• Structural Engineering and Mechanics
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• 제62권1호
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• pp.113-123
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• 2017

The bi-material elastic system consisting of the circular hollow cylinder and the infinite elastic medium surrounding this cylinder is considered and it is assumed that on the inner free face of the cylinder a point-located axisymmetric time harmonic force, with respect to the cylinder's axis and which is uniformly distributed in the circumferential direction, acts. The shear-spring type imperfect contact conditions on the interface between the constituents are satisfied. The mathematical formulation of the problem is made within the scope of the exact equations of linear elastodynamics. The focus is on the frequency-response of the interface normal and shear stresses and the influence of the problem parameters, such as the ratio of modulus of elasticity, the ratio of the cylinder thickness to the cylinder radius, and the shear-spring type parameter which characterizes the degree of the contact imperfectness, on these responses. Corresponding numerical results are presented and discussed. In particular, it is established that the character of the influence of the contact imperfection on the frequency response of the interface stresses depends on the values of the vibration frequency of the external forces.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2014년도 추계 학술논문 발표대회
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• pp.127-128
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• 2014

The aim of this research is selecting an economical aggregate type for ultra-high strength concrete with 80 to 120 MPa of compressive strength. As the tests, the effect of water-to-binder ratios and types of aggregate on autogenous shrinkage of ultra-high strength concrete were evaluated. as the results of a series of tests performed, the slump flow was satisfied the target range of 600 ± 100 mm, and the concrete mixture with RLA showed higher elastic modulus than the other cases. For the autogenous shrinkage preventing performance, in the case of water-to-binder ratio of 15, and 20 %, the mixture with BA showed slightly improved autogenous shrinkage reducing effect than the mixture with RLA while the mixture with RLA showed better performance at 25 % of water-to-binder ratio. Therefore, based on the tests results of slump flow, elastic modulus, and autogenous shrinkage, the RLA is considered as a better aggregate type for this purpose.

• Structural Engineering and Mechanics
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• 제74권5호
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• pp.671-678
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• 2020

In this work, the dynamic properties of a high performance concrete containing glass powder (GP) was studied. The GP is a new cementitious material obtained by recycling waste glass presenting pozzolanic activity. This eco-friendly material was incorporated in concrete mixes by replacing 20 and 30% of cement. The mechanical properties of building materials highly affect the response of the structure under dynamic actions. First, the resonant vibration frequencies were measured on concrete plate with free boundary conditions after 14, 28 and 90 curing days by using an alternative vibration monitoring technique. This technique measures the average frequencies of several excitations done at different points of the plate. This approach takes into account the heterogeneity of a material like concrete. So, the results should be more precise and reliable. For measuring the bending and torsion resonant frequencies, as well as the damping ratio. The dynamic properties of material such as dynamic elastic modulus and dynamic shear modulus were determined by modelling the plate on the finite element software ANSYS. Also, the instantaneous aroused frequency method and ultrasound method were used to determine the dynamic elastic modulus for comparison purpose, with the results obtained from vibration monitoring technique.

• Geomechanics and Engineering
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• 제24권4호
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• pp.349-358
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• 2021

The Brazilian test has been widely used to determine the indirect tensile strength of rock, concrete and other brittle materials. The basic assumption for the calculation formula of Brazilian tensile strength is that the elastic moduli of rock are the same both in tension and compression. However, the fact is that the elastic moduli in tension and compression of most rocks are different. Thus, the formula of Brazilian tensile strength under the assumption of isotropy is unreasonable. In the present study, we conducted Brazilian tests on flat disk-shaped rock specimens and attached strain gauges at the center of the disc to measure the strains of rock. A tension-compression bi-modular model is proposed to interpret the data of the Brazilian test. The relations between the principal strains, principal stresses and the ratio of the compressive modulus to tensile modulus at the disc center are established. Thus, the tensile and compressive moduli as well as the correct tensile strength can be estimated simultaneously by the new formulas. It is found that the tensile and compressive moduli obtained using these formulas were in well agreement with the values obtained from the direct tension and compression tests. The formulas deduced from the Brazilian test based on the assumption of isotropy overestimated the tensile strength and tensile modulus and underestimated the compressive modulus. This work provides a new methodology to estimate tensile strength and moduli of rock simultaneously considering tension-compression bi-modularity.

