• Magazine of the Korean Society of Agricultural Engineers
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• v.40 no.5
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• pp.68-79
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• 1998

In the years, the concern about high-strength concrete which is new material has been heightened as a result of active research and development. Recently, as the building structure has been being bigger, higher, longer and more specialized, the demand of material with high-strength concrete for building has been increasing. The demand of high -strength concrete is expected to increase with expansion of usage about the complex concrete structures such as bridge structure as well as nuclear plants, underground structures, hydraulic structures and arctic area sturctures. In this research, silica-fume was used as an admixture in order to get a high-strength concrete. Water/binder ration was limited no more than 18 percent and the amount of unit cement was increased. In this study, a number of trial in concrete mix was carried out to get optimal mix design, and the target slump with $10{\pm}2cm$ was set for in-situ construction. High-strength concrete with cylinder strength of 1,200kgf/$cm^2$ in the 28-days was produced and tested. The static test was carried out to measure the ultimate load, the initial load of flexural and diagonal cracking, crack patterns, fracture modes. The load versus strain and load versus deflection relations were obtained form the static test. The test results were compared with the shear strengths predicted by the equations of ACI code 318-89 and orther researchers. Based on the test results, shear strength equation of reinforced concrete beam using high strength concrete was proposed. Form an evaluation of the results of this experimental investigation, it was concluded that shear strength after diagonal tention cracking diminished with the increase in compressive strength for beams.

• The Journal of Engineering Geology
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• v.22 no.4
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• pp.449-458
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• 2012

A sound understanding of the structural characteristics of fractured rock masses is important in designing and maintaining earth structures because their strength, deformability, and hydraulic behavior depend mainly on the characteristics of discontinuity network structures. Despite considerable progress in understanding the structural characteristics of rock masses, the complexity of discontinuity patterns has prevented satisfactory analysis based on a 3-D rock mass visualization model. This paper presents the results of studies performed to develop rock mass visualization in 3-D to analysis the mechanical and hydraulic behavior of fractured rock masses. General and particular solutions of non-linear equations of disk-shaped fractures have been derived to calculated lines of intersection and equivalent pipes. Also, program modules have been developed to perform the calculations. The procedures developed for the 3-D fractured rock mass visualization model can be used to characterize rock mass geometry and network systems effectively. The results obtained in this study will be refined and then combined for use as a tool for assessing geomechanical problems related to strength, deformability and hydraulic behaviors of the fractured rock masses.

• The Journal of Advanced Prosthodontics
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• v.2 no.2
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• pp.39-45
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• 2010

PURPOSE. The aim of this study was to determine differences in shear bond strength to human dentin using immediate dentin sealing (IDS) technique compared to delayed dentin sealing (DDS). MATERIALS AND METHODS. Forty extracted human molars were divided into 4 groups with 10 teeth each. The control group was light-cured after application of dentin bonding agent ($Excite^{(R)}$ DSC) and cemented with $Variolink^{(R)}$. II resin cement. IDS/SE (immediate dentin sealing, $Clearfil^{TM}$ SE Bond) and IDS/SB (immediate dentin sealing, $Adapter^{TM}$ Single Bond 2) were light-cured after application of dentin bonding agent ($Clearfil^{TM}$ SE Bond and $Adapter^{TM}$ Sing Bond 2, respectively), whereas DDS specimens were not treated with any dentin bonding agent. Specimens were cemented with $Variolink^{(R)}$. II resin cement. Dentin bonding agent ($Excite^{(R)}$. DSC) was left unpolymerized until the application of porcelain restoration. Shear strength was measured using a universal testing machine at a speed of 5 mm/min and evaluated of fracture using an optical microscope. RESULTS. The mean shear bond strengths of control group and IDS/SE group were not statistically different from another at 14.86 and 11.18 MPa. Bond strength of IDS/SE group had a significantly higher mean than DDS group (3.14 MPa) (P < .05). There were no significance in the mean shear bond strength between IDS/SB (4.11 MPa) and DDS group. Evaluation of failure patterns indicates that most failures in the control group and IDS/SE groups were mixed, whereas failures in the DDS were interfacial. CONCLUSION. When preparing teeth for indirect ceramic restoration, IDS with $Clearfil^{TM}$ SE Bond results in improved shear bond strength compared with DDS.

