The newly-built Gaokan Hunhe Landscape Bridge on Shenyang Fourth Ring Expressway is located in the core area of Shenfu New Town. The main bridge is a single-tower self-anchored steel box girder suspension bridge with a span arrangement of 48m+2× 180m+48m and a total length of 456m. The superstructure of the main bridge is a steel box girder structure, and the two main spans are suspended cable structures. (Figure 1)
The fixed connection section of tower beam is T3 section of cable tower steel shell. Rigid consolidation connection is adopted between tower column and stiffening beam. The main tower passes through the stiffening beam in the central separation zone of the main bridge, and is connected with the top and bottom plates of the stiffening box girder through stiffening plates arranged outside the composite steel shell. The main reinforcement of the tower column is continuously reinforced at the consolidation point, and the steel-concrete connection between the tower beam transmits force through the shear key on the vertical and horizontal partition. T3 segment is made of T3- 1 and T3-2, and welded on the top and bottom plates of the middle block of the D beam segment of the steel box girder. The side wall plate of the steel shell of the tower wall in the reinforcement area adopts the straight web plate in the stiffening beam, the front and rear wall plates of the steel shell are welded with the side wall plate through penetration, and the front and rear wall plates are provided with PBL shear key holes and large-size pouring communication holes; Cylindrical head welding nails are set on the top, bottom and partition of the stiffening beam in the fixed connection area to ensure the connection with the filled concrete. At the same time, JL finish rolled rebar is set horizontally, and the tension control stress is 790.5MPa (Figure 2).
2, the main tower steel box girder in-situ bracket assembly
32 steel pipe piles with 630mm and δ=8mm are used as supports, of which 16 steel pipe piles are directly supported on the main tower foundation and welded firmly with embedded steel plates. Other steel pipe piles are driven into the soil to a depth of not less than 6m, and the bearing capacity of a single pile is not less than 50t. The longitudinal and transverse connections between the rows of pipe piles are made of steel pipes with the diameters of 273mm, δ=8mm and φ 152mm, δ= 6mm. Two 83cm-long 20b steel beams are longitudinally arranged at the pile head of the steel pipe pile as the pile head distribution beam. The on-site assembling support of the main tower is an independent assembling support, which is disconnected from the steel box girder sliding supports. The steel box girder of steel box girder segment is assembled and welded on site by ZSL34300 boom tower crane beside the main tower. (Figure 3)
3. Connection and installation of steel box girder with fixed connection section and tower shell
3. 1 T3-2 segmental installation
After the fabrication of T3-2 steel shell of the main tower is completed, it will be transported to the construction site, hoisted by ZSL34300 jib tower crane, and temporarily connected with T2 steel shell. The surveyors accurately measure and adjust T3-2 section and elevation to the design requirements with instruments, and the joints are constructed by Site welding connection.
After the connection construction of the steel shell section of the main tower is completed, cut off the temporary matching part and polish the smooth cutting part.
3.2 steel box girder segment assembly
The steel box girder with fixed section is divided into E section and D section. At the same time, the scheme of multi-section continuous matching assembly, welding and pre-assembly is adopted. According to the order of beam erection and construction period, supporting manufacturing will be carried out. During beam fabrication, the construction shall be carried out in the order of bottom plate, inclined bottom plate → transverse mediastinum plate → anchor web plate → top plate → cantilever block → temporary lifting lug, temporary connector and ancillary structure assembly and welding. When assembling, the tire frame is used for the outer tire and the diaphragm is used for the inner tire, which mainly controls the alignment of the bridge, the geometric shape and dimensional accuracy of the steel box girder, and the accurate matching of adjacent interfaces.
(1) After the erection of steel box girder and the installation of supporting system are completed, surveyors will accurately set out and locate the center line of Class D beam section of steel box girder. Determine the elevation of the fulcrum of the upper beam segment supporting the distribution beam.
