• Computers and Concrete
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• 제22권3호
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• pp.291-303
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• 2018

As the concept of "sponge city" is proposed, the pervious concrete for permeable pavement has been widely used in pavement construction. This paper aims at investigating the dynamic behavior and energy evolution of pervious concrete under impact loading. The dynamic compression and split tests are performed on pervious concrete by using split Hopkinson pressure bar equipment. The failure criterion on the basis of incubation time concept is used to analyze the dynamic failure. It is demonstrated that the pervious concrete is of a strain rate sensitive material. Under high strain rate loading, the dynamic strength increases while the time to failure approximately decreases linearly as the strain rate increases. The predicted dynamic compressive and split tensile strengths based on the failure criterion are in accordance with the experimental results. The total damage energy is found to increase with the increasing of strain rate, which means that more energy is needed to produce irreversible damage as loading rate increases. The fractal dimensions are observed increases with the increasing of impact loading rate.

• Structural Engineering and Mechanics
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• 제75권5호
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• pp.559-569
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• 2020

In the present study, the fracture toughness of U-shaped notches made of aluminum alloy Al7075-T6 under combined tension/out-of-plane shear loading conditions (mixed mode I/III) is studied by theoretical and experimental methods. In the experimental part, U-notched test samples are loaded using a previously developed fixture under mixed mode I/III loading and their load-carrying capacity (LCC) is measured. Then, due to the presence of considerable plasticity in the notch vicinity at crack initiation instance, using the Equivalent Material Concept (EMC) and with the help of the point stress (PS) and mean stress (MS) brittle failure criteria, the LCC of the tested samples is predicted theoretically. The EMC equates a ductile material with a virtual brittle material in order to avoid performing elastic-plastic analysis. Because of the very good match between the EMC-PS and EMC-MS combined criteria with the experimental results, the use of the combination of the criteria with EMC is recommended for designing U-notched aluminum plates in engineering structures. Meanwhile, because of nearly the same accuracy of the two criteria and the simplicity of the PS criterion relations, the use of EMC-PS failure model in design of notched Al7075-T6 components is superior to the EMC-MS criterion.

• Nuclear Engineering and Technology
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• 제36권4호
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• pp.316-326
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• 2004

The $40\%$ of wall criterion, which is generally used for the plugging of steam generator tubes, is applied only to a single crack. In a previous study, a total number of 9 failure models were proposed to estimate the local failure of the ligament between cracks, and the optimum coalescence model of multiple collinear cracks was determined among these models. It is, however known that parallel axial cracks are more frequently detected than collinear axial cracks during an in-service inspection. The objective of this study is to determine the plastic collapse model that can be applied to steam generator tubes containing two parallel axial through-wall cracks. Three previously proposed local failure models were selected as the candidates. Subsequently, the interaction effects between two adjacent cracks were evaluated to screen them. Plastic collapse tests for the plate with two parallel through-wall cracks and finite element analyses were performed to determine the optimum plastic collapse model. By comparing the test results with the prediction results obtained from the candidate models, a COD base model was selected as an optimum model.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2001년도 봄 학술발표회 논문집
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• pp.102-109
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• 2001

In order to take account of the statistical properties of probability variables used in the structural analysis, the conventional approach using the safety factor based on past experience usually estimated the safety of a structure. The real structures could only be analyzed with the error in estimation of loads, material characters and the dimensions of the members. But the errors should be considered systematically in the structural analysis. Structural safety could not precisely be appraised by the traditional structural design concept. Recently, new approach based on the probability concept has been applied to the assessment of structural safety using the reliability concept. Thus, the computer program by the Probabilistic FEM is developed by incorporating the probabilistic concept into the conventional FEM method. This paper estimated for the reliability of a plane stress structure by Advanced First-Order Second Moment method using von Mises, Tresca and Mohr-Coulomb failure criterions. The reliability index and failure probability of attained by the Monte Carlo Simulation method with the von Mises criterion were same as PFEM, but the Monte Carlo Simulation were very time-consuming. The variance of member thickness and load could influence the reliability and failure probability most sensitively among the design variables from the results of the parameter analysis. And proper failure criterion must be used to design safely.

