• Geomechanics and Engineering
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• v.19 no.4
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• pp.329-342
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• 2019

In this paper, the effect of a group of sand columns in the loose soil bed using triaxial tests was studied. To investigate the effect of geotextile reinforcement type on the bearing capacity of these sand columns, Vertical encased sand columns (VESCs) and horizontally reinforced sand columns (HRSCs) were used. Number of sixteen independent triaxial tests and finite element simulation were performed on specimens with a diameter of 100 mm and a height of 200 mm. Specimens were reinforced by either a single sand column or three sand columns with the same area replacement ratio (16%) to evaluate the Influence of the column arrangement. Effect the number of sand columns, the length of vertical encasement and the number of horizontal reinforcing layers were investigated, in terms of bearing capacity improvement and economy. The results indicated that the ultimate bearing capacity of the samples with three ordinary sand columns (OSCs) is eventually about 11% more than samples with an OSC. Also, comparison of the column reinforcing modes showed that four horizontal layers of geotextile achieved similar performance to a vertical encasement geotextile at the 50% of the column height, from the viewpoint of strength improvement, while from the viewpoint of economy, the geotextile needed for encasing the single column is around 2.5 times of the geotextile required for four layers.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.10
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• pp.59-67
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• 2020

Polycarbonate thermoplastic composite materials are anisotropic and exhibit physical properties in the longitudinal direction. Therefore, the physical properties depend on the type and direction of reinforcements. The thermal conductivity, electrical conductivity, and resin impregnation can be controlled by adding carbon nanotubes to polycarbonate resin. However, the carbon fiber used as a reinforcing material is expensive, interfacial adhesion issues occur, and simulation values are different from actual values, making it difficult to perform mathematical analysis. However, carbon nanotubes have advantages such as light weight, rigidity, impact resistance, and reduced number of parts compared to metals. Due to these advantages, it has been applied to various products to reduce weight, improve corrosion resistance, and increase impact durability. As the content of carbon nanotubes or carbon fibers increases, the mechanical properties and antistatic and electromagnetic shielding performance improve. It is expected that the amount of carbon nanotubes or carbon fibers can be optimized and applied to various industrial products.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.35 no.1
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• pp.21-28
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• 2019

This study investigates the applicability of composite polyurea to contain fiber reinforcement like fiber glass, steel fiber and carbon nanotube. Polyurea as elastomer is an excellent water-proofing material with many mechanical characteristics such as high tensile strength, ductility, high rate of expansion and contraction, and so on. The reinforcing fibers can be utilized for improving the load-carrying capacity of concrete structures. The polyurea plays a role to improve the ductility and toughness. Composite polyurea takes the mechanical advantages of the fibers and the polyurea. The test variables include the type of reinforcing fiber, its spraying thickness, and its weight ratio contained in the composite polyurea. It is observed that the load-carrying capacity, and the ductility and toughness are improved with the increase in the spraying thickness and the weight ratio contained in the composite polyurea. It is expected that the composite polyurea can be widely utilized in enhancing the structural and seismic performance.

• Structural Engineering and Mechanics
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• v.77 no.6
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• pp.705-720
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• 2021

Reinforced concrete (RC) columns are the primary type of vertical support used in building structures that sustain vertical loads. However, their strength may be insufficient due to fire, earthquake or volatile environments. The load demand may be increased due to new functional usages of the structure. The deformability of concrete columns can be greatly reduced under high axial load conditions. In response, a novel steel encasement that distinguishes from the traditional steel jacketing that is assembled by welding or bolt is developed. This novel strengthening method features easy installation and quick strengthening because direct fastening is used to connect the four steel plates surrounding the column. This new connection method is usually used to quickly and stably connect two steel components by driving high strength fastener into the steel components. The connections together with the steel plates behave like transverse reinforcement, which can provide passive confinement to the concrete. The confined column along with the steel plates resist the axial load. By this way, the axial load capacity and deformability of the column can be enhanced. Eight columns are tested to examine the reliability and effectiveness of the proposed method. The effects of the vertical spacing between adjacent connections, thickness of the steel plate and number of fasteners in each connection are studied to identify the critical parameters which affect the load bearing performance and deformation behavior. Lastly, a theoretical model is proposed for predicting the axial load capacity of the strengthened RC columns.

• Journal of Powder Materials
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• v.28 no.3
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• pp.253-258
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• 2021

There is increasing demand for the development of a new material with high strength, high stiffness, and good electrical conductivity that can be used for high-voltage direct current cables. In this study, we develop aluminum-based composites containing C₆₀ fullerenes, carbon nanotubes, or graphene using a powder metallurgical route and evaluate their strength, stiffness, coefficient of thermal expansion, and electrical conductivity. By optimizing the process conditions, a material with a tensile strength of 800 MPa, an elastic modulus of 90 GPa, and an electrical conductivity of 40% IACS is obtained, which may replace iron-core cables. Furthermore, by designing the type and volume fraction of the reinforcement, a material with a tensile strength of 380 MPa, elastic modulus of 80 GPa, and electrical conductivity of 54% IACS is obtained, which may compete with AA 6201 aluminum alloys for use in all-aluminum conductor cables.

