• 한국지반공학회논문집
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• 제24권9호
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• pp.33-40
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• 2008

본 연구에서는 해안 준설매립지반에 대한 연약지반 개량사례를 이용하여 연적배수공법 적용시의 현장계측 및 압밀침하 해석을 실시하였다. 대상현장은 원지반위에 대략 10m의 준설매립을 통해 조성된 부지로서 고함수비 및 고압축성의 해성점토로 구성되어 있다. 1년 동안의 현장 계측결과, 당초 설계시의 예측침하량에 비해 매우 큰 압밀침하가 발생하였고, 이 조건에서의 향후 침하거동을 예측하기 위한 추가 압밀침하 해석 및 계측결과를 이용한 역해석을 실시하였다. 상부시공 영향 등에 의해 준설매립지반에는 과다한 전단변형이 발생하였으며, 이에 대한 현장 계측결과의 평가 및 보정을 실시하였다. 압밀해석 및 원지반 조건을 평가하기 위해 실내시험 결과를 이용한 물질함수분석을 실시하였으며, 최종적으로 부지 인도후의 잔류침하량 및 최종 지반고를 만족시키기 위한 추가 성토고를 산정하였다. 추가 성토이후의 현장 계측결과와 당초 예측했던 압밀침하 거동을 비교하였으며, 이를 통해 당초 예측내용에 대한 검증을 수행할 수 있었다.

• Earthquakes and Structures
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• 제24권5호
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• pp.353-364
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• 2023

In this study, a method has been proposed for the static and dynamic nonlinear analysis of multi-storey buildings, which takes into account the contribution of axial deformations in vertical load-bearing elements, which are especially important in tall and narrow structures. Shear deformations on the shear walls were also taken into account in the study. The presented method takes into account the effects that are not considered in the fishbone and flexural-shear beam models developed in the literature. In the Fishbone model, only frame systems are modeled. In the flexural shear beam model developed for shear wall systems, shear deformations and axial deformations in the walls are neglected. Unlike the literature, with the model proposed in this study, both shear deformations in the walls and axial deformations in the columns and walls are taken into account. In the proposed model, multi-storey building is represented as a sandwich beam consisting of Timoshenko beams pieced together with a double-hinged beam. At each storey, the total moment capacities of the frame beams and the coupled beams in the coupled shear walls are represented as the equivalent shear capacity. On the other hand, The sums of individual columns and walls moment at the relevant floor level are represented as equivalent moment capacity at that floor level. At the end of the study, examples were solved to show the suitability of the proposed method in this study. The SAP2000 program is employed in analyses. In a conclusion, it is observed that among the solved examples, the proposed sandwich beam model gives good results. As can be seen from these results, it is seen that the presented method, especially in terms of base shear force, gives very close results to the detailed finite element method.

• Steel and Composite Structures
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• 제44권6호
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• pp.845-865
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• 2022

In this study, the performance of shear deficient reinforced concrete (RC) beams with rectangular cross-sections, which were externally bonded reinforced (EBR) with high strength CFRP and GFRP strips composite along shear spans, has been experimentally and analytically investigated under vertical load. In the study, the minimum CFRP and GFRP strips width over spacing were considered. The shear beam with turned end to a bending beam was investigated by applying different composite strips. Therefore various arising in each of strength, ductility, rigidity, and energy dissipation capacity were obtained. A total of 12 small-scaled experimental programs have been performed. Beam dimensions have been taken as 100×150×1000 mm. Four beams have been tested as unstrengthened samples. This paper focuses on the effect of minimum CFRP and GFRP strip width on behaviours of RC beams shear-strengthened with full-wrapping, U-wrapping, and U-wrapping+longitudinal bonding strips. Strengthened beams showed significant increments for flexural ductility, energy dissipation, and inelastic performance. The full wrapping strips applied against shear failure have increased the load-carrying capacity of samples 53%-63% interval rate. Although full wrapping is the best strengthening choice, the U-wrapping and U-wrapping+longitudinal strips of both CFRP and GFRP bonding increased the shear capacity by 53%~75% compared to the S2 sample. In terms of ductility, the best result has been obtained by the type of strengthening where the S5 beam was completely GFRP wrapped. The experimental results were also compared with the analytically given by ACI440.2R-17, TBEC-2019 and FIB-2001. Especially in U-wrapped beams, the estimation of FIB was determined to be 81%. The estimates of the other codes are far from meeting the experimental results; therefore, essential improvements should be applied to the codes, especially regarding CFRP and GFRP deformation and approaches for longitudinal strip connections. According to the test results, it is suggested that GFRP, which is at least as effective but cheaper than CFRP, may be preferred for strengthening applications.

