• Structural Engineering and Mechanics
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• 제17권1호
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• pp.15-27
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• 2004

A rational and simple analytical model to predict the time varying cracking moment of reinforced concrete sections under sustained loading is developed. The modeling procedure is based on equilibrium and compatibility requirements and takes into account the interdependent effects of creep and shrinkage as well as the presence of axial loading. A parametric study is conducted in which particular consideration is given to the effects of reinforcement ratio, level of loading, and creep and shrinkage characteristics of concrete. It is concluded that the reduction in cracking moment is mainly attributed to shrinkage. The effect of shrinkage is more pronounced at low levels of sustained loading and at high reinforcement ratios. This effect is lessened by the compression steel and creep particularly when the applied moment is near the cracking moment.

• Computers and Concrete
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• 제15권4호
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• pp.515-545
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• 2015

The paper presents results of FE simulations of the strain-rate sensitive concrete behaviour under dynamic loading at the macroscopic level. To take the loading velocity effect into account, viscosity, stress modifications and inertial effects were included into a rate-independent elasto-plastic formulation. In addition, a decrease of the material stiffness was considered for a very high loading velocity to simulate fragmentation. In order to ensure the mesh-independence and to properly reproduce strain localization in the entire range of loading velocities, a constitutive formulation was enhanced by a characteristic length of micro-structure using a non-local theory. Numerical results were compared with corresponding laboratory tests and available analytical formulae.

• Journal of Welding and Joining
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• 제9권1호
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• pp.40-47
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• 1991

The most fatigue tests carried out under the either stress or strain control, but machines and structures had taken variable stress. This variable stress was treated as statistics based on p-type distributions. In this paper, the cumulative fatigue damage of SM45C round bar specimens having a center hole resulting from block loading with p-distributions in rotating bending conditions, is presented. The value of p was changed in the range from 0.25 to 1; 0.25, 0.5, 0.75, 1. The following conclusions were obtained through the constant stress amplitude experiments and the block loading experiments. (1) In constant loading test, fatigue life was affected by cyclic rate. From experimental data, N$_{f}$ (100cpm)/N$_{f}$(3000cpm)equal to 0.56. (2) In case of the cyclic rate 100cpm and 3000cpm, at the high stress amplitude level the crack propagation life N$_{*}$f is longer than the low stress amplitude level. (3) Miner's hypothesis may be valid for p=0.75 and prediction of fatigue life by Haibach's method agree with experimental data well for the case p=0.5, while the modified Miner's method agree with experimental data well for the case p=0.25.5.

• 산업경영시스템학회지
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• 제35권2호
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• pp.30-36
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• 2012

This study is aimed to show that an asymmetric load in the frontal plane leads to an increase in low back loading and fatigue in comparison with a symmetric load when workers lift an external weight by investigating previous studies and verifying the phenomenon with an experiment. Ten male subjects are required to lift and hold an given external load at 70cm height during 50sec, then the EMG amplitude and median frequency on bilateral low back muscle groups (Longissimus, Iliocostalis, and Multifidus) are recorded and analyzed. Independent variables are two-level load weight (13kg, 20kg) and three-level LCG (Center, 6.5cm to the right, and 13cm to the right), and dependent variables are EMG amplitude average, difference, and Fatigue Index (FI). Results show that load weight increases significantly amplitude average and FI, but LCG does significantly amplitude difference and FI significantly (P-value < 0.05). Also the correlation coefficient between amplitude difference and FI is over 0.99. These implies that trunk loading should be explained by not EMG amplitude but muscle fatigue aspect since the association between an external load and amplitude is linear, but the relationship between an external load and median frequency as muscle fatigue index is almost exponential.

• 한국지반공학회논문집
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• 제28권8호
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• pp.65-78
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• 2012

탄성계수값은 퇴적암의 일축압축시험을 통하여 응력수준에 따라 넓은 범위로 변하며 거동특성도 다양하게 발현되고 있다. 즉 탄성계수는 정수가 아닌 변수로 볼 수 있는 것이다. 실무에서는 참고자료 및 실험값으로 사용하고 있으나 그 값은 사용하중 수준에서는 매우 큰 값을 채용하고 있다. 설계 및 시공과정에서는 재하-재(再)재하(loading-reloading) 시험을 통한 값을 사용하여 적절하고 합리적인 결과가 도출되어야 할 것이다. 또한 사용하중의 낮은 응력수준에서 발현되는 탄성계수값의 거동특성 역시 유의하여 보아야 할 점이다.

