• KSCE Journal of Civil and Environmental Engineering Research
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• v.42 no.6
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• pp.825-836
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• 2022

Micropiles can be used to support additional load in extended building structures. However, their use brings about a risk of exceeding the bearing capacity of existing piles. In this study, pre-compression was applied to distribute the load of an existing building to micropiles, and an indoor loading test was performed to confirm the structural applicability of a wedge-type anchorage device designed to improve its capacity. According to the test results, the maximum strain of the anchorage device was 0.63 times that of the yield strain, and the amount of slip generated at the time of anchorage was 0.11 mm, satisfying structural standards. In addition, using MIDAS GTS, a geotechnical finite element analysis software, the effect of the size of the pre-compression, the thickness of the soil layer, and the ground conditions around the tip on the reaction force of the existing piles and micropiles were analyzed. From the numerical analysis, as the size of the pre-compression load increased, the reaction force of the existing pile decreased, resulting in a reduction rate of up to 36 %. In addition, as the soil layer increased by 5 m, the reduction rate decreased by 4 %, and when the ground condition at the tip of the micropile was weathered rock, the reduction rate increased by 14 % compared with that of weathered soil.

• Korean Journal of Applied Biomechanics
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• v.33 no.3
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• pp.110-117
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• 2023

Objective: The purpose of this study was to find out kinematic and kinetic differences the lower extremity joint according to the landing type during vertical jump movement after jump landing, and to present an efficient landing method to reduce the incidence of injury in youth players. Method: Total of 24 Youth players under Korean Sport and Olympic Committee, who used either heel contact landing (HCG) or toe contact landing (TCG) participated in this study (HCG (12): CG height: 168.7 ± 9.7 cm, weight: 60.9 ± 11.6 kg, age: 14.1 ± 0.9 yrs., career: 4.3 ± 2.9 yrs., TCG height: 174.8 ± 4.9 cm, weight: 66.9 ± 9.9 kg, age 13.9 ± 0.8 yrs., career: 4.7 ± 2.0 yrs.). Participants were asked to perform jump landing consecutively followed by vertical jump. A 3-dimensional motion analysis with 19 infrared cameras and 2 force plates was performed in this study. To find out the significance between two landing styles independent t-test was performed and significance level was set at .05. Results: HCG showed a significantly higher dorsi flexion, extension and flexion angle at ankle, knee and hip joints, respectively compared with those of TCG (p<.05). Also, HCG revealed reduced RoM at ankle joint while it showed increased RoM at knee joint compared to TCG (p<.05). In addition, HGC showed greater peak force, a loading rate, and impulse than those of TCG (p<.05). Finally, greater planta flexion moment was revealed in TCG compared to HCG at ankle joint. For the knee joint HCG showed extension and flexion moment in E1 and E2, respectively, while TCG showed opposite results. Conclusion: Compared to toe contact landing, the heel contact landing is not expected to have an advantage in terms of absorbing and dispersing the impact of contact with the ground to the joint. If these movements continuously used, performance may deteriorate, including injuries, so it is believed that education on safe landing methods is needed for young athletes whose musculoskeletal growth is not fully mature.

• Journal of the Korean Geotechnical Society
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• v.39 no.5
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• pp.27-40
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• 2023

A pile is a structural element that is used to transfer external loads from superstructures and has been widely utilized in construction fields all over the world. The method of installing a pile into the ground should be selected based on geotechnical conditions, location, site status, environmental factors, and construction costs, among others. It can be divided into two types: direct hammering and preboring. The direct hammering method installs a pile into the bearing layer, such as rock, using a few types of hammer, generating a considerable amount of pile driving-induced vibration. The vibration from pile driving influences adjacent structures and the ground; therefore, quantitatively investigating the effects of vibration is inevitably required. In this study, two-dimensional dynamic numerical modeling and analysis are performed using the finite difference method to investigate the influence on the adjacent slope, including temporary supporting system. Time-dependent loading induced by pile driving is estimated and used in the numerical analysis. Consequently, large surface displacement is estimated due to surface waves and less wave deflection, and refraction at the surface. The total displacement decreases with the increase of the distance from the source. However, lateral displacement at the top of the slope shows a larger value than vertical displacement, and the overall displacement tends to be concentrated near the face of the slope.

