• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.25 no.2
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• pp.87-104
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• 1989

Recently, with the tendency of more lightening, high-strength and high-speed in the marine industries such as marine structures, ships and chemical plants, the use of the aluminium Alloy is rapidly enlarge and there occurs much interest in the study of corrosion fatigue crack characteristics. In this paper, the initiation of surface crack and the propagation characteristics on the base metal and weld zone of 5086-H116 Aluminium Alloy Plate which is one of the Al-Mg serious alloy(A5000serious) used most when building the special vessels, were investigated by the plane bending corrosion fatigue under the environments of marine, air and applying cathodic protection. The effects of various specific resistances on the initiation, propagation behavior of corrosion fatigue crack and corrosion fatigue life in the base metal and heat affected zone were examined and its corrosion sensitivity was quantitatively obtained. The effects of corrosion on the crack depth in relation to the uniform surface crack length were also investigated. Also, the structural, mechanical and electro-chemical characteristics of the metal at the weld zone were inspected to verify the reasons of crack propagation behavior in the corrosion fatigue fracture. In addition, the effect of cathodic protection in the fracture surface of weld zone was examined fractographically by Scanning Electron Microscope(S.E.M.). The main results obtained are as follows; (1) The initial corrosion fatigue crack sensitibity under specific resistance of 25Ω.cm% show 2.22 in the base metal and 19.6 in the HEZ, and the sensitivity decreases as specific resistance increases (2) By removing reinforcement of weldment, the initiation and propagation of corrosion crack in the HAZ are delayed, and corrosion fatigue life increases. (3) As specific resistance decreases, the sensitivity difference of corrosion fatigue life in the base metal and HAZ is more susceptible than that of intial corrosion fatigue crack. (4) Experimental constant, m(Paris' rule) in the marine environment is in the range of about 3.69 to 4.26, and as specific resistance increases, thje magnitude of experimental constant, also increases and the effect by corrosion decreases. (5) Comparing surface crack length with crack depth, the crack depth toward the thickness of specimen in air is more deeply propagated than that in corrosion environment. (6) The propagation particulars of corrosion fatigue crack for HAZ under initial stress intensity factor range of $\Delta$k sub(li) =27.2kgf.mm super(-3/2) and stress ratio of R=0 shows the retardative phenomenon of crack propagation by the plastic deformation at crack tip. (7) Number of stress cycles to corrosion fatigue crack initiation of the base metal and the welding heat affected zone are delayed by the cathodic protection under the natural sea water. The cathodic protection effect for corrosion fatigue crack initiation is eminent when the protection potential is -1100 mV(SCE). (8) When the protection potential E=-1100 mV(SCE), the corrosion fatigue crack propagation of welding heat affected zone is more rapid than that of the case without protection, because of the microfissure caused by welding heat cycle.

• Korean Journal of Construction Engineering and Management
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• v.5 no.6 s.22
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• pp.212-217
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• 2004

Carbon fiber reinforced plastic(CFRP) plate Is one of the alterative materials for soengthening of reinforced and prestressed connote members due to excellent strength and light weight In this paper, the behavior of beams strengthened with CFRP plate and CFS(Carbon fiber sheet) is observed and analyzed from the test results. Especially specimens with thick plate is tested when large moment and large shear lone appear in same position. The main failure mode is a peeling-off of the CFRP plate near the loading points due to flexural-shear crack, Because of this failure mode, failure load is not linearly proportional to the thickness of CFRP plates. When beam is wrapped with CFS around oかy loading point it does not influence on the failure loads. Depending on the loading pattern, it is necessary to consider different design criteria for reinforced concrete members with external reinforcement. When line moment and large shear force appear in same location, maximum thickness may limit to 0.6mm and ratio between moment of strengthened beam and moment of unstrengthened beam is proposed 1.5-2.0. In order to use the plate of thicker than 6mm, CFS may be extended to the location which moment of strengthened beam is 1.5 times than moment of unstrengthened beam.