• 조명전기설비학회논문지
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• 제26권10호
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• pp.111-117
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• 2012

Electric vehicles (EVs) are the most promising alternative substitute to a significant amount of gasoline vehicles for climate friendly transportation. This paper conducted an EV consumer survey through the telephone for 200 residents living in apartments to predict the EV penetration level in the year 2020. The results of EV consumer survey revealed that EV will be penetrated to 10% of the total vehicles in rental apartments and to 23.6% of the total vehicles in apartments for sale(condominium) until 2020. High EV penetration level, however, will lead to an increase of power consumption and over loading of electrical installations. Integrating more electric vehicles, the capacity of transformer related in apartments should be checked to prevent the over loading of the transformer. This paper checked the possibility of over loading at transformer and suggested the load control system as one of the solutions to reduce the over loading of transformers in apartments. Also this paper reviewed other components that should be checked in the designing of EV recharging infrastructure in apartments.

• Journal of Electrical Engineering and Technology
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• 제11권6호
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• pp.1527-1534
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• 2016

Online voltage stability monitoring using real-time measurements is one of the most important tasks in a smart grid system to maintain the grid stability. Loading margin is a good indicator for assessing the voltage stability level. This paper presents an Extreme Learning Machine (ELM) approach for estimation of voltage stability level under credible contingencies using real-time measurements from Phasor Measurement Units (PMUs). PMUs enable a much higher data sampling rate and provide synchronized measurements of real-time phasors of voltages and currents. Depth First (DF) algorithm is used for optimally placing the PMUs. To make the ELM approach applicable for a large scale power system problem, Mutual information (MI)-based feature selection is proposed to achieve the dimensionality reduction. MI-based feature selection reduces the number of network input features which reduces the network training time and improves the generalization capability. Voltage magnitudes and phase angles received from PMUs are fed as inputs to the ELM model. IEEE 30-bus test system is considered for demonstrating the effectiveness of the proposed methodology for estimating the voltage stability level under various loading conditions considering single line contingencies. Simulation results validate the suitability of the technique for fast and accurate online voltage stability assessment using PMU data.

• 전기화학회지
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• 제20권4호
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• pp.61-66
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• 2017

The cycle performance of Ti-Si alloy anode material for Li-ion batteries has been investigated as a function of loading level of electrode using a nodule type of substrate, in which the current collector of flat foil is also used for comparison. The Ti-Si alloy powders are prepared by mechanical alloying method. The electrodes with the nodule type of current collector exhibit enhanced cycling performance compared to those using the flat foil because the alloy particles are more strongly adhered to substrate and the stress caused by lithiation and delithiation reaction can be effectively relaxed by nodule-type morphology. It appears, however, that the cycle performance is critically dependent on the loading level of electrode, even when the nodule type of current collector is applied. With high loading level, cracks are initiated at surface of electrode due to a steep stress gradient through the electrode thickness during cycling, leading to capacity fading.

• 한국항공우주학회지
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• 제44권12호
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• pp.1035-1042
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• 2016

상용 비행시뮬레이션 게임 엔진 X-Plane을 이용하여 구성한 비행시뮬레이터에 대해 FTD level 5를 만족시킬 수 있는 QTG작성에 대해 연구하였다. 모델은 Cirrus사(社)의 SR-20을 대상으로 하였다. QTG의 테스트항목 중에는 조종반력을 측정하는 항목도 있다. 따라서 Brunner사(社)의 CLS(Control Loading System)을 조종 장치에 설치하여 조종반력을 측정할 수 있도록 구성하였다. X-Plane은 자체적으로 트림루틴을 제공하지 않으므로 외부에서 Autopilot을 구성하여 항공기가 트림상태에 도달할 수 있도록 하였다. 또한 테스트를 자동으로 수행할 수 있는 알고리듬을 개발하여 수동으로 조종하여 테스트하는 번거로움을 피하고 같은 테스트를 같은 조건으로 진행할 수 있도록 하였다. FTD Level 5의 경우 실제 비행데이터가 아닌 alternative data source를 적용할 수 있으며 이를 활용하여 모든 테스트 결과가 주어진 범위를 만족하였다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 춘계 학술발표회 제16권1호
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• pp.104-107
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• 2004

The crack widths of reinforced concrete flexural members are influenced by repetitive fatigue loadings. The bond stress-slip relation is necessary to estimate these crack widths realistically. The purpose of the present study is, therefore, to propose a realistic model for bond stress-slip relation under repeated loading. To this end, several series of tests were conducted to explore the bond-slip behavior under repeated loadings. Three different bond stress levels with various number of load cycles were considered in the tests. The present tests indicate that the bond strength and the slip at peak bond stress are not influenced much by repeated loading if bond failure does not occur. However, the values of loaded slip and residual slip increase with the increase of load cycles. The bond stress after repeated loading approaches the ultimate bond stress under monotonic loading and the increase of bond stress after repeated loading becomes sharper as the number of repeated loads increases. The bond stress-slip relation after repeated loading was derived as a function of residual slip, bond stress level, and the number of load cycles. The models for slip and residual slip were also derived from the present test data. The number of cycles to bond slip failure was derived on the basis of safe fatigue criterion, i.e. maximum slip criterion at ultimate bond stress.