Structural Physics

(Russian, stroitel’ naia fizika), the aggregate of the branches of applied physics that study the physical phenomena and processes associated with the construction and use of buildings and structures and develop appropriate structural design methods.

Among the most important and best developed branches of structural physics are construction heat engineering, construction acoustics, and construction illumination engineering. These disciplines study the laws governing heat transfer and the transmission of sound and light—that is, the phenomena that are directly perceived by the human sense organs and that determine the healthfulness of a person’s surroundings—in order to provide within buildings the necessary temperature, humidity, acoustic, and lighting conditions. Other branches of structural physics that are undergoing development include the theory of durability of structural members and building materials, structural climatology, and the aerodynamics of structures. The special branch of applied physics known as structural mechanics deals with problems of the strength, rigidity, and stability of buildings and structures.

The following are used in solving problems in structural physics: theoretical calculations based on established general laws, simulation methods by means of which processes under study are reproduced in a changed scale or on the basis of known similarities, laboratory tests of structural elements (for example, in climatic chambers), and observations and measurements of actual structures. Theoretical and experimental data from modern physics and physical chemistry are used in the development of structural physics.

The findings of structural physics are used to design structures efficiently, so that they satisfy the required service conditions throughout their specified lifetimes. The analysis and testing methods developed in structural physics make it possible to evaluate the quality of construction both during the design stage and after the buildings or structures have been erected.

The emergence of structural physics as a distinct field of study took place in the early 20th century. Previously, the problems of structural physics had usually been dealt with by engineers and architects on the basis of practical experience. In the USSR, the first research laboratories for structural physics were set up in the late 1920’s and early 1930’s at the State Institute of Structures and the Central Scientific Research Institute of Industrial Structures. Subsequently, the most important research in the principal branches of structural physics was carried out at the Institute of Structural Engineering, which is now the Institute of Structural Physics. Structural physics has undergone particularly intensive development because of the greatly increased use in various types of buildings of lightweight industrial structural elements and new materials that require preliminary evaluation of their properties. Soviet scientists have been responsible for a number of advances. O. E. Vlasov was the first to develop a theory of the heat resistance of the enclosing members of buildings. K. F. Fokin set forth methods for computing moisture conditions in structures. Soviet scientists have also developed methods of computing the permeability of structures to air and have carried out a number of other fundamental investigations on major problems of structural physics that are of great importance for modern construction.

The increased use of prefabricated construction has made it necessary to carry out comprehensive research on the durability of structural members and building materials. Because of irregular and variable-direction heat-exchange processes that occur in structures and, to a much greater degree, the phenomena of displacement and of the freezing of moisture, the structural and mechanical properties of materials gradually change. This change is reflected in the materials through swelling, shrinkage, the development of microcracks, and gradual irreversible failure. The principal causes of the gradual deterioration of the strength of structures are (1) the thermal stresses associated with unsteady heat exchange, (2) phase transitions, and (3) the three-dimensional stressed state of the materials (when the moisture distribution is nonuniform). The third cause is of particular importance. These three factors govern, to a considerable degree, the durability of structures. Excessive moisture in materials and structures accelerates their deterioration owing to cold weather, corrosion, and biological processes (seeFROST RESISTANCE and WET STRENGTH).

The necessary foundation for the creation of new materials having specified properties and for the development of the theory of durability is provided by the methods of analysis of structural physics and the basic principles of physicochemical mechanics, which studies the effect of physicochemical processes on the deformations of bodies. The theory of durability is of particular importance in view of the large-scale use of new materials and lightweight industrial structural elements that have not yet stood the test of many years of service. The structural and mechanical properties of building materials, such as concrete and bricks, depend on the heat- and moisture-transfer processes in baking, drying, and moist steam treatment. By varying the manufacturing conditions in accordance with the laws governing heat and mass transfer, the quality of building materials can be substantially improved. Thus, the methods of analysis of structural physics provide a scientific basis for improving manufacturing processes for construction materials and products.

To develop practical methods of calculating the long-term resistance of structural members to the destructive physicochemical effects of the air inside and outside buildings, the laws governing the variation of the “microclimate” of rooms and the variation of external climatic conditions must be investigated. The external effects of climate on buildings and their structural members are studied by the separate branch of structural physics called structural climatology, which is developing on the basis of advances in atmospheric physics and general climatology. In most cases, the effects of climate are complex; for example, the joint action of temperature and wind or of precipitation and wind must be considered. The intensive development of structural climatology is being furthered by the increase in construction under a variety of climatic conditions.

The aerodynamics of structures is a separate branch of structural physics. It investigates the effects on buildings and structures of wind and other air motions that occur in the presence of temperature and pressure differences. The distribution of aerodynamic pressures on external surfaces should be taken into account in planning natural and artificial (mechanical) ventilation, in preventing local accumulations of snow (for example, on the roofs of buildings), and in determining wind loads on buildings and structures. The climatic conditions in rooms depend on the location of the rooms in the building and the aerodynamic characteristics of the building, since the temperature and humidity distribution in rooms is associated with the conditions of natural interchange of air. By studying the aerodynamic characteristics of structures having various contours and volumes, good service qualities can be provided for industrial and public buildings, and efficient types of urban housing can be found for various climatic conditions.

The prospects for further development in structural physics depend on the use of new research equipment and methods. Thus, the structural and mechanical characteristics of materials and the moisture conditions of materials in structures are studied with, for example, ultrasound, laser radiation, gamma rays, and radioactive isotopes. Semiconductor devices are finding application in the development of efficient heating and air-conditioning facilities and in the development of enclosing structures having low heat losses. To investigate the temperature distribution over structural surfaces, in room atmospheres, and in air flows, simulation and thermographic methods are being used. This approach is based on the laws governing light interference in a medium under different thermal conditions.