Flexural Behavior of High Performance Fiber Reinforced Cementitious Composites (HPFRCC) Beam with a Reinforcing Bar (휨 철근이 배근된 HPFRCC 보 부재의 휨 거동)
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- Journal of the Korea Concrete Institute
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- v.23 no.2
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- pp.169-176
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- 2011
In this study, the flexural test for reinforced high performance fiber reinforced cementitious composites (R/HPFRCC) members has been conducted in order to investigate the flexural behavior including the effect of an ordinary tensile reinforcing bar. Through the test, it was observed that the flexural strength increased due to the stable tensile stress transfer of HPFRCC, even up to the ultimate state. In addition, no localized crack appeared until the yielding of the reinforcement. From the layered section analysis of the tested members, it was found that the analysis with the tensile model obtained from the tension stiffening test showed better agreement with the flexural test results, whereas the analysis with direct tension test results overestimated the flexural capacity. Through the experimental and analytical studies, two flexural failure modes have been defined in this paper; concrete crushing at the top compression layer or tensile failure at the bottom tensile layer of the beam section. Based on these two flexural failure modes, a simple formula that estimates the ultimate flexural strength of the member has been proposed in this paper. The proposed equations can be useful in a design and an analysis of R/HPFRCC members.
This descriptive correlational study was conducted to identify the variables related to a health promoting lifestyle in high school students. 304 high school students and 189 vocational high school students living in Taegu city were selected by a convenience sampling method. The data were collected by self-reported questionnaires from August 24 to September 4, 1998. Pender and others' Health Promoting Lifestyle Profile, Shere et al's. Self-Efficacy scale, Wallston et al.'s Internal Health Locus of Control scale, Wares' Health self rating scale and Cohen & Hoberman's Social support scale were used. The data were analyzed by using descriptive statistics, Pearson correlation coefficient, t-test, MANOVA, ANOVA. Tukey verification and Stepwise multiple regression with an SAS program. The results of this study were as follows: 1. The average score of a health promoting lifestyle performance was 2.38(SD=.36) of a 4 point scale .Self-actualization (mean = 2.80. SD = .60). interpersonal support(mean = 2.73, SD=.47), health responsibility (mean=1.53, SD=.47), nutrition(mean=2.64, SD=.63), exercise(mean=2.71. SD=.72) and stress management(mean=2.37, SD=.58) were also analyzed. 2. The combination of self-efficacy, social-support, internal health locus of control. father's educational level and perceived health status explained 37.97% of the variance in health promoting lifestyles. 3. A Health promoting lifestyle showed significant positive correlations with self efficacy(r=.5173. p=.0011), perceived health status(r=.254, p=.001) and internal health locus of control(r=.321. p=.001). 4. According to sex(t=7.38. p=.006). economic state(F=6.62, p=.00l), Father's educational level(F=4.25, p=.005), mother's educational level(F=6.94. p=.000l), the grade of educational performance(F=3.74, p=.024), sleeping hours(F=3.47. p=.032) and social support(F=40.76, p=.0001). there were significant differences and modifying factors in health promoting lifestyles. On the basis of the above findings. self-efficacy in cognitive factors, and social support in modifying factors were identified as the variables which explained most of Pender's health-promotion model. Nursing strategies enhancing self-efficacy and social support which have a more significant effect on health promoting lifestyles should be developed. Further research is required to find out the factors influencing health pormoting lifestyle of high school students.
