• Structural Engineering and Mechanics
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• v.55 no.1
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• pp.93-109
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• 2015

Finite element analysis (FEA) combined with the concepts of linear elastic fracture mechanics (LEFM) provides a practical and convenient means to study the fracture and crack growth of materials. In this paper, a numerical modeling of crack propagation in the cement mantle of the reconstructed acetabulum is presented. This work is based on the implementation of the displacement extrapolation method (DEM) and the strain energy density (SED) theory in a finite element code. At each crack increment length, the kinking angle is evaluated as a function of stress intensity factors (SIFs). In this paper, we analyzed the mechanical behavior of cracks initiated in the cement mantle by evaluating the SIFs. The effect of the defect on the crack propagation path was highlighted.

• Journal of Korean Neurosurgical Society
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• v.61 no.1
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• pp.114-119
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• 2018

Objective : The purpose of this study was to determine the feasibility of screw fixation in previously augmented vertebrae with bone cement. We also investigated the influence of cement distribution pattern on the surgical technique. Methods : Fourteen patients who required screw fixation at the level of the previous percutaneous vertebroplasty or balloon kyphoplasty were enrolled in this study. The indications for screw fixation in the previously augmented vertebrae with bone cement included delayed complications, such as cement dislodgement, cement leakage with neurologic deficits, and various degenerative spinal diseases, such as spondylolisthesis or foraminal stenosis. Clinical outcomes, including pain scale scores, cement distribution pattern, and procedure-related complications were assessed. Results : Three patients underwent posterior screw fixation in previously cemented vertebrae due to cement dislodgement or progressive kyphosis. Three patients required posterior screw fixation for cement leakage or displacement of fracture fragments with neurologic deficits. Eight patients underwent posterior screw fixation due to various degenerative spinal diseases. It was possible to insert screws in the previously augmented vertebrae regardless of the cement distribution pattern; however, screw insertion was more difficult and changed directions in the patients with cemented vertebrae exhibiting a solid pattern rather than a trabecular pattern. All patients showed significant improvements in pain compared with the preoperative levels, and no patient experienced neurologic deterioration as seen at the final follow-up. Conclusion : For patients with vertebrae previously augmented with bone cement, posterior screw fixation is not a contraindication, but is a feasible option.

• Transactions on Electrical and Electronic Materials
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• v.9 no.4
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• pp.147-150
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• 2008

Porcelain suspension insulators aged for 1, 5 and 10 years on Korean transmission lines and new insulators are tested for autoclave expansion. The compressive strength of the insulators aged in an autoclave with conditions of $250\;^{\circ}C$ and at 20 atm for 30 minutes, was about $7.6\;kgf/mm^2$, which is close to that measured on insulators aged for 10 years in the field. From simulation results, the cement displacement changed linearly with temperature. At a temperature of $200\;^{\circ}C$, the shear stress was approximately $7\;kgf/mm^2$; a stress that is brought about by a 0.07 % expansion of the cement. It is evident that the cement would fracture at a 0.07 % expansion, because the cement has about 7 to $9\;kgf/mm^2$ flexure strength. A turning point in the shear stress with mechanical load occurred at 0.02 % cement expansion. From an analysis of the porcelain body it is shown that there is sufficient margin of strength to guard against fracture of the porcelain body even for a cement expansion more than 0.12 %.

• Journal of the Korean Geosynthetics Society
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• v.17 no.4
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• pp.41-52
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• 2018

Since the composite ground design method is easy to apply for calculation or numerical analysis, it is applied to the design of cement mixing methods. However, the comparison studies between analysis and actual results such as a trial test and construction for the cement mixing method are few because the composite ground design method was developed for the compaction pile (SCP, GCP) methods. In this study, the results of various analysis methods, such as the composite ground analysis method (1 case) and the individual pile method (3 cases), were compared with actual measurements through a two-dimensional finite element numerical analysis. In case of the surface settlements, the results of study show that the individual plate method was larger than the actual measurements, while other methods are similar. The settlements at the under ground of the improved area is overestimated in all analysis methods. When comparing numerical analysis results for the horizontal displacement, and ground reaction forces, the individual pile method in equivalent wall concept was found to be the most similar to the measurements. The composite ground method was not able to predict the behavior of stress transfer (Arching effect) and it turned out that the prediction of horizontal displacement was too large.

• Earthquakes and Structures
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• v.24 no.6
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• pp.439-453
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• 2023

