• 지질공학
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• 제30권1호
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• pp.85-101
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• 2020

강도정수의 산정은 암반사면의 안정성 해석에 매우 중요하다. 강도정수를 결정하는 다양한 방법들이 여러 연구자들에 의하여 제안되었다. 암반사면의 안정성 해석을 위하여 강도정수 결정에 사용된 방법들의 빈도를 문헌조사를 통하여 조사하였다. 특히 파괴유형에 따른 강도정수 결정방법의 빈도수를 조사하였다. 사례연구를 통하여 암석과 불연속면의 점착력과 마찰각의 값을 조사하여 RMR값과 함께 제시하였다. 연구 결과에 의하면 점착력은 내부마찰각과 비교하여 상당히 큰 범위를 보였다. RMR은 점착력과는 상관관계를 보이지 않았으나 마찰각과는 뚜렷한 상관관계를 보였다. 파괴유형에 따라 강도정수 결정을 위하여 적절한 방법이 사용되어야 하며 문헌조사를 통하여 결과를 검증해야 한다. 향후 각 지역별로 역해석을 통하여 파괴가 발생한 사면에 대한 강도정수 자료가 축적된다면 강도정수 결정의 신뢰성이 향상될 것으로 기대한다.

• Advances in materials Research
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• 제13권4호
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• pp.299-319
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• 2024

Due to higher strength-to-weight ratio of composite laminates, they find uses in many weight-sensitive applications like aerospace, automobile and marine structures. From a reliability point of view, accurate prediction of failure of these structures is important. Due to the complexities in the manufacturing processes of composite laminates, there is a variation in the material properties and geometric parameters. Hence stochastic aspects are important while designing the composite laminates. Many existing works of composite laminate failure analysis are based on the deterministic approach but it is important to consider the randomness in the material properties, geometry and loading to predict accurate failure loads. In this paper the statistics of the ultimate failure load of the [0/θ]_s laminated composite plate (LCP) containing the edge crack and voids subjected to the tensile loading are presented in terms of the mean and coefficient of variance (COV). The objective is to better the efficacy of laminate failure by predicting the statistics of the ultimate failure load of LCP with random material, geometric and loading parameters. The stochastic analysis is done by using the extended finite element method (XFEM) combined with the second-order perturbation technique (SOPT). The ultimate failure load of the LCP is obtained by ply-by-ply failure analysis using the ply discount method combined with the Tsai-Wu failure criterion. The aim is to know the effect of the stacking sequence, crack length, crack angle, location of voids and number of voids on the mean and corresponding COV of the ultimate failure load of LCP is investigated. The results of the ultimate failure load obtained by the present method are in good agreement with the existing experimental and numerical results. It is observed that [0/θ]_s LCPs are very sensitive to the randomness in the crack length, applied load, transverse tensile strength of the laminate and modulus of elasticity of the material, so precise control of these parameters is important. The novelty of the present study is, the stochastic implementation in XFEM for the failure prediction of LCPs containing crack and voids.

• Geomechanics and Engineering
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• 제24권2호
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• pp.179-191
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• 2021

In this study, the strength and failure mechanism of red sandstones with combined defects were investigated by uniaxial compression tests on red sandstones with different crack angles using two-dimensional particle flow code numerical software, and their mechanical parameters and failure process were studied and analyzed. The results showed that the mechanical characteristics such as peak strength, peak strain, and elastic modulus of the samples with prefabricated combined defects were significantly inferior than those of the intact samples. With increasing crack angle from 15° to 60°, the weakening area of cracks increased, elastic modulus, peak strength, and peak strain gradually reduced, the total number of cracks increased, and more strain energy was released. In addition, the samples underwent initial brittle failure to plastic failure stage, and the failure form was more significant, leading to peeling phenomenon. However, with increasing crack angle from 75° to 90°, the crack-hole combination shared the stress concentration at the tip of the crack-crack combination, resulted in a gradual increase in elastic modulus, peak strain and peak strength, but a decrease in the number of total cracks, the release of strain energy reduced, the plastic failure state weakened, and the spalling phenomenon slowed down. On this basis, the samples with 30° and 45° crack-crack combination were selected for further experimental investigation. Through comparative analysis between the experimental and simulation results, the failure strength and final failure mode with cracks propagation of samples were found to be relatively similar.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 추계 학술발표회 제17권2호
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• pp.271-274
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• 2005

Existing strut-and-tie model cannot be applied to analysis of slender beams without shear reinforcement because shear transfer mechanism is not formed. In the present study, a new strut-and-tie model with rigid joint was developed. Basically, concrete strut is modeled as a frame element which can transfer shear force (or moment) as well as axial force. Employing Rankine failure criterion, failure strength due to shear-tension and shear-compression developed in compressive concrete strut was defined. For verification, various test specimens were analyzed and the results were compared with tests. The proposed strut-and-tie model predicted shear strength and failure displacement with reasonable precision, addressing the design parameters such as shear reinforcement, concrete compressive strength, and shear span ratio.

• Journal of Construction Engineering and Project Management
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• 제7권4호
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• pp.13-19
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• 2017

This study is based on the use and performance of bamboo reinforcements in construction of low-cost structures. This study investigated the physical and mechanical properties of bamboo reinforcements. Bamboo reinforced concrete beam specimens were tested with different reinforcement ratios and observed the load capacity, deflection and failure patterns. It was observed that, flexural strength of bamboo reinforced column is sufficient higher than plain cement concrete and comparable to steel reinforced concrete beams. Bamboo reinforced concrete columns with different reinforcement ratio also tested and observed the ultimate compressive strength and failure pattern. It found, all columns failed in a similar pattern due to crushing of concrete. According to cost analysis, bamboo reinforced beams and columns with moderate reinforcement ratio showed the best strength-cost ratio among plain cement concrete and steel reinforced concrete.