• 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.16 no.3
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• pp.31-39
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• 2017

Applicability of Skempton's and Hansbo's equation for estimating strength incremental ratio of Korean marine clayey soil was analyzed. These empirical equations have been commonly applied to design soft ground improvement by, especially, staged loading method. Strength incremental ratios proposed by Skempton (1954, 1957) and Hansbo (1957) using field vane tests(FVTs), measured in Scandinavia depends on plasticity index and liquid limit. Although lean clay in Scandinavia can be classified as clay based on USCS, this soil contains no clay mineral because it was produced by the glacial grinding of rock, sometimes, called rock flour. On the contrary, plasticity indices of Korean marine clayey soils increase linearly with the percentage of clay fraction (% finer than $2{\mu}m$ by weight). Except for strength incremental ratios using $q_u/2$ values in the case of soils having a low plasticity, such as Incheon, Hwaseong and Gunsan soils, these values are in the range of 0.25 to 0.35, independently of the plasticity index, $I_p$.

• Journal of the Korean Recycled Construction Resources Institute
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• v.2 no.4
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• pp.354-359
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• 2014

The objective of this study is to examine the fatigue behavior in compression of normal-weight and lightweight concrete mixtures with high volume supplementary cementitious material(SCM). The selected binder composition was 30% ordinary portland cement, 20% fly-ash, and 50% ground granulated blast-furnace slag. The targeted compressive strength of concrete was 40 MPa. For the cyclic loading, the constant maximum stress level varied to be 75%, 80%, and 90% of the static uniaxial compressive strength, whereas the constant minimum stress level was fixed at 10% of the static strength. The test results showed that fatigue life of high volume SCM lightweight concrete was lower than the companion normalweight concrete. The value of the fatigue strain at the maximum stress level intersected the descending branch of the monotonic stress-strain curve after approximately 90% of the fatigue life.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• v.y2005m4
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• pp.99-105
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• 2005

To evaluate structural safety factor of the jet vane for the thrust deflection system under the dynamic pressure and very high temperature($2700^{\circ}C$) of the combustion gas flow, the high temperature tension tests of refractory metals and 3-D nonlinear numerical simulations are performed. Through the analysis of high temperature structural behavior for jet vane, the structural safety of jet vane is evaluated, and numerical results are compared with static pound tests of jet vanes. It has been found that most of structural and thermal loading is concentrated on the vane shaft which worked as safe under $1400^{\circ}C$. From the comparison of static ground tests and numerical results, the evaluation criterion using the vane load and shaft displacement is more useful to estimate the structural safety than using the equivalent stress.

• Journal of the Korea Convergence Society
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• v.9 no.8
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• pp.301-309
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• 2018

The aim of this study was to investigate the relationship between the neurocognitive ability and the risk factors of non-contact anterior cruciate ligament injuries during landing in female recreational athletes. Thirty-two female athletes participated in computerized neurocognition test and motion analysis for drop vertical jump. Pearson's linear correlation analysis was performed to analyze the relationship between the raw scores of neurocognition test and biomechanical variables including 3D joint angle, moment, power, vertical ground reaction force, loading rate, and support time. There were correlations between the scores of neurocognition test and biomechanical variables as high the neurocognition score, it also increase landing strategies were used to maintain posture of the lower extremity. Therefore, the neurocognitive test might be used as a good screening method to detect the risk factors before injury.

• Journal of the Korean Geotechnical Society
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• v.35 no.11
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• pp.63-74
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• 2019

Numerical liquefaction model and response history analysis procedure are verified based on dynamic centrifuge test results. The test was a part of the Liquefaction Experiments Analysis Project (LEAP). The model ground was formed inside of rigid box by using the submerged Ottawa F65 sand with a relative density of 55% and 5° of surface inclination. A tapered sinusoidal wave with a frequency of 1 Hz was applied to the base of the model box. Numerical analyses were performed by two dimensional finite difference method in prototype scale. The soil is modeled to show hysteretic behavior before shear failure, and Mohr-Coulomb model is applied for shear failure criterion. Byrne's liquefaction model was applied to track the changes in pore pressure due to cyclic loading after static equilibrium. In order to find an appropriate flow condition for the liquefaction analysis, numerical analyses were performed both in drained and undrained condition. The numerical analyses performed under the undrained condition showed good agreement with the centrifuge test results.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.8 no.1
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• pp.77-85
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• 1988

A stochchastic analysis procedure of generating floor response spectra for proportionally damped linear systems subject to earthquake loading is presented. Theories of random vibration and mode acceleration method are used in the formulation of governing equations. The structure-oscillator interaction is not considered. It is assumed that the input motions and oscillator responses are stationary Gaussian processes with mean zero. The nonstationary characteristics of earthquake motion are incorporated in the peak factor which is based on Vanmarcke's theory. Floor response spectra for both resonance and non-resonance cases are calculated under the assumption that the peak factors for structure and oscillator are equal to that for ground response spectrum. The validity of this method is demonstrated by comparing the results obtained by proposed method with those by time history analyses. The results obtained by this method are conservative and accurate with tolerable precision. This method saves much computing time compared with time history analysis method.