• Computers and Concrete
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• 제20권4호
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• pp.469-481
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• 2017

This paper aims to analytically investigate the effect of shear stress at the concrete-steel interface on the mechanical behavior of the circular steel tube-confined concrete (STCC) stub columns with active and passive confinement subjected to axial compression. Nonlinear 3D finite element models divided into the four groups, i.e. circumferential-grooved, talc-coated, lubricated, and normal groups, with active and passive confinement were developed. An innovative method was used to simulate the actively-confined specimens, and then, the results of the finite element models were compared with those of the experiments previously conducted by the authors. It was revealed that both the predicted peak compressive strength and stress-strain curves have good agreement with the corresponding values measured for the confined columns. Then, the mechanical properties of the active and passive specimens such as the concrete-steel interaction, longitudinal and hoop stresses of the steel tube, confining pressure applied to the concrete core, and compressive stress-strain curves were analyzed. Furthermore, a parametric study was performed to explore the effects of the concrete compressive strength, steel tube diameter-to-wall thickness ratio, and prestressing level on the compressive behavior of the STCC columns. The results indicate that reducing or removing the interfacial shear stress in the active and passive specimens leads to an increase in the hoop stress and confining pressure, while the longitudinal stress along the steel tube height experiences a decrease. Moreover, prestressing via the presented method is capable of improving the compressive behavior of STCC columns.

• 대한토목학회논문집
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• 제28권1C호
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• pp.53-62
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• 2008

본 논문에서는 직접단순전단변형으로 발생하는 주응력 방향의 회전에 의한 소성변형을 고려할 수 있는 구성모델을 제안하였다. 이 모델은 두 개의 응력면에서 발생하는 응력상태의 변화를 이용하여 각 응력면의 소성변형률을 계산하였다. 두 개의 응력면에서 계산된 소성변형률을 합산하여 전체 소성변형률을 구하였다. 첫번째 응력면은 최대전단응력면을 나타내며 이 응력면은 응력변화에 따라 수평방향을 기준으로 회전한다. 두번째 응력면은 수평방향으로 고정된 수평면을 나타낸다. 초기 수직응력과 수평응력이 서로 다른 상태에 있는 직접단순전단시험의 공시체에서 전단변형으로 발생하는 주응력 방향의 회전현상을 두번째 응력면에 작용하는 응력상태를 이용하여 모델링하였다. 본 모델의 구성관계식은 전단변형으로 인한 흙의 골격변화 즉 체적변화를 수식화하였으며 응력-물의 상관관계를 동시에 묘사할 수 있는 FLAC을 이용하여 모델링하였다. 느슨한 Fraser River 모래의 배수 직접단순전단시험에서 발생하는 전단응력과 체적변화는 주응력 방향의 회전에 따른 소성변형을 포함하고 있으므로 이를 계산하여 구성모델을 검증하였다. 느슨한 모래 지반에 놓인 강성기초의 하중 증가에 따라 발생하는 지반침하를 주응력 방향의 회전을 고려하여 예측하였을 때 실제 계측된 침하량과 유사한 결과를 얻었다. 주응력 방향의 회전을 고려하지 않고 Mohr-Coulomb모델을 이용하여 계산된 침하량은 실제 침하량 또는 제안된 모델이 예측한 침하량의 약 20%정도에 해당하였다.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2001년도 가을 학술발표회 논문집
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• pp.393-400
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• 2001

A simple numerical modelling technique is proposed for estimating the shear stress distribution in beams of framed tube structures with multiple internal tubes. The structures are analysed using a continuum approach in which each tube is individually modelled by a tube beam that accounts for the flexural and shear deformations, as well as the shear lag effects. The method idealises the discrete tubes-in-tube structures as an assemblage of equivalent multiple beams, each composed of orthotropic plate panels. The numerical analysis of shear stress is based on the elastic theory in conjunction with the minimum potential energy principle. By simplifying assumptions regarding the form of strain distributions in external and internal tubes, the shear stress distributions are expressed in terms of a series of linear functions of the second moments of area of the structures and the corresponding geometric and material properties, as well as the applied loads. The simplicity and accuracy of the proposed method are demonstrated through the solutions of three numerical examples.

