• Journal of Korean Tunnelling and Underground Space Association
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• v.16 no.6
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• pp.599-614
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• 2014

When tunnelling with TBM (Tunnel Boring Machine), accessibility to tunnel face is very limited because tunnel face is mostly occupied by a bunch of machines. Existing techniques that can predict ground condition ahead of TBM tunnel are extremely limited. In this study, the TBM Resistivity Prediction (TRP) system has been developed for predicting anomalous zone ahead of tunnel face utilizing electrical resistivity. The applicability and prediction accuracy of the developed system has been verified by performing field tests at subway tunnel construction site in which an EPB (Earth Pressure Balanced) shield TBM was used for tunnelling work. The TRP system is able to predicts the location, thickness and electrical properties of anomalous zone by performing inverse analysis using measured resistivity of the ground. To make field tests possible, an apparatus was devised to attach electrode to tunnel face through the chamber. The electrode can be advanced from the chamber to the tunnel face to fully touch the ground in front of the tunnel face. In the 1st field test, none of the anomalous zone was predicted, because the rock around the tunnel face has the same resistivity and permittivity with the rock ahead of tunnel face. In the 2nd field test, 5 m thick anomalous zone was predicted with lower permittivity than that of the rock around the tunnel face. The test results match well with the ground condition predicted, respectively, from geophysical exploration, or directly obtained either from drilling boreholes or from daily observed muck condition.

• Journal of the Korean Geotechnical Society
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• v.28 no.6
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• pp.19-29
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• 2012

Pack micropiles were recently developed to improve pile capacity of general micropiles. Pack micropiles were made by warping thread bar or steel pipe of general micropile by geotexlile pack and grouting inside the pack with pressure. According to the pressure, the boring hole could be enlarged. A series of pile uplift tests were performed on three micropiles. Two out of the three piles were the pack micropiles and the other was the general micropile, in which a thread bar was used in the boring hole. According to the pressure applied to the pack micropiles, the diameter of boring hole was enlarged from 152 mm to 220 mm. Unit skin friction mobilized on side surfaces of micropiles increased with displacement of pile head and reached on a constant value, which represents that the relative displacement between piles (or thread bar) and soils was reached on critical state. And the uplift resistance of pack micropile was higher than that of general micropile. Two reasons can be considered: One is that the frictional surface increases due to enlarging diameter of boring holes and the other is that the unit skin friction could increase due to compressing effect of surrounding soils by soil displacement as much as the enlarging volume of boring hole. The compression effect appeared at deeper layer rather than surface layer. The unit skin friction mobilized on micropiles with small diameter was higher than the ones on large bored piles.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.4
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• pp.597-605
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• 2019

IPM bridge is an integral bridge that can be applied from span 30.0m up to 120.0m, the shape conditions of IPM bridge is also applicable to the rahmen bridge. In this study, to perform the structural analysis of Rahmen bridge and IPM Bridge, the researchers compared the distribution types such as load, moment, and displacement of those bridges. Structural analysis was carried out on four span models ranging from single span bridges to four spans of 120.0 m, based on span length of 30.0 m. Structural analysis was carried out on those bridge with span 30.0m up to 120.0m. The conclusions drawn from this study are as follows. 1) The bending moments were calculated to be large for the Rahmen bridge, and the horizontal displacements were estimated to be large for the IPM bridge. 2) Since the bending moments are derived by the span length rather than the extension of the bridge, the permissible bending moment for the span length should be considered in the design. 3) The pile bent of the IPM bridge did not exceed the plastic moment of the steel pipe pile at 120.0m span, but because the horizontal displacement in the shrinkage direction is close to 25mm, the design considerations are needed. 4) In the actual design, it is important to ensure stability against member forces, so review of the negative moment is most important.

• Journal of the Korea Concrete Institute
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• v.22 no.3
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• pp.325-333
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• 2010

In this study, new moment-resisting precast concrete beam-column joint made up of hybrid steel concrete was developed and tested. This beam-column joint is proposed for use in moderate seismic regions. It has square hollow tubular section in concrete column and connecting plate in precast U-beam. The steel elements in column and beam members were connected using bolt. Furthermore, in order to prevent the premature failure of concrete in hybrid steel-concrete connection, ECC(engineered cementitious composite) was used. An experimental study was carried out investigating the joint behavior subjected to reversed cyclic loading and constant axial compressive load. Two precast beam-column joint specimens and monolithic reinforced concrete joint specimen were tested. The variables for interior joints were cast-in-situ concrete area and transverse reinforcement within the joint. Tests were carried out under displacement controlled reverse cyclic load with a constant axial load. Joint performance is evaluated on the basis of connection strength, stiffness, energy dissipation, and displacement capacity. The test results showed that significant differences in structural behavior between the two types of connection because of different bonding characteristics between steel and concrete; steel and ECC. The proposed joint detail can induce to move the plastic hinge out of the ECC and steel plate. And proposed precast connection showed better performance than the monolithic connection by providing sufficient moment-resisting behavior suitable for applications in moderate seismic regions.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.1
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• pp.714-721
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• 2018

In this study, we investigate a design technology intended to radically increase the buckling strength of vertically curved panels. Recent studies proposed a buckling strength formula which properly reflects the effect on the local plate buckling strength of flat plates when they are stiffened by closed section ribs. Herein, we attempted to quantitatively evaluate this effect on curved panels and to reveal the correlations with the design parameters. The commercial finite element software, ABAQUS, was used to build a three dimensional numerical model and numerical parametric studies were conducted to evaluate the variation of the buckling strength. In the case of flat panels, the local buckling strength of stiffened curved panels increases proportionally with increasing rotational stiffness of the closed-section ribs. After attaining a limiting value, an obvious tendency was found that the local buckling strength of the stiffened curved panel would converge towards a fixed value when the panels are supported along both sides. The parametric studies performed using the influential design parameters confirmed that the estimated partially-restrained curved panel strength is well correlated with the proposed formula.

