However, as a whole, the construction of tower, beam and cable of cable-stayed bridge must cooperate with each other and obey the engineering design intention. Therefore, this chapter only excludes foundation construction, involving the construction of towers and beams, but takes the construction of beams, cables and various representative cable-stayed bridges as the main line of this chapter.
The first cable-stayed bridge in modern times was 1955 Str? m-Sunde Bridge in Str? m, Sweden. For the cable-stayed bridge with cable-stayed radiation, the mid-span 185.5752m, the side hole is 74.676m, the steel tower is installed by beam crane, the steel beams of the side span are assembled on scaffolding, and the mid-span is assembled by cantilever method. Cable is also installed on the beam by crane. As the steel beam is cantilever-propelled section by section, the lower end is connected first, then the crane retreats to the upper end of the bridge tower for installation, and it is tensioned by jack.
From 1955 to 1957, there are about 60 cable-stayed bridges in the world, almost all of which are steel ones. It was not until 1962 that the first concrete cable-stayed bridge, namely Lake Maracaibo Bridge, was built. Since 1975, the first Tangxihe Bridge in Yunyang, Sichuan Province was completed, the total number of cable-stayed bridges has reached more than 50, most of which are concrete cable-stayed bridges. Tables 1 1- 1, 1 1-2 respectively introduce the construction survey of famous cable-stayed bridges built at home and abroad in recent years.
A, tower construction
The pylon can be made of metal, reinforced concrete or prestressed concrete. The structure of cable tower is far more complicated than that of ordinary pier. The tower columns can be inclined, and there can be beams between the tower columns. The tower shall be provided with a pipeline crossing back and forth so that the stay cables can pass through the anchorage. The top of the tower should be equipped with a tower crown, aviation beacon lights and lightning arresters, and a maintenance ladder should be set along the tower wall, and a sightseeing elevator can be set in the tower. Therefore, the tower construction must be balanced according to the design and structural requirements.
The cable tower bears considerable axial force and may produce bending moment, so the size and axial position of the cable tower are required to be accurate.
The allowable deviation value should consider the following two principles: ① the deviation value has little influence on the stress of the structure; (2) the accuracy that can be achieved through hard work in construction. Referring to foreign data, the allowable deviation per meter along the tower height is 0.5mm, that is, the tangent value of inclination angle tga= 1/2000. At present, there is no uniform regulation on the construction accuracy of pylon of cable-stayed bridge in China. The allowable inclination of Shanghai Liugang Bridge is 1/200, and the allowable deviation of Xupu Bridge is shown in Table 1 1-3.
The construction of steel cable towers generally adopts prefabricated hoisting, and the construction of concrete cable towers can generally be divided into cast-in-place erection, prefabricated hoisting, slip-form casting and other methods, as follows:
1, cast-in-place erection
This method is mature in technology, does not need special construction equipment, can adapt to more complex cross-section forms, and is convenient to deal with the reserved channels and embedded parts in the anchorage zone, but it is labor-consuming, material-consuming and slow. For a cable-stayed bridge with a span of about 200m, the height of the pylon (above the deck) is generally about 40m, so it is more suitable to cast-in-situ with scaffolding. This method is used in the pylons of Hongshui River Bridge in Guangxi, Liugang Bridge in Shanghai and Yellow River Bridge in Jinan. For long-span cable-stayed bridges, the tower column can be divided into several sections, each section has different dimensions and inclination angles, and each section often adopts different methods. The lower section is more suitable for cast-in-place erection, such as nanpu bridge, Yangpu Bridge, Xupu Bridge and Wuhan Yangtze River Bridge, with a span of over 400m and a tower height of over 150m. The lower tower column adopts the traditional scaffolding formwork turnover technology, but the disadvantage is that the construction period is long.
2. Precast hoisting
This method requires strong specific gravity capacity and special lifting equipment. When the bridge tower is not too high, it can speed up the construction progress and reduce the difficulty and labor intensity of aerial work. The tower of Dongying Yellow River Bridge is 69.7 meters high, 56.4 meters higher than the deck. Steel box concrete is used for hoisting.
The pylon of steel cable-stayed bridge abroad is basically constructed by precast hoisting method.
There are not many prefabrication and hoisting methods for concrete cable-stayed bridges in China. Only 198 1 built Zeng Bridge in Jinchuan County, Sichuan Province, the tower is 24.5m high and the ground is prefabricated. It is lifted from the ground by winch and pulley block, and the lifting force is provided by wire rope and pulley anchored on the opposite mountain wall.
