• Journal of the Earthquake Engineering Society of Korea
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• v.11 no.3 s.55
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• pp.87-96
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• 2007

A new Energy-Dissipating Sacrificial Device (EDSD) is developed for steel plate girders, which can effectively dissipate the energy stored in the structures during seismic actions. To verify the performance of the EDSD, various seismic responses of a sample bridge with the EDSD are analyzed in terms of energy, member forces and deformation. The full scale model tests are conducted to certify the performance of the EDSD when it is applied on existing bridges. Using the improved hysteretic model of the sacrificial member, the seismic analysis for an example bridge is performed. The results show that the proposed EDSD under seismic excitations can significantly decrease the energy stored in the bridge structures and reduce the relative displacements of each superstructure to the ground. The EDSD is also found to function as a structural fuse under strong ground motions, sacrificing itself to absorb the excessive energy. Consequently, economical enhancement of the seismic performance of bridges can be achieved by employing the newly developed energy-dissipating sacrificial device.

• Journal of Korean Tunnelling and Underground Space Association
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• v.11 no.2
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• pp.175-188
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• 2009

When a new tunnel is excavated by the drill and blast method near pre-existing underground structures or tunnels due to the region restricted condition such as urban area, the ground will be relaxed by the excavation. In this case, issues can be created in terms of stability of pre-existing underground structures. One of major factors determining the stability of pre-existing underground structures can be a separation distance between pre-existing underground structures and a newly excavated tunnel. The region of ground relaxation defined by the plastic zone due to new excavation can be varied by separation distance. In this study, in other to estimate an influence of new tunnel excavation in terms of separation distance on the stability of pre-existing large pipelines, two-dimensional scaled model tests using plaster were performed for six models which have a different separation distance, The results show that based on the analysis of induced displacement during tunnel construction, the displacement decreases as the separation distance between large pipeline and new tunnel is increased until the distance is 2.5 times of pipeline diameter. Beyond this point, however, the displacement has become stabilized.

• Journal of the Korean Geotechnical Society
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• v.30 no.5
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• pp.55-65
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• 2014

Most shield tunnels are designed based on the assumption of a undrained condition. But they are operated as drained tunnels in which underground water flows and passes through a drainage facility. Therefore, it is necessary that the drainage condition be considered in the shield tunnel design. In this research, new testing device which can simulate the underground tunnel located below ground water level, was developed. Total stress and pore water pressure were examined and an inflow water into an inner pipe was measured using the testing device. Test results showed that the total stress, which was the sum of effective stress and pore pressure, increased more in an undrained condition and an inflow water into an inner pipe was proportional to the water pressure but inversely proportional to the loading stress. Consequently, if the drainage is considered in the shield tunnel design, the more economical design can be expected because of the stress reduction of the lining.

• Journal of the Korean Geosynthetics Society
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• v.18 no.4
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• pp.129-138
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• 2019

In this study, the rebar rock bolt sensor and GFRP rock bolt sensor, which can be monitored, were embedded in a large model slope, and the behavior of slopes occurred in the early stage of slope collapse was analyzed after performing the field failure test, numerical analysis of the individual element method and finite element method. By comparing and analyzing the field test and numerical analysis results, field applicability of rock slope collapse monitoring on the rebar rock bolt sensor and GFRP rock bolt sensor was investigated. Through this study, smart slope collapse prediction and warning system was developed, which can be used to induce effective evacuation of residents living in the collapsible area by detecting landslide and ground decay precursor information in advance.

• Korean Journal of Agricultural Science
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• v.45 no.1
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• pp.120-127
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• 2018

The rural labor force has gradually been decreasing due to the decrement of the farm population and the increment of the aging population. To solve these problems, it is necessary to develop and study autonomous agricultural machinery. Therefore, analyzing the dynamic behavior of vehicles in an autonomous agricultural environment is important. Until now, most studies on agricultural machinery, especially on ground vehicle dynamics, have been done by field tests. However, these field test methods are time consuming and costly with seasonal restrictions. A research method that can replace existing field test methods by using simulations is needed. In this study, we did basic research analyzing the effect of the travelling speed of a tractor on tire slip using simulation software. A tractor simulation model was developed based on field conditions following a straight path. The simulation was done for three ranges of speed: 20 - 30 km/h (considered the normal travelling speed range), 6 - 8 km/h (considered the plow tillage speed range) and 2 - 4 km/h (considered the rotary tillage speed range). The results of the simulation show that the slip ratio and slip angle values tended to increase as the traveling speed range of the tractor decreased. From the simulation results, it can be concluded that at low tractor speeds, it becomes more difficult to control the vehicle path. In future research, simulations will be done with various work environments such as a curved path as well as with various friction coefficient conditions, and the simulation results will be experimentally verified by applying them to an agricultural tractor.

