• Title/Summary/Keyword: 하중의 변화

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Influence of crestal module design on marginal bone stress around dental implant (임플란트 경부 디자인이 변연골 응력에 미치는 영향)

  • Lim, Jung-Yoel;Cho, Jin-Hyun;Jo, Kwang-Heon
    • The Journal of Korean Academy of Prosthodontics
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    • v.48 no.3
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    • pp.224-231
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    • 2010
  • Purpose: This study was to investigate how the crestal module design could affect the level of marginal bone stress around dental implant. Materials and methods: A submerged implant of 4.1 mm in diameter and 10 mm in length was selected as baseline model (Dentis Co., Daegu,Korea).A total of 5 experimental implants of different crestal modules were designed (Type I model : with microthread at the cervical 3 mm, Type II model : the same thread pattern as Type I but with a trans-gingival module, Type III model: the same thread pattern as the control model but with a trans-gingival module, Type IV model: one piece system with concave transgingival part, Type V model: equipped with beveled platform). Stress analysis was conducted with the use of axisy mmetric finite element modeling scheme. A force of 100 N was applied at 30 degrees from the implant axis. Results: Stress analysis has shown no stress concentration around the marginal bone for the control model. As compared to the control model, the stress levels of 0.2 mm areas away from the recorded implant were slightly lower in Type I and Type IV models, but higher in Type II, Type III and Type V models. As compared to 15.09 MPa around for the control model, the stress levels were 14.78 MPa, 18.39 MPa, 21.11 MPa, 14.63 MPa, 17.88 MPa in the cases of Type I, II, III, IV and V models. Conclusion: From these results, the conclusion was drawn that the microthread and the concavity with either crestal or trans-gingival modules maybe used in standard size dental implants to reduce marginal bone stress.

An Investigation of Reliability and Safety Factors in RC Flexural Members Designed by Current WSD Standard Code (현행(現行) 허용응력설계법(許容應力設計法)으로 설계(設計)되는 RC 휨부재(部材)의 신뢰성(信賴性)과 안전율(安全率) 고찰(考察))

  • Shin, Hyun Mook;Cho, Hyo Nam;Chung, Hwan Ho
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.1 no.1
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    • pp.33-42
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    • 1981
  • Current standard code for R.C. design consists of two conventional design parts, so called WSD and USD, which are based on ACI 318-63 and 318-71 code provisions. The safety factors of our WSD and USD design criteria which are taken primarily from ACI 318-63 code are considered to be not appropriate compared to out country's design and construction practices. Furthermore, even the ACI safety factors are not determined from probabilistic study but merely from experiences and practices. This study investigates the safety level of R.C. flexural members designed by the current WSD safety provisions based on Second Moment Reliability theory, and proposes a rational but efficient way of determining the nominal safety factors and the associated flexural allowable stresses of steel bars and concretes in order to provide a consistent level of target reliability. Cornell's Mean First-Order Second Moment Method formulae by a log normal transformation of resistance and load output variables are adopted as the reliability analysis method for this study. The compressive allowable stress formulae are derived by a unique approach in which the balanced steel ratios of the resulting design are chosen to be the corresponding under-reinforced sections designed by strength design method with an optimum reinforcing ratio. The target reliability index for the safety provisions are considered to be ${\beta}=4$ that is well suited for our level of construction and design practices. From a series of numerical applications to investigate the safety and reliability of R.C. flexural members designed by current WSD code, it has been found that the design based on WSD provision results in uneconomical design because of unusual and inconsistent reliability. A rational set of reliability based safety factors and allowable stress of steel bars and concrete for flexural members is proposed by providing the appropriate target reliability ${\beta}=4$.

