• Steel and Composite Structures
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• 제45권3호
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• pp.389-408
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• 2022

Residual capacity is defined as the load carrying capacity of an RC column after undergoing severe damage. Evaluation of residual capacity of RC columns is necessary to avoid damage initiation in RC structures. The central aspect of the current research is to propose an empirical formula to estimate the residual capacity of RC columns after undergoing severe damage. This formula facilitates decision making of whether a replacement or a repair of the damaged column is adequate for further use. Available literature mainly focused on the simulation of explosion loads by using simplified pressure time histories to develop residual capacity of RC columns and rarely simulated the actual explosive. Therefore, there is a gap in the literature concerning general relation between blast damage of columns with different explosive loading conditions for a reliable and quick evaluation of column behavior subjected to blast loading. In this paper, the Arbitrary Lagrangian Eulerian (ALE) technique is implemented to simulate high fidelity blast pressure propagations. LS-DYNA software is utilized to solve the finite element (FE) model. The FE model is validated against the practical blast tests, and outcomes are in good agreement with test results. Multivariate linear regression (MLR) method is utilized to derive an analytical formula. The analytical formula predicts the residual capacity of RC columns as functions of structural element parameters. Based on intensive numerical simulation data, it is found that column depth, longitudinal reinforcement ratio, concrete strength and column width have significant effects on the residual axial load carrying capacity of reinforced concrete column under blast loads. Increasing column depth and longitudinal reinforcement ratio that provides better confinement to concrete are very effective in the residual capacity of RC column subjected to blast loads. Data obtained with this study can broaden the knowledge of structural response to blast and improve FE models to simulate the blast performance of concrete structures.

• Wind and Structures
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• 제38권3호
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• pp.215-229
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• 2024

Guyed mast structures exhibit characteristics such as high flexibility, low mass, small damping ratio, and large aspect ratio, leading to a complex wind-induced vibration response mechanism. This study analyzed the time- and frequency-domain characteristics of the wind-induced response of a guyed mast structure using measured acceleration response data obtained from the Shenzhen Meteorological Gradient Tower (SZMGT). Firstly, 734 sets of 1-hour acceleration samples measured from 0:00 October 1, 2021, to 0:00 November 1, 2021, were selected to study the vibration shapes of the mast and the characteristics of the generalized extreme value (GEV) distribution. Secondly, six sets of typical samples with different vibration intensities were further selected to explore the Gaussian property and modal parameter characteristics of the mast. Finally, the modal parameters of the SZMGT are identified and the identification results are verified by finite element analysis. The findings revealed that the guyed mast vibration shape exhibits remarkable diversity, which increases nonlinearly along the height in most cases and reaches a maximum at the top of the tower. Moreover, the GEV distribution characteristics of the 734 sets of samples are closer to the Weibull distribution. The probability distribution of the structural wind vibration response under strong wind is in good agreement with the Gaussian distribution. The structural response of the mast under wind loading exhibits multiple modes. As the structural response escalates, the first three orders of modal energy in the tower display a gradual increase in proportion.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 추계 학술발표회 제20권2호
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• pp.289-292
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• 2008

본 논문에서는 고장력 철근이 적용된 휨부재의 구조성능과 사용성능에 대하여 실험적으로 연구하였다. 고장력 철근에 관련된 기존 연구결과에 따르면, RC보의 인장철근을 고장력 철근으로 사용할 경우, SD400에 비해 철근의 물량을 경감시킬 수 있는 장점이 있으나, 균열 폭과 처짐이 증가되는 등 부정적인 영향이 있다고 알려졌다. 따라서 본 논문에서는 고장력 철근을 사용함으로써 휨부재의 성능에 미치는 영향을 분석하는 것을 목적으로 하였다. 이에 철근강도를 변수로 SD400, SD600, SD700의 3개 시험체를 제작하여 실험을 수행하였다. 본 연구의 실험 결과, 동일 철근비 사용 시 고장력 철근의 부재 강성이 감소되는 현상을 나타내었으나, 부재의 전체적인 휨내력은 배근된 철근의 강도 및 철근량에 비례하여 나타나는 것을 확인할 수 있었다. 또한, 고장력 철근 사용시 균열갯수 및 최대 균열폭에 큰 변화가 없으므로 사용성 면에서 큰 문제는 없는 것으로 분석되었다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제42회 동계 정기 학술대회 초록집
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• pp.530-530
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• 2012

