The prefabricated concrete building was of interest in the early 20th century and was finally realized in the 1960s. Countries such as England, France, and the Soviet Union made the first attempts. Because of the speed of construction and the low production cost of prefabricated concrete buildings, they quickly spread worldwide. The early prefabricated concrete buildings were rather dull and looked the same. Later, design improvements were made to increase flexibility and diversity, making it possible to build prefabricated concrete buildings not only in batches but also in a variety of styles.
This article will introduce 5 prefabricated concrete buildings.
Block for prefabricated concrete building
The prefabricated building with prefabricated block materials built into the wall is suitable for building 3 to 5 stories. The number of stories can be increased if the strength of the blocks is increased or if steel reinforcement is deployed. Block building is highly adaptable, simple production process, easy construction, and low cost. Building blocks are small, medium, and large. Small blocks are suitable for manual handling and masonry, less industrialized, flexible and convenient, and more widely used. Medium-sized blocks can be lifted by small machines, which can save masonry labor. Large blocks are now replaced by prefabricated large panels.
There are two types of blocks, solid and hollow. Solid blocks are made of lightweight materials. The joints of the blocks are important to ensure the strength of the masonry and are generally built with cement mortar. Small blocks can also be used to socket without mortar dry masonry method, which can reduce the wet work in construction. Some block surfaces are treated to make fair-faced concrete walls.
Panel for prefabricated concrete building
Panel building is fabricated from prefabricated large interior and exterior wall panels, floor and roof panels, and other panels assembled, also known as large panel building. It is the main type of prefabricated building in industrialized system construction. Panel building can reduce the weight of the structure, improve labor productivity, and expand the usable area and earthquake resistance of the building.
The interior wall panels of panel buildings are mostly solid or hollow panels of reinforced concrete. The exterior wall panels are mostly reinforced concrete composite panels with insulation layers. It can also be made of light aggregate concrete, foam concrete, or macroporous concrete with external finish wall panels. The equipment in the building often uses centralized interior plumbing fittings or boxed bathrooms, etc., to improve fabrication.
The key issue of large slab construction is the node design. The structure should ensure the integrity of the connection of the components (the main connection methods between the panels are welding, bolting, and post-cast concrete integral connection). In the waterproof construction, the waterproofing of the joints of exterior wall panels and the thermal treatment of floor joints and corners should be properly solved.
The main disadvantage of large-slab construction is that it has a greater restriction on the building’s shape and layout. The internal separation of small openings in transverse load-bearing large-slab buildings lacks flexibility (the internal separation of longitudinal wall type, internal column type, and large-span floor type can be flexible).
Box for prefabricated concrete building
Box building is a prefabricated building developed from panel building. This kind of building is highly factorized and installed quickly on-site. The structural part of the box is usually completed in the factory, and the interior decoration and equipment are also installed. Even furniture and carpets can be installed altogether. The box is ready for use after it is lifted and connected to the piping.
There are four types of box building assemblies as follows.
Full box type
The building is made up entirely of overlapping load-bearing boxes.
Panel box type
Small openings such as kitchens, bathrooms, or stairwells are made into load-bearing boxes, and then the building is composed of wall panels and floor slabs, etc.
Core body box type
A load-bearing bathroom box is used as the core body and then surrounded by floor slabs, wall slabs, or skeletons to form a building.
Skeleton box type
A number of dwelling units or single-room boxes made of lightweight materials are supported on a load-bearing skeleton to form a building. There are also bathroom boxes made of lightweight materials, including equipment and plumbing, which are placed in buildings with other structural forms. The box building is highly industrialized. However, the development is limited by the large investment, inconvenient transportation, and the need for heavy lifting equipment.
Skeleton panel for prefabricated concrete building
It consists of prefabricated skeletons and panels. The load-bearing structure generally has two forms. One is a load-bearing frame composed of columns and beams. Then rests the frame structure system of floor slab and non-load-bearing internal and external wall panels. The other is a load-bearing slab-column structure system composed of columns and floor slabs, with non-load-bearing interior and exterior wall panels. The load-bearing skeleton is usually mostly a heavily reinforced concrete structure. Steel and wood are also used for the skeleton and panel combination. It is often used in the light assembly building. Skeleton panel construction is structurally sound and can reduce the self-weight of the building. The internal separation is flexible and suitable for multi-story and high-rise buildings.
There are two types of skeleton panel buildings with reinforced concrete frame structure systems: fully assembled and assembled monolithic with prefabricated and cast-in-place combinations. The key to ensuring that the structure of such buildings has sufficient stiffness and integrity is the member connection. The nodal connections between columns and foundations, columns and beams, beams and girders, beams and slabs, etc., should be designed and selected by calculation according to the needs of the structure and construction conditions. Node connection methods, common are mortise and tenon joint method, welding method, bull leg resting method, and stay reinforcement cast-in-place into the whole of the stack law.
The skeleton of the plate and column structural system is a square or nearly square prefabricated floor slab with a prefabricated column combination of structural systems. Most of the floor slabs are supported by the four corners on the column, but also in the floor slab joints’ left groove, from the column pre-drilled hole through the reinforcement, tensioned after filling concrete.
Raised slab and raised floor for prefabricated concrete building
Raised slab construction is a type of slab and column structural system, but the construction method is different. This kind of building repeatedly pours each floor slab and roof slab on the bottom concrete floor, erects prefabricated reinforced concrete columns, uses the columns as guide rods, and uses the hydraulic jacks placed on the columns to lift the floor slab and roof slab to the design height and fix them.
Exterior walls can be brick walls, block walls, prefabricated exterior wall panels, lightweight combination wall panels or curtain walls, etc. It is also possible to lift sliding formwork and pour exterior walls while lifting the floor slab.
A large number of operations are carried out on the ground when lifting slab construction, reducing overhead work and vertical transportation, saving formwork and scaffolding, and reducing construction site area.
The slab construction mostly adopts a beamless floor slab or two-way dense rib floor slab, and the node connecting the floor slab and column often adopts a post-cast column cap or adopts a bearing pin, shear block, and other nodes without a column cap.
The general column distance is larger, the floor bearing capacity is also stronger, mostly used in shopping malls, warehouses, workshops, and multi-story garages, etc.
The building of an elevated building is a building where the internal and external prefabricated walls are installed first when the floor slab of each floor of the elevated building is still on the ground and lifted together. It can speed up the construction speed and is more suitable for the place where the site is restricted.