Key Engineering Materials Vol. 1004

Abstract: Fiber-reinforced polymer (FRP) composites have increasingly been used in the past 40 years. They are ideal option for external strengthening of reinforced concrete (RC) structures due to their superior properties, including the high strength-to-weight ratio and ease of installment. The structural behavior of strengthened RC beams and the efficiency of the external FRP applied are both highly dependent on the bond performance between FRP and concrete. This paper presents an experimental study on the bond slip behavior of carbon fiber reinforced polymer (CFRP) sheets, applied to concrete structures under room temperature conditions. The experimental investigation involved the strengthening of three concrete prism specimens with CFRP sheets. The prism specimens were tested under a three-point bending setup. The bond slip phenomenon was analyzed using strain gauge readings attached to the CFRP laminate before testing. The calculated model aimed to accurately capture the bond slip behavior and its associated parameters, including the maximum shear stress, and maximum slip. These parameters were compared with theoretically derived formulas available in the literature. The theoretical equations overestimated the FRP stresses when compared to experimental measurements. The comparative analysis assesses the accuracy and reliability of the theoretical derivations by benchmarking it against the experimentally derived bond-slip model for CFRP-to-concrete joints.

Abstract: The presence of web openings in the shear span significantly impacts the structural behavior of reinforced concrete (RC) beams, affecting both shear capacity and crack propagation. This study explores the feasibility of strengthening web openings in the shear zone of RC beams using iron-based shape memory alloy (Fe-SMA) bars through numerical analysis with ABAQUS software. The investigation considered various web opening shapes; diamond, circular, and square strengthened with pre-stressed Fe-SMA bars. Results showed that web openings notably decrease the ultimate loads of beams by 53%, 44%, and 39% for square, circular, and diamond shapes, respectively. However, pre-stressed Fe-SMA bars enhanced the shear capacity of beams with unstrengthened web openings by approximately 60%, making their behavior comparable to solid beams. The proposed strengthening technique was most effective for diamond web openings, nearly restoring both shear strength and stiffness, while circular openings recovered nearly 90% of shear capacity and square openings about 75%. Additionally, Fe-SMA bars effectively controlled cracking at the corners of the openings. This study highlights the importance of strengthening web openings in RC beams, especially in shear zones, and provides significant insights into enhancing such beams, contributing to safer structural designs. Further laboratory experiments are recommended to validate and extend these numerical findings.

Abstract: The article focuses on the structural analysis of a steel cylindrical silo with a corrugated wall, following the guidelines of EN 1993-4-1 standard. The resistance and stability of silo vertical stiffeners under axisymmetric loads during grain storage are being studied. The design model of the ribs is based on a centrally compressed column. In the plane of minimal rigidity, it is further elastically supported by corrugated sheets of a cylindrical shell. The resistance and stability of ribs are analysed using design models of various levels of detail, ranging from simple analytical to complex finite element models. The analysis compares different design models, highlights their pros and cons, and provides recommendations for their practical use.

Abstract: The paper examines a complex methodology for calculating the slope stability of a tailing storage facility based on comparing the results obtained through deterministic and probabilistic approaches. The analysis is performed in GeoStudio software, based on the limit equilibrium method, and with a probabilistic approach that uses a Monte Carlo simulation to compute a probability distribution of the resulting factor of safety. A slope stability assessment of tailing dam was conducted on the example of Ferrexpo Poltava Mining, and a conclusion was reached about their reliability and safety. The results of the deterministic analysis showed that the calculated factor of safety is by those established in Ukrainian regulatory standards. It has been recognized that the factor of safety is not a consistent measure of risk for tailings dam. Considering the variability inherent in the soil materials of tailings dam is a way to achieve more accurate results. The importance of obtaining a failure probability and a reliability index due to tailing dam stability was highlighted by comparing deterministic and probabilistic approaches.

