• Steel and Composite Structures
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• 제24권5호
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• pp.549-559
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• 2017

As few multi-tower single-box multi-cell cable-stayed bridges with corrugated steel webs have been built, analysis is mostly achieved by combining single-girder model, beam grillage model and solid model in support of the design. However, such analysis methods usually suffer from major limitations in terms of the engineering applications: single-girder model fails to account for spatial effect such as shear lag effect of the box girder and the relevant effective girder width and eccentric load coefficient; owing to the approximation in the principle equivalence, the plane grillage model cannot accurately capture shear stress distribution and local stress state in both top and bottom flange of composite box girder; and solid model is difficult to be practically combined with the overall calculation. The usual effective width method fails to provide a uniform and accurate "effective length" (and the codes fail to provide a unified design approach at those circumstance) considering different shear lag effects resulting from dead load, prestress and cable tension in the construction. Therefore, a novel spatial grid model has been developed to account for shear lag effect. The theoretical principle of the proposed spatial grid model has been elaborated along with the relevant illustrations of modeling parameters of composite box girder with corrugated steel webs. Then typical transverse and longitudinal shear lag coefficient distribution pattern at the side-span and mid-span key cross sections have been analyzed and summarized to provide reference for similar bridges. The effectiveness and accuracy of spatial grid analysis methods has been finally validated through a practical cable-stayed bridge.

• 설비공학논문집
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• 제21권8호
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• pp.433-438
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• 2009

Experimental results for performance characteristics of small $NH_3$ absorption chiller/ heater are presented. The apparatus consists of 7RT water-cooled absorption system, solution pump, boiler, cooling tower and peripheral devices. The effect of experimental parameters, such as refrigerant mass flow rate, solution mass flow rate and cooling water temperature have been investigated in view of the system performance. The capacity of each heat exchanger increased as refrigerant mass flow rate increased in cooling mode. Also, a cooling capacity increased as a strong solution mass flow rate increased. The cooling and heating COP show 0.5, 1.5 regardless of refrigerant mass flow rate, respectively. The results focus on the evaluation for performance characteristics of system with respect to variation of refrigerant mass flow rate under standard design conditions.

• 건축역사연구
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• 제18권5호
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• pp.81-100
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• 2009

The study on Buddhism architecture in early Joseon dynasty was inactive. The period of King Sejo is important for studying the trend of Buddhism architecture in early Joseon, that was transmitted from the end of Goryeo dynasty, but it was difficult to know its exact situation due to lack of related records. The records were all written by Kim Su-ohn, which are Wongaksabi' 'Sangwonsajungchanggi' 'Bongseonsagi 'Geonginsajungchanggi'. The main hall was mainly second floor and there were necessarily annexed buildings at the right and left of the main hall. So the plane figure of $\Box\Box\Box$ was shown. It was a main stream for main hall. This layout may be referred to search for the origin of the layout in courtyard based structure(中庭形) in the late Joseon dynasty. Most of temples had 3 gates. Some part of horizontal corridor was used as 2 gates and the outer gate, far from main hall, was without corridor. The gate leading to front yard of main hall was called front gate, the next middle gate and the outer gate was Oisamun(外沙門) or Samun(沙門). Im most of the temples, people could enter into the front yard through pavilion which had the function of bell tower. The pavilions were located between front gate and first corridor. It is thought that this layout of the place for making bean curd outside the temple area will contribute to different studies on temples making bean cure in the future. The records about temples's foundation studied above are a little different between temples, but have more similarities. There common denominators represent the architecture tendency of Buddhist temples in the related period. It is thought that such a tendency was also shown on architecture of other temples during the reign of King Sejo as well as Buddhist temples.

• 한국건설순환자원학회논문집
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• 제3권4호
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• pp.335-341
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• 2015

각종 디스플레이 기기들이 개발되고 사용됨에 따라 LCD 폐유리 또한 증가하고 있으며 대부분이 매립 또는 소각되고 있는 실정이므로 LCD 폐유리의 재활용 방안에 관한 연구가 필요하다. 따라서 본 연구에서는 실내 배합 실험을 통하여 LCD 폐유리 미분말을 혼입한 콘크리트의 기본적인 역학 특성을 평가하고자 하였으며, 연구결과에 따르면, 치환율이 증가할수록 콘크리트 특성이 다소 저하되는 경향을 보였다. 하지만 그 값이 작은 것으로 보아 사용 재료의 입경을 정밀화하고 입형을 구형으로 가공한다면 앞선 실험값을 향상시킬 것으로 보인다.

