• Steel and Composite Structures
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• 제18권2호
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• pp.357-374
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• 2015

Orthotropic decks composed of deck plate, ribs, cross beams and wearing surface are frequently used in industry to span long distances due to their light structures and load carrying capacities. As a result they are broadly preferred in industry and there are a lot of bridges of this type exist in the world. Nevertheless, some of them cannot sustain the anticipated service life and damages in form of cracks develop in steel components and wearing surface. Main reason to these damages is seen as the repetitive wheel loads, namely the fatigue loading. Solutions to this problem could be divided into two categories: qualitative and quantitative. Qualitative solutions may be new design methodologies or innovative materials, whereas quantitative solution should be arranging dimensions of deck structure in order to resist wheel loads till the end of service life. Wearing surface on deck plate plays a very important role to avoid or mitigate these damages, since it disperses the load coming on deck structure and increases the bending stiffness of deck plate by forming a composite structure together with it. In this study the effect of Elastic moduli, Poisson ratio and thickness of wearing surface on the stresses emerged in steel deck and wearing surface itself is investigated using a FE-model developed to analyze orthotropic steel bridges.

• 드라이브 ㆍ 컨트롤
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• 제20권4호
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• pp.17-26
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• 2023

A forklift is an industrial vehicle that lifts or transports heavy objects using a hydraulically operated fork, and is equipped with an automatic transmission for the convenience of repetitive transportation, loading, and unloading work. The Transmission Control Unit (TCU) is a key component in charge of the shift control function of an automatic transmission. It consists of an electric circuit with an input/output signal interface function and firmware running on a microcontroller. To develop TCU firmware, the development process of shifting algorithm design, firmware programming, verification test, and performance improvement must be repeated. A simulator is a device that simulates a mechanical system having dynamic characteristics in real time and simulates various sensor signals installed in the system. The embedded transmission simulator is a simulator that is embedded in the TCU firmware. information related to the mechanical system that is necessary for TCU normal operation. In this study, an embedded transmission simulator applied to the originally developed forklift TCU firmware was designed and used to verify various forklift shift control algorithms.

• 한국도로학회논문집
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• 제13권4호
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• pp.103-115
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• 2011

온도와 수분의 불균일한 분포로 인하여 콘크리트 슬래브는 컬링과 와핑 거동을 하고 슬래브에는 항상 응력이 도입되어 있다. 따라서 교통하중 외에도 환경하중을 고려해야만 콘크리트 슬래브에 발생하는 응력을 보다 정확하게 예측할 수 있다. 콘크리트 포장에 반복적으로 재하되는 교통하중과 환경하중에 의해 콘크리트 슬래브의 강도는 지속적으로 감소하고 응력 이하로 낮아지게 되면 피로균열이 발생한다. 본 연구에서는 기존에 수행된 연구들로부터 피로실험 결과를 수집하고 피로 회귀모형을 개발하였다. 개발된 모형을 검증하기 위하여 모형개발에 사용되지 않은 실내 휨피로실험 결과를 예측하고 기존 모형으로 예측된 결과와 비교하였다. 콘크리트 포장 누적 피로손상 해석 프로그램을 개발한 후 본 연구에서 제안된 모형과 기존 모형들을 적용하고 예측 결과를 비교 및 평가하였다. 피로모형 별로 슬래브 두께, 줄눈간격, 복합 지지력계수, 그리고 하중전달률에 따른 누적 피로손상의 민감도 분석을 실시하였다. 그 결과 본 연구에서 개발된 모형이 최소-최대응력비 R을 고려하는 기존 모형들의 경향을 개선하여 환경하중을 더욱 합리적으로 반영할 수 있는 것으로 나타났다.

