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Since liquefaction was first observed in South Korea during the Pohang earthquake, public concerns regarding the seismic stability of major infrastructure have increased substantially. However, the seismic behavior of tunnel shafts, which are an important element of tunnel structures, has not been properly established, especially under liquefiable soil conditions. In this study, 3D numerical modeling with Fast Lagrangian Analysis of Continua in 3 Dimensions (FLAC3D) was performed to predict the dynamic behavior of a vertical tunnel shaft during liquefaction. This study demonstrates key aspects of the dynamic behavior of tunnel shafts by varying important parameters such as the thickness of the liquefiable soil layer and applied seismicity level. Moreover, important dynamic responses such as excess pore pressure generation, the seismic bending moment of the shaft, and lateral displacements are highlighted. Finally, meaningful discussion of the seismic risk analysis based on damage indices is conducted based on the analysis results.
Sun Kwon; Mintaek Yoo. A Study on the Dynamic Behavior of a Vertical Tunnel Shaft Embedded in Liquefiable Ground during Earthquakes. Applied Sciences 2021, 11, 1560 .
AMA StyleSun Kwon, Mintaek Yoo. A Study on the Dynamic Behavior of a Vertical Tunnel Shaft Embedded in Liquefiable Ground during Earthquakes. Applied Sciences. 2021; 11 (4):1560.
Chicago/Turabian StyleSun Kwon; Mintaek Yoo. 2021. "A Study on the Dynamic Behavior of a Vertical Tunnel Shaft Embedded in Liquefiable Ground during Earthquakes." Applied Sciences 11, no. 4: 1560.
This study evaluated the earthquake warning system for high-speed trains using onboard accelerometers instead of expensive seismometers. Onboard accelerometers measure the train data additional to the earthquake acceleration. The measured earthquake acceleration could also be modified by railroad-supporting bridges. To develop the data analysis system, the virtual onboard data sets are synthesized using the train acceleration data and earthquake data. Not only the earthquake acceleration data but also the earthquake responses of bridges are used for the virtual onboard data synthesis. For the analysis of synthesized data, the short-time Fourier Transform (STFT), the wavelet transform (WT), and Wigner–Ville Distribution (WVD) methods have been compared. Results show that WVD provides the best detection performance while the computational costs are large.
Mintaek Yoo; Jae Sang Moon. Comparison of Signal-Analysis Techniques for Seismic Detection System for High-Speed Train Data: Effect of Bridge Structures. Sensors 2020, 20, 6805 .
AMA StyleMintaek Yoo, Jae Sang Moon. Comparison of Signal-Analysis Techniques for Seismic Detection System for High-Speed Train Data: Effect of Bridge Structures. Sensors. 2020; 20 (23):6805.
Chicago/Turabian StyleMintaek Yoo; Jae Sang Moon. 2020. "Comparison of Signal-Analysis Techniques for Seismic Detection System for High-Speed Train Data: Effect of Bridge Structures." Sensors 20, no. 23: 6805.
In this study, for the establishment of a safety evaluation method, non-destructive tests were performed by developing a full-scale model pier and simulating scour on the ground adjacent to a field pier. The surcharge load (0–250 kN) was applied to the full-scale model pier to analyze the load’s effect on the stability. For analyzing the pier’s behavior according to the impact direction, an impact was applied in the bridge axis direction, pier length direction, and pier’s outside direction. The impact height corresponded to the top of the pier. A 1-m deep scour was simulated along one side of the ground, which was adjacent to the pier foundation. The acceleration was measured using accelerometers when an impact was applied. The natural frequency, according to the impact direction and surcharge load, was calculated using a fast Fourier transform (FFT). In addition, the first mode (vibratory), second mode (vibratory), and third modes (torsion) were analyzed according to the pier behavior using the phase difference, and the effect of the scour occurrence on the natural frequency was analyzed. The first mode was most affected by the surcharge load and scour. The stability of the pier can be determined using the second mode, and the direction of the scour can be determined using the third mode.
Myungjae Lee; Mintaek Yoo; Hyun-Seok Jung; Ki Hyun Kim; Il-Wha Lee. Study on Dynamic Behavior of Bridge Pier by Impact Load Test Considering Scour. Applied Sciences 2020, 10, 6741 .
AMA StyleMyungjae Lee, Mintaek Yoo, Hyun-Seok Jung, Ki Hyun Kim, Il-Wha Lee. Study on Dynamic Behavior of Bridge Pier by Impact Load Test Considering Scour. Applied Sciences. 2020; 10 (19):6741.
