Cable-stayed bridge across Suiyan Road is a key project from Guiguang to nanning-guangzhou railway. Located at Suiyan Road, crossing the intersection of urban road and Guangzhou West Ring Expressway viaduct. The surrounding buildings are dense, and it is adjacent to the Wuhan-Guangzhou high-speed rail viaduct after crossing the expressway bridge. Therefore, long-span light steel bridge is adopted to avoid or reduce the interference of railway bridge to residents, urban ground traffic and expressway viaduct. The bridge is arranged on the four-line track, with a span of (32.6+175+175+32.6) m, and adopts a single tower and double cable plane tower-beam consolidation system, with a steel box structure with a main span of 175m and a prestressed concrete structure with a secondary span of 32.6 m. ..
The main tower is a double-column tripod structure with beams. The tower height118.9m above the bridge deck is made of C55 concrete. Hurt? The center distance between columns is 46.3m at the bottom and 24.0m at the top. The tower column is equipped with three beams, and its bending shape is combined with the bending main beam, which increases the lateral stiffness of the bridge tower, effectively resists the radial cable force pointing to the inner side of the curve, reduces the lateral deformation of the bridge tower, and improves the stress state at the intersection of the beams and the bridge tower. (see figure 1)
2 main tower structure
The cable-stayed bridge across Suiyan Road is structurally divided into tower foundation, lower tower column, tower beam consolidation area, lower cross beam, tower body, middle tower column, middle cross beam, upper tower column and upper cross beam, which are divided into 24 construction sections. The horizontal transportation of materials and equipment is directly transported to the main tower pier by Suiyan road car. In order to facilitate the spatial transportation of construction materials, two types of tower cranes, TC7052 and D800-42, are set inside and outside the main tower curve to serve the tower column construction and protective scaffolding. The production of concrete is supplied by a nearby mixing station, transported to the bridge tower by a concrete mixer, and poured by two daily pumps. The overall construction process is as follows: construction preparation (tower crane installation) → tower foundation construction → lower tower column construction → pier side support and west ring protection shed construction → lower beam area (including lower beam) tower column construction → climbing formwork → tower body construction → middle tower column construction → upper tower column and tower crown construction → upper beam construction.
2. 1 tower structure
The standard section of the main tower construction is 6m, and non-standard sections are set as adjustment sections in the lower tower column area and upper and lower beams. The single tower column is divided into 24 sections, and the climbing formwork climbing method is mainly used for construction. Because the construction space is limited by the West Ring Expressway Bridge, the scaffold method is adopted in the first section of the lower tower column, and scaffolding can be installed on all three sides except the inside of the tower body in the second section of the tower column. The construction platform is provided by steel pipe scaffolding. In the third section, the climbing frame on the inner side of the tower can be installed, and the concrete pouring of the remaining tower columns is completed by climbing formwork climbing frame method. Because the surface of the main tower is streamlined, if steel formwork is used, too many specifications of steel formwork are needed, which is not conducive to the adjustment and assembly of formwork and is a great waste. Therefore, the climbing formwork panel of the main tower adopts assembled big wood composite formwork (wood plywood adopts imported visa plate), and the climbing formwork system mainly includes square timber, section steel, 2[ 14b steel belt, opposite pull rods, fasteners and so on. Climbing formwork system of main tower
Automatic hydraulic climbing formwork system is mainly composed of hydraulic climbing frame and formwork system. The climbing frame is mainly composed of pendants and embedded parts, climbing guide rails, hydraulic jacking equipment, upper operating platform, main working platform, lower operating platform and elevator entrance platform. Its composition is shown in Figure 2. 2. Force calculation of1.1climbing frame system
The model shown in Figure 3 is established in Midas, and the stressed members are numbered in turn. Because members 2, 4 and 6 are the same, 1 and 5 are the same, and1,13, 14, 15 and 16 are the same.
Working condition 1 is static, and the action form is shown in Figure 4; Under the second working condition, the action form is shown in Figure 5; Wind load values are all q1= 7.625kn; Q2=8. 17kN。 After Midas calculation, take the most dangerous truss and get the axial force diagram of each member. See table 1 for the calculation results of axial force and stability of members.
According to the table 1, the axial stress of each member is less than the strength design value f=2 10MPa, which meets the specification requirements.
2. 1.2 climbing frame construction method
Climbing frame system comes into play to complete assembly. When pouring the lower beam section, the embedded parts of climbing frame shall be embedded according to the design requirements. At the same time, considering that there is no obvious staggered joint and dislocation between the section to be poured and the poured section, H-bolts are embedded below the top of the poured section 15cm. When assembling the formwork, the bottom of the formwork shall be accurately landed on the fastener with special fasteners, and the formwork shall be clamped with fasteners, so that there is no gap between the formwork and concrete. After the technical security department has finished the inspection.
The lifting movement of self-climbing formwork is realized by alternately lifting the guide rail and climbing frame by hydraulic cylinders, and the guide rail and climbing formwork can move relatively. When the climbing frame is in working condition, both the guide rail and the climbing template are supported on the embedded parts bracket, and there is no relative movement between them. After demoulding, the stress bolt, hanger body and built-in bracket can be installed on the climbing cone left after demoulding, and the direction of the upper and lower yoke claws can be adjusted to jack up the guide rail. After the guide rail is jacked in place and positioned on the embedded part bracket, the construction personnel will go to the lower platform to dismantle the guide rail, the embedded part bracket and the climbing cone. After all the knots on the climbing formwork are untied, the climbing formwork can be lifted, and the guide rail remains motionless. After adjusting the direction of the upper and lower pawls, start the oil cylinder, and the climbing die moves upward relative to the guide rail. The guide rail and the climbing formwork are alternately attached to the wall, and the other side is lifted, and the climbing formwork rises along the wall until it is located on the reserved climbing cone, thus realizing step-by-step lifting. After reaching the design position, take safety protection measures, tie steel bars according to the conventional method, complete template assembly and rigid skeleton installation, and pour tower concrete after inspection and confirmation.
