• Geotechnical Engineering
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• v.13 no.3
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• pp.63-76
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• 1997

To investigate the engineering characteristics of crushed rockfill material, the large-scaled triaxial tests have been carried out, The rpckfill is made from the greywacke, and the 3 parallel gradations with different maximum particle size(dmu=38.1mm, 25.4mm and 19.1mm) were designed for the test. The dimension of the specimen is 300mm in diameter and 600mm in height, and the applied confining stress varied from 5t/$51.6^{\circ}$ to 60t/$51.6^{\circ}$. The test results show that the influence of the maximum particle size on the stress -strain r$51.6^{\circ}\; to\; 40.5^{\circ}$ when the confining stress increases from 5t/$51.6^{\circ}$ to 60t/$51.6^{\circ}$ The hyperbolic parameter values estimated from the test result for rockfill are much different from the recommended values by Duncan et. at(1980) for GW and GP material, especially in the $\phi$ ad K-values.

• Journal of the Korea Concrete Institute
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• v.23 no.1
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• pp.77-86
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• 2011

The concrete creep deformation of a hybrid composite section can cause additional deformation of the composite section and the stress relaxation of pre-compressive stress on the concrete section due to partial restraint of the deformation. In this study, the stress relaxation coefficient method (SRCM) is derived for simple analysis of complicate hybrid or composite sections for engineering purpose. Also, an equation of the stress relaxation coefficient (SRC) required for the SRCM is proposed. The SRCM is derived with the parameters of a creep coefficient, section and loading properties using the same method as the constant-creep step-by-step method (CC-SSM). The errors of the SRCM is improved by using the proposed SRC equation than the average SRC's which were estimated from the CC-SSM. The root mean square error (RMSE) of the SRCM with the proposed SRC equation for concrete with creep coefficient less than 3 was less than 1.2% to the creep deformation at the free condition and was 3.3% for the 99% reliability. The proposed SRC equation reflects the internal restraint of composite sections, and the effective modulus of elasticity computed with the proposed SRC can be used effectively to estimate the rigidity of a composite section in a numerical analysis which can be applied in analysis of the external restrain effect of boundary conditions.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.6
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• pp.1417-1431
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• 1994

In this study, shear strength characteristics of the Nak-Dong river sand in Taegu area are investigated by triaxial compression test, considering shear strain control velocity, relative density, and confining pressure. The results from Lade model and Modified Lade model are compared with the measured value in the laboratory test. The results by the change of shear strain control velocity, relative density, and confining pressure are as follows; 1) The stress limit, which can be Coulomb's law about the Nak-Dong river sand, have ranged 120~200 kpa at 0.08%/min and 120~150 kpa at 0.5%/min. These limits are smaller than that of the calcareous sand and the well-graded, quartz sand. 2) The parameters needed to Lade model and Modified Lade model are much affected by the strain control velocity and the relative density. Consequently, in the field, it is important to use parameters aptly after accurately understanding both the loading condition and subsoil condition. 3) Overall, the principal stress ratio obtained from constitutive model equations is not affected by the control velocity, but both the relative density and confining pressure affect the result of constitutive model equations. Consequently, the study on the various conditions about the relative density and confining pressure is needed to accurately predict the stress-strain behavior on the Nak-Dong river sand. 4) For the range of the used confining pressure in the study, the Lade model shows better agreements with the measured value than the Modified Lade model, comparing the measured value with the principal stress ratio at failure and the internal friction angle of failure envelope obtained from the Lade model and Modified Lade model.

• Proceedings of the Korean Fiber Society Conference
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• 2003.10b
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• pp.155-156
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• 2003

시멘트는 압축강도가 크고 내구성이 좋으며 가격이 저렴한 우수한 토목건축재료이다. 그러나 인장강도가 낮아서 사용 시 발생하는 휨에 의한 인장변형에 의하거나 양생 후 해 표면 크랙이 발생하는 결점이 있다. 이러한 결점을 보완하기위해 크랙의 발생 억제, 성장 지연을 목적으로 시멘트에 보강용 섬유를 투입하고 있다[1]. 시멘트에서의 보강섬유의 역할은 크랙발생에 필요한 에너지를 최대한 증가시키켜 시멘트가 경화되기 시작할 때, 구속에 의해 발생하는 인장응력 및 균열을 억제하구 내부에 형성되는 결함을 방지함에 있다[2]. (중략)

• KSCE Journal of Civil and Environmental Engineering Research
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• v.11 no.1
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• pp.153-166
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• 1991

