• Journal of the Korea Concrete Institute
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• v.15 no.5
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• pp.726-736
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• 2003

Concrete columns confined with high-strength fiber composites can enhance its strength as well as maximum strain. In recent years, several equations have been developed to predict the behavior of the concrete columns confined with fiber composites. While the developed equations can predict the compressive strength of the confined columns with reasonable agreement, these equations are not successful in predicting the observed maximum strain of the columns. In this paper, a total of 61 test results is analysed to propose an equation to predict both compressive strength and maximum strain of concrete cylinders. The proposed equation takes into account the effects of confining pressure and cylinder size. Furthermore, in order to verify the proposed stress-strain curve for concrete cylinders, six cylindrical specimens were tested. Comparisons between the observed and calculated stress-strain curves of the tested cylinders showed reasonable agreement.

• Journal of the Korea Concrete Institute
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• v.16 no.6 s.84
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• pp.767-776
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• 2004

Polymer concrete shows excellent mechanical properties and chemical resistance compared with conventional normal cement concrete. The polymer concrete is drawing a strong interest as high-performance materials in the construction industry. Resins using recycled PET offer the possibility of a lower source cost of materials for making useful polymer concrete products. Also the recycling of PET in polymer concrete would help solve some of the solid waste problems posed by plastics and save energy. The purposed of this paper is to propose the model for the stress-strain relation of recycled-PET polymer concrete at monotonic uniaxial compression and is to investigate for the stress-strain behavior characteristics of recycled-PET polymer concrete with different variables(strength, resin contents, curing conditions, addition of silane and ages). The maximum stress and strain of recycled-PET polymer concrete was found to increase with an increase in resin content, however, it decreased beyond a particular level of resin content. A ascending and descending branch of stress-strain curve represented more sharply at high temperature curing more than normal temperature curing. Addition of silane increases compressive strength and postpeak ductility. In addition, results show that the proposed model accurately predicts the stress-strain relation of recycled-PET polymer concrete

• Journal of the Korea Concrete Institute
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• v.15 no.1
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• pp.69-77
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• 2003

One directional and biaxial tension tests of 13 reinforced concrete panels were conducted to derive a constitutive law of concrete. Based on the test results, a model equation is derived for the stress-strain relationship of concrete in tension. Main test variables are reinforcement ratio and the load ratio applied in two directions. In addition a failure envelope of concrete in tension-tension region is suggested based on the initial crack occurrence. Test results show that the concrete carries substantial tensile stress even after cracking occurrence. However, the application of this proposed stress-strain relationship for concrete is limited to the case where the direction of reinforcement coincides with the direction of the applied principal stresses.

• Journal of the Korea Concrete Institute
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• v.22 no.4
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• pp.481-488
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• 2010

Since existing constitutive models developed for confined normal strength concrete overestimate ductility when they are applied to confined high strength concrete, these models cannot be directly applied to confined high strength concrete. In an effort to solve this problem, an accurate stress-strain relationship of the hihg strength concrete needs to be formulated by examining the confinement effects due to increase of the concrete strength. In this study, a constitutive model is developed to express the stress-strain relationship of confined high strength concrete by carrying out regression analysis of the main parameters affection strength and ductile behavior of reinforced high strength concrete columns. Twenty-five test specimens were chosen from the reported experimental studies in the literature. The experimental results of stress-strain relationships of show a good agreement with results of the stress-strain relationships of suggested high strength concrete, covering a strength range between 60 and 124 MPa.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.11a
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• pp.38-38
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• 2003

최근 나노기술의 발달과 더불어 나노재료에 대한 특성평가 요구가 높아지고 있고, 따라서 나노스케일로 재료의 기계적 거동을 분석할 수 있는 나노인덴테이션 기법이 심도있게 연구되고 있다. 본 연구에서는 나노인덴테이션을 이용하여 여러 가지 재료의 탄성 소성 변형 거동을 관찰 조사하고 이를 다시 유한요소법(FEM)으로 모사하여 해석하였다. 나노인덴테이션으로 재료 표면에 압입하여 탄소성 변형을 일으켰으며 이때의 가하중과 변형깊이를 측정하여 하중-변형 곡선을 얻었다. 매우 작은 접촉응력 조건하에서는 탄성변형의 비율이 매우 높았는데 하중-변형 곡선으로부터 재료의 나노 경도와 탄성 계수값을 얻을 수 있었다. 실험적으로 얻은 하중-변형 곡선을 3 차원의 유한요소법(FEM)을 이용하여 모사하였는데 상호간에 매우 근접한 결과를 얻을 수 있었다. 이 때 압자의 모양, 압입 깊이, 재료의 종류, 둥을 변수로 하여 여러 가지 조건하에서 압입실험을 하였으며 그 결과를 유한요소법으로 모사하였다.

