Vol 20, No 4 (2024)

The objects of research are orthogonally intersecting cylindrical shells and the surrounding soil. A numerical stress analysis of the shells has been conducted the effect of taking into account the stages of construction has been evaluated. The analysis was performed in ANSYS Mechanical software. The joint of orthogonally intersecting cylindrical shells is located at a depth of 30 m from the ground surface. The dimensions of the soil body are selected from the condition of stress release and are adopted as 5 diameters of the larger shell to the left and to the right of it. The problem takes into account the physical and contact nonlinearities. Contact nonlinearity is associated with the interaction of the joint of the orthogonally intersecting cylindrical shells and the soil body in the process of deformation and as a result of shell element activation at calculation stages. The contact between the bodies is modelled using contact pairs. The cases of 8, 4, 2 and 1 stages of the construction of the T-connection were designed (in each case an additional stage (zeroth) was allocated for determining the initial state of the soil). The case without taking into account the construction stages was also considered. The results showed that the stage analysis leads to significant changes in the values of the von Mises stresses in the T-connection compared to the case without taking into account construction stages. The potential for further research is associated with the use of nonlinear materials for the shell and various alternatives for the contact interaction of the shell and the soil.

The aim of the study is to develop a methodology for calculating the strength of normal sections of flexural reinforced concrete elements, which suffered corrosion damage and were strengthened with external composite reinforcement. The objects of the study are reinforced concrete elements used in various structures that are exposed to aggressive chloride environment that causes corrosion of concrete and rebars. The research method is based on the use of a diachronic model of deformation of corrosion-damaged elements. This model takes into account changes in the mechanical characteristics of concrete and reinforcement during corrosion and includes equations based on analytical relationships for determining the initial load-bearing capacity of intact structures. An important aspect of the method is taking into account external polymer composite reinforcement, which allows to increase the flexural rigidity and strength characteristics of damaged elements. The Picard’s iterative method, which is designed for approximate solutions of differential equations, was used to ensure the accuracy of calculations. The results of the study showed that the proposed method allows to effectively assess the strength of normal sections of reinforced concrete elements subjected to corrosion. It was found that the methodology, which takes into account the changes in strength and deformation characteristics of materials, as well as the effect of aggressive chloride environment, ensures high accuracy and reliability of the analysis. The use of external polymer composite reinforcement significantly increases the stability and durability of structures. Thus, the developed methodology is an important tool for increasing operational reliability and extending the service life of reinforced concrete structures exposed to aggressive environments, which is a relevant problem in the construction industry.

An effective way of ensuring seismic resistance of buildings and structures is the use of active seismic protection systems - seismic isolation. One known type of seismic isolation is a sliding belt at foundation level. However, the application of this seismic protection system is limited by the lack of necessary design justifications and studies. The behavior of a cast-in-situ reinforced concrete building with different number of storeys (5, 9, 16 floors) with sliding belt seismic isolation at foundation level containing fluoroplastic plates and an elastic limiter of horizontal displacements is considered. The main focus of the study is the effect of the size of the gap between the elastic limiter and the side faces of the upper foundation on the efficiency of the sliding belt. The analysis was carried out using the direct dynamic method. Comparative graphs of relative displacements and the stress intensity distributions for each calculation case are obtained. It is revealed that proximity of the elastic limiter to the foundation increases the likelihood of collision and the emergence of dangerous vibrations that can lead to the failure of the structure. The optimally selected gap size will allow the sliding belt to operate effectively, limiting excessive horizontal displacements, and reduce seismic loads on the superstructure.

A brief review of crack path calculation methods using integral principles of mechanics is presented. In twodimensional setting, a crack is considered as a geodesic line on the surface of a body with a metric that depends on the initial stress state. The possibility of approximate determination of crack path on the basis of integral principles is illustrated on a number of problems. In particular, crack paths in a half-plane under uniformly distributed load applied on its edge are determined. The calculations include the stress state of the half-plane taken from the solution for a body without a crack. The fruitfulness of the representation of displacements of crack edges using the Winkler’s hypothesis is shown. To study the subcritical behavior of the crack, the concept of cracon, a quasi-particle simulating the motion of the crack tip, can be introduced. The problem of determining the crack path on the basis of integral principles of mechanics is insufficiently investigated and requires further research.

Vibration isolation systems play a major role in protecting buildings from seismic damage. Since they consist of elements with non-linear characteristics, the calculation models of the vibration isolation system require taking into account changes in the dynamic characteristics of the structure (stiffness or compliance matrix), frequencies and forms of natural vibrations. The study proposes an algorithm and dependencies which are based on the possibility of the disconnection or the destruction of the additional connections (elements with non-linear characteristics) due to certain seismic forces and displacement of structures under seismic impact. The results showed that the amplitude-frequency response, displacement, and shear force at the base of the structure decreased when additional connections were disconnected or destroyed. Thus, the proposed method, which takes into account the operation of vibration isolation systems with nonlinear connections, allows reducing the material, economic and human damage during seismic action. The obtained results of the example show that the dependences of the calculation algorithm developed in the work can be used in engineering practice when evaluating the dynamic behavior of a vibration-insulated building system (amplitude-frequency response) during vibrations under seismic influence.