• ETRI Journal
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• v.43 no.4
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• pp.694-701
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• 2021

Catastrophic events cause casualties, damage property, and lead to huge social impacts. To build common standards and facilitate international communications regarding disasters, the relevant authorities in social management rank them in subjectively imposed terms such as direct economic losses and loss of life. Terrorist attacks involving uncertain human factors, which are roughly graded based on the rule of property damage, are even more difficult to interpret and assess. In this paper, we collected 114 183 open-source records of terrorist attacks and used a machine learning method to grade them synthetically in an automatic and objective way. No subjective claims or personal preferences were involved in the grading, and each derived common factor contains the comprehensive and rich information of many variables. Our work presents a new automatic ranking approach and is suitable for a broad range of gradation problems. Furthermore, we can use this model to grade all such attacks globally and visualize them to provide new insights.

• International Journal of Highway Engineering
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• v.17 no.3
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• pp.49-58
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• 2015

PURPOSES : The use of environmentally friendly construction methods has been recently encouraged to reduce fuel consumption and the effects of global warming. For this purpose, the roller compacted concrete pavement (RCCP) construction method has been developed. RCCP is more environmentally friendly and economically efficient than general concrete by reducing the amount of CO2 generated through the application of a smaller amount of cement. RCCP has a number of advantages such as an easy construction method, low cost, high structural hydration performance, and aggregate interlocking. However, mix design standards and construction guidelines of RCCP are required for domestic application. In addition, a study on aggregate selection, which has an effect on the characteristics of RCCP, is necessary owing to a limited number of researches. Thus, the aggregate effect on the performance of RCCP in securing the required strength and workability was evaluated in consideration of domestic construction. METHODS : Sand and coarse aggregates of both 19mm and 13mm in maximum size were used in this study. Four types of aggregate gradations (s/a = 30%, 58%, and 70% for the sand and coarse aggregate of 19mm in maximum size, and s/a = 50% for a combination of the three types of aggregates) were set up to investigate the effects of the PCA band on the RCC characteristics. The conditions of s/a = 30% and 70% were evaluated to check the gradation effect outside of the recommended band. The conditions of s/a = 58% and 50% were used because they are the optimum combination of the two and three types of aggregates, respectively. RCCP gradation band was suggested gradation with a proper construction method of RCCP by synthetically comparing and analyzing the correlation of optimum water content, maximum dry density, and strength of requirements through its consistency and compaction test. RESULTS : The lower and upper limit lines are insufficient to secure a relatively strong development and workability compared to an aggregate gradation in the RCCP gradation band region. On the other hand, the line in the RCCP gradation band and the 0.45 power curve in the RCCP gradation band region were satisfactory, ensuring the required strength and workability. CONCLUSIONS : The suitable aggregate gradation on RCCP process should meet the RCCP gradation band area; however, fine particles passing through a #60 sieve do not need to be within the recommended gradation band because the influence of this region on such fine particles is small.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.10
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• pp.1500-1508
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• 2004

Stress and displacement fields for a crack propagating along interface between isotropic material and functionally gradient one with linear property gradation along X direction are developed. The stress and displacement fields are obtained from the complex function of steady plane motion for isotropic and functionally gradient material (FGM). The stresses and displacement in isotropic material of bimaterial are not influenced by nonhomogeneity, however, the fields in FCM are influenced by nonhomogeneity in the terms of higher order, n$\geq$3. When the nonhomogeneous parameter in FGM is zero, or in area close to crack tip, the fields are identical to those of isotropic-isotropic bimaterial. Using these stress components, the effects of nonhomogeneity on stresses are discussed.

• Journal of the Korean Society of Industry Convergence
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• v.9 no.1
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• pp.37-44
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• 2006

Stress and displacement fields of a Mode III crack propagating along the normal to gradient in an orthotropic functionally gradient materials (OFGM), which has (1) an exponential variation of shear modulus and density, and (2) linear variation of shear modulus with a constant density, are derived. The equations of motion in OFGM are developed and solution to the displacement and stress fields for a propagating crack at constant speed though an asymptotic analysis. The first three terms in expansion of stress and displacement are derived to explicitly bring out the influence of nonhomogeneity. When the FGM constant ${\zeta}$ is zero or $r{\rightarrow}0$, the fields for OFGM are almost same as the those for homogeneous orthotropic material. Using the stress components, the effects of nonhomogeneity on stress components are discussed.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.113-118
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• 2003