• 구강회복응용과학지
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• 제18권2호
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• pp.81-91
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• 2002

Dental implant systems have shown many post-surgical problems and One of the most frequent problem is screw loosening. To reduce screw loosening, a number of methods have been tried and recently fundamental modification of fixture-abutment connection structure was developed and used the most frequently. Former implant system structure, such as Br${\aa}$nemark, had external hex with the height of 0.7 mm and later, fixture with external hex of 1.0 mm height and internal hex structure were developed. In addition, the method of morse taper application was introduced to reduce screw loosening. In this study, the level of screw loosening of each implant systems was compared based on the vibration loosening measurement of abutment screw of each implant systems. Analysis of measured value was performed using 3 kinds of methods, (i) Percentage of average of initial 3 times loosening-torque value(initial loosening value) to tightening-torque of 30 Ncm, (ii) Percentage of loosening-torque value after 200 N strength loaded(experimental value) to initial loosening value and (iii) Percentage of experimental value to 30 Ncm of tightening-torque. Each result of analyses shows the value of initial loosening, loosening by repetitive load and final loosening level. The results of this study were as follows. (1) Percentage of initial loosening value to tightening-torque was increased in order of 0.7 mm external hex, 1.0 mm external hex, internal hex and internal taper and all values between each groups showed statistical significance (p<0.05). (2) Percentage of experimental value to initial loosening value was increased in order of internal hex, 0.7 mm external hex, 1.0 mm external hex and internal taper. Value of internal taper showed significant difference with that of 0.7 mm external hex and internal hex (p<0.05). (3) Percentage of experimental value to tightening torque was increased in order of 0.7 mm external hex, 1.0 mm external hex, internal hex and internal taper. Values of all groups showed statistical significance (p<0.05) except between the groups of 1.0 mm external hex and internal hex. Based on those results, there was no significant difference of loosening-torque by repetitive loading except internal taper. It is supposed that implant system with high resistant capability against initial loosening could be recommended for clinical use. In addition, in case of single implant restoration, 1.0 mm external hex or internal hex could be recommended rather than 0.7 mm external hex, and the use of internal taper would be the most useful way to reduce screw loosening.

• 대한정형외과스포츠의학회지
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• 제2권1호
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• pp.28-36
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• 2003

목적: 전방십자인대재건술의성공에영향을미치는요인가운데수술후초기단계에는이식건에대한고정력이가장중요한인자로알려져있으며, 지금까지여러가지의고정방법들이사용되고있다. 저자는전방십자인대재건술후대퇴골측의초기안정성을알아보기위하여현재주로쓰이고있는6가지의고정방법들에대하여주기성인장부하검사를시행하기전,후의최대인장력을측정하여그결과를비교하고, 실패양상을관찰하고자하였다. 대상및방법: 돼지(Yorkshire) 슬관절72개를이용하여6가지고정방법(슬괵건-LA나사(R), 슬괵건-생체흡수성간섭나사, 슬괵건-Semifix 나사(R), 슬괵건-Endobutton(R)고정, 슬개건-티타늄간섭나사, 슬개건-생체흡수성간섭나사)으로이식건을고정하고 Instron(R) 인장검사기를이용하여주기성인장부하검사및최대실패인장력검사를시행하였다. 주기성인장부하검사는50 mm/min의속도로 30N에서 150N사이를1000회주기적으로반복하도록하였으며, 동일시편으로최대인장력검사를 시행하여주기성부하 후 최대 인장력의 변화를 비교, 분석하였다. 각 실험군에 따른 인장력 차이의통계적 유의성은ANOVA와Duncan 다중비교분석법을이용하였다. 결과: 주기성인장부하전,후이식건의최대인장력은슬괵건-LA나사(R) 군이평균1003.4$\pm$145N에서601.1$\pm$154N으로, 슬괵건-생체흡수성간섭나사군이평균 595.5$\pm$104N에서평균360.7$\pm$56N으로, 슬괵건-Semifix(R) 군이평균1431.7$\pm$135N에서평균710.7$\pm$114N으로, 슬괵건-Endobutton(R) 고정군이평균603.6$\pm$54N에서평균459.1$\pm$46N으로, 슬개건-티타늄 간섭나사군이평균 1067.4$\pm$145N에서평균 601.8$\pm$134N으로, 슬개건-생체흡수성간섭나사군이평균 987.1$\pm$168N에서588.7$\pm$124N으로각각40$\%$, 39$\%$, 50$\%$, 24$\%$, 44$\%$, 40$\%$가감소하였다. 결론: 수술후초기고정력은슬괵건을LA나사(R) 또는Semifix(R)로고정하는방법과슬개건을티타늄및생체흡수성간섭나사로고정하는방법등이우수하였으며, 슬괵건을생체흡수성간섭나사나Endobutton(R)으로 고정하는 방법 등은고정력이 상대적으로매우약함을 알수있었다. 최대인장력은단순인장검사로는이상의대퇴골측고정방법의고정력이초기부하를견뎌내는데충분하다고생각되었으나주기성부하실험후현저히감소되어충분한초기안정성을제공하지못함을알수있었다.