3. Slipform construction
The biggest advantage of this method is that the construction progress is fast and it is suitable for the construction of high towers. This method can be used whether the tower column is vertical or inclined, but it is difficult to deal with the reserved holes and embedded parts in the anchorage area of stay cables. In various projects, it is called climbing formwork or lifting formwork, and its structure is similar. The so-called sliding mode means that the formwork slides upward along the poured concrete driven by the jack (screw or hydraulic type), which requires that the strength of the poured concrete must reach the strength necessary for the formwork to slide upward. Lifting the template is to hang the template on the bracket after the formwork is removed, and the template will rise with the increase of the bracket. The lifting of the support is to set several groups of pulleys around the tower. The upper ends of the pulleys are connected with the embedded parts in the tower column, and the lower ends are connected with the support underframe, so that the chain block is pulled and the support slowly rises.
The tower of Changxing Island Cable-stayed Bridge in Liaoning Province is 43m high. In order to adapt to the construction of the tower, the lifting bracket is specially made, which can be used not only for the sliding mode of hydraulic jack lifting, but also for the lifting of formwork by subsection pouring. The lower section of cable tower 1 17m inclined leg section is poured by ordinary scaffold formwork, and the tower column in the vertical upper section is poured by slip form or rising formwork. Slipform construction was adopted for the No.2 pylon in the first construction, but the construction was stopped because it was not suitable for slipform in winter. After the construction, the 1 tower adopted the formwork lifting method and concrete steam curing, which solved the winter construction problem of -20℃, so the No.2 tower was changed to formwork lifting construction.
The beam between the two towers is cast-in-situ by the lower operating platform of the bracket, and the lower side of the lower operating platform is supported on the poured beam with I-beam.
The tower height of nanpu bridge Bridge is 150m, the slope of the lower tower column is 1: 527 1842, and the clear height is 29m. Using the traditional scaffolding turnover technology, the construction period is longer, with an average of 0.56m per day. The slope of the middle tower column is 1: 85 and the height is 55.0m, and the first inclined climbing formwork in China has been successfully developed. The principle of this inclined climbing formwork is the same as that of lifting formwork, and the construction speed is increased to 1. 14m per day. The upper tower column is also constructed by climbing formwork.
Second, the main girder construction
Generally speaking, any suitable concrete beam bridge construction method can be adopted in the superstructure construction of concrete cable-stayed bridge, such as bracket assembly or cast-in-place, cantilever assembly or casting, incremental launching method and dry rotation method.
Because the main girder of the cable-stayed bridge is small in size, and there is tension between the segments, auxiliary cables can be erected through the pylon, which is more conducive to the use of various construction methods without supports. Among them, cantilever construction method is widely used in the construction of concrete cable-stayed bridges. The main girder can be T-shaped, continuous beam or cantilever beam. Which method to adopt is the first problem that designers should study and decide. The main problems to be considered in decision-making are the obstacles that have been crossed, the structure and structure of the cable-stayed bridge itself, etc. , as follows:
1, construction on support
When the navigation requirements for crossing the river are not high or there is no navigation requirement for the bank span, and temporary piers are allowed to be set, they can be directly assembled or poured on the scaffolding, or temporary beams can be set on the temporary piers, and the temporary beams can be assembled or poured on them. If conditions permit, this method is always the cheapest and simplest.
For example, the Belgrade-sava river double-track railway bridge is a steel cable-stayed bridge, built in 1977, with a mid-span of 254m and a bridge width of16.5 m. Because there is no navigation requirement in sava river, the whole bridge span is installed on the construction scaffolding, so the installation of the main girder, tower column and stay cables can be carried out separately. After the installation of the main girder and tower column is completed, jack up the main girder with the jack on the bracket, and then install the stay cable. By releasing the jack and lowering the main beam, the stay cables installed in place are tightened, so the installation of stay cables does not require a large-tonnage jack.
Yonghe Bridge in Tianjin, China is also a typical one installed on temporary supports. Yonghe Bridge is a prestressed concrete cable-stayed bridge with a mid-span of 260m, which was completed in 1987. Because the main girder is weak, in order to avoid excessive stress, precast girder segments are not transported on the main girder with suspended cables. Precast beam segments are transported to the installation site through temporary bridges laid in the river. There are four temporary fulcrums under the delivered precast beam block. Immediately insert longitudinal prestressed steel bars, glue them together, and lift them with stay cables. The installation sequence is centered on the tower column, and both sides are symmetrical at the same time. Each section includes 4 precast beam sections with a length of 5.8m and 8 stay cables, and the time is about 7- 15 days.
