• Structural Monitoring and Maintenance
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• v.5 no.1
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• pp.151-171
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• 2018

Transmission tower-line systems are commonly slender and generally possess a small stiffness and low structural damping. They are prone to impulsive excitations induced by cable rupture and may experience strong vibration. Excessive deformation and vibration of a transmission tower-line system subjected to cable rupture may induce a local destruction and even failure event. A little work has yet been carried out to evaluate the performance of transmission tower-line systems in mountain areas subjected to cable rupture. In addition, the control for cable rupture induced vibration of a transmission tower-line system has not been systematically conducted. In this regard, the dynamic response analysis of a transmission tower-line system in mountain areas subjected to cable rupture is conducted. Furthermore, the feasibility of using viscous fluid dampers to suppress the cable rupture-induced vibration is also investigated. The three dimensional (3D) finite element (FE) model of a transmission tower-line system is first established and the mathematical model of a mountain is developed to describe the equivalent scale and configuration of a mountain. The model of a tower-line-mountain system is developed by taking a real transmission tower-line system constructed in China as an example. The mechanical model for the dynamic interaction between the ground and transmission lines is proposed and the mechanical model of a viscous fluid damper is also presented. The equations of motion of the transmission tower-line system subjected to cable rupture without/with viscous fluid dampers are established. The field measurement is carried out to verify the analytical FE model and determine the damping ratios of the example transmission tower-line system. The dynamic analysis of the tower-line system is carried out to investigate structural performance under cable rupture and the validity of the proposed control approach based on viscous fluid dampers is examined. The made observations demonstrate that cable rupture may induce strong structural vibration and the implementation of viscous fluid dampers with optimal parameters can effectively suppress structural responses.

• Journal of Korean Society of Environmental Engineers
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• v.33 no.7
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• pp.544-551
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• 2011

The objective of this study was to analyze VIRULO model, a probabilistic quantitative model, which had been developed by US Environmental Protection Agency. The model could assess the viral attenuation capacity of soil as hydrogeologic barrier using Monte Carlo simulation. The governing equations used in the model were composed of unsaturated flow equations and viral transport equations. Among the model parameters, those related to water flow for 11 soil types were from UNDODA data, and those related to 5 virus species were from the literatures. The model compared the attenuation factor with threshold of attenuation to determine the probability of failure and presented the exceedances and Monte Carlo runs as output. The analysis indicated that among 11 USDA soil types, the viral attenuation capacity of loamy sand and sand were far lower than those of clay and silt soils. Also, there were differences in the attenuation in soil among 5 viruses with poliovirus showing the highest attenuation. The viral attenuation capacity of soil decreased sharply with increasing soil water content and increased nonlinearly with increasing soil barrier length. This study indicates that VIRULO model could be considered as a useful screening tool for viral risk assessment in subsurface environment.

• Geomechanics and Engineering
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• v.13 no.2
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• pp.333-352
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• 2017

A comparison study is made between the dynamic properties of an argillaceous siltstone and its grouting-reinforced body. The purpose is to investigate how grout injection can help repair broken soft rocks. A slightly weathered argillaceous siltstone is selected, and part of the siltstone is mechanically crushed and cemented with Portland cement to simulate the grouting-reinforced body. Core specimens with the size of $50mm{\times}38mm$ are prepared from the original rock and the grouting-reinforced body. Impact tests on these samples are then carried out using a Split Hopkinson Pressure Bar (SHPB) apparatus. Failure patterns are analyzed and geotechnical parameters of the specimens are estimated. Based on the experimental results, for the grouting-reinforced body, its shock resistance is poorer than that of the original rock, and most cracks happen in the cementation boundaries between the cement mortar and the original rock particles. It was observed that the grouting-reinforced body ends up with more fragmented residues, most of them have larger fractal dimensions, and its dynamic strength is generally lower. The mass ratio of broken rocks to cement has a significant effect on its dynamic properties and there is an optimal ratio that the maximum dynamic peak strength can be achieved. The dynamic strain-softening behavior of the grouting-reinforced body is more significant compared with that of the original rock. Both the time dependent damage model and the modified overstress damage model are equally applicable to the original rock, but the former performs much better compared with the latter for the grouting-reinforced body. In addition, it was also shown that water content and impact velocity both have significant effect on dynamic properties of the original rock and its grouting-reinforced body. Higher water content leads to more small broken rock pieces, larger fractal dimensions, lower dynamic peak strength and smaller elastic modulus. However, the water content plays a minor role in fractal dimensions when the impact velocity is beyond a certain value. Higher impact loading rate leads to higher degree of fragmentation and larger fractal dimensions both in argillaceous siltstone and its grouting-reinforced body. These results provide a sound basis for the quantitative evaluation on how cement grouting can contribute to the repair of broken soft rocks.