• 한국산업보건학회지
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• 제18권3호
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• pp.239-247
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• 2008

Low back disorders (LBDs) have been the most common musculoskeletal problem in Korean workplaces. It affects many workers, and is associated with high costs to many companies as well as the individual, which can negatively influence even the quality of life of workers. The _evaluation of low back disorder risk associated with manual materials handling tasks can be performed using variety of ergonomic assessment tools such as National Institute for Occupational Safety and Health (NIOSH) Revised Lifting Equation (NLE), the Washington Administrative Code 296-62-0517 (WAC), the Snook Tables etc. But most of these tools provide limited information for choosing the most appropriate assessment method for a particular job and in finding out advantage and disadvantage of the methods, and few have been assessed for their predictive ability. The focus of this study was to _evaluate spinal loads in real time with lifting and pulling heavy cow leathers in variety of postures. Data for estimating mean trunk motions were collected as employees did their work at the job site, using the Lumbar Motion Monitor. Eight employees (2 males, 6 females) were selected in this study, in which the load weight and the vertical start and destination heights of the activity remained constant throughout the task. Variance components (three dimensional spaces) of mean trunk kinematic measures were estimated in a hierarchical design. They were used to compute velocity and acceleration of multiple employees performing the same task and to repetitive movements within a task. Therefore, a results of this study could be used as a quantitative, objective measure to design the workplace so that the risk of occupationally related low back disorder should be minimized.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 추계 학술발표회 제20권2호
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• pp.45-48
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• 2008

철근콘크리트 구조물은 일반적으로 지진에 연성적으로 거동하도록 설계되며, 연성적인 거동을 위하여 구조부재는 주의 깊게 상세설계 된다. 구조물에 지진하중이 작용하는 경우 수평방향이나 수직방향으로 작용하는 지진하중에 의해 하부층 기둥은 큰 축방향력과 수평력을 받게 된다. 지진발생시 건물에 입력되는 에너지를 부재의 소성변형에 의해 건물전체에 균등하게 분산시키기 위해서는 기둥보다 보에서 소성힌지가 발생되도록 하는 것이 안전하고 경제적이지만, 건물의 2개의 주축방향으로 동시에 작용 시 기둥의 소성힌지 발생은 피할 수 없으며 기둥 단부에는 높은 전단력이 발생되고, 철근콘크리트 기둥은 휨모멘트와 전단력에 의한 갑작스런 취성적 파괴에 이를 수 있다. 이와 같이 수평력에 대한 철근콘크리트 기둥에 구속력을 증진시키기 위하여 전단보강량을 주요 변수로 하여 반복가력 실험을 통하여 일반배근 된 시험체의 구조안전성 및 거동을 비교 분석하였다.