• Composites Research
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• 제21권2호
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• pp.25-30
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• 2008

A hemispherical microbond specimen adhered onto single carbon fiber has been proposed for evaluating the interfacial shear strength between epoxy and carbon fiber. Hemispherical microbond specimens showed low interfacial shear strength data and its small standard deviation as compared with the droplet one, which seemed to be caused by the reduction of the meniscus effects and of the stress concentration in the region contacting with the tip of pin hole. In comparison with the droplet specimen the hemispherical specimen showed the shear stress distribution similar to the cylindrical one in that low stress concentration arose around the contacting region. Average interfacial shear strength obtained by the hemispherical ones represented a good correlation with the hardness of the epoxy matrix.

• 한국습지학회지
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• 제19권2호
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• pp.202-210
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• 2017

전단응력은 여러 분야에서 사용하는 매우 중요한 역학 인자 중 하나이며, 인공수로의 설계를 위해서 중요하다. 현재 전단응력은 과거에 정해진 계산법을 사용하고 있지만, 사용되는 식에서 바닥전단응력과 에너지경사와 같이 실제로 측정하거나 계산하기 어려운 요소들이 존재한다. 특히, 에너지경사는 산정하기 매우 어려운 인자이며, 전단응력분포를 구하기위해서는 에너지경사가 있어야만 산정할 수 있지만, 경계층의 유속기울기와 유속을 측정하는 것은 현실적으로 어려운 부분이다. 또한 전단응력분포 중 바닥전단응력은 직접 측정하기 매우 어렵고, 유속에 비해 연구가 다소 더딘 실정이다. 전단응력분포를 정확하게 산정할 수 있다면, 바닥전단응력과 에너지경사를 손쉽게 산정할 수 있다. 본 연구에서는 에너지경사를 반영하지 않고 엔트로피 M을 이용하여 평균유속과 전단응력분포를 간단히 산정하는 연구를 진행하였고, 적용한 식의 효용성을 증명하기 위해 기존의 실험실 실측 자료를 사용하였다. 이는 그래프를 통해 응력분포를 나타내어 비교분석을 하였으며, 등류와 부등류에서 각각 결정계수는 0.930-0.998까지로 거의 일치하였다.

• 한국방사성폐기물학회:학술대회논문집
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• 한국방사성폐기물학회 2009년도 학술논문요약집
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• pp.187-187
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• 2009

Opening of fractures induced by shear dilation or normal deformation can be a significant source of fracture permeability change in fractured rock, which is important for the performance assessment of geological repositories for spent nuclear fuel. As the repository generates heat and later cools the fluid-carrying ability of the rocks becomes a dynamic variable during the lifespan of the repository. Heating causes expansion of the rock close to the repository and, at the same time, contraction close to the surface. During the cooling phase of the repository, the opposite takes place. Heating and cooling together with the, virgin stress can induce shear dilation of fractures and deformation zones and change the flow field around the repository. The objectives of this work are to examine the contribution of thermal stress to the shear slip of fracture in mid- and far-field around a KBS-3 type of repository and to investigate the effect of evolution of stress on the rock mass permeability. In the first part of this study, zones of fracture shear slip were examined by conducting a three-dimensional, thermo-mechanical analysis of a spent fuel repository model in the size of 2 km $\times$ 2 km $\times$ 800 m. Stress evolutions of importance for fracture shear slip are: (1) comparatively high horizontal compressive thermal stress at the repository level, (2) generation of vertical tensile thermal stress right above the repository, (3) horizontal tensile stress near the surface, which can induce tensile failure, and generation of shear stresses at the comers of the repository. In the second part of the study, fracture data from Forsmark, Sweden is used to establish fracture network models (DFN). Stress paths obtained from the thermo-mechanical analysis were used as boundary conditions in DFN-DEM (Discrete Element Method) analysis of six DFN models at the repository level. Increases of permeability up to a factor of four were observed during thermal loading history and shear dilation of fractures was not recovered after cooling of the repository. An understanding of the stress path and potential areas of slip induced shear dilation and related permeability changes during the lifetime of a repository for spent nuclear fuel is of utmost importance for analysing long-term safety. The result of this study will assist in identifying critical areas around a repository where fracture shear slip is likely to develop. The presentation also includes a brief introduction to the ongoing site investigation on two candidate sites for geological repository in Sweden.

• Korea-Australia Rheology Journal
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• 제13권3호
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• pp.109-123
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• 2001

A stress jump, defined as the instantaneous gain or loss of stress on startup or cessation of a deformation, has been predicted by various models and has relatively recently been experimentally observed. In 1993, Liang and Mackay measured shear stress jump data of xanthan gum solutions, and in 1996, Orr and Sridhar reported extensional stress jump data of Boger fluids. Shear stress jumps of suspensions and liquid crystal polymers have also been observed. In this contribution, experimental work as well as a variety of theoretical models, which are able to predict a stress jump, are reviewed.

