• Korean Journal of Remote Sensing
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• v.19 no.3
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• pp.223-231
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• 2003

With the negative influences and damage from Asian dust increasing, it's getting important to investigate the climate and soil condition of the source region of Asian dust. There is a high possibility that the desertification and the drastic decrease of plants in China and Mongolia make worse the situation (bad effects of Asian Dust). To detect the movement of Asian dust caused by air circulation, we need to watch the state of the source region to get useful information for the prevention of the dust pollution, and to predict what part of China will become the source region. Therefore, using TOMS aerosol index data, NCEP reanalysis data that is Remote Sensing data from 1981 to 2000 (except 1993~1996, 4 years), for 16 years, examined the relation between the dust occurrence and weather elements. Dust occurrence appeared much in spring season from March to May in study areas. It had a dry climate during that season as follows : relative humidity about 20~40%, temperature about -5~5$^{\circ}C$, precipitation about 33-180 mm, wind speed about 4-10 ms-1. Dust occurrence and weather element annual change in study areas decreased gradually till 1990, but in Gobi desert the incidence of dust occurrence increased since 1997. As a result, found out that the more the precipitation, the less dust occurrence, because the precipitation and surface wind speed had a direct influence on the soil of the source region of dust.

• Computers and Concrete
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• v.24 no.1
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• pp.73-83
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• 2019

Concrete reinforced with fiber reinforced polymer (FRP) bars (FRP-RC) has attracted a significant amount of research attention in the last three decades. A limited number of studies, however, have investigated the effect of bond slip on the performance of FRP-RC columns under eccentric loading. Based on previous experimental study, a finite-element model of eccentrically loaded FRP-RC columns was established in this study. The bondslip behavior was modeled by inserting spring elements between FRP bars and concrete. The improved Bertero-Popov-Eligehausen (BPE) bond slip model with the results of existing FRP-RC pullout tests was introduced. The effect of bond slip on the entire compression-bending process of FRP-RC columns was investigated parametrically. The results show that the initial stiffness of bond slip is the most sensitive parameter affecting the compression-bending performance of columns. The peak bond stress and the corresponding peak slip produce a small effect on the maximum loading capacity of columns. The bondslip softening has little effect on the compression-bending performance of columns. The sectional analysis revealed that, as the load eccentricity and the FRP bar diameter increase, the reducing effect of bond slip on the flexural capacity becomes more obvious. With regard to bond slip, the axial-force-bending-moment (P-M) interaction diagrams of columns with different FRP bar diameters show consistent trends. It can be concluded from this study that for columns reinforced with large diameter FRP bars, the flexural capacity of columns at low axial load levels will be seriously overestimated if the bond slip is not considered.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.34 no.2
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• pp.19-28
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• 2018

The progressive collapse resistance performance of a steel structure constructed using the moment frame with the WUF-B connection and the composite slabs was evaluated. GSA 2003 was adapted for the evaluation. Additionally the structural robustness and the sensitivity against the progressive collapse were analyzed. In the numerical analysis, a reduced model comprised of the beam and spring elements for WUF-B connection was adapted. The composite slab was modeled using the composite-shell element. Instead of the time-consuming dynamic analysis for the effect of the sudden column removal, the equivalent energy-based static analysis was effectively applied. The analysis results showed that the structure was the most vulnerable to in the case of the internal column removal, however it satisfied the chord rotation criterion of GSA 2003 due to the contribution of the composite slab which improved the stiffness of structure. In the robustness evaluation, the structural performance showed more than 2.5 times of the requirement according to GSA 2003, and the structural sensitivity analysis indicated the decrease of 33% of the initial structural performance.

