Arabian Journal for Science and Engineering最新文献

Beam-column (B-C) joints are recognized as critical regions in reinforced concrete (RC) moment-resisting frames when subjected to seismic loads. Furthermore, these joints may be subjected to high temperatures during their lifespan, which might cause severe structural damage. Accordingly, the seismic response of RC beam-column joints that were subjected to heat (i.e., 400 °C and 600 °C) was investigated in the present experimental work. The joint specimens were divided into three categories: Three joints were kept as is (i.e., reference joints; no strengthening is applied), whereas six joints were strengthened with one and two layers of stainless-steel expanded metal sheet mesh (SSEMSM) in order to improve their performance. To investigate the seismic performance of the joints, a quasi-static cyclic load was applied to the joints to simulate a seismic load. Results showed that the average maximum load for joints strengthened with one and two layers of SSEMSM, respectively, was increased by 11% and 21% at ambient temperature and by 2% and 9% at 400 °C, in comparison with the reference joint. In addition, using one and two layers of SSEMSM, respectively, led to achieving an average of 91% and 100% of the full capacity of the reference joint for B-C joints subjected to 600 °C. Furthermore, the experimental findings show a considerable improvement in the cyclic response of non-ductile RC joints that were strengthened with the SSEMSM strategy and subjected to high temperatures (i.e., higher load capacity, greater displacement, higher dissipated energy, higher ductility, and slower degradation in the secant stiffness).

In the current study, the synthesis of an imidazolium ionic liquid (imi@MCM‐41/Fe₃O₄) was carried out with the aim of its application as an additive to enhance the electrochemical properties of anion exchange membranes. In heterogeneous membranes, resin particles act as functional groups, and the uniform distribution of these particles on the membrane surface and their amount have a significant effect on the electrochemical properties of the resulting membranes. Imidazolium groups can act as functional groups in anion exchange membranes. Therefore, the addition of an ionic liquid with imidazolium functional groups was carried out with the double aim of increasing the number of functional groups and obtaining a more uniform distribution of resin particles on the membrane surface. The FTIR and SEM analyses confirmed the functionalization of ionic liquid with imidazolium groups and their size on a nanometer scale. The effect of the ionic liquid to the resin ratio on the electrochemical properties and on the hydrophilicity of the membrane was investigated. The results showed that the uniform distribution of resin particles on the membrane surface in the presence of ionic liquid nanoparticles as well as the presence of ionic liquid functional groups significantly improved the electrochemical properties of the membrane. At a concentration of 1 wt.%, the ion exchange capacity, permselectivity, and electrical resistance were enhanced by 73%, 9%, and 47%, respectively.

With the increasing demand for large and deep anchor projects in soft soil areas, issues related to settlement in circular foundation pits and damage to supporting structures have become significantly pronounced. The absence of pertinent design methods significantly impacts construction safety. Through on-site monitoring and statistical analysis, this study examines the spatiotemporal evolution of deformation in circular foundation pits, the deformation characteristics of retaining structures, and surface settlement features. Key design factors influencing the stability of circular foundation pits are explored. The research indicates that structural deformation and surface settlement are closely related over time and exhibit substantial spatial coordination. The deformation control capability of circular foundation pits is considerably stronger than that of square foundation pits, and it is less influenced by excavation depth. Diameter and soft soil thickness have a substantial impact on structural deformation and surface settlement. When the diameter is less than 40 m, the structural deformation remains below 0.1%. The study establishes an evaluation method for the deformation control of large and deep circular foundation pits in soft soil based on a significant amount of engineering monitoring data. It categorizes deformation control indicators for pit excavation based on different design factors, offering reliable theoretical support for relevant design professionals.