• Geomechanics and Engineering
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• 제5권5호
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• pp.419-445
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• 2013

This paper presents an experimental study on the influence of principal stress direction and magnitude of intermediate principal stress on the undrained stress-strain-strength behaviors of Bangkok Clay. The results of torsional shear hollow cylinder and advanced triaxial tests with various principal stress directions and magnitudes of intermediate principal stress on undisturbed Bangkok Clay specimens are presented. The analysis of testing results include: (i) stress-strain and pore pressure behaviors, (ii) stiffness characteristics, and (iii) strength characteristics. The results assert clear evidences of anisotropic characteristics of Bangkok Clay at pre-failure and failure conditions. The magnitude of intermediate principal stress for plane-strain condition is also investigated. Both failure surface and plastic potential in deviatoric plane of Bangkok Clay are demonstrated to be isotropic and of circular shape which implies an associated flow rule. It is also observed that the shape of failure surface in deviatoric plane changes its size, while retaining its circular shape, with the change in direction of major principal stress. Concerning the behavior of Bangkok Clay found from this study, the discussions on the effects of employed constitutive modeling approach on the resulting numerical analysis are made.

• Composites Research
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• 제29권2호
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• pp.66-72
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• 2016

고온에서 열화학적 분해 현상을 겪는 고분자 기지 복합재료는 기지 내부의 기공도가 급격히 증가한다. 기공의 생성은 재료의 탄성 계수와 파손 강도를 감소시키며, 기공 내부의 가스 압력은 재료의 열기계적 거동에 영향을 준다. 본 논문에서는 기지 내부에 많은 기공이 포함된 일방향 섬유 강화 복합재료의 이차원 대표 체적 요소를 설정하고 유한요소 해석을 수행하였다. 이를 통해 기공 상태에 따른 복합재료의 유효 탄성 계수, 기공 탄성 계수, 파손 강도 등을 산출하였다. 특히, 기지 재료의 특성에 많은 영향을 받는 섬유 수직 방향의 파손 강도가 원래 기지 강도보다 현격히 낮게 산출되며, 기공도가 증가함에 따라 지속적으로 떨어지는 경향을 확인하였다.

• Structural Engineering and Mechanics
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• 제24권2호
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• pp.137-154
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• 2006

The reliable pushover analysis of RC structures requires a realistic prediction of moment-curvature relations, which can be obtained by utilizing proper constitutive models for the stress-strain relationships of laterally confined concrete members. Theoretical approach of Mander is still a single stress-strain model, which employs a multiaxial failure surface for the determination of the ultimate strength of confined concrete. Alternatively, this paper introduces a simple and practical failure criterion for confined concrete with emphasis on introduction of significant modifications into the two-parameter Drucker-Prager model. The new criterion is only applicable to triaxial compression stress state which is exactly the case in the RC columns. Unlike many existing multi-parameter criteria proposed for the concrete fracture, the model needs only the compressive strength of concrete as an independent parameter and also implies for the influence of the Lode angle on the material strength. Adopting Saenz equation for stress-strain plots, satisfactory agreement between the measured and predicted results for the available experimental test data of confined normal and high strength concrete specimens is obtained. Moreover, it is found that further work involving the confinement pressure is still encouraging since the confinement model of Mander overestimates the ultimate strength of some RC columns.

• 한국지진공학회논문집
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• 제10권1호
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• pp.1-8
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• 2006

비내진 설계된 철근콘크리트 골조는 내진상세의 미확보로 인하여 전단파괴의 가능성이 있다. 이러한 전단파괴를 해석 모델링에 반영하기 위하여 Moehle과 ATC 40을 포함한 4개의 전단강도감소 모델을 선택하고 비교하였으며, 각 모델을 예제 건물에 적용하여 Push-over해석을 수행하였다. 해석용 예제 모델은 3층 규모로 하였으며 국내 콘크리트 설계기준에 따라 설계하였다. 전단강도 감소모델 비교 결과, Moehle의 모델은 NZSEE의 모델보다 전단내력을 작게 평가하고 ATC 40 모델에 비하여 휨 연성도에 따른 내력의 변동이 작으며, 대부분의 경우에 고찰된 모델들의 전단내력은 ACI 318의 공칭 전단강도보다 크게 나타남을 알 수 있었다. 예제 모델의 수치해석 비교 결과, 전단강도 감소모델에 따라 건물의 수평 저항 능력에 큰 차이가 나타나며, 전단스프링에 전단강도 감소를 고려한 모델에 비하여 ATC 40의 횡 소성 변형을 제한하는 모델을 사용하면 횡저항 능력을 과소평가하게 됨을 알 수 있었다.

• 터널과지하공간
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• 제24권4호
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• pp.289-296
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• 2014

압축공기에너지 및 고압 천연가스 등의 고압 유체의 지하저장을 위한 저장공동 상부 암반의 융기에 대한 안정성 검토를 위한 간이해석기법을 개발하고 그 적용사례를 소개하였다. 본 해석기법은 저장공동 상부에 원통형의 파괴모델을 가정하고 한계평형해석을 실시함으로써 융기에 대한 안전율을 계산한다. 원통형 파괴면에 작용하는 마찰저항력 계산에는 Mohr-Coulomb 강도기준식을 대신하여 Hoek-Brown 강도기준식을 적용함으로써 무결암의 강도특성 뿐만 아니라 암반 상태도 고려할 수 있도록 하였다. 다양한 암반 조건에서의 적용사례 및 암반 강도 정수의 민감도 분석 결과, 저장공동 상부 암반의 융기는 Mohr-Coulomb 강도기준식에 보다 민감함을 확인하였다.