• 콘크리트학회지
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• 제8권2호
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• pp.119-127
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• 1996

본 연구는 철근콘크리트 부재의 3차원 재료적 비선형해석을 하기 위한 것이다. 콘크리트는 3축 비선형 응력-변형률 거동, 균열, 파쇄 및 변형률완화를 포함하는 3차원 16절점 고체요소를 사용하고, 철근은 변형률경화를 갖는 3차원 3절점 트러스요소를 사용한다. 균열 후 골재의 맞물림을 고려하는 유효전단계수를 평가하기 위해서 균열의 진행여부에 따른 전단유지계수를 도입하였으며, 수치해를 얻기 위해 수정뉴턴방법을 사용하였다. 가우스점에서의 해석결과는 그래픽으로 확인된다. 수치예제로서 Krahl의 철근콘크리트 보와 Hedgren의 철근콘크리트 쉘을 채택하여 해석결과와 비교하였다.

• 대한토목학회논문집
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• 제32권3C호
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• pp.113-120
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• 2012

진주 잔류토 사면의 실제 붕괴사례에 대한 해석을 수행하였다. 강우시 침투로 인하여 불포화층에서 유효응력과 전단 강도가 감소하여 안전율이 저하된다. 본 연구에서는 함수특성곡선을 이용하여 흡수응력에 기반한 유효응력을 산정하였다. 대상 현장에서 채취한 시료로부터 함수특성곡선, 투수계수, 전단강도와 관련한 불포화 물성들을 획득하였다. 실제 강우에 대한 불포화층의 침투해석을 수행하고 사면 지층의 간극수압 분포를 구할 수 있었다. 유한요소 응력장에서 탄성 해석으로 지층내 전응력을 계산하고 활동면에 작용하는 전단응력의 분포를 계산하였다. 활동면에 작용하는 흡수응력 및 유효응력을 산정하여 전단강도를 평가할 수 있었다. 이로부터 강우에 따른 안전율을 계산하였으며, 실제 강우에 의하여 사면이 활동이 일어나는 것을 모의할 수 있었다. 또한 활동면에서 흡수응력이 증가하고 유효응력이 감소하는 동시에 전단강도가 감소하는 것을 추적할 수 있었다.

• Structural Engineering and Mechanics
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• 제83권2호
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• pp.179-193
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• 2022

The shear behaviour of reinforced concrete members has been studied over the past decades by various researchers, and it can be simulated by analysing shear panel elements which has been regarded as a basic element of reinforced concrete members subjected to in-plane biaxial stresses. Despite various experimental studies on shear panel element which have been conducted so far, there are still a lot of uncertainties related to what influencing factors govern the shear behaviour and affect failure mechanism in reinforced concrete members. To identify the uncertainties, a finite element analysis can be used, which enables to investigate the impact of specific variables such as the reinforcement ratio, the shear retention factor, and the material characteristics including aggregate interlock, tension stiffening, compressive softening, and shear behaviour at the crack surface. In this study, a non-linear probabilistic analysis was conducted on reinforced concrete panels using a finite element method optimized for reinforced concrete members and advanced sampling techniques so that probabilistic analysis can be performed effectively. Consequently, this study figures out what analysis methodology and input parameters have the most influence on shear behaviour of reinforced concrete panels.

• Computers and Concrete
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• 제12권4호
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• pp.565-583
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• 2013

Existing numerical models for strain-hardening cement-based composites (SHCC) are short of providing sufficiently accurate solutions to the failure patterns of coupling beams of different designs. The objective of this study is to develop an effective model that is capable of simulating the nonlinear behavior of SHCC coupling beams subjected to cyclic loading. The beam model proposed in this study is a macro-scale plane stress model. The effects of cracks on the macro-scale behavior of SHCC coupling beams are smeared in an anisotropic model. In particular, the influence of the defined crack orientations on the simulation accuracy is explored. Extensive experimental data from coupling beams with different failure patterns are employed to evaluate the validity of the proposed SHCC coupling beam models. The results show that the use of the suggested shear stiffness retention factor for damaged SHCC coupling beams is able to effectively enhance the simulation accuracy, especially for shear-critical SHCC coupling beams. In addition, the definition of crack orientation for damaged coupling beams is found to be a critical factor influencing the simulation accuracy.

• Computers and Concrete
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• 제8권6호
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• pp.735-755
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• 2011

The capability of a multi-directional fixed smeared crack constitutive model to simulate the flexural/punching failure modes of fiber reinforced concrete (FRC) laminar structures is discussed. The constitutive model is implemented in a computer program based on the finite element method, where the FRC laminar structures were simulated according to the Reissner-Mindlin shell theory. The shell is discretized into layers for the simulation of the membrane, bending and out-of-plane shear nonlinear behavior. A stress-strain softening diagram is proposed to reproduce, after crack initiation, the evolution of the normal crack component. The in-plane shear crack component is obtained using the concept of shear retention factor, defined by a crack-strain dependent law. To capture the punching failure mode, a softening diagram is proposed to simulate the decrease of the out-of-plane shear stress components with the increase of the corresponding shear strain components, after crack initiation. With this relatively simple approach, accurate predictions of the behavior of FRC structures failing in bending and in shear can be obtained. To assess the predictive performance of the model, a punching experimental test of a module of a façade panel fabricated with steel fiber reinforced self-compacting concrete is numerically simulated. The influence of some parameters defining the softening diagrams is discussed.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2010년도 추계 학술발표회 2차
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• pp.68-75
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• 2010

