• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.6A
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• pp.457-464
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• 2011

An experimental study was performed to evaluate the possibility of using stiff type PolyUrea(PU) on RC slab as a strengthening material. Stiff type PU(STPU) was sprayed on the bottom surface of the slab specimens, which were then attached with CFRP or GFRP sheets. Also the evaluation of the bond capacity, the single most influential parameter on strengthening of RC structures, was carried out the flexural capacity evaluation test results showed that the load carrying capacity of the PU specimen was greater and less than the unstrengthened and FRP sheet attached specimens, respectively. The STPU specimens showed a ductile flexural behavior in the plastic displacement range. With respect to bond capacity, the bond strength of all of the specimen exceeded the code required bond strength of 1.5 MPa. Also, the STPU sprayed specimen without using epoxy resin did not peel off when the tensile grip was applied for testing. The stability of the PU bond failure indicate a good bond strength of PU when applied to concrete.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.6
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• pp.1655-1665
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• 2014

Dynamic displacements of structures shows general behavior of structures. Generally, It is used to estimate structure condition and trustworthy physical quantity directly. Especially, measuring vertical displacement which is affected by moving load is very important part to find or identify a problem of bridge in advance. However directly measuring vertical displacement of the bridge is difficult because of test conditions and restriction of measuring equipment. In this study, Artificial Neural Network (ANN) is used to suggest estimation method of bridge displacement to overcome constrain conditions, restriction and so on. Horizontal strain and vertical displacement which are measured by appling random moving load on the bridge are applied for learning and verification of ANN. Measured horizontal strain is used to learn ANN to estimate vertical displacement of the bridge. Numerical analysis is used to acquire learning data for axis strain and vertical displacement for applying ANN. Moving load scenario which is made by vehicle type and vehicle distance time using Pearson Type III distribution is applied to analysis modeling to reflect real traffic situation. Estimated vertical displacement in respect of horizontal strain according to learning result using ANN is compared with vertical displacement of experiment and it presents vertical displacement of experiment well.

• Journal of the Korea Concrete Institute
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• v.13 no.3
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• pp.251-260
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• 2001

It is required to evaluate the axial strain of reinforced concrete beams in order to predict the ductility of reinforced concrete beams subjected to reversed cyclic loading. A model was proposed to determine the axial strains In reinforced concrete beams by analysing the behavior of reinforced concrete sections and comparing with published test results. The proposed axial strain model inclusively reflected four kinds of paths : Path 1-steel bar in an elastic stage or a unloading region; Path 2-after flexural yielding; Path 3-a slip region; and Path 4-a reversing loading region. The equations to predict the axial strains of each path were proposed. The proposed equations took into account the effects of the loading program. Comparison of axial strains between experimental results and the results from proposed equations showed to be in a good agreement with experimental results.

• Journal of the Korea Concrete Institute
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• v.14 no.3
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• pp.357-364
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• 2002

The resistance curves (R-curves) for 381 m crack extension of CLWL-DCB specimens had been determined. The average velocities of the crack extension measured with strain gages were 0.70 and 55 ㎜/sec. The measured rotation angle of the notch faces showed the existence of the singularity at least before 171 and 93 mm crack extensions for the 0.70 and 55 ㎜/sec crack velocities, respectively. The maximum slopes of the R-curves occurred between 25 and 89 ㎜ crack extensions for 0.70 ㎜/sec crack velocity and between 51 and 127 ㎜ crack extensions for 55 ㎜/sec crack velocity During the maximum slopes of the R-curves, the micro-crack localization can be expected, and faster crack velocity may form longer micro-cracking and micro-crack localizing zones. The fracture resistance of 0.70 ㎜/sec crack velocity reached a roughly constant maximum value of 143 N/m at 152 ㎜ crack extension, while that of 55 ㎜/sec crack velocity increased continuously to 245 N/m at 254 ㎜ crack extension and then decreased to the value of 0.70 ㎜/sec crack velocity. The R-curve of 55 ㎜/sec crack velocity was similar to that of the small size three-point bend test, and it showed that small size specimen or fast crack velocity could cause more brittle behavior.

