• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.9
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• pp.1059-1064
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• 2012

In this study, tensile tests were performed on specimens that simulated the cold-bending and heat-treatment of pipe bends to understand the mechanical properties of pipe bends manufactured by cold-bending followed by heat-treatment for relieving residual stress. The strength and ductility of cold-worked materials were respectively found to be higher and lower than those of the parent material although heat-treatment was carried out to relieve residual stress. In addition, the increase in strength and decrease in ductility were proportional to the applied strain levels for cold-working. It was thus inferred that the intrados and extrados regions of pipe bends that were cold-bended and heat-treated show higher strength and lower ductility compared to the parent straight pipe and that the mechanical properties at the crown region are nearly the same as those of the parent straight pipe.

• Tunnel and Underground Space
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• v.22 no.4
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• pp.284-295
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• 2012

Abrasiveness of rock plays an important role on the wear of rock cutting tools. In this study, Cerchar abrasiveness tests were carried out to assess the abrasiveness of 19 different Korean rocks. Cerchar abrasiveness test is widely used to assess the abrasiveness of rock because of its simplicity and inexpensive cost. This study examines the relationship between Cerchar Abrasiveness Index (CAI) and mechanical properties (uniaxial compressive strength, Brazilian tensile strength, Young's modulus, Poisson's ratio, porosity, shore hardness of rock), and the effect of quartz content, equivalent quartz content, which was obtained from XRD analysis. As a result of test, CAI was more influenced by petrographical properties than by the bonding strength of the matrix material of rock. CAI prediction model which consisted of UCS and EQC was proposed. CAI decreased linearly with the hardness of the steel pin. Numerical analysis was performed using Autodyn-3D for simulating the Cerchar abrasiveness test. In the simulations, most of pin wear occurred during the initial scratching distance, and CAI increased with the increase of normal loading.

• Tunnel and Underground Space
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• v.18 no.2
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• pp.107-117
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• 2008

In this study, the failure and deformation characteristics of steel fiber reinforced shotcrete (SFRS) which is a primary tunnel support was investigated to find out ground-support mutual behavior. To this end, a mock-up of a tunnel was made and experimented with the conditions of lateral earth pressure coefficient 0.5 and 1.0. During the tests, 11 hydraulic cylinders were used for loading. for better simulation of the lateral earth pressure effect, these cylinders were controlled separately by two groups; crown and side wall. Meanwhile, the deformation of shotcrete was measured by 11 LVDTs. Backfill material was also used fur better load transfer from hydraulic cylinders to shotcrete. For the validation of the mock-up test results, 3D numerical analysis is carried out. To do numerical analysis under the same condition as a mock-up test, the load history curve which was obtained during the test was tried to be simulated using an individual FISH routine in the numerical analysis.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.8
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• pp.759-764
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• 2017

This research investigated the hygrothermal effect on the strength of bolt jointed section and moisture contents of composites exposed to hygrothermal environment for composite aircraft radome. The decrease in strength in the test environment is mainly attributed to the change in the material properties of the matrix due to temperature and moisture. The composite specimens were tested in three different environmental conditions: RTD(room temperature and dry), CTD(cold temperature and dry) and ETW(elevated temperature and wet). The failure mode of the bolt jointed composite specimens were studied using tests and finite element analysis. Finite element analysis reasonably predicted the failure load and mode of the joints. A reliability-based design was carried out for the bolt jointed composites of radome.

• Journal of the Korean Geotechnical Society
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• v.33 no.5
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• pp.15-23
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• 2017

The evaluation of earthquake load on the surface is very important factor for the seismic reinforcement of existing building, and the magnitude of earthquake load depends on a shear wave velocity profile of soil under a building. To determine a shear wave velocity profile under a existing building, test method should be able to determine a reliable shear wave velocity profile under conditions such as heavy background noise and the small test area, and be sensitive to the variation of material property. In this research, HWAW (Harmonic Wavelet Analysis of Waves) method is applied to determine a shear wave velocity profile under a existing building. In this paper, through numerical simulations and field tests, the feasibility of the proposed method was shown.

• Journal of the Korean GEO-environmental Society
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• v.6 no.1
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• pp.23-31
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• 2005

The "Silt Pond" is 180 hectares in size and contained ultra soft slurry-like soil varying between 3 to 20 meters in thickness. Reclamation works in the Silt Pond commenced in the mid of 1990s. A considerable amount of subsurface investigation inclusive of sampling, field vane and density logging tests were carried out prior to the reclamation of the Silt Pond. Since material in the Silt Pond is extremely soft, filling was done by spreading sand with high water content in thin and equal thickness lifts, allowing the stability of the slurry-like foundation. Despite the extreme care taken, failures occurred during the sand spreading phase. A large piece of high strength geotextile measuring $900m{\times}700m$ was placed to strengthen the slurry like soil foundation at locations where the ultra-soft soil was found to be exposed. Following the remedial works, the Silt Pond was again reclaimed by sand spreading up to +4.0m CD. The success of the reclamation was confirmed by marine CPT profiling.

