Corrosion of reinforcement leads not only to a reduction in its cross-sectional area but, more importantly, to a disruption of the bond between steel and concrete. Corrosion products (rust) are larger in volume than the original metal, creating internal stress, cracking of the protective layer, and, consequently, a loss of mechanical adhesion. Existing regulatory documents reduce corrosion to a simple reduction in the cross-sectional area of the reinforcement. However, research shows that adhesion loss occurs significantly earlier and progresses more rapidly than metal loss.

Due to the restoration of architectural monuments and religious buildings, as well as in connection with the construction of such facilities as Orthodox churches, the study of arches and vaults operation becomes especially important nowadays. Over the last decades the practice of calculation and engineering of building structures has included the use of universal PC software, that made it possible to significantly improve the calculation models, bringing their functioning as close as possible to the operation of the actual structure. One of the most common types of vaults is the domical vault consisting of two intersecting cylinders with the same elevation and resting on four sides. The calculation scheme of a domical vault may be considered in general as a system of elementary semi-arches, forming troughs and transferring the strut to the conditional diagonal ribs of the vault if there is a central light drum and the support ring thereof. The calculation of the considered structures in a nonlinear formulation significantly affects their stress-strain state. The values of deflections are found to have significant differences in linear and nonlinear formulations. Calculations of masonry vaults under consideration (especially those with large elevation heights) are recommended to be made with consideration of physical and geometrical nonlinearities.

Under seismic impacts, plastic deformations develop in reinforced concrete structures of frame buildings. Their influence on the strength and deformability of the buildings under seismic effects has not been studied enough and is practically not taken into account in the current Russian standards for seismic resistant construction. Experimental studies of the effect of plastic deformations on the behavior of bent elements under alternating effects of high intensity have been carried out. They showed that after the start of yield in the tensile reinforcement, the opened cracks do not close during unloading. This leads to the formation of through cracks under the action of the bending moment of the opposite sign. To evaluate the effect of the longitudinal compressive force on this process, calculations were carried out by the engineering method. The results of calculations have shown that excessive plastic deformations of eccentrically compressed reinforced concrete elements under seismic impact even at the stage of increasing bending moment can lead to the destruction of the concrete of the compressed zone. In addition, it was revealed that the presence of compressive force leads to the closure of cracks during unloading even after the beginning of the yield in tensile reinforcement. It was concluded that it is necessary to limit the plastic deformations of reinforcement when calculating rein-forced concrete eccentrically compressed and bent elements under seismic impacts.

The Proster®21 permanent formwork system represents a technical solution that goes beyond the traditional concept of formwork systems. Unlike removable formwork, its role is not limited to shaping the geometry of the element, but becomes an integral part of its load-bearing structure, which alters the stress-strain state of concrete under load. However, the absence of approved calculation methods that account for this effect hinders its widespread adoption in design practice. In this study, an experimental comparison was conducted between two centrally loaded square columns made of B25 concrete with a cone slump of P2 and identical reinforcement. One column was constructed using traditional removable formwork, while the other was constructed using the Proster®21 permanent formwork system. Tests showed that the use of the Proster®21 system provides a 14.0 % increase in load-bearing capacity without changing the cross-sectional geometry or reinforcement. Based on the analysis of deformation characteristics and failure modes, it was found that this type of formwork also had a notable effect on the failure mechanism and altered the stress distribution in compressed elements, confirming its structural role in the performance of the column under load.

Reinforced concrete is widely used in engineering structures, transportation construction, power generation, and hydraulic engineering. All of these buildings and structures are subject to repeated loads (RL). When designing reinforced concrete structures (RCS) for these buildings, there are certain issues that have remained unresolved for decades, which therefore reduce the effectiveness of modern RC systems. This issue is ensuring the durability of RC structures. This article presents the scientific foundations of fatigue theory, new methods, and techniques for calculating the fatigue strength of RC structures.