• 토지주택연구
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• 제11권2호
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• pp.95-104
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• 2020

This study aims to explore a purely mechanistic pavement analysis approach where viscoelasticity and fracture of asphalt mixtures are considered to accurately predict deformation and damage behavior of flexible pavements. To do so, the viscoelastic and fracture properties of designated pavement materials are obtained through experiments and a fully mechanistic damage analysis is carried out using a finite element method (FEM). While modeling crack development can be done in various ways, this study uses the cohesive zone approach, which is a well-known fracture mechanics approach to efficiently model crack initiation and propagation. Different pavement configurations and traffic loads are considered based on three main functional classes of roads suggested by FHWA i.e., arterial, collector and local. For each road type, three different material combinations for asphalt concrete (AC) and base layers are considered to study damage behavior of pavement. A concept of the approach is presented and a case study where three different material combinations for AC and base layers are considered is exemplified to investigate progressive damage behavior of pavements when mixture properties and layer configurations were altered. Overall, it can be concluded that mechanistic pavement modeling attempted in this study could differentiate the performance of pavement sections due to varying design inputs. The promising results, although limited yet to be considered a fully practical method, infer that a few mixture tests can be integrated with the finite element modeling of the mixture tests and subsequent structural modeling of pavements to better design mixtures and pavements in a purely mechanistic manner.

• Structural Engineering and Mechanics
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• 제68권6호
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• pp.747-760
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• 2018

In the present study, a methodology for developing fragilities of arch concrete dams to assess their performance against seismic hazards is introduced. Firstly, the probability risk and fragility curves are presented, followed by implementation and representation of the way this method is used. Amirkabir arch concrete dam was subjected to non-linear dynamic analyses. A modified three dimensional rotating smeared crack model was used to take the nonlinear behavior of mass concrete into account. The proposed model considers major characteristics of mass concrete. These characteristics are pre-softening behavior, softening initiation criteria, fracture energy conservation, suitable damping mechanism and strain rate effect. In the present analysis, complete fluid-structure interaction is included to account for appropriate fluid compressibility and absorptive reservoir boundary conditions. In this study, the Amirkabir arch concrete dam is subjected to a set of 8 three-component earthquakes each scaled to 10 increasing intensity levels. Using proposed nonlinear smeared crack model, nonlinear analysis is performed where the structure is subjected to a large set of scaled and un-scaled ground motions and the maximum responses are extracted for each one and plotted. Based on the results, fragility curves were plotted according to various and possible damages indexes. Discrete damage probabilities were calculated using statistical methods for each considered performance level and incremental nonlinear analysis. Then, fragility curves were constructed based on the lognormal distribution assumption. Two damage indexes were introduced and compared to one another. The results indicate that the dam has a proper stability under earthquake conditions at MCE level. Moreover, displacement damages index is more conservative and impractical in the fragility analysis than tensional damage index.

• 콘크리트학회지
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• 제2권1호
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• pp.91-100
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• 1990

초기 균열을 갖는 대부분의 구조 부재의 있어서, 부재의 크기가 중가함에 따라 일반적으로 강도가 감소하는 현상을 보인다. 이를 크기효과라고 하며, 특히 콘크리트는 유리, 철과같은 구조 재료와는 달리 초기균열이 없는 경우에도 이러한 크기효과를 나타낸다는 것이 실험에 의해 나타나고 있다. 기존의 크기효과 법칙을 따르면 크기가 배우 큰 콘크리트 부재는 응력을 거의 받을 수 없는 것으로 나타나나, 실험에 의하면 강도의 감소율이 현저하게 감소되어 기존의 크기효과 법칙과 큰 차이를 보인다. 따라서, 본 논문에서는 콘크리트 구조물의 비선형 파괴역학에 근거하여 비유사 균열이 존재하는 경우에 대한 크기효과식을 유도하여 기존의 할열인장강도, 전단강도 및 압축강도 실험치에 대한 회귀분석을 통하여 보다 나은 모델식을 제시하였다.

• Advances in concrete construction
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• 제12권6호
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• pp.451-459
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• 2021

The mechanical behaviors and chloride resistance performance of fiber reinforced cementitious composites (FRCC) with hybrid polyethylene (PE) and steel fiber (in total 2% by volume) were investigated. Based on micro-mechanics and fracture mechanics, the reason why the tensile strain capacity of FRCC changed obviously was obtained. Besides, the effects of the total surface area of fiber in FRCC on compressive strength and chloride content were clarified. It is found that the improvement of the tensile strain capacity of FRCC with hybrid fiber is attributed to the growth of strain-hardening performance index (the ratio of complementary energy to crack tip toughness). As the total surface area of fiber related with the interfacial transition zone (ITZ) between fiber and matrix increases, compressive strength decreases obviously. Since the total surface area of fiber is small, the chloride resistance performance of FRCC with hybrid PE and steel fiber is better than that of FRCC containing only PE fiber.

• Advances in concrete construction
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• 제7권4호
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• pp.241-247
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• 2019

In this paper the effect of bedding layer on the failure mechanism of rock in direct shear test has been investigated using particle flow code, PFC. For this purpose, firstly calibration of pfc2d was performed using Brazilian tensile strength. Secondly direct shear test consisting bedding layer was simulated numerically. Thickness of layers was 10 mm and rock bridge length was 10 mm, 40 mm and 60 mm. In each rock bridge length, bedding layer angles changes from $0^{\circ}$ to $90^{\circ}$ with increment of $15^{\circ}$. Totally 21 models were simulated and tested. The results show that two types of cracks develop within the model. Shear cracks and tensile cracks. Also failure pattern is affected by bridge length while shear strength is controlled by failure pattern. It's to be noted that bedding layer has not any effect on the failure pattern because the layer interface strength is too high.

