1. incremental launching method Construction: Use the horizontal jack and its automatic traction device on the abutment to pull the jacking force transmission cable. Through the centralized control of the main console, the beam segments made on the beam-making pedestal are continuously pushed forward on the slideway until the beam top is pushed in place, and then the beam is hoisted, the slideway is dismantled, the support is installed, the beam is dropped, and the reaction force of the support is adjusted to complete the beam erection. In incremental launching method, China is mostly used to build large-scale bridges in cities, and to erect prestressed concrete continuous beams with equal sections with spans of 40 ~ 60m. Incremental launching method can erect straight bridges, curved bridges and skew bridges.
Incremental launching method construction principle:
The dynamic principle of (1) single-point pushing can be expressed by the following mathematical expression: when the concentrated tension is h >; σ ri (fi ai), the beam can advance.
(2) The dynamic principle of multi-point dispersed jacking construction can be expressed by the following mathematical expression: when σ fi >; σ (fi ai) ni, the beam can advance.
The physical meaning of this expression is to disperse the jacking equipment on the temporary piers of each pier (or abutment) to disperse the horizontal reaction force of each pier. If the sum of the forces exerted by the jack is less than the sum of the horizontal frictional resistance of all piers and the horizontal component of the beam (+for uphill thrust and-1 for downhill thrust), the beam will not move. Case: Baotou Yellow River Highway Bridge is located at the southern end of Baotou City, Inner Mongolia, with a total length of 8 10/0m and a width of12m. It was a continuous bridge with the largest span built in China at that time and constructed in incremental launching method. The bridge was completed and opened to traffic on June 1983. The span of the west approach bridge of Ganjiang Bridge is (3×48+ 12×48) meters. The jacking weight is 34,000 tons, ranking first in the world and highest in China. 2. Simply supported first and then continuous construction: simply supported first and then continuous beam is to erect several small simply supported beams on temporary supports; Then tie or weld the steel bars reserved at the end of the small simply supported beam, and then pour the concrete connected with the end with the formwork to make the small simply supported beam become a continuous whole; After the strength reaches the design, remove the temporary support and become a continuous beam.
(A), structural characteristics
1. From beam fabrication to installation (hoisting), it belongs to simply supported structure and is convenient for construction.
The construction of simply supported T-beam is the prefabrication and installation of components, which is suitable for standardized and industrialized production. Compared with continuous beam construction, the production conditions and working conditions are much less limited and restricted by environmental conditions and geological and hydrological conditions, which is also convenient for management and easy to ensure the construction quality.
2. The simply supported beam is transformed into a continuous beam through wet connection of pier top and secondary tension structure transformation. In other words, during the service period, it is the characteristic of continuous beam, which saves materials, reduces self-weight, increases span and stiffness, and makes driving comfortable.
3. Because it is statically indeterminate, it is sensitive to foundation requirements and other secondary stresses.
4. The load-bearing type of Pujiayuanzi Bridge is a wet connection structure with double load-bearing piers, which is easier to realize structural transformation than a single load-bearing structure.
5, deck pavement is an integral part of the bridge structure:
1), the stirrups of beam ribs become the connecting reinforcement of bridge deck pavement.
2) There are special connecting ribs on the wing plate.
All the above connecting steel bars have structural requirements with the bridge deck paving steel mesh.
(2) Stress (load) characteristics
Structural transformation is actually a mechanical transformation. To illustrate the problem, figure 1-1in the attached figure1is a structure diagram and a load diagram. 1-2 is the schematic diagram of bending moment of simply supported structure (m); Figure 1-3 shows the bending moment (m) of a continuous beam with two longitudinal joints.
If the secondary tension of pier top fails to meet the design requirements due to various reasons during construction, it is possible to change the bending moment diagram of simply supported beam from 1-3 to 1-2, so as to increase the mid-span bending moment, which is quite dangerous.
Under the condition of the same span and load, the absolute average of bending moment diagrams of simply supported beam and continuous beam is basically equal, but the difference is that the positive (mid-span) bending moment of continuous beam structure system decreases, and its reduction value is the average of negative bending moment values of adjacent piers.
