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유민택,백민철,이일화,이진선,Yoo, Mintaek,Back, Mincheol,Lee, Ilhwa,Lee, Jinsun 한국지진공학회 2017 한국지진공학회논문집 Vol.21 No.5
Dynamic numerical simulation of pile-supported slab track system embedded in a soft soil and embankment was performed. 3D model was formulated in a time domain to consider the non-linearity of soil by utilizing FLAC 3D, which is a finite difference method program. Soil non-linearity was simulated by adopting the hysteric damping model and liner elements, which could consider soil-pile interface. The long period seismic loads, Hachinohe type strong motions, were applied for estimating seismic respose of the system, Parametric study was carried out by changing subsoil layer profile, embankment height and seismic loading conditions. The most of horizontal permanent displacement was initiated by slope failure. Increase of the embedded height and thickness of the soft soil layer leads increase of member forces of PHC piles; bending moment, and axial force. Finally, basic guidelines for designing pile-supported slab track system under seismic loading are recommended based on the analysis results.
3차원 수치 모델을 이용한 건조사질토 지반-말뚝-구조물 동적 상호작용의 매개변수 연구
유민택,권선용 한국지반공학회 2016 한국지반공학회논문집 Vol.32 No.9
Parametric studies for various site conditions by using 3d numerical model were carried out in order to estimatedynamic behavior of soil-pile-structure system in dry soil deposits. Proposed model was analyzed in time domain usingFLAC3D which is commercial finite difference code to properly simulate nonlinear response of soil under strongearthquake. Mohr-Coulomb criterion was adopted as soil constitutive model. Soil nonlinearity was considered by adoptingthe hysteretic damping model, and an interface model which can simulate separation and slip between soil and pilewas adopted. Simplified continuum modeling was used as boundary condition to reduce analysis time. Also, initial shearmodulus and yield depth were appropriately determined for accurate simulation of system’s nonlinear behavior. Parametricstudy was performed by varying weight of superstructure, pile length, pile head fixity, soil relative density with proposednumerical model. From the results of parametric study, it is identified that inertial force induced by superstructure isdominant on dynamic behavior of soil-pile-structure system and effect of kinematic force induced by soil movementwas relatively small. Difference in dynamic behavior according to the pile length and pile head fixity was also numericallyinvestigated.
그라우팅 기법을 활용한 PHC 파일 기초의 지지력 증강 효과 연구
유민택,이수형,김석중,최영태,박정준 한국지반공학회 2017 한국지반공학회논문집 Vol.33 No.6
In this research, post grouting methods were applied on PHC piles, and static load tests were conducted to confirmthe effect of post grouting on bearing capacity enhancement of PHC piles. Grouting pressures of 1.9 MPa and 3.5 MPawere applied, and bearing capacities of grouted piles were compared with that of non-grouted pile. From the static loadtest results, the bearing capacities of grouted piles were about 3 times higher than that of non-grouted pile. In addition,the design efficiency (allowable bearing capacity/nominal bearing capacity) increased from 32% to 97% after postgrouting, and the axial stiffness of piles also increased by about 1.3 times per grouting pressure.
원심모형 실험을 이용한 지반-말뚝 상호작용의 정적 및 동적 거동 평가
유민택,권선용 한국지반공학회 2018 한국지반공학회논문집 Vol.34 No.7
In this study a series of centrifuge tests were carried out in dry sand to analyze the comparison of lateral pile behavior for static loading and dynamic loading condition. In case of static loading condition, the lateral displacement was applied up to 50% of pile diameter by deflection control method. And the input sine wave of 0.1 g~0.4 g amplitude and 1 Hz frequency was applied at the base of the soil box using shaking table for dynamic loading condition. From comparison of experimental static p-y curve obtained from static loading tests with API p-y curves, API p-y curves can predict well within 20% error the ultimate subgrade reaction force of static loading condition. The ultimate subgrade reaction force of experimental dynamic p-y curve is 5 times larger than that of API p-y curves and experimental static p-y curves. Therefore, pseudo-static analysis applied to existing p-y curve for seismic design could greatly underestimate the soil resistance at non-linear domain and cause overly conservative design.