• 반도체디스플레이기술학회지
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• 제22권2호
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• pp.30-34
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• 2023

Since dishing in the CMP process is a major factor that hinders the uniformity of the semiconductor thin film, many studies have focused this issue to improve the non-uniformity of the film due to dishing. In the metal layer, the dishing mainly occurs in the central part of the metal due to a difference in a selection ratio between the metal and the dielectric, thereby generating a step on the surface of the metal layer. Factors that cause dishing include the shape of the thin film, the chemical reaction of the slurry, thermal deformation, and the rotational speed of the pad and head, and dishing occurs due to complex interactions between them. This study analyzed the stress generated on the metal layer surface in the CMP process using ANSYS software, a commercial structure analysis program. The stress caused by the vertical load applied from the pad was analyzed by changing the area density and line width of the dummy metal. As a result of the analysis, the stress in the active region decreased as the pattern density and line width of the dummy metal increased, and it was verified that it was valid compared with the previous study that studied the dishing according to the dummy pattern density and line width of the metal layer. In conclusion, it was confirmed that there is a relationship between dishing and normal stress.

• Earthquakes and Structures
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• 제24권6호
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• pp.439-453
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• 2023

Older brick masonry structures generally suffer from low strength defects. Using a cement mortar layer (CML) or steel-meshed cement mortar layer (S-CML) to reinforce existing low-strength brick masonry structures (LBMs) is still an effective means of increasing seismic performance. However, performance indices such as lateral displacement ratios and skeleton curves for LBMs reinforced with CML or S-CML need to be clarified in performance-based seismic design and evaluation. Therefore, research into the failure mechanisms and seismic performance of LBMs reinforced with CML or S-CML is imperative. In this study, thirty low-strength brick walls (LBWs) with different cross-sectional areas, bonding mortar types, vertical loads, and CML/S-CML thicknesses were constructed. The failure modes, load-carrying capacities, energy dissipation capacity and lateral drift ratio limits in different limits states were acquired via quasi-static tests. The results show that 1) the primary failure modes of UBWs and RBWs are "diagonal shear failure" and "sliding failure through joints." 2) The acceptable drift ratios of Immediate Occupancy (IO), Life Safety (LS), and Collapse Prevention (CP) for UBWs can be 0.04%, 0.08%, and 0.3%, respectively. For 20-RBWs, the acceptable drift ratios of IO, LS, and CP for 20-RBWs can be 0.037%, 0.09%, and 0.41%, respectively. Moreover, the acceptable drift ratios of IO, LS, and CP for 40-RBWs can be 0.048%, 0.09%, and 0.53%, respectively. 3) Reinforcing low-strength brick walls with CML/S-CML can improve brick walls' bearing capacity, deformation, and energy dissipation capacity. Using CML/S-CML reinforcement to improve the seismic performance of old masonry houses is a feasible and practical choice.

• Structural Engineering and Mechanics
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• 제85권4호
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• pp.469-484
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• 2023

A deep recursive bidirectional Cuda Deep Neural Network Long Short Term Memory (Bi-CuDNNLSTM) layer is recruited in this paper to predict the entire force time histories, and the corresponding hysteresis and backbone curves of reinforced concrete (RC) bridge piers using experimental fast and slow cyclic tests. The proposed stacked Bi-CuDNNLSTM layers involve multiple uncertain input variables, including horizontal actuator displacements, vertical actuators axial loads, the effective height of the bridge pier, the moment of inertia, and mass. The functional application programming interface in the Keras Python library is utilized to develop a deep learning model considering all the above various input attributes. To have a robust and reliable prediction, the dataset for both the fast and slow cyclic tests is split into three mutually exclusive subsets of training, validation, and testing (unseen). The whole datasets include 17 RC bridge piers tested experimentally ten for fast and seven for slow cyclic tests. The results bring to light that the mean absolute error, as a loss function, is monotonically decreased to zero for both the training and validation datasets after 5000 epochs, and a high level of correlation is observed between the predicted and the experimentally measured values of the force time histories for all the datasets, more than 90%. It can be concluded that the maximum mean of the normalized error, obtained through Box-Whisker plot and Gaussian distribution of normalized error, associated with unseen data is about 10% and 3% for the fast and slow cyclic tests, respectively. In recapitulation, it brings to an end that the stacked Bi-CuDNNLSTM layer implemented in this study has a myriad of benefits in reducing the time and experimental costs for conducting new fast and slow cyclic tests in the future and results in a fast and accurate insight into hysteretic behavior of bridge piers.

