Keywords

1 Introduction

1.1 The Concept of Assembly Building

Assembled building refers to the concept of green development [1], supported by modern scientific and technological progress, industrialized production methods as a means, engineering project management innovation [2] as the core, the world’s advanced level as the goal, the extensive use of information technology, energy saving and environmental protection technology [3], etc., to link the whole process of production of building products as a complete integrated industrial chain system.

1.2 Assembly Building Characteristics

The differences between assembled buildings and traditional buildings are mainly reflected in the different construction methods, different operation modes, different construction concepts and so on. Compared with the traditional building mode, assembly building mainly has the following characteristics.

  1. (1)

    It is conducive to improving construction quality. Assembled components are prefabricated in the factory, which can maximize the improvement of quality problems such as wall cracking and leakage, and improve the overall safety level, fire resistance and durability of the residence.

  2. (2)

    Favorable to speed up the progress of the project. Efficiency is the return, according to incomplete calculation statistics, assembly type building is about 30% faster than the traditional way of progress.

  3. (3)

    Benefit from improving building quality. Assembled building components are unified production, compared with the traditional construction of the site pouring quality is better control.

  4. (4)

    Benefit from civilized construction and safety management. Traditional site has a large number of workers, now a large number of site operations moved to the factory, the site only need to stay a small part of the workers on it, greatly reducing the incidence of on-site safety accidents.

  5. (5)

    Benefit from environmental protection and resource saving [4]. The site of the original cast-in-place operation is very little, healthy and non-disturbing, from now on, goodbye to the “gray haze”. In addition, the reuse rate of steel mold plate can be improved, and the garbage, loss and energy saving can be reduced by more than half.

2 Status of Assembly Building Development in Chongqing

2.1 Policy Support System

In recent years, the state ministries and commissions have put forward corresponding requirements for the development of assembly building and issued corresponding documents, the relevant content of the documents from various angles to vigorously develop assembly building, some of the documents and the main relevant content involved in the following Table 1.

Table 1 Relevant national documents and contents.
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Following the footsteps of the national policy, Yu Jian [2019] No. 436 [10], Yu Jian [2018] No. 487 [11], Yu Jian [2018] No. 147 [12], Yu Fu Bufa [2017] No. 185 [13] documents and other documents came into being, the documents clearly put forward, the development of assembly construction is to promote the structural reform of the supply side and the development of the new type of urbanization, an important initiative, is the concrete embodiment of the implementation of the concept of green development concept and the concept of innovative development of the construction industry, and it is to promote the transformation and upgrading of the construction industry, and the realization of the modernization of the construction industry is an important hand.

3 Data Support System

By the end of 2022, the city had started construction of a total of 40 million square meters of assembled buildings, and the proportion of assembled buildings in new buildings exceeded 18%, with the central urban area reaching 36%; it had cultivated six national industrial bases, 29 municipal industrial bases, and more than 60 component part production enterprises. As of July 2023, the city has implemented a total of 47 million square meters of assembled buildings [14] and the proportion of assembled building applications in buildings started in the first half of 2023 reached 30%. In terms of talent, actions to cultivate construction enterprises’ own workforce have also been gradually carried out, and it has been proposed that it will strive to reach a ratio of more than 50% of construction enterprises’ own workers by 2025.

Assembly buildings are categorized into steel, concrete and wood structures. Concrete structures are more frequently used in the city, including residential and public buildings, while steel and wood structures are less frequently used in residential buildings in Chongqing due to their respective characteristics.

According to incomplete statistics, up to now, a total of 16 projects have passed the pre-evaluation of Chongqing assembled buildings in 2023, all of which are assembled concrete structures and involve an assembled floor area of about 850,000 m2, including about 80,000 m2 for public buildings, 700,000 m2 for residential buildings, and about 50,000 m2 for the combination of residential and public buildings, accounting for 10%, 82%, and 82% of the projects that have passed the pre-evaluation of Chongqing assembled buildings in 2023, respectively. 10%, 82% and 6% of the projects. Specific building types and area shares are shown in Fig. 1. Among them, projects belonging to Chongqing Liangjiang New District accounted for about 30%, Jiulongpo District accounted for about 10%, and the others were distributed in Jingkai District, Jiangbei District and Shapingba District.