• Journal of the korean academy of Pediatric Dentistry
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• v.23 no.4
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• pp.867-886
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• 1996

The purpose of this study was to evaluate the shearbond strength and resin-dentin interface of three different dentinal bonding systems in primary and permanent teeth. Thirty extracted human primary molars and premolars, which were non-carious and free of obvious defect, were selected for this study. All specimens were divided into six groups with two groups allocated for each of the three dentinal bonding system(All-bond 2, Scotchbond Multi-Purpose, Gluma bonding system). After completion of bonding composite to dentin using each tested dentin bonding system, bond strength measurement and histological observation were performed. The results are as follows: 1. All-bond 2 and Scotchbond Multi-Purpose, A good quality hybrid layer was identified, the morphology of which could be equated with the zone of H-E and Brown-Brenn staining. In Gluma bonding system, hybrid layer was very thin, and separated from the solid polymer. 2. All-bond 2 had the highest mean shearbond strength, followed by Scotchbond Multi-Purpose and Gluma bonding system in both primary and permanent teeth. There was no statistically significant difference between All-bond 2 and Scotchbond Multi-Purpose. Statistically significant difference could be found between Gluma bonding system and the other two groups(p<0.05). 3. The fracture patterns observed were mainly the mixture of adhesive failure and dentin dettachment pattern in All-bond 2 and Scotchbond Multi-Purpose while adhesive failure prevailed in Gluma bonding system.

• Journal of Korean society of Dental Hygiene
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• v.13 no.5
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• pp.819-826
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• 2013

Objectives : The purpose of this study was to analyze the types of dental emergencies. This study was carried out for dental trauma patients visiting the emergency room in H hospital from 2005 to 2006. Methods : Subjects were 252 patients. Demographic characteristics consisted of age, gender, dentition, and dental related injury. Results : Male patients had 1.65 times higher tooth injury than female. Teenagers had higher prevalence of tooth injury. Main cause of dental injury was falling down. Young children accounted for 41.7% of the injuries. Late evening was the highest outbreak time of injury. The most commonly affected teeth were central incisor and lateral incisor. The damage of oral soft tissue was more common than the that of alveolar bone. Main area of primary tooth loss was gingiva(10.7%), tongue or soft palate(7.5%), and frenulum(6.0%). Subluxation(28.6%) and luxation(28.6%) were main cause for the primary teeth. Tooth fracture(50.0%) were the most common injury. Conclusions : Thus, to understand the incidence, causes and patterns of dental trauma is to help preserving natural teeth. The results of this study could provide the clinical guidelines on the treatment of dental emergency patients.

• Tribology and Lubricants
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• v.11 no.4
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• pp.21-27
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• 1995

The effects of interface boundary strength on wear and wear transition during sliding have been investigated in silicon carbide ceramics. Three different microstructures, i.e., solid state sintered silicon carbide, liquid phase sintered silicon carbide and liquid phase sintered silicon carbide composite reinforced with TiB$_{2}$ particulates, were designed by hot pressing. Examinations of crack patterns and fracture modes indicated that interface boundaries were relatively strong between silicon carbide grains in the solid state sintered silicon carbide, intermediate in the liquid phase sintered silicon carbide and weak between silicon carbide grains and TiB$_{2}$ particles in the composite. Wear data and examinations of worn surfaces revealed that the wear behavior of these silicon carbide ceramics could be significantly affected by the interface strength. In the solid state sintered silicon carbide, the wear occurred by a grooving process. In the liquid phase sintered silicon carbide and composite, on the other hand, an abrupt transition in wear mechanism from initial grooving to grain pull-out process occurred during the test. The transition occurred significantly earlier in the composite than in the carbide.

• Journal of the Korean Society of Propulsion Engineers
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• v.16 no.4
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• pp.9-15
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• 2012

In this paper, the bearing strengths and fracture behaviors of the pin-jointed carbon fiber/epoxy composites were investigated through pin loading test with acoustic emission technique. The composites were fabricated by a filament winding process, and three types of laminated patterns were considered. Type 1 was fabricated with stitch, Type 2 was fabricated without stitich and Type 3 was fabricated with prepregs. According to the results, bearing strength of Type 1 was 3.3% lower than that of Type 2 and that of Type 3 was highest. Type 1 and Type 2 revealed a net-tension failure mode, respectively, whereas Type 3 pattern exhibited a bearing failure mode. Also, acoustic emission energy of the Type 3 was higher than that of the Type 1 and Type 2. Therefore, the Type 3 was found to be structurally safer than the Type 1 and Type 2.