• 콘크리트학회논문집
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• 제17권5호
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• pp.709-716
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• 2005

이 연구는 국내에서 상용 중인 재료를 이용하여 고인성 섬유복합 모르타르를 개발하고자 함에 목적이 있으며, 고인성 섬유복합 모르타르를 개발하기 위해서는 모르타르 매트릭스의 파괴역학(fracture mechanics)적 특성과 섬유-모르타르 경계 면의 마이크로역학(micromechanics)적 특성을 파악하여야 한다. 특히 시멘트계 재료(cementitious materials)의 역학적 특성에 가장 큰 영향을 미치는 물-시멘트비(water cement ratio)에 대한 연구에 초점을 맞추었으며, 3가지의 물-시멘트비에 대하여 섬유의 인발실험(fiber pullout test)과 모르타르의 쐐기쪼갬실험(wedge splitting test)을 수행하였고 이를 통하여 모르타르 매트릭스와 섬유-매트릭스 경계면(interface)의 역학적인 특성을 파악하였다. 이러한 연구에 의하여 결정된 섬유-매트릭스 경계면의 마이크로역학적 특성과 모르타르의 역학적 특성을 이용하여 물-시멘트비 범위 및 재료의 기본 배합을 제시하였고 또한 마이크로역학과 안정상태 균열이론(steady-state cracking theory)을 배경으로 하여 1축인장 하에서 인장변형률 경화거동을 나타내는 고인성 섬유복합 모르타르를 개발하였다. 개발된 재료는 1축인장 하에서 변형률 경화거동을 나타내었으며, 변형능력은 최대 2.2% 이었다. 이와 같은 높은 변형 능력은 일반 콘크리트(또는 모르타르)의 약 100배에 해당된다. 또한 압축하에서는 압축강도 이후 응력-변형률 곡선이 완만하게 감소하는 연성파괴의 형태를 나타내었으며 28일의 압축강도는 보통강도 콘크리트의 강도에 해당되는 26MPa, 34MPa인 것으로 측정되었다.

• 콘크리트학회논문집
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• 제16권3호
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• pp.375-382
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• 2004

콘크리트의 압축강도는 콘크리트 구조물의 설계 시에 재료상수로 사용되는데 이 값의 산정에 사용되는 공시체의 크기 및 형상이 각 나라마다 다르므로 현재까지도 문제가 되고 있다. 본 연구에서는 콘크리트 공시체의 압축강도에 공시체의 크기와 형상이 미치는 영향을 파괴역학적 이론과 실험을 통하여 검토하였다. 콘크리트의 두 가지 파괴모드 중의 하나인 모드 I에 대한 실험이 원주공시체, 입방체, 그리고 각주를 이용하여 수행되었다 먼저 원주공시체, 입방체와 각주 자체의 크기효과와 이들 사이의 형상효과를 살펴본 후, 공시체의 크기, 형상, 및 타설방향에 대한 압축강도의 상호관계에 대하여 검토하였다. 또한, 입방체와 각주에 대하여 타설방향이 압축강도에 미치는 영향을 검토하였다.

• Advances in concrete construction
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• 제3권1호
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• pp.15-37
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• 2015

Ongoing efforts for improved fracture toughness of engineered cementitious materials address the inherent brittleness of the binding matrix at several different levels of the material's geometric scale through the addition of various types of reinforcing fibers. Crack control is required for crack widths that cover the entire range of the grain size spectrum of the material, and this dictates the requirement of hybrid mixes combining fibers of different size (nano, micro, macro). Use of Carbon Nano-Tubes (CNT) and Carbon Nano-Fibers (CNFs) as additives is meant to extend the crack-control function down to the nanoscale where cracking is believed to initiate. In this paper the implications of enhanced toughness thus attained at the material nanostructure are explored, with reference to the global smeared constitutive properties of the material, through consistent interpretation of the reported experimental evidence regarding the behavior of engineered cementitious products to direct and indirect tension.

• 한국공작기계학회논문집
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• 제15권5호
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• pp.97-103
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• 2006

A meso-scale analysis method using the natural element method, which is a kind of meshless method, is proposed for the analysis of material damage of brittle microcracking solids such as ceramic materials, concrete and rocks. The microcracking is assumed to occur along Voronoi edges in the Voronoi diagram generated using the nodal points as the generators. The mechanical effect of microcracks is considered by controlling the material constants in the neighborhood of the microcracks. The macro elastic moduli of anisotropic as well as isotropic solids containing a number of randomly distributed microcracks are calculated in order to demonstrate the validity of the proposed method.

• Structural Engineering and Mechanics
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• 제84권2호
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• pp.253-268
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• 2022

Using non-destructive Acoustic Emission (AE) and optical Digital Image Correlation (DIC) methods, the moment-curvature behavior of steel and GFRP bars reinforced concrete beams under flexure was explored in this study. In the tension zone, laboratory studies were carried out on steel-RC and GFRP-RC beams with varying percentages of longitudinal reinforcement ratios of 0.33 %, 0.52%, and 1.11%. The distinct mechanism of cracking initiation and fracture progression of failure in steel-RC and GFRP-RC beams were effectively correlated and picked up using AE waveform characteristics of the number of AE hits and their amplitudes, AE energy as well as average frequency and duration. AE XY event plots and longitudinal strain profiles using DIC gives an online and real-time visual display of progressive AE activity and strains respectively to efficaciously depict the crack evolution and their advancement in steel-RC and GFRP-RC beams. They display a close matching with the micro and macro-cracks visually observed in the actual beams at various stages of loading.