• 국제초고층학회논문집
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• 제9권4호
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• pp.369-376
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• 2020

Given the importance of quickly recovering livelihoods and economic activity after an earthquake, the seismic performance of the pile foundation is becoming more critical than before. In order to promote seismic retrofit of the pile foundations, it is necessary to develop a method for evaluating the seismic performance of the pile foundation based on the experimental data. In this paper, we focus on the building that was suffered severe damage to the pile foundation, conduct simulation analyses of the building, and report the results of evaluating the dynamic characteristics when piles are damaged using a system identification method. As a result, an analysis model that can accurately simulate the behavior of the damaged building during an earthquake was constructed, and it was shown that the system identification method could extract dynamic characteristics that may damage piles.

• Geomechanics and Engineering
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• 제33권1호
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• pp.91-99
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• 2023

To test the effect of various pile tip shape series of model scale loading tests were carried out on test piles with special pile tips. Special pile tips were made using the 3D printer and were attached to the bottom end of the test pile for loading tests. The pile tips were made to have 30°, 45°, 60° inclined tips, as well as a rounded tip. The main objective of the test was to observe the effect of various pile tip shapes on settlement and penetrability of the pile. Moreover, a numerical model simulating the pile loading test carried out in this study was established and verified based on the loading test results. From this, the stress concentration around the pile tip was investigated. This will allow us to analyze the decrease of stress concentration around the pile tip which is the main cause of the pile tip damage during pile installation. However, modifying the pile tip shape will eventually increase the settlement of the pile. By estimating the degree of increase in pile settlement, the viability and the efficiency of the pile shape modification was judged. In addition, case studies on the effect of different pile tip shape and ground conditions on pile settlement and stress dispersion was conducted.

• 한국지반공학회논문집
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• 제39권1호
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• pp.27-38
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• 2023

본 연구에서는 3D 프린팅 기술을 활용하여 타입말뚝 선단의 모양에 따른 관입성 분석을 현장 축소모형시험을 통해 관찰하고, 대변형 수치해석을 통해 타입 중 말뚝 선단에 집중되는 최대응력의 변화를 확인하였다. 3D 프린터를 통하여 다양한 직경, 각도 그리고 모양의 말뚝 선단 모형을 제작하였고, 이를 현장 축소모형시험에 활용하였다. 이를 통해, 말뚝 선단 조건에 따른 말뚝의 침하량의 변화를 관찰하였다. 더 나아가, 대변형 수치해석 기법을 적용하여 다양한 말뚝 선단 조건에 따른 타입 중 말뚝 선단부의 최대응력의 변화와 최대응력 작용 위치 또한 확인하였다. 현장 축소모형시험과 대변형 수치해석의 결과 분석을 토대로 말뚝 선단 조건의 변화를 통해 타입말뚝의 관입성을 향상 시킬 수 있으며 선단부에 집중되는 최대응력 또한 완화 시켜 말뚝 시공 중 말뚝 손상을 방지할 수 있을 것으로 결론지을 수 있었다.

• Structural Monitoring and Maintenance
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• 제10권2호
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• pp.133-154
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• 2023

Obscured structural members are mostly under-evaluated during condition assessment due to lack of visual inspection capability. Insufficient information about the integrity of these structural members poses a significant risk for public safety. Time domain reflectometry (TDR) is a novel approach in structural health monitoring (SHM). Ordinary coaxial cables "as is" without a major modification are not suitable for SHM with TDR. The objective of this study is to propose a practical and cost-effective modification approach to commercially available coaxial cables in order to use them as a "cable sensor" for damage detection with the TDR equipment for obscured structural members. The experimental validation and assessment of the proposed modification approach was achieved by conducting 3-point bending tests of the model piles as a representative obscured structural member. It can be noted that the RG59/U-6 and RG6/U-4 cable sensors expose higher strain sensitivity in comparison with non-modified "as is" versions of the cables used. As a result, the cable sensors have the capability of sensing both the presence and the location of a structural damage with a maximum aberration of 3 cm. Furthermore, the crack development can be monitored by the RG59/U-6 cable sensor with a simple calibration.

• Nuclear Engineering and Technology
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• 제52권4호
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• pp.802-810
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• 2020

Three-dimensional finite element simulations are implemented for the in-pile thermo-mechanical behavior in U-Mo/Al monolithic fuel plates with different thermal creep rates of cladding involved. The numerical results indicate that the thickness increment of fuel foil rises with the thermal creep coefficient of cladding. The maximum Mises stress of cladding is reduced by ~85% from 344 MPa on the 98.0^th day when the creep coefficient of cladding increases from 0.01 to 10.0, due to its equivalent thermal creep strain enlarged by 3.5 times. When the thermal creep coefficient of Aluminum cladding increases from 0 to 1.0, the maximum mesoscale stress of fuel foil varies slightly. At the same time, the peak mesoscale normal stress of fuel foil can reach 51 MPa on the 98.0^th day for the thermal creep coefficient of 10, which increases by 60.3% of that with the thermal creep un-occurred in the cladding. The maximum through-thickness creep strain components of fuel foil differ slightly for different thermal creep coefficients of cladding. The dangerous region of fuel foil becomes much closer to the heavily irradiated side when the creep coefficient of cladding becomes 10.0. The creep performance of Aluminum cladding should be optimized for the integrity of monolithic fuel plates.