• Journal of the Korea Concrete Institute
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• v.22 no.6
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• pp.777-786
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• 2010

This paper examines the flexural behavior of full-scale prestressed concrete girders that were constructed of steel fiber reinforced ultra high performance concrete (UHPC). This study is designed to provide more information about the bending characteristics of UHPC girders in order to establish a reasonable prediction model for flexural resistance and deflection for future structural design codes. Short steel fibers have been introduced into prestressed concrete T-girders in order to study their effects under flexural loads. Round straight high strength steel fibers were used at volume fraction of 2%. The girders were cast using 150~190 MPa steel fiber reinforced UHPC and were designed to assess the ability of steel fiber reinforced UHPC to carry flexural loads in prestressed girders. The experimental results show that steel fiber reinforced UHPC enhances the cracking behavior and ductility of beams. Moreover, when ultimate failure did occur, the failure of girders composed of steel fiber reinforced UHPC was observed to be precipitated by the pullout of steel fibers that were bridging tension cracks in the concrete. Flexural failure of girders occurred when the UHPC at a particular cross section began to lose tensile capacity due to steel fiber pullout. In addition, it was determined that the level of prestressing force influenced the ultimate load capacity.

• Journal of Korean Neurosurgical Society
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• v.63 no.4
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• pp.433-443
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• 2020

Objective : Osteoporosis is a disease of unbalanced bone metabolism that results in low bone mineral density with increased bone fragility and propensity for fractures. The increased rate of bone fracture due to osteoporosis places a significant burden on public health care expenditures. Therefore, numerous studies have been designed and performed to identify the drugs or health foods that can improve the bone quality or quantity. This study was designed to evaluate and analyze the therapeutic effects of rutin on histomorphometric values of the spine and femur in an osteoporotic mouse model induced by bilateral ovariectomy. Methods : Thirty female ICR mice (8 weeks old) underwent either a sham operation (only abdominal incision, sham group, n=10) or bilateral ovariectomy (n=20). The ovariectomized (OVX) animals were randomly divided into two groups : untreated OVX group (OVX-C, n=10), or rutin-administered group (OVX-R, n=10). The OVX-C group received weight-adjusted doses of saline vehicle and the OVX-R group received 50 mg/kg of rutin intraperitoneally, starting 1 day after surgery. At 4 and 8 weeks after surgery, serum estrogen, osteocalcin, alkaline phosphatase (ALP), and the telopeptide fragment of type I collagen C-terminus (CTX-1) were analyzed. Interleukin (IL)-1β, IL-6, IL-10, and tumor necrosis factor (TNF)-α were also analyzed. Bone histomorphometric parameters of the 4th lumbar vertebra and femur were determined by micro-computed tomography. Results : In OVX-C group, ALP, osteocalcin, CTX-1, IL-1β, IL-6, and TNF-α levels were significantly increased at 4 and 8 weeks compared to sham operation group. Rutin administration after OVX statistically significantly reduced ALP, CTX-1, IL-1β, IL-6, and TNF-α levels at 4 and 8 weeks. Rutin administration also improves bone histomorphometric parameters including trabecular bone volume fraction, trabecular thickness, and trabecular number. Trabecular separation was also decreased in OVX-R group compared to OVX-C group. Conclusion : The present study demonstrated that rutin has therapeutic effects on improving bone histomorphometric values in an OVX mouse model. The improvement in histomorphometric values may be associated with the reduction of osteoclastic activity via inhibition of IL-1β, IL-6, and TNF-α. In future studies, the mechanism for the effect of rutin on osteoporosis should be demonstrated more clearly to use rutin in human osteoporosis.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.1
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• pp.100-108
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• 2015