• Computers and Concrete
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• 제31권4호
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• pp.307-314
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• 2023

In this paper we back-analyze a failure event of a 9 m high concrete cantilever wall subjected to earth loading. Granular soil was deposited into the space between the wall and a nearby rock slope. The wall segments were not designed to carry lateral earth loading and collapsed due to excessive bending. As many geotechnical programs rely on the Mohr-Coulomb (MC) criterion for elastoplastic analysis, it is useful to apply this failure criterion to the concrete material. Accordingly, the back-analysis is aimed to search for the suitable MC parameters of the concrete. For this study, we propose a methodology for accelerating the back-analysis task by automating the numerical modeling procedure and applying a machine-learning (ML) analysis on FE model results. Through this analysis it is found that the residual cohesion and friction angle have a highly significant impact on model results. Compared to traditional back-analysis studies where good agreement between model and reality are deemed successful based on a limited number of models, the current ML analysis demonstrate that a range of possible combinations of parameters can yield similar results. The proposed methodology can be modified for similar calibration and back-analysis tasks.

• 대한토목학회논문집
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• 제8권2호
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• pp.99-107
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• 1988

과압밀점토(過壓密粘土)에 대한 일련의 입방형삼축시험(立方型三軸試驗)이 실시되었다. 삼축시험(三軸試驗)은 세 주응력(主應力)을 서로 독립적으로 제어시킬 수 있는 입방체형삼축시험기(立方體型三軸試驗機)를 사용하여 실시되었다. 점토공시체(粘土供試體)로는 현장(現場)에서 직접 채취된 자연시료(自然試料)를 삼축(三軸) chamber 내(內)에서 과압밀비(過壓密比)가 5가 되게 만든 입방체형공시체(立方體型供試體)가 사용되었으며 본연구결과(本硏究結果), 중간주응력(中間主應力)은 과압밀점토(過壓密粘土)의 응력변형률(應力變形率), 비배수강도(非排水强度), 유효강도(有效强度), 유효내부마찰각(有效內部摩擦角) 및 간극압(間隙壓)에 큰 영향을 미치고 있음이 구명(究明)되었다. 중간주응력(中間主應力)이 최소주응력(最小主應力)과 같지 않은 경우의 과압밀점토파괴강도(過壓密粘土破壞强度)는 Mohr-Coulomb 파괴규준(破壞規準)에 의하여 과소평가(過小評價)되나 Lade규준(規準)에 의하여는 대단히 양호하게 산정된다. 또한 과압밀점토(過壓密粘土)의 비배수강도(非排水强度)는 Tresca규준(規準)에 일치하지 않는다.

• 한국지반공학회지:지반
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• 제6권3호
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• pp.65-76
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• 1990

압축성 모래의 3차원 전단강도 특성을 밝히기 위하여 육면체 시료로 성형하여 세 주응력을 각기 독립 적으로 조절하여 일련의 압밀배수 및 압밀비배수시험을 실시하였다. 그 결과 중간주응력은 파괴강도에 큰 영향을 미치고 있으며 파괴규준은 유효응력 해석을 할 경우 중간주덕력의 영향을 받고있다. 측정된 유효내부마찰각은 중간주응력의 상대적 크기를 나타내는 계수 b(=(o2-o3)/(o1-o3)값이 0인 삼축압축상태에서 최소치가 되고 점진적으로 b값의 증가와 더불어 담가하며 배수, 비배수시험 결과를 동-정팔면체면에 투영하여 얻은 응력으로 조정된 유효내부마찰각은 같은 b값에서 서로 일치하고 있다. 비배수시험에 있어서 전응력으로 해석한 결과는 Tresca의 파괴규준과 잘 일치하고 있다. 정팔면체면에 유효응력으로 표시된 파양면은 배수, 비배수시험결과가 같은 값을 가지고 Lade의 파양규준에 근접함을 보여준다.

