Andrii Plugin

Purpose – to establish the effect of tunnel settlement on the opening of joints between segments and to substantiate a strengthening method that will prevent further settlement accompanied by joint opening to critical values. Methodology. The effect of tunnel settlement on the opening of joints between segments was determined by theoretical analysis of survey monitoring data. To determine the effect of ground loss beneath the tunnel and to substantiate a lining strengthening method that will prevent settlement, the stress-strain state of the tunnel and the surrounding soil mass was analysed by the finite element method (FEM) using the LIRA-SAPR software package. Findings. An equation was derived for estimating the joint opening width between the segments of a reinforced concrete segmental metro tunnel lining based on survey monitoring data. This equation makes it possible to assess the hazard of tunnel settlement caused by soil washout through opened joints. For the case considered, it was established that at a settlement of 25 mm the joint opening width reaches 0.6 mm. This exceeds the particle size of fine sands (0.2 mm), which caused their washout into the joints and the observed settlement. Such tunnel sections require continuous instrumental settlement monitoring and strengthening of the lining where settlements occur. A structural and technological solution is considered for strengthening the reinforced concrete lining with longitudinal concrete beams reinforced with steel or composite (FRP) bars, placed within the track-bed concrete and anchored to the invert segment of the lining. A finite element model was developed of the segmental reinforced concrete metro tunnel lining without tension ties between segments and of the surrounding soil mass, and the patterns of strain and stress distribution caused by the formation of a settlement trough beneath the lining were obtained. The analysis of the stress-strain state of the tunnel lining and the surrounding soil mass showed that, when the foundation soil is removed, tunnel settlements can reach hundreds of millimeters, and the following stresses develop in the lining: compressive – not more than 9.9 MPa, tensile – up to 2.52 MPa. Such compressive stresses are not critical, whereas the tensile stresses may cause cracking of the lining. The proposed strengthening reduces the settlement by a factor of 1.55, the compressive and tensile stresses in the lining by a factor of 1.08 … 1.13, and the internal forces in the lining by a factor of 1.18-2.83. Originality. For the first time, an equation was derived for estimating the joint opening width between the segments of a reinforced concrete segmental metro tunnel lining based on survey monitoring data. An original finite element model was developed of the segmental reinforced concrete metro tunnel lining without tension ties between segments and of the surrounding soil mass, and the patterns of strain and stress distribution caused by the formation of a settlement trough beneath the lining were obtained. Practical value lies in the possibility of assessing the hazard of tunnel settlement caused by soil washout through opened joints and preventing it by strengthening with longitudinal beams placed within the track-bed concrete and anchored to the invert segment of the lining.

Railway structures such as bridges, culverts and tunnels are critical infrastructure facilities designed for long-term operation. During service life, their load-bearing structures undergo physical deterioration caused by cracking, spalling and local failures, which leads to a reduction in load-bearing capacity. Repair and rehabilitation of such structures should preferably be performed using technologies that preserve existing structural elements and ensure minimal interruption of railway traffic. At the Ukrainian State University of Railway Transport, innovative structural and technological solutions for restoring the load-bearing capacity of masonry, concrete and reinforced concrete linings of culverts and tunnels have been developed and successfully implemented. These solutions are based on the use of metal-injection jackets consisting of steel shells anchored to the damaged lining and injection of repair mortar into the gap between the shell and the existing structure. However, during design, the contribution of the steel shell to the overall load-bearing capacity has traditionally been neglected due to difficulties in verifying numerical calculation results. This paper presents the results of verification of finite element calculations of the stress–strain state of vaulted metal-injection structures. The verification is performed by comparing numerical results with experimental and analytical data obtained for similar steel–concrete arch systems. Nonlinear finite element analyses were carried out using a specialized structural analysis software, and the obtained deformation diagrams and ultimate load values were compared with experimental results reported in the literature. The study shows that nonlinear finite element calculations provide a satisfactory agreement with experimentally observed stress–strain behaviour. The calculated ultimate load values are, on average, approximately 17.5% lower than the experimental ones, indicating a conservative nature of the method. This confirms the feasibility of using nonlinear finite element modelling for the design and assessment of metal-injection jackets in underground railway structures, provided that the identified deviation is properly accounted for at the design stage.

