• Journal of the Korea Concrete Institute
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• v.26 no.3
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• pp.247-254
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• 2014

Strain properties of concrete member which acts as an important factor in the stability of the concrete structure in the event of fire, significantly affected the characteristics of the coarse aggregate, which accounts for most of the volume. For this reason, there are many studies on concrete using artificial lightweight aggregate which has smaller thermal expansion deformation than granite coarse aggregate. But the research is mostly limited on concrete using clay-based lightweight aggregate. Therefore, in this study, the high temperature compressive strength and elastic modulus, thermal strain and total strain, high temperature creep strain of concrete was evaluated. As a result, remaining rate of high-temperature strength of concrete using lightweight aggregate is higher than concrete with general aggregate and it is determined to be advantageous in terms of structural safety and ensuring high-temperature strength from the result of the total strain by loading and strain of thermal expansion. In addition, in the case of high-temperature creep, concrete shrinkage is increased by rising loading and temperature regardless of the type of aggregate, and concrete using lightweight aggregate shows bigger shrinkage than concrete with a granite-based aggregate. From this result, it is determined to require additional consideration on a high temperature creep strain in case of maintaining high temperature like as duration of a fire although concrete using light weight aggregate is an advantage in reducing the thermal expansion strain of the fire.

• Journal of the Korea Concrete Institute
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• v.29 no.3
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• pp.307-314
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• 2017

Concrete is a durable and cost-benefit construction material, however performance degradation occurs due to steel corrosion exposed to chloride attack. Penetration of chloride ion usually decreases due to hydrates formation and reduction of pores, and the reduced chloride behavior is considered through decreasing diffusion coefficient with time. In the work, HPC (High Performance Concrete) samples are prepared with 3 levels of W/B (water to binder) ratios of 0.37, 0.42, and 0.27 and 3 levels of replacement ratios of 0%, 30% and 50%. Several tests containing chloride diffusion coefficient, passed charge, and compressive strength are performed considering age effect of 28 days and 180 days. Chloride diffusion is more reduced in OPC concrete with lower W/B ratio and GGBFS concrete with 50% replacement ratio shows significant reduction of chloride diffusion in higher W/B ratio. At the age of 28 days, GGBFS concrete with 50% replacement ratio shows more rapid reduction of chloride diffusion than strength development, which reveals that abundant GGBFS replacement has effective resistance to chloride penetration even in the early-aged condition.

• Journal of the Korea Concrete Institute
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• v.27 no.1
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• pp.65-73
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• 2015

This study discussed the pozzolanic properties of calcined sewage sludge (CSS) according to calcination and fineness conditions. The chemical and mineralogical analysis of CSS according to calcination temperature and time were carried out and compared with that of the existing pozzolanic materials such as fly-ash, blast furnance slag and meta-kaolin. Various mortars were made by mixing those CSS and $Ca(OH)_2$ (1:1 wt. %), and their compressive strength and hydrates according to experimental factors such as fineness of CSS and curing age were also investigated in detail. The results show clearly the potentiality of calcined sewage sludge (CSS) as an admixture materials in concrete, but the CSS should be controlled by calcination temperature and time, and fineness etc. In this experimental condition, the calcination temperature of $800^{\circ}C$, calcination time of 2 hours and fineness of $5,000cm^2/g$ were optimum conditions in consideration of the mechanical properties and economic efficiency of CSS. The compressive strength of CSS mortars was higher than that of fly-ash mortars and blast furnace slag mortars, especially at the early ages. Then, the utilization of CSS in construction fields was greatly expected.

• Journal of the Korea Concrete Institute
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• v.28 no.1
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• pp.3-11
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• 2016

The concern about hollow core PC slab has been increased to improve the workability during a construction of building by reducing self weight of structural members. In this manner, recently, TRS (Tripple Ribs Slab) was developed as a new type of half PC slab system. TRS member consists of the triple webs and the bottom flange prestressed by strands. The slab system is completed by casting of topping concrete on the TRS after filling styrofoam between the webs. This paper, presents a flexural experiment to investigate the flexural capacity of the TRS. Five full scale TRS members were made and tested under simple support condition to be failed by flexure and their strength was evaluated by code equations; the variables in the test are the depth and the presence of topping or raised spot formed when slip-forming. In addition, a nonlinear sectional analysis was performed for the specimens and the result was compared with the test results. From the study, it was found that the TRS has enough flexural strength and ductility to resist the design loads and its strength can be suitably predicted by using code equations. The raised spot did not affect the strength so that the spot need not to be removed by doing additional work. For the more accurate prediction of TRS's flexural behavior by using nonlinear sectional analysis, it is recommended to consider the concrete's brittle property due to slip-forming process in the modeling.

• Journal of the Korea Concrete Institute
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• v.20 no.3
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• pp.393-404
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• 2008

The approaches in many design codes for the estimation of the deflection of flexural reinforced concrete (RC) members utilize the concept of the effective moment of inertia which considers the reduction of flexural rigidity of RC beams after cracking. However, the effective moment of inertia in design codes are primarily based on the ratio of maximum moment and cracking moment of beam subjected to loading without proper consideration on many other possible influencing factors such as span length, member end condition, sectional size, loading geometry, materials, sectional properties, amount of cracks and its distribution, and etc. In this study, therefore, an experimental investigation was conducted to provide fundamental test data on the effective moment of inertia of RC beams for the evaluation of flexural deflection, and to develop a modified method on the estimation of the effective moment of inertia based on test results. 14 specimens were fabricated with the primary test parameters of concrete strength, cover thickness, reinforcement ratio, and bar diameters, and the effective moments of inertia obtained from the test results were compared with those by design codes, existing equations, and the modified equation proposed in this study. The proposed method considered the effect of the length of cracking region, reinforcement ratio, and the effective concrete area per bar on the effective moment of inertia, which estimated the effective moment of inertia more close to the test results compared to other approaches.

