• Journal of the Korean Geotechnical Society
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• v.22 no.11
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• pp.55-64
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• 2006

It is very Important to predict the damage zone of a rock mass induced by blasting for the excavation of an underground cavity such as a tunnel, as the damage zones incur mechanical and hydraulic instability of the rock mass potentially. Complicated blasting processes that can hinder the proper characterization of the damage zone can be effectively represented by two loading mechanisms. The first mechanism is the dynamic impulsive load-generating stress waves that radiate outwards immediately after detonation. This load creates a crushed annulus along with cracks around the blasthole. The second is the gas pressure that remains for an extended time after detonation. As the gas pressure reopens some arrested cracks and extends these, it contributes to the final structure of the damage zone induced by the blasting. This paper presents a simple method to evaluate the damage zone induced by gas pressure during rock blasting. The damage zone is characterized by analyzing crack propagations from the blasthole. To do this, a model of a blasthole with a number of radial cracks that are equal in length in a homogeneous infinite elastic plane is considered. In this model, crack propagation is simulated through the use of only two conditions: a crack propagation criterion and the mass conservation of the gas. The results show that the stress intensity factor of a crack decreases as the crack propagates from the blasthole, which determines the crack length. In addition, it was found that the blasthole pressure continues to decrease during crack propagation.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.10 no.2
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• pp.23-38
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• 1990

In this study, decompositive optimization method of two levels was selected to optimize effectively the geometry of the truss which takes the multi-loading condition, and the allowable stress, bucking stress, displacement and natural frequency constraints into consideration. The algorithm of this study is made up of sectional optimization using the feasible direction method in level 1, and geometrical optimization employing Powell's one-direction search method which menimizes only objictive function in level 2. The results of this study acquired by beenning applied to structural model of the truss are as follows : 1. It is verified that the algorithm of this study effectively converges, independent of the initial geometry of the truss and the applied various constraints. 2. The optimum goemetry of the truss varies more considerably according to the constraints selected. 3. Under the condition of the same design, the weight of the truss can be decreased more considerably by means of optimizing even the geometry of truss than by means of optimizing the section of truss while fixing geometrical configuration of it, even though there might be a little difference according to the initial geometry of the truss and the design condition.

• Composites Research
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• v.23 no.3
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• pp.19-30
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• 2010

The present study describes a method for analytical solution to elastic field in structural elements of general symmetric laminated composite materials. The two dimensional plane stress elasticity problems under mixed boundary conditions are reduced to the solution of a single fourth order partial differential equation, expressed in terms of a single unknown function, called displacement potential function. In addition, all the components of stress and displacement are expressed in terms of the same displacement potential function, which makes the method suitable for any boundary conditions. The method is applied to obtain analytical solutions to two particular problems of structural elements consisting of an angle-ply laminate and a cross-ply laminate, respectively. Some numerical results are presented for both the problems with reference to the glass/epoxy composite. The results are highly accurate and reliable as all the boundary conditions including those in the critical regions of supports and loads are satisfied exactly. This verifies the method as a simple and reliable one as well as capable to obtain exact analytical solution to elastic field in structural elements of composite materials under mixed and any other boundary conditions.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.6
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• pp.614-627
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• 2018

Urban railway lines have been constructed adjacent to residential buildings and urban areas. The expansion of transportation networks and reconstruction of residential buildings in highly populated urban areas require deep excavations in areas adjacent to urban railways. Mobilized soil stresses and changes in the groundwater level induced by deep excavations results in track irregularities in urban railways. In this study, a three-dimensional finite difference model using the commercial program FLAC3D was adopted to estimate the horizontal displacements of earth retaining structures, settlements of backfill, the stability of track irregularity and underground box structure based on the criteria of each railway organization and its relationships. In deep excavations, a change in groundwater level induces relatively very small differences for track gauge irregularities, whereas relatively large differences for longitudinal irregularities of 72.5%, twist irregularities of 83.3%, cross level irregularities of 61.9%, and alignments of 43.3% were found to be the maximum differences when the horizontal displacement of earth retaining wall and settlement of backfill were 65.1% and 21.4%, respectively, because the groundwater level (GWL) on the ground surface-mobilized tensile strength of the underground box structure exceeds the allowable value. Therefore, three-dimensional numerical analysis was performed in this study. Overall, real-time monitoring should be carried out to prevent railway accidents in advance when a deep excavation adjacent to urban railway structures is constructed.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.2
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• pp.38-46
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• 2014