This study investigates the finite-element and physical models of railroad sleepers made of concrete with steel and composite prestressed reinforcement. Reinforced concrete sleepers withstand mechanical loads well but have low electrical resistance, which contributes to traction current losses, leakage currents and electrocorrosion of linear structures on electrified railroads, as well as disruption of auto-lock. Since low electrical resistance is due to the electrical conductivity of steel reinforcement, its replacement with composite makes it possible to solve a number of problems in railroad operation. However, its use for sleepers is complicated by the difference from steel reinforcement in elasticity and remains insufficiently studied. Sleeper models and a scheme for their testing have been devised, which corresponds to the standard sleeper test. Calculation and full-scale experiments with loading the models have been performed. It has been established that as the models are loaded and the deformation moment increases, it evolves in three stages: crack formation; their development to the formation of a plastic hinge; failure with reinforcement slipping. In the model with composite reinforcement, compared to steel reinforcement, the moments corresponding to these stages are smaller by values that correlate with lower tension forces and the modulus of elasticity of the reinforcement. The type of reinforcement affects all moments characterizing the strength and crack resistance of the models less than the pre-tensioning forces. The results from the calculated and full-scale experiments have been compared. Correction factors were proposed for calculating the moments of crack formation in sleepers. The results make it possible to design sleepers with composite reinforcement of the required crack resistance. Such sleepers could be implemented provided that a positive result is obtained from their experimental operation on an electrified section of the railroad

To reduce the electrical conductivity of concrete railway sleepers, minimize the leakage of traction currents from the rails, and mitigate their electrocorrosive impact on structural elements, the replacement of conventional steel reinforcement with composite reinforcement has been proposed. An analysis of current flow paths through the sleepers and a review of conventional methods for investigating corrosion caused by stray currents were performed. Based on this analysis, a comprehensive experimental methodology was developed to comparatively evaluate the electrocorrosion behavior of concrete sleepers and other reinforced elements with steel and composite reinforcement. The methodology focuses on processes occurring in concrete and reinforcement under the influence of externally applied electrical potentials. The experimental program involves applying either direct electrical potential or pulsating unidirectional electrical potential to specimens– sleeper models and subsequently examining extracted specimens using a combination of techniques, including nanoindentation and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS). Nanoindentation was employed to determine micromechanical properties of the cement paste, namely the elastic modulus (M) and microhardness (H), which are sensitive to the degree of electromigration-induced leaching. Experimental results showed that M and H decrease progressively from the surface exposed to the negative potential during the test. The highest values were retained in the core of the specimen, and their dependence on the distance from the negatively polarized surface was well approximated by power-law and polynomial functions. Baseline and maximum leaching values of M and H were established for cement paste with a water-to-cement ratio of 0.35, which is typical for sleeper concrete. It was further observed that the shape of the M and H profiles, and therefore the intensity of electrocorrosion processes in concrete, depends on both the type of applied electrical potential (constant or pulsating unidirectional) and the type of reinforcement (steel or composite).

An analysis of regulatory and literature sources regarding the service life of structures and elements of the railway track superstructure in tunnels has been carried out. It is shown that the regulatory documents of JSC «Ukrzaliznytsia» did not provide for the replacement of rails and fastenings in the quantity that actually fails in operation, which complicated the logistics and material support of current maintenance and capital repairs. Theoretical studies and analysis of the results of experimental and field investigations on corrosion and electrocorrosion of structures and elements of the track superstructure in tunnels have been conducted. It has been established that rail fastenings, the rail web, and especially the rail base are most intensively affected by corrosion. The mechanism of electrocorrosion damage has been revealed, and the factors influencing the intensity of electrocorrosion have been determined. A mechanism of rail base electrocorrosion has been developed. According to this mechanism, under the influence of a positive pulsating unidirectional electric potential induced on the rail during the passage of electric rolling stock, vertical polarization occurs, which alters the electro-surface potential of the pearlite grains in the steel similarly to how pH affects the absolute electro-surface potential in equilibrium. The dependencies of the electro-surface potential of pearlite, the equivalent pH value, and the corrosion rate in mm/year on the rail potential have been substantiated. A potential of 100 V on the rail is equivalent to the effect of an environment with pH = 2.6, corresponding to a steel corrosion rate of 0.91 mm/year. Based on the results of experimental and field studies, proposals have been developed to adjust the regulatory service life of structures and elements of the track superstructure in railway tunnels, particularly for rails.

