Keywords

1 Introduction

To illustrate the design and construction of architecture, we usually make a visual analogy, comparing architecture to living organisms. The building structure is the skeleton of an organism, responsible for supporting the entire organism and carrying other loads imposed on it. The external image of a building is the outer skin of an organism, responsible for creating the overall image and temperament of the building. The equipment pipelines of buildings are the veins of organisms, responsible for delivering energy and nutrients to organisms and maintaining their normal life activities. The internal decoration of a building is the inner surface of an organism, responsible for the image and sensory aspects of the internal space. It is obvious that for a complete building, the exterior skin, skeleton, vein, and inner skin are indispensable. Buildings without exterior skin are rough and crude, incompatible with the urban environment, making it difficult to establish a foothold; A building without a skeleton will collapse and cannot exist at all; A building lacking a vein means that it lacks water, power, and air conditioning, making it difficult for such buildings to be used for a long time; A building without an inner skin is actually a rough house, and the internal space of the building is a place for people to stay for a long time. Without decoration, the building cannot fulfill its intended function.

It is precisely this vivid and simple analogy that forms the theoretical foundation for the design and construction of prefabricated buildings. This theory was originally proposed by Nicholas John Habraken at a conference of the Dutch Institute of Architects in 1965. He proposed the idea of dividing the design and construction of residential buildings into “support” and “detachable units”. The proposal of this idea precisely responded to a difficult problem faced by industrial residential construction at that time. After World War II, large-scale industrialized residential construction solved the severe housing shortage after World War II. However, since the late 1960s, people have been dissatisfied with the monotonous prefabricated building and environment. The Dutch Association of Architects proposed the SAR architecture theory based on Professor Habrgen’s “support” and “detachable unit” ideas to address everyone’s dissatisfaction, which is the contradiction between standardization and diversification of prefabricated building. SAR theory suggests that: the skeleton of a building is designed by professionals such as architects based on the specific location, conditions, and standards of the project. The construction task of the skeleton is completed after the project is completed, and no further modifications can be made, except for daily inspection, maintenance, or reinforcement. Separable components, including partitions, equipment, decoration, etc., are products of industrial production, and not only can be installed, removed, modified, or adjusted, but many components are also available. It can be universal. The selection and arrangement of these separable components, that is, the layout within the household, can be entirely determined by the residents themselves. It is precisely this prefabricated residential construction model, in which architects make various feasible and selectable apartment plans in advance for residents to choose from, that theoretically solves the contradiction between standardization and diversity of prefabricated residential buildings [1].

2 The Guiding Effect of SAR Theory on Prefabricated Buildings in China

In the 1950s and 1960s, China had a period of development in the prefabricated single-story industrial factory building system, prefabricated multi-layer frame building system, and prefabricated large plate building system. However, due to insufficient research on structural seismic resistance, design, construction, management, and other aspects, and poor technical and economic performance, prefabricated concrete buildings were replaced by fully cast-in-place concrete building systems in the mid-1990s [2].

In the past decade, with the upgrading and iteration of the construction industry and related industries, prefabricated buildings have been given high expectations due to their potential advantages in large-scale emission reduction and high-precision manufacturing of building components [3]. On February 22, 2016, the State Council issued the “Guiding Opinions on Vigorously Developing Prefabricated Buildings”, which required the development of prefabricated concrete structures, steel structures, and modern wooden structures in accordance with local conditions, striving to achieve a 30% proportion of newly built buildings in approximately 10 years.

Looking back at the development process of prefabricated residential buildings both domestically and internationally, it is found that the development of prefabricated residential buildings has always been carried out under the theoretical framework of SAR. From the OB (Open Building) theory in the Netherlands in the 1970s, to the later SI (Skeleton Infill) housing, to the KSI (Kikou Skeleton Infill) housing in Japan, and to the China Skeleton Infill prefabricated building system in China, there is no exception [4].

