• Journal of Korean Society of Steel Construction
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• v.24 no.3
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• pp.349-360
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• 2012

This paper describes a detailed assessment of the structural safety, serviceability, capacity rating and long-term performance of a glass fiber-reinforced polymer (GFRP) slab bridge superstructure. This first all-GFRP slab bridge was installed in Korea on May 2002. The GFRP slab bridge is a simply supported, its length is 10.0 m, and is designed to carry two-lane traffic and has an overall width of 8.0m. The GFRP slab bridge is a sandwich structure with a corrugated core, fabricated by hand lay-up process with E-glass fibers and vinyl ester resins. The assessment of long-term performance for the GFRP slab bridge in 2004, 2011 includes a field load testing identical to that performed in 2002. The assessment indicates that the GFRP slab bridge has no structural problems and is structurally performing well in-service as expected. The assessment may provide a baseline data for the capacity ratings assessment of the GFRP slab bridge and also serve as part of a long-term performance of all-GFRP bridge superstructure.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.22 no.7
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• pp.949-955
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• 2018

Hardware-in-the-loop (HIL) simulation is a technique that can be employed for developing and testing complex real-time embedded systems. HIL simulation provides an effective platform for verifying power management system (PMS) performance of liquefied natural gas carriers, which are high value-added vessels such as offshore plants. However, HIL tests conducted by research institutes, including domestic shipyards, can be protracted. To address the said issue, this study proposes a field programmable gate array (FPGA) based PMS-HIL simulator that comprises a power supply, consumer, control console, and main switchboard. The proposed HIL simulation platform incorporated actual equipment data while conducting load sharing PMS tests. The proposed system was verified through symmetric, asymmetric, and fixed load sharing tests. The proposed system can thus potentially replace the standard factory acceptance tests. Furthermore, the proposed simulator can be helpful in developing additional systems for vessel automation and autonomous operation, including the development of energy management systems.

• Journal of the Korean Geotechnical Society
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• v.21 no.5
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• pp.187-196
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• 2005

Since the allowable bearing capacities of piles in weathered/fractured rock are mainly governed by settlement, the load-displacement behavior of pile should be known accurately. To predict pile head settlement at the design stage, the exact understanding of the load-transfer mechanisms is essential. Therefore, in this research, the load-transfer mechanism of drilled shaft socketed into weathered rock was investigated. For the investigation, five cast-in-place concrete piles with diameters of 1,000 mm were socketed into weathered gneiss. The static axial load tests and the load-transfer measurements were performed to examine the axial resistant behavior of the piles. A comprehensive field/laboratory testing program on weathered rock at the Held test sites was also performed to describe the in situ rock mass conditions quantitatively. And then, the effect of rock mass condition on the load transfer mechanism was investigated. The f-w (side shear resistance-displacement) curve of the pile in moderately weathered rock reached to yielding point at a for millimeter displacements, and after yielding point, the rate of resistance increment dramatically decreased. However, the f-w curve in the highly/completely weathered rock did not show the obvious yielding point, and the resistance gradually increased showing the hyperbolic pattern until relatively high displacement (>15 mm). The q-w (end bearing resistance-displacement) curves showed linear response at least until the base displacement of approximately 10 mm, regardless of rock mass conditions.

• Journal of the Korean Geotechnical Society
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• v.21 no.9
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• pp.13-23
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• 2005

The prefabricated vertical drains (PVDs) are one of the most widely used techniques to accelerate the consolidation of soft clay deposits and dredged soil. Discharge capacity is one of the factors affecting the behavior of PVDs. In the field, a PVD is confined by clay or dredged soil, which is normally remolded during PVD installation. Under field conditions, soil particles may enter the PVD drainage channels, and the consolidation settlement of the improved subsoil may cause 131ding of the PVD. These factors will affect the discharge capacity of the PVDs. In this study an experimental study was carried out to estimate the discharge capacity of three different types of PVDs by utilizing the large-scale laboratory model testing and small-scale laboratory model testing equipments. The several factors such as confinement condition (confined by soft marine clay or dredged soil) and variations of the discharge capacity were studied with time under soil specimen confinement, The test results indicated that discharge capacity decreases with increasing load, time, and hydraulic gradient. With load application, the cross-sectional area of the drainage channel of PVD decreases because the filter of PVD is pressed into the core. The discharge capacity of the soft marine clay-confined PVDs is much lower than that of the dredged soil-confined PVDs.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.24 no.1
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• pp.79-85
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• 2011

Bridge Weigh-in-Motion(BWIM) system calculates a travelling vehicle's weight without interruption of traffic flow by analyzing the signals that are acquired from various sensors installed in the bridge. BWIM system or data accumulated from the BWIM system can be utilized to development of updated live load model for highway bridge design, fatigue load model for estimation of remaining life of bridges, etc. Field test with moving trucks including various load cases should be performed to guarantee successful development of precise BWIM system. In this paper, a numerical simulation technique is adopted as an alternative or supplement to the vehicle traveling test that is indispensible but expensive in time and budget. The constructed numerical model is validated by comparison experimentally measured signal with numerically generated signal. Also vehicles with various dynamic characteristics and travelling conditions are considered in numerical simulation to investigate the variation of bridge responses. Considered parameters in the numerical study are vehicle velocity, natural frequency of the vehicle, height of entry bump, and lateral position of the vehicle. By analyzing the results, it is revealed that the lateral position and natural frequency of the vehicle should be considered to increase precision of developing BWIM system. Since generation of vehicle travelling signal by the numerical simulation technique costs much less than field test, a large number of test parameters can effectively be considered to validate the developed BWIM algorithm. Also, when artificial neural network technique is applied, voluminous data set required for training and testing of the neural network can be prepared by numerical generation. Consequently, proposed numerical simulation technique may contribute to improve precision and performance of BWIM systems.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.12
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• pp.1035-1044
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• 2013