• Journal of the Korean Institute of Landscape Architecture
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• v.40 no.4
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• pp.127-134
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• 2012

This study was carried out to suggest an experimental base in selecting the cold tolerance of plants. The cold tolerance of the plants were subject to laboratory low temperature treatments and cold processing time were evaluated using both electrolyte leakage and regrowth test. The Logistic model of nonlinear regression analysis was used to evaluate the lethal temperatures that were predicted with the range of $-16.1{\sim}-24.4^{\circ}C$. The order of low-temperature resistance was Sedum reflexum > S. spurium > Ophiopogon japonicus > S. album > S. takevimense > Dianthus chinensis. At the lowest temperature of $13.4^{\circ}C$ the electrolyte leakage value of the plants were lower than 50% demonstrating that they could be applied stably to the roof installed in Korea during the winter with the lowest temperature of $-13.5^{\circ}C$.

• Ocean and Polar Research
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• v.39 no.2
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• pp.159-168
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• 2017

To evaluate the accuracy of UAV photogrammetry for Hyangho coast, eastern coast of Korea, we conducted a field experiment wherein UAV photogrammetry test was repeated three times. Since the Haygho coast is located within a military reservation zone, it was necessary to obtain permission to gain access to the beach and to have sensitive aerial photographs showing military facilities inspected and cropped. The standard deviation of the UAV shooting position between the three tests was less than 1 m, but repeatability of footprint on the ground was low due to wind-driven variability of the UAV pose. Self-calibrating bundle adjustment(SCBA) of implementing non-metric camera calibration was failed in one test. In two tests, the vertical error was twice as large as the pixel size except for those areas that were subject to security inspection and cropping. Given the problems that can arise with regard to the repeatability of the shooting area as well as the possibility of failure with regard to SCBA, we strongly recommend that UAV photogrammetry in coastal areas needs to be repeated at least twice.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.8
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• pp.99-104
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• 2005

The major role of a spacecraft structure is to keep and support the spacecraft safely in all the launch environment, on-orbit condition and during ground-transportation and handling. In a satellite development, a structural and thermal model (STM) is developed for two goals ; demonstration of a structural and a thermal stability. In the structure point of view, STM is used to verify the static/dynamic characteristics of structure in the initial stage of development. In this paper, the structure design/analysis of high resolution LEO earth observation satellite STM is described. Also, a low level sine vibration test is performed and compared to the results of finite element analysis.

• Economic and Environmental Geology
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• v.35 no.5
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• pp.421-428
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• 2002

Lab-scale experiments were conducted to evaluate the effect of surface tension reduction on the extension of the influence zone and the VOC removal efficiency of ground water sparging. A glass column packed with coarse sand was used for VOC removal test at two different surface tensions. A glass column without porous media was also used fer control purpose prior to sand-packed column test. A quasi-two-dimensional glass box model, packed with a sand, was used fer sparging zone tests at different water surface tensions. Surface tension of the aquoues solution used in this study was controlled using sodium dodecyl sulfate (SDS). For the glass, sand column experiments, total amount of air filled in the media increased as surface tension decreased. Toluene (used as VOC in this study) removal rate increased slightly with decreased surface tension f3r both free water column and sand-packed column. Air sparging zone extended up to 500% as the surface tension decreased. Combining the results from two different experiments, VOC removal efficiency is expected to increase significantly with surface tension reduction.

• Journal of the Korean GEO-environmental Society
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• v.9 no.5
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• pp.53-59
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• 2008

The purpose of the study was to evaluate how much gastropod shell effected its properties better than crushed stone as coarse grained materials by comparing friction properties of a contact surface between coarse grained materials and geosynthetics with the large-scale direct shear test. To achieve the purpose, the study compared and analyzed friction coefficient and friction angle by making crushed stone or gastropod shell into model ground and by installing and shearing non-woven fabric or geostrip geosynthetics. As the results of the analysis, crushed stone had the internal friction angle of $33.8^{\circ}$ when its unit weight was $13.7kN/m^3$ and gastropod shell had the internal friction angle of $35.4^{\circ}$ when its unit weight was $5.4kN/m^3$. Also, the friction angle of a contact surface between geosynthetics and crushed stone was larger than the friction angle of a contact surface between geosynthetics and gastropod shell.