Purpose:Epilepsy of child may cause high level of psychosocial difficulties for parents including stigmatization and stress and therefore worsen their quality of life (QOL). The purpose of this study was to evaluate the mediating effect of perceived stigma against epilepsy on QOL among parents with epileptic child. Methods:Two hundred and sixty parents of epileptic child recruited from five separated university hospital child neurology clinics specializing in epilepsy completed a demographic questionnaire, a medical questionnaire, a perceived stigma questionnaire and the Ro's Quality of Life Inventory, a popular tool for evaluating QOL of adults in Korea which is composed of 6 domains and 47 questions. Data was analyzed with SPSS 14.0 program using frequency analysis and descriptive analysis and with AMOS 7.0 program using Structural Equation Model (SEM) analysis. Results:The level of parents' QOL was relatively fair. SEM analysis on the quality of life level of parents showed that all variables (especially having religion, the monthly income, employment state, age of child, the leisure time, the perceived stigma level against epilepsy, and seizure frequency) directly affect the quality of life level of parents and that disease-related variables also affect the quality of life level of parents indirectly through the mediating factor (the perceived stigma), where the indirect effect is large with the existence of combined disabilities. The total effect on the quality of life level of parents is large with the existence of combined disabilities, the perceived stigma level, the leisure time, having religion, and the monthly income. Conclusion:The results of this study indicated that many factors including parents' perceived stigma may affect the quality of life of parents with epileptic children directly, and that some disease-related factors may affect indirectly through a mediating factor, the perceived stigma. Multidisciplinary collaboration would be imperative for their welfare.
In this study, it is carried out to analyze the international design standards such as Eurocode 8, API 650, NZSEE and etc for the seismic design of steel liquid storage tanks. From the comparison and analysis, the data for the required parameters and factors are provided for the establishment of Korean seismic design standard for steel liquid storage tanks. The simplified mechanical models have been presented for the seismic design of steel liquid storage tanks in all design standards and the parameters of mechanical models in design standards have similar values. Although the models for the seismic design of steel liquid storage tanks are similar in design standards, design approaches are given differently in accordance with the design methods, allowable stress design or limit state design. Therefore it is not easy to compare seismic forces presented in design standards directly. After comparison of design standards, it is concluded that establishment of Korean design standard for the seismic design of steel liquid storage tanks is necessary.
A condition evaluation procedure for the pavement foundations using multi-load level Falling Weight Deflectometer(FWD) deflections is presented in this paper. A dynamic finite element program incorporating a stress-dependent material model, was used to generate the synthetic deflection database. Based on this synthetic database, the relationships between surface deflections and critical responses, such as stresses and strains in base and subgrade layers, have been established. FWD deflection data, Dynamic Cone Penetrometer(UP) data, and repeated load resilient modulus testing results used in developing this procedure were collected from the Long Term Pavement Performance (LTPP) and North Carolina Department of Transportation (NCDOT) database. Research effort focused on investigation of the effect of the FWD load level on the condition evaluation procedures. The results indicate that the proposed procedure can estimate the pavement foundation conditions. It is also found that structurally adjusted Base Damage Index (BDI) and Base Curvature Index (BCI) are good indicators for the prediction of stiffness characteristics of aggregate base and subgrade respectively. A FWD test with a load of 66.7 kN or less does not improve the accuracy of this procedure. Results from the study for the nonlinear behavior of a pavement foundations indicate that the deflection ratio obtained from multi-load level deflections can predict the type and quality of the pavement foundation materials.
Reinforced-concrete (RC) columns are frequently designed and constructed. other types of columns includes composite types such as concrete-filled tube columns (CFT). Hollow RC columns may be effective in reducing both the self weight of columns and total amount of materials used. This is due to the fact that a hollow RC column possesses larger moment of inertia than that of solid RC columns of same cross sectional area. Despite the effectiveness the hollow RC column has not been popular because of its poor ductility performance. While the transverse reinforcements are effective in controlling the brittle failure of the outside concrete, they are not capable of resisting the failure of concrete of inner face which is in unconfined state of stress. To overcome these drawbacks, the internally confined hollow reinforced concrete (ICH RC), a new column type, was proposed in the previous researches. In this study, the fire resistance performance of the ICH RC columns was analyzed through a series of extensive heat transfer analyses using the nonlinear-material model program. Also, effect of factors such as the hollowness ratio, thickness of the concrete, and thickness of the internal tube on the fire resistance performance were extensively studied. Then the factors that enhance the fire-resistant performance of ICH RC were presented and analyzed.