Because of the high specific stiffness and strength inherent in the sandwich structure composed of facesheet that resists in-plane loads and a core that resists out-of-plane loads, it is often used for large and light-weighted structures. However, inevitably the increased flexibility allows greater deformation-based disturbances in the structures. Thus, it is necessary to analyze the structural safety. To obtain more accurate analytical results, the input disturbances must more closely simulate real load conditions; to improve accuracy, non-linear elements such as gust effects were considered. In addition, the structural safety was analyzed for the iso-grid sandwich panel structure using fluid-structure interactions. For a more realistic simulation, flow velocity fields, which consider the effects of irregular gust fluctuation, were generated and the coupled field was analyzed by mapping the pressure and displacement.

• Journal of the Korean Geotechnical Society
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• v.32 no.10
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• pp.67-79
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• 2016

Waveform micropile is an advanced construction method that combined the concept of conventional micropile with jet grouting method. This new form of micropile was developed to improve frictional resistance, which consequently leads to achieving higher bearing capacity and cost efficiency. Two field tests were conducted to examine the field applicability as well as to verify the effects of bearing capacity enhancement. In particular, waveform micropile construction using jet grouting method was performed to evaluate the viability of waveform micropile installation. After testing, the surrounding ground was excavated to check the accomplishment on the shape of waveform micropile. The result showed that waveform micropile can be installed by adjusting the grouting time and pressure. In the loading tests, waveform micropile's bearing capacity increased by 1.4 to 2.3 times depending on their shapes when compared with conventional micropile. Overall results clearly demonstrated that waveform micropile is an enhanced construction method that can improve bearing capacity.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.21 no.2
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• pp.349-353
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• 2012

As the world wind energy market grows rapidly, the productions of wind power generation equipment have recently increased, but manufacturers are not able meet this requirement. Particularly offshore wind energy industry is one of the most popular renewable energy sectors. To generalize welding processes, the welding automation is considered for steel structure manufacturing in offshore wind energy to get high quality and productivity. Welding technology in construction of the wind towers is depended on progress productivity. In addition, the life of wind tower structures should be considered by taking account of the natural weathering and the load it endures. The root passes are typically deposited using Gas Tungsten Arc Welding(GTAW) with a specialized backing gas shield. Not only the validation consists of welders experienced in determining the welding productivity of the baseline welding procedure, but also the standard testing required by the ASME section IX and API1104 codes, toughness testing was performed on the completed field welds. This paper presents the welding characteristics of the root-pass welding of high tensile steel in manufacturing of offshore wind tower. Based on the result from welding experiments, optimal welding conditions were selected after analyzing correlation between welding parameters(peak current, background current and wire feed rate) and back-bead geometry such as back-bead width(mm) and back-bead height performing root-pass welding experiment under various conditions. Furthermore, a response surface approach has been applied to provide an algorithm to predict an optimal welding quality.

• Journal of the Korean Society for Nondestructive Testing
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• v.32 no.1
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• pp.27-33
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• 2012

Photoelasticity is a technique of experimental methods and has been widely used in various domains of engineering to determine the stress distribution of structures. Without complicated mathematical formulation, this technique can conveniently provide a fairly accurate whole-field stress analysis for a mechanical structure. Here, stress distribution around an inclined crack tip of finite-width plate is studied by 8-step phase-shifting method. This method is a kind of photoelastic phase-shifting techniques and can be used for the determination of the phase values of isochromatics and isoclinics. According to stress-optic law, the stress distribution could be obtained from fringe patterns. The results obtained by polariscope arrangement combined with 8-step method and ABAQUS FEM simulations are compared with each other. Good agreement between them shows that 8-step phase-shifting method is reliable and can be used for determination of stress by experiment.

• Wind and Structures
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• v.34 no.2
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• pp.199-213
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• 2022

The current study investigates the dynamic effects in the tornado-structure response of an aeroelastic self-supported lattice transmission tower model tested under laboratory simulated tornado-like vortices. The aeroelastic model is designed for a geometric scale of 1:65 and tested under scaled down tornadoes in the Wind Engineering, Energy and Environment (WindEEE) Research Institute. The simulated tornadoes have a similar length scale of 1:65 compared to the full-scale. An extensive experimental parametric study is conducted by offsetting the stationary tornado center with respect to the aeroelastic model. Such aeroelastic testing of a transmission tower under laboratory tornadoes is not reported in the literature. A multiaxial load cell is mounted underneath the base plate to measure the base shear forces and overturning moments applied to the model in three perpendicular directions. A three-axis accelerometer is mounted at the level of the second cross-arm to measure response accelerations to evaluate the natural frequencies through a free-vibration test. Radial, tangential, and axial velocity components of the tornado wind field are measured using cobra probes. Sensitivity analyses are conducted to assess the variation of the structural dynamic response associated with the location of the tornado relative to the lattice transmission tower. Three different layouts representing the change in the orientation of the tower model relative to the components of the tornado-induced loads are considered. The structural responses of the aeroelastic model in terms of base shear forces, overturning moments, and lateral accelerations are measured. The results are utilized to understand the dynamic response of self-supported transmission towers to the tornado-induced loads.