Unsupported installation of concrete-filled steel tubular tied arch bridge

Unsupported installation of CFST tied arch bridge Zhang Zhihua (Jiangsu Tongzhou Basic Engineering Corporation Tongzhou 226300) Zhu Peng (Suzhou City Highway Bureau, Suzhou 234100) Zhangla control technology.

The Zhengchang Bridge is located in Tongzhou City, Jiangsu Province, across the Tonglu Canal, bordering Jintong Highway in the north and Zhengchang Town in the south. The total length of the bridge is 12444m, and the upper part of the main span adopts a 50m steel tubular concrete tie arch structure. The arch shaft adopts an arc arch with a span ratio of 10/50 and a radius of 36.25m. The arch rib is 0800X14mm steel pipe, and there are two upper and lower pipes. The design is divided into two sections: 7 949+36526+7949 (mm). The arch rib joint is flanged and the pipe is filled with C40 micro-expansion concrete. The drawbars are made of 0150X10mm seamless steel tubes with a total of nine pairs. The tie beam is cast-in-place C50 reinforced concrete beam and concrete. The beam is a prefabricated C40 reinforced concrete beam.

1 Selection of installation plan The bridge crosses the Tonglu Canal for the Yangtze River to enter the main river channel of the region. The navigation level is five, the shipping is quite busy. The contract requires the construction without the bracket method. The design proposal suggests that the arch ribs should be installed by floating crane. According to the structure of the project, combined with the analysis of the site conditions, it is considered that the installation by the floating crane method is susceptible to water flow, wind waves and ships coming and going. The joint alignment and arch axis are difficult to adjust, and the accuracy is difficult to guarantee. At the same time, the navigation time is long and the installation is long. The cost is also high, so this option is not considered.

The bracketless installation method conventionally used for the tie arch structure is also the overall lifting method and the cable hoisting method. Because the bridge tie rods are designed according to the sectional (segment) installation method, the overall lifting scheme cannot be adopted; Located in the town, it is inconvenient to install a large number of wind cables, and the implementation of the cable hoisting scheme is also limited.

In view of the problems and shortcomings of the above-mentioned various schemes, after repeated research, the guide beam type gantry lifting scheme was proposed. This solution is an installation method that combines the guide beam with the gantry crane. The method can effectively overcome the shortcomings of the above-mentioned schemes, and has the advantages of stable lifting, convenient rib rib position, accurate alignment of the joint centering and arch shaft, complete no bracket, basically no airway, and low installation cost.

2 Installation method The equipment assembly guide beam has two blessings. Each guide beam consists of two pieces of six-four-four steel trusses with a total length of 52m. The gantry is made of steel pipe and the gantry span is 4m. It satisfies the requirements of arch rib lifting and installation requirements. Under the gantry height should be reduced as much as possible to reduce the size of the gantry frame components and increase the stability during component installation.

After the steel truss is transported to the site, it is assembled into a beam on the approach bridge, and the crane is transported across the river with the vessel and placed on the transverse steel beret. Lay the rails on the guide beams, install the gantry, and carry out trial lifting. See the general arrangement of the guide beam type gantry lifting.

The overall arrangement of the gantry guide beam type gantry lifting method indicates the arch rib joint. 2.2 The arch rib assembly arch rib is processed by the factory and transported to the site for assembly, and the middle arch rib is spliced ​​into a whole, according to the rib between the two sides. The measured distance cuts the length of the middle arch rib. Due to the difficulty in docking the flange joints, the joint processing time is long. Therefore, the joint ends of the arch ribs at both ends and the side sections of the middle arch rib are processed into a step shape, and an inner sleeve is arranged at the joint end of the side arch rib joints.

2.3 Arch rib installation section The arch rib is buried in the arch, and is installed by the crane and is fixed by the forward.

The middle section of the arch rib is lifted by two cranes at the same time and transported to the guide beam type gantry crane under the lifting point. The gantry frame is hoisted and transported to the installation position, and the arch rib is suspended from the upper side of the casing on both sides. The longitudinal axis of the arch rib, the elevation and verticality of each feature point are reviewed and adjusted. When the measured values ​​meet the design and specification requirements, the middle arch rib is positioned. Symmetrically welded arch rib joints, after temporary stabilization measures are applied to the arch ribs, the guide beams are displaced and the next arch rib is installed.

