• Structural Engineering and Mechanics
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• 제53권5호
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• pp.939-956
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• 2015

In this study, in order to propose an efficient model to predict the torque capacity of steel fiber reinforced concrete (SFRC) beams, the existing experimental data related to torsional response of beams is reviewed. It is observed that existing data neglects the effects of some parameters on the variation of torque capacity. Thus, an experimental research was also conducted to obtain the effects of neglected parameters. In the experimental study, a total of seventeen SFRC beams are tested against torsion. The parameters considered in the experiments are concrete compressive strength, steel fiber aspect ratio, volumetric ratio of steel fibers and longitudinal reinforcement ratio. The effect of each parameter is discussed in terms of torque versus unit angle of twist graphs. The data obtained from this experimental research is also combined with the data got from previous studies and employed in artificial neural network (ANN) analysis to estimate the ultimate torque capacity of SFRC beams. In addition to parameters considered in the experiments, aspect ratio of beam cross-section, yield strengths of both transverse and longitudinal reinforcements, and transverse reinforcement ratio are also defined as parameters in ANN analysis due to their significant effects observed in previous studies. Assessment of the accuracy of ANN analysis in estimating the ultimate torque capacity of SFRC beams is performed by comparing the analytical and experimental results. Comparisons are conducted in terms of root mean square error (RMSE), mean absolute error (MAE) and coefficient of efficiency ($E_f$). The results of this study revealed that addition of steel fibers increases the ultimate torque capacity of reinforced concrete beams. It is also found that ANN is a powerful method and a feasible tool to estimate ultimate torque capacity of both normal and high strength concrete beams within the range of input parameters considered.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.1518-1523
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• 2003

The objective of the present work is to investigate an effect on the solution crystallization temperature difference and the cooling capacity of the absorption chiller by a solution cooler in the absorber. The cooling capacity of the absorption chiller can be higher, with the enhanced performance of the solution heat exchangers. But, because the solution crystallization temperature difference becomes smaller at the absorber inlet, the heat capacity of the solution heat exchangers might be limited by the danger of crystallization, which can cause the serious damages. In this paper, the heat capacity ratio of the solution cooler is defined as the ratio of the heat capacity of the solution cooler to that of the absorber. If it becomes larger in the additional type solution cooler, the solution crystallization temperature difference is augmented and the cooling capacity is also increased.

• 한국산학기술학회논문지
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• 제16권2호
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• pp.1477-1482
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• 2015

기초의 근입비가 보상기초의 극한지지력과 침하량에 미치는 영향을 살펴보고자 수치해석을 수행하였다. 수치해석에 의한 극한지지력비는 이론식에 의한 극한지지력비보다 컸으며 전체적으로 극한지지력비가 근입비에 비례하는 결과를 보였으나 정사각형기초에 대한 수치해석결과만 극한지지력비가 근입비에 따라 급격하게 증가하는 양상을 보였다. 모래지반에 놓인 띠기초의 경우 근입비에 따른 극한지지력비는 수치해석과 Meyerhof 방법에 의한 경우가 비슷하였으며 대체로 근입비의 제곱에 가까운 값을 나타내었으며 점토지반에 놓인 띠기초의 경우 이론식에 의할 경우 극한지지력비는 근입비의 영향을 크게 받지 않았고 수치해석결과에 따르면 근입비를 약간 상회하는 값들을 보였다. 수치해석결과에 따르면 근입비에 따른 정사각형기초의 극한지지력비가 띠기초의 그것에 비하여 크게 계산되었다. 수치해석결과를 통해 볼 때 전체적으로 근입비가 1인 경우 침하량비는 0.4 정도의 값을 보이다가 근입비가 커짐에 따라 침하량비가 감소하는 양상을 보였으며 느슨한 모래의 경우 상대적으로 침하량비가 가장 작았다.

• 한국농공학회논문집
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• 제52권6호
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• pp.1-7
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• 2010

This study was carried out to investigate the effect of hydro power factors (e.g., irrigation area, watershed area, active storage, gross head) on annual generation capacity and operation ratio for agricultural reservoirs in Chungbuk Province with active storage of over 1 million $m^3$. The annual generation capacity and operation ratio were estimated using HOMWRS (Hydrological Operation Model for Water Resources System) from last 10-year daily hydrological data. The correlation coefficients between annual generation capacity and the hydro power factors except gross head were high (over 0.87), but the correlation coefficients between operational rate and the factors were low (below 0.28). The optimum multiple regression equations of the annual generation capacity were expressed as the functions of watershed area, active storage, and gross head. Also, the simple regression equation of annual generation capacity was expressed as a function of watershed area. The average relative root-mean-square-error (RRMSE) between observed and estimated values by the optimum multiple regression equations was smaller than that by the simple regression equation, suggesting that the former has more accuracy than the latter.

• 한국구조물진단유지관리공학회 논문집
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• 제15권1호
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• pp.198-208
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• 2011

연약 점성지반 위에 상대적으로 낮은 하중의 구조물이 얹어질 때, 상부에 모래층을 두어 지지력을 증진시킬 수 있다. 이와같은 점토 위 모래층이 놓이는 조건에 대한 지지력 검증은 현장에서 평판재하시험 등을 통해 지지력 검증이 어렵기 때문에 설계단계에서부터 정확한 지지력 예측이 필요하다. 따라서, 본 연구는 점토 위 모래층이 놓이는 지반의 지지력 거동을 파악하기 위해 2차원 실내토조실험과 FEM 해석을 수행하였다. 주요 인자로 깊이비 H/B와 지지력비 $q_c/q_s$를 선정하여, 모래층 높이, 점토의 비배수전단강도 그리고 재하 폭을 변수로 하였다. 그 결과, 실내토조실험은 FEM 해석과 적합성이 상당히 높게 나타났다. 이론식과의 비교에 있어서 보다 최신 연구인 Okamura et al.(1998)의 메커니즘보다 관입전단 메커니즘과 그 유사성이 크게 나타났으며, 하중확산 메커니즘의 적용성을 위하여 등가하중확산각을 제시하였다. 또한, $q_c/q_s$에 대하여 무차원 단위의 한계깊이비 $H_f$의 선형 회귀식을 제안하였다.