• 한국농공학회논문집
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• 제53권6호
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• pp.153-163
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• 2011

This research describe improved algorithm that is able to decide terminal criterion of Evolutionary Structural Optimization (ESO), reducing load of calculation to search load path of concrete beam, and apply to agricultural facilities. The ESO method is that make to discrete structure, structural analyze each element stress through FEM. And repeat generation with next material condition to become for most suitable composing. Individual element introduces concept of zero stiffness, but zero stiffness decisions are gone to direction of exclusion. In this stduy, improve algorithm to be convergence by 'Rule of Alive or Die' in arrival because is most suitable. Also, existing terminal criterion lack consistency because that used depend on experience of researcher. This research procedure is fellowed. First, all modulus of elasticity assume a half of elasticity modulus of material, Second, structural analysis by FEM, Third, apply to the remove ratio and restoration ratio for the 'rule of alive or die'. Forth, reconstruct the element and material conditions. And repeat the first to forth process. The terminal time of evolutional procedure is the all elastic modulus of element changed to blank value or elasticity modulus value of original. Therefore, in this study, consist the algorithm for programming, and apply to the agricultural facilities with concrete.

• 한국가스학회:학술대회논문집
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• 한국가스학회 1997년도 추계학술발표회 논문집
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• pp.78-85
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• 1997

Indentation and small punch tests are very powerful methods to monitor the materials reliability since they are very simple, easy and almost non-destructive. First, recently-developed continuous indentation test can provide the more material properties such as hardness, elastic modulus, yield strength, work-hardening exponent, etc., than the conventional hardness test. In our study, the true stress-strain curve was derived from the indentation load-depth curve for spherical indentation. In detail, the strain was able to be obtained from plastic depth/contact radius ratio, and the flow stress was from mean contact pressure through the analysis of elastic-plastic indentation stress field. Secondly, the small punch test was studied to evaluate the fracture toughness and defomation properties such as elastic modulus and yield strength. Like the indentation test, this test can be applied without severe damage of the target structure.

• 한국지반공학회논문집
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• 제31권12호
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• pp.29-43
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• 2015

본 연구에서는 매입말뚝공법의 충전재료로 사용하는 시멘트밀크의 공학적 특성 시험을 실시하였다. 이를 위해 고속도로공사 전문시방서에서 사용하고 있는 표준공시체를 기준으로 다양한 물/시멘트 비율로 공시체를 제작하였다. 또한, 재령일에 따른 일축압축강도, 점하중강도, 탄성계수, 그리고 포아송비 시험을 실시하였다. 시험결과 물/시멘트 비의 변화에 따른 시멘트밀크의 표준 공시체 제작을 위한 주입높이를 제시하였다. 재령 7일과 28일에 대한 일축압축강도와 점하중강도와의 비인 시멘트밀크의 상관계수, K는 각각 $K_7=4.55{\sim}13.65$와 $K_{28}=5.28{\sim}16.84$ 이었다. 재령일과 무관하게 물/시멘트 비가 65~150%일 때 탄성계수와 포아송비의 증감은 크게 나타났고, 150~300%는 상대적으로 매우 작게 나타났다. 마지막으로 재령별 물/시멘트 비에 따른 시멘트밀크의 일축압축강도, 점하중강도, 일축압축강도와 점하중강도와의 상관계수, 탄성계수, 포아송비의 식을 제안하였다.