• Journal of Korean Association for Spatial Structures
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• v.22 no.1
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• pp.41-49
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• 2022

In the case of columns in buildings with soft story, the concentration of stress due to the difference in stiffness can damage the columns. The irregularity of buildings including soft story requires retrofit because combined load of compression, bending, shear, and torsion acts on the structure. Concrete jacketing is advantageous in securing the strength and stiffness of existing members. However, the brittleness of concrete make it difficult to secure ductility to resist the large deformation, and the complicated construction process for integrity between the existing member and extended section reduces the constructability. In this study, two types of Steel Grid Reinforcement (SGR), which are Steel Wire Mesh (SWM) for integrity and Steel Fiber Non-Shrinkage Mortar (SFNM) for crack resistance are proposed. One reinforced concrete (RC) column with non-seismic details and two columns retrofitted with each different types of proposed method were manufactured. Seismic performance was analyzed for cyclic loading test in which a combined load of compression, bending, shear, and torsion was applied. As a result of the experiment, specimens retrofitted with proposed concrete jacketing method showed 862% of maximum load, 188% of maximum displacement and 1,324% of stiffness compared to non-retrofitted specimen.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.20 no.1
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• pp.127-131
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• 2022

The structural safety of prototype transport and storage containers for very low-level radioactive liquid waste was experimentally estimated for its localization development. Transport containers for radioactive liquid waste have been researched and developed, however, there are no standardized commercial containers for very low-level radioactive waste in Korea. In this study, the structural safety of the designated IP-2 type container capable of transporting and temporarily storing large amounts of very low-level liquid waste, which is generated during the operation and decommissioning of nuclear power plants, was demonstrated. The stacking and drop tests, which were conducted to determine the structural integrity of the container, verified that there was no external leakage of the contents in spite of its structural deformation due to the drop impact. This study shows the effort required for the localization of the technology used in manufacturing transport and storage containers for very low-level radioactive liquid waste, and the additional structural reinforcement of the container in which the commercial intermediate bulk container (IBC) external frame was coupled.

• Structural Engineering and Mechanics
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• v.78 no.4
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• pp.455-471
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• 2021

The present work focuses on experimental and numerical performance of the ferrocement RC walls reinforced with welded steel mesh, expanded steel mesh, fiber glass mesh and tensar mesh individually. The experimental program comprised twelve RC walls having the dimensions of 450 mm×100 mm×1000 mm under concentric compression loadings. The studied variables are the type of reinforcing materials, the number of mesh layers and volume fraction of reinforcement. The main aim is to assess the influence of engaging the new inventive materials in reinforcing the composite RC walls. Non-linear finite element analysis; (NLFEA) was carried out to simulate the behavior of the composite walls employing ANSYS-10.0 Software. Parametric study is also demonstrated to check out the variables that can mainly influence the mechanical behavior of the model such as the change of wall dimensions. The obtained numerical results indicated the acceptable accuracy of FE simulations in the estimation of experimental values. In addition, the strength gained of specimens reinforced with welded steel mesh was higher by amount 40% compared with those reinforced with expanded steel mesh. Ferrocement specimens tested under axial compression loadings exhibit superior ultimate loads and energy absorbing capacity compared to the conventional reinforced concrete one.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.12
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• pp.8-15
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• 2021

Cold forging is a method in which molding is performed at room temperature. It has a high material recovery rate and dimensional precision and produces excellent surface quality, and it is mainly used for the production of bolted or housing products. The lifespan of cold forging molds is generally determined by the wear of the mold, plastic deformation of the mold, and fatigue strength. Cold forging molds are frequently damaged due to fatigue destruction rather than wear and plastic deformation in a high-temperature environment as it is molded at room temperature without preheating the raw material and mold. Based on the results analyzed through FEM, an effective mold structure design method was proposed by analyzing the changes in tensile and compressive stresses on molds according to the number of molds and reinforcement rings and comparing the product geometry and mold stress using three existing mold models.

• Structural Engineering and Mechanics
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• v.85 no.2
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• pp.147-161
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• 2023

Based on the ideas of variational differential quadrature (VDQ) and finite element method (FEM), a numerical approach named as VDQFEM is applied herein to study the large deformations of plate-type structures under static loading with arbitrary shape hole made of functionally graded graphene platelet-reinforced composite (FG-GPLRC) in the context of higher-order shear deformation theory (HSDT). The material properties of composite are approximated based upon the modified Halpin-Tsai model and rule of mixture. Furthermore, various FG distribution patterns are considered along the thickness direction of plate for GPLs. Using novel vector/matrix relations, the governing equations are derived through a variational approach. The matricized formulation can be efficiently employed in the coding process of numerical methods. In VDQFEM, the space domain of structure is first transformed into a number of finite elements. Then, the VDQ discretization technique is implemented within each element. As the last step, the assemblage procedure is performed to derive the set of governing equations which is solved via the pseudo arc-length continuation algorithm. Also, since HSDT is used herein, the mixed formulation approach is proposed to accommodate the continuity of first-order derivatives on the common boundaries of elements. Rectangular and circular plates under various boundary conditions with circular/rectangular/elliptical cutout are selected to generate the numerical results. In the numerical examples, the effects of geometrical properties and reinforcement with GPL on the nonlinear maximum deflection-transverse load amplitude curve are studied.