• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.5
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• pp.1957-1968
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• 2013

Design criteria for rock load on tunnel concrete lining has not been established yet. Generally rock load on tunnel concrete lining is empirically estimated, which leads to a conservative design. Ordinary estimation method of rock load includes various problems. Estimating by numerical analysis is very complicated and has not been verified with field measurements. Therefore, it is necessary to conduct a study on practical method of estimating rock load which is more accurate to the real rock load on tunnel concrete lining. This study, presents estimation method of rock load on tunnel concrete lining. Crown settlement of the tunnel construction site has been measured and it was been back analyzed to estimate the rock load. The rock load was estimated to be smaller compare to the ordinary estimation method.

• Tunnel and Underground Space
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• v.21 no.4
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• pp.307-319
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• 2011

Cyclic loading due to traffic, excavation and blasting causes microcrack growth in rocks over long period of time, and this type of loading often causes rock to fail at a lower stress than its monotonically determined strength. Thus, the crack growth and coalescence under cyclic loading are important for the long-term stability problems. In this research, experiments using gypsum as a model material for rock are carried out to investigate crack propagation and coalescence under monotonic and cyclic loading. Both monotonic and cyclic tests have a similar wing crack initiation position, wing crack initiation angle, cracking sequence and coalescence type. Three types of crack coalescence were observed; Type I, II and III. Type I coalescence occurs due to a shear crack and Type II coalescence occurs through one wing or tension crack. For Type III, coalescence occurs through two wing or tension cracks. Fatigue cracks appear in cyclic tests. Two types of fatigue crack initiation directions, coplanar and horizontal directions, are observed.

• Journal of the Korean Recycled Construction Resources Institute
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• v.4 no.1
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• pp.47-54
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• 2016

In this study, the flexural capacity of fiber reinforced concrete floor slabs were evaluated using main design loads, racking and moving loads. Based on design standards and guidelines, the magnitude and loaded area of each load were determined, and its relationship was assessed. For the application of a single load, flexural capacity should be evaluated in the edge of a floor slab. In addition, the slab with thickness and concrete strength, greater than 180mm and 35MPa, respectively, sufficiently satisfied flexural capacity with a minimum of equivalent flexural strength ratio. The combination of racking loads required the largest equivalent flexural strength ratio to satisfy the flexural capacity of the floor slab. The combination of racking and moving loads showed equivalent flexural strength ratio smaller than the case of combination of racking loads, but larger than the application of single racking or moving loads. The results of this study indicated that the flexure of fiber reinforced concrete floor slabs should be designed using the combination of design loads.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.9
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• pp.853-860
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• 2017

To evaluate the effects of mode II on the crack initiation and propagation stages, the effects in the fatigue threshold region under a mixed-mode I+II loading state was experimentally investigated. In the case of mixed-mode I + II, during the crack initiation stage, as the loading application angle (${\theta}$) increased, cracks occurred in the lower load owing to the effects of mode II, while the crack propagation rate decreased. The effects of mode II were experimentally investigated in the crack propagation stage by means of multilevel loading direction variation. Following mixed-mode I+II ($0^{\circ}{\rightarrow}{\theta}{\rightarrow}60^{\circ}$), as the load application angle increased, the fatigue crack propagation rate decreased, as did the fatigue crack propagation rate, which occurred later. Following mixed-mode I + II in case of(${\theta}{\geq}75^{\circ}$), the fatigue crack propagation rate was found to increase, while the fatigue life decreased.

• Journal of the Earthquake Engineering Society of Korea
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• v.5 no.5
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• pp.35-45
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• 2001

Recently, the floor systems those require large open space may have low inherent damping due to the decline of the use of curtain walls. Furthermore, the use of the high strength materials has resulted in more flexible and longer spanning in floor systems. The long span structures such as shopping malls, offices and large assembly rooms may lead to significant dynamic response due to human activities. Excessive vibrations make the occupants uncomfortable and deteriorate the serviceability of buildings. It is now proved that footfall loading is the major source of floor vibrations. The common method of application of walking loads for the vibration analysis of structures subjected to walking loads is to inflict measured walking loads and periodic function at a node. But this method could not account for the moving effect of walking. In this study, natural frequency and damping ratio of example structure are evaluated by heel drop tests. And the application of equivalent walking loads is used for on efficient vibration analysis of the plate structures subjected to walking loads.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.4
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• pp.47-52
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• 2017

PSC (Prestressed Concrete) structures have been used widely for its engineering advantage with using total concrete area as effective compressive section. However tendon inside is exposed to such a high tensile stress that and more attentions should be paid for corrosion control. This work is for changing corrosion current and ultimate strength in tendon with increasing prestressing force in a constant corrosive condition. With increasing prestressing force, corrosion current, corrosion amount, and ultimate load are changed linearly. When prestressing force increases from 20.0 % to 40.0 %, corrosion current increases to 124.4 % and 168.0 % and ultimate load decreases to 87.8 % and 78.4 %, respectively. With inducing constant electrical potential, increasing corrosion current and reduction of strength are evaluated to be linearly related with increasing prestressing load.