• Geomechanics and Engineering
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• 제11권2호
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• pp.253-267
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• 2016

The stability of surrounding rock will be poor when the tunnel is excavated through nearly horizontal stratum. In this paper, the instability mechanism of local nearly horizontal stratum in super-large section and deep buried tunnel is revealed by the analysis of the macro failure and micro fracture. A structural model is proposed to explain the mechanics of surrounding rock collapse under the action of stress redistribution and shed light on the macroscopic analytical approach of the stability of surrounding rock. Then, some highly effective formulas applied in the tunnel engineering are developed according to the theory of mixed-mode micro fracture. And well-documented field case is made to demonstrate the effectiveness and accuracy of the proposed analytical methods of mixed-mode fracture. Meanwhile, in order to make the more accurate judgment about yield failure of rock mass, a series of comprehensive failure criteria are formed. In addition, the relationship between the nonlinear failure criterion and $K_I$ and $K_{II}$ of micro fracture is established to make the surrounding rock failure criterion more comprehensive and accurate. Further, the influence of the parameters related to the tension-shear mixed-mode fracture and compression-shear mixed-mode fracture on the propagation of rock crack is analyzed. Results show that ${\sigma}_3$ changes linearly with the change of ${\sigma}_1$. And the change rate is related to ${\beta}$, angle between the cracks and ${\sigma}_1$. The proposed simple analytical approach is economical and efficient, and suitable for the analysis of local nearly horizontal stratum in super-large section and deep buried tunnel.

• 터널과지하공간
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• 제25권3호
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• pp.284-292
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• 2015

일반화된 Hoek-Brown 파괴함수는 GSI 지수를 이용하여 현장 암반의 강도정수를 결정하는 경험적 비선형 파괴조건식으로서 오늘날 다양한 암반공학적 설계에 널리 활용되고 있다. 그러나 여전히 많은 암반공학 전문가들이 암반의 강도를 마찰각과 점착력으로 표현하는 것에 익숙하다. 또한 거의 대부분의 암반안정성해석 수치해석 프로그램이 간편한 선형 Mohr-Coulomb 파괴조건식을 채택하고 있다. 이에 따라 Hoek-Brown 파괴함수를 Mohr-Coulomb 파괴함수 틀에서 이해하는 방법의 제시가 필요하다. 이 연구에서는 한계해석 상계정리를 적용하여 유도된 줄기초의 지지력 공식을 활용하여 Hoek-Brown 파괴조건을 따르는 천부 암반의 등가마찰각과 등가점착력을 계산하는 방법을 제안하였다. 일반화된 Hoek-Brown 파괴함수가 내포하는 접선점착력-접선마찰각 관계식을 이용하여 지지력 상계해를 마찰각의 함수로 표현한 후 최소 지지력 조건의 마찰각을 탐색하여 이를 등가마찰각으로 간주하였다. 제안된 방법을 활용하여 GSI, $m_i$, 교란계수 D가 등가마찰각과 등가점착력에 미치는 영향을 분석하였다.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2004년도 추계학술발표대회 논문집
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• pp.73-77
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• 2004

Failure predictions of composite single-lap bonded joints were performed considering both of composite adherend failure and bondline failure. An elastic-perfectly plastic model of adhesive and a delamination failure criterion are used. The failure prediction results such as failure mode and strength have very good agreements with the test results of joint specimens with various bonding methods and parameters. The influence of variations in the effective strength (that is, adhesion performance) and plastic behavior of adhesive on the failure characteristics of composite bonded joints are investigated numerically. The numerical results show that optimal joint strength is archived when adhesive and delamination failure occur in the same time.