• Fibers and Polymers
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• 제7권2호
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• pp.129-138
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• 2006

Using a strain-controlled rheometer, the steady shear flow properties of aqueous xanthan gum solutions of different concentrations were measured over a wide range of shear rates. In this article, both the shear rate and concentration dependencies of steady shear flow behavior are reported from the experimentally obtained data. The viscous behavior is quantitatively discussed using a well-known power law type flow equation with a special emphasis on its importance in industrial processing and actual usage. In addition, several inelastic-viscoplastic flow models including a yield stress parameter are employed to make a quantitative evaluation of the steady shear flow behavior, and then the applicability of these models is also examined in detail. Finally, the elastic nature is explained with a brief comment on its practical significance. Main results obtained from this study can be summarized as follows: (1) Concentrated xanthan gum solutions exhibit a finite magnitude of yield stress. This may come from the fact that a large number of hydrogen bonds in the helix structure result in a stable configuration that can show a resistance to flow. (2) Concentrated xanthan gum solutions show a marked non-Newtonian shear-thinning behavior which is well described by a power law flow equation and may be interpreted in terms of the conformational status of the polymer molecules under the influence of shear flow. This rheological feature enhances sensory qualities in food, pharmaceutical, and cosmetic products and guarantees a high degree of mix ability, pumpability, and pourability during their processing and/or actual use. (3) The Herschel-Bulkley, Mizrahi-Berk, and Heinz-Casson models are all applicable and have equivalent ability to describe the steady shear flow behavior of concentrated xanthan gum solutions, whereas both the Bingham and Casson models do not give a good applicability. (4) Concentrated xanthan gum solutions exhibit a quite important elastic flow behavior which acts as a significant factor for many industrial applications such as food, pharmaceutical, and cosmetic manufacturing processes.

• 한국지반환경공학회 논문집
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• 제11권1호
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• pp.27-34
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• 2010

본 연구에서는 유한요소해석을 실시하여 지반굴착으로 인해 융기(heaving)가 발생하는 지반에 사전에 근입된 말뚝의 거동에 대한 분석을 실시하였다. 수치해석에서는 말뚝과 점토사이 경계면에서의 미끄러짐(소성항복)을 고려하여 그 상호거동에 대하여 고찰하였다. 본 연구에서는 말뚝의 상향변위, 말뚝과 인접지반의 상대변위, 말뚝에 작용하는 전단응력 및 인장력을 분석하였다. 특히, 수직응력의 감소로 인해 말뚝과 인접지반에서의 전단응력이 전이되는 메커니즘에 대한 심도있는 분석을 실시하였다. 굴착에 의해 수직응력이 감소하여 말뚝과 인접지반 사이에서의 상대변위 및 전단응력이 변화하였다. 말뚝 대부분의 위치(Z/L=0.0-0.8)에서는 상향의 전단응력이 발생하였으나, 말뚝 선단부 부근(Z/L=0.8-1.0)에서는 하향의 전단응력이 발생하였고, 이로 인해 말뚝에는 인장력이 발생하였다. Z는 임의의 심도, L은 말뚝의 길이이다. 수치해석을 통해서 분석된 말뚝의 거동에 대하여 상세히 보고하였다.

• 한국지반공학회논문집
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• 제18권3호
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• pp.73-85
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• 2002

본 논문에서는 비등방 압밀된 낙동강 포화모래의 비배수 반복 전단강도 거동이 연구되었으며, 등방압밀된 시료의 반복삼축시험은 비등방 압밀시료와의 비교를 위하여 수행되었다. 초기 정적 전단음력과 상대밀도의 다양한 조합하에 반복 전단강도는 고찰되었다. 음력반전과 비응력반전 모두에 대하여 반복하중을 받는 시료의 파괴는 5%의 양진폭변형율과 5%의 잔류축변형율로서 정의하였다. 비등방 압밀된 시료의 반복 전단강도는 초기 정적 전단강도에 영향을 받는 것으로 나타났다. 비등방 압밀 낙동강 모래의 반복 전단강도는 Toyoura 실리카 모래의 전단강도 보다는 크지만, Dogs Bay 카보나이트 모래의 전단강도 보다는 작게 나타났다. 실험결과와 예측결과의 비교에 의하면, 낙동강 모래의 잔류 간극수압에 대한 Hyodo 모델의 적용성이 입증되었다.