• Earthquakes and Structures
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• 제19권5호
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• pp.379-393
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• 2020

The purpose of this study is to first evaluate the seismic behavior of ageing arch bridges by using the Intensity Measure - based demand and DCFD format, which is referred to as the fragility-hazard format. Then, an investigation is performed for their seismic vulnerability. Analytical models are created for bridges concerning different features and these models are subjected to Incremental Dynamic Analysis (IDA) analysis using a set of 22 earthquake records. The hazard curve and results of IDA analysis are employed to evaluate the return period of exceeding the limit states in the IM-based probabilistic performance-based context. Subsequently, the fragility-hazard format is used to assess factored demand, factored capacity, and the ratio of the factored demand to the factored capacity of the models with respect to different performance objectives. Finally, the vulnerability curves are obtained for the investigated bridges in terms of the loss ratio. The results revealed that decreasing the span length of the unreinforced arch bridges leads to the increase in the return period of exceeding various limit states and factored capacity and decrease in the displacement demand, the probability of failure, the factored demand, as well as the factored demand to factored capacity ratios, loss ratio, and seismic vulnerability. Finally, it is derived that the probability of the need for rehabilitation increases by an increase in the span length of the models.

• 한국지하수토양환경학회:학술대회논문집
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• 한국지하수토양환경학회 2001년도 총회 및 춘계학술발표회
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• pp.111-115
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• 2001

Durability of tunnel drains is important, because the accumulation of groundwater around the tunnel due to clogging of filter or reduction of discharge capacity of drain causes reduction of the life time of tunnel linings. In this paper, clogging and discharge capacity of drain and filter of tunnels are evaluated using a gradient ratio test and filter design criteria. The results of the gradient ratio test showed that gradient ratio(GR) is high when fine content is high in the soil samples and equivalent opening size(EOS) of filter materials is small. Measured GR was less than allowable critical gradinet ratio : 3.0, which is the clogging criteria of U.S. Army Corps of Engineers.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2000년도 가을 학술발표회논문집(I)
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• pp.297-302
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• 2000

This paper presents the effect of diaphragm spacing ratio(depth to span) on behavior and capacity of composite steel-concrete structures of sandwich system. Numerical analysis has been performed variety diaphragm ratio, behavior and load condition. As a results of this study, in case of shear behavior and concentrated load, the capacity of structure such as yielding and ultimate load improve according to diaphragm ratio because of concrete confining effect by steel plate and stress redistribution by diaphragm. But in case of bending behavior or uniform load, it proved that diaphragm ratio don't influence on behavior and capacity of composite structures of sandwich system.

• Steel and Composite Structures
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• 제27권4호
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• pp.417-426
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• 2018

This paper presents the seismic behaviors and restoring force model of ring beam joints of steel tube-reinforced concrete column structure under cyclic loading. First, the main failure mode, ultimate bearing capacity, stiffness degradation and energy dissipation capacity are studied. Then, the effects of concrete grade, steel grade, reinforcement ratio and radius-to-width ratios are discussed. Finally, the restoring force model is proposed. Results show that the ring beam joints of steel tube-reinforced concrete column structure performs good seismic performances. With concrete grade increasing, the ultimate bearing capacity and energy dissipation capacity increase, while the stiffness degradation rates increases slightly. When the radius-width ratio is 2, with reinforcement ratio increasing, the ultimate bearing capacity decreases. However, when the radius-to-width ratios are 3, with reinforcement ratio increasing, the ultimate bearing capacity increases. With radius-to-width ratios increasing, the ultimate bearing capacity decreases slightly and the stiffness degradation rate increases, but the energy dissipation capacity increases slightly.

• 한국지반신소재학회논문집
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• 제12권4호
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• pp.99-107
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• 2013

매입말뚝의 수평저항 특성을 고찰하기 위하여 매입말뚝에 대한 수평재하시험을 실시하여 수평하중과 수평변위관계를 분석하였다. 말뚝수평재하시험은 시멘트 밀크가 말뚝매입길이의 50%, 70%, 100%로 주입된 6개의 말뚝에 대하여 실시하였다. 시멘트 밀크의 주입비(시멘트 밀크 주입길이/말뚝의 길이)는 매입말뚝의 수평변위, 항복하중, 수평지지력에 큰 영향을 미치는 것으로 나타났다. 시멘트 밀크의 주입비가 증가할수록 매입말뚝의 수평변위가 발생되기 시작하는 위치는 지표면에 가까워지며 말뚝의 수평변위는 감소한다. 그리고 말뚝의 수평지지력과 항복하중은 시멘트 밀크 주입비가 증가할 수록 크게 나타났다. 시멘트 밀크 주입비가 1인 매입말뚝의 항복하중과 극한수평지지력은 시멘트 밀크 주입비가 0.5인 경우보다 약 2~3배 정도 크게 나타났다.