• Journal of the Society of Disaster Information
• /
• v.7 no.3
• /
• pp.206-219
• /
• 2011

The important elements in pavement design criteria are the stress and strain distributions. To obtain reasonable stress and strain distribution, tire contact area and tire pressures are very important. This study presents a viscoelastic characterization of flexible pavement subjected to moving loads. During the test, both longitudinal and lateral strains were measured at the bottom of asphalt layers and in-situ measurements were compared with the results of numerical analysis. A 3-dimension finite element model was used to simulate each test section and a step loading approximation has been adopted to analyze the effect of a moving vehicle on pavement behaviors. For viscoelastic analysis, relaxation moduli, E(t), of asphalt mixtures were obtained from laboratory test. Field responses reveal the strain anisotropy (i.e., discrepancy between longitudinal and lateral strains), and the amplitude of strain normally decreases as the vehicle speed increases. In most cases, lateral strain was smaller than longitudinal strain, and strain reduction was more significant in lateral direction.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.20 no.5
• /
• pp.491-497
• /
• 2008

The effect of wave and current interactions on jet-like current flowing against waves was investigated based on numerical simulations. The numerical simulations were conducted using a model system of REF/DIF(a wave model) and SHORECIRC(a current model). In the simulations, irregular waves refracted due to the jet-like opposing current were focused along the centerline of current, and the jet-like current was spreaded earlier when the wave heights become larger. The numerical results show that the rapid change of wave height distribution in transverse direction near current inlet plays a significant role to spread the jet-like current. In other words, the radiation stress gradients acting in transverse direction have a more significant effect on the jet-like current than its gradients acting in flowing direction which tend to accelerate the current do. In conclusion, it is indispensible to take into account the interaction between waves and current when the jet-like current such as river mouth meets opposing waves.

• Journal of the Korea Concrete Institute
• /
• v.13 no.5
• /
• pp.499-506
• /
• 2001

Eight direct tension tests were conducted to study the bond characteristics and crack behavior in high-strength concrete axial members. The main variable was the concrete strength up to 61-63 MPa. The specimens consisted of two different types of the short specimens modeled the part between transverse cracks and the long specimens having numerous transverse cracks. The results obtained show that the bond strength increases in proportion to compressive strength. Thereby, in high-strength concrete the length of stress-disturbed region is shortened and the space of adjacent transverse cracks become smaller. Although the concrete strength varies from 25 MPa to 61 MPa, the split cracking loads remain constant, while transverse cracking loads vary as variation of concrete tensile strength. Accordingly, the current code provisions for development length may need reconsideration in high-strength concrete members, and it is recommended that either thicker cover or transverse reinforcement should be additionally provided for high-strength concrete members.

• Journal of Korean Society of Steel Construction
• /
• v.16 no.1 s.68
• /
• pp.155-167
• /
• 2004

In this paper, the inelastic buckling behavior of the beam under uniform bending was investigated using the energy-based method, which can tackle problems in fourth order eigenvalue. The pattern of residual stress was not available to satisfy the I-sections manufactured in Korea. however; therefore, the well-known polynomial and simplified pattern of residual stress was adopted in this study. The inelastic lateral-distortional buckling behavior of the beam with I-sections manufactured in Korea was investigated. The study was then extended to the inelastic lateral-torsional buckling of the beam by minimizing the out-of-plane web distortion. The inelastic lateral-torsional buckling results obtained in this paper were compared with the prediction of allowable bending stress given in the Korean steel designers' manual (1995). Results showed that the importance of inelastic lateral-distortional buckling did not arise for beams under uniform bending. Likewise, the design method in KSDM (1995) was proven to bo too conservative for intermediate and short spans of beams without intermediate bracing.

• Proceedings of the KAIS Fall Conference
• /
• 2008.11a
• /
• pp.101-104
• /
• 2008

일반적으로 연속경간을 가지는 강합성 I-형강 교량에 있어서 내부 지점 부근에서 상대적으로 큰 부모멘트가 발생하므로, 이에 경제적인 단면 활용을 위하여 변단면을 적용하여 휨강도를 증가시킨다. 본 연구에서는 기존 강도계산식에 관한 연구를 토대로 하여 비탄성 구간에 있는 변단면 I형보의 횡-비틀림 좌굴강도를 유한요소해석프로그램 ABAQUS(2007)를 이용하여 산정하고, 간편한 설계식을 제안하고 있다. 지간 한쪽 끝에 계단식 단면변화를 가지는 보에 대해서 고려하였으며, 플랜지 길이방향 비, 너비방향 비, 두께의 비로 계단식 I형보를 나타내었다. 해석에 사용된 단면매개변수는 36가지 조합이며, 비탄성 횡-비틀림 거동을 고려하기위하여 잔류응력 및 초기결함을 고려한 비선형해석을 실시하였는데, Pi(1995)등이 고려한 잔류응력의 형상과 국내 I형강 표준 치수 허용치에 근거하여 부재 길이의 0.1%를 초기제작오차로 고려하였다. 해석모델의 양쪽 끝단에는 모멘트하중을 재하하였다. 개발 제한된 식은 선형 모멘트 하중이 작용할 때 적용가능한 식으로 경제적이고 합리적인 설계에 적극 활용될 수 있을 것이다.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.8 no.2
• /
• pp.101-113
• /
• 2006

