최근 국내에서는 안전하고 고품질인 농산물에 대한 소비자의 선호도가 높아지고 있다. 고품질 농산물 생산과 환경오염을 줄이기 위해서는 화학비료와 같은 농자재의 과잉투입 문제를 해결하여야 하며 이를 위하여 변량시비에 관한 연구가 수행되고 있다. 변량시비용으로 널리 사용되는 원판식 입제 살포기의 경우 시비량이 변화함에 따라 살포패턴이 변화하는 문제점이 있다. 본 연구에서는 시비량 변화에 따른 살포패턴 변화 요인을 찾기 위하여 이산 요소 모델링과 고속카메라 촬영을 통하여 살포기 원판 위에서 의 입자거동을 분석하였다. 그 결과, 시비량이 증가함에 따라 원판회전 반대방향으로 비산되는 입자량 이 증가하게 되고 출구방향 조절장치의 출구 시작지점에서 빠져나가지 않고 출구 끝 부분에서 빠져나가 는 입자가 증가하여 원판 위에서 회전방향으로 더 많이 이동되어 살포되므로 살포패턴에 변화를 가져오 는 것으로 파악되었다. 이러한 문제를 해결하기 위하여 회전원판 위에 내부날개를 설치하여 회전 축 주 변에 낙하하는 입자를 원심력에 의해 출구방향 조절장치의 벽 쪽으로 강제 이동하도록 장치를 개선하여 원판 위 입자거동을 분석하였다. 그 결과, 시비량의 변화와 상관없이 회전축 주변의 입자가 출구방향 조절장치의 벽 쪽으로 이동하여 원판 위에서 회전하다가 조절장치의 출구 시작 부분에서 빠져나가 살포 되는 것으로 나타나 시비량의 변화에 따른 살포패턴의 변이가 줄어들 것으로 판단되었다. 차후, 균일한 살포패턴을 만들기 위해서 내부날개를 설치한 원판식 입제 살포기를 이용하여 다양한 시비조건에 따른 살포패턴 데이터를 수집 및 분석 하고자 한다.

일반적인 콘크리트 구조물은 길이가 길 경우 수축에 의한 인장균열의 발생을 억제하기 위하여 수축줄 눈을 설치된다. 하지만 연속철근 콘크리트 구조물은 별도의 수축줄눈을 설치하지 않고 그 대신 자연적으 로 발생하는 횡방향 균열을 허용하며 이러한 횡방향 균열의 과도한 벌어짐을 구속하기 위하여 연속철근이 설치된다. 대표적인 연속철근 콘크리트 구조물은 도로포장에 사용되고 있는 연속철근 콘크리트 포장 (CRCP)와 연속철근 콘크리트 궤도(CRCT)가 있다. CRCP의 횡방향 균열은 대략 0.8 - 1.5m 간격으로 발 생하며, CRCT는 레일을 지지하기 위한 프리캐스트 침목이 슬래브 내에 설치되기 때문에 침목과 슬래브 의 분리에 의하여 0.325m마다 균열이 발생하게 된다. 본 연구에서는 현장실험을 통하여 CRCP와 CRCT의 균열폭 거동을 각각 계측하고 이에 대한 분석 및 비교를 수행하였다. 그림 1~4는 CRCP와 CRCT의 슬래브 깊이에 따른 온도와 균열폭을 나타내었다. 분석 결과 균열간격이 상대적으로 작은 CRCT의 거동이 CRCP의 균열폭의 거동과 비교하여 큰 차이가 발생하 지 않는 것으로 나타나 균열간격에 비례하여 균열폭이 거동하지 않음을 알 수 있다.

