by 1、 Overview in the past few decades, China’s construction industry has developed vigorously, which has greatly promoted the growth of the national economy.
Facing the increasing cost of land transfer, the rising price of labor and the gradual improvement of people’s awareness of energy conservation and environmental protection requirements, the construction industry is facing increasing international competitive pressure.
In order to improve the core competitiveness, a new industry model – precast building came into being.
Firstly, understand three definitions: (1) precast concrete structure refers to the concrete structure assembled by precast concrete components through reliable connection, including assembled integral concrete structure, fully assembled concrete structure, etc.
In construction engineering, it is referred to as precast building for short; In structural engineering, it is referred to as cast structure for short.
（2） Precast assembly rate refers to the proportion of the volume of precast component concrete used in the part of precast buildings that is suitable for the use of precast components in accordance with the technical specification for precast concrete structures (jgj1-2014) to the volume of all component concrete in the appropriate part.
Precast assembly rate = concrete volume of precast members ÷ concrete volume of all members.
（3） Precast components refer to concrete components made in advance in the factory or on site, such as beams, plates, walls, columns, balconies, stairs, canopy, etc.
The traditional housing construction technology has low production efficiency, slow construction speed, long construction cycle, high material consumption and high labor intensity.
This series of conditions can not meet the rigid demand for housing in modern society.
Precast buildings have the following characteristics: ① diversified design, which can be designed according to housing requirements; ② Modern function, can use a variety of new materials such as energy conservation and environmental protection; ③ Manufacturing factory can make the building components and parts produce in a unified factory at one go; ④ Construction assembly can greatly reduce labor and material waste; ⑤ Optimize the time to significantly accelerate the construction period.
Therefore, in the face of China’s increasing housing demand, it is imperative to optimize the construction industry model as soon as possible.
Precast buildings pay attention to the protection of environment and resources.
During the construction process, they effectively reduce the emission of construction sewage, harmful gas and dust and the pollution of construction noise, reduce various impacts of construction on the surrounding environment, improve the labor productivity of buildings, promote the refinement of design and buildings, and improve the overall quality of buildings and the rate of energy conservation and emission reduction, It promotes the healthy and sustainable development of China’s construction industry and meets the needs of national economic development.
In the annual land supply area ratio of construction land, each block needs to implement precast buildings with a certain proportion of area.
It can be seen that the transformation of the construction industry model has attracted the attention of the government, and the future development tends to be a sunrise industry.
Table 1 differences in construction management between precast buildings and conventional buildings precast buildings conventional building construction components and accessories factory finalized assembly line processing products, on-site workers, artificial reinforcement workers, carpenters, concreters and other construction equipment, large mechanical equipment, hoisting small manual equipment, organizing a large number of manual work to complete the concrete, and the accuracy requires on-site installation, The size requirements are high, the structure of each floor is completed on site, the size accuracy is low, the safety management on site focuses on the professional training of mechanical equipment and workers, the management requirements of safety personnel are high, the on-site safety management pays attention to the construction progress of workers, the construction progress is accelerated, there are many on-site construction processes, the construction progress is slow, and the site environment is well managed, Environmental management is good, there are many on-site objects, and environmental management is more difficult.
The on-site decoration is suitable for finalized residential office decoration (due to processing and finalized construction and assembly) and the on-site secondary decoration is more suitable (due to changes in manual construction technology).
II.
The development of precast concrete building and housing industrialization in China.
The development process of housing industrialization in China can be divided into three stages.
The first stage: the establishment and starting period from the 1950s to 1980s.
In the 1950s, China proposed to learn from the Soviet Union the experience of industrialization construction and the policy of design standardization, industrialization and modularization.
There were many discussions and practices on industrialization and standardization in the development of precast components and precast assemblies in the construction industry.
In the 1950s and 1960s, we began to study the design and construction technology of precast concrete buildings, and formed a series of precast concrete building systems.
The more typical building systems include precast single-layer industrial plant building system, precast multi-storey frame building system, precast large slab building system, etc.
In the 1960s and 1970s, drawing on foreign experience and combined with national conditions, Yugoslavia’s prestressed slab column system, namely post tensioned prestressed cast structure system, was introduced, the standardized method was further improved, and the construction technology and construction speed were improved to a certain extent.
The policy of “three modernizations and one reform” was put forward in the 1980s, that is, design standardization, production and industrialization of components and fittings, construction mechanization and wall transformation.
Residential construction forms such as large block assembled large plate and large formwork cast-in-situ appeared.
However, due to the monotonous products, high manufacturing price and unresolved key technical problems at that time, the comprehensive benefits of building industrialization were not high.
This period can be said to be a period promoted by the government in the form of planned economy and centered on the construction of residential structure.
The second stage: the exploration period from the 1980s to 2000.
Since the 1980s, housing began to implement the market-oriented supply form, and the scale of housing construction has been unprecedented rapid.
At this stage, China has made many positive explorations in the direction of industrialization.
For example, modular standards are closely related to industrialization.
In 1987, China formulated gbj2-1986 unified standard for building modular coordination, It is mainly used for the unification and coordination of modules..
