• Steel and Composite Structures
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• 제51권1호
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• pp.73-91
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• 2024

This paper has focused on presenting vibration analysis of trapezoidal sandwich plates with a damaged core and FG wavy CNT-reinforced face sheets. A damage model is introduced to provide an analytical description of an irreversible rheological process that causes the decay of the mechanical properties, in terms of engineering constants. An isotropic damage is considered for the core of the sandwich structure. The classical theory concerning the mechanical efficiency of a matrix embedding finite length fibers has been modified by introducing the tube-to-tube random contact, which explicitly accounts for the progressive reduction of the tubes' effective aspect ratio as the filler content increases. The First-order shear deformation theory of plate is utilized to establish governing partial differential equations and boundary conditions for the trapezoidal plate. The governing equations together with related boundary conditions are discretized using a mapping-generalized differential quadrature (GDQ) method in spatial domain. Then natural frequencies of the trapezoidal sandwich plates are obtained using GDQ method. Validity of the current study is evaluated by comparing its numerical results with those available in the literature. After demonstrating the convergence and accuracy of the method, different parametric studies for laminated trapezoidal structure including carbon nanotubes waviness (0≤w≤1), CNT aspect ratio (0≤AR≤4000), face sheet to core thickness ratio (0.1 ≤ ${\frac{h_f}{h_c}}$ ≤ 0.5), trapezoidal side angles (30° ≤ α, β ≤ 90°) and damaged parameter (0 ≤ D < 1) are carried out. It is explicated that the damaged core and weight fraction, carbon nanotubes (CNTs) waviness and CNT aspect ratio can significantly affect the vibrational behavior of the sandwich structure. Results show that by increasing the values of waviness index (w), normalized natural frequency of the structure decreases, and the straight CNT (w=0) gives the highest frequency. For an overall comprehension on vibration of laminated trapezoidal plates, some selected vibration mode shapes were graphically represented in this study.

• Structural Engineering and Mechanics
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• 제55권1호
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• pp.79-92
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• 2015

In this study, free vibration analyses of symmetric laminated cantilever and simply supported damaged composite beams are investigated by using finite element method (FEM). Free vibration responses of damaged beams are examined using Euler Bernoulli beam and classical lamination theories. A computer code is developed by using MATLAB software to determine the natural frequencies of a damaged beam. The local damage zone is assumed to be on the surface lamina of the beam by broken fibers after impact. The damaged zone is modeled as a unidirectional discontinuous lamina with $0^{\circ}$ orientations in this study. Fiber volume fraction ($v_f$), fiber aspect ratio ($L_f/d_f$), damage length ($L_D$) and its location (${\lambda}/L$), fiber orientation and stacking sequence parameters effects on natural frequencies are investigated. These parameters are affected the natural frequency values significantly.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2003년도 춘계 학술발표회논문집
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• pp.385-392
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• 2003

Experimental investigation was conducted into the flexure/shear-critical behavior of earthquake-damaged reinforced concrete columns with lap splicing of longitudinal reinforcement in the plastic hinge region. Six test specimens in the aspect ratio of 2.5 were made with test parameters: confinement ratios, lap splices, and retrofitting FRP materials. They were damaged under series of artificial earthquakes that could be compatible in Korean peninsula. Directly after the pseudo-dynamic test, damaged columns were retested under inelastic reversal cyclic loading simultaneously under a constant axial load, P = 0.1 $f_{ck}$ $A_{g}$. Residual seismic performance of damaged columns was evaluated and compared to that of the corresponding original columns. Test results show that RC bridge piers with lap-spliced longitudinal steels in the plastic hinge region appeared to fail at low ductility. This was due to the debonding of the lap splice, which resulted from insufficient development of the longitudinal steels. The specimens externally wrapped with composite FRP straps in the potential plastic hinge region indicated significant improvement both in flexural strength and displacement ductility.y.

