Approaches to assessment of stability of reinforced concrete columns in case of horizontal emergency impact have been investigated. For this purpose, finite-element modeling of the system in spatial formulation, calculation according to the deformed scheme in the scope of nonlinear static analysis and dynamic transient process have been implemented. When constructing the model, the hexahedral elements were used, working in accordance with the Drucker-Prager model for concrete, and the rebars deformed according to the Prandtl model were used to modelling the reinforcement.

The impact action was considered as a short-term pulse of constant intensity. Dependence diagrams for critical force on various scenarios of emergency impacts on the column have been obtained. Results of researches can be used for an estimation of resistance to the progressive collapse of reinforced concrete structures at their variants design and optimization.

The article provides an overview of the existing methods of early loading of monolithic structures. It is shown that keeping concrete up to standard strength without taking into account the stages of loading leads to a significant increase in the cost of work, especially in winter. Based on experimental studies, formulas are proposed for calculating the required strength by the moment of loading of monolithic foundations, walls, columns, ceilings. Instructions are given on the design of early loading technology. The results of full-scale tests of floors under conditions of early loading are given. The technology of tiered heat treatment of monolithic structures is described.

Ribbed ceilings in reinforced concrete, and more recently in steel-reinforced concrete and wood-concrete versions, occupy a significant place in the total volume of buildings and structures. An analysis of the regulatory and technical literature shows that in domestic and foreign sources, empirical dependencies are proposed for assigning the effective width of a T-section flange, which does not lead to economical and reliable design solutions.

The purpose of the study is to determine the calculated effective width of a flange of a tee monolithic section or a composite section of a floor. Based on the analysis of the stress-strain state of a bent tee section, analytical ex-pressions are written and formulas are obtained for determining the design flange width.

An analysis of the calculation methods found in the normative literature on strengthening reinforced concrete structures with composite materials arranged in the transverse direction by the method of wrapping structures showed that there is no calculation method for the second group of limit states.

The Code of Rules 164.1325800.2014 does not consider options for strengthening flexible compressed reinforced concrete structures, with the arrangement of composite materials in the transverse direction, introducing restrictions to the dimensions of structures. However, our research suggests the opposite. In this paper, experimental values of deflections of reinforced concrete struts in the transverse direction by composite materials, characteristics and testing methods of prototypes are given. The results of the theoretical calculation of deflections are presented and, based on the comparison of experimental and theoretical values of deflections, an algorithm for calculating the second group of limit states was developed.

During the reconstruction, or upon expiration of the service life, as well as after external impact, reinforced concrete structures require examination and verification calculations. Existing diagrams of concrete deformation are focused on designing new structures and are not adapted to the concretes of the reconstructed structures.

Using the exponential model of concrete deformation makes it possible to describe the resistance of concrete during reconstruction, including after repeated cyclic loading.

A technique for creating an individual deformations model under cyclic load during the reconstruction is demonstrated on a specific example.

In the practice of modern construction, flexible centrally and eccentrically compressed reinforced concrete elements are becoming more common. In this regard, the relevance of studying their work and the mechanism of bearing capacity exhaustion increases. There are two directions in determining the bearing capacity of these elements: calculation for stability and calculation for strength. The loss of stability in a number of cases, obviously, can cause the destruction of not only centrally, but also eccentrically compressed rods with small eccentricities, since under certain conditions they can practically turn out to be close in their work. The stability of these eccentrically compressed rods is calculated by multiple integration. Such a calculation is especially laborious for reinforced concrete elements. This article is devoted to the study of the stability of centrally and eccentrically compressed reinforced concrete rods with small eccentricities, taking into account the creep of concrete. An eccentrically compressed rod with a small eccentricity of length l is replaced by a centrally compressed rod of length l0 so that the bending arrow includes the eccentricity. The numerical values of the rheological coefficients are determined from the boundary values of the reduced stiffness, which varies along the length of the rod. Complicated integration is replaced by the solution of the differential equation of the bent axis of the rod in the form of a sinusoid half-wave.

When performing structural calculations for dynamic loads including seismic impacts, the STARK ES software package allows to implement various damping models. In this paper, a comparative analysis of three types of the damping models used to increase the calculated seismic resistance of structures is carried out. These are the models of nonlinear viscous dampers, in which the reactive force depends non-linearly on the velocity of the rod movement, equivalent (for an energy dissipated) linear-viscous dampers and equivalent (for a maximum force and an energy dissipated) elastic – perfectly plastic elements. As an example, an analytical model of the structural system of a projected building on a site with a seismicity of more than 8th intensity level is used.

The paper considers the influence of various factors on the consumption of transverse reinforcement in the design of sections of linear bending reinforced concrete elements. The aim of the work is to determine the degree of influence of the pitch, diameter and class of transverse rods, as well as other factors, on the minimum consumption of clamps at various levels of loading of a linear bending element. The calculation and analytical method of research was used, based on the results of applying various diameters of transverse rods, reinforcement classes. The object of the study was a beam of rectangular cross section, in which the step of the clamps varied from the minimum to the maximum allowable standards, with a stepwise changing load. Research results. It has been established that the optimal longitudinal single reinforcement of the beam is achieved by applying a maximum force of 255 kN from the studied load range. When a concentrated force of less than 125 kN is applied to the beam, the transverse reinforcement is installed according to the design requirements. The most economical solution for reinforcing a beam with transverse bars is achieved with class A240 and a step of 0.235 m and 0.140 m, with an overrun of 0% and 6.9%, respectively. The use of transverse bars made of A500C class reinforcement, with the accepted beam parameters of 0.3×0.5 m, with single reinforcement, with the application of a force of 255 kN, is not advisable, since the assortment of reinforcing steels does not provide for diameters less than 10 mm. The dependencies and the levels of influence of the use of different pitches, diameters and classes of transverse rods, with a stepwise changing load, on the minimum consumption of transverse reinforcement in the design section of the beam are established. The presented work specifies the consumption of transverse reinforcement for its most economical use.