• Wind and Structures
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• 제10권3호
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• pp.233-247
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• 2007

The insertion of steel braces has become a common technique to limit the deformability of steel framed buildings subjected to wind loads. However, when this technique is inadequate to keep floor accelerations within acceptable levels of human comfort, dampers placed in series with the steel braces can be adopted. To check the effectiveness of braces equipped with viscoelastic (VEDs) or friction dampers (FRDs), a numerical investigation is carried out focusing attention on a three-bay fifteen-storey steel framed building with K-braces. More precisely, three alternative structural solutions are examined for the purpose of controlling wind-induced vibrations: the insertion of additional diagonal braces; the insertion of additional diagonal braces equipped with dampers; the insertion of both additional diagonal braces and dampers supported by the existing K-braces. Additional braces and dampers are designed according to a simplified procedure based on a proportional stiffness criterion. A dynamic analysis is carried out in the time domain using a step-by-step initial-stress-like iterative procedure. Along-wind loads are considered at each storey assuming the time histories of the wind velocity, for a return period $T_r=5$ years, according to an equivalent wind spectrum technique. The behaviour of the structural members, except dampers, is assumed linear elastic. A VED and an FRD are idealized by a six-element generalized model and a bilinear (rigid-plastic) model, respectively. The results show that the structure with damped additional braces can be considered, among those examined, the most effective to control vibrations due to wind, particularly the floor accelerations. Moreover, once the stiffness of the additional braces is selected, the VEDs are slightly more efficient than the FRDs, because they, unlike the FRDs, dissipate energy also for small amplitude vibrations.

• Earthquakes and Structures
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• 제12권1호
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• pp.135-144
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• 2017

Near-fault ground motions are characterized by high values of the ratio between the peak of vertical and horizontal ground accelerations, which can significantly affect the nonlinear response of a base-isolated structure. To check the effectiveness of different base-isolation systems for retrofitting a r.c. framed structure located in a near-fault area, a numerical investigation is carried out analyzing the nonlinear dynamic response of the fixed-base and isolated structures. For this purpose, a six-storey r.c. framed building is supposed to be retrofitted by insertion of an isolation system at the base for attaining performance levels imposed by current Italian code in a high-risk seismic zone. In particular, elastomeric (e.g., high-damping-laminated-rubber bearings, HDLRBs) and friction (e.g., steel-PTFE sliding bearings, SBs, or friction pendulum bearings, FPBs) isolators are considered, with reference to three cases of base isolation: HDLRBs acting alone (i.e., EBI structures); in-parallel combination of HDLRBs and SBs (i.e., EFBI structures); FPBs acting alone (i.e., FPBI structures). Different values of the stiffness ratio, defined as the ratio between the vertical and horizontal stiffnesses of the HDLRBs, sliding ratio, defined as the global sliding force divided by the maximum sliding force of the SBs, and in-plan distribution of friction coefficient for the FPs are investigated. The EBI, EFBI and FPBI base-isolation systems are designed assuming the same values of the fundamental vibration period and equivalent viscous damping ratio. The nonlinear dynamic analysis is carried out with reference to near-fault earthquakes, selected and scaled on the design hypotheses adopted for the test structures.

• Structural Engineering and Mechanics
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• 제9권6호
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• pp.615-636
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• 2000

Some elevated water tanks have failed due to torsional vibrations in past earthquakes. The overall axisymmetric structural geometry and mass distribution of such structures may leave only a small accidental eccentricity between centre of stiffness and centre of mass. Such a small accidental eccentricity is not expected to cause a torsional failure. This paper studies the possibility of amplified torsional behaviour of elevated water tanks due to such small accidental eccentricity in the elastic as well as inelastic range; using two simple idealized systems with two coupled lateral-torsional degrees of freedom. The systems are capable of retaining the characteristics of two extreme categories of water tanks namely, a) tanks on staging with less number of columns and panels and b) tanks on staging with large number of columns and panels. The study shows that the presence of a small eccentricity may lead to large displacement of the staging edge in the elastic range, if the torsional-to-lateral time period ratio $({\tau})$ of the elevated tanks lies within a critical range of 0.7< ${\tau}$ <1.25. Inelastic behaviour study reveals that such excessive displacement in some of the reinforced concrete staging elements may cause unsymmetric yielding. This may lead to progressive strength deterioration through successive yielding in same elements under cyclic loading during earthquakes. Such localized strength drop progressively develop large strength eccentricity resulting in large localized inelastic displacement and ductility demand, leading to failure. So, elevated water tanks should have ${\tau}$ outside the said critical range to avoid amplified torsional response. The tanks supported on staging with less number of columns and panels are found to have greater torsional vulnerability. Tanks located near faults seem to have torsional vulnerability for large ${\tau}$.