Chicago/Turabian StyleMyungjae Lee; Mintaek Yoo; Hyun-Seok Jung; Ki Hyun Kim; Il-Wha Lee. 2020. "Study on Dynamic Behavior of Bridge Pier by Impact Load Test Considering Scour." Applied Sciences 10, no. 19: 6741.
Piles installed to increase bearing capacities of super structures in soft soil layers are vulnerable to horizontal loads such as seismic loads. This study aims to verify the stability of piles used for a pile supported slab track system using dynamic centrifuge test and numerical analysis. First of all, validation of the numerical analysis method was performed by comparing the seismic response from the two methods: dynamic centrifuge test and its numerical model. Verifications were also obtained for four different centrifuge test model setups. Numerical models were designed similar to the physical models on a prototype scale. The numerical method solves the dynamic problem by an explicit method in the time-integration stage. The acceleration response of the slab track and bending moment of the pile show good agreement between the two methods. Based on the verified numerical analysis model, the parametric studies for embankment thickness and soft ground stiffness were performed, in addition, the seismic stability of pile supported slab track was evaluated.
Jinsun Lee; Il-Wha Lee; Yun Wook Choo; Mintaek Yoo. Centrifuge and Numerical Simulation of Pile Supported Slab Track System Behavior on Soft Soil under Seismic Loading. KSCE Journal of Civil Engineering 2020, 1 -10.
AMA StyleJinsun Lee, Il-Wha Lee, Yun Wook Choo, Mintaek Yoo. Centrifuge and Numerical Simulation of Pile Supported Slab Track System Behavior on Soft Soil under Seismic Loading. KSCE Journal of Civil Engineering. 2020; ():1-10.
Chicago/Turabian StyleJinsun Lee; Il-Wha Lee; Yun Wook Choo; Mintaek Yoo. 2020. "Centrifuge and Numerical Simulation of Pile Supported Slab Track System Behavior on Soft Soil under Seismic Loading." KSCE Journal of Civil Engineering , no. : 1-10.
As the occurrence of earthquakes is increasing in South Korea, the earthquake early warning (EEW) system becomes indispensable for the protection of high-speed railways. Although the importance of EEW system has been increasing, the number of installed seismic accelerometers in South Korea is not sufficient to provide rapid information. This study uses a stochastic signal analysis technique to utilize the smartphone sensors for the rapid EEW system. From the train vibration data from the low fidelity on-board accelerometer, the virtual earthquake detection data in the train by smartphone sensor has been constructed. To analyze the stochastic characteristics of the constructed data, the short time Fourier transform (STFT) approach has been applied. The study’s overall objective is to offer stochastic approaches that provide effective analysis of the low fidelity sensor data, such as smartphone sensor data, for the rapid EEW system.
Jae Sang Moon; Mintaek Yoo. Development of a Seismic Detection Technology for High-Speed Trains Using Signal Analysis Techniques. Sensors 2020, 20, 3708 .
AMA StyleJae Sang Moon, Mintaek Yoo. Development of a Seismic Detection Technology for High-Speed Trains Using Signal Analysis Techniques. Sensors. 2020; 20 (13):3708.
Chicago/Turabian StyleJae Sang Moon; Mintaek Yoo. 2020. "Development of a Seismic Detection Technology for High-Speed Trains Using Signal Analysis Techniques." Sensors 20, no. 13: 3708.
When an off-road tracked vehicle travels, shearing action and ground sinkage occur on the soil–track interface, severely affecting the tractive performance of the vehicle. Notably, ground sinkage, which is induced by the vehicle’s weight (static sinkage) and longitudinal forces in the direction of travel producing slip (slip sinkage), develops motion resistance, directly restricting the tracked vehicle’s performance. Thus, it is critical to consider both static sinkage and slip sinkage to assess the tractive performance of a tracked vehicle. In this research, model track experiments were conducted to investigate slip sinkage. The experimental results showed that the slip sinkage increased as the slip ratio increased, but the rate of increase decreased. The slip sinkage was found to increase as the density of the ground decreased and imposed vertical load increased. The experimental results were used to calculate normalized slip sinkage, and an empirical equation for slip sinkage in terms of slip ratio was developed. This equation will allow vehicle operators to predict the slip sinkage and associated motion resistance for given soil and vehicle conditions.
