• Journal of the Korean Geotechnical Society
• /
• v.19 no.4
• /
• pp.167-178
• /
• 2003

Damage and overbreak of the remaining rock induced by blasting can not be avoided during tunnel construction which may result in either short-term or long-term tunnel instability. Therefore, in this paper, a methodology to take into account the effect of blast-induced damage in tunnel stability assessment is proposed. Dynamic numerical analysis was executed to evaluate damage and overbreak of the remaining rock for the most common blasting pattern in road tunnel. Rock damage was quantified by utilizing the damage variable factor which is adopted proposed in continuum damage mechanics. The damaged rock stiffness and the damaged failure criteria are used to consider the effect of rock damage in tunnel stability analysis. The damaged geological strength index of the damaged rock was newly proposed from the relationship between deformation modulus and geological strength index. Also the Hoek-Brown failure criteria of the damaged rock was obtained using the damaged geological strength index. Analysing the tunnel stability with the consideration of the blast-induced damage of remaining rock, it was found that the extend of plastic zone and deformation increased compared to the undamaged rock. Therefore the short-term or long-term tunnel stability will be threatened when the rock damage from blasting is ignored in the tunnel stability analysis.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2005.11a
• /
• pp.109-112
• /
• 2005

In this paper described is the basic concept of the Guideline for Post-earthquake Damage Assessment of RC buildings, revised in 2001, in Japan. This paper discusses the damage rating procedures based on the residual seismic capacity index R, the ratio of residual seismic capacity to the original capacity, that is consistent with the Japanese Standard for Seismic Evaluation of Existing RC Buildings, and their validity through calibration with observed damage due to the 1995 Hyogoken-Nambu (Kobe) earthquake. Good agreement between the residual seismic capacity ratio and damage levels was observed.

• Wind and Structures
• /
• v.21 no.6
• /
• pp.657-675
• /
• 2015

In this study, the feasibility of vibration-based damage detection methods for the wind turbine tower (WTT) structure is evaluated. First, a frequency-based damage detection (FBDD) is outlined. A damage-localization algorithm is visited to locate damage from changes in natural frequencies. Second, a mode-shape-based damage detection (MBDD) method is outlined. A damage index algorithm is utilized to localize damage from estimating changes in modal strain energies. Third, a finite element (FE) model based on a real WTT is established by using commercial software, Midas FEA. Several damage scenarios are numerically simulated in the FE model of the WTT. Finally, both FBDD and MBDD methods are employed to identify the damage scenarios simulated in the WTT. Damage regions are chosen close to the bolt connection of WTT segments; from there, the stiffness of damage elements are reduced.

• Structural Engineering and Mechanics
• /
• v.63 no.6
• /
• pp.751-760
• /
• 2017

In recent years, multifractal-based analysis methods have been widely applied in engineering. Among these methods, multifractal detrended cross-correlation analysis (MFDXA), a branch of fractal analysis, has been successfully applied in the fields of finance and biomedicine. For its great potential in reflecting the subtle characteristic among signals, a structural health monitoring (SHM) system based on MFDXA is proposed. In this system, damage assessment is conducted by exploiting the concept of multifractal theory to quantify the complexity of the vibration signal measured from a structure. According to the proposed algorithm, the damage condition is first distinguished by multifractal detrended fluctuation analysis. Subsequently, the relationship between the q-order, q-order detrended covariance, and length of segment is further explored. The dissimilarity between damaged and undamaged cases is visualized on contour diagrams, and the damage location can thus be detected using signals measured from different floors. Moreover, a damage index is proposed to efficiently enhance the SHM process. A seven-story benchmark structure, located at the National Center for Research on Earthquake Engineering (NCREE), was employed for an experimental verification to demonstrate the performance of the proposed SHM algorithm. According to the results, the damage condition and orientation could be correctly identified using the MFDXA algorithm and the proposed damage index. Since only the ambient vibration signal is required along with a set of initial reference measurements, the proposed SHM system can provide a lower cost, efficient, and reliable monitoring process.

• Structural Engineering and Mechanics
• /
• v.36 no.4
• /
• pp.463-479
• /
• 2010

Based on damage accumulation of multi-grid composite walls, a method of dynamic reliability estimations is proposed. The multi-grid composite wall is composed of edge frame beam, edge frame columns, grid beams, grid columns and filling blocks. The equations including stiffness, shear forces at filling blocks cracking and multi-grid composite walls yielding, ultimate displacement, and damage index are obtained through tests of 13 multi-grid composite wall specimens. Employing these equations in reliability calculations, procedures of dynamic reliability estimations based on damage accumulation of multi-grid composite walls subjected to random earthquake excitations are proposed. Finally the proposed method is applied to the typical composite wall specimen subjected to random earthquake excitations which can be specified by a finite number of input random variables. The dynamic reliability estimates, when filling blocks crack under earthquakes corresponding to 63% exceedance in 50 years and when the composite wall reach limit state under earthquakes corresponding to 2-3% exceedance in 50 years, are obtained using the proposed method by taking damage indexes as thresholds. The results from the proposed method which show good agreement with those from Monte-Carlo simulations demonstrate the proposed method is effective.