2. Incremental emission method
When too many temporary supports are not allowed under the bridge, such as overhead corrosion across roads and railways, incremental launching method can be considered. The steel cable-stayed bridge was first erected in incremental launching method, which is a highway viaduct in the urban area of Dü sseldorf, the former Federal Republic of Germany, and is called Yuli West Street Bridge. The bridge was completed at 1963 with a mid-span of 98.7m. The installation process is shown in figure11-1.
After the west abutment, first assemble the east half span, with temporary fulcrums 1 to 6. In the jacking process, the self-weight of the cable-stayed bridge is transferred to the longitudinal box girder through the diaphragm beam in the steel box, so the cables are only partially tensioned. A jacking machine is installed on the saddle at the top of the tower to eliminate the cantilever deflection of the outermost jacking section. When the outermost edge of the bridge is pushed to the permanent pier ⅷ, the bearing is lifted by the jack by about 10cm, and the bearing pressure on the permanent pier ⅷ is eliminated. When the bridge is further advanced, the pressure on pier 8 will increase; When the outermost edge exceeds the temporary pier Ⅳ by about 7.3m, the bearing pressure reaches the allowable value. At this point, restore the bearing of pier No.8 to its original position, continue to advance to the final position, and dismantle temporary piers No.4 and No.10. ..
Dnieper River Steel Cable-stayed Bridge was built in the former Soviet Union 1976. It is a single tower system with a river span of 300 m. After comparing various erection methods, it is found that the jacking longitudinal displacement method is the most favorable. Three sliding bearings are installed within a span of 300 meters with a spacing of 75 meters, and all the work of beam assembly and sliding is completed within 13 months.
The cable-stayed pipe bridge system of Shicheng River in Wuxi, which was built in 1993, dragged 4 1.8m water pipes into place on the temporary pier. In addition, the approach bridge of Chongqing Shimen Bridge (completed by 1989) is a 5×690m prestressed concrete continuous beam, and the continuous box girder bridge of Nanhai Jiujiang Bridge (completed by 1988) is also erected by incremental launching method.
3. Swing structure
Rotary construction is not widely used in cable-stayed bridge construction. The Bonnern Bridge and the single tower across the Meuse River, built in Belgium in 1988, are located on the banks parallel to the Meuse River, with the main span of 3×42m on the left bank and 168m on the right bank. After installation and adjustment, the cable beam of the whole bridge tower rotates 700 in situ around the tower axis.
Liu Da Bridge in Jinchuan County, Sichuan Province is the first cable-stayed bridge with swivel construction in China, which was completed on 198 1. The bridge is a single tower, with span arrangement of 4 1m+70m+70m, deck width of 5.5m, and pier, tower and beam are consolidated. The main girder is a reinforced concrete three-room box girder. The floodplain near the bridge site is dry and the pier shaft is short, which is suitable for horizontal rotation construction. Firstly, a low-support beam is erected on the floodplain, and a cable tower is prefabricated on the ground. Suspend the tower, reinforce and install the stay cables with beams, and then balance the swivel structure in place. The rotating device is concrete ball hinge and steel roller, and the short span is equipped with counterweight.
Tanghe Daliguan Railway Cable-Stayed Bridge, built in 1997, is located on the relief line of Qinhuangdao Station, under the Beijing-Qinhuangdao Line and diagonally across. It is a channel beam rigid cable-stayed bridge with oil tower, with a main span of 50m and a side span of 42m (Figure 1 1-2). During construction, firstly, a cable-stayed bridge, including towers, beams and rigid cables, is built along the crossing line on the support. After the concrete reaches the design strength, the prestressed tendons in the beams and cables are tensioned, and then the whole cable-stayed bridge rotates around the turntable. When rotating, the rear end of the side hole moves along the circular track, and the front end of the main hole is suspended. In order to prevent the suspension of the front line from generating excessive tensile stress on the upper edge of the main girder at the suspension point of the outer main cable, temporary vibration is added to suspend the front wall during rotation. After the swivel is in place, remove the temporary cable, seal the turntable with concrete, and then lay the ballast line and sidewalk.
4. Cantilever assembly
Most steel cable-stayed bridges built in foreign countries in the early days were assembled by cantilever. China Dongying Yellow River Bridge is the only steel cable-stayed bridge in China at present, with a mid-span of 288m and a bank span of 1987. It is assembled on the bracket, and the cantilever is assembled by the river and welded by bolts. The main spans of nanpu bridge, Yangpu Bridge and Xupu Bridge are all steel and reinforced concrete composite beams with upper plates, all of which are cantilever assembled.
Cantilever assembly construction of concrete cable-stayed bridge is to prefabricate the main girder in sections in the prefabrication yard, which consists of the following parts.