• 콘크리트학회논문집
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• 제18권5호
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• pp.695-702
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• 2006

본 연구는 콘크리트 포장에 복륜 단축, 복륜 복축, 복륜 삼축 등 복륜 다축 차량 하중이 작용할 때 포장의 응력 분포와 최대 응력을 변환영역에서의 해석법을 이용하여 분석하였다. 우선 변환영역에서의 해석법을 이용한 결과와 유한요소법을 이용한 결과를 비교하여 해석법의 정확성을 파악하였다. 그리고 종방향과 횡방향을 따라 응력의 분포형태를 분석하고, 콘크리트 슬래브의 두께, 콘크리트 탄성계수, 지반 탄성계수 등이 응력 분포에 미치는 영향을 분석하였다. 또한 하중 접지면적과 연관된 하중 접지압의 변화에 따른 콘크리트 포장의 응력 분포도 분석하였으며 콘크리트 포장에서 최대 응력이 어느 위치에서 발생하는지에 대한 연구도 수행하였다. 연구 결과 다축 하중에 의한 콘크리트 포장의 최대 응력은 콘크리트의 탄성계수가 증가할수록, 슬래브의 두께가 감소할수록, 그리고 지반 탄성계수가 감소할수록 증가하였다. 이러한 변수 등이 변할 때 축수에 따른 최대 응력 비율의 변화는 대체적으로 미소하지만 지반 탄성계수가 작을 때는 축수가 증가 할수록 최대 응력 비율이 급격히 증가한다. 횡방향의 최대 응력 발생 위치는 일반적으로는 접지압이 증가하면 바깥쪽에서 안쪽으로 이동하며 콘크리트 탄성계수나 슬래브 두께가 증가하거나 지반 탄성계수가 감소할 때도 최대 응력 발생 위치는 바깥쪽에서 안쪽으로 이동한다. 종방향 상의 최대 응력 위치는 하중 접지압에 영향을 받지 않으며 단축과 복축 하중일 경우는 축의 위치이며 삼축 하중일 경우에는 콘크리트 탄성계수나 슬래브 두께가 증가하던지 또는 지반 탄성계수가 감소하면 최대 응력이 생기는 종방향 위치가 양쪽 바깥축에서 중간축의 위치로 바뀌게 된다.

• 한국도로학회논문집
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• 제3권1호
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• pp.185-197
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• 2001

본 연구는 온도에 따라 특성이 변하는 아스팔트 콘크리트의 파괴인성을 규명하기 위하여 기존의 유효균열 모델을 수정하는 연구를 다루고 있다. 본래의 ECM모델은 콘크리트와 같은 고체에 적용되도록 개발되어 재료의 포아슨 비를 고려하지 않는다. 하지만 아스팔트 콘크리트는 온도변화에 민감하여 온도에 따라 포아슨 비가 변화하므로 다양한 온도하에서 정확한 파괴 특성을 알기 위해서는 포아슨 비가 고려되어져야 한다. 3개의 개질아스팔트 결합재를 포함한 4가지 결합재를 사용하여 밀입도 아스팔트 혼합물을 제조하여 초기균열 보에 대한 3점 휨 시험을 $-5^{\circ}C$부터 $-35^{\circ}C$까지에서 수행하였다. 탄성계수, 휨강도 및 파괴인성을 시험을 통하여 구하였다. 시험결과 포아슨비가 고려되는 수정 ECM 공식을 사용하므로서 보다 정확한 값들을 얻을 수 있었다. 폴리머 개질 아스팔트 혼합물이 일반아스팔트 혼합물에 비하여 더 낮은 저온하에서 더 높은 강성과 파괴인성을 유지함을 알 수 있었다.

• Steel and Composite Structures
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• 제16권1호
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• pp.77-96
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• 2014

In this paper, magneto-thermo-elastic problem of a thick truncated conical shell immersed in a uniform magnetic field and subjected to internal pressure is investigated. Material properties of the shell including the elastic modulus, magnetic permeability, coefficients of thermal expansion and conduction are assumed to be isotropic and graded through the thickness obeying the simple power law distribution, while the poison's ratio is assumed to be constant. The temperature distribution is assumed to be a function of the thickness direction. Governing equations of the truncated conical shell are derived in terms of components of displacement and thermal fields and discretised with the help of differential quadrature (DQ) method. Results are obtained for different values of power law index of material properties and effects of thermal load on displacement, stress, temperature and magnetic fields are studied. Results of the present method are compared with those of the finite element method.