Fig. 1.
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Area and percentage of assembled building types in Chongqing, 2023

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4 Technical Support System

In Chongqing, in addition to the expansion of new assembly building area, some assembly technologies are also applied in the production and construction procedures. For example: non-load-bearing peripheral parapet wall adopts self-insulating autoclaved aerated concrete precise block thin masonry process wall; internal partition wall adopts autoclaved aerated concrete slats, adopts the integration technology of internal partition wall and pipeline; only the public area and the area of determining the function of use is fully decorated, adopts the integrated bathroom, pipeline separation technology, the building floor adopts the modular heat preservation and acoustic isolation of the functional parts of the dry working method, and the decoration and the pipeline of the equipment adopts the full decoration, integrated kitchens and integrated bathrooms, and the adoption of information technology for engineering and construction. The application of these technologies fully reflects the design standardization, production factory, construction assembly, decoration integration, management informationization and application intelligence of the assembly building.

5 Analysis of the Application of Some Assembly Structure Projects in Chongqing City

Chongqing Urban Construction Archives Project, as shown in Fig. 2, as the first case of assembly type clear water outer enclosure insulation integration structure project in Chongqing, the total land area of about 36,000 square meters, the total construction area of about 112,200 square meters, the main body of the steel structure project, the assembly rate of about 70%, belongs to the ultra-limit high-rise building projects and technically complex projects, technical difficulties. During the construction process, some or all of the components are prefabricated in the factory and then transported to the construction site for assembly.

The experimental building project of Chongqing University Huxi Science Center covers an area of about 172 acres, with a construction area of about 247,700 square meters, and is located in the center of the Western (Chongqing) Science City, as shown in Fig. 3. The construction environment is complex, in order to effectively reduce the construction of the environment, noise pollution, in order to speed up the construction progress at the same time, the project selected the green assembly slope support technology, compared with the traditional spray anchor support, has the characteristics of fast construction speed, large turnover.

Fig. 2.
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Chongqing Urban Construction Archives

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Fig. 3.
figure 3

Huxi Science Center Laboratory Building, Chongqing University

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Tongan high-speed (Chongqing Tongliang to Sichuan Anyue) Chongqing section, as shown in Fig. 4, total length of about 48.64 km, designed for two-way six-lane, two toll booths using assembly, integration of steel structure canopy, compared with the previous brick structure, the construction is more convenient, more beautiful shape, more economical cost.

The mainline of the Cha Hui Avenue project is 8.96 km long, and the cantilevered cover girders of the mainline bridges are supported by an assembled SPS truss-type support system, as shown in Fig. 5, in which steel pipes with a diameter of 133 mm and a wall thickness of 5.6 mm are connected and secured with reinforcing bowls and fasteners to form the support. This construction method provides higher strength and better member stability than traditional support systems.

Fig. 4.
figure 4

Steel Structure Canopy of Pingtan Toll Station

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Fig. 5.
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Cantilever cover beam for Cha Wai Avenue

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Fig. 6.
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Construction effect of Kui Zhou Yangtze River Bridge

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Fig. 7.
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Shinsen Avenue

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Kui Zhou Yangtze River Bridge, shown in Fig. 6, is the largest center-bearing mesh arch bridge in the world in terms of span, and the first such bridge in China. A major feature of the bridge is the adoption of fully prefabricated assembly construction, which transforms the “design-site construction” mode into the “design-factory manufacturing-site assembly” mode. In addition to the foundation part, the bridge substructure, steel arch, bridge deck and other “parts”, according to the size and standards in the factory to do a good job and then transferred to the construction site, like “building blocks” for assembly, effectively improve the construction efficiency, save personnel costs, energy saving and environmental protection.

The 2.5-km-long, two-way, eight-lane Xinsen Avenue, shown in Fig. 7, is China’s first cut-and-cover assembly tunnel, where the tunnel lining is completed like building blocks. Each prefabricated component is shaped like a quarter-circle arc, weighs more than 70 tons, and needs to be lifted by a gantry crane.

6 Conclusion

In recent years, the assembly structure of Chongqing Municipality has been fully developed, including the increase of assembly area, and the improvement of the assembly rate of the project, etc. The assembly building has also changed from a simple frame structure to the current use of tunnels and bridges and other parts of the building, which greatly improves the application of assembly in the city, which is not lacking in some of the country’s leading use of new technologies, such as the largest span of medium-bearing netted arch bridge in China, which is also the first cross-river bridge of its type. The first cross-river bridge, which are all breakthroughs brought about by the vigorous development of assembly type construction. However, there are certain problems in the development, in order to fundamentally solve these problems, we must reform today’s inherent concepts, based on technological innovation, increase the assembly construction technology research efforts, improve the corresponding management system, improve the relevant testing standards, the prefabricated components of the production enterprises to carry out a reasonable layout, so that the production of safer, more reliable quality.