site neatly, compactly and orderly.
(2) Mud on the construction site, especially mud, spoil and other wastes generated by drilling, should be removed in time and transported to the designated place to keep the site clean and tidy during construction. After the completion of the construction task, the temporary facilities that must be dismantled shall be dismantled.
(3) Optimize the construction methods and techniques to protect the surrounding environment from pollution; For the process with high noise, try to arrange the construction during the day to reduce the interference to nearby residents at night.
(4) The sewage discharged from the construction site must be treated before it can be discharged into the nearby trench, and it is forbidden to pollute the land and the surrounding environment.
(5) Do a good job in sanitary management of living quarters. Toilets should have septic tanks, and domestic garbage should be piled up in designated places. Domestic wastewater should be discharged into the trench to keep the living area clean and tidy.
(6) The construction site shall be provided with necessary temporary fences, grade crossing and obvious signs for vehicles and pedestrians, so as to make the construction site self-contained as far as possible and reduce mutual interference with the outside world.
(7) The construction access road shall be well maintained, the road surface shall be smooth, the drainage on both sides shall be good, and there shall be no potholes and water accumulation in rainy season; Sprinkle water properly in dry season to prevent dust from flying.
7. Conclusion
The organization and management of urban overpass construction is a huge systematic project, including construction technology management and organization management. Construction technology is to ensure that the project can be constructed according to the design, and only strict organization and management can successfully complete the project according to the contract. Construction units should attach importance to scientific management, stress economic accounting, improve efficiency and pay attention to social benefits.
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