• Journal of radiological science and technology
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• v.44 no.3
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• pp.247-252
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• 2021

As the number of single-person households increases, the consumption of bottled water is increasing. In addition, as the public's interest in radioactivity increases, interest in the field of living radioactivity is also increasing. Since drinking water is an essential element in our daily life, it must be safe from radioactivity. In this study, gamma radiation of drinking spring water was measured and internal exposure dose evaluation was performed to determine its harmfulness. K-40 and uranium-based radioactivity analysis was performed through a high-purity germanium detector, and as a result, drinking water was detected somewhat higher than that of mixing water. Since there is no regulation on the natural radioactivity concentration in Korea, it was compared with the U.S. Environmental Protection Agency Drinking Water Regulations and World Health Organization standard. As a result, there were some items that exceeded standards. Internal exposure was evaluated according to the effective dose formula of ICRP 119. As the result was derived that a maximum of 1.17 mSv per year could be received. This result means that the dose limit for the general public may be exceeded, and it was judged that it is necessary to set an appropriate standard value and present a recommendation value through continuous monitoring in the future.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.34 no.6
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• pp.393-401
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• 2021

In this paper, we proposed a numerical model based on moment-curvature, to evaluate the resistance of reinforced concrete (RC) members subjected to blast loading. To consider the direct shear failure mode, we introduced a dimensionless spring element based on the empirical direct shear stress-slip relation. Based on the dynamic increase factor equations for materials, new dynamic increase factor equations were constructed in terms of the curvature rate for the section which could be directly applied to the moment-curvature relation. Additionally, equivalent bending stiffness was introduced in the plastic hinge region to consider the effect of bond-slip. To verify the validity of the proposed model, a comparative study was conducted against the experimental results, and the superiority of this numerical model was confirmed through comparison with the analytical results of the single-degree of freedom model. Pressure-impulse (P-I) diagrams were produced to evaluate the resistance of members against bending failure and direct shear failure, and additional parametric studies were conducted.

• Structural Engineering and Mechanics
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• v.83 no.6
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• pp.709-727
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• 2022

Fastening systems have a significant role in the response of railway slab track systems. Although experimental tests indicate nonlinear behavior of fastening systems, they have been simulated as a linear spring-dashpot element in the available literature. In this paper, the influence of the nonlinear behavior of fastening systems on the slab track response was investigated. In this regard, a nonlinear model of vehicle/slab track interaction, including two commonly used fastening systems (i.e., RFFS and RWFS), was developed. The time history of excitation frequency of the fastening system was derived using the short time Fourier transform. The model was validated, using the results of a comprehensive field test carried out in this study. The frequency response of the track was studied to evaluate the effect of excitation frequency on the railway track response. The results obtained from the model were compared with those of the conventional linear model of vehicle/slab track interaction. The effects of vehicle speed, axle load, pad stiffness, fastening preload on the difference between the outputs obtained from the linear and nonlinear models were investigated through a parametric study. It was shown that the difference between the results obtained from linear and nonlinear models is up to 38 and 18 percent for RWFS and RFFS, respectively. Based on the outcomes obtained, a nonlinear to linear correction factor as a function of vehicle speed, vehicle axle load, pad stiffness and preload was derived. It was shown that consideration of the correction factor compensates the errors caused by the assumption of linear behavior for the fastening systems in the currently used vehicle track interaction models.

• Structural Engineering and Mechanics
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• v.87 no.6
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• pp.529-540
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• 2023

