Structural Mechanics of Engineering Constructions and Buildings

The issue of ensuring the mechanical safety of load-bearing structures in buildings and facilities is currently of particular relevance. One critical aspect of this problem is the strength of compressed and compressed-bent elements under transverse impact loading. Several failure mechanisms can occur in reinforced concrete (RC) columns. This paper develops an analytical methodology for determining the ultimate load capacity of square cross-section elements under horizontal impact, specifically for the failure mode associated with diagonal shear. Such scenarios are possible in cases of vehicle collision with a column or impacts near the support zone of the structure. The analytical model is based on static equilibrium equations, which incorporate the ultimate mechanical characteristics of the materials, accounting for dynamic strengthening effects. The concrete deformation model considers the confining effect in the direction perpendicular to compression, which enhances the concrete’s calculated resistance but induces additional stresses in the transverse reinforcement. A numerical example of the calculation for a building’s RC column is provided, yielding specific numerical results. A comparison is made between the outcomes of the proposed methodology and those obtained from a detailed numerical simulation performed using a verified solid finite element model. The limitations of the proposed analytical method are identified, and its sufficiently high accuracy and efficiency are demonstrated. Finally, prospects for further development are outlined, and recommendations for the practical application of the method to ensure the mechanical safety of reinforced concrete columns are provided.

The effect of asymmetric load on the deformation of the frame and on the stress state of the main elements of the ribbed-ring dome was studied. The aspects of the dome frame resistance under asymmetric load compared with a symmetrical one with increase in the distance between the columns supporting the dome were investigated. At the same time, the relationship between the stress-strain state of the dome frame and the type of nodal connections of its elements was also established. A metal ribbed-ring dome made of steel pipes was considered as the object of the study. The dome had four different support arrangements, characterized by the fact that the columns were not located under each rib, but cyclically symmetrical along the contour. For each support scheme in the dome, the types of nodal connections of the frame elements to each other varied. There were five different connection type combinations. The research was carried out by calculating different frame systems as computer models. There were twenty computer models studied in total. During the calculations, strain and stress in the main elements of each dome model were determined. Data on the stress-strain state of all models under asymmetric and symmetrical loads were obtained, which were compared with each other. Comparative diagrams of the relationships the dome deformations and stress in its main elements and asymmetric and symmetrical loads for all the considered models have been compiled. The diagrams showed a significant influence of the asymmetric load on the deformation of the dome and the stress state of the elements of the ribbed-ring dome for all support arrangements and types of nodal connections. It is noted that with an asymmetric load, the greatest increase in stresses compared to a symmetrical one occurs in the meridional ribs and a significant increase - in the upper ring of the dome. The greatest increase in deformations and stress occurs with hinged nodal connections and depends on the support arrangement of the dome frame.

Industrial building structures operate under severe conditions. An apt example of such structures are fan cooling towers, which resist significant vibration loads caused by a running fan; at the same time, the internal surfaces of the structures are exposed to relatively high temperatures from contact with cooled water, and the external surfaces are constantly exposed to the environment. The well-known approach to structural diagnostics does not take into account changes in the integral mechanical properties of thin-walled structural elements and the formation of local depressions and holes. Using the example of a large-sized fan cooling tower, an approach to diagnostics of structures affected by vibration from a running fan and the temperature of the cooled water, as well as the environment, is described. The effect of vibration and temperature on the process of corrosion wear of thin-walled structural elements has been studied experimentally and theoretically. Based on a new version of the finite element method developed for calculating structures in a cylindrical coordinate system, the initial and current state of the metal part of the fan cooling tower is investigated, taking into account plastic deformations. When analyzing the current state, corrosion defects and changes in the stiffness properties of thin-walled elements caused during operation as a result of the combined effects of vibration and relatively high temperatures were taken into account. It has been established that the presence of vibration and elevated ambient temperature contribute to accelerated corrosion; at the same time, the effect increases with increasing temperature and time of exposure to vibration. Corrosion wear leads to a significant increase in stresses and the formation of plastic deformations, which leads to a redistribution of stresses. It is noted that the discovered effects must be taken into account in the design and service of metal structures that experience significant vibration loads and operate at high temperatures.

