• 한국물환경학회지
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• 제34권6호
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• pp.569-578
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• 2018

To minimize the negative alterations in hydrologic and water quality environment in urban areas due to urbanization, Low Impact Development (LID) techniques are actively applied. In Korea, LID facilities are classified as Non-point Pollution Reduction Facilities (NPRFs), and therefore they are evaluated using the performance evaluation method for NPRFs. However, while LID facilities are generally installed in small, distributed configuration and mainly work with the infiltration process, the existing NPRFs are installed on a large scale and mainly work with the reservoir process. Therefore, some limitations are expected in assessing both facilities using the same method as they differ in properties. To solve these problems, in this study, a new method for performance evaluation was proposed with focus on bio-retention LID facilities. EPA SWMM was used to reproduce the hydrologic and water quality phenomena in study area, and SWMM-LID module used to simulate TP interception performance by installing a bio-retention cell under various conditions through long-term simulations. Finally, an empirical formula for Load Capture Ratio (LCR) was derived based on storm water interception ratio in the same form as the existing method. Using the existing formula in estimating the LCR is likely to overestimate the performance of interception for non-point pollutants in the extremely low design capacity, and also underestimate it in the moderate and high design capacity.

• Structural Engineering and Mechanics
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• 제82권1호
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• pp.81-92
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• 2022

Ultra-high performance fiber reinforced concrete (UHPFRC) is a composite building material with high ductility, fatigue resistance, fracture toughness, durability, and energy absorption capacity. The aim of this study is to develop a nonlinear finite element model that can simulate the response of the UHPFRC beam exposed to impact loads. A nonlinear finite element model was developed in ABAQUS to simulate the real response of UHPFRC beams. The numerical results showed that the model was highly successful to capture the experimental results of selected beams from the literature. A parametric study was carried out to investigate the effects of reinforcement ratio and impact velocity on the response of the UHPFRC beam in terms of midpoint displacement, impact load value, and residual load-carrying capacity. In the parametric study, the nonlinear analysis was performed in two steps for 12 different finite element models. In the first step, dynamic analysis was performed to monitor the response of the UHPFRC beam under impact loads. In the second step, static analysis was conducted to determine the residual load-carrying capacity of the beams. The parametric study has shown that the reinforcement ratio and the impact velocity affect maximum and residual displacement value substantially.

• Wind and Structures
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• 제38권2호
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• pp.119-128
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• 2024

The aerodynamic damping is an essential factor that can considerably affect the dynamic response of the cable-stayed bridge induced by crosswind load. However, developing an accurate and efficient aerodynamic damping model is crucial for evaluating the crosswind load-induced response on cable-stayed bridges. Therefore, this study proposes a new method for identifying aerodynamic damping of the bridge structures under crosswind load using an extended Kalman filter (EKF) and the particle filter (PF) algorithm. The EKF algorithm is introduced to capture the aerodynamic damping ratio. PF technique is used to select the optimal spectral representation of the noise. The effectiveness and accuracy of the proposed solution were investigated through full-scale vibration measurement data of the crosswind-induced on the bridge's girder. The results show that the proposed solution can generate an efficient and robust estimation. The errors between the target and extracted values are around 0.01mm and 0.003^o, respectively, for the vertical and torsional motion. The relationship between the amplitude and the aerodynamic damping ratio is linear for small reduced wind velocity and nonlinear with the increasing value of the reduced wind velocity. Finally, the results show the influence of the level of noise.

• Journal of Advanced Marine Engineering and Technology
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• 제35권7호
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• pp.899-906
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• 2011

Generally, load conditions of machine or structure in fatigue destruction is occurred not under single load conditions but under mixed load conditions. However, the experiment under mixing mode is insufficient because of no having test standard to the behavior of crack under mixing mode and variety of test methods, and many tests are required. In this paper measured crack direction path by created figure capture system when a experiment. Also, we studied by comparison the behavior of crack giving the change of stress ratio and inserting beach mark. Through the test under mixing mode, advancing path of crack is indicated that advancing inclined angle ${\Theta}$ (direction of specimen length) has increased depending on the increase of mixed mode impaction. It is indicated that according to the increase of mixed mode loading condition impaction under mixing mode, advancing speed of crack gets slow. Also, we found that inner crack(cross section of specimen) is progressed more rapidly than outer crack based on data through beach mark.