원심모형 실험을 통한 궤도지지말뚝구조의 동적 거동 평가
유민택,이명재,백민철,추연욱,이일화 한국지반공학회 2019 한국지반공학회논문집 Vol.35 No.2
Dynamic centrifuge model test was conducted to evaluate the dynamic stability of the pile-supported slab track method during dynamic railway loading and earthquake loading. The centrifuge tests were carried out for various condition of embankment height and soft ground depth. Based on test results, we found that the bending moment was increased with embankment height and decreased with soft ground depth. In addition, it was confirmed that the pile-supported slab track system could have dynamic stability for short-period seismic loading. However, in case of long-period seismic loading, such as Hachinohe earthquake, the observed maximum bending moment reached to pile cracking moment at the return period of 2,400 year earthquake. The criterion of ratio between embankment height and soft ground depth was suggested for dynamic stability of pile-supported slab track system.
지반-기초-구조물 상호작용을 고려한 말뚝 기초 구조물에서의 지진 하중 평가
유민택,하정곤,조성배,김동수 한국지진공학회 2014 한국지진공학회논문집 Vol.18 No.3
In this study, a series of dynamic centrifuge tests were performed for a soil-foundation-structural interaction system in dry sand with various embedded depths and superstructure conditions. Sinusoidal wave, sweep wave and real earthquake were used as input motion with various input acceleration and frequencies. Based on the results, a natural period and an earthquake load for soil-structure interaction system were evaluated by comparing the free-field and foundation accelerations . The natural period of free field is longer than that of the soil-foundation-structure system. In addition, it is confirmed that the earthquake load for soil-foundation-structure system is smaller than that of free-field in short period region. In contrast, the earthquake load for soil-foundation-structure interaction system is larger than that of free-field in long period region. Therefore, the current seismic design method, applying seismic loading of free-field to foundation, could overly underestimate seismic load and cause unsafe design for long period structures, such as high-rise buildings.
원심모형 실험을 이용한 건조토 지반에서의 군말뚝 효과 분석
유민택,차세환,최정인,한진태,김명모 한국지반공학회 2012 한국지반공학회논문집 Vol.28 No.1
In this study, a series of centrifuge shaking-table tests for a 3 × 3 group pile and a single pile applied by sinusoidal wave was performed in dry sand for various pile spacings, ranging from three to seven times the pile diameter. A comparison of centrifuge tests of both single pile and group pile showed that the lateral ground response of the group pile was smaller than that of the single pile. In addition, the reduction in subgrade reaction for the group pile increased with decreasing pile spacing. The side piles, that is, the 1st row and 3rd row piles showed identical dynamic p–y behavior and the center pile in the 2nd row caused a lower reduction effect compared with the 1st and 3rd row piles. From the comparison between the p-y curves of the 2nd row piles, it was found that the lateral ground response of the outer pile in the 2nd row was less than that of the center pile in the 2nd row. The p-multipliers for the side piles, for the center pile and for the outer pile ranged from 0.28 to 0.77, from 0.55 to 1.0 and from 0.39 to 0.87, respectively.
유민택,양승훈,문재상,곽동엽 대한토목학회 2022 KSCE Journal of Civil Engineering Vol.26 No.10
We propose the inverse transfer function (TFinv) changing the ground motion amplitude recorded at the train to the free-field equivalent ground motion supposing that the train is on the bridge. This process is needed to estimate the free-field motions from the seismic records observed at the on-board accelerometer which is used for the on-board earthquake warning system. To estimate the TFinv, evaluation of two transfer functions is needed: a transfer function of the bridge (TFbridge), and the other transfer function of the train (TFtrain). For the estimation of the TFbridge, we simplified an example bridge (named Yunjung bridge) located in the Honam high-speed railway as SDOF models finding its natural frequency dependent on the girder type and span length. Then, using time-domain integration methods (Newmark and Duhamel), SDOF response and TFbridge is calculated. For the TFtrain, we modeled the rail base and train following the similitude law and performed the shaking table test with various earthquake ground motions, and evaluated the TFtrain empirically comparing the responses at the train and the rail base. Two models of TFinv based on the moment magnitude ranges of input ground motions are proposed.