MECHANICAL PROPERTIES OF CONCRETE UNDER THEIR COMPLEX LOAD

Abstract

Complex loads, understood as cumulative phenomena arising from the collision of moving bodies, are very often encountered in engineering practice during construction and operation of both individual structures and entire buildings. In this case, complex loads can be taken into account in the design, for example, the design of foundations of forging hammers and pressure of roll presses, heads of driven piles, etc., and can also be associated with chance, for example, the accidental collision of some body (transport, ice, stones, etc.) with elements of structures or buildings. Simultaneously with the complex action (planned or accidental), the material of the structure perceives loads associated with changes in temperature and humidity conditions of operation. Repeated freezing and thawing, moisture saturation, operation at elevated temperatures lead to changes in material structure and cause reduction of service life. The combined effect of impulse, anthropogenic and environmental influences can lead to premature destruction of structures. The probability of this is based on the established phenomenon that under conditions of complex action the material fails at lower stresses compared to static loads. According to many experts, concrete is a roughly heterogeneous material with a polystructural structure. The objective structural parameters of such materials should be considered as technological cracks and residual deformations, which occur during the period of obtaining the material itself and its formation into structural forms during subsequent curing. The main cause of materials destruction under the action of complex and environmental impact is irreversible growth of technological cracks to fracture cracks or backbone cracks. In turn, the kinetics of transformation of technological cracks into operational cracks with their subsequent development depends to a large extent on the nature of the distribution of initial imperfections. The latter are determined by the initial composition and technological conditions of obtaining the material and products from it. Thus, revealing the mechanisms of formation of technological cracks in order to regulate the nature of their distribution at different structural levels to improve the durability of concrete under conditions of complex loading under the influence of the environment is a timely and relevant task. Especially it is necessary to emphasize the importance of studies of the influence of complex loads on the destruction of structures and facilities, taking into account significant disasters caused by earthquakes, explosions of technological and technical equipment, etc. In this connection, the solution of the problem of increasing the resistance of concrete against complex loads, taking into account the unfavorable effects of the environment, is justified and practically necessary.