• 한국환경복원기술학회지
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• 제20권1호
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• pp.143-150
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• 2017

In this study, we intend to integrate the database(DB) method into one logical structure that is related to damage such as cause and type of damages occurring in the DMZ area. We divided the DMZ members into two types, which are classified into qualitative and quantitative aspects based on the current status survey for three years as a study of database construction, So that the actual data can be utilized in future restoration. The database construction through each restoration direction regarding the type of DMZ corruption is as follows. First, we recognized the necessity of restoration of the damaged area of the DMZ, and approached it as a plan to select the damaged mark. Second, DMZ database reconstruction can be used as a restoration of damages, suggesting more information and restoration type through building an ecological database for education and research. Third, in order to maintain and restore restoration of damaged areas continuously at the national level, it is necessary to institutionalize guidelines for reasonable internal restoration in the national level as data that can be credited externally and can be acknowledged as the latest data.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 봄 학술발표회 논문집
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• pp.505-511
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• 2003

Experimental investigation was conducted into the flexure/shear-critical behavior of earthquake-damaged reinforced concrete columns with lap splicing of longitudinal reinforcement in the plastic hinge region. Six test specimens in the aspect ratio of 2,5 were made with test parameters: confinement ratios, lap splices, and retrofitting FRP materials. They were damaged under series of artificial earthquakes of which magnitude could be compatible in Korean peninsula. Directly after the pseudo-dynamic test, damaged columns were retested under inelastic reversal cyclic loading simultaneously under a constant axial load, P=$0.1f_{ck}A_g. Residual seismic performance of damaged columns was evaluated and compared to that of the corresponding original columns. Test results show that RC bridge piers with lap-spliced longitudinal steels in the plastic hinge region appeared to fail at low ductility. This was due to the debonding of the lap splice, which resulted from insufficient development of the longitudinal steels. The specimens externally wrapped with composite FRP straps in the potential plastic hinge region indicated significant improvement both in flexural strength and displacement ductility, and strain energy ductility.

• 대한공간정보학회지
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• 제6권2호
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• pp.105-117
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• 1998

본 연구에서는 Landsat-5 TM 데이터를 사용하여, 강원도 양양군, 인제군, 홍천군 일부지역을 대상으로 솔잎혹파리 피해지역과 경년변화를 효율적으로 추출할 수 있는 기법을 연구 제시하였다. 또한 피해상황을 파악하여 피해지역의 지형적 상관관계를 규명하고, 피해확산방향을 예측하여, 인공위성 화상데이터가 산림의 병충해 감시에 유용함을 입증함과 아울러, 효과적인 방제를 위한 기초자료를 제공하는데 그 목적이 있다. 연구결과 수치표고화상을 이용한 BRCT(Backwards Radiance Correction Transformation)기법을 통하여 지형영향으로 인한 그림자지역을 효과적으로 제거시켜, 피해지역 추출시 그 유효성을 높일 수 있었다. 분류된 피해지역은 분석결과 경사 $31^{\circ}{\sim}38^{\circ}$, 온도 $21^{\circ}C{\sim}25^{\circ}C$, 남서 남동 사면 및 산지 최고 표고의 $23%{\sim}39%$에서 피해가 주로 발생하며, 피해가 확산되는 신규지역은 경사향 $46^{\circ}{\sim}180^{\circ}$, 경사도 $27^{\circ}{\sim}30^{\circ}$, 온도 $11^{\circ}C{\sim}12^{\circ}C$ 및 산지최고표고의 $27%{\sim}39%$ 지역에서 피해가 주로 확산됨을 알 수 있었으며, 신규피해지역의 환경인자와 식생지수를 이용하여 피해예측지수(NDI; New Damaged Index)를 개발하였다.

• 패션비즈니스
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• 제12권6호
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• pp.11-22
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• 2008

The goal of this study is to provide beauticians with the fundamental material to use effectively heat permanent wave in beauty industry as well as their customer's satisfaction. It carried out an experiment with damaged hair of a woman in her late twenties to investigate the change of physical and morphological characteristics by its water content when performing heat permanent wave. After spreading 0g, 1g, 2g, 3g, and 4g of water on damaged hair respectively, heat permanent wave was treated and the change of hair was observed. The change of physical characteristic was compared through permanent wave form of hair, tensile strength and elongation. The change of morphological characteristic was observed through Scanning Electron Microscope(SEM) and Transmission Electron Microscope(TEM). The result of experiment on the physical specificity revealed that permanent wave form was the most ideal when the water content was 2g, also 3g. Though the materials with much moisture content formed the results were not satisfied. The material with 0g of water content didn't make the wave. In terms of tensile strength and elongation, tensile strength was generally reduced as per the damaged degree of hair. On the contrary, elongation was increased. It observed the changes of morphological characteristic that the damage on hair cuticle was deepen, as its moisture content was decreased, and cuticle's surface was worn away. The observation of fine structure on hair section by transmission electronic microscope also certainly showed the result that damaged hair having experience with chemical treatment had got much damaged to hair cuticle as well as hair cortex. Generally chemical treatment makes hair damaged. Under consideration of this aspect, the ultimate goal of this thesis is to minimize the damage of hair caused by chemical treatment and get the satisfaction on the hair style. According to the result of experiment, the damaged hair whose moisture content was 3g showed the best permanent wave form.

