Axially compressed circular steel tube confined concrete columns have been parametrically analyzed through numerical simulation with the general aim to confirm the effectiveness of concrete confinement and quantitatively estimate it. Numerical models have been assembled using SIMULIA Abaqus finite element analysis commercial software and its relevant tools, in particular Abaqus/Explicit module, the general contact algorithm, and the concrete damaged plasticity model. The limit states of the first group and corresponding failure mechanisms have been defined for the considered columns and investigated, qualitatively and quantitatively, with regard to their dependence onto column structural scheme, steel tube thickness and concrete grade. Totally, 33 different cases have been simulated and analyzed.
This study investigates an experimental-analytical approach to improving the accuracy of calculating the nominal composition of heavy concrete using a database of test protocols from NEFU (2015–2025). Particular attention is paid to working with low-quality aggregates – sand with a fineness modulus below 1.4. Significant discrepancies between the calculated and actual concrete compositions were identified, reaching up to ±250 kg/m³. A corrective coefficient linking the cement-to-water ratio (C/W) with the proportion of aggregates is proposed. Its application reduced the error to ±60–150 kg/m³ and improved the convergence of results to 1.5% without loss of strength. It is shown that the strength of concrete incorporating very fine sand (fineness modulus ≤ 1.4) exhibits higher sensitivity to variations in the C/W ratio within a narrow range of 1.3–2.7. The discrepancy between calculated and actual concrete density varies widely, leading to material overconsumption and reducing the reliability of computational mix design methods. An empirical relationship has been established linking the key variable mix parameters (water-cement ratio and aggregate proportion), which can be used as a correction factor. Without the coefficient, the deviation range was 1.8–5.0%, while with its application it ranged from –0.6% to 1.5% without deterioration of concrete mixture properties or physical and mechanical characteristics.
It is noted that the curing of cement composites is impossible without effects and is a reaction to them. In this case, the forces of the resulting resistance, according to the laws of thermodynamics, are aimed at weakening the impact. Experimental prerequisites and arguments are given that by choosing the time, intensity and duration of aggressive action on cement composites during their curing, it is possible to obtain more impact-resistant or ordered and durable structures of the material. The creation of conditions for the hardening of cement composites using liquid aggressive media leads to the formation of a dense inert layer on their surface, more adapted to the effects of this type. Using temperature and humidity influences, freezing and thawing, and loads, more durable composites were obtained. Thus, the curing of cement composites using time- and intensity-determined harsh temperature and humidity conditions, freezing and thawing, aggressive liquids, and loads makes it possible to obtain more durable or resistant structures of the material to specific destructive factors.
A series of large-eddy simulations (LES) was performed to investigate the effects of computational domain size and grid resolution on flow prediction within an idealized urban street canyon. Three streamwise domain lengths were examined in combination with coarse, medium, and fine grid resolutions. The building height, H, was kept constant, and the canyon aspect ratio (street width to building height) was set to unity. Flow statistics were evaluated at the central canyon of each configuration and compared with available wind-tunnel data.The LES results indicate that the simulated mean velocity profiles agree well with experimental measurements for all cases. Both domain size and grid resolution exhibited minimal influence on the mean velocity components, suggesting that mean flow within a street canyon can be reliably predicted using a relatively small computational domain when combined with medium or fine grid resolutions. This offers a computationally efficient option for mean flow analysis. In contrast, turbulence statistics were found to be more sensitive to grid resolution than to domain size. Fine grid resolution significantly improved the prediction of velocity fluctuations and momentum transport, whereas smaller domains tended to produce less consistent turbulence results. Consequently, while small or medium domains may be suitable for mean flow assessment, they are not recommended for detailed turbulence analysis.Overall, this study highlights the importance of balancing domain size and grid resolution to obtain reliable LES results while minimizing computational cost, providing practical guidance for CFD–LES studies of urban street canyon flows.
The purpose of this work is to study the effect of synthetic polysaccharides on the structure formation and properties of lime coatings. Information is provided on the influence of synthetic polysaccharides on the structure formation of lime coatings. It has been shown that due to the water-retaining effect of the additive, more favorable conditions are created for lime carbonation. Using X-ray phase and thermographic analysis, optical and infrared spectroscopy, the presence of inter- and intracrystalline organic compounds was established, which modify the (nano)structure of newly formed calcite crystals and increase the strength of lime coatings.
