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비선형 유효응력해석을 이용한 Takahama 잔교식 안벽의 내진성능 평가
Tran, Nghiem Xuan,이진선,김성렬 한국지반공학회 2017 한국지반공학회논문집 Vol.33 No.4
Aseismic designs of pile-supported wharves are commonly performed utilizing simplified dynamic analyses, such asmulti-mode spectral analyses. Simplified analyses can be useful for evaluating the limit state of structures. However,several pile-supported wharves, that have been damaged during past earthquakes, have shown that soil deformationand soil-pile dynamic interaction significantly affect the entire behavior of structures. Such behavior can be capturedby performing nonlinear effective stress analyses, which can properly consider the dynamic interactions among thesoil-pile-structure. The present study attempts to investigate the earthquake performance of a pile-supported wharf utilizinga three-dimensional numerical method. The damaged pile-supported wharf at the Kobe Port during the Hyogo-ken Nambuearthquake (1995) is selected to verify the applicability of the numerical modeling. Analysis results showed a suitableagreement with the observations on the damaged wharf, and the significant effect of excess pore pressure developmentand pile-soil dynamic interaction on the seismic performance of the wharf.
Evaluation of Liquefaction-induced Lateral Force on Pile in Slope by Centrifuge Tests
유병수,황병윤,Nghiem Xuan Tran,윤정원,김성렬 대한토목학회 2023 KSCE Journal of Civil Engineering Vol.27 No.3
Pile foundations in liquefied ground may be subjected to a substantial force induced by lateral soil movement, which is crucial in the seismic design of pile-supported structures. Thus, this study aims to investigate the liquefaction-induced lateral force to piles by conducting centrifuge tests. Pile–deck systems installed in liquefiable finite slope with an angle of 27° were constructed and tested with different base motions. Results show that the liquefied slope pushes the piles toward the downslope, causing a large bending moment. The linear and uniform distributions of lateral soil pressure, which have been previously suggested for pile analysis in liquefied ground, were examined and compared with the measured maximum bending moment. The linear soil pressure profile reasonably predicted the bending moment compared to the results of the uniform profile. The empirical gradient factor of the linear profile was calibrated for the single piles and then implemented in the pile group analysis. The calibrated factor improved conventional methods for predicting the bending moment profile of group piles.
원심모형실험을 이용한 무리말뚝의 동적 p-y 곡선 산정
Bao Ngoc Nguyen,Nghiem Xuan Tran,김성렬 한국지반공학회 2018 한국지반공학회논문집 Vol.34 No.5
Dynamic soil-pile interaction is the main concern in the design of group piles under earthquake loadings. The lateral resistance of the pile group under dynamic loading becomes different from that of a single pile due to the group pile effect. However, this aspect has not yet been properly studied for the pile group under seismic loading condition. Thus, in this study the group pile effect was evaluated by performing a series of dynamic centrifuge tests on 3×3 group pile in dry loose sand. The multiplier coefficients for ultimate lateral resistance and subgrade reaction modulus were suggested to obtain the p-y curve of the group pile. The suggested coefficients were verified by performing the nonlinear dynamic analyses, which adopted Beam on Nonlinear Winkler Foundation model. The predicted behavior of the pile group showed the reasonable agreement compared with the results of the centrifuge tests under sinusoidal wave and artificial wave.
2차원 수치해석을 이용한 말뚝 지지구조물의 동적 원심모형실험 거동 모사
팜 비엣 찬,Nghiem Xuan Tran,김성렬 한국지반공학회 2018 한국지반공학회논문집 Vol.34 No.8
Recently, as the seismic performance based design methods have been introduced, dynamic numerical analyses need to be performed to evaluate the actual performance of structures under earthquakes. The verification of the numerical modeling is the most important for the performance based design. Therefore, 2-dimensional numerical analyses were performed to simulate the seismic behavior of a pile-supported structure, to provide the proper numerical modeling and to determine of input parameters. A dynamic centrifuge test of a pile group in dry loose sand was simulated to verify the applicability of the numerical model. The numerical modeling was carefully made to reflect the actual condition of the centrifuge test including dynamic soil properties, soil-pile interaction, boundary condition, the modeling of the group pile and structure and so on. The predicted behavior of the numerical analyses successfully simulated the acceleration variation in ground, the moment and displacement of the pile, and the displacement and acceleration of the structure. Therefore, the adopted numerical modeling and the input parameters can be used to evaluate the seismic performance of pile groups.