• International Journal of Highway Engineering
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• v.7 no.3 s.25
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• pp.11-21
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• 2005

To examine adequacy of existing multi-layer elastic analysis of layer interface conditions, this study compared outputs of finite element analysis and multi-layer elastic analysis as vertical load was applied to the surface of asphalt pavements. Structural pavement analysis considering influence of a horizontal load was also carried out in order to simulate passing vehicle loads under various interface conditions using ABAQUS, a three dimensional finite element program. Pavement performance depending on interface conditions was quantitatively evaluated and fundamental study of layer interface effect was performed in this study. As results of the study, if only vertical load is applied, subdivision of either fully bonded or fully unbonded is enough to indicate interface condition. On the other hand, when horizontal load is applied with vertical load, pavement behavior and performance are greatly changed with respect to layer interface condition.

• Proceedings of the Korea Water Resources Association Conference
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• 2010.05a
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• pp.674-678
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• 2010

하천 형상은 자연적인 흐름과 인간의 활동에 의해 다양한 형태로 변화되며, 이러한 변화과정을 통해 안정된 형상을 갖추어간다. 이러한 변화는 흐름과 상호작용 과정을 통해 진전되며, 하천의 형태를 변화시키는 흐름 또한 저수로 형태 및 수량적인 변화 등에 의해 다양한 특성을 갖게 된다. 본 연구에서는 하천 내의 형태가 인간의 활동에 의해 인공적으로 변화되었을 경우 하천의 수리학적 특성에 미치는 영향을 3차원 수치해석 모형인 EFDC(Environmental fluid Dynamics Code, 미국 버지니아 해양연구소 개발) 모형을 이용하여 검토하였다. EFDC 모형은 크게 유동, 퇴적물 이송, 수질의 세 부분으로 구성되어 있으며, 유동 모델은 수온과 염분이 고려된 3차원 천수방정식을 기본으로 하고 있다. EFDC 모형의 적용을 위한 Case1은 일반적인 저수로 형태 갖는 하천이며, Case2에서는 하천 저수로 내 인공적으로 하중도가 설치되었을 경우에 대하여 수리학적 특성을 모의하였다. 수치모의 결과 다음과 같은 결과를 확인 할 수 있었다. 수위변화는 하중도 유무에 따라 상하류 부분에서 전혀 다른 결과를 나타냈다. 유속분포는 Case1에 비하여 Case2의 경우 하중도 설치에 의해 하천의 상류부에서는 흐름의 정체부분이 나타났으며, 하류부에서는 급확대에 의한 유속의 감소가 나타났다. 그리고 하중도에 의해 저수로가 분기됨에 따라 저수로의 급축소부가 발생되고, 이로 인해 유속이 급속히 증가되었다. 본 연구의 Case2와 같이 하천에 하중도를 설치할 경우 만곡부 외측 부분에서는 유속의 현저한 증가가 발생하는 것을 확인할 수 있었다. 이와 같이 하중도의 설치 위치, 하중도의 규모 등에 따라 하중도 부분의 급격한 수위 및 유속 변화이 발생되는 것을 확인하였으며, 만곡부에 이와 같은 것을 설치할 경우 보다 정밀한 수리계산을 통해 안전성이 확보되는 하중도 설치가 필요할 것으로 판단된다.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.2
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• pp.8-15
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• 2018

Hollow Core Slab is a very efficient system that can reduce weight and its use has increased. Void slab is a concrete slab that has voids substituted with void material. Because of its saved volume of concrete, void slab can reduce weight of slabs. Also, it can't only save concrete but also can reduce carbon-emission. However, because of the unclear bearing strength at the part of void substituted with voiding material, several problems occur in constructing field. In this study, void slab including void material was built and local bearing strength test was carried out for 3 types of load(truck load, support load and Jack support load). As a result, bearing strength of void neck and upper void material is more than allowable load. And also, bearing strength of specimens with using deck and not using deck are also over allowable loads.

• Journal of the Korea institute for structural maintenance and inspection
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• v.8 no.1
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• pp.129-138
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• 2004

In this study we determine a dynamic analysis of the existing two-span prestressed concrete box girder bridge subjected to moving vehicle loads using the experimental measurements. The moving loads applied in this paper are classified as general travelling, suddenly brake, continuous travelling, reversely travelling and reversely travelling impact loads for increasing velocities. For each travelling load, we search dynamic behaviors and characteristic in various measuring point of box girder section. In addition, the three-dimensional numerical results analyzed by the developed finite element program using flat shell element with six degrees of freedom per a node are compared with the measured experimental data. Dynamic behaviors caused impact loads by suddenly braking, reversely travelling, are bigger than by general travelling in box girder. Three-dimensional numerical results are better than one-dimensional results.