Older brick masonry structures generally suffer from low strength defects. Using a cement mortar layer (CML) or steel-meshed cement mortar layer (S-CML) to reinforce existing low-strength brick masonry structures (LBMs) is still an effective means of increasing seismic performance. However, performance indices such as lateral displacement ratios and skeleton curves for LBMs reinforced with CML or S-CML need to be clarified in performance-based seismic design and evaluation. Therefore, research into the failure mechanisms and seismic performance of LBMs reinforced with CML or S-CML is imperative. In this study, thirty low-strength brick walls (LBWs) with different cross-sectional areas, bonding mortar types, vertical loads, and CML/S-CML thicknesses were constructed. The failure modes, load-carrying capacities, energy dissipation capacity and lateral drift ratio limits in different limits states were acquired via quasi-static tests. The results show that 1) the primary failure modes of UBWs and RBWs are "diagonal shear failure" and "sliding failure through joints." 2) The acceptable drift ratios of Immediate Occupancy (IO), Life Safety (LS), and Collapse Prevention (CP) for UBWs can be 0.04%, 0.08%, and 0.3%, respectively. For 20-RBWs, the acceptable drift ratios of IO, LS, and CP for 20-RBWs can be 0.037%, 0.09%, and 0.41%, respectively. Moreover, the acceptable drift ratios of IO, LS, and CP for 40-RBWs can be 0.048%, 0.09%, and 0.53%, respectively. 3) Reinforcing low-strength brick walls with CML/S-CML can improve brick walls' bearing capacity, deformation, and energy dissipation capacity. Using CML/S-CML reinforcement to improve the seismic performance of old masonry houses is a feasible and practical choice.

• Journal of the korean academy of Pediatric Dentistry
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• v.10 no.1
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• pp.35-45
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• 1983

This study was undertaken to evaluate the pulpal responses to the intermediate restorative materials such as Zinc phosphate cement, Polycarboxylate cement, IRM (zinc oxide eugenol cement), Dycal, Life, Cresatin, and Fluoride in caivties which were cut with high speed instrument. 5 dogs were used as experimental animals and devided into 8 groups. The intervals of observaobservation ranged 3 days, 1, 3, 4, 8 weeks after experiment respectively. The specimens were fixed with 10% formalin and decalcified in 5% nitric acid. All slides were stained with hemtoxylin-eosin and examined histopathologically. The results were as follows: 1. In control group, severe vacuolar degeneration and atrophy of odontoblasts were seen in 3 days, hemorrhage and congestion continued until 8 weeks. Necrosis of odontoblastic layer was seen in zinc phosphate cement group and polycarboxylate cement group. 2. In dycal group, vacuolar degeneration and atrophy of odontoblast were not seen. but in Life group, these were seen in 3 days and partially continued until 3 weeks. In 4 weeks, regeneration of odontoblast was occured. 3. In Crcsatin group, there was no pathosis except odontoblastic displacement. In Fluoride group, vacuolar degeneration of odontoblast was seen and soon disappeared. As compared with control group, pathological change of the pulp tissue in experimental group were decreased after amalgam restoration.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.04b
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• pp.499-504
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• 1998

Objective of this study is to investigate experimentally the flexural behavior of reinforced high-strength concrete beams with Belite cement by comparing with those of normal reinforced concrete beams. The flexural tests are conducted on fourteen specimens having concrete compressive strength of 350 and 600kg/$\textrm{cm}^2$. The main experimental variables are compressive strength of concrete and reinforcement ratios. The load-displacement relationships, the section behavior of beam as a function of the location neutral axis, and ductility capacity are investigated. From the test results, the flexural behavior of reinforced high-strength concrete beams wite Belit cement are similar to the behavior of normal reinforced concrete beams.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2014.05a
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• pp.238-239
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• 2014

It is well known that the bond characteristics of fiber govern the performance of fiber reinforced composite material. A preliminary study was carried out to investigate the pull-out behavior of amorphous and conventional single fiber in cement mortar in accordance with the JCI(Japan Concrete Institute) SF-8. The test was performed under displacement control, and results showed that the bond strength decreased with increasing fiber length. In addition, the amorphous steel fiber showed much higher pull-out load per unit weight compared to conventional steel fiber.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05b
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• pp.369-372
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• 2005

This study is about physical properties of concrete with changing displacement ratio of calcium sulfa aluminates(CSA) type admixture. Firstly, test shows that as displacement ratio of CSA increases and setting properties changes, fluidity and air contents decreases. In water to binder ratio 35$\%$ and 45$\%$, concrete using the cement replacing CSA 4$\%$ by volume shows that bleeding decreases 94.7$\%$ and 74.3$\%$ respectively, compared with plain concrete. In addition, setting time was promoted around 3 to 6 hour and 1 to 4 hour respectively. For harden concrete, increase of displacement ratio caused tendency of higher compressive strength as OPC has at early age. Replacing higher CSA admixture led to reduce of drying shrinkage.

• Journal of the Korean Ceramic Society
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• v.41 no.9
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• pp.690-695
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• 2004

In this study, inorganic (steel, asbestos and carbon) and organic (polyacryl and polyamide) fibers were used to investigate their reinforcing effects of the physical properties of Portland cement. From the load-displacement curve of each reinforced specimen, fracture strength, Young's module, fracture energy and fracture toughness were computed and compared with each other. In addition, the experiment of their impact toughness was carried out and compared with the fracture energy. For the improvement of fracture strength the inorganic (asbestos) fiber reinforcement was most effective, while the best reinforcing effect of impact toughness was achieved by organic (polyacryl) fiber. And steel fiber proved to be most adequate for improvement of both fracture strength and impact toughness. Steel fiber also showed the highest fracture energy and fracture toughness among all of the fibers.