Purpose. During operation on electrified direct current railways, reinforced concrete contact network pole of railways are damaged by electrical corrosion. Therefore, the development of alternative support structures, in particular, concrete with composite reinforcement, and the assessment of their bearing capacity is an urgent task. The purpose of the study is to compare the bearing capacity of conical centrifuged poles of the contact network of railways made of concrete reinforced with steel and composite reinforcement. Methodology. The comparison of the load-bearing capacity of the pole of the contact network of railways made of concrete reinforced with composite and steel reinforcement was carried out by means of a calculation experiment with the analysis of the stress-strain state of the risers using the finite element method and the LIRA-SAPR software complex. Findings. A finite-element model of poles with steel and composite reinforcement with the same cross-section and prestress was constructed. Their load during the calculation experiment was carried out until destruction, the calculation was performed in a non-linear setting. As a result of the calculated experiment, the isofield of deformations, stresses in concrete, forces in longitudinal and transverse reinforcement was obtained. It has been established that poles with both steel and composite reinforcement are destroyed due to the development of the working reinforcement. In the stretched zone of the pole with steel reinforcement, cracks do not form before failure, the pole with composite reinforcement works with cracks in the stretched zone. In a pole with steel reinforcement, the distribution of stretched and compressed zones along the cross section is uniform, in a pole with composite reinforcement, a wide stretched zone is observed, precisely in which cracks form, and a minimal compressed zone. The design of the reinforced concrete pole provides the necessary load-bearing capacity of the pole - normative bending moment, the pole with composite reinforcement - does not provide it by 21% due to the 5.4 times smaller modulus of elasticity of the composite reinforcement compared to steel. The deformation of the pole with composite reinforcement exceeds the deformation of the pole with steel reinforcement by 64%. Ensuring the required load-bearing capacity is possible by increasing the cross-section of the reinforcement and the tension of its package. Originality. For the first time, a finite-element model of a conical ring cross-section of a structure made of concrete reinforced with pre-stressed composite reinforcement and the regularity of the distribution of deformations and stresses during bending was obtained. Practical value lies in the creation of an opportunity to design poles of the contact network of railways that are resistant to electrocorrosive influences.

The object of this study is fine-grained concrete from the waste of mining and processing plants. These wastes are fine-grained dusty sands of polymineral composition. Their use as an aggregate for concrete is restrained by high water consumption, which does not make it possible to obtain sufficient strength for concrete. Therefore, the problem to be solved was the substantiation of the composition of fine-grained concrete from these wastes with mineral and chemical additives, which would ensure obtaining physical-mechanical and hydrophysical properties reasonable for the production of construction articles. The composition of fine-grained concrete from the waste at the Poltava Mining and Processing Plant and slag Portland cement in a ratio of 3:1 and additives of micro silica (15 % of the cement mass) and polycarboxylate superplasticizer (2 % of the cement mass) with W/C=0.5 was obtained. The compressive strength of this concrete reaches 40 MPa, which exceeds the strength of fine-grained concrete of a similar composition on natural fine-grained sand by 3 times. This is due to a greater degree of cement hydration, a greater number of formed hydration products, the presence of silica and quartz particles, a more uniform alternation of gel, silica particles, and crystal hydrates in the structure of cement stone. As a result, the structure contains a larger number of electro heterogeneous contacts between particles and grains that have negative (quartz, calcium hydro silicates) and positive (crystal hydrates of portlandite, hydro aluminates and calcium hydrosulfoaluminate) surface charges. This is what determines the achieved strength and water resistance of fine-grained concrete. The resulting composition of fine-grained concrete is recommended for the production of construction articles.

A comprehensive study of the technical condition, corrosion processes, damage and load-bearing capacity of the reinforced concrete chimney pipe, which removes the gas-smoke mixture formed in the technological processes of coke-chemical production and is an aggressive environment, was performed. A methodology for predicting the remaining resource of the pipe structure has been developed. It was established that the damage that determines the ultimate resource is the collapse of the lining, after which active corrosion damage of the reinforced concrete structure occurs. An analysis of the composition and temperature-moisture regime of the aggressive medium was performed. It was established that it is gaseous, the most aggressive components of which are acid gases, the degree of aggressive action is moderately aggressive, possibly strongly aggressive. Corrosion of concrete progresses in a concentric front from the inner surface of the chimney to the outer surface at a rate of 1.2 to 4.8 mm/year. The corroded layer of concrete loses its strength and protective properties to the reinforcement. An analysis of the stress-strain state of the pipe taking into account corrosion damage was performed, the most heavily loaded dangerous zone and its structure were determined, and the limit values of the wall thickness and the depth of corrosion damage in this zone were determined, which ensure the fulfillment of the conditions for bearing capacity. Based on the values of the corrosion rate, the time to reach the limit state is determined. It is shown that without repair and protection measures, the remaining service life of the pipe does not exceed 11 years. It is recommended to carry out a major repair of the pipe as soon as possible with the elimination of damage and restoration of the lining, or no later than after 10 years to carry out the liquidation of the structure with the construction of a new one.