3 Prestressed Tension Control 3.1 Prestressed Tension Control Principle The sub-pieces (sections) of the arch members are unsupported, so that the steel pipe arch ribs are in the state of the first arched back beam. After the arch rib is installed and the tie rod is stretched, the arch rib is in the state of no tie rod; with the continuous installation of the tie rod member, the force of the arch is constantly changing, and the thrust generated by the arch foot is also continuously increased. The tie rod steel bundle is tensioned to maintain the rib force in a relatively balanced state.

The prestressed tension control principle of the tie rod is that after each stage of the component installation (for the strength of the cast-in-place concrete member to be designed or specified), the prestressed tension of the tie rod should be slightly larger than the arch at this time. thrust. However, when the tension of the tie rod is less than the thrust of the next stage arch, the tension should be added during the installation of the next stage component. Before the longitudinal beam and the concrete are designed to strength, the tension of the tie rod is excessively greater or smaller than the thrust of the arch at the time, which will cause the arch to be displaced to the middle or the outer side. These displacements cannot be reset before the concrete of the longitudinal beam is poured. , after the longitudinal beam is formed, it will not recover, causing the arch axis to deform and changing the stress state of the arch rib.

3.2 Prestressed Tensile Values ​​Before the installation of the arches, the thrust of the arches at each stage of the installation is accurately calculated to determine the tension and tension values ​​of the tie steel bundles. The calculation of the arch thrust and prestressed tension at each stage of the installation of the bridge tie arch is shown in Table 1. Since the arch thrust will add 408.7kN during the installation of the tie rod and the beam, the rods and beams are 1, 9, 2, 8 After installation, N5 and N6 are supplemented by 100kN; in addition, the tensioning is added once during the longitudinal beam installation process, so that the arch is completely reset at this stage, thus ensuring the length of the longitudinal beam and the span of the arch rib are accurate.

Table 1 The arching force of the arch and the tie-pull value of each stage of the installation of the tied arches. Single arch foot thrust (N) Tied steel beam tension value (kN) Arch rib (including wind bracing) After installation, the rib concrete is poured After the tie rod and beam are installed, the concrete of the longitudinal beam is poured after the concrete is poured. Note: The former value in the table is the supplementary tension value during the installation of this stage. The value of */* is the tension value pretensioned tension after the installation of this stage. The procedure is closely related to the order in which the tie rods are installed. The specific tensioning procedure is as follows.

N9, N10 steel bundles are stretched to 150kN; pulled to 210kN; tie rods N5, N6 are stretched to 200kN; tie rods N5, and N9, N10 are stretched to 230kN; tie rods are covered with concrete to achieve design strength 90 After %, all the steel bundles of the tie rod ~N10 are stretched to the design value of 848. After the anchor is closed and the relevant temporary restraint is released, the drawbars are all pulled to the design value, wherein the drawbars 1, 9 are pulled to 720kN, 2, 8 sheets 4 Key issues of construction The installation of steel pipe ribs shall be carried out when the wet joint concrete between the end beams and the arches reaches 80% of the design strength; the rib supports shall be temporarily fixed before the arch ribs are installed, and the tie arches shall be formed. After the tie beam is pulled to the design tonnage, it is released; during the installation process of the tie rod, pay attention to the displacement of the arch and the deformation of the arch, and adjust the tie steel bundle according to the displacement of the arch and the deformation of the arch. Pulling timing and tension value; the first arch rib is temporarily fixed after installation. If the lateral stability coefficient is greater than or equal to 4, no temporary fixing measures can be taken.

5 Conclusions The single arch rib installation of the bridge has only been found to have relative displacement during the 2d installation. After installation, the measured lateral deviation of the arch shaft, the elevation of each feature point, the span of the arch rib and the verticality meet the design and specification requirements. The bridge has been in operation since July 2000 and has been operating smoothly.

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