• Journal of the Korea Concrete Institute
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• v.17 no.1 s.85
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• pp.121-128
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• 2005

A RC column-bent pier represents one of the most popular piers used in highway bridges. Seismic performance of reinforced concrete (RC) column-bent piers under bidirectional seismic loadings was experimentally investigated. Six column bent-piers were constructed with two circular supporting columns which were made in 400 mm diameter and 2,000 mm height. One single column specimen was additionally made to comparatively evaluate the seismic response of RC column-bent piers. Test parameters are different transverse reinforcement and loading pattern. These piers were tested under lateral load reversals with the axial load of $0.1 f_{ck}A_g$. Three specimens were subjected to bidirectional lateral load cycles which consisted of two main longitudinal loads and two sub transverse loads in one load cycle. Other three specimens were loaded in the opposite way. Test results indicated that lateral strength and ductility of the latter three specimens were generally bigger than those of the former three specimens. Plastic hinges were formed with the spall of cover concrete and the fracture of the longitudinal reinforcing steels in the bottom plastic hinge of two supporting columns for the former three specimens. Similar behavior was observed in the top and bottom parts of two supporting columns for the latter three specimens.

• Journal of the Korea Concrete Institute
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• v.17 no.5 s.89
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• pp.679-686
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• 2005

The corrosion of reinforcement induced by chloride ingress is the main deterioration cause of coastal reinforced concrete structures. In this paper, an experimental study was executed to investigate the effect of the kinds and replacement ratios of mineral admixtures (fly-ash, ground granulated blast-furnace slag silica fume and meta-kaolin), W/B and curing time on chloride diffusion of concrete by long-time immersion test in chloride solution. According to the result, the use of mineral admixtures was effective in improving the resistant to chloride ingress. The chloride penetration depth and diffusion coefficient were decreased as replacement ratios of mineral admixture were increased. The kind and replacement ratio of the mineral admixture are more important than the W/B in reducing the chloride diffusion of concrete. Chloride binding capacity of mineral admixture, which was sequenced in the order of MK

• Journal of Science Education
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• v.37 no.1
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• pp.170-185
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• 2013

The purpose of this study is to investigate a cognitive model of task commitment on biology classification inquiry. To achieve this goal, first, this study analyzed several literatures on task commitment in biology inquiry, and invented the tentative model of the task commitment. To investigate a tentative model invented, 2 main tasks were developed. These tasks were administered to 8 high-school students, first grade. Raw protocols were collected by thinking aloud method and a retrospective interview method. Collected protocols were converted to segmented protocols and coded by analyzing frame based invented model. The codes were analyzed. As a result, some problems were discovered, tentative model were revised. New analyzing frame based on Improved model were composed, and raw protocols were re-analyzed. Finally, a cognitive model of task commitment on biology classification inquiry was investigated. The investigated cognitive model of task commitment on biology classification inquiry was constructed 3 steps, 'Task commitment Induction', 'Task commitment Reinforcement', 'Task commitment Maintenance'. And each steps were consisted of several sub-factor. And commitment component were changed in each steps. Through this results, base information for strategy that improvement task commitment on biology classification inquiry is provided. Furthermore, the cognitive model of task commitment on biology classification inquiry will assist on evaluation and feedback by stage on task commitment.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.8
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• pp.4048-4057
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• 2013

In the composite beam subjected to the hogging moment it is very difficult to evaluate the influence of the reduction of slab stiffness due to cracks and their development on the horizontal shear behavior of shear connection. In this study, a 3D FE model is developed by which one can analyze the composite action in the composite beam subjected to the hogging moment. In this FE model, each structural member and shear connection are modeled as similar as possible to details of the composite beam. Bending behaviour, and composite action which could not be analyzed using the existing 1D or 2D FE model are investigated by the 3D model. Analysis results show that the reinforcement ratio and crack behaviour of the slab are main factors which exert a strong influence on the composite action. According to the analysis results about load-slip behavior, initial crack of slab and yielding of rebars have a influence on the slip stiffness of shear connection. The existing experimental results, that the design of partial interaction can be more efficient in designing of shear connection of the composite beams, are indirectly verified by the FE analysis.

• Journal of the Korean GEO-environmental Society
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• v.21 no.6
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• pp.19-25
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• 2020

In the recent downtown works, there are frequent cases where the work on existing piles is impossible due to the influence from lack of space and surrounding environment. In such cases, there has been growing cases of using the micropile method that is available to work with the small equipment and asserts the bearing capacity of the existing piles. The micropile method is a type of drilled shaft with the diameter of a pile to be around 75 mm~300 mm that, even for a case where it has certain surrounding structure, foundation and spatial obstacle, there is almost no work difficulty and the work is feasible under all types of soil conditions. In addition, the work can be done in places where the ceiling of the building is low with less vibration and noise in the work process that such method is significantly used for foundation reinforcement of existing buildings. With respect to the motion characteristics that are changed depending on the foundational characteristics or when the micropile is applied with compression or tensile force, there is very few studies conducted. Therefore, under this study, through the data analysis of the field loading test regarding the micropile worked in the fields, it clarifies the settlement and characteristics of bearing capacity following the embedded condition of the ingredients and piles that consist the foundation if the compression and tensile force are applied to the micropile, and by facilitating the statistical analysis program, SAS, to carry out the analysis on the main elements influencing on settlement of the micropile and bearing capacity.