• 소음진동
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• 제6권2호
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• pp.163-177
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• 1996

An investigation on thermohydraulic stability of flow oscillations in the CANada Deuterium Uranium-600(CANDU-6) heat transport system has been conducted. Flow oscillations in reactor coolant loops, comprising two heat sources and two heat sinks in series, are possibly caused by the response of the pressure to extraction of fluid in two-phase region. This response consists of two contributions, one arising from mass and another from enthalpy change in the two-phase region. The system computer code used in the investigation os SOPHT, which is capable of simulating steady states as well as transients with varying boundary conditions. The model was derived by linearizing and solving one-dimensional, homogeneous single- and two-phase flow conservation equations. The mass, energy and momentum equations with boundary conditions are set up throughout the system in matrix form based on a node-link structure. Loop stability was studied under full power conditions with interconnecting the two compressible two phase regions in the figure-of-eight circuit. The dominant function of the interconnecting pipe is the transfer of mass between the two-phase regions. Parametric survey of loop stability characteristics, i. e., damping ratio and period, has been made as a function of geometrical parameters of the interconnection line such as diameter, length, height and orifice flow coefficient. The stability characteristics with interconnection line has been clarified to provide a simple criterion to be used as a guide in scaling of the pipe.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2007년도 추계학술대회 논문집
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• pp.1267-1272
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• 2007

철도교량의 경우 교면방수 시공 후 방진매트, 궤도자갈 및 침목부설, 레일 설치 등의 후속공정이 뒤따르고, 시공 및 경제적인 여건으로 인해 위의 공정이 연속적으로 시행되지 못하고 일정 구간 단위로 후속공정이 이루어지는 특수성을 갖고 있다. 이로 인해 교면방수 시공 이후 표면의 노출이 장기화 되는 것이 불가피한 실정으로, 시간 경과에 따른 열화현상으로 인해 발수재의 분해 및 용출이 발생하여 방수시공 초기의 침투깊이를 유지하지 못하고 있는 경우가 많다. 이처럼, 철도교량이 갖고 있는 시공적인 특수성과 궤도자갈이 부설되지 않고 영구적으로 표면이 노출되는 부분을 고려한다면 표면의 장기적인 노출에도 방수성능이 저하되지 않는 내구성을 갖고 있는 방수공법을 선택하는 것이 무엇보다 중요하다고 할 수 있다. 본 연구의 목적은 장기간 표면노출에 따른 열화현상을 방지하는 열화억제형 방수공법(DRA방수공법)에 대하여 시험시공을 통한 객관적인 분석 결과를 도출하고, DRA 방수 공법의 KNOW-HOW를 습득하는 것으로, 이를 통하여 철도교량의 교면방수 열화현상으로 인해 발생하는 하자를 방지하여 잦은 보수와 보강으로 인한 경제적 손실을 최소화하고 현장에서의 시공관계자들이 방수공법을 선정하는데 따른 합리적인 판단 기준을 제공하는데 있다.

• 한국전산구조공학회논문집
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• 제27권4호
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• pp.223-230
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• 2014

본 논문에서는 FSI해석을 이용하여 비정형 초고층 빌딩의 풍응답 특성을 연구하였다. 해석모델은 Twist모델이며, 뒤틀림 각도와 풍가속도의 상관관계에 대해 연구 중점을 두었다. 먼저 단방향 해석을 수행하여 100년 재현주기 풍속에 대한 최대 횡 변위를 구하고, 제한조건을 만족하는 탄성계수를 산출한다. 그리고 양방향 해석을 수행, 시간이력해석을 통해 산출된 탄성계수와 임의의 밀도를 가지는 풍가속도를 예측하게 된다. 정방형 모델은 높이 400m, 변장비 1:1, 세장비 8로 설정, 뒤틀림 모델은 0도에서 90도까지 15도 간격으로, 90도에서 360도까지 90도 간격으로 비틀어 회전시켰다. 형상에 따른 풍가속도 예측 결과, 정방형 모델이 뒤틀림 모델보다 크게 산출되어 풍진동 영향에 더 민감한 것을 검증하였다.

