Prefabricated buildings refer to prefabricated buildings in factories, construction sites or other places in advance, and then these building structures are transferred to the construction site by means of transportation, and these transported scattered prefabricated buildings are assembled into a whole building structure through certain splicing technology and certain mechanical hoisting. With the sustained and rapid development of China's economy, the continuous improvement of labor costs and the increasing awareness of energy conservation and environmental protection, in recent years, the research on prefabricated buildings in China has gradually warmed up, and many units have carried out some technical research. Among them, Vanke, the representative enterprise, has become a national pilot real estate enterprise for prefabricated structural buildings, and has completed more than ten practical projects, achieving good economic benefits.
1 Classification and advantages of prefabricated buildings
1. 1 Classification of prefabricated buildings can be divided into two categories according to the degree of assembly: (1) Full assembly. Like mechanical products, all components of such buildings are mass-produced in factories and then transported to the construction site for assembly. These components mainly include assembled slab, beam, frame structure, slab-column structure and box structure. The maintenance structure around the fully assembled building can be built or poured on site, or prefabricated wallboard can be used. The main advantages of this fully assembled building are the high production efficiency of building components, the quality of mass-produced components is guaranteed, the construction speed of direct splicing is fast, and the construction process is less affected by seasons. Therefore, in areas with large and relatively stable engineering quantities, if building components are produced in factories, better results will be achieved. (2) semi-assembly. Some of the main load-bearing members of this kind of buildings are prefabricated members, and some will be built on site. For example, in building structures, brick walls are generally used for vertical load bearing, so such components can be built on site. Such as floors and beams. Under normal circumstances, prefabricated components are used for on-site hoisting of horizontal load-bearing components such as stair platforms. In large-scale buildings, it is common to use prefabricated components for external walls and cast-in-place templates for internal walls. The main advantages of this kind of building are that the one-time investment cost of the production base is less than that of the fully assembled building, and the adaptability is wider, which saves a large part of the transportation cost and is easy to popularize. Under certain conditions, it can also shorten the construction period, which is more conducive to the realization of large-scale mobile construction in various places, and can obtain good economic effects and better structural integrity. At present, a kind of semi-assembled structure which is widely used in Chinese architecture is assembled integral structure. Advantages of 1.2 According to foreign statistical data, this paper introduces the advantages of prefabricated buildings from aspects of construction speed and project cost: (1) labor saving. Similarly, according to the data, in France, the average time per square meter of traditional buildings is 20 working hours. However, after adopting the assembly building and assembly technology of industrial production components, the labor without square meters has dropped to 1 1.5 man-hours. Obviously, after changing into an assembled building structure, the construction labor is saved by nearly 50%. In addition, it also reduces the labor intensity. (2) Shorten the construction period. In Japan, under normal circumstances, it takes 240 days for a five-story residential building with 100 households to adopt the traditional construction method. However, after adopting the construction method of prefabricated buildings and building components prefabricated in the factory in advance and mechanically hoisted on site, it only takes 100 households 0/80 days to complete the construction of a five-story residential building, which shortens the construction period by 25%. (3) reduce costs. The construction cost per square meter is lower than that of the traditional structure when the prefabricated structure building and industrial construction are adopted. However, due to the different economic conditions and building structures in different countries, the data of cost reduction are not the same.
2. Assembly integral structure construction technology
Assembled integral structure is a structural form based on cast-in-place structure and assembled structure, which belongs to semi-assembled structure. This structure has the advantages of flexible construction, good integrity, reducing construction waste, strong adaptability, shortening construction period, reducing cost and improving engineering quality. It is an ideal composite structure in engineering. The main construction techniques for assembling the whole structure are as follows. 2. 1 production of precast beams, columns and walls The production of precast members mainly depends on the preparation plan in advance, and the production progress will depend on the construction progress on site and the production capacity and storage capacity of the precast factory, and will be decided in coordination with the delivery plan. The manufacturing process of precast column is as follows: from cleaning the mould and positioning the end mould, to fixing the casing joint, to placing the reinforcing cage, to installing the embedded parts, to fixing the closed side formwork, to pouring concrete and smoothing it, and finally to cleaning the reserved pipeline blockage and repairing the damaged parts. The fabrication process of precast beam is as follows: from cleaning the mould and positioning the side formwork, to pre-binding the reinforcing cage, to hoisting the reinforcing cage, to installing the embedded parts, to sealing and fixing the side formwork, to pouring and smoothing the concrete, and finally to cleaning the reserved pipeline blockage and repairing the damaged parts. The manufacturing process of prefabricated wallboard tiles is as follows: firstly, select and determine the grid of the brick mold, put the tiles into the grid of the mold, then embed the customized spacer, flatten it with a roller, then paste protective paper, then stick it firmly with a special brush, then press and stick the spacer with a special tool, and finally form a product with block tiles. 2.2 Transportation and stacking of precast beams, columns and walls Because precast building products are generally heavy, most of them rely on cars for land transportation during transportation. However, it is often affected by bridges and tunnels during transportation, so special consideration should be given to the selection and stacking of vehicles, and prefabricated products should also be fixed and protected. Under normal circumstances, there are two kinds of transport vehicles. One is external, which is mainly used for the transport of external panels and walls, with a load of 16 tons; The other is plug-in type, which is mainly used for the transportation of internal partitions, with a maximum load of 8 tons. External hanging type has the advantages of low lifting height, convenient loading and unloading and beneficial to product protection. After the components arrive at the construction site, they should be placed in a flat, compact place with good drainage effect. When in place, it is necessary to properly place the wooden pad according to the stress when placing it. Some overlapping parts should be padded with wooden mats or something. 2.3 Precast beam, column and wall hoisting (1) Precast column hoisting should pay attention to: before hoisting, the damage inspection and internal cleaning of precast column should be carried out first; Before hoisting, the tools needed for installation should be prepared, such as brackets, bolt hoisting tools, verticality measuring rods, etc. Installation method, embedded pipes, number of components, lifting points, etc. Need to be confirmed; According to the actual situation, analyze and determine the appropriate hoisting method. (2) Precautions for hoisting precast beam: Check whether the supporting frames at both ends of the beam are ready and whether the heights of supporting points at both ends meet the requirements; Check whether the reinforcement and reinforcement position of the beam meet the requirements; According to the actual situation, four lifting points were determined. (3) Lifting of prefabricated external wall panels: After the prefabricated external wall panels enter the construction site, every link should be well protected, especially the panel parts. In the process of hoisting, it is necessary to ensure that there is no collision and pollution on the surface of the wallboard. 2.4 After the positioning of precast members and the pouring and hoisting of concrete, it is necessary to position all the placed members, so as to make the elevation, centerline and other heights meet the design requirements. Only after confirming the correct pouring can the concrete of beam-column joints and composite slabs be poured. The common pouring method is pressure grouting. 2.5 Waterproof treatment causes prefabricated buildings to be easily invaded by water, such as the influence of gravity of components themselves and external pressure. These problems can be waterproof by closing and opening seams.
3 Conclusion
With the rapid development of China's construction industry, prefabricated structure buildings will probably be widely used in buildings. This paper briefly analyzes some characteristics of prefabricated buildings, hoping to play a certain reference role for the future development of prefabricated buildings.
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