3 The Guiding Role of SAR Theory in the Research of Prefabricated Building Wall Technology in China

Compared with advanced prefabricated residential technology abroad, prefabricated buildings in China are still in their early stages, and the proportion of prefabricated building projects completed is lower than that of many developed countries [5]. The research on prefabricated buildings mainly focuses on the seismic resistance of components, the application of BIM technology, quasi-static testing, finite element analysis construction technology, prefabricated residential buildings, node connections, and other fields [6]. These fields are the phased target topics in the early stages of prefabricated construction. From the perspective of SAR theory, it can be considered that China’s main research focus is on the skeleton. The safety of the skeleton is a prerequisite for carrying out prefabricated buildings. Leaving this premise and discussing prefabricated buildings is meaningless.

In countries with relatively mature development of prefabricated buildings, research hotspots seem to have already crossed the primary stage of structural safety, and entered the study of micro performance improvement and its laws of prefabricated components, energy consumption research of prefabricated buildings, waste discharge research, and full lifecycle perspective management research. That is to say, countries with advanced assembly technology have delved into research on the diversity, functionality, and sustainability of separable components. The wall system is the main component of separable components, so it is necessary to study the technology of prefabricated building walls.

The prefabricated building wall technology belongs to the application technology, and the improvement and development of this technology should be carried out through the cooperation and collaboration of multiple disciplines such as architectural design, structural design, equipment design, and interior design. SAR theory suggests that the structural discipline is responsible for providing a reliable skeleton and setting universal nodes on the skeleton for walls and other ancillary components to attach to it. Equipment pipelines and interior decoration are attached to structural or non structural building components. This is a connection pattern similar to having long branches on the trunk and leaves on the branches. The design of connection nodes between the skeleton and separable components, as well as between separable components, is crucial in this connection mode. These nodes must be safe, stable, durable, and universal within a certain range, and can be repeatedly installed and removed.

In today’s highly developed engineering technology, there are actually many ready-made technologies that can be used for reference and even integrated in the research on connecting nodes and connecting entities. Taking the wall system as an example, this article explains how to use the inspiration of existing technology to carry out research on prefabricated residential technology.

4 Research on Prefabricated Building Wall Technology Based on SAR Theory

4.1 Technical Research on Prefabricated Building Wall Support System

Based on the guidance of SAR theory, it seems easy to find similarities between the exterior wall system of prefabricated residential buildings and the building curtain wall system. Building curtain wall refers to the non load-bearing outer wall enclosure of a building, usually composed of panels (glass, metal, stone, ceramic, etc.) and supporting structures (aluminum columns, beams, steel structures, glass ribs, etc.) at the back. At present, this system technology is mature and stable, and there are many technical points that can be transplanted and referenced.

Fig. 1.
figure 1

Schematic diagram of vertical connection and external hanging of wall panels on the entire floor

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The supporting structure of the curtain wall system often uses aluminum alloy columns, beams, steel structures, glass ribs, etc. These load-bearing components serve as intermediate components to connect the current panel and the main structure of the building. The extensive use of aluminum alloys, steel structures, etc. is expensive and uneconomical, making it unsuitable for ordinary residential buildings with large quantities. Therefore, it is considered to directly use the main body of civil engineering structures such as floors, beams, and columns as the support body, so that the external wall panels can be vertically connected and hung externally throughout the entire floor, or horizontally connected and hung externally throughout the entire bay (As shown in Fig. 1.).

4.2 Research on the Technology of Prefabricated Building Exterior Wall Panels

There are several key technologies that need to be addressed when comparing curtain wall system technology with prefabricated exterior wall systems. The first is the performance of exterior wall materials. The second is the problem of prefabricated connection nodes, and the third is the design of the size, shape, and texture of prefabricated exterior walls. From the perspective of production, transportation, installation, and final effects, we hope that prefabricated exterior wall panels, like curtain wall panels, are lightweight and high-strength, insulated, processable, drillable, and sawable. Not only it is convenient to connect the main body, but the size of the exterior wall panel is moderate and the exterior facade effect is rich and varied. This type of wall panel can meet the requirements of standardized mass production, simplified transportation and storage, and has low difficulty in construction lifting and convenient installation. In case of non-standard dimensions, secondary processing can be carried out on the construction site.

How to obtain such excellent performance exterior wall materials is not only a material research issue, but also a design issue. This requires collaborative work between architectural design and material development researchers.

Firstly, prefabricated residential designers need to understand material technology, compare the advantages and disadvantages of current mainstream materials used for exterior walls of prefabricated residential buildings, and propose improvement suggestions for material performance requirements, so that material researchers’ research has directionality.