The purpose of this study is to evaluate the effect of improvement on the impact resistance and strength properties of cement composites by surface modification of aramid fiber. For aramid fiber reinforced cement composites, therefore, dispersion capability and the bonding efficiency between the fibers and the cement composite material need to be improved. It is possible by modifying surface properties to hydrophobic, it is considered that oiling agent ratio of 1.2 % and improvement of performance is in need to be investigated. In this study, short aramid fibers were mixed by different fiber length and oiling agent ratio. And improvement of strength properties and impact resistance performance of hybrid cement composites were evaluated under the influence of steel fiber. As a result, strength properties of aramid fiber reinforced cement composites are different by mixing ratio of fiber, oiling agent ratio and length of fiber. In case of cement composites which have same volume fraction and fiber length, tensile strength and flexural strength were improved with increase of the emulsions throughput of the fiber surface. The results of evaluation on the static strength properties had effects on impact resistance performance by high-velocity impact. And it was observed that the scabbing of rear was suppressed with increase of the oiling agent ratio.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.2
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• pp.111-118
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• 2020

In this paper, the flexural creep behavior of hooked-end steel fiber reinforced high-strength concrete was evaluated to investigate the steel fiber content influence on long-term behavior of flexural members. An experimental program consisted of nine prismatic beam specimens with dimensions of 150 × 150 × 600mm reinforced with different contents of steel fiber (0, 0.75 and 1.5% at the volume fraction). To introduce flexural creep loading to notched prismatic beam specimens, a four-point bending test setup was used. The sustained load with 40% of the flexural strength was applied by means of a lever system and controlled by a load cell for 90 days. During sustained loading, crack mouth opening displacement (CMOD) was monitored. Conventional flexural test after creep tests were carried out to evaluate the residual capacity of each specimen. Test results showed that steel fiber content has a significant effect on the flexural creep behavior of high-strength concrete and long-term flexural load with 40% of flexural strength doesn't generate negative effects on the residual capacity of steel fiber reinforced high-strength concrete.

• Journal of the Korean Chemical Society
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• v.37 no.12
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• pp.1035-1046
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• 1993

Some iron(III)porphyrin complexes were prepared, and identified by the spectroscopic methods. Elution behavior of iron(III)porphyrin complexes was investigated by reversed-phase HPLC. The optimum conditions for the separation of iron(III)porphyrin complexes were examined with respect to flow rate and mobile phase strength. These complexes were successfully separated on NOVA-PAK $C_{18}$ column using methanol / water(95/5) for $[T_pCF_3PP)Fe(R)]$ and methanol / water (98/2) for $[(P)Fe(C_6F_5)]$ as a mobile phase. It was found that these complexes were largely eluted in an acceptable range of capacity factor value ($0{\leq}logk'{\leq}1$). The dependence of the capacity factor (k') on the volume fraction of water in the binary mobile phase as well as the dependence of k' on the liquid-liquid extraction distribution ratio$(D_c)$ in methanol-water / n-pentadecane extraction system showed a good linearity. It means that the retention of iron(III)porphyrin complexes on NOVA-PAK $C_{18}$ column is largely due to the solvophobic effect. Also, there was a good linear dependence of the capacity factor(k') on the column temperature and enthalpy calculated by van't Hoff plot. From these results, it was confirmed that the retention mechanism of iron(III)porphyrin complexes in reversed-phase liquid chromatography was invariant under the condition of various temperature, and the solvophobic binding process exhibited isoequilibrium behavior.

• Investigative Magnetic Resonance Imaging
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• v.17 no.3
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• pp.200-206
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• 2013

Purpose : To assess the effect of applying an automated heart model based measurements of left ventricle (LV) and compare with manual and semi-automated measurements at Cardiovascular MR Imaging. Materials and Methods: Sixty-two patients who underwent cardiac 1.5T MR imaging were included. Steady state free precession cine images of 20 phases per cardiac cycle were obtained in short axis views and both 2-chamber and 4-chamber views. Epicardial and endocardial contours were drawn in manual, automated, and semi-automated ways. Based on these acquired contour sets, the end-diastolic (ED) and end-systolic (ES) volumes, ejection fraction (EF), systolic volume (SV) and LV mass were calculated and compared. Results: In EDV and ESV, the differences among three measurement methods were not statistically significant (P = .399 and .145, respectively). However, in EF, SV, and LV mass, the differences were statistically significant (P=.001, <001, <001, respectively) and the measured value from automated method tend to be consistently higher than the values from other two methods. Conclusion: An automatic heart model-based method grossly overestimate EF, SV and LV mass compared with manual or semi-automated methods. Even though the method saves a considerable amount of efforts, further manual adjustment should be considered in critical clinical cases.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.5
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• pp.553-561
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• 2015

