• Structural Engineering and Mechanics
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• 제59권1호
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• pp.101-122
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• 2016

Elasticity solutions for bi-directional functionally graded beams subjected to arbitrary lateral loads are conducted, with emphasis on the end effects. The material is considered macroscopically isotropic, with Young's modulus varying exponentially in both axial and thickness directions, while Poisson's ratio remaining constant. In order to obtain an exact analysis of stress and displacement fields, the symplectic analysis based on Hamiltonian state space approach is employed. The capability of the symplectic framework for exact analysis of bi-directional functionally graded beams has been validated by comparing numerical results with corresponding ones in open literature. Numerical results are provided to demonstrate the influences of the material gradations on localized stress distributions. Thus, the material properties of the bi-directional functionally graded beam can be tailored for the potential practical purpose by choosing suitable graded indices.

• 한국지반공학회논문집
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• 제18권5호
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• pp.169-178
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• 2002

토목섬유 보강점성토의 응력~변형특성을 삼축압축시험을 통하여 조사하였다. 모든 시험은0.05kgf/$cm^2$의 낮은 응력 증분으로 필요한 유효응력 수준까지 등방압밀 혹은 이방압밀한 후 배수조건으로 수행되었다. 보강토벽, 보강토교대, 보강성토와 같은 토류 구조물의 경우 일반적으로 이방응력 상태에 있으며, 이방압밀 배수전단시험의 경우 이러한 현장조건을 재현하기 위한 것이다. 일련의 시험결과로부터 이방압밀 보강점성토의 거동은 등방압밀 보강점성토의 응력~변형특성과 매우 상이한 것으로 나타났다. 특히, 이방압밀 보강점성토의 초기변형계수의 경우 등방압밀의 경우에 비하여 현저히 높은 것으로 나타났다. 또한, 등방압밀의 경우(약 1.0~5.0%)에 비하여 이방압밀의 경우 매우 낮은 축변형률(0.01%)에서 보강효과가 발생하였다.

• Steel and Composite Structures
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• 제22권1호
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• pp.203-216
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• 2016

To study the stress concentration factors (SCFs) of concrete-filled tubular Y-joints subject to in-plane bending, experiments were used to investigate the hot spot stress distribution along the intersection between chord and brace. Three concrete-filled tubular chords forming Y-joints were tested with different reinforcing components, including doubler-plate, sleeve, and haunch-plate reinforcement. In addition, an unreinforced joint was also tested for comparison. Test results indicate that the three different forms of reinforcement effectively reduce the peak SCFs compared with the unreinforced joint. The current research suggests that the linear extrapolation method can be used for chords, whereas the quadratic extrapolation method must be used for braces. The SCF is effectively reduced and more evenly distributed when the value of the axial compression ratio in the chord is increased. Furthermore, the SCFs obtained from the test results were compared to predictions from some well-established SCF equations. Generally, the predictions from those equations are very consistent for braces, but very conservative for concrete-filled chords.

• Geomechanics and Engineering
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• 제27권6호
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• pp.595-604
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• 2021

With the advantages of high permeability and strength, pervious concrete piles can be suitable for ground improvement with high water content and low bearing capacity. By comparing the strength and permeability of pervious concrete with different aggregate sizes (3-5 mm and 4-6 mm) and porosities (20%, 25%, 30% and 35%), the recommended aggregate size (3-5 mm) and porosity (30%) can be achieved. The model tests of the pervious concrete piles in soft soil (silt and clay) foundations were conducted to evaluate the bearing characteristics, results show that, for the higher consolidation efficiency of the silty foundation, the bearing capacity of the silty foundation is 16% higher, and the pile-soil stress ratio is smaller. But when it is the ultimate load for the piles, they will penetrate into the underlying layer, which reduces the pile-soil stress ratios. With higher skin friction of the pile in the silty foundation, the pile penetration is smaller, so the decrease of the pile axial force can be less. For the difference in consolidation efficiency, the skin friction of pile in silt is more affected by the effective stress of soil, while the skin friction of pile in clay is more affected by the lateral stress. When the load reaches 4400 N, the skin friction of the pile in the silty foundation is about 35% higher than that of the clay foundation.

• Structural Engineering and Mechanics
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• 제59권4호
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• pp.621-652
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• 2016

A new cable-supported bridge model consisting of suspension parts, self-anchored cable-stayed parts and earth-anchored cable-stayed parts is presented. The new bridge model can be used for suspension bridges, cable-stayed bridges, cable-stayed suspension bridges, and partially earth-anchored cable-stayed bridges by varying parameters. Based on the assumption that each structural member is in either an axial compressive or tensile state, and the stress in each member is equal to the allowable stress of the material, the material quantity for each component is calculated. By introducing the unit cost of each type of material, the estimation formula for the cost of the new bridge model is developed. Numerical examples show that the results from the estimation formula agree well with that from the real projects. The span limit of cable supported bridge depends on the span-to-height ratio and the density-to-strength ratio of cables. Finally, a parametric study is illustrated aiming at the relations between three key geometrical parameters and the cost of the bridge model. The optimization of the new bridge model indicates that the self-anchored cable-stayed part is always the dominant part with the consideration of either the lowest total cost or the lowest unit cost. It is advisable to combine all three mentioned structural parts in super long span cable supported bridges to achieve the most excellent economic performance.