• Korean Journal of Acupuncture
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• v.35 no.4
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• pp.174-186
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• 2018

Objectives : The aim of this survey was to investigate the general characteristics of sports injury patients in Korean medical institutions by Korean Medicine Doctors (KMDs) and the treatment patterns of Korean medicine for ankle sprain which is one of the common sports injuries. Methods : An online survey was conducted on KMDs interested in sports injuries to assess their experience and perception of sports injuries including diagnosis, intervention, and treatment plan for ankle sprain. Results : A total of 276 KMDs participated in the survey. They answered that 12% (median, range 0~80%) of patients visiting a Korean medical institution had sports injuries. Sports injuries frequently occur in the ankle, back, shoulder, knee, and elbow and the most common sports injury was sprain/strain. Many participants were aware that sports injuries should be treated differently from other musculoskeletal diseases in general. They reported that confirmation of fracture, swelling, and tenderness was essential to diagnose ankle sprains. Acupuncture was the most commonly used treatment and reported to need 2 to 6 weeks of treatment period, depending on the severity. Conclusions : Based on the findings regarding treatment of sports injury patients by KMDs, this study would be utilized as basic information for pragmatic clinical research design related to sports medicine in the future.

• Maxillofacial Plastic and Reconstructive Surgery
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• v.42
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• pp.22.1-22.6
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• 2020

Introduction: Facial fractures (FFs) occur after high- and low-energy trauma; differences in associated injuries and outcomes have not been well articulated. Objective: To compare the epidemiology, management, and outcomes of patients suffering FFs from high-energy and low-energy mechanisms. Methods: We conducted a 6-year retrospective local trauma registry analysis of adults aged 18-55 years old that suffered a FF treated at the Santa Barbara Cottage Hospital. Fracture patterns, concomitant injuries, procedures, and outcomes were compared between patients that suffered a high-energy mechanism (HEM: motor vehicle crash, bicycle crash, auto versus pedestrian, falls from height > 20 feet) and those that suffered a low-energy mechanism (LEM: assault, ground-level falls) of injury. Results: FFs occurred in 123 patients, 25 from an HEM and 98 from an LEM. Rates of Le Fort (HEM 12% vs. LEM 3%, P = 0.10), mandible (HEM 20% vs. LEM 38%, P = 0.11), midface (HEM 84% vs. LEM 67%, P = 0.14), and upper face (HEM 24% vs. LEM 13%, P = 0.217) fractures did not significantly differ between the HEM and LEM groups, nor did facial operative rates (HEM 28% vs. LEM 40%, P = 0.36). FFs after an HEM event were associated with increased Injury Severity Scores (HEM 16.8 vs. LEM 7.5, P <0.001), ICU admittance (HEM 60% vs. LEM 13.3%, P <0.001), intracranial hemorrhage (ICH) (HEM 52% vs. LEM 15%, P <0.001), cervical spine fractures (HEM 12% vs. LEM 0%, P = 0.008), truncal/lower extremity injuries (HEM 60% vs. LEM 6%, P <0.001), neurosurgical procedures for the management of ICH (HEM 54% vs. LEM 36%, P = 0.003), and decreased Glasgow Coma Score on arrival (HEM 11.7 vs. LEM 14.2, P <0.001). Conclusion: FFs after HEM events were associated with severe and multifocal injuries. FFs after LEM events were associated with ICH, concussions, and cervical spine fractures. Mechanism-based screening strategies will allow for the appropriate detection and management of injuries that occur concomitant to FFs. Type of study: Retrospective cohort study. Level of evidence: Level III.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.3A
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• pp.309-316
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• 2010

This paper proposed a nonlocal anisotropic damage model to simulate the behavior of plain and reinforced concrete structures that are predominantly tensile and compressive load. This model based on continuum damage mechanics, used a symmetric second-order tensor as the damage variable. For quasi-brittle materials, such as concrete, the damage patterns were different in tension and in compression. These two damage states were modeled by damage evolution laws ensuring a damage tensor rate proportional to the total strain tensor in terms of principal components. To investigate the effectiveness of proposed model, the double edge notched specimen experimented by nooru-mohamed and reinforced concrete bending beam were analyzed using the implementation of the proposed model. As the results for the simulation, the nonlocal anisotropic damage model with an adequate control of rupture correctly represented the crack propagation for mixed mode fracture. In the structural failure of reinforced concrete bending beam, the proposed model can be showed up to a very high damage level and yielding of the reinforcements.