The exponential and power law functionally graded material(FGM) theory is reformulated considering the refined shear and normal deformation theory. This theory has ability to capture the both normal deformation effect and exponential and power law function in terms of the volume fraction of the constituents for material properties through the plate thickness. Navier's method has been used to solve the governing equations for all edges simply supported plates on Pasternak elastic foundation. Numerical solutions of vibration analysis of FGM plates are presented using this theory to illustrate the effects of power law index and 3-D theory of exponential and power law function on natural frequency. The relations between 3-D and 2-D higher-order shear deformation theory are discussed by numerical results. Further, effects of (i) power law index, (ii) side-to-thickness ratio, and (iii) elastic foundation parameter on nondimensional natural frequency are studied. To validate the present solutions, the reference solutions are discussed.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.2
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• pp.1109-1117
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• 2014

We study free vibration analysis of sigmoid functionally graded materials(S-FGM) nano-scale plates, using a nonlocal elasticity theory of Eringen in this paper. This theory has ability to capture the both small scale effects and sigmoid function in terms of the volume fraction of the constituents for material properties through the plate thickness. Numerical solutions of S-FGM nano-scale plate are presented using this theory to illustrate the effect of nonlocal theory on natural frequency of the S-FGM nano-scale plates. The relations between nonlocal and local theories are discussed by numerical results. Further, effects of (i) power law index (ii) nonlocal parameters, (iii) elastic modulus ratio and (iv) thickness and aspect ratios on nondimensional frequencies are investigated. In order to validate the present solutions, the reference solutions are compared and discussed. The results of S-FGM nano-scale plates using the nonlocal theory may be the benchmark test for the free vibration analysis.

• Korean Journal of Materials Research
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• v.9 no.12
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• pp.1252-1262
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• 1999

The effect of microstructures on the strength-flangeability of Nb bearing hot-rolled high strength steel was investigated in order to improve the strength-flangeability of conventional TS 580MPa grades HSLA steel for the automotive wheel disc. The low temperature coiling method using 3-step controlled cooling pattern after hot rolling was effective to produce the Nb-bearing high strength steel with the polygonal ferrite and bainite duplex microstructures. It was suggested that the suppressed precipitation of grain boundary cementites and the decreased hardness difference between ferrite matrix and bainite cause the excellent stretch-flangeability of ferrite-bainite duplex microstructure steel. Therefore, the formation and propagation of microcracks were suppressed relative to the conventional HSLA steel with ferrite and pearlite microstructure. In addition, the elongation was improved as compared with that of hot-rolled steel sheets using conventional early cooling pattern because the volume fraction of polygonal ferrite was increased.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.1
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• pp.148-156
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• 2020

The paper is a summary of the results of the basic pullout test which is conducted to evaluate the anchorage capacity of high strength headed bars that is mechanical anchored vertically on steel fiber reinforced concrete members. The main experimental parameters are volume fraction of steel fiber, concrete strength, anchorage length, yield strength of headed bars, and shear reinforcement bar. Both sides of covering depth of the specimen are planned to double the diameter of the headed bars. The hinged point is placed at the position of each 1.5𝑙_dt and 0.7𝑙_dt around the headed bars, and the headed bars are drawn directly. As a result of pullout test experiment, concrete fracture and steel tensile rupture appear by experimental parameters. The compressive strength of concrete is 2.7~5.4% higher than that of steel fiber with the same parameters, while the pullout strength is 20.9~63.1% higher than that of steel fiber without the same parameters, which is evaluated to contribute greatly to the improvement of the anchorage capacity. The reinforcements of shear reinforcements parallel to the headed bars increased 1.7~7.7% pullout strength for steel fiber reinforced concrete, but the effect on the improvement of the anchorage capacity was not significant considering the increase in concrete strength. As with the details of this experiment, it is believed that the design formula for the anchorage length of KCI2017and KCI2012 are suitable for the mechanical development design of SD600 head bar that is perpendicular to the steel fiber reinforced concrete members.