Key words: long-span continuous rigid frame bridge; Construction technology of block 0
1. Introduction
Block 0 refers to the first part of the cantilever casting method for long-span high-pier continuous rigid frame bridge. The most important and critical link in the construction process is the construction of block 0 of long-span continuous rigid frame bridge. There are three typical problems in the construction process: first, the main reinforcement of steel structure is formed by the fixed main pier extending into the box girder. The code requires that the steel structure reinforcement formed by the main pier extending into box girder block 0 must be at a certain distance and not on the same horizontal plane. If it is too long, it will be very difficult to locate and extend. Second, concrete pouring is very difficult, because the prestressed steel beam of block 0 is very concentrated, and its steel bars are also quite dense. In addition, the prestressed steel beams in Block 0, including longitudinal and vertical ribbed beams, are densely arranged vertically, and the middle beams and beams in Block 0 are very complicated in structure, with high beams and dense steel bars. Reliable technical measures can be taken to ensure the pouring quality of Block 0 concrete. Third, Block 0 is constructed at high altitude, which is very difficult to operate because it is high from the ground. According to the actual construction experience, aiming at the key points and difficulties in the construction of long-span rigid frame bridge, this paper introduces the construction technology of block 0, hoping to provide some reference for similar construction.
2.0 subsection construction scheme
Cantilever pouring of pier top beam began to be composed of block 0, which concentrated many prestressed pipes and laid many ordinary steel bars. The concrete of block 0 has the characteristics of large quantities, high beam height and large side area, so the quality requirements are very high, the construction is very difficult and the construction conditions are very poor. In the process of construction, the cast-in-place method of triangular support is put forward.
2. 1 Scaffolding and formwork construction
Temporary support has the following two functions: first, it can be used as a supporting structure to bear the force during the construction of section 0; Second, when the cantilever casting method of prestressed continuous beams with supports is adopted in the construction, the temporary supports can bear the unbalanced bending moment generated during the cantilever casting process. As shown in the figure below:
According to the mechanical characteristics, the support can be divided into two types, one is floor-standing support, which is suitable for low piers, and the other is cantilever support, which is suitable for high piers. Section steel, universal bar and Bailey frame are the main forms of bracket bars. Bolt connection and welding are the connection methods of the support pestle. These two methods have their own advantages and disadvantages. Bolts are easier to disassemble, but materials such as connecting plates and high-strength bolts and installation costs increase. In order to reduce the inelastic deformation of the structure, electric welding is used for connection. However, when the members are disassembled, the damage is great, and the materials are reused very few times, so it is difficult to ensure the weld quality.
According to previous practical experience, triangular support is generally considered first in design. Triangular bracket has the following advantages: small volume and clear force transmission path. The triangular bracket is the vertical support member of block 0. It is welded by steel plate and embedded triangular steel bracket. Three triangular steel beams are welded on each side of the pier, and the whole steel beam embedded in the top column of the pier is used at the top to ensure the stability of the steel bracket structure.
(2) Preloading of 0 # triangular steel support
The transverse I-beam distribution beam is installed on the bracket and covered with square wood. The specification is 15cm× 15cm, with 5 layers in total, and the bottom die is laid on the square wood. In this way, the distribution beam can not only bear the load transmitted by the bottom die, but also evenly distribute the uneven load of the beam box and reduce the local compression. The width of the square wood transverse plate is 5 meters. The support can be loaded with sandbags for preloading, and its load is designed to be 1.2 times the safety factor, and the transverse and longitudinal bridge directions are 4.5m and 16m respectively. The specific height of the pre-pressed sandbag is determined according to the water content calculation, and the height is between 4.3 and 4.8 meters ... But the high pre-pressed sandbag will make the triangle steel support out of balance. Symmetrical and uniform loading should be carried out in the preloading stage. Every time the loading height is 1 m, carefully check the deformation degree of triangle steel and joint welding. This process can be observed with a total station. If there is deformation, the loading should be stopped. This is because it exceeds the calculated deformation and needs to be dealt with. After the preloading sandbags are loaded, in order to prevent rain from affecting them, plastic sheets can be covered to avoid the instability of triangular steel supports due to local eccentric loads.
2.2 template
(1) bottom mold
0 bottom formwork adopts 1.5cm thick bamboo veneer. The transverse steel distribution beam is installed on the triangular steel bracket, and the longitudinal distribution beam can be made of square wood with appropriate inclination and specifications of 15cm× 15cm, which can be used as the structure for supporting the bottom die bamboo veneer.
