• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11a
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• pp.494-497
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• 2001

Identification of damage of structures has recently received considerable attention in the light of maintenance and safety assessment. In this respect, the vibration characteristics of buildings have been applied steadily to obtain a damage index of the whole building, but it cannot be established as a practical method until now. A practical method for the estimation of structural damage using the first natural frequency and mode shape of building is proposed in this paper. The effectiveness of the proposed method is verified by numerical and experimental tests. From the results, it is observed that severity and location of damage can be estimated with a relatively small error by using modal properties of building.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.2
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• pp.14-22
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• 2017

The frequency and scale of natural disasters due to the abnormal climate phenomena caused by global warming have being increasing all over the world. Various natural disasters, such as typhoons, earthquakes, floods, heavy rain, drought, sweltering heat, wind waves, tsunamis and so on, can cause damage to human life. Especially, the damage caused by natural disasters such as the Earthquake of Japan, hurricane Katrina in the United States, typhoon Maemi and so on, have been enormous. At this stage, it is difficult to estimate the scale of damage due to (future) natural disasters and cope with them. However, if we could predict the scale of damage at the disaster response level, the damage could be reduced by responding to them promptly. In the present study, therefore, among the many types of natural disaster, we developed a function to estimate the damage due to wind waves caused by sea winds and waves. We collected the damage records from the Disaster Report ('91~'14) published by the Ministry of Public Safety and Security about wind waves and typhoons in the western coastal zone and, in order to reflect the inflation rate, we converted the amount of damage each year into the equivalent amount in 2014. Finally, the meteorological data, such as the wave height, wind speed, tide level, wave direction, wave period and so on, were collected from the KMA (Korea Meteorological Administration) and KHOA (Korea Hydrographic and Oceanographic Agency)'s web sites, for the periods when wind wave and typhoon damage occurred. After that, the function used to estimate the wind wave damage was developed by reflecting the regional characteristics for the 9 areas of the western coastal zone.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.6
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• pp.90-96
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• 2009

Ultrasonic method using SH(shear horizontal) wave has been developed to determine the surface damage in fatigued material. Fatigue damages based on propagation energy were analyzed by multi-regression analysis in interrupted fatigue test specimen including CrMoV and 12Cr alloy steel. From the test results, as the fatigue damage increased the propagation time of the launched waves increased and amplitude of wavelet decreased. Also, analysis for the waveform modulation showed a reliable estimation, with confidence limit of 97% for 12Cr steel and 95% for CrMoV steel, respectively. Therefore, It is thought that SH ultrasonic wave technique can be applied to determine fatigue damage of in-service component nondestructively.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.870-874
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• 2004

This work presents a study on development of a practical and quantitative technique for assessment of the structural health condition by Piezoelectric impedance-based technique associated with longitudinal wave propagation method. The bolt fastening condition is adjusted by torque wrench. In order to estimate the damage condition numerically, three damage indices, impedance peak frequency shift ${\Delta}F$, peak amplitude ratio $\delta$ and quality factor ratio $\gamma$, are proposed in this paper. Furthermore, an assessment method is described for estimation of the damage by using these three damage indices.

• Earthquakes and Structures
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• v.8 no.4
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• pp.821-841
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• 2015

This paper proposes a two-stage imaging approach for quantitative inspection of damages in metallic plates using the fundamental anti-symmetric mode of ($A_0$) Lamb wave. The proposed approach employs a number of transducers to transmit and receive $A_0$ Lamb wave pulses, and hence, to sequentially scan the plate structures before and after the presence of damage. The approach is applied to image the corrosion damages, which are simplified as a reduction of plate thickness in this study. In stage-one of the proposed approach a damage location image is reconstructed by analyzing the cross-correlation of the wavelet coefficient calculated from the excitation pulse and scattered wave signals for each transducer pairs to determine the damage location. In stage-two the Lamb wave diffraction tomography is then used to reconstruct a thickness reduction image for evaluating the size and depth of the damage. Finite element simulations are carried out to provide a comprehensive verification of the proposed imaging approach. A number of numerical case studies considering a circular transducer network with eight transducers are used to identify the damages with different locations, sizes and thicknesses. The results show that the proposed methodology is able to accurately identify the damage locations with inaccuracy of the order of few millimeters of a circular inspection area of $100mm^2$ and provide a reasonable estimation of the size and depth of the damages.