• Smart Structures and Systems
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• 제15권3호
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• pp.505-522
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• 2015

Variation of temperature is a primary environmental factor that affects the behavior of structures. Therefore, understanding the mechanisms of normal temperature-induced variations of structural behavior would help in distinguishing them from anomalies. In this study, we used the structural health monitoring data of the Shanghai Yangtze River Bridge, a steel girder cable-stayed bridge, to investigate the mechanisms of thermally induced vertical deflection ($D_T$) at mid-span of such bridges. The $D_T$ results from a multisource combination of thermal expansion effects of the cable temperature ($T_{Cab}$), girder temperature ($T_{Gir}$), girder differential temperature ($T_{Dif}$), and tower temperature ($T_{Tow}$). It could be approximated by multiple linear superpositions under operational conditions. The sensitivities of $D_T$ of the Shanghai Yangtze River Bridge to the above temperatures were in the following order: $T_{Cab}$ > $T_{Gir}$ > $T_{Tow}$ > $T_{Dif}$. However, the direction of the effect of $T_{Cab}$ was observed to be opposite to that of the other three temperatures, and the magnitudes of the effects of $T_{Cab}$ and $T_{Gir}$ were found to be almost one order greater than those of $T_{Dif}$ and $T_{Tow}$. The mechanisms of the thermally induced vertical deflection variation at mid-span of a cable-stayed bridge as well as the analytical methodology adopted in this study could be applicable for other long-span cable-stayed bridges.

• Wind and Structures
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• 제13권6호
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• pp.529-556
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• 2010

This paper investigates the correlation of wind characteristics monitored on a cable-stayed bridge. Total five anemoscopes are implemented into the bridge. Two out of 5 anemoscopes in inflow and two out of 5 anemoscopes in wake-flow along the longitudinal direction of the bridge are installed. Four anemoscopes are respectively distributed at two cross-sections. Another anemoscope is installed at the top of the tower. The correlation of mean wind speed and direction, power spectral density, the turbulent intensity and integral length of wind in flow at two cross-sections are investigated. In addition, considering the non-stationary characteristics of wind, the spatial correlation in time-frequency is analyzed using wavelet transform and different phenomenon from those obtained through FFT is observed. The time-frequency analysis further indicates that intermittence, coherence structures and self-similar structures are distinctly observed from fluctuant wind. The flow characteristics around the bridge deck at two positions are also investigated using the field measurement. The results indicate that the mean wind speed decrease when the flow passing through the deck, but the turbulence intensity become much larger and the turbulence integral lengths become much smaller compared with those of inflow. The relationship of RMS (root mean square) of wake-flow and the mean wind speed of inflow is approximately linear. The special structures of wake-flow in time-frequency domain are also analyzed using wavelet transform, which aids to reveal the forming process of wake-flow.

• 한국유체기계학회 논문집
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• 제18권2호
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• pp.14-21
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• 2015

Design lifetime of a wind turbine is required to be at least 20 years. The most important step to ensure the deign is to evaluate the loads on the wind turbine as accurately as possible. In this study, extreme design load of a offshore wind turbine using Garrad Hassan (GH) Bladed and National Renewable Energy Laboratory (NREL) FAST codes are calculated considering structural dynamic loads. These wind turbine aeroelastic analysis codes are high efficiency for the rapid numerical analysis scheme. But, these codes are mainly based on the mathematical and semi-empirical theories such as unsteady blade element momentum (UBEM) theory, generalized dynamic wake (GDW), dynamic inflow model, dynamic stall model, and tower influence model. Thus, advanced CFD-dynamic coupling method is also applied to conduct cross verification with FAST and GH Bladed codes. If the unsteady characteristics of wind condition are strong, such as extreme design wind condition, it is possible to occur the error in analysis results. The NREL 5 MW offshore wind turbine model as a benchmark case is practically considered for the comparison of calculated designed loads. Computational analyses for typical design load conditions such as normal turbulence model (NTM), normal wind profile (NWP), extreme operation gust (EOG), and extreme direction change (EDC) have been conducted and those results are quantitatively compared with each other. It is importantly shown that there are somewhat differences as maximum amount of 18% among numerical tools depending on the design load cases.

