• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.3A
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• pp.221-228
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• 2010

External bonding of carbon fiber reinforced polymer (CFRP) sheets has been widely accepted as a popular method for strengthening of deteriorated RC structures. The long-term behavior of CFRP-strengthened RC structure is often affected by that of the interface between CFRP sheets and concrete. This study aims at applying a viscoelastic model to describe the creep behaviour of the adhesive layer bonding CFRP sheet to concrete, the CFRP-concrete interface. Reviews of available models on concrete creep behavior have been first carried out and then new FE analysis model is proposed. The proposed FE analysis model based on the maxwell model has been verified by previous experimental results. It is shown that the creep effect of interfacial adhesive layer is very important on the long-term behavior of concrete structures strengthened with CFRP.

• Geotechnical Engineering
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• v.9 no.4
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• pp.93-102
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• 1993

Soil structures which are constructed over the soft ground settle continuously by the self-weight of embankment for a long time. It is because of timetependent behaviours . consolidation and creep occurring simultaneously. This paper tries to determine the required parameters for analysis of the creep behaviour in marine clays and studied the effect of the confining stress and stress level on the creep parameters . As a result, it presents an equation for the determination of creep parameters according to stress level considering that elastic modulus El and creep parameter f are found to be affected by the applied stress level.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.8
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• pp.703-709
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• 2017

Creep analysis takes much more time than elastic or elastic-plastic analysis. In this study, we conducted elastic and elastic-plastic analysis and compared the results with creep analysis results. In the elastic analysis, we used primary stress, which can be classified by the $M{\alpha}-tangent$ method and stress intensities recommended in the ASME code. In the elastic-plastic analysis, we calculated the parameters recommended in the R5 code. For the FE models, a bending load, uniaxial load, and biaxial load were applied to the cross shaped welded plate, and a bending load and internal pressure were applied to the elbow pipe. To investigate the element size sensitivity, we conducted FE analysis for various element sizes for the cases where bending load was applied to the cross shaped welded plate. There was no significant difference between the creep stress and the alternative methods; however, in the $M{\alpha}-tangent$ method, the results were affected by the element size.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.3
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• pp.405-412
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• 2013

This paper reports the steady-state stresses within the heat affected zone (HAZ) of a welded straight pipe subject to creep. The creep constants and exponent are varied systematically to see the effect of various mismatches in creep properties on the steady-state creep stresses, via detailed two-dimensional finite element (FE) creep analyses. The weldments consist of the base metal and weld metal with the HAZ, which are characterized using the idealized power creep laws with the same creep exponent. The internal pressure and axial loading are considered to see the effect of the loading mode. To quantify the creep stresses, a creep mismatch factor is introduced as a function of the creep constants and exponent. It is concluded that the ratio of the section-averaged stresses for a mismatched case to those for an evenmatched case are linearly dependent on the mismatch factor. The results are compared with the FE results, including the Type IV region, as well as the R5 procedure.

• Magazine of the Korea Concrete Institute
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• v.10 no.1
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• pp.179-188
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• 1998

캔틸레버 공법으로 시공되는 프리스트레스트 콘크리트 박스거더 교량의 구조적 거동은 단계적 시공에 따른 구조물의 순차적 변화 및 콘크리트의 재료적 특성에 의해 시간 의존적 거동을 나타낸다. 콘크리트의 시간의존적 특성, 즉 콘크리트의 크리프 및 건조수축 특성은 현장타설 세그멘탈 캔딜레버공법으로 가설되는 콘크리트 교량의 설계 및 시공에서 매우 중요한 역할을 한다. 본 연구에서는 콘크리트의 크리프 및 건조수축 특성이 교량의 시간의존적 거동, 특히 처짐 및 텐던응력예측에 미치는 영향을 연구하였다. 교량해석은 본 연구진에 의해 개발된 프리스트레스트 콘크리트 교량해석기법 및 프로그램을 이용하여 크리프의 ACI 모델, CEB-FIB모델, 그리고 국내 도로교 시방서 모델을 고려하여 해석하였다. 해석결과 최종크리프 값의 크기에 따라 장기처짐의 발생량이 차이가 큰 것으로 나타나고 있으며, 최종건조수축량과 상대습도도 영향을 주는 것으로 나타났다. 또한 ACI 모델과 CEB-FIB모델간에도 차이가 큰 것으로 나타나 실제교량의 크리프 특성 및 건조수축 특성의 정확한 예측이 교량의 정밀시공 및 거동예측에 매우 중요한 것으로 나타나고 있다.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2011.04a
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• pp.123-126
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• 2011