Stress and displacement fields for a propagating crack in a functionally gradient material (FGM) which has exponentially varying elastic and physical properties along the direction of the crack propagation, are derived. The equations of motion in nonhomogeneous material are developed using displacement potentials. The solutions to the displacement fields and the stress fields for a crack propagating at constant speed along the gradient are obtained through an asymptotic analysis. The influences of nonhomogeneity on the higher order terms of the stress fields are explicitly brought out. Using these stress components, isochromatic fringes around the stationary crack are generated at crack for different nonhomogeneity and the effects of nohonhomgeneity on these fringes are discussed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.3 s.246
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• pp.249-259
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• 2006

Stress and displacement fields of a propagating Mode III crack in an orthotropic functionally gradient material (OFGM), which has (1) linear variation of shear modulus with a constant density, and (2) an exponential variation of shear modulus and density, are derived. The equations of motion in OFGM are developed and solution to the displacement and stress fields fer a propagating crack at constant speed though an asymptotic analysis. The stress terms associated with $\gamma^{-1/2}\;and\;\gamma^{0}$ are not affected by the FGM constant $\zeta$ which is nonhomogeneous parameter, only on the higher order terms, the influences of nonhomogeneity on the stress are explicitly brought out. When the FGM constant $\zeta\;is\;zero\;or\;\gamma{\rightarrow}0$, the fields for OFGM are almost same as the those for homogeneous orthotropic material. Using the stress components, the effects of nonhomogeneity on stress components are discussed.

• Computers and Concrete
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• v.4 no.6
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• pp.425-436
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• 2007

This study is mainly focused on applying Fuller's ideal gradation curve to theoretically design blended ratio of all solid materials of a reactive powder mortar (RPM), also known as reactive powder concrete (RPC), with the aid of error function, and then to study the effect of fly ash/slag on the performance of RPM. The solid particle is assumed to be spherical particles. Then, the void volume of paste ($V_{\nu}$) and the paste content with specific quality can be obtained. As conclusion, under Fuller's ideal grading curve, the amount of fly ash/slag mixture is higher than that with silica fume along due to it better filled the void within solid particle and obtains higher packing density.

• Computers and Concrete
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• v.20 no.4
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• pp.503-509
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• 2017

In this study, fire-damaged concrete was investigated by a nonlinear resonance vibration (NRV) technique, in order to evaluate its residual material properties. For the experiments, five cubic concrete specimens were prepared and four of them were damaged at different temperatures using a furnace. With a thermal insulator wrapped at the sides of specimen, thermal gradation was applied to the samples. According to the peak temperatures and depths of the samples, nonlinearity parameters were calculated with the NRV technique before the tendency of the parameters was evaluated. In addition, compressive strength and dynamic elastic modulus were measured for each sample and a comparison with the nonlinearity parameter was carried out. Through the experimental results, the possibility of the NRV technique as a method for evaluating residual material properties was evaluated.

• Advances in materials Research
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• v.9 no.1
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• pp.33-48
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• 2020

With the use of differential quadrature method (DQM), forced vibrations and resonance frequency analysis of functionally graded (FG) nano-size beams rested on elastic substrate have been studied utilizing a shear deformation refined beam theory which contains shear deformations influence needless of any correction coefficient. The nano-size beam is exposed to uniformly-type dynamical loads having partial length. The two parameters elastic substrate is consist of linear springs as well as shear coefficient. Gradation of each material property for nano-size beam has been defined in the context of Mori-Tanaka scheme. Governing equations for embedded refined FG nano-size beams exposed to dynamical load have been achieved by utilizing Eringen's nonlocal differential law and Hamilton's rule. Derived equations have solved via DQM based on simply supported-simply supported edge condition. It will be shown that forced vibrations properties and resonance frequency of embedded FG nano-size beam are prominently affected by material gradation, nonlocal field, substrate coefficients and load factors.

• Journal of the Korea Concrete Institute
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• v.14 no.4
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• pp.623-629
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• 2002

Porous concrete enables water and air to pass through a firmly hardened material and allows required nutrients to reach roots of plants. The purpose of this study is to analyze void ratio, strength property and planting ability when using silica fume and fly ash, the change of aggregate gradation and ratio of paste to aggregate. The results of an experiment from the planting ability of the porous concrete to its influence on the compressive strength are reported in this paper. As a result of the experiment, the compressive strength is higher when the gradation of aggregate is smaller, and it also goes higher when the ratio of paste to aggregate gets larger. The planting ability of porous concrete is decided by the germination and the grass length of perennial ryegrass. The grass length of perennial ryegrass is longer when the gradation of aggregate is greater and the ratio of paste to aggregate gets smaller. Therefore the efficiency of planting goes through the perennial ryegrass is in compliance with the void ratio, aggregate gradation.