In an attempt to investigate the effect of intermedate principal stresses which are related to the stress-strain behavior of standard sands, a series of three-Principal stress control tests were conducted for individual stress paths. The results have shown that shear strengths of sands vary with the stress paths. The variations in internal friction angle are accorded with the Habibs stress parameter, b which represents Stress paths, showing on abropt increase at the values between 0.0 and 0.268, a moderate level between 0.268 and 0.682, and a slight decrease between 0.682 and 1.0 However, the friction angles under a triaxial extention state, were found relatively larger than under a triaxial compression state. In general, such veriations were found to have the same tendency without any relevant relation with the density of specimens and confining pressures. Therefore, it is concluded, that the shear strength of sands are positively influeced by the intermediate principal stresses present in the media. And the influnce of intermediate principal stresses on shear strengths of sands found from the present study are well compared with the previous studies by Lade-Duncan and Matsuoka-Nakai revealing a similar tendency within the failure criteria proposed by them.

• Journal of the Earthquake Engineering Society of Korea
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• v.12 no.3
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• pp.29-36
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• 2008

The TR-CFT(Transversely Reinforced Concrete Filled Steel Tube) column is proposed to control or at least delay the state of local buckling at the critical section by wrapping the CFT columns with a carbon fiber sheet. In this study, an equation to determine the flexural strength of TR-CFT is proposed. The ACI-318 code, in which the contribution of the confining effect in the concrete filled steel tube is not appropriately accounted for, may be conservative. Therefore, flexural strength design equations for CFT columns and TR-CFT columns are proposed based on the concrete strain-stress curve, which contributes to the confining effect. Finally, the predicted results for the CFT and TR-CFT columns are shown to be in good agreement with actual test results.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.4
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• pp.771-781
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• 1994

The heat generation of cement causes the internal temperature rise and volume change at early age, particulary in massive concrete structures. As the results of the temperature rise and restraint conditions, the thermal stress may induce cracks in concrete. Therefore, the prediction of the thermal stress is very important in the design and construction in order to control the cracks developed in mass concrete. In case of young concrete, creep effect by the temperature load is larger than that of old concrete. Thus, the effect of creep must be considered for checking the cracks, serviceability, durability and leakage. This paper is concentrated on the development of a finite element program which is capable of simulating the temperature history and the thermal stress considering creep and the modified elastic modulus due to inner temperature change and maturity. The analytical results in the inner parts highest important to control cracks are in good agreement with experimental data. Therefore this study may provide available method to control the cracks.

• Geotechnical Engineering
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• v.13 no.2
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• pp.17-28
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• 1997

In this study sodium chloride solution is employed for chemicals, and several cylindrical triaxial tests are performed on the sand-bentonite mixtures saturated with sodium chloride solution. Deformation(elastic modulus, E) and strength(cohesion, c', and angle of friction, f') parameters are obtained from the triaxial tests as functions of confining pressure and sodium chloride solution concentrations. The results here indicate an increase in the value of effective cohesion with increase in the concentration of NaCl solution, which can be explained by using the Gouy-Chapman model. The value of the effective angle of shearing resistance does not show significant change with the increase in concentration of NaCl solution. The Young's modulus also increases with the increase in concentration of NaCl solution.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.12 no.2
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• pp.185-199
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• 1999

본 연구에서는 새로운 spline 유한대판 요소를 제안하였다. 제안된 정식화는 등매개 개념에 의해 기하학적 형상과 변위장을 가정함에 있어 길이방향은 3차의 B-spline 곡선으로, 횡방향에 대해서는 Lagrange 다항식에 의해 표현된다. 이 논문은 평판과 쉘해석에 있어서의 등매개 spline 유한대판 요소의 개선에 목적을 두고 있다. 이 새로운 요소는 스트립의 내부 절점에서 6개의 자유도를 갖는 합-응력 감절점 쉘 요소로부터 유도하였다. 스트립의 기하학적 형상은 강체 회전에 대한 정의에 위배되지 않고도 두께 방향을 따라 Jacobian이 일정하다는 가정을 따랐으며 고체역학에서 정의되는 면내 회전을 penalty 함수에 의한 구속조건으로 간주하여 면내 회전에 관계된 자유도를 생성하였다. 제안된 요소에 대하여 쉘의 전형적인 문제에 대한 수치예제를 보였으며 이 스트립 요소의 성능을 평가하였다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.15 no.3
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• pp.501-510
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• 2002

The middle diaphragm of box girder is to prevent the deformation of the cross section of box girder, to distribute load produced at upper flange onto the both sides of web. But if inner space of box girder is barred by the middle diaphragm, it is impossible to use in inner space of box girder and it is felt constraint on maintenance-management. The effect of middle diaphragm of box girder is intended to be expressed by the stiffness of diaphragm in comparing the diaphragm with opening of box girder with diaphragm without opening of box girder through the experiment.