Concrete cover separation (CCS) is a common type of delamination failures that occurs at the plate end in reinforced concrete (RC) beams strengthened in flexure using fiber-reinforced polymer (FRP) materials. The effectiveness of FRP U-wrap anchorage has been demonstrated in mitigating CCS failure, resulting in increased utilization of FRP composites for strengthening purposes. The current study presents the development of a nonlinear three-dimensional finite element (FE) model using ABAQUS software in order to simulate the flexural behavior and debonding failure of FRP-strengthened RC beams end-anchored with vertical FRP U-wraps. The cohesive zone model (CZM) is used in the developed FE model to predict the debonding failure of the anchored beams, considering the influence of relevant parameters. The validation of the FE model was achieved through comparisons with experimental data from the literature, which demonstrated good agreement. A parametric study was then conducted to investigate the impact of the design parameters of FRP U-wrap on the behavior of the anchored beams. The examined parameters included the width, layout, and height of the vertical FRP U-wraps. The findings of the FE parametric study have revealed that to successfully prevent plate-end debonding, it is critical to not only use the required area of vertical FRP U-wrap but also carefully consider the U-wrap layout. The FRP U-wrap should be placed at the plate-end region covering the concrete tooth created by the shear cracks, and the U-wrap layout should consider the detailing recommended in this study.

The synthesis of multifunctional composites still relies on the use of conventional methods. However, these methods are expensive, time consuming and require high volumes of reducing agents which are often toxic. In this study, composites of bentonite-supported silver nanoparticles were prepared comparatively by the conventional heating method and the rapid microwave method; and their antibacterial activity was investigated against Escherichia coli and Staphylococcus aureus. The crystalline nature of the composites was evaluated by X-ray diffraction (XRD), while transmission electron microscope (TEM) coupled with energy-dispersive spectroscope was used for morphology and elemental analysis, respectively. Surface area and pore size analysis of the composites were conducted by the Brunauer, Emmett and Teller analyzer. TEM images revealed successful synthesis of the composites with a better dispersion of the nanoparticles achieved through microwave, where nanoparticle sizes were 6–38 nm and 9–56 nm by the conventional method. It is worth noting that the composites were prepared in less than 30 min using microwave as compared to 2 h of the conventional method. The XRD spectra confirmed the formation of silver and not any other impurities of the metal. These results revealed that, although the two methods are comparable, microwave method is efficient and time saving and can, therefore, synthesize composites with well-dispersed and narrow distributed nanoparticles. The antibacterial results demonstrated that the prepared composites are effective in the inactivation of various bacteria. These composites could be applied in water treatment, wound dressing, packaging, etc.

This study explores the mechanical properties of incompressible isotropic material polydimethylsiloxane (PDMS) using hyper-elastic constitutive models. It comprises two main parts: an experimental phase involving the creation of a new PDMS formulation and stress–strain evaluation through uniaxial tensile loading, and a theoretical phase where six hyper-elastic models are applied to the stress–strain data using finite element methods and optimization algorithms. Elastic compatibility and Drucker’s stability criterion provide the determination of material constants, integrated into the generalized reduced gradient and constrained particle swarm optimization (C-PSO) algorithm for optimization. The performance of these models is assessed via the coefficient of determination. The Reduced Polynomial model, with six material parameters optimized through C-PSO, emerges as the top choice, closely matching experimental data at various strain levels. Subsequent finite element simulations validate the behavior of the Reduced Polynomial model under the same conditions as the tensile testing, showing excellent agreement with experimental results. Analyzing rubber-like materials and their composites using commercial finite element software is challenging due to their non-linear properties, motivating the use of optimization algorithms to determine material properties accurately. This research’s novelty lies in using C-PSO and GRG solver to examine polymeric materials, yielding highly efficient and precise results.