Effects of various parameters on bond property between reinforcing bar and concrete are investigated in many researchers, and various study is on going to improve the bond strength. Properties of interface between reinforcement and concrete is important role in bond property. This study analyzed the interfacial bond mechanism between deformed bar and concrete by finite element analysis (FEA) to evaluate the effect of rib shape. The FEA model in this study is simplified 2D plane stress model. The variables of analysis are selected by rib angle, rib height, rib spacing and relative rib area. From the results of analysis, reinforcing bars with rib angle $30{\sim}60^{\circ}$ showed better bond strength than the others. Bond strength ratio following to the rib height is proportionally increased up to the $0.12d_b$, but rib spacing has little effect on bond strength. The results also indicated that relative rib area can be efficiently represented the properties of deformed shape in reinforcing bars, and zigzagged rib height shape showed excellent bond strength increase.

• Geotechnical Engineering
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• v.10 no.2
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• pp.41-56
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• 1994

Under the groundwater level, the tunnel face is affected by the seepage force and the groundwater flow may cause a trouble to the tunnel support systems. The appropriate methods of analysis and design in the tunnel face and the lining, considering groundwater flow according to tunnel drainage condition are presented in this thesis. First, the effect of seepage on the stability of tunnel face was studied. Seepage force was estimated by the 3-D finite element analysis and the stability of tunnel face was checked by analytical method. Furthermore, using the finite difference method the stress and displacement on the face were computed for either case, where the seepage force is or is not considered, and the effect of seepage on the tunnel face stability was evaluated. Second, the effect of seepage force on the tunnel lining when construction is finished and steady state seepage flow occurs was studied and a design methodology considering seepage effect was made. Consequently, in case where the groundwater level remains almost unchanged and the steady state groundwater flow occurs, the proper countermeasures for face staility are required according to the condition of groundwater flow. Moreover, the tunnel lining should be designed and constructed considering the seepage force occuring by the groundwater flow toward the tunnel linings.

• 한국지구과학회:학술대회논문집
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• 2010.04a
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• pp.48-50
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• 2010

Stommel(1948)은 서안경계류의 원인이 베타효과($\beta$-effect)라 일컫는 코리올리 파라미터(f)의 위도 변화 때문인 것을 밝혔다. 서안경계류는 고등학교나 대학 교양에서 중요하게 다뤄지고 있다. 학생들은 보통 이론 수업만으로 서안경계류의 발생 과정, 이에 관련된 코리올리 힘, 베타효과 등을 이해해야 한다. 때문에 서안경계류와 관련된 실험이 있다면 이를 이해하는 데 큰 도움이 될 것이다. 또한 연구에서 검토한 6종의 고등학교 지구과학 2 교과서는 서안경계류를 본문과 더불어 삽화로 설명하고 있다. 그러나 이 중 3종의 교과서 삽화에서는 서안경계류의 발생 원인을 코리올리 힘만으로 지적하고 있다. 따라서 일부 학생은 서안경계류의 원인을 코리올리 힘으로 오해 할 수 있다. 위와 같은 이유로 우리는 서안경계류가 코리올리 힘의 작용과 베타효과에 의해 나타나는 것을 쉽게 확인 할 수 있는 실험 장치와 다양한 실험 방법을 개발하였다. 개발한 실험 장치는 직육면체의 수조와 회전 속도를 조절할 수 있는 테이블로 구성된다. (Fig. 1) 이와 같은 회전수조는 대기와 해양의 움직임을 실험실에서 모사하기 위해 자주 사용되었다(Beardsely 1969, 소선섭 등 1995; 1997). 우리의 수조는 경사진 바닥과 평평한 바닥으로 두종류를 제작하였다. 바닥이 경사진 수조는 베타효과를 구현하기 위한 것이다. 반시계 방향으로 회전하는 테이블은 중위도 어떤 위도에 접하는 가상의 평면이 지구 자전에 의해 회전하는 것을 나타낸다. 그리고 수조 상부에는 회전원판을 물에 접하여 시계방향으로 회전시킨다. 회전원판은 북반구 중위도 해양에 작용하는 바람 응력을 나타낸다. 우리는 테이블의 회전유무와 바닥의 경사유무에 따라 4개 실험을 수행하였다(Table. 1). 각 실험에서 물을 채운 수조를 원판에 올려놓고, 회전원판을 작동시킨 후 20분 동안 그대로 두어 수조안의 미세규모의 운동을 최소화 시킨 후 잉크를 떨어뜨리고 관찰하였다. 그 결과 실험 SB_f1은 베타효과와 코리올리 힘이 존재하여 서쪽 경계에서 좁고 빠른 흐름을 만들고 수조의 중간 부근에서 경계를 벗어나 동쪽으로 향하고 있다. 이 모습은 실제 해양의 서안경계류의 분리 현상과 비슷하다. FB_f1은 코리올리 힘만 존재하여 서쪽 경계에서 좁고 빠른 순환과 경계를 벗어나 동쪽으로 분리되는 흐름이 나타나지 않으며 전반적으로 크게 회전하는 모습을 보인다. SB_f0은 바람의 응력만 존재하는 경우로 잉크가 확산하는 모습을 보이며 나선팔의 모양으로 회전하면서 넓게 퍼져나간다. FB_f0의 모양도 이와 비슷하게 나타난다. 실험 SB_f1과 FB_f1을 비교하여 서안경계류는 코리올리 힘의 위도변화 효과인 베타효과가 있을 때 발생한다는 것을 알 수 있다(Fig. 2). 이 결과는 "단순히 코리올리 효과에 의해 서안경계류가 발생한다"는 생각을 바꾸게 할 것이다. 덧붙여 서안경계류 분리와 수조 바닥의 경사의 관계를 살펴보기 위한 실험을 실시하였다. 경사가 더 급하면 ($\alpha=20^{\circ}$) 서쪽 경계를 벗어나는 지점이 좀 더 북쪽에 나타났다. 현재 서안경계류는 개발한 실험 장치와 방법을 학교 현장에 적용하여 그 교육적 활용 가치를 평가하는 연구를 진행하고 있다.