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Simple Formulae for Buckling and Ultimate Strength Estimation of Plates Subjected to Water Pressure and Uniaxial Compression (수압(水壓)과 압축력(壓縮力)을 받는 평판(平板)의 좌굴(挫屈) 및 최종강도(最終强度) 추정식(推定式))

  • Jeom-K.,Paik;Chang-Y.,Kim
    • Bulletin of the Society of Naval Architects of Korea
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    • v.25 no.4
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    • pp.69-80
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    • 1988
  • This paper proposes simple formulae for buckling and ultimate strength estimation of plates subjected to water pressure and uniaxial compression. For the construction of a formula for elastic buckling strength estimation, parametric study for actual ship plates with varying aspect ratios and the magnitude of water pressure is carried out by means of principle of minimum potential energy. Based on the results by parametric study, a new formula is approximately expressed as a continuous function of loads and aspect ratio. On the other hand, in order to get a formula for ultimate strength estimation, in-plane stress distribution of plates is investigated through large deflection analysis and total in-plane stresses are expressed as an explicit form. By applying Mises's plasticity condition, ultimate strength criterion is then derives. In the case of plates under relatively small water pressure, the results by the proposed formulae are in good agreement compared with those by other methods and experiment. But present formula overestimates the ultimate strength in the range of large water pressure. However, actual ship plates are subjected to relatively small water pressure except for the impact load due to slamming etc.. Therefore, it is considered that present formulae can be applied for the practical use.

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ABRASION AND CHEMICAL DEGRADATION OF LIGHT-CURED COMPOSITE RESIN FOR UPDATED RESIN DEVELOPMENT (차세대 레진개발을 위한 광중합형 복합레진의 마모와 화학적 분해)

  • Yang, Kyu-Ho;Choi, Nam-Ki;Yook, Geun-Young
    • Journal of the korean academy of Pediatric Dentistry
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    • v.31 no.4
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    • pp.685-695
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    • 2004
  • The aim of this study was to evaluate the resistance to degradation and to compare the wear resistance characteristics of four composite resins in an alkaline solution. The resistance to degradation was evaluated on the basis of mass loss(%), degradation depth(${\mu}m$), Si loss(ppm) and wear depth. The brands studied were Heliomolar flow, Filtek supreme, Point4, Tetric flow. The results were as follows: 1. The sequence of the mass loss was in descending order by Heliomolar flow, Filtek supreme, Point4, Tetric flow. There was significant differences among the materials except Heliomolar flow and Filtek supreme. 2. The sequence of the degree of degradation layer depth was in descending order by Filtek supreme, Heliomolar flow, Tetric flow, Point4. There were significant differences among the materials except Heliomolar flow and Tetric flow. 3. The sequence of Si loss was in descending order by Filtek supreme, Heliomolar flow, Point4, Tetric flow. There were significant differences among the materials except Point 4 and Tetric flow. 4. The sequence of maximum wear depth was in descending order by Heliomolar flow, Point4, Fillet supreme, Tetric flow and there was increasing wear depth on soaking in 0.1N NaOH solution. 5. When observed with SEM, destruction of bonding between matrix and filler was observed and when observed with CLSM, the depth of degradation layer of specimen surface was observed. There results indicate that wear and hydrolytic degradation could be considered to be evaluation factors of composite resins.

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Development of Devices for Improving the Reducibility of Patient Positioning on a Breast Board (Breast Board를 이용한 방사선치료에서 환자 위치 재현성 향상 방안에 대한 연구)