Pumped storage is an important green, low-carbon, and clean flexible regulating power source in the power system, which can provide regulation services for the power system, promote the construction of a new type of power system, and facilitate the green transformation of energy. To improve the efficiency and stability of the centrifugal pump turbine under multiple operating conditions, a surrogate model combining radial basis functions with a high-dimensional model is used for performance optimization. Taking the active guide vane of the centrifugal pump turbine as the research object, the airfoil profile is parameterized, and the surrogate model's independent variables and training range are determined. Combining programming and numerical simulation software, an efficiency prediction model for the centrifugal pump and water turbine based on guide vane airfoil control variables is constructed. The particle swarm algorithm is used to globally optimize the constructed model to obtain the optimal efficiency point and corresponding airfoil-related parameters. Finally, numerical simulation and experimental research methods are used to validate the predicted data. The results show that under the premise of ensuring grid performance and operational stability, the numerical simulation efficiency of the pump turbine under the optimization scheme is increased by 1.6 and 0.32%, respectively, compared to the numerical efficiency of the prototype guide vane. In the experimental case, the efficiency of the water turbine and pump is increased by 0.76 and 0.14%, respectively, compared to the prototype guide vane.

Sesbania gum (SG), as an environmentally friendly natural polymer, was chemically modified in heterogeneoususing systems using a combination of cross-linking, carboxymethylation and oxidation to broaden its applications. The experimental results showed that the cross-linking was chiefly conducted on the smaller particles of SG, while the carboxymethylation and oxidation were primarily carried out on the larger particles. The carboxymethylation and oxidation obviously increased the average size of SG. The dialdehyde oxidation destroyed the crystalline structure of SG more severely than cross-linking and carboxymethylation. The cross-linking, carboxymethylation and oxidation increased the thermal stability of SG, but decreased its enthalpy change. The pasting properties of tapioca starch were influenced by the addition of SG and modified SG. The crystalline structure of polyethylene oxide (PEO) was influenced by addition of SG and modified SG. The reduction in crystallinity degree and introduction of dialdehyde carboxymethyl cross-linked sesbania gum (DCCLSG) with aldehyde groups were beneficial for ameliorating the ion migration through the solid electrolyte membrane.

This research addressed the compressive performance of slender reinforced concrete (RC) columns containing steel fibers and strengthened with carbon fiber-reinforced polymer (CFRP) under eccentric loading. Here, 12 slender RC columns were manufactured in four groups: plain concrete columns, plain concrete columns strengthened with CFRP, steel fiber-reinforced concrete (SFRC) columns, and SFRC columns strengthened with CFRP. Synergistic effects of steel fibers and CFRP sheets on the energy absorption level, load-carrying capacity, and curvature of the slender RC columns under eccentric compressive loads were investigated. The results demonstrated that using either CFRP sheets or steel fibers improved the eccentric compressive behavior of the slender columns. Moreover, the simultaneous use of steel fibers and CFRP sheets had the most significant effect on the performance improvement among all the experimental groups under the eccentric load. This performance improvement consisted of an increase in the displacement ductility, tangent stiffness, and longitudinal strain at failure with a decrease in the secant stiffness. In addition, increasing the eccentricity mitigated the effect of these two materials on the mentioned mechanical parameters. Finally, a formula was presented for predicting the load-carrying capacity of CFRP-wrapped slender RC columns containing steel fibers under load eccentricity.

In this work, a computational study for the investigation of the absorbing boundaries influence to the dynamic soil structure interaction is presented. More specifically, an analysis of the influence of the Lysmer boundaries to hexahedral finite element models that are seismically excited is portrayed hereinafter. The influence to the time history analyses of the free field and the structure with the soil, the amplification factors due to the presence of the boundaries and the soil, and the maximum displacements and accelerations is investigated numerically. The seismic excitation is the Athens 1999 Earthquake which is considered as a palm force. It has been demonstrated that the absorbing boundaries influence is prominent when the ratio of the FEM width to the corresponding height is less than ten. Moreover, the amplification factor due to boundaries expresses a not usual behaviour as a result of the standing waves. Also, the soil amplification factor is slightly influenced but in all cases is estimated with a substantial accuracy while the soil structure interaction’s main attributes with the decrease in the equivalent forces and the increase in the displacement is in all cases evident.