• Journal of the Korea Concrete Institute
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• v.14 no.4
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• pp.503-512
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• 2002

Generally, the girder spacing of the two-girder composite bridge is from 5m up to 15m. To ensure the structural safety according to Korean Bridge Design Specification, the deck depth should be from 33 cm upto 73 cm. Using the transversal prestressing strands in concrete deck, we can reduce its depth about 10％. However, there is little experience on the design and construction of prestressed concrete(PSC) decks in Korea. This paper focuses on the behaviors of PSC deck. A literature survey is performed widely. Considering the characteristics of the two-girder bridge and the construction conditions in Korea, a cast-in-place PSC deck is recommended for the two-girder bridge with 6m girder spacing. To examine its structural behaviors and safety, three partial model deck specimens(3 m$\times$5 m) with real scale are fabricated md tested. One(PS34-RS) is 34cm depth with the stiffness restraint in longitudinal edges for simulating the real bridge deck. Another(PS34-NS) is same depth without the stiffness restraint, and the other(PS28-NS) is 28cm depth with the stiffness restraint. Under the static patch loading, each specimen had a larger ultimate flexural strength than the design value. Specimens with the stiffness restraint (PS34-RS and PS28-RS) showed the punching shear failure mode and specimen without that(PS34-NS) showed the flexural failure mode.

• Magazine of the Korea Concrete Institute
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• v.4 no.1
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• pp.119-126
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• 1992

AC] 318-H9 Recommended that when the specified compressive strength of concrete in a column is greater than 1. 4 times that specified for a floor system, top surface of the colurrm concrete shall extend 2ftU;OOrrun) into the slab from the face of colUlml to avoid unexpected brittle failure. The purpose of this investigation is to suggest the basic information for the structural safety, The major variables are com preSSlve strength of concrete, shear confinement ratio, and loading types. The test results showed that the load capaCIty of speCImen subjected to monotOI1lC loading had more than that of specimen subjected to one way cyclic loading. The failure modes of specimens under cyclic loading were concentrated at 5-20cm apart region from beam-column joint face and ductility index are increased with increasing of shear confinement ratio. Keywords: ACI 318-89, High and Low Strength Concrete, Beam-Column Joint, Shear Confinement Ratio, Loading Type, Ductility Index, Extension Distance.

• Journal of the Korea Concrete Institute
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• v.23 no.6
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• pp.723-730
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• 2011

It is very important to experimentally evaluate concrete behavior at elevated temperature because aggregates make up approximately 80 percent of volume in concrete. In this study, an experiment to evaluate mechanical properties of normal weight and light weight concrete of 60 MPa was conducted. Based on loading level of 0, 20 and 40 percent, the tests of 28 days compressive strength, elastic modulus, thermal strain, total strain, and transient creep using ${\phi}100{\times}200mm$ cylindrical specimens at elevated temperature were performed. Then, the results were compared with CEB (Committes Euro-international du Beton) model code. The results showed that thermal strain of light weight concrete was smaller than normal weight concrete. Also, the results showed that compressive strength of light concrete at $700^{\circ}C$ was higher than normal weight concrete and CEB code, similar to that obtained at ambient temperature. Transient creep developed from loading at a critical temperature of $500^{\circ}C$ caused the concrete strains to change from expansion to compression. The transient creep test result showed that internal force was high when the ratio of shrinkage between concrete and aggregate was more influential than thermal expansion.

• Journal of the Korean Data and Information Science Society
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• v.27 no.1
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• pp.155-168
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• 2016

The purpose of this study was to investigate the prevalence of allergic diseases and its related factorsin Korean adolescents. The subjects were 72,435 middle and high school students. The data were analyzed by ${\chi}^2$ test and multiple logistic regression analysis. The prevalence of asthma, allergic rhinitis, and atopic dermatitis was 9.3%, 30.6%, and 23.4%, respectively. According to multiple logistic regression analysis, asthma was associated with gender, age, economic state, obesity, stress, sleep satisfaction, secondhand smoking, drug use, other allergic diseases and physical activity. Allergic rhinitis was associated with age, economic state, residential area, type of residence, obesity, stress, sleep satisfaction, smoking experience, secondhand smoking, alcohol drinking, other allergic diseases and physical activity. Finally, atopic dermatitis was associated with gender, age, economic state, residential area, obesity, stress, other allergic diseases and physical activity. Conclusion: These results will provide database for prevention and management of allergic diseases.

