1. Overview of the toll station canopy project
The main structure of the canopy of the toll station is mainly composed of four parts: the support, the main arch truss, the truss, and the roof derrick, as well as the roof truss. The length of the toll station is 183.6m, the width is 24m, the height of the center line of the main arch truss structure is 28m, and the height of the shed roof is 11m. 26 toll turns are arranged in both directions. The distance between them is 5.4m, and there are three functions: ETC lane, automatic card issuing machine lane, and ordinary manual toll gate.
The materials used for the main structure of the toll station are seamless steel pipes and welding. There are 12 main specifications of steel pipes. The largest steel pipe is 600×30, and the minimum is ф76×4. The total steel consumption of the main structure is about 700t. The roof tolling greenhouse is connected by two vertical and horizontal trusses, and the connection forms are mainly KT-type nodes, Y-type nodes, and T-type nodes; the steel pipes used are high-frequency welded pipes or hot-rolled seamless steel pipes, steel pipes and connecting steel plates. The material is Q345B, and the purlin and other unspecified steel are Q235B. All steel structure surfaces of this project should be mechanically derusted, and the derusting level should reach Sa2.5 level of GB8923-88 standard. After derusting, brush epoxy zinc-rich antirust primer twice, the topcoat is chlorocarbon paint, and the total paint Film thickness: The main arch truss is not less than 200μm, and other components are not less than 150μm.
2 Characteristics and key points of design and construction
2.1 The architectural scheme is complex
This toll station project is a high-speed entrance and exit. After several rounds of plans, an arched truss system with a span of more than 180 meters was determined. Due to the special requirements of various functions of the toll station, the design scheme of the project has given great challenges. The steel structure has a large amount of engineering and many structural nodes. At the same time, most of the steel plates used are thick. All the nodes need to be welded on site, and the welding workload is large, and the connecting nodes are all three-dimensional space structures. Therefore, the core task of the design of the steel structure of this project is to fully understand the original design intent, comply with the relevant specifications and standards and ensure the structural safety of the premise of structural design and research and application, combined with specific manufacturing and welding processes, in order to ensure the safety of the entire project. The production accuracy and welding quality, detailed and reasonable process design for the node structure, to ensure the realization of the construction of the entire structure. When formulating a solution for each problem in the design, various factors must be considered comprehensively, and the best balance point can be found among these mutually restrictive factors. Software such as ANSYS8.0, SAP2000, MTS, 3D3S and other software are used to compare the structure calculation. Analyze and ultimately determine the best structural solution.
2.2 The steel structure arch truss has large span and complex structural form, and it is difficult to waterproof the roof
Although the main steel structure of the toll station project is only 700t, the number of steel components is about 7,500, and the number of additional parts is about 30,000. The span of the main arch truss is 170.6m, and the space is curved in both directions, making it difficult to make explosions. They are all tied by the main arch truss suspenders, and there are many tie-down nodes, which makes the roof waterproofing difficult. High, and cannot be hoisted as a whole, it is difficult to temporarily support.
2.3 The high level of structure and the difficulty of vertical transportation
The installation positions of steel components are distributed between 1.000m and 28.000m, especially the main arch truss. The span and segmented hoisting volume is large, the single component is heavy, and the segmented hoisting and docking are difficult, and the construction work surface must ensure road use Operation, whether the hoisting equipment station, the selection of subsections, etc. are reasonably equipped horizontal and vertical transportation machinery, and optimization of on-site stacking and pre-assembly site layout, etc., are of great significance for advancing the construction progress.
2.4 Large volume of structural deformation control
Due to the large span of the main arch truss of the toll station, the long length of components, the shrinkage of subsection and joint welding, the self-weight of the structure, the construction live load, the change of the direction of sunlight, the change of temperature, the wind load, the load of other auxiliary structures, the relative settlement of the foundation, etc. The change will have different effects on the construction process, especially in the high-altitude butt welding construction of the main arch truss, the preset adjustment value of the sub-plate and the process deformation measurement and control are very important in the whole construction process, and also the key to ensure the final state of the structure.