Sung-Ha Baek; Gyu-Beom Shin; Seung-Hwan Lee; Mintaek Yoo; Choong-Ki Chung. Evaluation of the Slip Sinkage and its Effect on the Compaction Resistance of an Off-Road Tracked Vehicle. Applied Sciences 2020, 10, 3175 .
AMA StyleSung-Ha Baek, Gyu-Beom Shin, Seung-Hwan Lee, Mintaek Yoo, Choong-Ki Chung. Evaluation of the Slip Sinkage and its Effect on the Compaction Resistance of an Off-Road Tracked Vehicle. Applied Sciences. 2020; 10 (9):3175.
Chicago/Turabian StyleSung-Ha Baek; Gyu-Beom Shin; Seung-Hwan Lee; Mintaek Yoo; Choong-Ki Chung. 2020. "Evaluation of the Slip Sinkage and its Effect on the Compaction Resistance of an Off-Road Tracked Vehicle." Applied Sciences 10, no. 9: 3175.
The dynamic behavior of structures in liquefiable sand exhibits more complicated characteristics, due to the development of excess pore pressure caused by cyclic loading, than that in dry sand. Therefore, it is crucial to accurately predict the soil–pile structure behavior during liquefaction to prevent damage to the structures. In this study, three-dimensional numerical modeling was performed to predict the dynamic soil–pile behavior during liquefaction. To directly simulate pore pressure generation due to soil shear deformation, the Finn liquefaction model was applied and coupled with the Mohr-Coulomb elasto-plastic model. Soil nonlinearity was considered by applying hysteretic damping, and the interface model was applied to simulate various dynamic phenomena between the soil and pile. Simplified continuum modeling was introduced to prevent reflection wave generation and increase analysis efficiency. The applicability of the proposed numerical model was validated using the experimental results. Thereafter, a parametric study was conducted to provide a better understanding of the dynamic behavior of pile foundation during liquefaction. From a series of parametric studies, several important factors that can affect the dynamic pile responses in liquefiable sand were identified. Also, the characteristics of the dynamic soil–pile structure interactive behavior, which are significantly different from each other in liquefied and dry sand, were analyzed qualitatively and quantitatively.
Sun Yong Kwon; Mintaek Yoo. Study on the Dynamic Soil-Pile-Structure Interactive Behavior in Liquefiable Sand by 3D Numerical Simulation. Applied Sciences 2020, 10, 2723 .
AMA StyleSun Yong Kwon, Mintaek Yoo. Study on the Dynamic Soil-Pile-Structure Interactive Behavior in Liquefiable Sand by 3D Numerical Simulation. Applied Sciences. 2020; 10 (8):2723.
Chicago/Turabian StyleSun Yong Kwon; Mintaek Yoo. 2020. "Study on the Dynamic Soil-Pile-Structure Interactive Behavior in Liquefiable Sand by 3D Numerical Simulation." Applied Sciences 10, no. 8: 2723.
A 3D numerical model based on finite-difference approximation was formulated to predict the dynamic soil-pile-structure interaction (SPSI) in dry sand. A non-linear elastic, Mohr–Coulomb plastic soil-constitutive model was adopted for the proposed methodology with a hysteretic damping model which can simulate nonlinear behavior of soil and an interface model which can predict separation and slippage between soil and pile according to the external load condition. Simplified continuum model was used to properly simulate the semi-infinite boundary and improve analysis efficiency. The proposed numerical model was validated by comparison with experimental results performed by Yoo (2013). Thereafter, a parametric study was also carried out to investigate the complex dynamic behavior of pile foundation under varying conditions. It was demonstrated that inertial force induced by superstructure is dominant for dynamic SPSI in dry sand whereas the kinematic force induced by soil deformation is relatively insignificant. Pile peak bending moment occurs at 30% of the pile length when pile length is no longer than 5 T and at about 30% of 5 T (1.6 T) when the pile length is longer than 5 T. The pile head fixity governed the peak bending moment profile of pile and affected the dynamic responses of the system in conjunction with other factors, such as pile rigidity.
Sun Yong Kwon; Mintaek Yoo. Evaluation of Dynamic Soil-Pile-Structure Interactive Behavior in Dry Sand by 3D Numerical Simulation. Applied Sciences 2019, 9, 2612 .