(2) External mold
Supported on the cantilever beam of the support is a factory-made steel formwork. The side formwork is hoisted by tower crane, and the position is adjusted by vertical shaft. In order to prevent the film from expanding, the bottom of the formwork is tightened by the formwork on both sides of the tamping chain, and the top is tightened by the pull screw.
(3) Internal mold and end mold
Water truss bamboo veneer is assembled into internal formwork and diaphragm formwork of box girder block 0, and chamfering can be specially made according to the design size. The main hole formwork adopts wooden formwork, which is more convenient for construction.
2.3 Fabrication and Installation of Steel Ribs
(1) steel bar blanking
Be sure to straighten the steel bar before blanking. The winch can straighten the wire reinforcement, and the straightener can adjust other reinforcement greater than or equal to10 mm. ..
(2) Bending and forming of steel bars
Firstly, all kinds of steel bars are placed on the cement floor and floor according to the ratio of 1: 1, and their bending points are marked. The bending point cannot be broken. If it is a long steel bar, it should be bent from the middle to both sides.
(3) Reinforcement installation
The following is the construction sequence of steel bars. The first step is to bind the bottom plate reinforcement, the second step is to bind the transverse diaphragm and the web plate reinforcement, the third step is to arrange the thick reinforcement with vertical stress L32, and the last step is to bind the top plate reinforcement and bury the longitudinal prestressed pipeline.
2.4 Prestressed pipeline
(1) Installation and connection of bellows
Mark the curve position of side formwork or stirrup on the design drawing, and support it with steel bars. The straight line segment 1m and the curve segment are set at 0.5m. In order to prevent the pouring concrete from moving, it is necessary to weld positioning bars in stirrups and tie the wave tube.
(2) protection of bellows
The installation of bellows should avoid repeated bending to prevent tube explosion. In order to prevent burning the pipe wall, the spark of spot welding should not touch the bellows. According to the situation, damaged and bent prestressed pipes should be treated or replaced in time.
(3) Paddle irrigation holes, exhaust holes and exhaust pipes
In order to facilitate paddle pressing, the grouting hole at the anchorage end of vertical prestressed tendons should be set in the box girder cavity, and the exhaust hole should be set at the top of the beam.
If the bend is greater than the height difference of 50 cm, it is necessary to arrange a drain pipe as an auxiliary paddle irrigation pipe.
2.5 concrete construction
70.88 cubic meters of C50 concrete block 0 was poured at one time. On-site mixing station provides concrete, and concrete pump can transport concrete to the formwork of box girder block 0, and the formwork is placed next to the pier position of the main pier. Use the flexibility of tower crane to hoist concrete, prolong the concrete mixing time, control the concrete slump according to the mixture ratio, and prevent the concrete from blocking the pipe. If there is pipe blockage, it should be dealt with immediately to ensure that the concrete pouring process of block 0 is not interrupted.
The construction sequence of concrete pouring is from the bottom plate to the web plate, and the partition wall to the top plate, and it must be balanced and symmetrical with the concrete thickness of the bottom plate of 50 cm.
Plug-in vibrator can vibrate the concrete of bottom plate, web plate and top plate, and 10 sets are provided at the pouring site. After pouring concrete, the surface should be leveled in time and the oars should be closed for maintenance.
The roof is covered with wet geotextile, which can prevent the influence of sun and rain on block 0 concrete.
2.6 Prestressed tensioning
If the concrete is tensioned, the strength of the concrete must reach the designed 1 0,000%. The 0 # tensioned steel beam will be woven into 1 and 2 # steel beams, and the longitudinal beams will be tensioned symmetrically, and then the web vertical prestressed tendons will be tensioned at one time.
Tension the prestressed vertical beam strictly according to the drawing, then tighten the steel wire anchor, and then use the jack to tension again. The longitudinal beam with self-anchoring function is designed to be tensioned according to 1.03 times, and directly anchored after 3 minutes. YC-60T piercing type is used for vertical beam tensioning, and YCW series 450T jack is used for longitudinal beam tensioning.
3. Concluding remarks
China Railway Corporation also applied the construction technology of Block 0 to the long-span continuous rigid frame bridge project, and achieved very good results. The construction technology of block 0 of long-span continuous rigid frame bridge has played a very important guiding role in engineering practice and ensured the engineering quality. This technology has also accumulated a lot of experience for the design and trial construction of similar bridges in the future. It is believed that this technology will bring huge comprehensive benefits and broad application and promotion prospects.
refer to
Tamia Liu, Zhang Jian. Construction technology of 0# block of long-span continuous rigid frame bridge [J]. Science and Technology Information, 2006, (29).
[2] Zhu Chuandi. Construction technology of O-block support method for long-span continuous rigid frame bridge with high piers [J]. Shanghai Architecture, 2009, (4).