(2) The D-class beam is installed on the on-site assembly bracket with ZSL34300 boom tower crane. After the steel box girder is processed in the factory, it will be transported to the tower crane hoisting construction area by 100t flat car. The tower crane will be hoisted by temporary lifting points on the steel box girder, and the position of the temporary lifting points can meet the construction requirements after checking by the design unit, which will not cause structural deformation of the steel box girder.
(3) Set the assembling jig on the steel box girder erection bracket, and assemble the D beam section on the jig. The jig must have sufficient rigidity and geometric dimension accuracy. Beam segments shall be assembled continuously, and the number of beam segments assembled at each time shall not be less than 3 segments. The influence of sunlight should be avoided in the assembly process, and the main positioning dimensions should be monitored and measured by total station.
(4) The assembling bracket is provided with an assembling jig for supporting the steel box girder segments and welding the beams according to the design requirements. The sequence of hoisting and welding construction is central block, carriageway block and cantilever beam block. (Figure 4)
(5) The assembled jig is welded firmly with the distribution beam at the top of the pile, so as to ensure that the steel box beam segments do not shake or run off during installation. Mark the steel box girder and the assembled jig in blocks, so as to align it during hoisting and ensure the accurate installation of the steel box girder.
(6) Assembly method:
A, the top and bottom plate unit width assembly welding
Before assembly, check the positioning baseline on each plate unit. During lateral positioning, welding shrinkage is retained in the width direction of the plate unit. Align the assembly baseline of the U-shaped rib with the positioning end of the groove in the longitudinal direction, control the straightness of the positioning end of the unit, and strictly control the dislocation of the connecting plate on the partition at the same position on the upper and lower plate units to be less than 0.5 mm ..
B, assembling and welding the bottom plate unit
Place the middle bottom plate unit on the jig frame, accurately align its horizontal and vertical baselines with the baselines on the jig frame with theodolite, and fix the bottom plate near the horizontal baseline with the jig frame tooth plate by spot welding to ensure that the horizontal and vertical positions of the bottom plate will not slide.
C, assembling and welding the bottom plate
Assemble and weld bottom plate units and inclined bottom plate units on both sides symmetrically in turn. When welding, strictly implement the welding process specification and weld symmetrically.
D, assembling and welding the central straight web, the middle diaphragm and the inner straight web unit.
According to the horizontal and vertical baselines of the bottom plate, the middle straight web plate and the middle diaphragm plate are assembled in turn, and the weld between them and the bottom plate is welded; Then assemble the inner straight web elements in turn, check the end angle and straightness of each element with theodolite, and weld symmetrically from the middle of the beam section to both sides during welding.
E, assembling the welded edge diaphragm and the outer straight web unit.
Based on the horizontal and vertical datum lines of the bottom plate, the side partition plate and the outer straight web plate unit are assembled in turn, and the weld between them and the bottom plate is welded; Check the end angle and straightness of each unit with theodolite, and weld symmetrically from the middle of the beam section to both sides during welding.
F, assembling and welding the middle top plate unit
Accurately locate and assemble the middle roof unit to ensure the central height of the beam section and the cross slope of the bridge deck. Weld the longitudinal butt weld of the roof first, and then weld the weld between the partition and the roof. Pay attention to the reserved weld shrinkage to ensure the beam height.
G, assembling and welding the edge top plate and the cantilever plate unit.
Assemble the side roof and cantilever plate units in turn, weld the longitudinal butt weld between the roof and the weld between the partition and the roof, pay attention to the welding sequence, and reduce the deformation of the beam section. 3.3 T3 section of tower shell is connected with D-beam section.
After the installation of the D-class beam section is completed, the joint between the stiffening upper end of the vertical angle steel of T3-2 section and the bottom plate of the D-class beam section is welded by single fillet weld, and the stiffening plate is welded on the periphery of the tower shell according to the design position.
Measure the position of T3- 1 segment released from D-beam segment, install T3- 1 segment in place with ZSL34300 arm tower crane, and surveyors will adjust and retest its position. Weld stiffening plates outside the tower shell according to the design position.
