Total-Prefabricated Construction

a generalized designation for modern, highly improved methods of constructing buildings and structures from large sectional units and components prefabricated in the factories of the construction industry.

In total-prefabricated construction, the erection of buildings or structures becomes basically a mechanized process of assembly and installation. This process utilizes completed and standardized structural components: large blocks or panels, modular construction units, and other integrated structures. As a result, labor requirements, costs, and construction time are reduced and the quality of construction is improved.

During the mid-1950’s the USSR became the first country in the world to organize total-prefabricated construction on a large scale. These building methods became especially widespread in the construction of residences and public works after the adoption of two administrative measures. The first was the 1954 resolution of the Central Committee of the CPSU and the Council of Ministers of the USSR On the Development of the Manufacture of Prefabricated Reinforced-concrete Structures and Components for Construction; the second was the 1959 resolution of the USSR Council of Ministers On the Development of Prefabricated Housing Construction. These resolutions led to the establishment of a wide network of highly mechanized enterprises serving the construction industry and determined the trends for further industrialization and technological advance in the construction industry. The Twenty-fourth Congress of the CPSU issued Directives of the Ninth Five-year Plan for Developing the Economy of the USSR that emphasized the necessity of increasing total-prefabricated construction. Total-prefabricated construction in state and cooperative residential construction accounted for 29.5 percent in 1965 and 37.2 percent in 1970 and according to plan will exceed 50 percent in 1975. In many cities of the USSR total-prefabricated construction accounted for 80 to 90 percent of all new housing (1974). The volume of total-prefabricated construction is also growing rapidly in industrial and agricultural construction.

The economic efficiency of total-prefabricated construction depends on such factors as quality and quantity of local materials and technical facilities, available transportation, and distances to be covered. Efficiency is determined by three interrelated technical and economic indexes: the unit weight of the component, the degree of enlargement of the prefabricated components to be assembled, and the degree of their prefabrication.

The unit weight of structures (weight related to the area or volume of the structure) defines the outlay of basic materials. As a rule, this outlay is much smaller for total-prefabricated buildings than for conventional buildings constructed on the building site. For example, the outlay for houses assembled from precast panels is about half that for conventional brick houses. The lower weight and the consequent reduced materials consumption substantially cut the construction cost.

The degree of enlargement of prefabricated components is the mean number of components per unit of area or per unit of volume of the building or structure. It varies widely, depending on the type of building, the method of construction, and the materials utilized. In residential total-prefabricated construction using concrete and reinforced-concrete components, the degree of enlargement per 1 m² of living space is, for above-ground structures, 1.4-1.7 components per m² for prefabricated unit construction systems, 0.7-1.0 components per m² for precast panel systems, and 0.06–0.10 components per m² for single-room modular-unit construction systems. As the degree of enlargement of the components increases, that is, as the index of the degree of enlargement decreases, construction proceeds more rapidly, the construction period is shortened, and labor requirements are reduced.

The degree of prefabrication of components and of the structure as a whole is defined as the relation of labor expended at the factory for prefabricating units to the total expenditure of labor at the factory and on the construction site. The higher the percentage of factory expenditures, the greater the saving that may be achieved by utilizing total-prefabricated construction. The degree of prefabrication for modern total-prefabricated housing is 30-35 percent for prefabricated unit systems, 40–60 percent for precast panel systems, and a projected 70-85 percent for modular-unit construction systems.

In residential structures and public works with a honeycomb plan and relatively small room areas, such prefabricated building components as panels and units are generally of single-room size, and occasionally of two-room size. Components with such dimensions do not exceed transportation clearances and may be transported on panel carriers or freight platforms and mounted in the building directly from their carrier with the aid of mobile tower cranes.

Prefabricated components whose dimensions make them convenient to manufacture and transport are also used in industrial and other large-span buildings with widely spaced vertical supports. Such components, which include trusses, girders, beams, flooring, and panels, are assembled to form the roof and other parts of the building. In erecting such structures, the components are often preassembled on the ground. With this method, prefabricated structures and items brought from factories to the construction site are assembled at a specially equipped area into units, or such structural parts as certain sections of roofs or walls; such sections may be of a considerable length. The assembled components are then hoisted by a crane and installed in position according to plan.

The areas of sections erected in this way may reach several hundreds of m²; the dimensions depend on the method of erection, the design of the building, and the capacity of the hoisting equipment. When construction takes place in newly settled regions where access to the site is difficult, as in the Far North, structural components are often delivered to the site by air. Under these conditions, it is better to preassemble units at the factory that manufactures the prefabricated parts.