• 한국치위생학회지
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• 제4권2호
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• pp.225-236
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• 2004

It has been suggested in research results thai dental hygienists have high risk of carpal tunnel syndrome, mainly caused by the repeated motion of extensor and flexor or the use of vibration tools, compared to other occupations. To find out the situation of the carpal tunnel syndrome of dental hygienists, who are exposed to work-related musculoskeletal disorders, this study used 132 questionnaires given on May 22, 2004, the period of continuing education of the first half year in the Gwangju Jeonnam area, and obtained the following results. 1. Subjects worked at a dental ciinic(32.6%), a hospital(31.8%), and a public health center(35.6%). Age by work was under 24 in a clinic(17.4%) and a hospital(15.9%), and over 30 in a public health center(35.6%). 2. In practice conducted over one time a day, a scaling accounted for 90.7% in a doctor's office; 595% in a hospital; and 3.0% in a public health center, suggesting significant difference(p<0.01). Pit and fissure sealant accounted for 53.5% in a clinic; 53.2% in a hospital; and 95% in a public health center, also suggesting significant difference(p0.01). 3. Symptoms of carpal tunnel syndrome appeared in a wrist(12.1%), a right hand(14.4%), and a left hand(5.3%). 4. In case of temporary crown practice, symptoms appeared in a wrist(22.0%), a right hand(14.0%), and a left hand(4.0%), suggesting significant difference(p<0.01). The above results showed that 12.1% of dental hygienists was exposed to carpal tunnel syndrome. Thus, it is considered very important that dental hygienists should be given education of the danger of continuous work in certain motions and prevention education of improving repeated position, and make efforts to reinforce self-control ability.

• 화약ㆍ발파
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• 제36권4호
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• pp.48-61
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• 2018

본 사례연구는 성남시 분당구에 위치한 한국가스공사(KOGAS) 분당사옥 건물의 발파해체 프로젝트에 관한 것이다. 대상건물은 긴 경간을 갖는 보 구조물이라는 특징 때문에 프로젝트 초기에는 잭 서포트를 이용한 기계식 해체공법이 고려되었다. 하지만 과도한 보강비용과 안전상의 불확실성, 그리고 공사기간의 장기화 우려 때문에 발파해체공법을 대안공법으로 적용하였다. 폭약의 기폭순서는 붕괴과정 중에 주변의 건물 및 시설물 방호를 목적으로 정교하게 설계하였으며, 대상건물은 왼쪽 전방을 향해 붕괴되도록 유도하였다. 1층, 2층 및 5층에 위치한 발파기둥들에 설치된 폭약을 순차적으로 기폭시키는 데에는 총 550개 이상의 전자뇌관(Unitronic 600)이 사용되었다. 분진발생을 저감하기 위해 각각의 발파대상 기둥과 바닥에는 작은 물주머니와 큰 물주머니를 각각 설치하였다. 이와 같이 본 프로젝트에서는 대상건물의 발파해체 시에 발생될 것으로 예상되는 소음, 분진 및 충격진동을 경감시키기 위해 총체적인 노력을 경주하였다.

• 한국정보통신학회:학술대회논문집
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• 한국정보통신학회 2015년도 춘계학술대회
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• pp.735-737
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• 2015

본 논문은 SaaS(Software as a Service) 기반의 건설공정전송 및 안전관리 시스템을 건설작업에 활용하여 공정관리와 안전관리에 적용함으로써 초고속 무선인터넷을 통해 이루어지는 다양한 유형의 건설 공정에 대한 일정 및 결과와 안전관리에 대한 체계적인 수단을 확보할 수 있고 공정 내에서 이루어지는 모든 관리 체계를 신속하고 정확하게 관리할 수 있다.작업자는 스마트폰을 활용하여 감독관으로 작업을 지시받고 작업의 현황과 결과를 보고한다. 또한 비상상황 시 감독관에게 보고를 즉시 할수 있으며 일정시간 이상 스마트 폰 진동 발생이 없는 경우 작업자에게 위험 상황을 체크하게 된다. 감독관의 경우 수립된 공정별 업무를 지시하고 결과를 확인하며 현장 작업자 위험 상황의 조치명령을 내리고 미흡한 부분을 제시함으로써 만족되는 결과를 얻게 된다. 또한 소프트웨어(서버)의 경우 작업에 관련된 모든 자료를 저장하고 회원관리 및 보안을 담당하였다.

• 한국해양공학회지
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• 제23권1호
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• pp.74-80
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• 2009

In this study, the static and modal analyses to find the characteristic of eigenvalues for a towed cable were with a free boundary condition at the bottom end carried out with numerical study. The resulting numerical code with finite element method was used to study sample problems for a cable with towing speeds. After tracing the equilibrium state with a towing speed through the static analysis, modal analysis on the basis of static results was performed. The static top tension for a critical towing speed is nearly 50 percent of what it was for a free hanging pipe. From static analyses, it is found that towing speed has a noticeable effect on top tension of a towed pipe. At a high towing speed, differences between the first and second periods become larger. Compared to the fundamental period for a free hanging pipe, that for a towed pipe with a critical towing speed is approximately 1.4 times larger. This result is very important point in that the lock in condition and tension of the towed cable system with top excitation can be predicted. The corrected close form solution to solve natural periods for a towed cable was presented in this study. The code is validated by comparison of the results of theoretical and numerical studies. Two results were in very good agreement. This study can contribute to predicting the lock-in condition and tension for a towed cable or pipe with top excitation.