Secondly, the key technology to be solved is the design of connection nodes. Like traditional residential buildings, prefabricated houses are a giant rooted in the earth and must withstand various loads from nature and internal human activities. How to achieve safe and stable connection of fragmented factory components, and ensure that the thermal and sound insulation performance can meet the requirements after the connection is completed, is a highly refined technical issue. In the curtain wall system, metal parts such as bolts, slots, claws, and metal frames are used to fix the plates, and the joints between the plates are directly sealed with sealant. These technologies have some inspiration for the design of prefabricated residential wall panels. Therefore, when designing wall panels, it is necessary to split them reasonably and consider the appropriate connection design, which can utilize grooves and tenons, as well as embedded bolt fasteners and connectors. Overhang wall panels should be avoided, and windows should be placed within one wall panel as much as possible. The connection between the wall panel and the main structure should be flexible, and rigid connectors should not be set between the wall panels [7].

In addition, there are requirements for the size, shape, and texture of the exterior wall panels. The exterior wall panels can be pulled through in the direction of the floor height or fully opened in the direction of the bay based on the building’s floor height and bay size, as well as whether the building’s facade windows are horizontal or vertical. The dimensions in the other direction should be modular, standardized, and small-sized as much as possible.

In prefabricated construction sites, large lifting equipment and prefabricated components require a large amount of space, and multidimensional parallel lifting operations pose a severe challenge to the allocation of space resources on the construction site. It is easy to cause unreasonable allocation of spatial resources, which can lead to spatial conflicts during the lifting process of prefabricated components, reduce construction efficiency, and cause safety accidents [8]. Therefore, standardization of exterior wall dimensions and miniaturization can effectively solve production, transportation, construction and other problems. The specific dimensions can be determined based on the building’s own situation, or can refer to the commonly used dimensions of curtain wall panels.

The current mainstream materials used for prefabricated residential exterior walls include thin-walled concrete rock wool composite exterior panels, concrete polystyrene composite exterior panels, concrete expanded perlite composite exterior panels, aerated concrete exterior panels, etc. [9].

The UHPC unit concrete exterior wall panel system of Huajian Group integrates material technology and curtain wall technology of ultra-high performance concrete, coupled with refined design, to achieve integrated production of various peripheral protective structures and accessories such as doors, windows, sunshades, balconies, and the detailed design of dripping and water blocking of unit concrete exterior wall panels. This technology not only achieves multiple basic functional requirements such as wall insulation and drainage, but also enriches and diversifies the design of building spaces, completely breaking the rigid impression of prefabricated buildings. This technology perfectly integrates multiple mature technologies and endows it with superb design skills, which has a great inspiration for future prefabricated building wall technology (As shown in Fig. 2).

Fig. 2.
figure 2

UHPC unit concrete external wall panel system

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4.3 Research on the Diversity of Exterior Walls in Prefabricated Buildings

In addition, the exterior wall system not only has maintenance functions, but also plays a role in creating an exterior facade effect. The exterior facade of prefabricated residential buildings is constrained by technological level, and currently the exterior design is still slightly monotonous. Under the principles of standardization, systematization, and modularization, a large number of prefabricated residential facades currently use a single component, single line replication, and the facades are neat and uniform without any characteristics. In fact, the so-called standardization is not as simple as single element single line replication. Throughout the facade of curtain wall system buildings, there is a lively and rich rhythm that greatly enriches the appearance of the building. These building facades are designed and constructed under the guidance of standardization, systematization, and modularization. Standardized modules can create rich architectural facades through design ideas such as multi line replication and nonlinear replication. It can be said that diversified design ideas promote technological innovation, and the research and development of new technologies and materials also provide infinite possibilities for design.

5 Conclusion

SAR theory has been proposed for more than half a century, and over a period of over 70 years, it has provided strong theoretical support for the research of prefabricated building technology. Even today, the prefabricated building technology in many countries has been highly developed, SAR theory still maintains its progressiveness.

This article is a summary and reflection of the author’s research on relevant literature and years of experience in residential design engineering, based on SAR theory. It is hoped that it can serve as a reference for the development of prefabricated residential design technology in China.