"Вестник МГСУ"

The proposed calculation method is specific in terms of determining the carrying capacity of eccentrically compressed concrete elements, in contrast to the calculation by error method, as in the existing regulations, where in the result of the calculation is not known what is the limit load the eccentric compression element can withstand. The proposed calculation method, the publication of which is expected in the next issue of the "Vestnik MGSU" the above mentioned shortcomings of the existing calculation methods, as well as the shortcomings listed in this article are eliminated, which results in the higher convergence of theoretical and experimental results of eccentrically compressed concrete elements strength and hence a high reliability of their operation.

At the present time the nonlinear deformation model based on deformation diagrams of the materials is believed to be the most promising for estimation of stress-strain state of reinforced concrete elements at different stages of their compression: before crack formation, in the process of crack formation, at the stage of cracked element operation, at destruction stage. Reliability of estimates depends largely on accuracy of analytical description of curvilinear diagram of concrete deformation. On the other hand we should remember that the calculated construction may be subject to different loading modes: short-term, long-term or competitive. In this regard the universal character is required from the used deformability diagrams. They should be easily transformed for calculation with different modes.The authors suggest methods of constructing such a deformation diagram using elasticity coefficient. Using the corresponding elasticity coefficients in calculations it is possible to account for different loading modes of structures (for example long-term loading). Such an analytical representation of concrete deformation diagram is more generalpurpose as compared to dependence on European standards.

In the article the dependences of concrete compression strength from fluidity of concrete and water cementitious ratio for non-modified and modified concrete with superplasticizing and organo-mineral admixtures are cited and analyzed. The problems of application efficiency assessment of concrete and reinforcing steel of high classes of strength in reinforced concrete elements are examined. Calculating algorithms are presented with the use of an economic-mathematical method, which allow to improve calculation and designing of a monolithic reinforced concrete framework. Results of the researches are applied in the process of designing some objects in Ufa. The article presents design solutions using concrete and reinforcing steel of higher strength classes.The co-authors present the generalizing approach to the solution of the problems of optimized application of high-strength concrete and efficient armature classes in bendable ferroconcrete elements. The decision is made by the criteria of reducing reinforced concrete and concrete consumption.The methods of analysis offered and developed by the authors are widely used in the Republic of Bashkortostan and allow to reveal effective fields of application of the effective classes of concrete and reinforcement steel in reinforced concrete elements with evaluating expediency at the design stage and in order to estimate their efficiency. That is especially important in the process of choosing modified concrete and modern steel for building frame and monolithic structures.

Subject: the article is devoted to investigation of prestress losses and force distribution in the reinforcement of span reinforced concrete structures. As the long-term studies have shown, these quantities are very unstable, which should be taken into account in structures design. However, the existing normative documents take into account the possible deviations of losses and forces in prestressed reinforcement from their design values in a fairly general form. Since each of the types of losses, according to the formulas, depends on one or several random factors, they should be considered from a probabilistic point of view. Research objectives: determine the scattering of different losses and acting forces in the prestressed reinforcement to identify the factors affecting its value. Materials and methods: in this work, we used the normative technique of prestress losses calculation and characteristics of the variability of physical and mechanical properties of concrete and reinforcement, obtained from the previous studies. The distribution laws of investigated parameters were assumed to be normal (the Gaussian law). To calculate the coefficients of variation, the method of statistical testing (the Monte-Carlo method) and the linearization method (the Taylor series expansion) implemented in MATLAB software package were applied. Results: in the process of numerical experiment, the values of prestress losses and forces scatter in the reinforcement were obtained for all prestressing methods stipulated by the current design codes. It was established that both values depend significantly on the method of reinforcement tensioning, its type and class, and also on the diameter of wire. Moreover, many concomitant factors affect the variability of the above-mentioned characteristics such as the plant-manufacturer, stability of technological process, qualification of the service staff, etc. Conclusions: the obtained data is recommended to be used to determine the accurate values of strength, deformability and crack resistance of span reinforced concrete structures as well as in probabilistic calculations related to the assessment of their reliability by various limit states. In particular, the described technique was applied in calculating the reliability of bent prestressed elements from the viewpoint of strength of oblique sections.