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the supporting and enclosing elements of buildings and other structures.
The classification of building systems according to functional purpose into supporting and enclosing types is to a great extent arbitrary. Whereas arches, trusses, and frames are only supporting elements, wall and roofing panels, shells, vaults, and folded plate structures usually serve both enclosing and supporting functions, thereby corresponding to one of the most important trends in modern construction.
Supporting elements are said to be planar (for instance, beams, trusses, frames) or three-dimensional (shells, vaults, domes). Of the two types, three-dimensional supports typically have a better distribution of forces and, correspondingly, a lesser material outlay; however, their fabrication and erection in many cases are laborious. New types of three-dimensional constructions, such as structural systems with rolled cross sections and bolted joints, are notable for both economy and the comparative simplicity of fabrication and assembly. Depending on the material used, building systems are classified as concrete, reinforced concrete, steel, masonry, and wood.
Concrete and reinforced-concrete building systems are used most frequently, since they have a variety of applications. The use of industrially fabricated reinforced-concrete sectional systems is widespread in the construction of modern residential, public, and commercial buildings, as well as many engineering structures. Monolithic reinforced-concrete systems are particularly suitable for the construction of hydroengineering structures, road and airfield surfaces, tanks, towers, elevators, and the foundations of industrial equipment. Special types of concrete and reinforced concrete are used to build structures that function at high and low temperatures or under conditions with chemically aggressive media (heating plants, chemical plants, enterprises of the ferrous and nonferrous metallurgical industries). A reduction in the mass and the material outlay of reinforced-concrete systems is possible by using high-strength concrete and reinforcement, by increasing the use of prestressed structures, and by extending the areas of application for lightweight and cellular concretes.
Steel constructions are used mainly for the framework of buildings and other structures having great spans and for shops using heavy crane equipment. Blast furnaces, large-capacity tanks, bridges, and towers are generally made of steel. Reinforced concrete and steel may often be substituted for one another. The choice of the material in such cases is made by considering cost ratios and availability. An important advantage of steel structures over those made of reinforced concrete is their small mass. Thus, the use of steel is preferable in seismic regions, in the hard-to-reach areas of the Far North, in deserts, and in high-mountain regions. Increasing the amount of high-strength steels used along with those having economical rolled cross sections and designing efficient three-dimensional structures (including those made of thin sheet steel) substantially reduce the weight of buildings and other structures.
Masonry construction is primarily used for walls and partitions. Buildings made of brick, natural stone, or small blocks meet the requirements of industrial construction to a lesser degree than large-panel structures (seeLARGE-PANEL STRUCTURES). Consequently, their use is gradually decreasing. However, the use of high-strength brick, reinforced masonry, and composite constructions (masonry constructions strengthened with steel reinforcement or reinforced-concrete elements) makes it possible to increase substantially the supporting capability of buildings with masonry walls. By turning from hand-laid masonry to the use of factory-made brick and ceramic panels, the degree of industrialized construction is greatly increased and the labor required in construction is reduced.
The principal trend in modern wooden construction is the use of bonded-wood designs, whose advantages over other types of wood construction include the possibility of industrial fabrication of elements having the required dimensions. Supporting and enclosing bonded constructions are widely used in rural construction.
New types of industrial constructions have recently become popular; these include asbestos cement products and structural components, pneumatic systems, and systems made of lightweight alloys and plastics. Their chief advantages are their low specific mass and the possibility of factory production on mechanized production lines. Lightweight three-layer panels (with sheathings of profiled steel, aluminum, and asbestos cement and with plastic heat insulators) are now being used as enclosing constructions in place of heavy reinforced-concrete and keramzit-comrete panels (seeKERAMZIT).
From the standpoint of service requirements, building systems should perform their function and should be fire and corrosion resistant. Their maintenance must be safe, convenient, and economical. The quantities and rates of large-scale construction impose certain requirements on building systems, for example, industrialization of fabrication (under factory conditions), economy (both with regard to the cost and material outlay), ease of transport, and speed of assembly. Reducing the labor requirements is particularly important, both during fabrication and erection. One of the major goals of modern construction is the reduction of mass by the general use of lightweight, efficient materials and the improvement of construction designs.
The design of building systems must take into consideration strength, stability, and flexibility. It is also necessary to take account of the stress to which each element is subjected while in service (external loads and its own weight), the influence of temperature, shrinkage, the shifting of supports, and the forces that occur during transport and assembly. The principal method of design in the USSR is the method of limit states, whose mandatory use was decreed by the State Committee on Construction of the USSR on Jan. 1,1955. Before this date building systems were designed, according to the materials used, for permissible stresses (metal and wood) or for maximum stresses (concrete, reinforced concrete, masonry, and reinforced masonry). The principal flaw of these methods is the use of a single safety factor for all the effective loads, which does not permit proper evaluation of the amount of variability of the different types of loads (constant, temporary, snow, wind) and the maximum carrying capability. In addition, design based on permissible stresses does not take into account the plastic phase of the strength of construction materials, thus leading to unjustifiable material expenditures.
When designing any structure, building systems and materials that optimally suit the specific construction and service conditions are selected. Due regard is given to the necessity of using local materials and saving on transportation expenditures. When designing large structures, standard building constructions and modular structural plans are most commonly used.
REFERENCESBaikov, V. N., S. G. Strongin, and D. I. Ermolova. Stroitel’nye konstruktsii. Moscow, 1970.
Stroitel’nye normy ipravila, part 2, sec. A, ch. 10.
Stroitel’nye konstruktsii i osnovaniia. Moscow, 1972.
Stroitel’nye konstruktsii, 2nd ed. Edited by A. M. Ovechkin and R. L. Mailian. Moscow, 1974.
G. SH. PODOLSKII