Many practical applications of carbon nanotubes(CNTs) have been proposed and there have been attempts to utilize CNT films as transparent electrodes for solar cells and displays. Our group has considered the use of the CNT film as a thin film heater (TFH) and proposed it for the first time and reported the thermal behavior of the TFH made of single walled CNTs. However, due to the relatively high electrical resistance of the CNT film, using the TFH in application areas requiring high heat flux has been a difficult problem. To overcome this obstacle, we adopted a 'branch electrodes' concept to increase the film conductance dramatically. If two branch electrodes are inserted into a TFH whose original electrical resistance is R, the total resistance will be reduced to R/9. Because of the increased aspect ratio, the resistance of each segmented TFH will be reduced to R/3. Furthermore, since they are connected in parallel, the total resistance reduces to R/9. This could be extended to n branch electrodes, and the total resistance of the film will be reduced to R/(n+1)2, if the resistance of electrodes are negligibly small. We fabricated the heaters with different number of branch electrodes. The number of branch electrodes of the fabricated heaters are 0, 2, 4, 8 and their electrical resistance are 101.4, 39.5, 20.0, $15.4{\Omega}$, respectively. We applied 20V to each heater and monitored the temperature variations. We could achieve high heating temperature even with low voltage supply. This technique could be applied to relevant industrial applications which need high power film heater.

• 대한조선학회논문집
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• 제59권1호
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• pp.39-45
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• 2022

Normal strategy of structure optimization procedure has been minimum cost or weight design. Minimum weight design satisfying an allowable stress has been used for the ship and offshore structure, but minimum cost design could be used for the case of high human cost. Natural frequency analysis and forced vibration one have been used for the strength estimation of marine structures. For the case of high precision experiment facilities in marine field, the structure has normally enough margin in allowable stress aspect and sometimes needs high natural frequency of structure to obtain very high precise experiment results. It is not easy to obtain a structure design with high natural frequency, since the natural frequency depend on the stiffness to mass ratio of the structure and increase of structural stiffness ordinary accompanies the increase of mass. It is further difficult at the grillage structure design using the profiles, because the properties of profiles are not continuous but discrete, and resource of profiles are limited at the design of grillage structure. In this paper, the grillage structure design system under the constraint of high natural frequency is introduced. The design system adopted genetic algorithm to realize optimization procedure and can be used at the design of the experimental facilities of marine field such as a towing carriage, PMM, test frame, measuring frame and rotating arm.

• Journal of Welding and Joining
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• 제6권2호
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• pp.30-39
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• 1988

Generally, as the welded region of weld structures has the incomplete bead and welded deposit which are able to behave like the surface cracks occasinally, there is a high possibility that the fatigue fracture of the weld structures is due to the surface cracks on the wlded region. This study was done to investigate the effects of post weld heat treatment (PWHT) on the fatigue behaviors of the surface crack of the heat affected zone (HAZ) for the multi-pass welds under the repetitive pure bending moment. The obtained results are summarized as follows : 1. The crack grows to the depth direction initially as the number of cylces increase, the amount of crack length is increased for the surface dir3ction and cive versa for the depth direction. 2. The fatigue life is increased in a order of as weld, PWHT specimens and parent. 3. As the number of cycles increase, the crack length is increased to th surface direction. The increase of the depth length is blunted at the center of specimen thickness. 4. The fatigue crack growth of PWHT specimens to the surface direction is dependent upon the holding time and applied stress during PWHT. In order words, the crack growth rate decreases with the holding time and increases with the applied stress during PWHT. 5. As the crack grows, the aspect formed in the course of crack propagation approaches to semicircle for parent and ellipse with the largest semidiameter for PWHT ($1/4hr, 15kgf/mm^2$) 6. At depth direction, it is difficult to apply to the paris' equation because of the scattered data between the crack growth rate and the stress intensity factor range.

• 에너지공학
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• 제24권1호
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• pp.78-87
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• 2015

중대사고시 금속용융물층의 열속 집중 현상(Focusig effect)에 대해 상부와 측면벽의 냉각 조건과 높이를 변화시키면서 실험과 수치해석을 수행하였다. 상사성(Analogy) 원리를 이용해 열전달 실험 대신 물질전달 실험을 수행하였으며 황산-황산구리 수용액의 전기도금계를 물질전달계로 채택하였다. $Ra_H$ 수 $8.49{\times}10^7{\sim}5.43{\times}10^9$ 범위에서 상부와 측면벽의 냉각 조건을 세 가지로, 높이를 네 가지로 변화시키면서 열전달을 측정하였다. 상부만 냉각인 경우의 실험결과를 동일한 조건인 Rayleigh-Benard 자연대류 상관식과 비교한 바 Dropkin과 Somerscales, Globe와 Dropkin의 상관식과 매우 일치하였다. 측면벽만 냉각인 경우, 상부와 측면벽 모두 냉각인 경우, 상부만 냉각인 경우 순으로 열전달이 감소하였고, 냉각 조건을 고정한 상태에서 높이를 감소시킬수록 측면 열전달이 향상되었다.