• Journal of Korean Academy of Nursing
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• v.17 no.3
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• pp.184-194
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• 1987

The purposes of this study were; 1) to gather data relevant to demographic features. major main management practices, and the level of impairment of the activities of daily living (ADL) of patients with back pain, 2) to test the sensitivity of the Korean Pain Rating Scale and the Graphic Rating Scales, and 3) to identify indirect indicators of back pain by analysing pain related-behaviors. The level of pain was measured by Korean Pain Rating Scale(KPRS) and Graphic Rating Scales(GRS) developed by the reserchers. The GRS consists of two dimensions; the pain intensity (sensory) and unpleasantness (affective) measures. Of the 1,650 diagnosed back pain patients, from January 4 through June 30, 1987 by visiting outpatients' clinics of orthopedic and neurosurgical departments at 11 university hospitals in different districts of Korea, 330 men and women patients were self-selected by responding to the mailed questionnaires. The results were summarised as follows: Male exceeded female patients in number and onset of back pain were more prevalent in the age groups of 20s and the 30s. The average duration of suffering from the pain were 11 months, sixty three (19.1%) of the subjects retired from their jobs, one third(36.7%) have teen hospitalized for the treatment of back pain. In two thirds(64.8%) of the cases pain was characterized as lower back pain. The average sleep hour was 6.8 hours per 24 hours and the average rest hour during the day was 3.3 hours. The mean percentage of pain measured by GRS was higher than that of KPRS. The level of sensory intensity as well as the affective level of pain measured by KPRS and GRS were not highly correlated (sensory intensity r=0.4986, affective r=0.5029) which indicated low discriminative power. On the other hand, intercorrelation between sensory and affective dimension measured by KPRS and GRS showed moderate interrelation(r=0.7247; r=0.7899). One-third(32.5%) of the subjects complied with the hospital prescribed treatment while the other one-third(31.5%) depended on self-remedy and traditional practices, and the last one-third did not imply any pain management practices. The following 6 pain-related behaviors such as length of hospitalization, rest hour during day hours, varieties of pain management practice implied, number of pain sites, need for ADL and discomfort accompanied by ADL revealed to be important indicators of back pain. An investigation of sociodemographic features of patients with back pain in a larger context, i.e. with bigger number of respondents is recommended. Tests for construct validity of KPRS, i.e. factor analysis is further recommended.

• Journal of Korean Academy of Nursing
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• v.38 no.6
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• pp.822-830
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• 2008

Purpose: The purpose of this study was to analyze effects of a community-based case management program for clients with hypertension living in the community. Methods: The research design was a one group pre and post-test design with 30 participants with hypertension who agreed to participate in the 8-12 week case management program provided by case managers from the National Health Insurance Corporation in 2002. Data were collected three times, before and after the case management services, and 6 months later. Outcomes included changes in blood pressure, knowledge of hypertension and daily life practices, including alcohol consumption, smoking, exercise, and medication adherence. Results: Repeated-measures ANOVA and post-hoc tests of means revealed significant differences before and after service for systolic blood pressure, daily life practices (monitoring body weight and BP, low salt and cholesterol and high vegetable diet, and stress-relief practices), and exercise. The goal for medication adherence was attained after service. Significant improvements from baseline to 6 months after service were observed in measures of salt and vegetables in diet. There were no significant differences on hypertension knowledge, alcohol consumption or smoking behavior between before service and after, and at 6 months. Conclusion: The findings provide preliminary evidence that case management intervention can have positive outcomes on BP control, daily life practices, exercise, and medication adherence for clients with hypertension. However, additional interventions are needed to sustain long-term effects.