노면의 요철은 차량의 동역학적 거동에 의해 시트의 진동 또는 움직임을 유발하여 탑승자의 승차감을 저해시키는 요인이 된다. 차량의 동역학적 거동을 단순화한 모델 중 IRI(International Roughness Index)를 비롯하여 널리 적용되고 있는 Quarter-car모델은 그림 1과 같이 네 바퀴 차량의 1/4 모델로서, 현가상질량(sprung mass)의 수직 변위를 계산하는 모델이다. 그러나 실제 차량의 거동은 수직 방향 거동 외에도 네 바퀴의 거동 차이에 의해 그림 2와 같이 중심축에 대한 회전 운동을 하며, 이로 인해 시트에 앉아 있는 탑승자의 회전진동을 유발한다. 탑승자의 진동방향은 3축 병진운동과 각 축의 회전운동으로 그 림 3과 같이 정의할 수 있으며, 직진 주행 중인 차량으로 가정할 경우 z축에 대한 회전운동인 yaw 거동은 발생하지 않는다. 따라서 본 연구에서는 roll, pitch 회전거동과 연직 z방향 거동에 노출된 탑승자의 승차 감을 모사, 평가하기 위해 그림 4와 같이 시뮬레이터를 개발하였다. 또한 sin파형에 반응하는 시뮬레이터 패널 평가결과를 바탕으로 인체에 민감하게 영향을 주는 차량 거동요소의 주파수 특성을 분석하였다. 시뮬레이터 분석을 통하여 roll, pitch 및 z방향 거동의 특성에 따라 시뮬레이터에 탑승한 패널의 정성 적인 승차감 평가가 달라지는 것을 그림 5와 같이 확인하였다. roll과 pitch거동의 경우 8Hz 대역에서, z방향 거동은 4~8Hz대역에서 패널의 승차감에 가장 민감한 영향을 주는 것으로 분석되었다. 또한 양호- 불량의 경계에 해당하는 거동특성을 비교한 결과, 동일한 회전변위에 대해서 전반적으로 pitch의 영향이 더 큰 것으로 나타났다. 향후 본 연구결과를 토대로 승차감을 정량적으로 표현할 수 있는 방안을 마련할 계획이며, 도로이용자에게 보다 우수한 승차감을 제공하는데 기여할 수 있을 것으로 판단된다.

제조나노물질의 발전으로 이를 이용한 제품들이 늘어남에 따라 상수 내 나노 물질에 대한 잠재 위해성 논란이 제기되어 왔다. 응집과 같은 기존 나노물질 처리 방법에 비해 막 분리법은 2차 오염물이 없고 재사용이 가능하기 때문에 각광받고 있다. 하지만 수계환경 변화로 인한 나노물질의 특성변화에 따른 막 기 반 공정 내 나노물질 거동에 대한 연구는 미미한 실정이다. 따라서 본 연구에서 는 국내에서 사용되고 있는 대표 제조나노물질인 Ag, ZnO, TiO2의 수계 내 유 기물 존재여부에 따른 특성을 분석하고 막기반 상수처리 공정에서의 거동을 평가하고자 하였다. SR-NOM을 대표 자연유기물로 평가하였으며 상수 내 SR-NOM의 유/무에 따른 나노물질들의 응집성 등의 변화가 막기반 공정 결과에 영향을 주었음을 확인하였다.

PURPOSES : The field application and performance of continuously reinforced concrete pavement (CRCP), constructed by using the mechanical tube-feeding method, are evaluated in this study. METHODS: The location of the rebar was evaluated by using the MIRA system. The early-age CRCP performance was evaluated via visual survey, in which the crack spacing and crack width were examined. RESULTS: The location of longitudinal reinforcing bars was evaluated via MIRA testing and the results showed that the longitudinal rebars all lie within a given tolerance limit (±2.5 cm) of the target elevation. In addition, owing to the low temperature when the concrete was pured, the crack spacing in the Dae-Gu direction is slightly wider than that of the Gwang-Ju direction. Almost all of the crack spacings lay within the range of 1.0 m~3.0 m. A crack width of <0.3 mm was measured at the pavement surface. However, as revealed by the field survey, the crack spacing was not correlated with the crack width. CONCLUSIONS : In CRCP constructed by using the mechanical tube-feeding method, almost all of the longitudinal reinforcing bars lay within the tolerance limit (2.5 cm) of the target elevation. The concrete-placing temperature affects the crack spacing, owing to variations in the zero-stress temperature. Crack survey results show that there is no correlation between the crack spacing and crack width in CRCP.

PURPOSES: The behavior of a concrete pavement in a tunnel was investigated, based on temperature data obtained from the field and FEM analysis. METHODS: The concrete pavement in a tunnel was evaluated via two methods. First, temperature data was collected in air and inside the concrete pavement both outside and inside the tunnel. Second, FEM analysis was used to evaluate the stress condition associated with the slab thickness, joint spacing, dowel, and rock foundation, based on temperature data from the field. RESULTS : Temperature monitoring revealed that the temperature change in the tunnel was lower and more stable than that outside the tunnel. Furthermore, the temperature difference between the top and bottom of the slab was lower inside the tunnel than outside. FEM analysis showed that, in many cases, the stress in the concrete pavement in the tunnel was lower than that outside the tunnel. CONCLUSIONS : Temperature monitoring and the behavior of the concrete pavement in the tunnel revealed that, from an environmental point of view, the condition in the tunnel is advantageous to that outside the tunnel. The behavior in the tunnel was significantly less extreme, and therefore the concrete pavement in the tunnel could be designed more economically, than that outside the tunnel.