AMA StyleSun Yong Kwon, Mintaek Yoo. Evaluation of Dynamic Soil-Pile-Structure Interactive Behavior in Dry Sand by 3D Numerical Simulation. Applied Sciences. 2019; 9 (13):2612.
Chicago/Turabian StyleSun Yong Kwon; Mintaek Yoo. 2019. "Evaluation of Dynamic Soil-Pile-Structure Interactive Behavior in Dry Sand by 3D Numerical Simulation." Applied Sciences 9, no. 13: 2612.
Load and resistance factor design (LRFD) is a limit state design method that has been applied worldwide. Because the data for determining LRFD factors in Korea has been insufficient, the resistance factors suggested by American Association of State Highway and Transportation Officials (AASHTO) in the US have been used for design in Korea; however, these resistance factors were defined based on the characteristics of the predominant bedrock types in the U.S. As such, it remains necessary to determine resistance factors that reflect the bedrock conditions in Korea. Accordingly, in this study, LRFD resistance factors were determined using 13 sets of drilled shaft load test data. To obtain accurate resistance factors, calibration of the elastic modulus of the drilled shaft and the equivalent load–displacement curve considering the axial load and elastic settlement was conducted. After determining accurate resistance values, a reliability analysis was performed. The resistance factors were determined to be within 0.13–0.32 of the AASHTO factors for the shaft resistance, 0.19–0.29 for the base resistance, and 0.28–0.42 for the total resistance. This is equivalent to being 30–60% of the AASHTO-recommended values for the shaft resistance and 40–60% of the AASHTO-recommended values for the base resistance. These differences in resistance factors were entirely the result of discrepancies in the conditions of the rock in the US and Korea in which the shafts were founded.
Seok Jung Kim; Sun Yong Kwon; Jin Tae Han; Mintaek Yoo. Development of Rock Embedded Drilled Shaft Resistance Factors in Korea based on Field Tests. Applied Sciences 2019, 9, 2201 .
AMA StyleSeok Jung Kim, Sun Yong Kwon, Jin Tae Han, Mintaek Yoo. Development of Rock Embedded Drilled Shaft Resistance Factors in Korea based on Field Tests. Applied Sciences. 2019; 9 (11):2201.
Chicago/Turabian StyleSeok Jung Kim; Sun Yong Kwon; Jin Tae Han; Mintaek Yoo. 2019. "Development of Rock Embedded Drilled Shaft Resistance Factors in Korea based on Field Tests." Applied Sciences 9, no. 11: 2201.
In this study, centrifuge model tests were used to examine the lateral behavior of amonopile embedded in dry sand through cyclic lateral loading tests. The soil specimens used in thetests were dry Jumunjin sand with a relative density of 80% and a friction angle of 38°. A staticloading test was performed once, and cyclic loading tests were performed four times using fourmagnitudes of cyclic load (30%, 50%, 80%, and 120% of static lateral capacity). The experimentalcyclic p‐y curve was obtained through the tests, and the maximum soil resistance points that werefound for each load were used to find the cyclic p‐y backbone curve for each depth. The twovariables which are needed to define the cyclic p‐y backbone curve, i.e., the initial modulus ofsubgrade reaction (kini) and ultimate soil resistance (pu), were suggested as functions of the soil’sphysical properties and the pile. The cyclic p‐y curve of the first cycle and the 100th cycle wereformulated to present the upper limit and lower limit. The suggested cyclic p‐y curve had anoverestimated soil resistance compared with the existing API (1987) method, but the initial modulusof subgrade reaction was underestimated.
Lee; Kyung-Tae Bae; Mintaek Yoo; Bae; Yoo; Myungjae Lee; Il-Wha Lee. Cyclic p-y Curves of Monopiles in Dense Dry Sand Using Centrifuge Model Tests. Applied Sciences 2019, 9, 1641 .
AMA StyleLee, Kyung-Tae Bae, Mintaek Yoo, Bae, Yoo, Myungjae Lee, Il-Wha Lee. Cyclic p-y Curves of Monopiles in Dense Dry Sand Using Centrifuge Model Tests. Applied Sciences. 2019; 9 (8):1641.
Chicago/Turabian StyleLee; Kyung-Tae Bae; Mintaek Yoo; Bae; Yoo; Myungjae Lee; Il-Wha Lee. 2019. "Cyclic p-y Curves of Monopiles in Dense Dry Sand Using Centrifuge Model Tests." Applied Sciences 9, no. 8: 1641.