Experimental investigation of the vertical pullout cyclic response of bucket foundations in sand
Hung, Le Chi,Lee, Sihoon,Tran, Nghiem Xuan,Kim, Sung-Ryul Elsevier 2017 Applied ocean research Vol.68 No.-
<P><B>Abstract</B></P> <P>A series of 1g model tests was conducted to investigate the accumulated vertical pullout displacement and unloading stiffness of bucket foundations embedded in dry and saturated sands. The foundations were subjected to vertical pullout cyclic loading with different load amplitudes. Cyclic load was applied up to 10<SUP>4</SUP> cycles. Test results showed that the accumulated vertical pullout displacement increased with the increase in the number of load cycles and cyclic load amplitudes. The unloading stiffness of the bucket foundations decreased with the increase in load amplitude and number of cycles. Empirical equations were proposed based on the test results to evaluate the accumulated vertical pullout displacement and unloading stiffness of the bucket foundations in saturated sand. These equations can be used for the preliminary design of single or tripod bucket foundations.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Cyclic response of bucket foundations in saturated sand under cyclic vertical pullout load was examined by 1 <I>g</I> model tests. </LI> <LI> Accumulated displacement increased with the increase in number of load cycles and load magnitude. </LI> <LI> Unloading stiffness decreased with the increase in number of load cycles and load magnitude. </LI> <LI> Empirical equations have been proposed. </LI> </UL> </P>
점성토 지반에 근입된 그룹 석션파일에 대한 비선형 스프링 모델링 기법 개발
이시훈(Si-Hoon Lee),이주형(Ju-Hyung Lee),Tran Xuan Nghiem,김성렬(Sung-Ryul Kim) 한국지반신소재학회 2015 한국지반신소재학회 논문집 Vol.14 No.1
최근 해양구조물의 건설이 활발해짐에 따라 해상 부유식 구조체를 경제적으로 지지할 수 있는 새로운 앵커형식을 개발하려는 연구가 이루어지고 있다. 본 연구에서는 기존의 대구경 단일형 석션파일 대신에 다수의 중구경 석션파일을 콘크리트 파일캡으로 결합한 그룹 석션파일에 대하여 연구하였다. 그룹 석션파일은 이동과 회전이 함께 발생하는 복잡한 지지거동을 보이기 때문에 일반적인 설계법을 적용하기 어렵다. 그러므로, 본 연구에서는 점성토 지반에 근입된 그룹 석션파일의 수평방향 지지력을 산정하는 수치 모델링 기법을 개발하였다. 본 기법은 파일을 보요소, 주변지반의 저항력을 비선형 스프링으로 모사한다. 본 기법의 적용성을 분석하기 위하여 동일한 조건에 대하여 3차원 유한요소해석을 수행하여 수평방향 하중-변위 곡선을 서로 비교하였다. 비교결과, 제안된 기법이 지지력을 과소평가하고 최대 지지력이 발생하는 변위는 크게 산정하는 것으로 나타났다. 그러므로, 유한요소해석 결과를 실제거동을 모사할 수 있는 정밀해로 가정한 후 개발된 설계 모델링 기법의 결과를 보정할 수 있는 지반저항력 보정계수를 제안하였다. Recently, several researches on the development of new economical anchor systems have been performed to support floating structures. This study focused on the group suction piles, which connect mid-sized suction piles instead of a single suction pile with large-diameter. The group suction pile shows the complex bearing behavior with translation and rotation, so it is difficult to apply conventional design methods. Therefore, the numerical modeling technique was developed to evaluate the horizontal bearing capacity of the group suction piles in clay. The technique models suction piles as beam elements and soil reaction as non-linear springs. To analyze the applicability of the modeling, the horizontal load-movement curves of the proposed modeling were compared with those of three-dimensional finite element analyses. The comparison showed that the modeling underestimates the capacity and overestimate the displacement corresponding to the maximum capacity. Therefore, the correction factors for the horizontal soil resistance was proposed to match the bearing capacity from the three-dimensional finite element analyses.