• Nutrition Research and Practice
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• v.14 no.3
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• pp.230-241
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• 2020

BACKGROUND/OBJECTIVES: Inadequate nutrition in infants and young children affects physical growth and neurocognitive development. Therefore, early nutritional intervention is important to promote catch-up growth in young children with faltering growth. The aim of this study was to evaluate the effect of nutritional supplementation with a pediatric concentrated and balanced nutritional supplement formula on promoting growth and improving nutritional status in children with nonorganic faltering growth. SUBJECTS/METHODS: Children aged 12-36 months whose body weight-for-age was < 5^th percentile on the Korean Growth Charts were enrolled. Children born premature or having organic diseases were excluded. Children were instructed to consume 400 mL of formula per day in addition to their regular diet for 6 months. Pediatricians and dietitians educated the parents and examined the subjects every 2 months. Anthropometric parameters were measured at baseline and at 2, 4, and 6 months, and laboratory tests were done at baseline and 6 months. The good consumption group included children who consumed ≥ 60% of the recommended dose of formula. RESULTS: Total 82 children completed the 6-month intervention. At baseline, there were no significant differences in all variables between the good consumption and poor consumption groups. Weight and weight z-scores were significantly improved in the good consumption group compared to the poor consumption group at the end of the intervention (P = 0.009, respectively). The good consumption group showed a significant trend for gaining weight (P < 0.05) and weight z-score (P < 0.05) compared to the poor consumption group during 6 months of formula intake. The concentration of blood urea nitrogen was significantly increased in the good consumption group (P = 0.001). CONCLUSIONS: Nutritional supplementation with a concentrated and balanced pediatric nutritional formula along with dietary education might be an effective approach to promote catch-up growth in children with nonorganic faltering growth.

• Tunnel and Underground Space
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• v.24 no.2
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• pp.155-165
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• 2014

Multiple thermal energy storage (TES) caverns can be used for storing thermal energy on a large scale and for a high-aspect-ratio heat storage design to provide good thermal performance. It may also be necessary to consider the use of multiple caverns with a reduced length when a single, long tunnel-shaped cavern is not suitable for connection to aboveground heat production and injection equipments. When using multiple TES caverns, the separation distance between the caverns is one of the significant factors that should be considered in the design of storage space, and the optimal separation distance should be determined based on a quantitative stability criterion. In this paper, we described a numerical approach for determining the optimal separation distance between multiple caverns for large-scale TES utilization. For reliable stability evaluation of multiple caverns, we employed a probabilistic method which can quantitatively take into account the uncertainty of input parameters by probability distributions, unlike conventional deterministic approaches. The present approach was applied to the design of a conceptual TES model to store hot water for district heating. The probabilistic stability results of this application demonstrated that the approach in our work can be effectively used as a decision-making tool to determine the optimal separation distance between multiple caverns. In addition, the probabilistic results were compared to those obtained through a deterministic analysis, and the comparison results suggested that care should taken in selecting the acceptable level of stability when using deterministic approaches.

• Tribology and Lubricants
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• v.36 no.2
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• pp.105-115
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• 2020

This paper presents a numerical study on the rotordynamic analysis of a dual-spool turbofan engine in the context of blade defect events. The blades of an axial-type aeroengine are typically well aligned during the compressor and turbine stages. However, they are sometimes exposed to damage, partially or entirely, for several operational reasons, such as cracks due to foreign objects, burns from the combustion gas, and corrosion due to oxygen in the air. Herein, we designed a dual-spool rotor using the commercial 3D modeling software CATIA to simulate blade defects in the turbofan engine. We utilized the rotordynamic parameters to create two finite element Euler-Bernoulli beam models connected by means of an inter-rotor bearing. We then applied the unbalanced forces induced by the mass eccentricities of the blades to the following selected scenarios: 1) fully balanced, 2) crack in the low-pressure compressor (LPC) and high pressure compressor (HPC), 3) burn on the high-pressure turbine (HPT) and low pressure compressor, 4) corrosion of the LPC, and 5) corrosion of the HPC. Additionally, we obtained the transient and steady-state responses of the overall rotor nodes using the Runge-Kutta numerical integration method, and employed model reduction techniques such as component mode synthesis to enhance the computational efficiency of the process. The simulation results indicate that the high-vibration status of the rotor commences beyond 10,000 rpm, which is identified as the first critical speed of the lower speed rotor. Moreover, we monitored the unbalanced stages near the inter-rotor bearing, which prominently influences the overall rotordynamic status, and the corrosion of the HPC to prevent further instability. The high-speed range operation (>13,000 rpm) coupled with HPC/HPT blade defects possibly presents a rotor-case contact problem that can lead to catastrophic failure.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.04a
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• pp.774-780
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• 1999