• Structural Engineering and Mechanics
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• v.39 no.6
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• pp.795-812
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• 2011

Estimation of damage probability of buildings under a future earthquake is an essential issue to ensure the seismic reliability. Fragility curves are useful tools for showing the probability of structural damage due to earthquakes as a function of ground motion indices. The purpose of this study is to compare the damage probability of R/C buildings with low and high level of strength and ductility through fragility analysis. Two different types of sample buildings have been considered which represent the building types mentioned above. The first one was designed according to TEC-2007 and the latter was designed according to TEC-1975. The pushover curves of sample buildings were obtained via pushover analyses. Using 60 ground motion records, nonlinear time-history analyses of equivalent single degree of freedom systems were performed using bilinear hysteretic model and peak-oriented hysteretic model with stiffness - strength deterioration for each scaled elastic spectral displacement. The damage measure is maximum inter-story drift ratio and each performance level considered in this study has an assumed limit value of damage measure. Discrete damage probabilities were calculated using statistical methods for each considered performance level and elastic spectral displacement. Consequently, continuous fragility curves have been constructed based on the lognormal distribution assumption. Furthermore, the effect of hysteresis model parameters on the damage probability is investigated.

• Nuclear Engineering and Technology
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• v.46 no.1
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• pp.73-80
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• 2014

A concrete cask is an option for spent nuclear fuel interim storage. A concrete cask usually consists of a metallic canister which confines the spent nuclear fuel assemblies and a concrete overpack. When the overpack undergoes a missile impact, which might be caused by a tornado or an aircraft crash, it should sustain an acceptable level of structural integrity so that its radiation shielding capability and the retrievability of the canister are maintained. A missile impact against a concrete overpack produces two damage modes, local damage and global damage. In conventional approaches [1], those two damage modes are decoupled and evaluated separately. The local damage of concrete is usually evaluated by empirical formulas, while the global damage is evaluated by finite element analysis. However, this decoupled approach may lead to a very conservative estimation of both damages. In this research, finite element analysis with material failure models and element erosion is applied to the evaluation of local and global damage of concrete overpacks under high speed missile impacts. Two types of concrete overpacks with different configurations are considered. The numerical simulation results are compared with test results, and it is shown that the finite element analysis predicts both local and global damage qualitatively well, but the quantitative accuracy of the results are highly dependent on the fine-tuning of material and failure parameters.

• Journal of Ocean Engineering and Technology
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• v.8 no.1
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• pp.144-153
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• 1994

An algorithm to locate and estimate severity of damage in jacket-type offshore structures for which modal responses are availabit' for very few vibrational modes is presented. First, a theory of damage locaization and severity estimation(which yields information on the location and severity of damage directly from changes in mode shapes) is formulated. Next, the feasibility the damage detection algorithm is demonstrated by using a numerical example of an offshore jacket platform for which only three vibration modes are measured. Form the material presented here, two major results are observed. First, all damage locations in the offshore jacket platform are correctly predicted. Next, predicted damage is relatively correctly estimated.

• Journal of KIBIM
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• v.10 no.2
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• pp.21-28
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• 2020

As the number of aging bridges increases, more studies are being conducted on developing effective and reliable methods for the assessment and maintenance of bridges. With the advancement in new sensing systems and data learning techniques through AI technology, there is growing interests in how to evaluate bridges using these advanced techniques. This paper presents a CNN(Convolution Neural Network) deep learning based technique for evaluating the damage existence and for estimating the damage location in PSC bridges using static strain data. Simulation studies were conducted to investigate the proposed method with error analysis. Damage was simulated as the reduction in the stiffness of a finite element. A data learning model was constructed by applying the CNN technique as a type of deep learning. The damage status and its location were estimated using data set built through simulation. It was assumed that the strain gauges were installed in a regular interval under the PSC bridge girders. In order to increase the accuracy in evaluating damage, the squared error between the intact and measured strains are computed and applied for training the data model. Considering the damage occurring near the supports, the results of error analysis were compared according to whether strain data near the supports were included.

• International Journal of Concrete Structures and Materials
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• v.1 no.1
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• pp.29-36
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• 2007

The purpose of this paper is the assessment of the capacity of the reinforced concrete (RC) elements of an arch bridge when they are subjected to contact and near-contact explosive charges of various amounts, and the estimation of the critical charges for these components. The bridge considered is the Tenza Viaduct, a decommissioned structure south of Naples, Italy. Its primary elements, deck, piers and arches were analyzed. The evaluation was accomplished via numerical analyses that made possible to obtain the elements dynamic response when they are exposed to blast loading conditions. To evaluate the member's capacities, failure criteria for deck, piers and arches were proposed based on concrete damage parameters. Additionally, curves relating the explosive charge to the residual capacity and to damage level of the elements were also developed. The results of this work were taken into account to investigate the progressive collapse of the global structure.