  • Huh Soon Nyung;Cho Woong;Park Yang Kyun;Ha Sung Whan
    • Radiation Oncology Journal
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    • v.23 no.2
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    • pp.123-130
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    • 2005
  • Purpose: We wanted to improve the setup reproducibility of breast cancer patients when utilizing a commercially available breast board for radiation therapy. The breast board was modified by using a new head rest and 2 types of board fixation devices. Materials and Methods: A conventional head/neck rest was modified to be positioned in various slots of the breast board, and it was fabricated 1 cm thinner to provide more comfort to a patient when the patient's neck was rotated. This rest improves the uncertainty of the daily setup. Also, the sagging problems at the left and right sides became negligible with the two types of board fixation devices: (1) the stair type, and (2) the arm type. The first device consists of an upper/lower holder with 4 stair-types of grooves and 4 rectangular Inserts. In order to cover the whole range of vertical setup of the breast board, 4 rectangular inserts were needed, and each covered 10 steps. The arm-type fixation device was also fabricated and attached to the breast board, It had two aluminum bars that were fixed by utilizing a lock-type of screw. These devises were evaluated with two volunteers in order to prove the effectiveness of the improved setup accuracy. Results; The developed cranio-caudal fixation device demonstrated that it could reduce the cranio-caudal error by nearly $55\%$ compared to the old device. As for left-and-right inclination, the stair-type and arm-type fixation devices can reduce the relative inclination by nearly $80\%$ and $90\%$, respectively, compared to the breast board without the fixation device. Conclusion: It was verified that the developed devices were effective for positioning the patients and for avoiding inclination of the breast board.

Numerical Simulation of Nonlinear Interaction between Composite Breakwater and Seabed under Irregular Wave Action by olaFlow Model (olaFlow 모델에 의한 불규칙파 작용하 혼성방파제-해저지반의 비선형상호작용에 관한 수치시뮬레이션)

  • Lee, Kwang-Ho;Bae, Ju-Hyun;Jung, Uk Jin;Choi, Goon-Ho;Kim, Do-Sam
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.31 no.3
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    • pp.129-145
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    • 2019
  • For the design of composite breakwater as representative one of the coastal and harbor structures, it has been widely discussed by the researchers about the relation between the behavior of excess-pore-water pressure inside the rubble mound and seabed caused by the wave load and its structural failure. Recently, the researchers have tried to verify its relation through the numerical simulation technique. The above researches through numerical simulation have been mostly applied by the linear and nonlinear analytic methods, but there have been no researches through the numerical simulation by the strongly nonlinear mutiphase flow analytical method considering wave-breaking phenomena by VOF method and turbulence model by LES method yet. In the preceding research of this study, olaFlow model based on the mutiphase flow analytical method was applied to the nonlinear interaction analysis of regular wave-composite breakwater-seabed. Also, the same numerical techniques as preceding research are utilized for the analysis of irregular wave-composite breakwater-seabed in this study. Through this paper, it is investigated about the horizontal wave pressures, the time variations of excess-pore-water pressure and their frequency spectra, mean flow velocities, mean vorticities, mean turbulent kinetic energies and etc. around the caisson, rubble mound of the composite breakwater and seabed according to the changes of significant wave height and period. From these results, it was found that maximum nondimensional excess-pore water pressure, mean turbulent kinetic energy and mean vorticity come to be large equally on the horizontal plane in front of rubble mound, circulation of inflow around still water level and outflow around seabed is formed in front of rubble caisson.

The Structual Restoration on Gyeongju-Style Piled Stone-Type Wooden Chamber Tombs (경주식 적석목곽묘의 구조복원 재고)

