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This article falls within vital question in quickly builds construction – theoretical method for calculating the slabs and columns of such buildings. Calculation research of buildings with reinforced concrete frame slabs is described in the article. The features of work the collapsible flat plate ceiling in composition of reinforced concrete framework of building are analyzed. Problems in the design of framework building are considered in order to increase its reliability. The suggestions for directions of perfection the calculation of flat plate frame construction elements are proposed in the article. The novelty of this work is to get new theoretical data about bearing capacity and deformability of structural system for the affordable housing construction from reinforced concrete.

The wide distribution of elements of reinforced concrete structures operating in biaxial bending conditions requires a comprehensive theoretical and experimental study of their work. At the present stage, in order to find out the real work of biaxially bended elements, it is necessary to determine all parameters that can affect the fracture pattern of such elements. Comparisons of the numerical modelling results of the work of biaxially bended elements with experimental data are not enough in the literature. Therefore, an important task is to carry out a numerical simulation of the work of biaxially bended reinforced concrete beams in order to compare its results with experimental data and to give recommendations on the possibility and advisability of such modelling for practical use. 15 samples of rectangular reinforced concrete beams made of heavyweight concrete were used for experimental and numerical studies. The experimental beams were tested for biaxial pure bending at various inclination angles of the external load plane. Carrying out numerical calculations by the finite element method using a PC made it possible to obtain graphs of the distribution of strains and stresses about the principal axes on the surface of the models, as well as in reinforcing bars, and their numerical values with an indication of the extrema. The position of the neutral axis and its change during the loading of sample models were experimentally and numerically studied. As a result of the study, it was determined that finite-element modelling of the work of biaxially bended beams allows to take into account the features of the exhaustion of their bearing capacity. The computational models of beams adopted during the simulation are adequate in the software package and correspond to real designs. The considered numerical model of reinforced concrete biaxially bended beam is quite simple and allows studying the stress-strain state at different percentages of reinforcement and at different inclination angles of external load plane.

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