본 논문에서는 점탄성 매트릭스와 탄성 강화입자로 구성된 복합재료의 크리프 거동예측을 미세역학 기반의 시뮬레이션을 통하여 수행하였다. 에폭시 고분자로 이루어진 복합재료의 경우 재료 특성상 탄성적 거동뿐 아니라 점성적 거동도 함께 발생하게 된다. 이렇듯 점탄성 거동을 보이는 재료의 경우 탄성만을 고려한 해석방법으로는 한계가 있으며 점성적인 특성 또한 고려되어야 한다. 점탄성 복합재료의 해석을 위해서 손상을 고려한 미세역학 기반의 해석 (Ju and Chen, 1994) 과 Mesquita and Coda (2002)의 근사식을 사용하였다. 이를 통해 구한 재료 물성은 복합재료의 크리프 거동예측을 위한 Kelvin-Voight (KV) 모델과 Standard Linear Solid (SLS) 모델에 적용되었다. 최종적으로 본 연구에서 제안한 손상을 고려한 점탄성 모델의 예측과 시험결과를 비교 수행하여 결과의 타당성을 검증하였다.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2009.04a
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• pp.327-330
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• 2009

PSC 박스 교량의 시공 중 거동 특성을 고려하기 위하여 뼈대 요소를 이용한 시공단계의 설계가 수행되고 있다. 그러나 PSC 박스 교량 중 곡선 램프교 등의 경우는 교량의 외측 및 내측의 변위 및 응력 값이 현저히 다르다. 따라서 PSC 박스 교량의 텐던량 및 시공 중 긴장력이 외측 및 내측에서 다르게 산정되어야 함에도 불구하고 현실적으로는 계산이 불가능하여 같은 양의 텐던과 부적절한 긴장력을 사용하고 있어 비효율적인 설계와 시공이 이루어지고 있다. 이러한 문제점을 해결하기 위하여 내외측의 텐던량을 다르게 고려할 수 있고 교량의 내외측 반력, 응력, 변위 분포를 얻을 수 있는 3차원 해석이 필수적으로 요구 되고 있다. 본 연구에서는 PSC 박스 교량의 3차원 거동 해석을 위하여 텐던 및 크리프, 건조수축을 반영한 준적합 쉘요소를 이용하여 수치해석을 수행하였으며 크리프 및 건조수축의 특성은 ACI코드와 CEB/FIP 코드를 적용하여 비교분석하였다. 각각의 결과 값이 상이한 경우도 있지만 대체로 두 코드는 비슷한 양상을 보였으며 CEB/FIP 가 좀 더 경제적인 설계가 됨을 알 수 있었다.

• Journal of the Korean GEO-environmental Society
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• v.11 no.4
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• pp.19-24
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• 2010

Generally, slope behavior is analyzed by 2-dimensional creep model. Creep behavior shows the deformation variation as time goes by without stress increment. Convention 2-dimensional creep analysis does not have the term of stress variation, it means creep analysis could not figure out the relationship of shear strength variation according to the stress variation and displacement. The slope weight and shear strength is directly related and interlocked to the safety variation and displacement of slope, therefore, this phenomenon could be treated and analyzed as combining the hysteresis and creep, the iteration of this process will result in the slope safety. Furthermore, the combined analysis will be the slope analysis considering shear stress, displacement and shear strength with time variation. In real case, because the variation of shear stress and strength happen at the same time, they should be changed into safety factor which is function of them. This paper shows the 3-dimensional variation of unit weight of soil with hybrid analysis considering creep and hysteresis on the seepage and drainage of rainfall, futhermore variations of shear stress and strength which make the safety factor change.

• Journal of Advanced Marine Engineering and Technology
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• v.22 no.4
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• pp.490-497
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• 1998

An elast-biscoplastic finite element analysis is performed to investigate detailed growth behavior of creep cracks and the numerical results are compared with experimental results. The results of mesh translation method are compared with those of node release method. Load line displancement curve obtained from the crack growth analysis by mesh translation shows the improved results than that obtained from the crack growth by node release method when the secondary creep rate is only used as creep material property. The results of accounting for primary creep rate and instantaneous plasticity shows a good agreement with the experimental result.

• Fire Science and Engineering
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• v.24 no.4
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• pp.33-40
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• 2010

A numerical model considering the vapor pressure and the creep models, in the form of a analytical program, for tracing the behavior of high strength concrete (HSC) members exposed to fire is presented. The two stages, i.e., spalling procedure and fire resistance time, associated with the thermal, moisture flow, creep and structural analysis, for the prediction of fire resistance behavior are explained. The use of the analytical program for tracing the response of HSC member from the initial pre-loading stage to collapse, due to fire, is demonstrated. The validity of the numerical model used in this program is established by comparing the predictions from this program with results from others fire resistance tests. The analytical program can be used to predict the fire resistance of HSC members for any value of the significant parameters, such as load, sectional dimensions, member length, and concrete strength.