Materials Science Forum Vol. 968

Abstract: At the present time, it is necessary to strengthen the economy mode, the resources efficiency and reduce the material consumption in construction. Modern building constructions must meet all the requirements of economy, resource conservation, which are required for construction. The main direction of their development is reducing the cost of steel (14-16%), saving cement (10-12%) and saving forest materials (12-14%). These tasks can be solved, including at the expense of reduction of material content and reduction of the cross-section of structures, due to the rational combination of concrete and steel in their joint work and through the use of high-strength materials. These requirements are satisfied with building constructions from tube confined concrete. With a relatively small cross-section, such structures can withstand significant efforts, while the concrete at the expense of a volumetric stressed state receives stresses that far exceed the prism strength, which saves steel and concrete. Applying high-strength concrete, concrete, compacted by pressing, centrifugation, it is possible to obtain significant cement savings, as due to industrial technological factors of sealing concrete mix significantly increases the concrete strength. It is possible to increase the concrete strength also due to the use of indirect reinforcement, which allows, at low cost of steel, to significantly increase the strength of structures. Improving the well-known effective methods of strengthening concrete in relation to tube confined concrete constructions with strengthened cores suitable for industrialization is an urgent and important task. The purpose of the research presented in this paper was the experimental study of tube confined concrete elements with reinforced in different methods concrete cores; the development of methods for calculating the carrying capacity and the stress-strain state of tube confined concrete elements with strengthened cores.

Abstract: The paper studies the influence of various constructive factors on the parameters of design reliability and bearing capacity of span prestressed reinforced concrete structures. With the help of experimental design techniques and an effective software package, 12 adequate mathematical models have been developed and brought to the level of practical use. They allow to predict the reliability and bearing capacity of normal and oblique sections of specified structures for any combinations of concrete class, reinforcement class and reinforcement ratio. These models also allow to investigate both the direction of the change in bearing capacity and reliability index of prestressed reinforced concrete elements with the change of the above-mentioned factors, which is useful in solving some optimization problems at the design stage.

Abstract: The approach to calculating CFST elements is considered in which physical non-linearity of materials, geometric non-linearity of the tube and the effect of increasing the strength of the core are taken into account. Finite element models are developed and proposed as the basis for more accurate method of calculating concrete-filled steel elements consisting of differentiated profile tubes filled with reinforced concrete. The technique uses a step iteration algorithm involving analytical dependencies and finite element simulation. The criterion for determining the load bearing capacity of CFST elements was the achievement of the stresses in the tube of the characteristic strength. The possibility of estimating the load bearing capacity of elements by limiting stresses in the core concrete is also implemented. The result of the calculations was obtaining the stress-strain and limiting state of the differentiated profile tubes with CFST elements, and graphic analysis of the regularities of stress redistribution at different stages of performance of columns. In general, with the accepted problem statement we could establish the exact stress-strain state, take into account the elastic-plastic deformations of concrete, its cracking and destruction, and geometric nonlinearity of the tube. The effect of performance of the corrugated sheet as a tube was established.

Abstract: Calculations on the example of a steel column showed that with the combined effect of an explosion that causes deformation and subsequent fire, even without damaging the fire-retardant coat, there is a significant decrease in the fire resistance of the structure due to a decrease in the critical temperature. It is shown that, on the basis of the methodology proposed in this work, for hazardous operations industrial facilities, it is possible to predict the stability of steel columns in crash explosions followed by fire, as well as to recommend the values ​​of workloads and parameters of fire-retardant coats providing the necessary stability. It is also shown that when calculating the fire resistance limit of a steel structure with intumescent fire-retardant coat, it is necessary to take into account the proper heating time of steel structures until they lose strength.

Abstract: This work is about the influence of rotational component of earthquake excitation to the response of high steel slender frames. In most of studies seismic input is being represented by translational only component of ground accelerations while the rotational one is ignored. This was due to the luck of records which measure the rotational component. Nowadays, technology provides such an instruments and relative records can be found. Elastic design response spectra for rotational components are introduced in regulations. Furthermore, the rotational component was not taken into account since its influence in low structures is not significant. In this paper the results in response and in internal forces of rotational component to the slender steel frame is examined. Time history analysis of a ten-story steel frame with and without rotational excitation component is performed. From the numerical results it is shown that the impact of rotational component in response and the internal forces of the frame is significant and should not be ignored to the design of structures.

Abstract: It is presented the study of the beam samples reinforced with metal armature, BFRP armature and beams with hybrid reinforcement using metal and BFRP armature. Half of the tested samples of beams were manufactured on concrete with river sand, as a fine aggregate. The others were made on concrete with fractionated fine wastes of Mining and Beneficiary complex (MBC) instead of the river sand. The tests were carried out by static loading of the scheme of a single-run free beam loaded in the thirds of gear. It was established that the beams reinforced with BFRP armature and the beams with hybrid reinforcement showed an increase of strength, about 40%, compared with the beams reinforced with metal reinforcement. The deflections of the beams reinforced with BFRP armature were 315% -331% higher than the deflections of the beams reinforced with metal reinforcement and 165% -205% higher than it is allowed by standards. The use of hybrid reinforcement allowed reducing their deflections in two times compared to the beams reinforced with BFRP armature. At a load level of 60% of the destructive, the deflections of beams with hybrid reinforcement BFRP and metal armature did not exceed the maximum permissible norm. When concrete samples manufactured, the substitution of the river sand with fine fractionated wastes from the Mining and Beneficiary complex (MBC) did not affect their durability and deformability (the difference between the values according to these indicators is within the statistical error).

Abstract: The paper is dedicated to the analytical determination of stress and deformation parameters of reinforced anisotropic elements of round and annulus section, including columns, risers, supports, pipes, piles. The exact solution of stress-strain state equations for cross-sections of structures within initial data is performed on the basis of recurrence formula for integral of differential binominal.

Abstract: Problem of heat insulation and reliability of enclosing structures of buildings is the current issue nowadays due to strict requirements thereto. Protection of exterior walls of autoclaved aerated concrete blocks against negative impacts may be achieved by waterproof plastering combining decorative function either, i.e. decorative and protective system. Such system is possessing hydrophobic properties protecting against inflow of rainwater and condensate accumulating in the wall surface during seasonal periods. Application of decorative and protective “Baumit” system has been tested in heat efficient walls of autoclaved aerated concrete blocks in the Republic of Bashkortostan. It has been found that after several years of operating the protective system revealed no failures, and the wall has proved to be reliable as to heat protection, indoor conditions and interior surface of the walls.

Abstract: Deformations are actively involved in the structural organization of a construction at different levels of heterogeneities. Regulation of the development of deformation allows initiating structures with a given set of initial cracks and inner surfaces of partition. Integral damage of material determines the level of mechanical and deformative properties of products. It is possible to create certain conditions for manifestation of deformations by changing geometric parameters of the characteristic subsystem of the structural levels of a construction-system.

Abstract: The paper discusses the principles of precast concrete hollow-core slabs taking into account their spatial work. It is shown that consideration of spatial work makes it possible to determine the forces in individual floor slabs significantly more precise. The fact that strain redistribution between precast floor slabs depends on slabs’ bending and torsional stiffness is shown. The research has been mostly devoted to determination of the bending stiffness with regard to formation of cracks and the change in torsional stiffness, especially considering the presence of normal cracks, which is still unstudied. This paper presents the technique for determining the torsional stiffness of hollow-core slabs with normal cracks. In order to determine the components included in the resolving system of equations, it is proposed to use an approximation method based on the processing of numerical data using spatial finite elements.