• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 춘계 학술발표회
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• pp.993-998
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• 2009

This study was conducted to propose the model that is able to predict long-term settlement of sands containing carbonates. We can observe that in addition to the initial elastic compression, a considerable additional compression occurs with long-term period in some sands. The compressibility of sands is significantly dependent on particle characteristics. Some sands have many pores and particularly has an angular shape. To predict of long-term settlement of these sands which contain carbonates, first of all a variety of tests which are to assess chemical, physical and compression characteristics of these sands were conducted. Second, in order to know settlement with time, the time parameter was determined by analyzing the measured data obtained from $\bigcirc\bigcirc$ area. The measured settlement of this area shows that in addition to the initial elastic compression, a considerable additional compression occurring with time. It was caused by the crushing, shattering, and rearrangement of particles, which were real phenomena in sandy soils under loading condition. Based on this case study, we proposed that a simple method is able to predict settlement with time of sandy soil containing carbonates.

• 한국구조물진단유지관리공학회 논문집
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• 제14권2호
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• pp.67-74
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• 2010

철근콘크리트 지붕 슬래브에 작용하는 온도변화는 여름에는 부재를 팽창시키고 겨울에는 수축시키기 때문에 콘크리트의 응력변화를 야기시키며 이와 같은 거동은 년단위로 반복되어 사용성과 극한상태 모두에 대해서 부재의 구조성능에 영향을 미친다. 본 논문에서는 최근 20년 동안 한국의 기상변화를 분석하여 온도변화의 패턴을 계산하였으며 또한 이와 같이 장기적으로 반복되는 온도변화에 대한 영향을 실험적으로 연구하였다. 6개의 동일한 형태를 가진 철근콘크리트 슬래브를 제작하고 가력주기와 손상유무를 주 변수로 실험을 실시하였다. 실험으로부터, 1년, 10년 20년 동안의 가력기간 변화에 따른 슬래브의 강성변화에서, 여름의 경우에는 10년에서 1년 일 때의 강성과 비교하여 약 30% 정도 감소되고 겨울의 경우에는 30년 이후부터 약 31%(1년과 비교) 저하되는 것으로 나타났다. 또한 이들 손상된 RC슬래브에 대한 파괴실험을 통하여 슬래브 부재의 보유성능을 평가한 결과, 외기에 노출된 기간의 변화에 따른 슬래브 부재의 초기강성 및 최대내력의 변화는 크지 않은 것으로 나타났다. 단, 20년 이상의 반복온도하중을 받은 경우에는 항복내력이 낮아지는 경향을 보이는 것으로 나타났다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 춘계 학술발표회 초청강연 및 논문집
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• pp.251-258
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• 2008

The use of reinforced earth walls in permanent structures is getting it's popularity. Despite a number of advantages of reinforced earth walls over conventional concrete retaining walls, there exit concerns over long-term residual deformation when subjected to repeated and/or cyclic loads, during their service period. In this investigation, the effect of preloading in reducing long term residiual deformation of back-to-back reinforced soil wall under sustained and/or repeated loading enviormentment using a series of reduced-scale model tests. It is found that the preloading technique can be an effective means of controlling residual deformations of reinforced soils under varisous loading conditions.

• 반도체디스플레이기술학회지
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• 제22권3호
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• pp.41-45
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• 2023

Currently, the method of loading items in the warehouse, the worker directly decides the loading location, and the most used method is to load the product at the location closest to the entrance. This can be effective when there is no difference in the required amount for goods, but when there is a difference in the required amount for goods, it is inefficient because items with a small required amount are loaded near the entrance and occupy the corresponding space for a long time. Therefore, in order to minimize the release time of goods, it is essential to select an appropriate location when loading goods. In this study, a method for determining the loading location by predicting the required amount of goods was studied to select the optimal loading location. Deep learning based bidirectional long-term memory networks (Bi-LSTM) was used to predict the required amount for goods. This study compares and analyzes the release time of goods in the conventional method of loading close to the entrance and in the loading method using the required amount for goods using the Bi-LSTM model.

• Geomechanics and Engineering
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• 제19권2호
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• pp.115-126
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• 2019

The long-term settlement characteristics for the cast-in-place bored pile in the deep-thick soft soil are investigated by post-grouting field tests. Six cast-in-place bored engineering piles and three cast-in-place bored test piles are installed to study the long-term settlement characteristics. Three post-grouting methods (i.e., post-tip-grouting, post-side-grouting, and tip and side post-grouting) are designed and carried out by field tests. Results of the local test show that decreased settlements for the post-side-grouted pile, the post-tip-grouted pile and the tip and side post-grouted pile are 22.2%~25.8%, 30.10%~35.98% and 32.40%~35.50%, respectively, compared with non-grouted piles. The side friction resistance for non-grouted piles, post-side-grouted pile, post-tip-grouted pile and the tip and side post-grouted pile undertakes 89.6~91.3%, 94.6%, 92.4%~93.0%, 95.7% of the total loading, respectively. At last, the parameters back analysis method and numerical calculation are adopted to predict the long-term settlement characteristics of the cast-in-place bored pile in the deep-thick soft soil. Determined Bulk modulus (K) and a creep parameter (Ks) are used for the back analysis of the long-term settlement of the post-grouted pile. The settlement difference between the back analysis and the measurement data is about 1.11%-7.41%. Long-term settlement of the post-grouted piles are predicted by the back analysis method, and the predicted results show that the settlement of the post-grouted pile are less than 6 mm and will be stable in 30 days.