If scour is occurred at shallow foundation of bridge, seismic performance of the bridge will be reduced. In order to evaluate accurate seismic response of bridge according to scour depths, modeling of foundation reflecting scour effect is important. In this study, taking into account the effect of the reduction in embedment depth of the shallow foundation by scouring, the soil around the foundation is modelled as an equivalent soil spring with various stiffness. Seismic fragility analyses for 3 types of bridges subjected to 4 types of ground motions classified into Site Class A, B, C, D are evaluated according to several scour depths. From the fragility analysis results, it can be observed that the deeper the scour depth, the higher probability of exceeding damage states. Also, seismic failure probability of asymmetric bridge is higher than that of symmetric bridge.

PURPOSES: The purpose of this study is to validate the design criteria of the concrete modular road system, which is a new semi-bridgetype concept road, through a comparison of numerical analysis results and actual loading test results under static axial loads. METHODS : To design the semi-bridge-type modular road, both the bridge design code and the concrete structural design code were adopted. The standard truck load (KL-510) was applied as the major traffic vehicle for the design loading condition. The dimension of the modular slab was designed in consideration of self-weight, axial load, environmental load, and combined loads, with ultimate limit state coefficients. The ANSYS APDL (2010) program was used for case studies of center and edge loading, and the analysis results were compared with the actual mock-up test results. RESULTS : A full-scale mock-up test was successfully conducted. The maximum longitudinal steel strains were measured as about 35 and 83.5 micro-strain (within elastic range) at center and edge loading locations, respectively, under a 100 kN dual- wheel loading condition by accelerating pavement tester. CONCLUSIONS: Based on the results of the comparison between the numerical analysis and the full-scale test, the maximum converted stress range at the edge location is 32~51% of the required standard flexural strength under the two times over-weight loading condition. In the case of edge loading, the maximum converted stresses from the Westergaard equation, the ANSYS APDL analysis, and the mock-up test are 1.95, 1.7, and 2.3 times of that of the center loading case, respectively. The primary reason for this difference is related to the assumption of the boundary conditions of the vertical connection between the slab module and the crossbeam module. Even though more research is required to fully define the boundary conditions, the proposed design criteria for the concrete modular road finally seems to be reasonable.

Reinforced concrete shear walls are effective for resisting lateral loads imposed by wind or earthquakes. Observed damages of the shear wall in recent earthquakes in Chile(2010) and New Zealand(2011) exceeded expectations. Various analytical models have been proposed in order to incorporate such response features in predicting the inelastic response of RC shear walls. However, the model has not been implemented into widely available computer programs, and has not been sufficiently calibrated with and validated against extensive experimental data at both local and global response levels. In this study, reinforced concrete shear walls were modeled with fiber slices, where cross section and reinforcement details of shear walls can be arranged freely. Nonlinear analysis was performed by adding nonlinear shear spring elements that can represent shear deformation. This analysis result will be compared with the existing experiment results. To investigate the nonlinear behavior of reinforced concrete shear walls, reinforced concrete single shear walls with rectangular wall cross section were selected. The analysis results showed that the yield strength of the shear wall was approximately the same value as the experimental results. However, the yielding displacement of the shear wall was still higher in the experiment than the analysis. The analytical model used in this study is available for the analysis of shear wall subjected to high axial forces.