• Computers and Concrete
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• 제16권4호
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• pp.503-529
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• 2015

Traditionally, multi-story buildings are designed to provide stiffer structural support to withstand lateral earthquake loading. Introducing flexible elements at the base of a structure and providing sufficient damping is an alternative way to mitigate seismic hazards. These features can be achieved with a device known as an isolator. This paper covers the design of base isolators for multi-story buildings in medium-risk seismicity regions and evaluates the structural responses of such isolators. The well-known tower building for police personnel built in Dhaka, Bangladesh by the Public Works Department (PWD) has been used as a case study to justify the viability of incorporating base isolators. The objective of this research was to establish a simplified model of the building that can be effectively used for dynamic analysis, to evaluate the structural status, and to suggest an alternative option to handle the lateral seismic load. A finite element model was incorporated to understand the structural responses. Rubber-steel bearing (RSB) isolators such as Lead rubber bearing (LRB) and high damping rubber bearing (HDRB) were used in the model to insert an isolator link element in the structural base. The nonlinearities of rubber-steel bearings were considered in detail. Linear static, linear dynamic, and nonlinear dynamic analyses were performed for both fixed-based (FB) and base isolated (BI) buildings considering the earthquake accelerograms, histories, and response spectra of the geological sites. Both the time-domain and frequency-domain approaches were used for dynamic solutions. The results indicated that for existing multi-story buildings, RSB diminishes the muscular amount of structural response compared to conventional non-isolated structures. The device also allows for higher horizontal displacement and greater structural flexibility. The suggested isolation technique is able to mitigate the structural hazard under even strong earthquake vulnerability.

• 한국농림기상학회지
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• 제7권1호
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• pp.115-123
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• 2005

농림생태계에서의 물과 탄소의 순환을 연구하려면, 먼저 관측지의 공간적 특성을 정량적으로 이해해야 한다 특히, 우리나라와 같은 복잡한 경관에 관측지가 위치한 경우에는 공간 특성의 이해가 더욱 더 중요하다. 본 연구에서는 광릉 산림 소유역의 지형, 식생 및 토양과 관련된 변수들의 공간적 특성을 정량화하였다 지형의 공간 특성을 산출하기 위해 수치고도 모형 (DEM)에서 계산된 고도, 경사 및 사면 정보를 분석하였다. 식생과 토양 정보는 LANDSAT TM 영상으로부터 제작된 지표 피복 지도를 사용하였다. 계절 특성을 살펴보기 위해 1999년 6월 30일, 2000년 9월 4일, 2001년 9월 23일, 2002년 2월 14일의 네 위성 영상을 사용하였다. CO₂와 수증기의 플럭스 지수로서, 위성 영상으로부터 식생지수 NDVI를 세 격자 크기 (7km x 7km MODIS 격자, 3km x 3km 집중관측 격자, 1km x 1km 단위 격자)에 대해 각각 도출하였다. 반분산 분석에 근거해서 이 자료들을 사용하여 관측지의 비균질성의 공간 규모를 계산하였다. 예상한대로, 격자의 크기가 작아질수록 비균질성의 규모가 작아졌고, 식생의 계절 변화에 민감하였다. 40m 플럭스 타워가 위치한 두 단위 격자의 경우, 비균질성의 공간 규모는 200～1000m 이었고, 이러한 공간 규모는 모형에서 계산된 타워 플럭스 발자국의 기후도와 잘 일치하였다.

• Korean Chemical Engineering Research
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• 제52권3호
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• pp.314-320
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• 2014

산성가스 처리를 위한 흡수탑의 설계에 있어 탑 내부로 투입되는 가스의 분산성 향상은 흡수탑에서 산성가스의 제거율 향상 및 탑의 높이를 낮출 수 있으므로 전체 공정의 투자비를 저감할 수 있는 매우 중요한 연구 분야이다. 특히 최근 온실가스 저감의 한 방안으로 국내외에서 활발하게 개발 중인 습식 이산화탄소 포집기술의 경우 대규모 산성가스 처리가 요구됨에 따라 흡수탑 내 가스 분산성을 향상시킬 수 있는 연구의 필요성이 더욱 증대되고 있다. 본 연구에서는 관련하여 현재 한국중부발전 보령화력본부에 설치된 10MW급 연소 후 습식 이산화탄소 포집플랜트 기본설계 자료를 바탕으로 배가스 투입 시 흡수탑 내 가스의 분산성을 향상시킬 수 있는 다양한 방안을 도출하고 전산유체역학(Computational Fluid Dynamics)을 활용하여 각각의 경우에 있어서 분산성에 대한 효과를 분석하였다. 가스 분산성 향상을 위해 본 연구에서 도출된 3가지 방안(splash plate, 나선형 가스라인 및 U-tube 적용)에 대한 정량적 정성적 분석결과 흡수탑 내부에 계단형 U-tube를 설치하는 경우 탑 내부에 아무런 분산장치가 없는 경우 대비 흡수탑 내 가스의 분산성이 약 30% 증가되는 반면 분산장치 설치에 따른 차압의 증가는 기존 대비 10% 수준으로 크지 않아서 가스 분산성 향상을 위한 우수한 방안으로 평가되었다.