• Advanced Composite Materials
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• 제18권1호
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• pp.21-42
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• 2009

The vibration characteristics of post-buckled laminated composite doubly curved shells are investigated. The finite element method is used for the analysis of post-buckling and free vibration of post-buckled laminated shells. The geometric non-linear finite element model includes the general non-linear terms in the strain-displacement relationships. The shell geometry used in the present formulation is derived using an orthogonal curvilinear coordinate system. Based on the principle of virtual work the non-linear finite element equations are derived. Arc-length method is implemented to capture the load-displacement equilibrium curve. The vibration characteristics of post-buckled shell are performed using tangent stiffness obtained from the converged deflection. The code is first validated and then employed to generate numerical results. Parametric studies are performed to analyze the snapping and vibration characteristics. The relationship between loads and fundamental frequencies and between loads and the corresponding displacements are determined for various parameters such as thickness ratio and shallowness.

• Steel and Composite Structures
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• 제36권2호
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• pp.179-186
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• 2020

In this paper, the forced resonance vibration of porous functionally graded (FG) curved nanobeam is examined. In order to capture the hardening and softening mechanisms of nanostructure, the nonlocal strain gradient theory is employed to build the size-dependent model. Using the Timoshenko beam theory together with the Hamilton principle, the equations of motion for the curved nanobeam are derived. Then, Navier series are used in order to obtain the dynamical deflections of the porous FG curved nanobeam with simply-supported ends. It is found that the resonance position of the nanobeam is very sensitive to the nonlocal and strain gradient parameters, material variation, porosity coefficient, as well as geometrical conditions. The results indicate that the resonance position is postponed by increasing the strain gradient parameter, while the nonlocal parameter has the opposite effect on the results. Furthermore, increasing the opening angle or length-to-thickness ratio will result in resonance position moves to lower-load frequency.

• Earthquakes and Structures
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• 제24권6호
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• pp.455-475
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• 2023

The present study investigates the non-linear soil-pile interaction using three-dimensional (3D) non-linear finite element models. The numerical models were validated by using the results of extensive pile load and shaking table tests. The pile performance in liquefiable and non-liquefiable soil has been studied by analyzing the liquefaction ratio, pile lateral displacement (LD), pile bending moment (BM), and frictional resistance (FR) results. The pile models have been developed for the different ground conditions. The study reveals that the results obtained during the pile load test and shaking cycles have good agreement with the predicted pile and soil response. The soil density, peak ground acceleration (PGA), slenderness ratio (L/D), and soil condition (i.e., dry and saturated) are considered during modeling. Four ground motions are used for the non-linear time history analyses. Consequently, design charts are proposed depended on the analysis results to be used for design practice. Eleven models have been used to validate the capability of these charts to capture the soil-pile response under different seismic intensities. The results of the present study demonstrate that L/D ratio slightly affects the lateral displacement when compared with other parameters. Also, it has been observed that the increasing in PGA and decreasing L/D decreases the excess pore water pressure ratio; i.e., increasing PGA from 0.1 g to 0.82 g of loose sand model, decrease the liquefaction ratio by about 50%, and increasing L/D from 15 to 75 of the similar models (under Kobe earthquake), increase this ratio by about 30%. This study reveals that the lateral displacement increases nonlinearly under both dry and saturated conditions as the PGA increases. Similarly, it is observed that the BM increases under both dry and saturated states as the L/D ratio increases. Regarding the acceleration histories, the pile BM was reduced by reducing the acceleration intensity. Hence, the pile BM decreased to about 31% when the applied ground motion switched from Kobe (PGA=0.82 g) to Ali Algharbi (PGA=0.10 g). This study reveals that the soil conditions affect the relationship pattern between the FR and the PGA. Also, this research could be helpful in understanding the threat of earthquakes in different ground characteristics.

• 한국산학기술학회논문지
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• 제14권11호
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• pp.5930-5938
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• 2013

Erigen의 비국소 탄성이론을 이용한 S형상 점진기능재료 나노-스케일 판의 전단변형이론을 정식화하여 평형방성식을 유도하였다. 비국소 탄성이론은 미소 규모 효과를 고려할 수 있고 S형상함수는 점진기능재료의 정확한 특성 변화를 고려할 수 있다. 4변이 단순지지된 나노-스케일 판의 지배방정식을 풀기 위해 Navier 방법을 사용하였다. 거듭 제곱 지수와 비국소 변수의 효과를 나타내기 위한 나노-스케일 판의 해석적 좌굴하중을 제시하였고, 국소 탄성이론과의 관계를 수치해석 결과를 통하여 고찰하였다. 또한 (i) 거듭제곱 지수, (ii) 나노-스케일 판의 크기, (iii) 비국소 계수, (iv) 형상비 그리고 (v) 모드 수 등이 나노-스케일 판의 이축 무차원 좌굴하중에 미치는 효과에 대하여 관찰하였다. 본 연구의 결과를 검증하기 위해 참고문헌의 결과들과 비교 분석하였다.