Many numerical methods of analysis of rigid shells, such as the displacement-based finite element method (FEM), finite difference energy method, method of separation of variables, kinematic method of the theory of limit equilibrium, and so on, were proposed and tested until 2000. Most problems of static and dynamic analysis of canonical shells were successfully solved at the same time. All these methods were used actively after the 2000, too. However, new problems began to appear before structural engineers, architects, and builders. These problems are associated with multi-layer shell walls, with the emergence of new composite construction materials, and therefore, with the solution of physically nonlinear problems. Geometricians presented several hundred new forms of middle surfaces of shells, and that is why the need to select optimal forms from several alternatives using criteria of optimality came into existence. The selection of necessary computing software from many of their types began to be a problem. New problems demanded new methods of approach for their solution. In this paper, a critical evaluation of proposed solutions on strength, stability, and vibration analysis of shells was conducted in connection with new problems that appeared after the year 2000. Rigid shells in the form of analytical surfaces, designed using the canon of parametric architecture, were taken as an example. Analytical middle surfaces of shells, which attracted the attention of architects after 2000, are pointed out, and suitable methods of analysis of these shells are noted for the first time. The review was compiled based on 112 fundamental scientific works published after 2000. Other scientific reviews devoted to the investigation of joint problems of geometry, application, and calculation of assembled rigid thin-walled shells with analytical middle surfaces were not found.

The environmental impact of using different building materials to make sustainable concrete is important. The use of nanotechnology in industry has become increasingly important since sustainable development was established as a necessity to protect the environment and the interests of future generations. However, cracking is still a big problem, causing structural deterioration and shorter service life. Novel approaches to self-healing concrete have been made possible by recent developments in nanotechnology and biotechnology, which have improved the material’s endurance and mechanical qualities. This study investigates the use of microbial agents, namely alkali-resistant bacteria like Bacillus, and nanomaterials, including carbon nanotubes and nano-silica, to create self-repairing concrete. While microorganisms incorporated in porous expanded clay (LECA) create calcium carbonate to seal cracks on their own, nanomaterials enhance the strength, impermeability, and resistance of concrete to external conditions. In addition, technologies like as shape-memory alloys, hollow fibers, and microencapsulation are being researched for crack repair. Additionally, by comprehending self-healing nano-concrete’s remarkable mechanical qualities and durability performance, environmental effects and retrofitting expenses related to structures can be reduced. According to experimental findings, bacterial self-healing concrete closes all cracks in two months, but conventional concrete only closes 33% of them. These technologies promise a fundamental change toward sustainable, long-lasting, and intelligent infrastructure, despite obstacles including high costs, nanoparticle dispersion, and long-term viability. Future studies seek to refine these techniques for widespread use while maintaining environmental safety and economic viability.

The purpose of the study is to develop an integral criterion for choosing an aluminum alloy for tank construction at low temperatures. In the course of the work, experimental studies of four aluminum alloys 1915T, 6082-T6, AD35T1, 1565ch were carried out in accordance with Russian standards. Standard mathematical statistics algorithms were used to process the test results: calculating sample characteristics, checking samples for the normality of the distribution, and eliminating gross measurement errors. Groups of characteristics that affect the effectiveness of the alloy are identified: standard mechanical properties, impact strength, crack resistance characteristics, fatigue characteristics, corrosion resistance, cost and weight characteristics. The expert surveys conducted during the study allowed to determine the weighting coefficients both within the groups and when forming the integral criterion. It is shown that fatigue characteristics and crack resistance characteristics have the greatest weight, which indicates the need to include the calculation of fatigue and crack resistance parameters in regulatory documents for the design of aluminum alloy tanks. The importance of increasing the fatigue characteristics and crack resistance of aluminum alloys for use in Arctic conditions should be taken into account when designing new alloys and thermal treatments of existing ones. Of the alloys considered in the study, alloy 1915T has the best integral index. This alloy has significantly higher fatigue characteristics and impact strength compared to the other alloys studied. The AD35T1 alloy has the worst integral index, which indirectly confirms the advantages of natural aging of aluminum alloys. Alloy 1565ch has the best cost and weight characteristics. Further research suggests expanding the indicators included in the proposed integral criterion by introducing weldability indicators.