From the above analysis, it is concluded that the key to the structural transformation of simply supported continuous beam system is whether the secondary tensioning of pier top can meet the design requirements.
Case: The first cross-sea bridge of Zhoushan Continental Link Island Project. Cengang Bridge spans the cengang Waterway, connecting cengang and Diaoli Island. The whole bridge is 793 meters long, with a deck width of 22.5 meters, two-way four lanes, a navigation grade of 300 tons, a clear navigation height of 17.5 meters and a clear navigation width of 2×40 meters. The main bridge is a 3-span 50m prestressed concrete T-beam which is simply supported first and then continuous.
3. Cantilever construction: it is suitable for long-span prestressed concrete cantilever beam bridge, continuous beam bridge, T-shaped rigid frame bridge and continuous rigid frame bridge. Its characteristic is that there is no need to build a landing bracket and large lifting and transportation machinery, and the main equipment is a pair of walking baskets.
Suspended pouring construction process:
① Hanging basket: in front of the hanging basket. 0, 1 block must be poured and tensioned, and temporary reinforcement measures shall be taken for the bearing.
(2) the template correction, in place.
(3) General steel bars and prestressed pipes.
(4) in addition to meet the requirements of general construction technology, special attention should be paid to the layout of prestressed pipes in strict accordance with the design requirements. In case of conflict with ordinary steel bars, the correct position of prestressed pipes should be given priority; Fix the prestressed positioning bar firmly to ensure the thickness of its protective layer; There are many longitudinal pipe joints, so the joints must be handled carefully and measures should be taken to prevent the hole pipe from being blocked; Due to the long longitudinal pipeline, it is generally necessary to add several grouting tees in the middle of the pipeline to serve as exhaust holes or grouting holes during grouting, so as to ensure the compactness of hole grouting.
⑤ Concrete pouring.
⑥ The concrete strength of cantilever box girder is generally high, and the concrete mix design must be careful. Depending on the conditions, concrete can be mixed on land, transported to the site by water, or directly mixed on water. Hanging casting, must be symmetrical casting, weight deviation shall not exceed the requirements specified in the design. Pouring should be carried out from the front end to the back end, and finally connected with the poured beam end. When pouring in stages, before pouring the second concrete, the contact surface of the first concrete must be chiseled and rinsed clean, and the contact surface of the upper and lower beams should also be chiseled and rinsed clean. The vibrating of concrete at the bottom and ribs is mainly based on attached vibrator, supplemented by plug-in, and the vibrating of concrete at the top and wing plate is mainly based on attached vibrator, supplemented by flat vibrator. After the concrete is formed, it should be covered and watered in time.
⑦ Tension and grouting.
Before tensioning, the jack and oil pump should be calibrated according to the specification requirements, and the pipeline should be cleaned and bound to prepare the tensioning platform.
Pet-name ruby when the tensile strength of concrete meets the design and specification requirements, it shall be tensioned symmetrically in design order, batch and in strict accordance with the tensioning procedure. After tensioning, the pipeline shall be grouted according to the specification requirements.
Attending to dismantle the template and move the hanging basket. After tensioning this beam section, drop the bottom formwork, lay the forward track, move the hanging basket in place, and start the construction of the next beam section.
Case: Ganjiang Bridge is the first double-deck three-dimensional urban highway bridge in China, located in Taohua Township, Nanchang City, with a total length of 2,780 meters, of which the main bridge length is 1 0,982.45 meters, the approach bridge length is 797.5 meters, the deck roof is 23 meters wide, and it can parallel six large trucks. The lower floor is a non-motor vehicle lane and sidewalk, with a width of 5 meters on both sides, which is the first in China. The main bridge and the west approach bridge are double-layer single-box single-room three-way prestressed reinforced concrete continuous beam bridges. The span of the main bridge is (56+ 1 1×80+56) meters, and the cantilever method is adopted for construction. The west approach bridge spans (3×48+ 12×48) meters and has a jacking weight of 34,000 tons, which is first-class in the world and the highest in China. The east approach bridge is a 20m perforated plate beam, which is prefabricated by pretensioning method and erected by gantry crane. The whole bridge foundation is bored pile foundation. Construction started in May 1 0990, and was completed in May 10/994+10.