Around the Nakdong River which is one part of the repairing business of 4 Grand Rivers currently being constructed, sandy ground is distributed throughout the wide area. Many civil engineering structures such as small and medium sized dams, flood control basins, and redevelopment of reservoirs and retention reservoirs are scheduled to be constructed, so the prevention measures for liquefaction are surely needed. To identify such liquefaction, a lot of factor affecting the strength of liquefaction were studied through laboratory investigation. Most of the conducted study was about clean sands, but in the case of the real ground the sand can exist not in the clean conditions but in the conditions mostly including sand of fine grained soil. The sand of fine grained soil has become a significant factor to assess liquefaction because many cases of liquefaction happened in the silty and clayer soil. In this study, un-drained tests of plasticity index of fine grained particles were conducted with the sands from Nakdong River. In result, the study shows that dynamic shear strength characteristics differ according to the plasticity index.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2005년도 춘계 학술발표회 논문집
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• pp.433-439
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• 2005

This paper describes a reinforced concrete crack model, which utilizes a strain decomposition technique. The strain decomposition technique enables the explicit inclusion of physical behavior across the cracked concrete surface such as aggregate interlock and dowel action rather than intuitively defining the shear retention factor. The proposed concrete crack model is integrated into the commercial finite element software ABAQUS shell elements through a user-supplied material subroutine. The FE results have been compared to experimental results reported by other researchers. The proposed bridge FE model is capable of predicting the initial cracking load level, the ultimate load capacity, and the crack pattern with good accuracy.

• 대한토목학회논문집
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• 제13권5호
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• pp.99-107
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• 1993

본 논문에서는 콘크리트 균열 사이의 인장강성 효과를 고려한 임의의 기하하적 형상을 갖는 철근 콘크리트 쉘을 해석하기 위하여 재료비선형 유한요소 프로그램을 작성하였다. 본 논문은 연속적인 컴퓨터 해석으로 탄성, 비탄성 및 극한 범위에서의 철근과 콘크리트의 응력은 물론, 하중-변위 응답과 균열전파를 추적할 수 있었다. 골재억물림과 철근의 다울작용을 포함하는 유효전단계수를 평가하기 위하여 균열상태의 전단유지계수를 도입하였다. 콘크리트는 인장에서는 취성으로 압축에서는 탄소성으로 가정하였다. 콘크리트의 소성거동은 Drucker-Prager 항복기준과 결합유동법칙에 따르는 것으로 가정하였다. 철근은 Von Mises 항복기준으로 가정하였으며 등가의 두께를 가지는 철근층으로 모델화 하였다. 수치해석을 위하여는 증분형접선강성도 방법을 사용하였다. 수치예제를 제시하여 본 연구결과를 Hedgren의 실험 결과와 Lin의 수치해석과 비교하였다.

• Composites Research
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• 제36권4호
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• pp.259-263
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• 2023

This study investigated the open hole tensile (OHT) properties of carbon fiber/epoxy composites and compared them to bolt joint tensile (BJT) properties. The net nominal modulus and strength (1376 MPa) were found to be higher than the gross nominal strength (1041 MPa), likely due to increasing hole size. The OHT and BJT specimens exhibited similar stiffness, as expected without bolt rotation causing secondary bending. OHT specimens experienced a sharp drop in stress indicating unstable crack propagation, delamination, and catastrophic failure. BJT specimens failed through shear out on the bolt side and bearing failure on the nut side, involving fiber kinking, matrix splitting, and delamination, resulting in lower strength compared to OHT specimens. The strength retention of carbon fiber/epoxy composites with open holes was 66%. Delamination initiation at the hole's edge caused a reduction in the stress concentration factor. Filling the hole with a bolt suppressed this relieving mechanism, leading to lower strength in BJT specimens compared to OHT specimens. Bolt joint efficiency was calculated as 15%. The reduction in strength in bolted joints was attributed to fiber-matrix splitting and delamination, aligning with Hart Smith's bolted joint efficiency diagram. These findings contribute to materials selection and structural reliability estimation for carbon fiber/epoxy composites. They highlight the behavior of open hole and bolt joint configurations under tensile loading, providing valuable insights for engineering applications.

• 한국지반환경공학회 논문집
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• 제16권1호
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• pp.45-53
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• 2015

본 연구에서는 불포화토에 대한 압력판 추출시험을 수행하여 함수특성곡선을 구하고 불포화토의 삼축압축시험을 실시한 후, Geostudio 2007의 SEEP/W 해석 프로그램을 이용하여 부정류 침투해석을 수행하였으며, SLOPE/W 해석프로그램으로 비탈면 안정성을 검토하였다. 그 결과 모관흡수력 증가에 따라 순체적응력과 축차응력이 증가하고 겉보기점착력도 선형적으로 증가함으로 써 전단강도가 증가함을 알 수 있었다. 강우침투해석 결과 높은 음의 간극수압에서는 적은 강우량에도 간극수압의 증가폭이 크게 나타났고, 일정깊이 이하의 심도에서 지하수위의 상승을 제외하면 강우의 영향을 받지 않음을 알 수 있었다. 비탈면의 파괴양상과 동일한 단면으로 파괴면을 일정하게 고정시켜 안정 해석한 결과 실제로 비탈면 파괴 시에 안전율이 1.0 이하로 낮아지는 것을 확인할 수 있었다.