Abstract: The problems of stress corrosion or hydrogen blistering of gas pipelines are relevant and require careful study of the causes and factors that cause this type of corrosion-mechanical destruction of pipelines. The analysis of numerous publications on this problem revealed contradictions of information regarding the mechanism of stress corrosion and a lack of experimental materials on the substantiation of the nature and peculiarities of the nature of destruction on gas pipeline networks. Systematic experimental studies using different brands of pipe steels allowed to determine the brands of steels, which according to their characteristics are the most resistant to VBR in harsh operating conditions, including even in the most aggressive NACE environment with H₂S and CO₂ additives at a pressure of 10-15 atm. Moreover, the experimental studies were as close as possible to the operating conditions of pipelines of the gas transportation network. The obtained results of experimental studies can serve as a basis for developing methods of technical diagnostics and forecasting the actual state of pipelines, which will significantly prevent the occurrence of sudden destruction caused by stress corrosion. The influence of the service life of gas pipelines on the degree of flooding and microhardness of pipe steels was established, which made it possible to substantiate the embrittlement of the metal with the increase of service life. The values of impact toughness on samples with sharp and round notches and the amount of work of crack growth depending on the service life of the pipe steels were determined, which made it possible to choose steel grades characterized by the highest resistance to brittle fracture. It is shown that with the service life, the destruction occurs according to a brittle mechanism, which is confirmed by the increase in the share of the fibrous component in the fractured samples after impact tests. It was established that the lowest corrosion rate is possessed by new grades of improved steel grades 20А and 08 KhMChA.The PRFNV parameter proposed in the paper makes it possible to assess the susceptibility of pipe steels to stress corrosion cracking and provides an opportunity to regulate the corrosion crack resistance of pipelines by metallurgical methods.

Abstract: This study examines the potential to customize the bending and transverse shear behavior of aluminum honeycomb sandwich panels by introducing sinusoidal perturbations to their cell walls. Finite element analysis is used to investigate the effect of varying the amplitude and frequency of the introduced perturbations on the flexural and transverse shear stiffness and strength of perturbed aluminum cores. Results show that increasing the amplitude and frequency of the perturbations generally decreases the flexural and transverse shear stiffness and yield strength. Local deformations in the perturbed cores indicate that imposing perturbations encouraged the development of localized deformations in the curved cell walls, which increased the perturbed cores' compliance. The transverse shear and flexural responses at the highest frequencies and amplitudes exhibited a very smooth and compliant behavior compared to the unperturbed cores. The response of the perturbed cores can be attractive for applications involving impact energy mitigation, as they demonstrate an enhanced capacity to reduce and limit the force transmitted through them.

Abstract: The article presents a simulation model for determining the required area of easily removable structures to protect against progressive collapse. The simulation model allows you to calculate the area of easily removable structures depending on the input parameters, to obtain the dynamics of the change in the parameters of the combustible medium depending on the change in the properties of the combustible gases that are in the room.

Abstract: The article deals with the simple two-dimensional axis-symmetric mechanical model of the technological system of the operation to distribute a steel pipe into a steel pipe grid is considered. The pressure amplitude during pulsed flaring and explosion welding of pipes with pipe grids is given. For solution under the Wilkins method, the pipe was divided into quadrilateral elements. Further, the deformed state was analyzed at a number of characteristic points located on the pipe outer surface and the bushing inner surface. The graph shows the radial displacements of points on the pipe surface in the initial period of time. The non-simultaneity of the collisions and the out-of-phase oscillations indicate bending and bending vibrations of the pipe. The dependence of the node displacements on the bushing inner surface in the radial direction on the deformation time and the dependence of the point radial velocity on the outer contact surface of the pipe on the deformation time are also shown. The dependence of the displacement speed of the points of the nodes located on the sleeve surface on time in the initial period of the process is given. The stressed condition of the system elements is characterized by the occurrence of stress waves generated by pipe being struck and spreading in the bushing and pipe. The process of pipe fastening is analyzed using the model of a flat deformed state. The co-deformation of a pipe and a pipe board with a hexagonal hole arrangement is considered for the case if a single pipe needs flaring inside the pipe grid.

Abstract: An electrochemical sensor was enhanced with magnetite nanoparticles for biosensor application. Nanoparticles of magnetite (Fe₃O₄) ranging in size from 5 to 30 nm were produced by the co-precipitation method and further modified with an amine functional group (Fe₃O₄@SiO₂_NH₂). During the process, the functional amine served as a supporting biomaterial and coating agent, regulating particle size and aggregation. The Fe₃O₄@SiO₂_NH₂ nanoparticles were incorporated into gold nanoparticle planes on a conductive graphene electrode in a diluted solution of the ultrafast redox probe K₃[Fe(CN)₆]. Using scanning electron microscopy to investigate the morphology of the modified graphene sheets and gold (Au) nanoparticles on screen printed electrodes (SCPE). The results clearly demonstrated the even distribution of Fe₃O₄ nanoparticles, almost always less than 30 nm in size, on AuNPs and graphene sheets. Adding these magnetite particles has created active sites, facilitating the movement of electrons from redox-active species in the solution. In addition, the electrochemical reduction of flawed graphene sheets has greatly limited the oxygen groups, making the material more conductive or enhancing signal. The sensor was subsequently investigated with the use of magnetite nanocomposites for electrochemical biosensing applications with (bovine serum albumin) BSA.