• Journal of Korean Academy of Nursing
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• v.27 no.3
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• pp.614-626
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• 1997

The main purposes of the study were to develop and test a model which explains the dynamic relationship among factors reported as affecting to the quality of life of individuals with rheumatoid arthritis and to examine the relationship between self-help response and quaility of life. Data for the study were collected from March 1996 to December 1996 from 153 female patients who regularly visited a clinic for people with rheumatism. The patients were introduced to the investigators by nurses who worked at that clinic, and then the investigator interviewed the patients for 30 to 40 minutes to collect the data. Instruments used in the study were modified self-report questionaires from the ones which were already developed in previous studies or from related literature. Data analysis were performed using LISREL(Lineal Structural Relations) 8 program to test whether the proposed hypothesized model fit the collected data. To test the fitablity of the hypothesized model both a general fit measure and a detailed fit measure were used. Based on the test results from the various fit measures, the hypothesized model was found to be well suited to the real data. As characteristics related to illness becomes severe, the feasibility for these characteristics leading to the perception of uncertainty about the illness tend to increase, but, the direct effects from the illness characteristics(such as level of physical symptoms, sense of social-psychologic change, limitations of action) as they are related to the other intrinsic variables (self-efficacy or self-help behavior and quality of life), were found to be not significant. It was found that uncertainty had a direct effect on self-efficacy but did not have a direct effect on self-help behavior or quality of life. Also, it is noted that self-efficacy had a positive effect on self-help behavior and quality of life and there was a bilateral relationship between self-efficacy and self-help behavior. Lastly, the hypothesis proposed from the theoretical model in this study was supported basis of the results that self-help behavior provides both direct and positive effects to quality of life. Particularity, since a bilateral relationship was also found between self-help behavior and quality of life in the modified model, as self-help behavior increased, so did quality of life. And, reversely, as quality of life increased, so did self-help behavior. In conclusion, the results of this study suggest that focusing on both acquirement and reinforcement of adjustment factors or self-help behavior is more efficient than focusing on the characteristics of illness in establishing the stategies for improving quality of life of individuals with rheumatoid arthritis.

• Journal of the Korea Concrete Institute
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• v.27 no.1
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• pp.37-44
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• 2015

This paper describes the effect of strain hardening cement composite (SHCC) material on structure performance of reinforced concrete (RC) beams with high-strength reinforcing bar. Also, this paper explores the structure application of SHCC in order to mitigation cracking damage and improve the ductility of flexural RC members. The prediction model for flexural strength of doubly reinforced SHCC beams are investigated in this study. To achieve the these objectives, a total of 6 rectangular beam specimens were tested under four point monotonic loading condition. The main parameters included the types of cement composite and reinforcing bar. Test results indicated that reinforced beam specimens with SHCC material were improved the structure performances and damage characteristics. Specifically, replacement of conventional high-strength concrete with SHCC materials has the potential of high-strength steel bar as flexural reinforcement on RC members. It is remarkable that suggested method of reinforced SHCC beams with high-strength reinforcing bar could be used usefully to the structure design.

• Journal of the Korea Concrete Institute
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• v.26 no.5
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• pp.581-589
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• 2014

This paper presents the tension stiffening behavior from experimental results of each 6 amorphous steel fibers and normal steel fibers reinforced direct tensile specimens with the main variables such as cover thickness to bar diameter ratio. A tension stiffening effect for steel fiber reinforced RC tension members improve on the increase in cover thickness, and also amorphous steel fiber is usually superior to normal steel fiber. The reinforcement of steel fibers controlled the splitting cracks and led to significant increase in the tension stiffening effect. In particular, if cover thickness is more than twice the bar diameter, the amorphous steel fiber reinforced specimen is controlled the splitting crack and increased the tension stiffening effect. And, the tension stiffening effect of amorphous steel fiber reinforced concrete tension members is different to current structural design code provision.