• 콘크리트학회논문집
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• 제16권1호
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• pp.111-124
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• 2004

축방향철근의 연결상세에 따라 7개 그룹 총 21개의 원형나선철근 기둥 시험체를 제작하여 준정적 실험을 수행하였다. 축방향철근 연결상세(단일철근, 겹침이음 및 기계적연결), 심부구속철근비, 축력비 등을 주요 실험변수로 채택하였으며 실험결과 축방향철근 연결상세에 따라 다른 파괴거동을 나타내었고, 내진성능에서도 차이를 나타내었다. 축방향철근이 겹침이음된 시험체의 실험결과, 모든 축방향철근이 겹침이음된 시험체는 내진성능이 상당히 저하되는 것으로 나타났으나, 축방향철근의 $50\%$가 겹침이음된 시험체의 경우 제한적이지만 한정적인 연성능력을 나타내었다. 또한, 축방향철근을 커플러를 사용하여 기계적으로 연결한 시험체는 축방향철근이 단일철근으로 구성된 시험체와 유사한 파괴거동 및 강도저감거동을 나타내었다.

• Structural Engineering and Mechanics
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• 제27권6호
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• pp.697-711
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• 2007

Though extensive research has been carried out for the ultimate strength of steel reinforced concrete (SRC) members under static and cyclic load, there was only limited information on the applied analysis models. Modeling of the inelastic response of SRC members can be accomplished by using a microcosmic model. However, generally used microcosmic model, which usually contains a group of parameters, is too complicated to apply in the nonlinear structural computation for large whole buildings. The intent of this paper is to develop an effective modeling approach for the reliable prediction of the inelastic response of SRC columns. Firstly, five SRC columns were tested under cyclic static load and constant axial force. Based on the experimental results, normalized trilinear skeleton curves were then put forward. Theoretical equation of normalizing point (ultimate strength point) was built up according to the load-bearing mechanism of RC columns and verified by the 5 specimens in this test and 14 SRC columns from parallel tests. Since no obvious strength deterioration and pinch effect were observed from the load-displacement curve, hysteresis rule considering only stiffness degradation was proposed through regression analysis. Compared with the experimental results, the applied analysis model is so reasonable to capture the overall cyclic response of SRC columns that it can be easily used in both static and dynamic analysis of the whole SRC structural systems.

• 콘크리트학회지
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• 제10권6호
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• pp.291-301
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• 1998

본 논문은 공용년수가 오래되어 노후화된 철근콘크리트 교량의 파괴가지의 거동에 예측하기 위한 비선형 파괴해석 모델링 기법이 개발에 관한 연구이다. 본 논문에서는 비선형파괴해석을 위해철근부식으로 인하여 철근주변 콘크리트의 열화를 고려한 인장경화모델을 제안하였으며 교량의 노후화된 지점조건을 고려할 수 있는 지점 모델링 기법을 제안하였다. 제안된 모델을 사용하여 반복하중을 받는 노후화된 철근콘크리트 T형 교량이 파괴될 때까지의 2차원 및 3차원 파괴해석을 수행하였으며 파괴시험으로부터 분석된 교량의 파괴거동과 비교하였다. 해석결과와 실험결과의 비교로부터 본 논문의 모델링기법이 노후화된 교량의 파괴해석에 유용하게 사용될 수 있으며 노후화된 지점조건의 모델링이 교량의 강도평가에 매우 큰 영향을 주는 것을 규명하였다.

• 한국지반공학회논문집
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• 제20권2호
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• pp.15-26
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• 2004

반복삼축시험에 의한 반복하중 후 강도 및 강성의 예측법을 이용하여, 세립토에 대해서 직접단순 전단시험에서도 그 방법의 사용 가능성을 확인하여 보았다. 사용한 흙은 실트질 점토, 소성 실트와 비소성 실트이다. 반복삼축시험을 통해서 얻은 강도 및 강성 예측법을 직접단순 전단시험에 맞게 수정하여 시험 결과와 비교하였다. 특히, 세립토의 소성지수와 초기전단응력(ISSS)의 영향이 강조되었다. 연구결과는 (i) 세립토의 액상화강도비는 소성지수의 감소와 초기전단응력의 증가에 따라 감소한다. (ii)등가강성과 전단변형률의 관계에 미치는 소성지수와 초기전단응력의 영향은 그리 크지 않다. (iii) 정규화한 과잉간극수압의 증가에 따른 강도비의 저하는 세립토의 소성지수가 증가할수록 느리다. (iv) 활성도가 큰 소성실트의 강성은 과잉간극 수압의 증가에 따라 급속히 감소한다. (v) 반복삼축시험 결과를 이용한 반복하중후 강도 및 강성의 예측법을 이용하여 직접단순 전단시험 결과에 수정한 방법은 시험결과와 잘 어울리는 것으로 나타났다.

• Steel and Composite Structures
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• 제29권6호
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• pp.735-748
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• 2018

In this paper, the cyclic behavior of steel beam-concrete encased steel (CES) column joints was investigated experimentally and numerically. Three frame middle joint samples with varying concrete slab widths were constructed. Anti-symmetrical low-frequency cyclic load was applied at two beam ends to simulate the earthquake action. The failure modes, hysteretic behavior, ultimate load, stiffness degradation, load carrying capacity degradation, displacement ductility and strain response were investigated in details. The three composite joints exhibited excellent seismic performance in experimental tests, showing high load-carrying capacity, good ductility and superior energy dissipation ability. All three joint samples reached their ultimate loads due to shear failure. Numerical results from ABAQUS modelling agreed well with the test results. Finally, the effect of the concrete slab on ultimate load was analyzed through a parametric study on concrete strength, slab thickness, as well as slab width. Numerical simulation showed that slab width and thickness played an important role in the load-carrying capacity of such joints. As a comparison, the influence of concrete grade was not significant.