• Journal of Bio-Environment Control
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• v.26 no.4
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• pp.402-410
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• 2017

The effect of the steel pipe member joint on the design performance of a plastic multi-span greenhouse was analysed through the comparing full-scale experiment and numerical analysis. The design performance of the greenhouse is generally evaluated through numerical analysis, but it is rare to consider the characteristics of the connections or joints of the members. In this study, the effect of the column-gutter beam-rafter-wind break wall joint on the design performance of the whole structure of a plastic multi-span greenhouse was analysed. The numerical results with assuming that the member joint are rigid condition were compared with the full-scale load test results using member joints used in the field. The stiffness of the entire structure was compared using the load-displacement relationship and the change of the load sharing ratio that the main members such as column, rafters, and wind break wall was analysed. The results of the load test were about 40% larger than the numerical result and the member stress was more than twice as large as those of the loaded columns. In order to increase the reliability of the design performance of the greenhouse, it is necessary to develop a numerical analysis model which can consider the characteristics of various joints.

• Journal of radiological science and technology
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• v.32 no.3
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• pp.277-283
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• 2009

It is important to get clinical ultrasonic images of good quality for accurate diagnosis. In this study, it observed the change of ultrasonic images against setting frequency, dynamic range(DR) and type of probes on ultrasonic scanner. In the experiment it evaluated image of LCS (Low Contrast Sensitivity) targets(-15, -6, -3, +3, +6, +15 dB) of a standard ultrasonic test phantoms(539,551, ATS, USA) similar to solid and cystic lesions. Its imaged from convex (C3-7IM) and linear probe (L5-12IM) on SA-9900 (Medison Ltd, Korea) scanner. The images obtained altering the setting parameters which are frequency(gen, pen, res, harmonic) mode and DR($40{\sim}100\;dB$). The quality of images evaluated compare with the nominal LCS value of target and measured LCS value. The results show that there was no significant changing of quality images altering DR 40, 60, 80, 100 dB against frequency in Convex probe but the image being the highest in LCS target at DR 60 dB, harmonic of frequency mode in the -15 dB target close to cystic lesion. In Linear probe, DR 40 dB, harmonic mode at -15 dB LCS target close to nominal value. It discussed necessity of evaluation about ROC(Receiver Operating Characteristic) from the psychological viewpoint and limit of evaluation from quantified images.

• The Journal of the Acoustical Society of Korea
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• v.24 no.5
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• pp.271-281
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• 2005

An electromagnetic type shock wave generator suitable for extracorporeal shock wave therapy has been constructed by employing a solenoid coil. The Property of the shock waves produced by the shock wave generator was evaluated using a needle hydrophone. It was shown that, as the capacitor discharging voltage increased from 8 to 18 kV, the Positive Peak Pressure (P+) of the shock wave increased non-linearly from 10 to 77 Wa. In contrast. the negative peak Pressure (f) varied between -3.2 and -6.8 MPa. had its absolute maximum of -6.9 ma at 14 kV The peak amplitudes P+ measured repeatedly under the same voltage setting varied within $5\;\%$ from mean values and this is very small compared to about $50\;\%$ for electrohydraulic type shock wave generators. It could be observed, from the hydrophone signal recorded over 1 ms. several sequential acoustic impulses representing bubble collapses. namely. acoustic cavitation. induced by the shock wave. A technique based on wavelet transformation was used to accurately measure the time delay between the 1st and 2nd collapse known to be closely related to the shock strength. It was observed that the measured time delay increased almost linearly from 120 to $700\;{\mu}s$ with the shock wave Pressure P+ increasing from 10 to 77 MPa.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.2
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• pp.44-50
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• 2019

The underwater structures of landing pier are not easy to access and it is difficult to check the damage. Lately, typhoons and earthquakes have occurred frequently, which may cause damage to underwater structures of landing pier. In this study, to prevent collapse of underwater structures and to maintain systematically, the application method of FBG sensors and safety evaluation methods were studied. In order to confirm the application of the FBG sensor to the circular steel pipe used as a pile on the landing pier, we conducted laboratory tests and confirmed that the FBG sensor should be applied by welding. As a result of structural analysis of the landing pier structure, the optimal position of FBG sensor confirmed. The stresses on the dead load were calculated by structural analysis, the stresses on the live load were calculated by using the data obtained from the FBG sensor, and then the stress acting on the pile was calculated by adding the two stresses. The calculated stress was compared with the allowable stress to evaluate the safety of the pile. This study was carried out as a basic study to find a way to evaluate the safety of the landing pier in real time.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.2
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• pp.1-10
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• 2021

In this study, a circular pipe can be installed by suction pressure for construction on soft ground with a low-water level. A series of laboratory-scale model tests were conducted in sandy ground to comprehend the suction pressure of the circular pipe in low-water levels. For repeated tests on saturated sandy soil, a container was mounted with three vibration generators on the floor. A repetitive vibration was applied using the vibration system for ground compaction. In the model tests, different diameters and thicknesses on saturated sandy soil with a water depth were considered. The result showed that the suction pressure increased with increasing penetration depth of the circular pipe. Moreover, the suction pressure required to penetrate the pipe decreased with increasing diameter. In the low-water level, the total suction pressure measured at the top lid increased because additional suction pressure is required to lift the water column. On the other hand, this led to a decrease in suction pressure to penetrate the circular pipe because the weight of the water column is applied as a dead load. Therefore, it is necessary to consider the water level to design the required suction pressure accurately.