• Journal of Ocean Engineering and Technology
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• v.27 no.5
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• pp.93-98
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• 2013

Fuel gas is an important energy source that is being increasingly used because of the convenience and clean energy provided. Natural gas is supplied to consumers safely through an underground gas-pipe network made of a polyethylene material. In electrofusion, which is one of the joining methods used, copper wire is used as the heating wire. However, it takes a long time for fusion to occur because the electrical resistance of copper is low. In this study, therefore, electrofusion was conducted by replacing the copper heating wire with carbon fiber to reduce the fusion time and improve the production when joining large pipes. Fusion and tensile tests were performed after the electrofusion joint was made in the polyethylene pipe using carbon fiber. The results showed that the fusion time was shorter and the temperature inside the pipe was higher with an increase in the current value. The ultimate tensile strength of specimens was higher than that of virgin polyethylene pipe, except for polyethylene pipes joined using a current of 0.8 A. The best fusion current value was 0.9 or 1.0 A because of the short fusion time and lack of transformation inside the pipe. Thus, it was shown that carbon fiber can be used to replace the copper heating wire.

• Journal of the Geological Society of Korea
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• v.54 no.6
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• pp.605-614
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• 2018

For physical experiments like analogue modeling that designed for studying geological deformation, reproducibility of the deformation is important to guarantee the reliability of the experiment. In this study, the normal fault generated by extensional stress is benchmarked using a sand box model. The scaling factors for the modeling test are considered and the experiments are conducted by setting the appropriate material, extensional stress, and boundary condition in the same way as in a benchmark experiment. In addition, a large centrifuge facility is used to vary the centrifugal acceleration and extension rate in the same sized model to account for the scaling factors of the physical quantity during extensional behavior. At 1 g benchmark condition and a centrifugal field at 10 g, a constant rate of the extensional stress is implemented and the topographic evolution is reliably measured. In this study, the reliability and applicability of large centrifuge model tests are evaluated for formulating experiments designed to study geological deformation.

• Journal of The Korean Society of Agricultural Engineers
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• v.61 no.6
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• pp.103-110
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• 2019

The purpose of this study is to investigate the reaction mechanism of soil and bacteria solution by various mixing ratios. For this purpose, in order to understand the reaction mechanisms of microorganisms and weathered granite soil, the tests were carried out under various mixing ratios additives such as soil, bacteria solution, $Ca(OH)_2$ and fixture. The test results from this study are summarized as follows. Firstly, the reaction between the bacteria solution and fixture produced a precipitate called vaterite, a type of silicate and calcium carbonate. Secondly, as a result of SEM analysis, the resulting precipitates generated from the test results using the specimens with various mixing ratios except SW condition and the irregular spherical microscopic shapes were formed in the size of $150{\mu}m$ to $20{\mu}m$. In addition, it can be seen that the bacteria solution and the fixture reacted between the granules to form an adsorbent material layer on the surface, and the microorganisms had a biological solidifying effect when the pores are combined into hard particles. Finally, The XRD analysis of the sediment resulting from the reaction between the microorganism and the deposit control agent confirmed the presence of a type of calcium carbonate ($CaCO_3$) vaterite, which affects soil strength formation, as well as silicate($SiO_2$).

• Steel and Composite Structures
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• v.33 no.4
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• pp.595-614
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• 2019

In cold-formed steel (CFS) structures, such as trusses, transmission towers and portal frames, the use of back-to-back built-up CFS unequal angle sections are becoming increasingly popular. In such an arrangement, intermediate welds or screw fasteners are required at discrete points along the length, preventing the angle sections from buckling independently. Limited research is available in the literature on axial strength of back-to-back built-up CFS unequal angle sections. The issue is addressed herein. This paper presents an experimental investigation on both the welded and screw fastened back-to-back built-up CFS unequal angle sections under axial compression. The load-axial shortening and the load verses lateral displacement behaviour along with the deformed shapes at failure are reported. A nonlinear finite element (FE) model was then developed, which includes material non-linearity, geometric imperfections and modelling of intermediate fasteners. The FE model was validated against the experimental test results, which showed good agreement, both in terms of failure loads and deformed shapes at failure. The validated FE model was then used for the purpose of a parametric study to investigate the effect of different thicknesses, lengths and, yield stresses of steel on axial strength of back-to-back built-up CFS unequal angle sections. Five different thicknesses and seven different lengths (stub to slender columns) with two different yield stresses were investigated in the parametric study. Axial strengths obtained from the experimental tests and FE analyses were used to assess the performance of the current design guidelines as per the Direct Strength Method (DSM); obtained comparisons show that the current DSM is conservative by only 7% on average, while predicting the axial strengths of back-to-back built-up CFS unequal angle sections.