• Journal of Radiation Industry
• /
• v.7 no.1
• /
• pp.55-59
• /
• 2013

Ionizing radiation causes the massive generation of reactive oxygen species, resulting in cellular and tissue damage. The present study was performed to evaluate ${\gamma}$-irradiation induced cellular damage in ICR mice. The mice were divided into four groups with ten mice in each group. Group 1 served as an unexposed control group. Groups 2, 3, and 4 were exposed to 3, 5, and 7 Gy of ${\gamma}$-radiation, respectively. Five mice per group were sacrificed 1 and 7 days after ${\gamma}$-radiation. Exposure to ${\gamma}$-irradiation resulted in hematopoietic damage in a dose-dependent manner when compared with the unexposed control group, which featured a significantly decreased spleen index. However, the exposed mice showed no significant differences in their serum AST, ALT and in the histopathological change of their liver. These results suggest that ${\gamma}$-irradiation is a good tool to prepare a hematopoietic damage model. This animal model can be employed to study the hematopoietic efficacy of biologically active compounds.

• Journal of the Korean Geosynthetics Society
• /
• v.17 no.4
• /
• pp.103-108
• /
• 2018

The fragility curves for CFRD dams are derived in this study for probabilistic damage estimation as a function of a ground motion intensity. The dam crest settlement, which is a widely used damage index, is used for minor, moderate, and extensive damage states. The settlement is calculated from nonlinear dynamic numerical simulations. The accuracy of the numerical model is validated through comparison with a centrifuge test. The fragility curve is represented as a log normal distribution function and presented as a function of the peak ground acceleration. The fragility curves developed in this study can be utilized for real time assessment of the damage of dams.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.19 no.4
• /
• pp.567-576
• /
• 2017

In a performance-based design, the structural safety is estimated from pre- defined damage states and corresponding damage indices. Both damage states and damage indices are well defined for above-ground structures, but very limited studies have been performed on underground structures. In this study, we define the damage states and damage indices of a cut-and-cover box tunnel which is one of typical structures used in metro systems, under a seismic excitation from a series of inelastic frame analyses. Three damage states are defined in terms of the number of plastic hinges that develop within the structure. The damage index is defined as the ratio of the elastic moment to the yield moment. Through use of the proposed index, the inelastic behavior and failure mechanism of box tunnels can be simulated and predicted through elastic analysis. In addition, the damage indices are linked to free-field shear strains. Because the free-field shear strain can be easily calculated from a 1D site response analysis, the proposed method can be readily used in practice. Further studies are needed to determine the range of shear strains and associated uncertainties for various types of tunnels and site profiles. However, the inter-linked platform of damage state - damage index - shear wave velocity - shear strain provides a novel approach for estimating the inelastic response of tunnels, and can be widely used in practice for seismic designs.

• Journal of Korean Society for Atmospheric Environment
• /
• v.6 no.1
• /
• pp.103-110
• /
• 1990

To investigate the damage on the black pine(Pinus thunbergii) by the air pollution around Ulsan Industrial Complex, forty-six plots were set up and the effects of air pollution were evaluated with the injured index of black pine. The injured index of black pine showing the degree of air pollution from 1987 to 1988 indicated that the central area of Yeochun-dong and Youngjam-dong were heavily damaged. The effective indicaters of black pine damage from air pollution in the order of importance were the color change of one-year-old branch, the ratio of fallen needle of two-year-old branch, the degree of reducing needle, and the degree of growing shoot growth. There was a reliable relationship between the content of $SO_3$ and F in the air and the injured index of black pine. There was no significant correlation between the injured index of the black pine and the content of chemical properties in soil.

• International Journal of Railway
• /
• v.7 no.4
• /
• pp.94-99
• /
• 2014

Urban railway systems are located under populated areas and are mostly constructed for underground structures which demand high standards of structural safety. However, the damage progression of underground structures is hard to evaluate and damaged underground structures may not effectively stand against successive earthquakes. This study attempts to examine initial damage-stage and to access structural damage condition of the ground structures using Earthquake Damage Monitoring (EDM) system. For actual underground structure, vulnerable damaged member of Ulchiro-3ga station is chosen by finite element analysis using applied artificial earthquake load, and then damage pattern and history of damaged members is obtained from measured acceleration data introduced unsupervised learning recognition. The result showed damage index obtained by damage scenario establishment using acceleration response of selected vulnerable members is useful. Initial damage state is detected for selected vulnerable member according to established damage scenario. Stiffness degrading ratio is increasing whereas the value of reliability interval is decreasing.