• Journal of the Korean Institute of Telematics and Electronics C
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• v.36C no.12
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• pp.78-89
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• 1999

Previous wavelet network structures are determined by considering the relationship between wavelet windows distribution of training patterns that are transformed into time-frequency space. Because it is separated two algorithms that determines wavelet network structure and that modifies parameters of network, learning process that minimizes output error of network is executed after the network structure is determined. But this method has some weakness that training patterns must be transformed into time-frequency space by additional preprocessing and the network structure should be fixed during learning process. In this paper, we propose a new constructing method for wavelet network structure by using differences between the output and the desired response without preprocessing. Because the algorithm perform network construction and error minimizing process simultaneously, it can determine the number of hidden nodes adaptively as with the complexity of problems. In addition, the network structure is optimized by inserting new hidden nodes in the area that has maximum error and extracting hidden nodes that has no effect to the output of network. This algorithm has no constraint condition that all training patterns must be known, because it removes preprocessing procedure for training patterns and it can be applied effectively to systems that has time varying outputs.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.1D
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• pp.149-155
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• 2011

The aim of this study is to grasp how the dwellers of apartment cognize the real condition of the management such as general control of janitor office or management of maintenance, environment, account and imposing price of management. The analysed results of recognition are as following. First, as the dwellers judged that the janitors are incapable to control dispute among the households, it needs to develop the ability to cope with the demand of control dispute by various curriculum. There should be more strict management of parking lot for the handicapped. Second, it needs to establish the plan to improve maintenance of the rest facility. Third, as dwellers thought the management expenses not to be made public clearly, it needs to use various way, not only by neighborhood meeting but also information system such as establishing web page or E-mail notice for better announcement of the settled matters such as management expenses. Forth, the audit result of management expenses and the measures conducted after audit should be reported widely, contract of construction work services needs to be publicized by neighborhood meeting or other information system.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.1
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• pp.31-37
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• 2016

Co-firing of biomass with coal is a promising combustion technology in a coal-fired power plant. However, it still requires verifications to apply co-firing in an actual boiler. In this study, data from the Thermogravimetric analyzer(TGA) and Drop tube furnace(DTF) were used to obtain the combustion characteristics of biomass when co-firing with coal. The combustion characteristics were verified using experimental results including reactivity from the TGA and Unburned carbon(UBC) data from the DTF. The experiment also analyzed with the variation of the biomass blending ratio and biomass particle size. It was determined that increasing the biomass blending ratio resulted in incomplete chemical reactions due to insufficient oxygen levels because of the rapid initial combustion characteristics of the biomass. Thus, the optimum blending condition of the biomass based on the results of this study was found to be 5 while oxygen enrichment reduced the increase of UBC that occurred during combustion of blended biomass and coal.

• Asian Journal of Turfgrass Science
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• v.19 no.2
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• pp.141-149
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• 2005

This study was carried out to assess the present condition of domestic and foreign patented technologies in turfsrass cultivar area. Patented technologies about turfsrass were analyzed by web site(www.kipris.or.kr) from 1948 to 2005. The results are summarized as follows; 1. Number of patents on turfgrass fertilizer(866) was more than the other patents on turfgrass. 2. Total number of Japan's patents on turfgrass was 1,565. This is more than America's. The foreign patents are mostly on cultivar, sod, seed, disease, construction, and management. 3. Number of patents from company(2,328) was the most and the others are private individuals, research institutes, university professors. However commercialization rate of patants was low. 4. Turfgrass cultivars patented in Korea are 'Konwoo', 'Senock' 'Anyanjungji', etc., and in foreign countries 'Zenith', 'Miyako', etc. Among them 'Zenith', 'Miyako' and 'Konhee' were commercialized.

• Asian Journal of Turfgrass Science
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• v.23 no.1
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• pp.23-34
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• 2009

Research was initiated to investigate early establishment characteristics and germination pattern of tall fescue(TF, Festuca arundinacea Shreb.). Four varieties of TF were evaluated in the study. Experiment was conducted under a room temperature condition of $5^{\circ}C$ to $25^{\circ}C$(natural conditions). Daily and cumulative germination patterns were measured and analyzed on a daily basis. Significant differences were observed in germination patterns, days to the first germination, days to 50% germination, days to 75% germination, and germination percentage with different environments and varieties. Germination percentage was variable with varieties at the end of study. It was 85.25 to 97.00% under natural conditions. There were considerable variations in early germination characteristics and patterns among the entries according to different conditions. The first germination was initiated between 7 and 9 DAS(days after seeding) under natural conditions, being 2 to 3 days later as compared with ISTA conditions. It was 11 to 12 DAS in days to the 50% germination, which was 3 to 4 days after the first germination. Days to the 75% germination were 12.38 to 14.29 DAS, being 1.55 to 4.77 days slower as compared with ISTA conditions. Olympic Gold was regarded as the fastest variety and Tar Heel II was slowest. Data from this study demonstrated that information on differences in germination characteristics and patterns among varieties would be usefully applied for TF establishment such as golf course construction.