• Structural Engineering and Mechanics
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• 제27권6호
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• pp.713-739
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• 2007

Nowadays computers can perform symbolic computations in addition to mere number crunching operations for which they were originally designed. Symbolic computation opens up exciting possibilities in Structural Mechanics and engineering. Classical areas have been increasingly neglected due to the advent of computers as well as general purpose finite element software. But now, classical analysis has reemerged as an attractive computer option due to the capabilities of symbolic computation. The repetitive cycles of simultaneous - equation sets required by the finite element technique can be eliminated by solving a single set in symbolic form, thus generating a truly closed-form solution. This consequently saves in data preparation, storage and execution time. The power of Symbolic computation is demonstrated by six examples by applying symbolic computation 1) to solve coupled shear wall 2) to generate beam element matrices 3) to find the natural frequency of a shear frame using transfer matrix method 4) to find the stresses of a plate subjected to in-plane loading using Levy's approach 5) to draw the influence surface for deflection of an isotropic plate simply supported on all sides 6) to get dynamic equilibrium equations from Lagrange equation. This paper also presents yet another computationally efficient and accurate numerical method which is based on the concept of derivative of a function expressed as a weighted linear sum of the function values at all the mesh points. Again this method is applied to solve the problems of 1) coupled shear wall 2) lateral buckling of thin-walled beams due to moment gradient 3) buckling of a column and 4) static and buckling analysis of circular plates of uniform or non-uniform thickness. The numerical results obtained are compared with those available in existing literature in order to verify their accuracy.

• Physical Therapy Rehabilitation Science
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• 제5권3호
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• pp.120-124
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• 2016

Objective: Chronic lateral epicondylitis is a condition which becomes sore and tender on the lateral side of the elbow joint damaged from overuse and repetitive use of the extensor muscles of the forearm. The purpose of this study was to investigate the effects of flexion degrees in the elbow joint on extensor carpi radialis longus and brevis and biceps brachii muscles in individuals with healthy young adults. The main purpose of this study was to suggest the feasibility of optimal elbow angle during therapeutic eccentric exercise with resistance for strengthening of wrist extensors. Design: Cross-sectional study. Methods: Thirty health young adults (male 15, female 15) participated in this study. This study measured muscle activation in four different conditions of elbow flexion, $0^{\circ}$, $30^{\circ}$, $60^{\circ}$, and $90^{\circ}$ during eccentric exercise with weight loading in wrist extensors, extensor carpi radialis longus and brevis and biceps brachii muscles using surface electromyography. Results: The muscle activation of extensor carpi radialis showed a negative relationship with the degrees of elbow joint flexion. With increasing elbow flexion angles, the ECRL muscle activation amount was significantly lower (p<0.05). In contrast, the muscle activation of the ECRB muscle activation amount was significanlty higher (p<0.05). Conclusions: This study suggests that the eccentric exercise of wrist extension with selected activation of wrist extensor muscles according to elbow flexion positions, and suggests that the extensor carpi radialis longus and brevis will need to be strengthened for preventing and treating chronic lateral epicondylitis regardless of degrees of elbow joint flexion.

• 비파괴검사학회지
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• 제21권3호
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• pp.261-268
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• 2001

열-음향방출(thermo-AE) 기법을 이용하여 두께 3mm, $[+45_6/-45_6]_s$ 복합재료 적층판의 열응력 유기 손상에 대한 비파괴평가의 유효성을 연구하였다. 반복적인 열부하 사이클에 의해서 thermo-AE 사상수가 감소하는 경향이 뚜렷하게 나타나서 열부하에 따른 카이저효과가 관찰되었다. 열부하사이클중의 thermo-AE거동을 분석하여 복합재료의 응력자유온도를 결정할 수 있었다. 초음파 C스캔, 광학현미경, 주사형 전자현미경을 통해 섬유파단과 모재파손이 관찰되었으며, 이들 파손 인자는 thermo-AE 신호의 단시간 퓨리에 변환처리에 의해 생성된 3종류의 서로 다른 시간-주파수 특성과 대응하였나 이 특성을 이용하여 복합재료의 냉각열처리 및 반복 열부하사이클시의 손상발생과정 및 내부 마찰거동 내역을 추적할 수 있었다.