The study of bond behavior between concrete and rebar has been performed for a long time. On this study, we tried to analysed variation of bond behaviors quantitatively with varying the strength of concrete. Bond stress which observed below the neutral surface of beam and at connecting part of beam and column is affected by various bond parameters. Resistance of deformed bars which embedded in concrete to the pullout force is divided 1) chemical adhesive force 2) frictional force 3) mechanical resistance of ribs to the concrete and these horizontal components of resistance is being bond strength. We selected the most common and typical variable which is concrete strength among various variables. So we used two kinds of concrete strength like as 25MPa(NSC) and 65MPa(HSC). Tension Test was performed to verify how bond behavior varied with two kinds of concrete strength. Concentration of bond stress was observed at load-end commonly in Tension Test of the initial load stage. At this stage stress distribution was almost coincident at each strength. As tension load added, this stress distribution had difference gradually and movement of pick point of bond stress to free-end and central section was observed. This tendency was observed at first and moving speed was more fast in NSC. At the preceeding result the reason of this phenomenon is considered to discretion of chemical adhesion and local failure of concrete around rebar in load-end direction. Especially, when concrete strength was increased 2.6 times in tension test, ultimate bond strength was increased 1.45 times. In most recent used building codes, bond strength is proportioned to sqare root of concrete compressive strength but comparison of normalized ultimate bond strength was considered that the higher concrete strength is, the lower safety factor of bond strength is in each strength if we use existing building codes. In Tension Test, in case of initial tensile force state, steel tensile stress of central cross section is not different greatly at each strength but tensile force increasing, that of central cross section in NSC was increased remarkably. Namely, tensile force which was shared in concrete in HSC was far greater than that of concrete in NSC at central section.

• Journal of the Korea Concrete Institute
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• v.18 no.5 s.95
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• pp.595-602
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• 2006

An experimental study was conducted to investigate seismic behaviour of post-tensioned(PT) exterior slab-column connections used for the purpose to resist gravity loads only. For these, 2/3-scale, two PT post-tensioned exterior connections with two different tendon arrangement patterns and one conventional reinforced concrete(RC) exterior connection was tested under quasi-static, uni-directional reversed cyclic loading. During the lateral testing, gravity forces transferred to the column were kept constant to closely simulate a moment to shear ratio of a real building. One of the objectives of this study was to assess the necessity and/or the quantity of bottom bonded reinforcement needed to resist moment reversal which would occur under significant inelastic deformations of the adjacent lateral force resisting systems. The ACI 318 and 352 provisions for structural integrity were applied to provide the bottom reinforcement passing through the column for the specimens. Prior test results were also collected to conduct comparative studies for some design parameters such as the tendon arrangement pattern, the effect of post-tensioning forces and the use of bottom bonded reinforcement. Consequently, the impact of tendon arrangement on the seismic performance of the PT connection, that is lateral drift capacity and ductility, dissipated energy and failure mechanism, was considerable. Moreover, test results showed that the amount of bottom reinforcement specified by ACI 352. 1R-89 was sufficient for resisting positive moments arising from moment reversal under reversed cyclic loads. Shear strength of the tested specimens was more accurately predicted by the shear strength equation(ACI 318) considering the average compressive stress over the concrete($f_{pc}$) due to post-tensioning forces than that without considering $f_{pc}$.

• Journal of the Korea Concrete Institute
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• v.21 no.4
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• pp.431-439
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• 2009

These days the amount of demolished concrete waste has been increasing due to reconstruction and redevelopment of aged buildings. So the use of recycled aggregates is recommended to solve environmental problems. Some investigations have been carried out to study the flexural behavior of reinforced concrete beams with recycled aggregates. But these have some limitation due to the use of low quality recycled aggregates and small-scale specimens in the laboratory. The purpose of this experimental study is to evaluate the flexural behavior of simply supported RC beams subjected to four-point monotonic loading and made with recycled aggregates. Seven full-scale RC beams were manufactured with different replacement level of recycled aggregates. The main parameters of the study are combination of aggregates. From the test results, the flexural behavior of the beam is described in terms of crack patterns and failure modes. And the flexural strength of RC beam with different types of recycled coarse aggregates and recycled fine aggregates is compared with the provision of KCI code.

• Journal of the Korea Concrete Institute
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• v.21 no.4
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• pp.457-464
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• 2009

Fiber is an important ingredient in fiber-reinforced cement composite (FRCC) which can control fracture of cement composite by bridging action. In compliance with the action of the fiber and the aggregate size, it also showed a different failure mechanism. For practical application, it is needed to investigate the fracture behavior of the FRCC and to understand the micro-mechanism of cement matrix with reinforcing fiber. In order to evaluate a characteristics of fracture process in the FRCC, acoustic emission (AE) technique was used for the analysis and evaluation of FRCC damage by acoustic emission under flexural and cyclic compressive loadings. The AE signals were monitored by AMSY4 AE instrument during the entire loading period. The specimens are reinforced with 0, 1.0, 1.5 and 2.0% (by volume) Polyvinyl alcohol (PVA) fiber. The test results showed that the damage progress of the FRCC was characteristic for the fiber replacement ratio. As a result of analyzing the felicity ratio (FR) values, it is shown that this values can be used for evaluating the degree of FRCC damage. On the whole the felicity ratio values of FRCC are shown between 0.4 and 1.1. And, the AE kaiser effect was shown in the all FRCC specimen. In addition, the damage behavior and the microscopic fracture process of the FRCC are evaluated using the AE parameters, such as calm ratio, b-value and felicity ratio. The purpose of this reserch was to advance the state of knowledge regarding the applicability of acoustic emission as an evaluation method for FRCC.