A novel laminated-hybrid-composite-beam (LHCB) of glass-epoxy infused with flyash and graphene is constructed for this study. The conventional mixture-rule and constitutive-relationship are modified to incorporate filler and lamina orientation. Eringen's non-local-theory is used to include the filler effect. Hamilton's principle based on fifth-order-layer-wise-shear-deformation-theory is applied to formulate the equation of motion. The analogous shear-spring-models for LHCB with multiple-cracks are employed in finite-element-analysis (FEA). Modal-experimentations are conducted (B&K-analyser) and the findings are compared with theoretical and FEA results. In terms of dimensionless relative-natural-frequencies (RNF), the dynamic-response in cantilevered support is investigated for various relative-crack-severities (RCSs) and relative-crack-positions (RCPs). The increase of RCS increases local-flexibility in LHCB thus reductions in RNFs are observed. RCP is found to play an important role, cracks present near the end-support cause an abrupt drop in RNFs. Further, multiple cracks are observed to enhance the nonlinearity of LHCB strength. Introduction of the first to third crack in an intact LHCB results drop of RNFs by 8%, 10%, and 11.5% correspondingly. Also, it is demonstrated that the RNF varies because of the lamina-orientation, and filler addition. For 0° lamina-orientation the RNF is maximum. Similarly, it is studied that the addition of graphene reduces weight and increases the stiffness of LHCB in contrast to the addition of flyash. Additionally, the response of LHCB to moving mass is accessed by appropriately modifying the numerical programs, and it is noted that the successive introduction of the first to ninth crack results in an approximately 40% to 120% increase in the dynamic-amplitude-ratio.

• The Journal of the Acoustical Society of Korea
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• v.41 no.6
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• pp.691-697
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• 2022

In this work, a straightforward component design of a direct current (DC) relay equipped in electric vehicles is discussed. The work aims to provide and evaluate effective measures for reducing high-frequency sound from the DC relay carrying electric power. From the operation experiments for the relay, it is observed that noise is caused by the resonance from the forced vibration by the electromagnetic repulsive force originating at the area of electric contacts with a resonance frequency of around 710 Hz ~ 730 Hz. A finite element model for the relay was established to conduct vibration mode analysis, consisting of stationary and movable contacts and a contact spring. Vibration mode analysis indicates that in the resonance frequency, the movable contact with two-point contacts experiences rotational vibration mode. For the proposed relay with a three-point contact, vibration mode analyses give reasonable results of reducing noise at that frequency. Furthermore, for the fabricated relays with the three-point contact, similar results have been obtained. In conclusion, one can see that the proposed measures provide one of the feasible solutions to the reduction of relay noise.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.1D
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• pp.49-54
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• 2009

The excellent load transfer at transverse joints ensures the high performance of jointed plane concrete pavements(JPCP). Load transfer efficiency(LTE) is affected by dowel-bars, aggregate interlock and types of underlying layers, and these factors have to be modelled adequately for a reasonable analysis of JPCP. Generally, the joint stiffness has been represented by a spring model for the shear transfer by aggregate interlock or dowels. However dowel-bars, aggregate interlock and types of underlying layers have not been considered together in the design of joints. In this study, the joint stiffness that considered those factors was presented by comparing LTE obtained using FWD(Falling Weight Deflectometer) with theoretical results obtained using the finite element analysis. In addition, the effects of temperature and concrete age, on the joint stiffness were investigated.

• Transactions of Materials Processing
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• v.33 no.2
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• pp.103-111
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• 2024

With the increasing global interest in carbon neutrality, the automotive industry is also transitioning to the production of eco-friendly cars, specifically electric vehicles. In order to achieve comparable driving distances to internal combustion engine vehicles, the application of high-capacity battery packs has led to an increase in vehicle weight. To achieve light-weighting and durability requirements of automotive components simultaneously, there is a demand for research on the application of Ultra-High Strength Steel (UHSS). However, when manufacturing chassis components using UHSS, there are challenges related to fracture defects due to lower elongation compared to regular steel sheets, as well as spring-back issues caused by high tensile strength. In this study, a simulated specimen that is not affected by the property changes of four materials was designed to improve formability of the rear cross member, which is the most challenging automotive chassis component. The influence and correlation of material-specific variables were analyzed through finite element analysis (FEA) for each material with tensile strength of 440, 590, 780, and 980 MPa grades, resulting in the development of a predictive equation. To validate the equation, the simulated specimens of 980 MPa grade were produced from the test molds. Then the reliability of the FEA and predictive equation was verified with measured specimen data using a 3D scanner. The results of this study can be proposed to improve the formability of UHSS chassis components in future researches.