• Journal of Korean Dental Science
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• 제12권1호
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• pp.29-37
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• 2019

Purpose: This study was aimed to compare the survival and success rates, and long-term crestal bone loss according to the use of 2 connection types of dental implants (submerged-USII and non-submerged-SSII; Osstem $Implant^{(R)}$) by analyzing the change in alveolar bone height after 1 year under load and during final follow-up period. Materials and Methods: Between December 2004 and August 2008, patients with two types of Osstem implants (USII and SSII) were retrieved retrospectively. A total of 92 patients with 284 implants (USII=60, SSII=224) was finally selected. Their mean follow-up period was 7.5 years. The mesial and distal alveolar crestal bone changes were measured using radiographic images and the average was calculated at 1 year after loading and during final follow-up period. Result: Among the 284 implants, 4 USII and 7 SSII implants were removed, indicating 93.3% and 96.9% survival rates. Of the survived implants, mean crestal bone loss 1 year after loading was 0.39 mm for USII and 0.19 mm for SSII (P=0.018). During the final follow-up, mean crestal bone loss was 0.63 mm and 0.35 mm for USII and SSII, respectively, without statistical significance (P=0.092). According to the criteria for the success and failure of the implant by Albreksson and colleagues, final success rate was estimated as 86.7% for USII and 91.5% for SSII, respectively. Conclusion At 1 year after loading, the average crestal bone loss was significantly different between USII and SSII; however, both types met the criteria for implant success. During the final follow-up, both groups showed insignificant bone resorption patterns and did not show any pathological clinical symptoms. Therefore, both implants exhibited high long-term stability.

• 콘크리트학회논문집
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• 제20권1호
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• pp.43-50
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• 2008

본 연구는 지속하중 하에서의 골재 종류에 따른 철근콘크리트보의 장기거동 특성에 대한 연구의 일환으로 천연골재를 사용한 실험체와 순환굵은골재 대체율 100% 실험체, 순환잔골재 대체율 50% 실험체 총 3개로 제작하여 약 1년 동안 지속하중을 가력하였다. 탄성계수와 압축강도의 차이를 고려시 순환골재를 사용한 실험체의 장기처짐이 천연 골재를 사용한 실험체보다 다소 크게 처짐이 발생하였으나 큰 차이를 보이지 않아 순환골재 실험체가 천연골재 실험체와 대등한 장기 휨 성능을 갖는 것으로 판단된다. 장기처짐 예측시 장기처짐 예측식에 적용하는 크리프계수와 건조수축은 CEB-FIP 기준을 적용하는 것이 ACI-209 기준을 적용하는 것보다 좋은 예측을 보였다. ACI-318의 예측 방법은 장기처짐을 과대평가하고 Mayer의 방법, Neville의 방법은 본 연구에서는 실험체의 낮은 인장철근비로 큰 오차를 보였다. Branson의 방법, EMM, AEMM은 장기처짐을 양호하게 예측하였으며 본 연구에서 제안된 방법이 순환골재 콘크리트 보의 장기처짐을 좋은 예측을 보여 순환골재 콘크리트 구조물의 장기거동을 합리적으로 반영할 수 있는 방안이 될 것으로 사료된다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 춘계 학술발표회
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• pp.164-178
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• 2009

The importance of long-term performance of reinforced earth structures has been gaining its attention as the use of reinforced earth structures as load supporting structures is increasing. When using reinforced earth structures as loading supporting structures the stability as well as serviceability requirements must be met. In that respect the time-dependent long term deformation characteristics should be well understood. In this study the applicability of power law-based creep models for modeling of creep deformation of the components of reinforced earth structures are examined.

• Structural Engineering and Mechanics
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• 제62권4호
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• pp.477-485
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• 2017

The structural designs of RC flat plates that have no flexural stiffness by boundary beams may be governed not by strength conditions but by serviceabilities. Specially, since over-loading and tensile cracking in early-aged slabs significantly increase the short- and long-term deflections of a flat plate system, a construction sequence and its impact on the slab deflections may be decisive factors in designs of flat plate systems. In this study, the procedure of simulating slab deflections with considering construction sequences, concrete cracking, and long-term effects is proposed. The proposed method is practically useful, as it can predict well the slab deflections at construction and service stages only with a few input data. The proposed method is verified by comparisons with measured results in a real-scale test.

• 한국지반환경공학회 논문집
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• 제22권10호
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• pp.31-36
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• 2021

풍력발전기 기초의 누적 회전각과 침하량을 예측하는 것은 매우 중요하다. 하지만 반복하중에 따른 버킷기초의 장기거동을 분석하는 연구는 거의 이루어지지 않았다. 본 연구에서는 사질토 지반에 설치된 버킷기초의 다양한 3차원 유한요소해석을 수행하였다. 반복 삼축압축시험으로부터 도출된 강성감소 경험식을 수치모델에 사용자 서브루틴으로 적용하여 해석을 수행하였다. 강성감소 모델을 사용하여 버킷기초의 누적 회전각을 산정하였으며, 반복하중 작용 시 거동에 영향을 주는 주요인자에 대한 분석이 이루어졌다.