• 한국강구조학회 논문집
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• 제13권2호
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• pp.123-131
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• 2001

본 연구의 목적은 고강도 H형강 기둥재(beam-column)의 폭두께비에 관한 기준을 조사하고 좌굴내력을 평가하여, 강구조 한계상태설계기준과 허용응력설계기준(안)과 비교함으로써, 고강도강을 사용한 기둥부재 설계시 적용된 기준식의 타당성을 검토하기 위한 것이다. 실험에 사용된 고강도강은 SM520TMC, SM570Q 등을 사용하였고, 강재의 기계적 성질과 단주의 응력-변형도 관계를 파악하기 위하여 인장시험 및 단주압축시험을 실시하였다. 또한 고강도강 기둥재의 좌굴내력을 산정하기 위하여 수치해석을 수행하였다. 수치해석에 사용된 축력-모멘트-곡률 관계는 단주압축실험에서 구해진 응력-변형도 관계를 사용하였다

• 방사성폐기물학회지
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• 제19권2호
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• pp.197-204
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• 2021

In this study, the well-known non-destructive acoustic emission (AE) and electrical resistivity methods were employed to predict quantitative damage in the silo structure of the Wolsong Low and Intermediate Level Radioactive Waste Disposal Center (WLDC), Gyeongju, South Korea. Brazilian tensile test was conducted with a fully saturated specimen with a composition identical to that of the WLDC silo concrete. Bi-axial strain gauges, AE sensors, and electrodes were attached to the surface of the specimen to monitor changes. Both the AE hit and electrical resistance values helped in the anticipation of imminent specimen failure, which was further confirmed using a strain gauge. The quantitative damage (or damage variable) was defined according to the AE hits and electrical resistance and analyzed with stress ratio variations. Approximately 75% of the damage occurred when the stress ratio exceeded 0.5. Quantitative damage from AE hits and electrical resistance showed a good correlation (R = 0.988, RMSE = 0.044). This implies that AE and electrical resistivity can be complementarily used for damage assessment of the structure. In future, damage to dry and heated specimens will be examined using AE hits and electrical resistance, and the results will be compared with those from this study.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 봄 학술발표회 논문집
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• pp.891-896
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• 2001

The determination of compressive zone at the critical section of concrete walls under in-plane flexure is important in both assessing the ductility and designing the seismic retrofit. Recognizing this, the once-predominated code approach to determine the compressive zone was advanced by considering concrete rectangular stress block parameters varying with the extreme fiber strain in compression. It is shown that the major factors influencing the magnitude of compressive zone are axial load ratio, concrete strength, longitudinal steel ratio, yield strength and the level of strain at extreme compression fiber of wall sections. The present paper closes with the discussion for the research agenda requiring further study to investigate the behavior of reinforced concrete walls.

• 대한기계학회논문집A
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• 제29권4호
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• pp.606-613
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• 2005

Effects of circumferentially local wall thinning on the fracture behavior of pipes were investigated by monotonic four-point bending. Local wall thinning was machined on the pipes in order to simulate erosion/corrosion metal loss. The configurations of the eroded area included an eroded ratio of d/t= 0.2, 0.5, 0.6, and 0.8, and an eroded length of ${\ell}\;=10mm,$ 25mm, and 120mm. Fracture type could be classified into ovalization, local buckling, and crack initiation depending on the eroded length and eroded ratio. Three-dimensional elasto-plastic analyses were also carried out using the finite element method, which is able to accurately simulate fracture behaviors excepting failure due to cracking. It was possible to predict the crack initiation point by estimating true fracture ductility under multi-axial stress conditions at the center of the thinned area.

• 대한기계학회논문집A
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• 제24권5호
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• pp.1203-1214
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• 2000

In this paper, a failure model for co-cured steel-composite tubular single lap joints has been proposed incorporating the nonlinear mechanical behavior of steel adherends and different failure mode s such as steel adherend failure and composite adherend failure. The characteristics of the co-cured steel-composite tubular single lap joint were investigated with respect to the test temperature, the stacking sequence of composite adherend, the thickness ratio of steel adherend to composite adherend, and the scarf ratio of steel adherend. Thus, the optimum design method for the co-cured steel-composite tubular single lap joint was suggested.