• Journal of the Korean Geotechnical Society
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• v.34 no.11
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• pp.57-70
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• 2018

In this study, verification of the nonlinear effective stress analysis is performed for introducing performance based earthquake resistance design of port and harbor structures. Seismic response of gravitational caisson quay wall in numerical analysis is compared directly with dynamic centrifuge test results in prototype scale. Inside of the rigid box, model of the gravitational quay wall is placed above the saturated sand layer which can show the increase of excess pore water pressure. The model represents caisson quay wall with a height of 10 m, width of 6 m under centrifugal acceleration of 60 g. The numerical model is made in the same dimension with the prototype scale of the test in two dimensional plane strain condition. Byrne's liquefaction model is adopted together with a nonlinear constitutive model. Interface element is used for sliding and tensional separation between quay wall and the adjacent soils. Verification results show good agreement for permanent displacement of the quay wall, horizontal acceleration at quay wall and soil layer, and excess pore water pressure increment beneath the quay wall foundation.

• Journal of Korean Society of Steel Construction
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• v.16 no.2 s.69
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• pp.201-213
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• 2004

A GA-based optimum design algorithm and a program for plane steel frame structures with semi-rigid connections are presented. The algorithm is incorporated with the refined plastic hinge analysis method wherein geometric nonlinearity is considered by using the stability functions of beam-column members, and material nonlinearity, by using the gradual stiffness degradation model that includes the effects of residual stresses, moment redistribution through the occurrence of plastic hinges, semi-rigid connections, and geometric imperfection of members. In the genetic algorithm, the tournament selection method and micro-GAs are employed. The fitness function for the genetic algorithm is expressed as an unconstrained function composed of objective and penalty functions. The objective and penalty functions are expressed as the weight of steel frames and the constraint functions, respectively. In particular, the constraint functions fulfill the requirements of load-carrying capacity, serviceability, ductility, and construction workability. To verify the appropriateness of the present method, the optimal design results of two plane steel frames with rigid and semi-rigid connections are compared.

• The Journal of Engineering Geology
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• v.5 no.3
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• pp.237-274
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• 1995

This study was focused on the improvement of the measurement technique of P-wave velocity for the assesment of the anisotropy of the engineering property of rock. Samples used were collected from a working quarry within the Carnmenellis granite area on which series of engineering geological data have been accumulated. This study mainly concerned the development of measurement technique at the curved surface of rock, the use of natural honey-based coupling agent and the drying method for rock specimen over $P_2O_5$. According to the results, the range of the P-wave velocity anisotropy in two dimensional plane, fell between 0 and 4.68 (%). The direction where maximum velocity occurred was parallel to the orientation of the maximum in-situ stress. The result showed that P - wave velocity is a useful measure to asses the anisotropy of the engineering property of rock and it is suggested that the improvements adopted here can be applied to the experimental work on the rocks in Korea.