• Journal of Korean Society of Steel Construction
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• v.8 no.4 s.29
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• pp.43-50
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• 1996

Damage estimation of bridge structures has recently received considerable attention in the light of maintenance and retrofitting of existing structures under service loads and after natural disasters. A method for the damage assessment of bridge structures using a damage index technique is presented. The damage index is formulated for the changes of modal properties due to the change of the stiffness. In order to verify the method which is presented, numerical analysis is conducted on simple beam models. Each FE model is subjected to different damage scenarios, i.e., locations and degrees of damage. Results of numerical analysis indicate that the proposed method is capable of detecting inflicted damages using the eigenvalue of only first mode.

• Structural Monitoring and Maintenance
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• v.6 no.3
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• pp.237-254
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• 2019

This paper presents an improved time series based damage detection approach with experimental verifications for detection, localization, and quantification of damage in shear-type structures under varying mass effects using output-only vibration data. The proposed method can be very effective for automated monitoring of buildings to develop proactive maintenance strategies. In this method, Auto-Regressive Moving Average models with eXogenous inputs (ARMAX) are built to represent the dynamic relationship of different sensor clusters. The damage features are extracted based on the relative difference of the ARMAX model coefficients to identify the existence, location and severity of damage of stiffness and mass separately. The results from a laboratory-scale shear type structure show that different damage scenarios are revealed successfully using the approach. At the end of this paper, the methodology limitations are also discussed, especially when simultaneous occurrence of mass and stiffness damage at multiple locations.

• 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.

• Earthquakes and Structures
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• v.11 no.4
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• pp.583-607
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• 2016

One of the main applications of seismic risk assessment is that an specific design could be selected for a bridge from different alternatives by considering damage losses alongside primary construction costs. Therefore, in this paper, the focus is on selecting the shape of pylon, which is a changeable component in the design of a cable-stayed bridge, as a double criterion decision-making problem. Different shapes of pylons include H, A, Y, and diamond shape, and the two criterion are construction costs and probable earthquake losses. In this research, decision-making is performed by using developed seismic risk assessment process as a powerful method. Considering the existing uncertainties in seismic risk assessment process, the combined incremental dynamic analysis (IDA) and uniform design (UD) based fragility assessment method is proposed, in which the UD method is utilized to provide the logical capacity models of the structure, and the IDA method is employed to give the probabilistic seismic demand model of structure. Using the aforementioned models and by defining damage states, the fragility curves of the bridge system are obtained for the different pylon shapes usage. Finally, by combining the fragility curves with damage losses and implementing the proposed cost-loss-benefit (CLB) method, the seismic risk assessment process is developed with financial-comparative approach. Thus, the optimal shape of the pylon can be determined using double criterion decision-making. The final results of decision-making study indicate that the optimal pylon shapes for the studied span of cable-stayed bridge are, respectively, H shape, diamond shape, Y shape, and A shape.

• Structural Engineering and Mechanics
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• v.76 no.3
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• pp.355-365
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• 2020

In this study, considering the hydroelastic response represented by the springing and whipping phenomena, we propose a method of estimating the fatigue damage in the longitudinal connections of ships. First, we screened the design sea states using a load transfer function based on the frequency domain. We then conducted a time domain fluid-structure interaction (FSI) analysis using WISH-FLEX, an in-house code based on the weakly nonlinear approach. To obtain an effective and robust analytical result of the hydroelastic response, we also conducted an experimental model test with a 1/50-scale backbone-based model of a ship, and compared the experimental results with those obtained from the FSI analysis. Then, by combining the results obtained from the hydroelastic response with those obtained from the numerical fatigue analysis, we developed a fatigue damage estimation method. Finally, to demonstrate the effectiveness of the developed method, we evaluated the fatigue strength for the longitudinal connections of the real ship and compared it with the results obtained from the model tests.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2019.05a
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• pp.125-126
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• 2019

This study aims to recognize damage indicators of typhoon and to develop damage function's indicators, using information derived from the actual loss of typhoon Maemi. As typhoons engender significant financial damage all over the world, governments and insurance companies, local or global, develop hurricane risk assessment models and use it in quantifying, avoiding, mitigating, or transferring the risks. For the reason, it is crucial to understand the importance of the risk assessment model for typhoons, and the importance of reflecting local vulnerabilities for more advanced evaluation. Although much previous research on the economic losses associated with natural disasters has identified the risk indicators that are indispensable, more comprehensive research addressing the relationship between vulnerability and economic loss are still called for. Hence this study utilizes and analyzes the actual loss record of the typhoon Maemi provided by insurance companies to fill such gaps. In this study, natural disaster indicators and basic building information indicators are used in order to generate the vulnerability functions; and the results and indicators suggest a practical approach to create the vulnerability functions for insurance companies and administrative tasks, while reflecting the financial loss and local vulnerability of the actual buildings.

