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초기재령에서 보통골재 및 경량골재 콘크리트의 시간경과에 따른 초음파 속도 변화
김원창 ( Kim¸ Won Chang ),최형길 ( Choi¸ Hyeong Gil ),남정수 ( Nam¸ Jeong Soo ),김규용 ( Kim¸ Gyu Young ),이태규 ( Lee¸ Tae Gyu ) 한국건축시공학회 2021 한국건축시공학회 학술발표대회 논문집 Vol.21 No.2
Because of the problem of increasing self-weight due to the enlargement and high-rise of buildings using normal aggregate concrete, the need for structural lightweight aggregate concrete increases. However, early strength prediction is required when placing structural lightweight aggregate concrete, but research is insufficient. In this study, the ultrasonic pulse velocity of normal aggregate concrete and lightweight aggregate concrete was measured at early age. As a result, the ultrasonic pulse velocity of lightweight aggregate concrete was lower than normal aggregate concrete according to elapsed time at early age.
Strength Reduction of Concrete Subjected to High Temperatures: Effects of Various Aggregates
Wonchang Kim(Wonchang Kim),Keesin Jeong(Keesin Jeong),Hyeonggil Choi(Hyeonggil Choi),Taegyu Lee(Taegyu Lee) 한국화재소방학회 2023 International Journal of Fire Science and Engineer Vol.37 No.1
Previous studies on the strength degradation of concrete subjected to high temperatures were analyzed. To analyze the effect of the coarse-aggregate type on strength degradation, data from previous studies were collected, and the coarse aggregate used, physical properties of the aggregate, and heating conditions were analyzed. The concrete types were classified into normal, heavyweight, and lightweight concrete. Their high-temperature characteristics were analyzed and evaluated according to the mixed coarse aggregate. Finally, the correlations derived from the analysis results were compared with the CEB Code. The analysis results were different for different concrete and coarse-aggregate types, and different tendencies from the CEB Code were observed.
Wonchang Kim,Keesin Jeong,Heeyong Choi,Hyeonggil Choi,Taegyu Lee 한국화재소방학회 2022 International Journal of Fire Science and Engineer Vol.36 No.1
In this study, the compressive strength and ultrasonic pulse velocity (UPV) behaviors of concrete at high temperatures by aggregate type were comparatively analyzed in accordance with the CEN and CEB Codes. The aggregates adopted were divided into limestone, granite, river gravel, and crushed stone, and the target temperatures were set to 100 °C, 200 °C, 300 °C, 400 °C, 500 °C, and 600 °C. The analysis items were specified as compressive strength (Fc), UPV, ratio of compressive strength (Fcratio), and UPV ratio (UPVratio); in addition, the correlations between Fcratio and UPV were analyzed and compared to the previously proposed estimation equations for concrete at room temperature. Accordingly, the Fcratio of limestone and river gravel aggregates exceeded the UPVratio at temperatures lower than 300-400 °C; however, UPVratio tended to be higher at subsequent temperatures. For granite aggregates, UPVratio was higher than Fcratio over the entire temperature range, while crushed stone aggregates exhibited higher Fcratio than UPVratio. Both Fcratio and UPVratio of granite aggregates exceeded those of limestone aggregates, while the UPVratio and Fcratio of river gravel aggregates were higher and lower than those of crushed stone aggregates, respectively. Consequently, a strength estimation equation was proposed by analyzing the correlations between Fcratio and UPV, and was inferred to be better than the existing strength estimation equations.
Impact of Market Openness on Growth and Stability in Korea
Wonchang Jang 인하대학교 정석물류통상연구원 2013 JOURNAL OF INTERNATIONAL LOGISTICS AND TRADE Vol.11 No.2
A controversy about whether liberalization through market opening is a necessary and sufficient condition for a stable and balanced growth in the developing countries was retriggered by the 2008 global financial crisis. This paper aims to analyze 1) the impact of market openness on the economic growth and financial development, 2) the dynamic correlation between the compositional change in foreign investments and the returns of domestic financial markets, 3) the effect of foreign portfolio investment on the stock market activity (liquidity and profitability). Our empirical findings infer that the income level has a positive relationship with financial openness and the foreign portfolio investments cause price fluctuations in the domestic stock market. These results imply that the precautionary and effective policies such as prudential regulations on the short-term capital transactions are strongly needed to emerging markets in order to prevent the excessive fluctuations in the financial markets over the macroeconomic fundamentals.
Asset Ownership, Business Format and Market Structure of Online Retail Market
Wonchang Jang,Ilsoon Shin 서울대학교 경제연구소 2008 Seoul journal of economics Vol.21 No.3
The domestic online retail market consists of three different business models: independent retailer, merchant and market place. When we look at the growth process of these business models, some interesting characteristics are found; first, the average sales amount of the independent model has been decreasing steadily for several years, and second, the market share of the marketplace model shows a steady and significant growth. This paper investigates these characteristics with a formal theoretical model. Based on the asset ownership and business format, the model explicitly considers the retails' decision on the online retail business model. By introducing several parameters to affect the retailers' decision, we found that the model's prediction is consistent with the characteristics aforementioned.