  • Gweon, Yong Dae
    • Korean Journal of Heritage: History & Science
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    • v.42 no.3
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    • pp.66-87
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    • 2009
  • The definition of the structure of wooden chamber tomb(piled stone-type) is as follows. It is a tomb with wooden chamber, and stones were piled on top of the wooden chamber, and then a wooden structure was placed on top of the piled stones, and more stones were piled on top of the wooden structure, and sealed with clay. Of course this definition can vary according to periods, the buried, etc. Gyeongju-style piled stone type wooden chamber tombs have some distinguished characteristics compared to general definition of piled stone type wooden chamber tombs. Outside the wooden chamber, either stone embankments or filled-in stones were layed out, and pilet-in stones are positioned right above the wooden chamber, and almost every class used this type, and finally, it is exclusively found in Gyeongju area. First generations of this Gyeongju-style piled stone type wooden chamber tombs appeared in first half of 5th century. These tombs inherited characteristics like ground plan, wooden chamber, double chamber(inner chamber and outer chamber), piled stones, burial of the living with the dead, piled stones, from precedent wooden chamber tombs. However these tombs have explicit new characteristics which are not found in the precedent wooden chamber tombs such as stone embankments, wooden pillars, piled stones(above ground level), soil tumuluses. stone embankments and wooden pillars are exclusively found on great piled stone type above-ground level wooden chamber tombs such as the Hwangnamdaechong(皇南大塚). Stone embankments, wooden pillars, piled stones(above ground level) are all elements of building process of soil tumuluses. stone embankments support outer wall of above-ground level wooden chambers and disperse the weight of tumuluses. Wooden pillars functioned as auxiliary supports with wooden structures to prevent the collapse of stone embankments. Piled stones are consists of stones of regular size, placed on the wooden structure. And after the piled stones were sealed with clay, tumulus was built with soil. Piled stones are unique characteristics which reflects the environment of Gyeongju area. Piled stone type wooden chamber tombs are located on the vast and plain river basin of Hyeongsan river(兄山江). Which makes vast source of sands and pebbles. Therefore, tumulus of these tombs contains large amount of sands and are prone to collapse if soil tumulus was built directly on the wooden structure. Consequently, to maintain external shape of the tumulus and to prevent collapse of inner structure, piled stones and clay-sealing was made. In this way, they can prevent total collapse of the tombs even if the tumulus was washed away. The soil tumulus is a characteristic which emerges when a nation or political entity reaches certain growing stage. It can be said that after birth of a nation, growing stage follows and social structure will change, and a newly emerged ruling class starts building new tombs, instead of precedent wooden chamber tombs. In this process, soil tumulus was built and the size and structure of the tombs differ according to the ruling class. Ground plan, stone embankments, number of the persons buried alive with the dead, quantity and quality of artifacts reflect social status of the ruling class. In conclusion, Gyeongju-style piled stone type wooden chamber tombs emerged with different characteristics from the precedent wooden chamber tombs when Shilla reached growing stage.

Frequency analysis for annual maximum of daily snow accumulations using conditional joint probability distribution (적설 자료의 빈도해석을 위한 확률밀도함수 개선 연구)

  • Park, Heeseong;Chung, Gunhui
    • Journal of Korea Water Resources Association
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    • v.52 no.9
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    • pp.627-635
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    • 2019
  • In Korea, snow damage has been happened in the region with no snowfalls in history. Also, casual damage was caused by heavy snow. Therefore, policy about the Natural Disaster Reduction Comprehensive Plan has been changed to include the mitigation measures of snow damage. However, since heavy snow damage was not frequent, studies on snowfall have not been conducted in different points. The characteristics of snow data commonly are not same to the rainfall data. For example, some parts of the southern coastal areas are snowless during the year, so there is often no values or zero values among the annual maximum daily snow accumulation. The characteristics of this type of data is similar to the censored data. Indeed, Busan observation sites have more than 36% of no data or zero data. Despite of the different characteristics, the frequency analysis for snow data has been implemented according to the procedures for rainfall data. The frequency analysis could be implemented in both way to include the zero data or exclude the zero data. The fitness of both results would not be high enough to represent the real data shape. Therefore, in this study, a methodology for selecting a probability density function was suggested considering the characteristics of snow data in Korea. A method to select probability density function using conditional joint probability distribution was proposed. As a result, fitness from the proposed method was higher than the conventional methods. This shows that the conventional methods (includes 0 or excludes 0) overestimated snow depth. The results of this study can affect the design standards of buildings and also contribute to the establishment of measures to reduce snow damage.