• 한국지진공학회논문집
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• 제7권3호
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• pp.79-88
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• 2003

1992년 내진규정 도입이전에 설계시공된 공용중의 철근콘크리트 교각은 대체로 소성힌지구간에 겹침이음 시공되었다. 본연구는 형상비 2.5의 철근콘크리트 교각실험체의 내진 연성도 평가를 위한 실험적 연구이다. 실험에 사용된 6기의 실험체는 횡방향 구속력, 주철근의 겹침이음 그리고 섬유보강을 변수로 가지고 있다. 이 실험체는 한국도로공사가 개발한 인공지진동을 사용하여 유사동적실험을 수행하여 지진이력을 주었으며, 유사동적실험 후에는 일정한 축력, P＝0.1 $f_{ck}$ $A_{g}$을 유지하면서 변위제어방식으로 유사정적실험을 실시하여 잔류내진성능을 평가하였다. 실험 결과 소성힌지구간에 겹침이음 된 RC 교각이 낮은 연성에서 파괴에 도달하였다. 이는 주철근 겹침이음이 주철근의 충분한 연성발달을 저하시킨 결과라 할 수 있다. 또한, 섬유보강된 실험체는 ？강성과 변위연성도의 현저한 개선능력을 보였다..

• 농촌계획
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• 제20권3호
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• pp.67-74
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• 2014

The purpose of this study is to estimate regional economic effects of spatial diffusion of wildfire using Cobb-Douglas production function of agriculture and forestry. The analysis is applied to Gangwon and Gyeongbuk provinces where are the most damaged of wildfire in Korea. The damaged areas are derived from multiplied by the occurrence probability of wildfire and diffusion areas of wildfire for micro-spatial unit level with ArcGIS techniques. The models of wildfire provides that the spatial diffusion of wildfire increases with the rising of highest temperature and average wind speed. Through the production function, value added of Agriculture and Forest sectors get damaged where the Cos-converted slope aspect of mountains are toward the South. The production model provides reductions of regional value added by increasing damaged areas of wildfire. It reveals that the most damaged region is Andong city in Gyeongbuk province, where value added loss is 1.25 billion Won, which is about 0.72% of total value added in agriculture and forestry of the city. As a view of policy makers, it needs to be considered to establish prevention policies against wildfires because regional economic losses from wildfire are depending on geographical conditions and performances of the major industry related to wildfire's diffusion such as agriculture or tourism sector according to the result of analysis.

• 한국측량학회지
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• 제15권2호
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• pp.287-298
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• 1997

본 연구에서는 Landsat-5 TM 데이터를 사용하여, 경상남도 남해군 일대를 대상으로 솔껍질깍지벌레 피해지역과 경년변화를 효율적으로 추출할 수 있는 기법을 연구 제시하였다. 또한 피해상황을 파악하여 피해지역의 지형적 상관관계를 규명하고, 피해확산방향을 예측하여, 인공위성 화상데이터가 산림의 병충해 감시에 유용함을 입증함과 아울러, 효과적인 방제를 위한 기초자료를 제공하는데 그 목적이 있다. 연구결과 수치표고화상을 이용한 BRCT (Backwards Radiance Correction Transformation) 기법을 통하여 지형영향으로 인한 그림자지역을 효과적으로 제거함으로서, 피해지역 추출시 그 유효성을 높일 수 있었다 피해지역과 경년변화 화상을 작성, 분석하여 피해 초기에는 남서사면, 경사도 $7-18^\circ$,산지 최고 표고의 50~70%의 위치에서 집중적으로 발생하여 주로 바람방향(북동방향) 피해가 확대됨을 알 수 있었다.