In this paper, experimental program and associated numerical study were carried out to evaluate the fire resistance of unprotected concrete-filled rectangular steel tubular (CFT) columns subjected to the standard fire. The key testing parameters included the length effect, the load ratio, and the sectional dimensions of the CFT columns. Temperature distribution and axial deformation of the CFT column specimens were measured and analyzed. Rather early local buckling of steel tubes was observed in all the specimens. This caused subsequent load transfer from steel tube to concrete, and eventually triggered concrete crushing, or complete loss of the load bearing capacity of the column. This implies that the limit state of local buckling as well as overall flexural buckling should be incorporated in fire design procedure. As expected, the fire resistance time of specimen with higher load ratio consistently lessened. The prediction of fire resistance time of unprotected CFT columns based on the limiting steel temperature in current design codes or the formula proposed by previous studies is slightly conservative compared to the fire test results available. To establish the finite element analysis model that can be used to predict the thermal and structural behaviour of unprotected CFT columns in fire, the fully coupled thermal-stress analysis was also tried by using the commercial code ABAQUS. The numerical results showed a reasonable global correlation with the experimental results.
In this study, in order to evaluate the damage and deterioration of the track components of sleeper floating track (STEDEF), the field samples(specimens) were taken from the serviced line over 20 years old, and the track components were visually inspected, and investigated by laboratory tests and finite element analysis. As a result of visual inspection, the damage of the rail pad and fastener was slight, but the rubber boot was worn and torn at the edges of bottom. The resilience pads were clearly examined for thickness reduction and fatigue hardening layer. As a result of spring stiffness test of rail pad and resilience pad, the deterioration of rail pad was insignificant, but the deterioration of resilience pad exceeded design standard value. Therefore resilience pad was directly affected by train passing tonnage. As a result of comparing the deterioration state of the field sample and the numerical analysis result, the stress and displacement concentration position of the finite element model and the damage position of the field sample were coincident.
The wall shear stress in the vicinity of end-to end anastomoses under steady flow conditions was measured using a flush-mounted hot-film anemometer(FMHFA) probe. The experimental measurements were in good agreement with numerical results except in flow with low Reynolds numbers. The wall shear stress increased proximal to the anastomosis in flow from the Penrose tubing (simulating an artery) to the PTFE: graft. In flow from the PTFE graft to the Penrose tubing, low wall shear stress was observed distal to the anastomosis. Abnormal distributions of wall shear stress in the vicinity of the anastomosis, resulting from the compliance mismatch between the graft and the host artery, might be an important factor of ANFH formation and the graft failure. The present study suggests a correlation between regions of the low wall shear stress and the development of anastomotic neointimal fibrous hyperplasia(ANPH) in end-to-end anastomoses. 30523 T00401030523 ^x Air pressure decay(APD) rate and ultrafiltration rate(UFR) tests were performed on new and saline rinsed dialyzers as well as those roused in patients several times. C-DAK 4000 (Cordis Dow) and CF IS-11 (Baxter Travenol) reused dialyzers obtained from the dialysis clinic were used in the present study. The new dialyzers exhibited a relatively flat APD, whereas saline rinsed and reused dialyzers showed considerable amount of decay. C-DAH dialyzers had a larger APD(11.70
The wall shear stress in the vicinity of end-to end anastomoses under steady flow conditions was measured using a flush-mounted hot-film anemometer(FMHFA) probe. The experimental measurements were in good agreement with numerical results except in flow with low Reynolds numbers. The wall shear stress increased proximal to the anastomosis in flow from the Penrose tubing (simulating an artery) to the PTFE: graft. In flow from the PTFE graft to the Penrose tubing, low wall shear stress was observed distal to the anastomosis. Abnormal distributions of wall shear stress in the vicinity of the anastomosis, resulting from the compliance mismatch between the graft and the host artery, might be an important factor of ANFH formation and the graft failure. The present study suggests a correlation between regions of the low wall shear stress and the development of anastomotic neointimal fibrous hyperplasia(ANPH) in end-to-end anastomoses. 30523 T00401030523 ^x Air pressure decay(APD) rate and ultrafiltration rate(UFR) tests were performed on new and saline rinsed dialyzers as well as those roused in patients several times. C-DAK 4000 (Cordis Dow) and CF IS-11 (Baxter Travenol) reused dialyzers obtained from the dialysis clinic were used in the present study. The new dialyzers exhibited a relatively flat APD, whereas saline rinsed and reused dialyzers showed considerable amount of decay. C-DAH dialyzers had a larger APD(11.70