• 한국병원경영학회지
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• 제25권4호
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• pp.38-47
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• 2020

Purposes: The problem in the recent immigration policy and social policy changes for foreigners is that the preliminary analysis or research on the actual impact of the influx of foreigners has not been done enough in Korea yet.. This study is to examine the impact of the Korean health insurance finances on the influx of foreigners. Approach: This study analyzed the health insurance statistics for foreigners and overseas Koreans of the Health Insurance Corporation from 2013 to 2017. The data is the "Status of Health Insurance Premiums for Nationals, Foreigners, and Overseas Koreans from 2013 to 2017" submitted by the National Health Insurance Service to the Health and Welfare Committee during the 2018 National Audit Period. Findings: To summarize the analysis, first, the proportion of foreigners was only 1% of all subscribers (1.7% at work, 1.9% in regions) until 2017. Second, employees at work have a lower pay-to-pay ratio, and local subscribers have a higher pay-to-pay rate, regardless of nationality. Third, as immigrants are mostly concentrated in younger ages, they are healthy and use of hospitals is relatively low. Fourth, in terms of gender distribution, there are many women of childbearing age due to marriage immigration among foreign local subscribers, and more men use hospitals than workers who have a high proportion of males due to childbirth. In conclusion, the impact of immigration on health insurance finances is not large, and has a positive effect on finances. Practical Implications: If we simply consider the financial aspect, encouraging foreigners to subscribe to health insurance has a positive effect on finances. In particular, the more foreign workers are enrolled, the greater the financial gain. In particular, increasing the employment of foreign women through language education, vocational training, and employment support will help finance health insurance. One of the reasons foreign subscribers have a positive impact on health insurance finance is the low medical utilization rate. It can be said that young and healthy foreigners use fewer hospitals and clinics, but another aspect means that foreigners have difficulty using health insurance for various reasons. Therefore, various supports must be accompanied so that foreign subscribers can use medical services when necessary.

• 아태비즈니스연구
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• 제14권3호
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• pp.187-204
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• 2023

Purpose - This study deals with the manager's overconfidence and stock price delay, and verified whether the stock price delay phenomenon changes as the overconfidence increases. Design/methodology/approach - Manager overconfidence means that managers have over confidence in their positions or abilities, and was measured according to Schrand and Zechman (2012). Stock price delay is a phenomenon in which information of company is not immediately reflected in the stock price, but is reflected over time, and was measured by the method suggested in a study by Hou and Moskowitz (2005). The analysis subjects used in this study are companies listed on the KOSPI market between 2011 and 2019, and the final sample is 5,509 company-years. Findings - As a result of the verification, it was shown that the stock price delay decreased as the manager's overconfidence increased, and this effect was amplified as the foreign shareholder's share ratio increased and the number of follow-up financial analysts increased. This means that as the manager's overconfidence increases, he actively provides high-quality information to the capital market. In addition, as a result of subdividing the manager's overconfidence into the investment and capital raising aspects, the capital raising aspect has a significant effect on reducing stock delays. This can be interpreted as the fact that managers with overconfident tendencies have a greater incentive to satisfy investors' information needs. Research implications or Originality - In previous studies, the characteristics of managers with strong overconfidence have both positive and negative aspects. The results of this study are significant in that they clearly demonstrated the positive aspect through the market variable of stock price delay, and it is expected to help capital market stakeholders understand the characteristics of managers with a strong propensity for overconfidence.

• 한국정밀공학회지
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• 제30권6호
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• pp.573-577
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• 2013

The one of the most important issue in roll-to-roll gravure printing is increase of ink transfer ratio or printability. As the result of high ink transfer ratio or printability, we can assess the quality of the printed patterns. The rheological properties are the important factors for the printability of electrodes patterning. In this study, the rheological properties of conductive ink are controlled by adding the solvent. The inks with different rheological properties are used for the patterning of the electrodes of $100{\mu}m$ by gravure printing equipment. The various printing speed, which also affect the rheological properties of conductive ink, is applied and the printed patterns are compared for their width and aspect ratio. Decreasing in the ink viscosity as well as increasing in the printing speed decreases the printability in gravure patterning, which shows that the rheological properties are important factors for the printability of gravure patterning.