An Archaeological Study on the Foundations of Five Palaces of the Joseon Period (조선시대 5대 궁궐 건물지 기초의 고고학적 연구)

  • Choi, Inhwa
    • Korean Journal of Heritage: History & Science
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    • v.54 no.1
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    • pp.120-137
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    • 2021
  • There were five palaces built during the Joseon Period. Gyeongbokgung Palace was the first one, founded in the 4th year of King Taejo (1395), and depending on the historical interpretation, Changdeokgung Palace, Changgyeonggung Palace, Gyeongungung Palace (Deoksugung), and Gyeongdeokgung Palace (Gyeonghuigung) were also built. The palaces represent the best architecture of the time. In addition, the palaces of the Joseon period have been rebuilt several times, so they contain the architectural history of the Joseon period over the last 500 years. In this paper, all the excavations of five palaces in the Joseon Period were surveyed, and the foundations of the buildings were analyzed. In particular, the aim of this paper is to investigate Jeoksim (foundations of buildings under cornerstone) to understand the characteristics of each palace by period. Accordingly, the changes of the construction techniques of the foundations of the palaces were studied. There are a total of 23 types of Jeoksim. All five palaces have a certain type (I~V) of construction technique, thus it was confirmed that there was a certain pattern in the method of constructing the foundations of palace buildings in the Joseon Dynasty. In addition, Jeoksim was mainly built by certain materials and construction methods (I-1) during the 14th to the 17th century, but new types of Jeoksim were built in the palaces starting from the 18th century, during the reign of King Jeongjo. In the 19th century, when King Gojong sat on the throne, the Jeoksim was built in various shapes, materials, and in 22 types of construction methods. Up to now, research on the remains of palaces were mainly conducted on the Gyeongbokgung Palace, so it was not possible to confirm the foundations of 17th-18th century buildings, where reconstruction had stopped after the Imjin War in 1592. However, through this study, it was possible to classify the transition periodsstheir features periods of palace building foundation construction from the 14th to the 20th century by comparing the remains of five palace building sites.

Lodging Liability and Response to Paclobutrazol Application of High Eating Quality Japonica Rice Varieties (밥맛이 좋은 Japonica 벼 품종들의 도복저항성과 도복경감제 paclobutrazol에 대한 반응)

  • Lee, Eun-Woong;Kwon, Yong-Woong;Soh, Chang-Ho
    • KOREAN JOURNAL OF CROP SCIENCE
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    • v.32 no.2
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    • pp.224-233
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    • 1987
  • Most of the japonica rice varieties preferred for high eating quality are liable to lodging even under moderate rate of nitrogen application. This lodging liability has been a critical limit even for proper evaluation of physio-logical characteristics of those varieties exhibitable under higher nitrogen levels. Use of recent inhibitors of gibberellin biosynthesis such as ‘Pac1obutrazol’ may allow us to overcome this barrier. The responses of four high eating quality varieties to nitrogen application to the level of 150kg N per ha were evaluated with and without use of Paclobutrazol in comparison with a non-lodging, improved short japonica, Dongjin and a non-lodging, high yielding indica x japonica Milyang 23. The four were Damageum (the best eating quality in the 1930s), Nongrim 6 (the best in the 1960s), Chuchung (the best since 1970s), Koshihikari (the best in Japan since 1960s). As expected increased application of nitrogen increased plant height, length of the 3rd internode, and lodg-ing liability, being measured as culm breaking load, in all varieties tested and caused actual lodging in the fiel from the 50kg Nfha level in Damageum and Koshihikari and at the level of l50kg Nfha in Nongrim 6. Applica-tion of Pac1obutrazol (0.6%G) 15 days before heading reduced plant height, length of the 3rd internode and lodging liability being measured as culm breaking load in all varieties tested. However, the application of Pac1obutrazol during active tillering stage resulted in decreased culm breaking load in Damageum, Nongrim 6, and Koshihikari in spite of the decreased plant height and culm length as in the other varieties. Maximum yield was obtained with 100kg Nand 30kg Pac1obutrazol at 15 days before heading in Nongrim 6, 150kg N and 30kg Pac1obutrazol at 15 days before heading in Damageum, and 150kg N and 20kg Paclobutrazol at 20 days after transplanting plus 30kg Paclobutrazol at 15 days before heading in the variety Koshinhikari and Chuchung. Under a sensory evaluation of cooked rice, the four high eating quality varieties were not different in rank and Paclobutrazol treated rice was not distinguished from the untreated in eating quality.

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