2.2 Lower beam structure
The lower beam construction adopts floor-standing support, which is mainly composed of steel tube column+longitudinal distribution beam+transverse truss beam. The steel pipe column consists of three rows, one row of steel pipe columns is erected on the inner and outer bearing platforms of the bend through embedded parts, and the other row of steel pipe columns is erected at the central separation zone of the West Ring Expressway. The column foundation adopts the way of bored pile and cap, and the layout is shown in Figure 6. The lower beam of the main tower is 8m wide, 5m high in the middle section and 7.4m high at both ends, spanning the West Ring Expressway. The gap between its bottom and the bridge deck of Xihuan Expressway is 7.73 meters, and its own weight is about 3068 tons. Pouring in two times, 3m for the first time and 2m for the second time. Because the bottom surface of the lower beam is an arched surface, it is necessary to process a special arched truss as the beam.
The main construction steps are: measurement and positioning → beam support installation → preloading → beam bottom formwork installation → binding bottom plate, web reinforcement, corrugated pipe and beam piercing → installing internal and external formwork → checking and verifying → arranging pouring platform and pouring concrete → installing top bottom formwork → binding top steel → pouring concrete → curing and dismantling top bottom formwork → tensioning → grouting → sealing end → dismantling beam bottom formwork and support.
2.3 construction of middle beam and upper beam
The middle beam and the upper beam are constructed by bracket support method, and the main beam of the support adopts arch truss structure according to the structural bottom line. See Figure 7 for the layout. The bracket is embedded in the side wall of the tower column, and the force is transmitted to the poured tower column entity through the tension of the finishing screw.
Because the upper and lower contour lines of the middle beam and the upper beam are elliptical, the curvature is small, the construction structure is complex and the construction is difficult. In order to reduce the stress on the bracket and facilitate the pouring and vibrating of concrete, the concrete pouring of the middle beam and the upper beam is carried out in three times (the upper beam in the bracket is? M beam pouring layered height), the first pouring 8.5m(9.0m), mainly pouring elliptical arc bottom plate, part of the web concrete. After the concrete strength reaches the design strength, the second pouring is carried out, and the pouring height is 4.5m(4.0m), which mainly completes the concrete of the partition, part of the web and the top plate between two transverse partitions. After the concrete reaches the design strength, it will be poured for the third time to complete the pouring of the remaining roof and web concrete. Before the concrete construction of the upper beam, the upper beam is supported by the bearing load. In order to enhance the rigidity of the middle beam, the construction of the upper beam can only be continued after the prestress of the middle beam is tensioned.
Its construction steps are as follows: measuring and setting out → constructing the tower column to the middle and upper beam areas → burying the middle and upper beams in the steel bars in the tower column → burying the corbel → chiseling off the side faces of the tower column in the middle and upper beam areas → installing the middle and upper beam supports (installing the protective platform) → laying the bottom formwork → erecting the scaffold platform → installing the floor steel bars and web steel bars (pre-embedded prestressed corrugated pipes) → installing the internal formwork → installing the partition steel bars → chiseling.
3 main tower linear monitoring monitoring
The linear control of bridge tower is an important content of construction monitoring, and its linear quality is directly related to the quality of bridge tower, the hoisting accuracy of cable and the installation accuracy of steel box girder. Therefore, it is necessary to establish a real-time measurement system at the construction site to track and measure the displacement, alignment, temperature and settlement of the structure during construction, and provide measured data for construction monitoring, that is, to monitor the alignment of the bridge tower by using the plane and elevation control network established by construction and applying triangulation and precise leveling methods.
The deflection measuring points of the main tower are arranged at suitable points on the top surface of the inner and outer sides of the tower column, and are measured with a precision level. Other geometric positions are mainly measured by total station. The elevation measuring instrument is Leica NA2 automatic leveling level, and the ranging accuracy is 0.7mm per kilometer. TOPCONGTS-60 1A total station is used for axis deviation measurement and tower deviation measurement, with angle measurement accuracy of 1 "and ranging accuracy of 2mm+2ppm. The linear survey in the controlled construction stage is arranged at the end of each tower construction stage and 3-4 hours after sunset (4-5 hours after sunset in summer and autumn) and before sunrise the next morning.
4 conclusion
The main tower construction of cable-stayed bridge across Suiyan Road is influenced by urban traffic environment, construction space, seasonal typhoon and other factors, and the construction is difficult. After detailed scheme comparison and calculation research in the early stage, the scientific and advanced climbing formwork climbing method is adopted for tower column construction, and different types of supports are used for beam construction. Each step is combined with the actual situation on site, and the construction is successfully completed in strict accordance with the scheme of different measures at different stages. At present, the cable-stayed bridge has been put into use and has been in normal operation for 4 years, without any later problems, which has important reference significance for the construction of similar bridges in the future.
(1) According to Calculation Manual for Road and Bridge Construction (published by People's Communications Publishing House) (Zhou Shuixing, etc.), the axial stress [σ] of No.45 steel in Schedule 3-20 is 2 10MPa.
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