• Journal of Environmental Impact Assessment
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• v.18 no.5
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• pp.313-319
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• 2009

A complex maritime resort combined marina and with course of Korea is required to improve international tourism competitiveness by taking advantage of her environmental favorable circumstances. The development of tourism, however, is focused on land-oriented that incurred lower tourism efficiency and international tourism competitiveness. In addition, the regulation of "Preliminary environmental assessment for golf courses" by the Ministry of Environment is emphasized on land geography and geology that can cause damage of tourist attractions in an island region. In particular, the development of 6th or 7th ridges in mountainous island region within 2km from the sea, that holds scenic and academic value, can go against environment-friendly by geographical and geological damage. According to the regulation for consultation for golf courses and forestry is to preserve regional ecosystem over 6th ridge, but it cannot be applicable to island region because that can form excessive slopes where marine ecosystem is required to be maintained. It, therefore, can be desirable that the development of over 6th ridge in an island region. It is suggested that continuous comparative studies of geographical and geological characteristics between land and island region will be carried on to establish feasible and reasonable development model so that balanced development of land and island, and versatile international environment-friendly maritime resort can be achieved and developed.

• Journal of Wind Energy
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• v.9 no.4
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• pp.16-23
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• 2018

A damage detection method for the tripod support structure of offshore wind turbines is presented for structural health monitoring. A finite element model of a prototype tripod support structure is established and the modal properties are calculated. The degree and location of the damage are estimated based on the neural network technique using the changes of natural frequencies and mode shape due to the damage. The stress distribution occurring in the support structure is obtained by a dynamic analysis for the wind turbine system to select the output data of the neural network. The natural frequencies and mode shapes for 36 possible damage scenarios were used for the input data of the learned neural network for damage assessment. The estimated damages agreed reasonably well with the accurate ones. The presented method could be effectively applied for damage detection and structural health monitoring of various types of support structures of offshore wind turbines.

• Earthquakes and Structures
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• v.18 no.4
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• pp.423-435
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• 2020

An accurate evaluation of structural damage is essential to performance-based seismic design for the structure across the earth fissure. By comparing the calculation results from three commonly used damage models and the experimental results, a weighted combination method using Chen model was selected in this paper as the seismic damage evaluation. A numerical model considering the soil-structure interaction (SSI) was proposed using ABAQUS software. The model was calibrated by comparing with the experimental results. The results from the analysis indicated that, for the structure across the earth fissure, the existence of earth fissure changed the damage distribution of the structural members. The damage of structural members in the hanging wall was greater than that in the foot wall. Besides, the earth fissure enlarged the damage degree of the structural members at the same location and changed the position of the weak story. Moreover, the damage degree of the structure across the earth fissure was greater than that of the structure without the earth fissure under the same excitation. It is expected that the results from this research would enhance the understanding of the performance-based seismic design for the structure across the earth fissure.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.49 no.4
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• pp.177-184
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• 2000

In this paper, we proposes a method for assessing the effect of voltage sag in power distribution systems using fuzzy model. The proposed method is based on the reliability data of distribution system and specified computer business equipment manufacturer association(SCBEMA) curve that express the representative power acceptability curve by voltage sag for each customer type. The SCBEMA curves are made by using the CBEMA curves obtained from the experiment for the customers sensitive equipment. In order to transform SCBEMA curves to the differential damage by voltage sag, a fuzzy model is used. The proposed fuzzy model is composed to reflect two parameters of customers damage by voltage sag. One is the duration and magnitude of voltage sag and the other is the different risk due to the customer types. The Monte Carlo simulation method and the historical reliability data in KEPCO ae used for case studies.