• Structural Engineering and Mechanics
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• 제45권6호
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• pp.741-758
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• 2013

In this study, inelastic displacement ratios are investigated for existing systems with known lateral strength considering soil structure interaction. For this purpose, SDOF systems for period range of 0.1-3.0 s with different hysteretic behaviors are considered for a number of 18 earthquake motions recorded on soft soil. The effect of stiffness degradation on inelastic displacement ratios is investigated. The Modified Clough model is used to represent structures that exhibit significant stiffness degradation when subjected to reverse cyclic loading and the elastoplastic model is used to represent non-degrading structures. Soil structure interaction analyses are conducted by means of equivalent fixed base model effective period, effective damping and effective ductility values differing from fixed-base case. For inelastic time history analyses, Newmark method for step by step time integration was adapted in an in-house computer program. A new equation is proposed for inelastic displacement ratio of system with SSI with elastoplastic or degrading behavior as a function of structural period ($\tilde{T}$), strength reduction factor (R) and period lengthening ratio ($\tilde{T}$/T). The proposed equation for $\tilde{C}_R$ which takes the soil-structure interaction into account should be useful in estimating the inelastic deformation of existing structures with known lateral strength.

• Structural Engineering and Mechanics
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• 제28권1호
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• pp.39-52
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• 2008

Column shear failures observed during recent earthquakes and experimental data indicate that shear deformations are typically associated with the amount of transverse reinforcement, column aspect ratio, axial load, and a few other parameters. It was shown that in some columns shear displacements can be significantly large, especially after flexural yielding. In this paper, a piecewise linear model is developed to predict an envelope of the cyclic shear response including the shear displacement and corresponding strength predictions at the first shear cracking, peak strength, onset of lateral strength degradation, and loss of axial-load-carrying capacity. Part of the proposed model is developed using the analysis results from the Modified Compression Field Theory (MCFT). The results from the proposed model, which uses simplified equations, are compared with the column test data.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 춘계학술발표회 논문집(I)
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• pp.482-485
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• 2006

The response of a reinforced concrete element under cyclic shear is characterized by the hysteretic loops of the shear stress-strain curves. These hysteretic loops can exhibit strength deterioration, stiffness degradation, and a pinched shape. Recent tests have shown that the orientation of steel grids in RC shear elements has a strong effect on the "pinching effect" in the post-yield hysteretic loops. When the steel grid was set at a 45 degree angle to the shear plane, there was no pinching effect and no strength deterioration. However, when the steel grid was set parallel to the shear plane, there was a severe pinching effect and severe strength deterioration with increasing shear strain magnitude. In this paper, two RC elements subjected to revered cyclic shear stresses are considered to study the effect of the steel grid orientation. The presence and absence of the pinching mechanism in the post-yield shear hysteretic loops is studied using the Rotating Angle Softened Truss Model (RA-STM) theory.

• 한국초전도ㆍ저온공학회논문지
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• 제17권3호
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• pp.13-17
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• 2015

In superconducting coil applications particularly in wet wound coils, coated conductor (CC) tapes are subjected to different type of stresses. These include hoop stress acting along the length of the CC tape and the Lorentz force acting perpendicular to the CC tape's surface. Since the latter is commonly associated with delamination problem of multi-layered CC tapes, more understanding and attention on the delamination phenomena induced in the case of coil applications are needed. Difference on the coefficient of thermal expansion (CTE) of each constituent layer of the CC tape, the bobbin, and the impregnating materials is the main causes of delamination in CC tapes when subjected to thermal cycling. The CC tape might also experience cyclic loading due to the energizing scheme (on - off) during operation. In the design of degradation-free superconducting coils, therefore, characterization of the delamination behaviors including mechanism and strength in REBCO CC tapes becomes critical. In this study, transverse tensile tests were conducted under different loading conditions using different size of upper anvils on the GdBCO CC tapes. The mechanical and electromechanical delamination strength behaviors of the CC tapes under transverse tensile loading were examined and a two-parameter Weibull distribution analysis was conducted in statistical aspects. As a result, the CC tape showed similar range of mechanical delamination strength regardless of cross-head speed adopted. On the other hand, cyclic loading might have affected the CC tape in both upper anvil sizes adopted.

• 한국세라믹학회지
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• 제40권7호
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• pp.662-666
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• 2003

인공치관용 알루미나-유리 복합체를 유사 구강분위기인 인공타액 하에서 200-1000 N의 하중 조건으로 $10^{6}$ 횟수까지 헤르찌안 반복하중 피로특성을 조사하였다. 200 N의 하중에서 $10^{6}$까지 반복피로 실험결과, 강도 저하 및 균열 현상은 관찰되지 않았다. 하중이 1000 N으로 증가함에 따라 링 균열에서 방사상 균열로 전이되었을 때 급격한 강도 저하 현상이 발생하였다. 강도 저하 현상은 유사 구강 분위기하에서 반복 하중 접촉 시 발생한 방사상 균열을 통해 침투한 인공타액과 유리상의 화학적 반응으로 더욱 가속화 되었다.