2.5 The steel structure design has a large amount of engineering and high requirements
The steel structure design of the toll station adopts the overall modeling of Xsteel software, and all the pre-adjusted values are considered in the component design drawing; in addition to meeting the joint strength requirements, the joint design should also fully consider the use of materials, the rationality of processing and manufacturing, and the control of welding residual stress and other factors.
2.6 Measurement and control requirements are high and difficult
Because the steel structure of this project is basically on-site welded joints, the spatial forms of each rod are variable, the angles are different, the spatial measurement and positioning are difficult and the number is large, especially since the main arch truss must be hoisted in sections and sections, and the docking parts are High-altitude docking is very difficult. At the same time, due to the long length of the overall steel structure and the bidirectional bending, the steel structure components are constantly changing in the three-dimensional direction due to the influence of climate changes such as the weight of the structure, wind load, sunshine and temperature difference, which is not suitable for the use of reasonable steel structure. The reasonable measurement control method, the guarantee of measurement accuracy, and the real-time monitoring of structural deformation have put forward very high requirements.
2.7 Large welding workload and high-quality requirements
The steel structure welding workload is large, with many related nodes, varied welding angles and welding methods, large welding at the nodes, and the welding seam is concentrated. Controlling welding deformation and eliminating residual stress are the key contents of steel structure welding in this project.
2.8 High requirements for construction safety protection
The main arch truss with a span of 170.6m needs to be split into 3 sections for hoisting due to its space volume and single frame weight. Before forming the frame, temporary support and reinforcement measures are required to ensure its stability. At the same time, to ensure the use and operation of the road, an auxiliary platform needs to be erected And the surrounding enclosure can be assembled and welded. It is difficult to set up a safety protection operation platform. Due to the short construction period of the project, there are many rush jobs and cross operations, and there are many safety hazards. Therefore, safety management during the construction period is difficult and demanding.
2.9 The overall process of installing steel structures for toll stations is complex
Due to the construction site being small and the construction period is very short. Therefore, the feasibility of construction should be fully considered in the design, and the design should be feasible and pertinent to the construction. Therefore, the construction process should be considered in the design plan according to the following steps: measuring and laying out positioning → positioning of embedded parts → erection of temporary supports → Installation of the main arch truss of the left half of the toll station (the first section of the subsection → installation of the right half of the main arch truss of the toll station (the second section of the subsection → the middle part of the toll station is closed and docked) (the third section of the subsection → Removal of temporary supports of tolling greenhouses → Installation of vertical and horizontal trusses on the roof of tolling greenhouses → Installation of roof markings → Installation of roof horse paths → Installation of stairs for viewing platform of main arch truss → Installation of viewing platform of main arch truss → roof gutter installation→ roof glass installation→ roof fire prevention and treatment of edge closing.
3 Key control of the construction process
①Due to the complexity of the construction, the quality control of the raw material procurement of the steel structure is strictly controlled during the construction process. For the on-site construction of the main arch truss, the steel plate layout, scribing and cutting, bending panels and forming, longitudinal seam welding, and round pipe joints must be strictly controlled. Each process of segment rounding, barrel section and barrel section pairing, and girth weld welding.
②The hoisting process adopts reasonable and detailed technological measures and technological processes according to the pre-determined overall construction plan. According to the measurement control points, lead the measurement control points before the project construction, lay out the steel structure measurement control network, make each control point a permanent coordinate pile and a horizontal reference point pile, and take protective measures to prevent damage.
③Strengthen structural measurement and monitoring, establish a survey quality management account and measurement quality tracking and monitoring system, regularly check the steel structure installation survey control network on site and correct errors in time.
④The truss members in the arch truss are made by on-site splicing and butt welding (the factory is made into two sections, transported to the site and spliced into a whole and then hoisted), and the splicing adopts the full penetration weld and manual arc welding method. In the design, the construction procedures are strictly required to ensure the welding quality during the construction process.