4, tower beam fixed section construction
Tower reinforcement shall be installed after processing and acceptance. The installation of reinforcement depends on the arc stiffening of steel shell and the positioning of tie rod. First, install the steel shell of the main tower, extend the main reinforcement, and then install stirrups to complete the horizontal bracing. Under normal circumstances, steel binding should be carried out from one end to the other end in turn, and marked according to the requirements of drawings, with stirrups on, and bound and shaped.
In order to reduce the influence of shrinkage, creep and temperature change of concrete, C50 micro-expansive concrete is used in the fixed section of tower beam. In order to ensure the quality of concrete pouring in the tower-beam consolidation area, the particle size of coarse aggregate in this part of concrete is required to be 5 ~ 25mm, and the maximum particle size is not more than 25mm.
5. Construction quality control of three-dimensional junction area of main tower
5. 1 quality control of beam assembly
(1) Welding sequence of steel box girder: In order to ensure the shape and geometric size of steel box girder and prevent excessive internal stress, the welding of steel box girder should be carried out step by step, following the welding principles of first inside and then outside, first down and then up, and from center to both sides. COB2B welding method is the first choice, and the welding process of single-sided welding and double-sided molding of ceramic liner is completely adopted.
(3) Plate unit assembly and positioning: In order to control the assembly accuracy of steel box girder and reduce the influence of temperature difference, the positioning and assembly of bottom plate unit, top plate unit and anchor web unit on the center line of the bridge should be carried out without the influence of sunlight.
(4) The assembly and positioning of the top (bottom) plate unit, diaphragm unit and anchor web unit shall be tested by laser theodolite in addition to the alignment of the baseline, focusing on controlling the longitudinal straightness and the verticality between the port and the center line, and strictly controlling the vertical and horizontal center distance of the lifting point to meet the requirements of the tender documents.
(5) When adjusting, the positioning method of controlling the front and rear points on the longitudinal axis of the steel box girder can accurately complete the positioning of the steel box girder in a short time.
(6) After the positioning of the steel box girder is completed, measure the elevation and axis of the four corners of the steel box girder for further accurate positioning. Before the beam section is welded, the position of the beam section needs to be rechecked, and the error meets the requirements of installation accuracy before the next welding work can be carried out.
(7) Site welding must take measures to effectively protect the welding parts of parent materials, and be equipped with corresponding wind-proof and moisture-proof equipment and preheating and dehumidification facilities. Welding can only be carried out in accordance with the process. It is forbidden to carry out open-air welding on the base metal surface in snowy, rainy, humid or windy weather without any protective measures.
(8) Welding environmental conditions: wind power
5.2 Bridge Tower Construction Monitoring
(1) During the construction, the stress of the bridge tower should be monitored to ensure the safety of the bridge tower. The internal force monitoring of the main tower generally monitors the absolute stress of the main tower by embedding strain gauges, and takes corresponding measures to ensure the safety of the main tower according to the test results. Generally speaking, the root section of the main tower and the section at the junction of the tower and beam are the most unfavorable sections.
(2) At the same time, observe the temperature field of the bridge tower for a long time, and measure it every 2 hours every day to find out the law of the deformation of the bridge tower changing with the temperature in one day, so as to ensure the accuracy of the installation coordinates of the bridge tower. Moreover, the positioning and installation of bridge tower segments are generally carried out under the condition of stable at night, and resistance temperature sensors are used.
6. Concluding remarks
Suspension bridge can make full use of the strength of materials and has the characteristics of saving materials and light weight. Therefore, the suspension bridge has the largest spanning capacity among all kinds of bridges, and its appearance is beautiful, which will be a new direction of bridge development in the future. This project will provide guidance for the construction of similar conditions, and control the above points in the construction process to ensure and improve the construction quality of steel box girder, and strive for national high-quality projects for the promotion of new technologies and materials and the development of expressways.
The above are collected and sorted by Zhong Da Consulting Company.
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