• 대한토목학회논문집
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• 제28권4C호
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• pp.221-230
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• 2008

캐나다 서부 밴쿠버 지역의 Fraser강 바닥의 사질토 지반에 위치한 George Massey 침매터널이 지진 시에 어떻게 거동하는 지를 연구하였다. 지진으로 발생하는 간극수압을 계산할 수 있는 유효응력모델인 UBCSAND모델을 이용하여 지진하중으로 인한 지반의 변위와 침매터널의 거동을 예측하였으며, 이를 미국 Rensselaer Polytechnic Institute(RPI)에서 실시한 원심모형실험 결과와 비교하였다. 본 연구에서 해석한 George Massey 침매터널의 원심모형실험은 2개의 모델로 구성되었으며, Model 1은 기본 모델로서 원상태 지반을, Model 2는 다짐공법으로 지반개량을 실시한 지반을 모델링하였다. 원심모형실험 Model 1에서 설계지진으로 인한 주변 지반의 액상화로 모형터널의 변위가 크게 발생하였다. Model 2에서 다짐공법으로 터널 주변 지반을 개량하였을 때 모형터널의 수직 및 수평 변위는 Model 1보다 50% 정도 감소하였다. UBCSAND모델은 원심모형실험에서 계측된 과잉간극수압, 가속도, 변위를 비교적 잘 예측할 수 있었다. 이와 같이 검증된 수치해석방법은 유사한 지반에 설치된 침매터널의 지진 시 변위와 거동을 예측할 수 있으며, 액상화에 대한 지반개량공법과 개량범위를 체적화할 수 있을 것으로 판단된다.

• 대한토목학회논문집
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• 제28권5C호
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• pp.313-320
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• 2008

본 연구에서는 Plastic Board Drain(PBD)이 타설된 지반의 압밀거동 특성을 파악하고, 배수재 통수능력을 알아보기 위하여 현장의 타설조건을 실험실에서 모사할 수 있는 관입식 복합 통수능 시험기를 개발하였다. 개발된 시험기는 배수재를 타설하고 교란된 시료를 투기하는 기존 방법과 달리, 예비압밀로 시료를 조성한 후 mandrel과 관입장치를 이용하여 PBD를 지반에 타설하도록 고안하였다. 개발된 관입식 복합 통수능 시험기의 적용성을 평가하기 위하여 기존 복합 통수능 시험을 함께 실시하여 결과를 분석하였다. 실험 결과, 기존 방법은 시료 전체의 교란에 의해 압밀이 지연되는 현상으로 나타났으며, 시료의 불균질성 등에 의해 배수재 변형도 국부적으로 발생하였다. 이로 인하여 기존 시험법에 의한 통수능력은 예상치 보다 다소 크게 산정되는 경향을 보였으며, 관입식 방법에 의해 현장조건과 유사하게 통수능력을 분석할 수 있을 것으로 판단되었다.

• 대한토목학회논문집
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• 제30권3D호
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• pp.271-278
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• 2010

반강성 포장은 공극률이 큰 개립도 아스팔트 혼합물의 공극에 시멘트 페이스트를 침투시켜 아스팔트 포장의 연성과 콘크리트 포장의 강성을 동시에 이용하는 포장형식이다. 반강성 포장은 콘크리트 포장에 비해 평탄성이 좋고 주행에 의한 진동이나 소음을 저감할 수 있으며, 아스팔트 포장에 비해 소성변형이 적고 온도저감 효과가 있는 것으로 알려져 있다. 본 연구에서는 반강성 덧씌우기 포장을 시험시공하여 반강성 포장의 온도저감 효과를 조사하였고 시편을 제작하여 옥외에서 온도 및 중량을 측정하여 반강성 포장의 온도저감 및 보수 효과를 확인하였다. 상용 3차원 유한요소해석 프로그램인 Abaqus 6.8로 반강성 포장과 아스팔트 포장을 구조해석하여 하중재하 위치에서의 수평 및 연직방향 응력과 변형률을 비교하고 다층탄성해석 프로그램 Bisar 3.0으로 검증하였다. 구조해석 결과를 바탕으로 피로균열을 예측하여 반강성 포장과 아스팔트 포장의 공용성을 비교하였다.

• Geomechanics and Engineering
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• 제34권2호
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• pp.209-220
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• 2023

In this study, a series of three-dimensional numerical analyses were carried out to investigate the penetration performance of a dynamically installed Hall anchor. The advanced coupled Eulerian-Lagrangian (CEL) technique was adopted to accurately simulate the large soil deformation during the vertical penetration of a Hall anchor. In total, 52 numerical analyses were conducted to investigate the relationship between anchor penetration depth and the initial kinematic energy. Moreover, a sensitivity analysis was performed to investigate the effects of soil shear strength and soil type on the penetration mechanism of a drop anchor under self-weight. There is a monotonic increase in the penetration depth with an increasing anchor weight when the topsoil of the riverbed is not subjected to erosion. On the other hand, all the computed depths significantly increase when soil erosion is taken into consideration. This is mainly due to an enhanced initial kinematic energy from an increased dropping depth. Both depths increase exponentially with the initial kinematic energy. An enhanced shear strength can potentially increase the side resistance and end-bearing pressure around a drop anchor, thus significantly reducing the downward penetration of a hall anchor. Design charts are developed to directly estimate penetration depth and associated plastic zone due to dynamically installed anchor at arbitrary soil shear strength and anchor kinematic energy.