Arching effect occurs around the unsupported excavation surface near to tunnel face when a tunnel is excavated in a stable rock mass. If a weak fracture zone exists in front of tunnel face, a displacement occurs between tunnel face and weak fracture zone due to stress concentration. If three-dimensional absolute coordinates (longitudinal, transverse, vertical direction) is measured at tunnel face by geodetic method, the ground change in front of the tunnel face can be predicted by analysing three-dimensional absolute displacement. The purpose of this study is to verify the analysis method of three-dimensional absolute displacement by comparing the trend of displacement ratio at crown and sidewall of tunnel and the influence line/trend line of crown settlement compared with TSP results in the same section.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.12 no.2
• /
• pp.185-199
• /
• 1999

본 연구에서는 새로운 spline 유한대판 요소를 제안하였다. 제안된 정식화는 등매개 개념에 의해 기하학적 형상과 변위장을 가정함에 있어 길이방향은 3차의 B-spline 곡선으로, 횡방향에 대해서는 Lagrange 다항식에 의해 표현된다. 이 논문은 평판과 쉘해석에 있어서의 등매개 spline 유한대판 요소의 개선에 목적을 두고 있다. 이 새로운 요소는 스트립의 내부 절점에서 6개의 자유도를 갖는 합-응력 감절점 쉘 요소로부터 유도하였다. 스트립의 기하학적 형상은 강체 회전에 대한 정의에 위배되지 않고도 두께 방향을 따라 Jacobian이 일정하다는 가정을 따랐으며 고체역학에서 정의되는 면내 회전을 penalty 함수에 의한 구속조건으로 간주하여 면내 회전에 관계된 자유도를 생성하였다. 제안된 요소에 대하여 쉘의 전형적인 문제에 대한 수치예제를 보였으며 이 스트립 요소의 성능을 평가하였다.

• Journal of the Korean Geotechnical Society
• /
• v.34 no.12
• /
• pp.19-27
• /
• 2018

Terzaghi proposed a 2D formula for arching based on the assumption of a vertical sliding surface induced in the upper part due to the downward movement of a trapdoor. The formula was later expanded to consider 3D tunnel excavation conditions under inclined sliding surfaces. This study further extends the expanded formula to consider the effects of different ground properties and inclined sliding conditions in the transverse and longitudinal directions considering anisotropic ground conditions, as well as 3D tunnel excavation conditions. The 3D formula proposed in this study was examined of the induced vertical stress under various conditions (ground property, inclined sliding surface, excavation condition, surcharge pressure, earth pressure coefficient) and compared with the 2D Terzaghi formula. The examination indicated that the induced vertical stress increased as the excavation width and length increased, the inclination angle increased, the cohesion and friction angle decreased, the earth pressure coefficient decreased, and the surcharge pressure increased. Under the conditions examined, the stress was more affected at low excavation lengths and by the ground properties in the transverse direction. In addition, The comparison with the 2D Terzaghi formula showed that the induced vertical stress was lower and the difference was highly affected by the ground properties, inclined sliding conditions, and 3D tunnel excavation conditions. The proposed 3D arching formula could help to provide better understanding of complex arching phenomena in tunnel construction.

• Journal of the Korea Concrete Institute
• /
• v.19 no.3
• /
• pp.253-263
• /
• 2007

Previous researches showed that confined concrete with Fiber-Reinforced Plastic (FRP) sheets significantly improves the strength and ductility of concrete compared with unconfined concrete. However, the retrofit design of concrete with FRP materials requires an accurate estimate of the performance enhancement due to the confinement mechanism. The object of this research is to predict the compressive strength and strain of concrete confined with FRP wraps. For the purpose of this research, 102 test specimens were fabricated and loaded statically under uniaxial compression. Axial load, axial and lateral strains were investigated to predict the ultimate stress and strain. Also, to achieve reliability of proposed strength and strain models for FRP-confined concrete, another series of uniaxial compression test results were used. This paper presents strength and strain models for FRP-confined concrete. The proposed models to estimate the ultimate stresses and failure strains produce satisfactory predictions as compared to current design equations. In conclusion, it is proposed that the modified stress-strain model of concrete cylinders could be effectively used for the repair and retrofit of concrete columns.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.20 no.5
• /
• pp.102-108
• /
• 2016

The purpose of this study is to examine the reduction effect of shrinkage reducing agent for drying shrinkage induced cracking and suggest the method of controlling the cracking in concrete box culvert for power transmission. Based on drying shrinkage cracking mechanism, it is necessary to perform the numerical analysis, which involves shrinkage reducing effect of shrinkage reducing agent. From the numerical results, it is found that cracking behavior for longitudinal direction and transverse direction due to differential drying shrinkage of box culvert can occur and the experimental observation of concrete cracks support the numerical predictions. The shrinkage reducing agent reduced the concrete cracking by 40~50%, which shows the methodology of controlling of drying shrinkage cracks in box culverts in real construction site.