• 대한인간공학회지
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• 제31권3호
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• pp.445-453
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• 2012

The aim of this paper was to prove that if the risk level in combined tasks was improved through evaluation of postural load of liquid weight measurement process, the workload level and ratio of exposure time would be changed, and the time of process would be seen concurrently. Background: According to results of epidemiological studies conducted by Korea Occupational Safety & Health Agency, 122 musculoskeletal disorders occurred during 1992 to 2008, in which manufacturing industry covers 96(78.7%) of total. However, this is an insufficient level and only occupies 39% based on the South Korea's manufacturing standard industrial classification(246 industries). Method: Firstly, the number of batches weighed on one day(460min) was investigated based on the work performed and Weight measured weekly. VCR recording was taken based on the level of liquid ingredients prescribed for 1batch using the Camcorder. After dividing a 356 sec video into 1 sec using the screen capture function in Gom player, the job classification was performed by analyzing the change of working postures, which revealed 148 working postures. Time measurement was decided by time of the postures was being maintained. Then, the REBA analysis was performed for the working postures. The ratio of Exposure time was calculated based on the measurement time and REBA Score. In addition, the recommendations were designed and implementation was carried out for the working postures with REBA Score higher than 3. Finally, after the intervention, REBA measurement, time measurement, and ratio of exposure time were calculated for the comparison of works before and after improvement. Results: The number of work elements was decreased by 30.4% from 148 to 103 after improvement. The results of time measurement showed that the time was reduced by 46.3% from 356 sec to 191 sec. And the ratio of exposure time was also improved by 52.1% from 0% to 52.1% after improvement. Conclusion: The reduction of time was found to improve the productivity of management. Furthermore, because the reduction of ratio of exposure time and the improvement of workload level are the improvement of discomfort, it would contribute to the improvement of the worker's psychological working posture. Application: These results would contribute to musculoskeletal disease prevention and management performance. Further studies for other industries would be needed based on this case study.

• Computers and Concrete
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• 제33권5호
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• pp.497-507
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• 2024

In squat reinforced concrete walls, the displacement capacity for lateral deformation is low and the ability to resist the axial load can quickly be lost, generating collapse. This work consists of testing two squat reinforced concrete walls. One of the specimens is built with conventional detailing of reinforced concrete walls, while the second specimen is built applying an alternative design, including stirrups along the diagonal of the wall to improve its ductility. This solution differs from the detailing of beams or coupling elements that suggest building elements equivalent to columns located diagonally in the element. The dimensions of both specimens correspond to a wall with a low aspect ratio (1:1), where the height and length of the specimen are 1.4 m, with a thickness of 120 mm. The alternative wall included stirrups placed diagonally covering approximately 25% of the diagonal strut of the wall with alternative detailing. The walls were tested under a constant axial load of 0.1f'cAg and a cyclic lateral displacement was applied in the upper part of the wall. The results indicate that the lateral strength is almost identical between both specimens. On the other hand, the lateral displacement capacity increased by 25% with the alternative detailing, but it was also able to maintain the 3 complete hysteretic cycles up to a drift of 2.5%, reaching longitudinal reinforcement fracture, while the base specimen only reached the first cycle of 2% with rapid degradation due to failure of the diagonal compression strut. The alternative design also allows 46% more energy dissipation than the conventional design. A model was used to capture the global response, correctly representing the observed behavior. A parametric study with the model, varying the reinforcement amount and aspect ratio, was performed, indicating that the effectiveness of the alternative detailing can double de drift capacity for the case with a low aspect ratio (1.1) and a large longitudinal steel amount (1% in the web, 5% in the boundary), which decreases with lower amounts of longitudinal reinforcement and with the increment of aspect ratio, indicating that the alternative detailing approach is reasonable for walls with an aspect ratio up to 2, especially if the amount of longitudinal reinforcement is high.