The theoretical substantiation of the production of especially fine-grained concrete (EFC) from the waste of the Poltava Mining Concentration Plant as a fine-grained aggregate has been performed. Its structure is substantiated taking into account the contacts between the angular aggregate grains, the possibility of increasing strength by introducing mineral fillers and microfillers with particles 5 times smaller than the aggregate grains and cement particles, respectively, is proved. The determination of the composition of EFC from the waste of the Poltava MCP was substantiated by determining and ensuring the optimal value of the coefficient of displacement of aggregate grains by cement paste m opt = 1.89 with the inclusion of dusty fractions of the aggregate. The optimal composition of EFC Aggregate : Cement : Water = (3–3.15):1:0.5 with mandatory use of superplasticizer additive to ensure W/C = 0.5 was determined and experimentally confirmed. The dependences of compressive and tensile strength of EFC on: type and content of superplasticizer additives were experimentally investigated; ratio of aggregate content to cement content; microsilica content; pressing pressure. It was established that the maximum strength of EFC is achieved in the case of the use of superplasticizers: polycarboxylate 1.5 % or sulfonaphthalinformaldehyde 1 % by weight of cement. It was also established that with the same A:C = 3:1 and W/C = 0.5, the strength of EFC on the waste of Poltava MCP exceeds the strength of fine-grained concrete on natural, especially fine-grained sand: in compression - by 2 times, in tension - by 1.9 times and reaches 35 MPa at the age of 28 days. The addition of microsilica in the amount of up to 15 % of the mass of cement allows to further increase the compressive strength by 44 %, and the tensile strength by 20 %. It is proposed to form EFC products by layer-by-layer pressing with a layer thickness of 5 mm. It was experimentally established that the maximum strength is achieved at a pressing pressure of 12 MPa.

Experimental studies of the influence of electric potentials on the intensity of corrosion processes in reinforced concrete structures of under-rail foundations have been conducted.A research methodology has been developed that involves the creation of these influences on models and the assessment of their consequences. The effects of capillary rise, evaporation, diffusion, crystallization of salts, electric potential have been created, and the impact of electric potential on the acceleration of transfer processes and manifestations of corrosion signs has been estimated.Models and experimental installations were made, research was conducted. The exposure of the models was carried out in an aqueous environment and in a sodium chloride solution without electrical influence (as a control) and under the influence of a pulsating unidirectional electric potential of the PUEP. It was established that the current through the models decreases under the influence of PUEP, and the specific electrical resistance of the models increases. PUEP accelerates the penetration of ions into the model by 4.43 times, and also causes stronger manifestations of signs of electrocorrosion of the armature. As a result of the exposure of the models without electrical influence in the water environment, weak corrosion of the armature outlets was noted, no corrosion of the armature was observed inside the model; in the sodium chloride solution, strong corrosion of the armature outlets and weak corrosion inside the model was observed. As a result of the influence of PUEP in the water environment, weak corrosion of the fittings was observed, inside the model, no corrosion of the fittings was observed; in the sodium chloride solution, weak corrosion of the armature outlets and strong corrosion was observed inside the model. It has been confirmed that the influence of PUEP significantly accelerates the transfer of ions in concrete and intensifies the corrosion processes of reinforcement. Acceleration of ion transport should also accelerate corrosion processes in concrete, but it is advisable to conduct their research with longer exposure periods of models and with the use of physicochemical methods. Means of draining the currents flowing from the rails through the sleepers were recommended and it was suggested to eliminate the armature discharges from their ends. Проведено експериментальні дослідження впливу електричних потенціалів на інтенсивність корозійних процесів у залізобетонних конструкціях підрейкових основ.Розроблено методику досліджень, яка передбачає створення цих впливів на моделі, та оцінювання їхніх наслідків. Створено впливи капілярного підняття, випаровування, дифузії, кристалізації солей, електричного потенціалу, передбачено оцінювання впливу електричного потенціалу на прискорення процесів перенесення та проявів ознак корозії. Виготовлено моделі та експериментальні установки, проведено дослідження. Експозицію моделей здійснювали у водному середовищі та розчині хлориду натрію без електричного впливу (як контроль) і під впливом пульсуючого однонаправленого електричного потенціалу (ПОЕП). Встановлено, що під час впливу ПОЕП сила струму крізь моделі знижується, питомий електричний опір моделей зростає. ПОЕП прискорює проникнення іонів у модель у 4,43 раза, а також обумовлює більш сильні прояви ознак електрокорозії арматури. Прискорення перенесення іонів має прискорювати й корозійні процеси в бетоні, але їхнє дослідження доцільно проводити з більшими термінами експозиції моделей і з застосуванням фізико-хімічних методів. Рекомендовано засоби дренування струмів, що стікають із рейок крізь шпали, і запропоновано усунути випуски арматури з їхніх торців.