• Wind and Structures
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• 제24권5호
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• pp.431-446
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• 2017

As concrete is most usable material in construction industry it's been required to improve its quality. Nowadays, nanotechnology offers the possibility of great advances in construction. In this study, buckling of horizontal concrete columns reinforced with Zinc Oxide (ZnO) nanoparticles is analyzed. Due to the presence of ZnO nanoparticles which have piezoelectric properties, the structure is subjected to electric field for intelligent control. The Column is located in foundation with vertical springs and shear modulus constants. Sinusoidal shear deformation beam theory (SSDBT) is applied to model the structure mathematically. Micro-electro-mechanic model is utilized for obtaining the equivalent properties of system. Using the nonlinear stress-strain relation, energy method and Hamilton's principal, the motion equations are derived. The buckling load of the column is calculated by Difference quadrature method (DQM). The aim of this study is presenting a mathematical model to obtain the buckling load of structure as well as investigating the effect of nanotechnology and electric filed on the buckling behavior of structure. The results indicate that the negative external voltage applied to the structure, increases the stiffness and the buckling load of column. In addition, reinforcing the structure by ZnO nanoparticles, the buckling load of column is increased.

• Steel and Composite Structures
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• 제24권1호
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• pp.113-128
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• 2017

This paper highlights a study undertaken on the free vibration of a precast steel-concrete composite slab panel for track support. The steel-concrete composite slab track is an evolvement from the slab track, a form of ballastless track which is becoming increasingly attractive to asset owners as they seek to reduce lifecycle costs and deal with increasing rail traffic speeds. The slender nature of the slab panel due to its reduced depth of construction makes it susceptible to vibration problems. The aim of the study is driven by the need to address the limited research available to date on the dynamic behaviour of steel-concrete composite slab panels for track support. Free vibration analysis of the track slab has been carried out using ABAQUS. Both eigenfrequencies and eigenmodes have been extracted using the Lanczos method. The fundamental natural frequencies of the slab panel have been identified together with corresponding mode shapes. To investigate the sensitivity of the natural frequencies and mode shapes, parametric studies have been established, considering concrete strength and mass and steel's modulus of elasticity. This study is the world first to observe crossover phenomena that result in the inversion of the natural orders without interaction. It also reveals that replacement of the steel with aluminium or carbon fibre sheeting can only marginally reduce the natural frequencies of the slab panel.

• 한국철도학회논문집
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• 제12권6호
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• pp.835-843
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• 2009

최근 철도의 고속화 및 중량화로 인하여 보다 안정적인 토공노반 구조가 요구된다. 그 대안으로 강화노반이 도입되어 적용하고 있다. 하지만 현 설계기준에 적용되어진 콘크트궤도 강화노반의 강성 및 두께는 국내의 지반의 특성 및 공학적인 평가 없이 외국의 기준을 임의적이고 보수적으로 결정하고 있다 따라서 본 논문에서는 콘크리트궤도 흙쌓기 구간에서의 강화노반 두께를 합리적으로 결정하기 위하여 국내 시공조건을 고려, 적정 탄성계수, 배수성능, 동결심도, 경제성, 지지력 등을 검토하고 이를 바탕으로 유한요소해석을 실시하여 적정 두께를 제시하였다.

• KSTLE International Journal
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• 제1권2호
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• pp.69-75
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• 2000

The paper compares topography, phase contrast and force spectroscopy in atomic force microscopy data for evaluating the microheterogeneity of surface layer. The worn surface of ion-plated TiN coating was measured using both a laboratory-built and a commercial AFM. The results of analysis revealed structural and micromechanical heterogeneity of the worn surfaces. We demonstrated that the phase image allows relatively qualitative estimation of elastic modulus of the sample surface. The tribolayer formed in the worn surface possessed much lower stiffness than the original coating. It is shown that the most stable phase imaging is provided with a stiff cantilever. In this case, phase contrast is well conditioned, first of all, by microheterogeneity of elastic properties of the investigated surfaces. In this study an attempt was also made to correlate the results of phase imaging with that of the farce spectroscopy. The joint analysis of information on the surface properties obtained by the phase imaging and quantitative data measured with the force spectroscopy methods allows a better understanding of the nature of the surface micromechanical heterogeneity.

• Computers and Concrete
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• 제6권2호
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• pp.167-185
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• 2009

Reinforced concrete floors constructed between movement restraints often crack seriously due to shrinkage after completion. One common mitigation measure is to construct the concrete floors in stages to allow part of the shrinkage movement to take place before completion. However, shrinkage movement analysis of concrete floors constructed in stages is quite cumbersome, as the structural configuration changes during construction, thus necessitating reanalysis of the partially completed structure at each stage. Herein, a finite element method for shrinkage movement analysis of concrete floors constructed in stages is developed. It analyses the whole structure, including the completed and uncompleted portions, at all stages. The same mesh is used all the time and therefore re-meshing and location matching are no longer necessary. This is achieved by giving negligibly small stiffness to the uncompleted portions, which in reality do not exist yet. In the analysis, the locked-in strains due to increase in elastic modulus as the concrete hardens and the creep of the hardened concrete are taken into account. Most important of all, this method would enable fully automatic shrinkage movement analysis for the purpose of construction control.