The purpose of this study is to develop a new seismic resistant method by using precast concrete wall panels for existing low-rise, reinforced concrete beam-column buildings such as school buildings. Three quasi-static hysteresis loading tests were experimentally performed on one unreinforced beam-column specimen and two reinforced specimens with L-type precast wall panels. The results were analyzed to find that the specimen with anchored connection experienced shear failure, while the other specimen with steel plate connection principally manifested flexural failure. The ultimate strength of the specimens was determined to be the weaker of the shear strength of top connection and flexural strength at the critical section of precast panel. In this setup of L-type panel specimens, if a push loading is applied to the reinforced concrete column on one side and push the precast concrete panel, a pull loading from upper shear connection is to be applied to the other side of the top shear connection of precast panel. Since the composite flexural behavior of the two members govern the total behavior during the push loading process, the ultimate horizontal resistance of this specimen was not directly influenced by shear strength at the top connection of precast panel. However, the RC column and PC wall panel member mainly exhibited non-composite behavior during the pull loading process. The ultimate horizontal resistance was directly influenced by the shear strength of top connection because the pull loading from the beam applied directly to the upper shear connection. The analytical result for the internal shear resistance at the connection pursuant to the anchor shear design of ACI 318M-11 Appendix-D except for the equation to predict the concrete breakout failure strength at the concrete side, principally agreed with the experimental result based on the elastic analysis of Midas-Zen by using the largest loading from experiment.

This study aims at developing a new seismic resistant method by using precast concrete wall panels for existing low-rise, reinforced concrete beam-column buildings such as school buildings. Three quasi-static hysteresis loading tests were performed on one unreinforced beam-column specimen and two reinforced specimens with U-type precast wall panels. Top shear connection of the PC panel was required to show the composite strength of RC column and PC wall panel. However, the strength of the connection did not influence directly on the ultimate loading capacities of the specimens in the positive loading because the loaded RC column push the side of PC wall panel and it moved horizontally before the shear connector receive the concentrated shear force in the positive loading process. Under the positive loading sequence(push loading), the reinforced concrete column and PC panel showed flexural strength which is larger than 97% of the composite section because of the rigid binding at the top of precast panel. Similar load-deformation relationship and ultimated horizontal load capacities were shown in the test of PR1-LA and PR1-LP specimens because they have same section dimension and detail at the flexural critical section. An average of 4.7 times increase in the positive maximum loading(average 967kN) and 2.7 times increase in the negative maximum loading(average 592.5kN) had resulted from the test of seismic resistant specimens with anchored and welded steel plate connections than that of unreinforced beam-column specimen. The maximum drift ratios were also shown between 1.0% and 1.4%.

PURPOSES : In this study, a fracture-based finite element (FE) model is proposed to evaluate the fracture behavior of fiber-reinforced asphalt (FRA) concrete under various interface conditions. METHODS: A fracture-based FE model was developed to simulate a double-edge notched tension (DENT) test. A cohesive zone model (CZM) and linear viscoelastic model were implemented to model the fracture behavior and viscous behavior of the FRA concrete, respectively. Three models were developed to characterize the behavior of interfacial bonding between the fiber reinforcement and surrounding materials. In the first model, the fracture property of the asphalt concrete was modified to study the effect of fiber reinforcement. In the second model, spring elements were used to simulated the fiber reinforcement. In the third method, bar and spring elements, based on a nonlinear bond-slip model, were used to simulate the fiber reinforcement and interfacial bonding conditions. The performance of the FRA in resisting crack development under various interfacial conditions was evaluated. RESULTS : The elastic modulus of the fibers was not sensitive to the behavior of the FRA in the DENT test before crack initiation. After crack development, the fracture resistance of the FRA was found to have enhanced considerably as the elastic modulus of the fibers increased from 450 MPa to 900 MPa. When the adhesion between the fibers and asphalt concrete was sufficiently high, the fiber reinforcement was effective. It means that the interfacial bonding conditions affect the fracture resistance of the FRA significantly. CONCLUSIONS: The bar/spring element models were more effective in representing the local behavior of the fibers and interfacial bonding than the fracture energy approach. The reinforcement effect is more significant after crack initiation, as the fibers can be pulled out sufficiently. Both the elastic modulus of the fiber reinforcement and the interfacial bonding were significant in controlling crack development in the FRA.

In this study, effect of core-shell structure on compaction behavior of harmonic powder is investigated. Harmonic powders are made by electroless plating method on Fe powders. Softer Cu shell encloses harder Fe core, and the average size of Fe core and thickness of Cu shell are 34.3 μm and 3.2 μm, respectively. The powder compaction procedure is processed with pressure of 600 MPa in a cylindrical die. Due to the low strength of Cu shell regions, the harmonic powders show better densification behavior compared with pure Fe powders. Finite element method (FEM) is performed to understand the roll of core-shell structure. Based on stress and strain distributions of FEM results, it is concluded that the early stage of powder compaction of harmonic powders mainly occurs at the shell region. FEM results also well predict porosity of compacted materials.