• Proceeding of KASS Symposium
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• 2008.05a
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• pp.31-36
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• 2008

Architectural membrane are now used in the roof of large span structures throughout the world with the merits of free shape and lightness. Some membrane have some problems of structural capacity by the wind or snow load conditions, large span structures was shown to the tearing of the membrane. This paper is the experimental test on the stress strain curve of cycling load for the glass fiber membrane. In the result of stress strain relationship curve by the cycling load, glass fiber membrane was reduced the tensile strength, the polyester membrane was shown to occur the increase of displacement without load reduction in each load step.

• Journal of the Korean Society of Hazard Mitigation
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• v.8 no.1
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• pp.47-55
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• 2008

Recently, it has been reported that buried pipes' crack is concentrated on curved parts. In this study, 3D-Finite element analysis is performed for Analytical Evaluation on the Structural Safety of Horizontally Curved Parts of Buried Pipe. The constructed pipe cracked in curved parts of pipe is analyzed and all kinds of loads affected to buried pipes are considered. Displacement, stresses and buckling analysis are performed. The stress analysis shows that stress in curved parts is larger than stresses in straight parts and exceeds allowable stress in some parts. So, stress analysis on curved parts is needed for safety for buried pipe.

• Korean journal of food and cookery science
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• v.5 no.1
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• pp.49-52
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• 1989

Stress relaxation tests with different percent deformation were performed for crude and refined starch gels of acorn. With no relation to percent deformation, refined starch gel had higher initial stress ($\sigma_e$) and lower equilibrium stress ($\sigma_e$) than crude starch gel. But the ratio of equilibrium stress to initial stress ($\sigma_e$/$\sigma_o$) was minimum at 60 percent deformation. The analysis of relaxation curves by successive residual method revealed that the rheological behavior of acorn starch gels could be expressed by generalized Maxwell model. The element numbers of models for crude and refined starch gel were 7-element and 5-element at 60 percent deformation, and 5-element and 3-element at 45 percent deformation, respectively.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.16 no.4
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• pp.353-367
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• 2003

This paper describes the extension of the numerical model, which was developed to simulate the nonlinear behavior of reinforced concrete (RC) structures subjected to monotonic in plane shear and introduced in the companion paper, to simulate effectively the behavior of RE structures under cyclic loadings. While maintaining all the basic assumptions adopted in defining the constitutive relations of concrete under monotonic loadings, a hysteretic stress strain relation of concrete, which across the tension compression region, is defined. In addition, unlike previous simplified stress strain relations, curved unloading and reloading branches inferred from the stress strain relation of steel considering the Bauschinger effect we used. The modifications of the stress strain relation of steel are also introduced to reflect pinching effect depending on the shear span ratio and an average stress distribution in a cracked RC element. Finally, correlation studies between analytical results and experimental studies are conducted to establish the validity of the proposed model.

• Journal of the Korean Society for Nondestructive Testing
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• v.26 no.5
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• pp.306-314
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• 2006

Instrumented indentation technique is a new way to evaluate nondestructive such mechanical properties as flow properties, residual stress and fracture toughness by analyzing indentation load-depth curves. This study evaluated quantitatively the flow properties of steels and residual stress of weldments. First, flow properties can be evaluated by defining a representative stress and strain from analysis of deformation behavior beneath the rigid spherical indenter and the parameters obtained from instrumented indentation tests. For estimating residual stress, the deviatoric-stress part of the residual stress affects the indentation load-depth curve, so that by analyzing the difference between the residual-stress-induced indentation curve and residual-stress-free curve, the quantitative residual stress of the target region can be evaluated. The algorithm for flow property evaluation was verified by comparison with uniaxial tensile test and the residual stress evaluation model was compared to mechanical cutting and ED-XRD results.