• 대한치과보철학회지
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• 제42권3호
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• pp.267-279
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• 2004

A modelling scheme for the stress analysis taking into account load transfer characteristics of the osseointegrated interfaces between dental implant and surrounding alveolar bone was investigated. Main aim was to develop a more realistic simulation methodology for the load transfer at the interfaces than the prefect bonding assumption at the interfaces which might end up the reduced level in the stress result. In the present study, characteristics of osseointegrated bone/implant interfaces was modelled with material nonlinearity assumption. Bones at the interface were given different stiffness properties as functions of stresses. Six different models, i.e. tens0, tens20, tens40, tens60, tens80, and tens100 of which the tensile moduli of the bones forming the bone/implant interfaces were specified from 0, 20, 40, 60, 80, and 100 percents, respectively, of the compressive modulus were analysed. Comparisons between each model were made to study the effect of the tensile load carrying abilities, i.e. the effectivity of load transfer, of interfacial bones on the stress distribution. Results of the present study showed significant differences in the bone stresses across the interfaces. The peak stresses, however, were virtually the same regardless of the difference in the effectivity of load transfer, indicating the conventional linear modelling scheme which assumes perfect bonding at the bone/implant interface can be used without causing significant errors in the stress levels.

• Composites Research
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• 제15권6호
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• pp.30-37
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• 2002

꼰 섬유(twisted yarn)로 이루어진 복합재료의 탄성계수를 예측하기 위한 강성모델을 제시하였다. 이 모델은 단위 셀 구조를 바탕으로 하여 좌표변환과 구성 재료의 연성 상수를 체적 평균함으로써 복합재료의 탄성계수를 예측하는 방법이다. 해석적인 결과와 실험치와의 비교를 위하여 두 종류의 꼬임 각을 가지는 섬유로 구성된 복합재료에 대한 시험을 하였으며 인장, 압축, 전단 강도와 탄성계수를 구하였다. 이 시험편은 유리섬유 및 에폭시 수지를 사용한 RTM 성형법으로 제조하였다. 탄성계수에 대한 비교 곁과 예측치와 실험치는 비교적 잘 일치하였다. 이 모델에 의해 구해진 3차원적인 탄성계수 값은, 꼬인 섬유로 이루어진 직조형 복합재료 구조물의 구조해석을 위한 기본 물성치 입력값으로 사용될 수 있다.

• 대한토목학회논문집
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• 제10권2호
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• pp.49-58
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• 1990

캔틸레버 시공법에 의해 가설되는 프리스트레스트 콘크리트 교량의 시간 단계별 장기 처짐을 정확하게 해석하지 위해 프리스트레스트 콘크리트의 시간 의존적 재료 특성과 캔틸레버 공법에 있어서의 분할시공 과정을 고려할 수 있는 해석 모델을 개발하고, 이에 기초하여 콤퓨터 프로그램을 작성하였다. 본 프로그램에서는 시간의 경과에 따른 콘크리트의 크리프, 건조 수축 및 탄성 계수의 변화 그리고 PS 강재의 리락세이션을 고려한다. 그리고 시공 단계별 세그먼트의 발생, 다단계 프리스트레싱 그리고 지점조건의 변화를 고려한다. 또한 철근으로 인한 단면의 강성 증가를 고려하고 전단변형의 영향을 고려하여 보다 정확하게 해석할 수 있도록 하였다. 본 프로그램을 이용하여 다경간 PS 콘크리트 교량을 해석함으로써, 프로그램의 실제 적용성과 캔틸레버공법에 의한 교량의 거동 특성을 규명하고자 하였다.

• 한국소음진동공학회논문집
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• 제21권8호
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• pp.714-719
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• 2011

This paper presents vibration characteristics of magnetorheological(MR) elastomer, whose elastic modulus are controllable by applied magnetic field. By using this property, the material can be applied to vibration absorber, so that the stiffness of the absorber can be changed and actively controlled according to the magnetic flux density. However, the various performances of MR elastomer depends on different polarized direction of particles by applied magnetic field and dimension during the manufacturing process. In this paper, in order to obtain the optimal characteristics of MR elastomer, MR elastomers with different types and dimensions are prepared for a series tests. Using this test setup, extent of natural frequency shifted against magnetic field at various excitation frequencies can be measured. Specimens are prepared with 3 types, as cylinder samples exposed to magnetic field vertically, horizontally and unexposed during cure, respectively. Also, a set of design variables are considered to produce MR elastomers. Through the modal tests of mass structure with MR elastomer, the optimal design as well as the polarization direction of MR elastomer is obtained among the various dimensions and 3 directional types of MR elastomers.

• Structural Engineering and Mechanics
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• 제9권1호
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• pp.17-35
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• 2000

Dynamic response of a three span continuous bridge has been determined by full scale experiments on the bridge. In the experiments, a heavy vehicle was driven across the bridge at different speeds and along different lanes of travel and the strains were recorded at different locations. The bridge was made of reinforced concrete and was asymmetric in plan and in elevation. Frequencies and modes of vibration excited by the vehicle were determined. The dependence of the dynamic amplification on bridge location and vehicle speed was investigated and dynamic amplifications up to 1.5 were recorded, which was higher than values predicted by bridge design codes. It was evident that when this asymmetric bridge was loaded by an asymmetric forcing function, higher modes, which are lateral and/or torsional in nature, were excited. Dynamic modulus of elasticity and the support stiffness influenced the natural frequencies of the bridge, which in turn influenced the dynamic amplifications. Larger than anticipated dynamic amplification factors and the excitation of lateral and/or torsional modes should be of interest and concern to bridge engineers.