• 한국조명전기설비학회:학술대회논문집
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• 한국조명전기설비학회 2004년도 춘계학술대회 논문집
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• pp.546-549
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• 2004

This paper describes the electrical characteristics of the polymer lightning arresters(L.As) used to protect distribution lines and power facilities from surge. For the relative comparison, the characteristics assessment was done for 2 states of L.As before and after water immersion treatment. The L.As for the comparative test were immersed with water of $95[^{\circ}C]$ considered a severe condition. After the immersion treatment, the assessment was carried out for material analyses in chemical structure(FTIR : fourier transform infrared spectrophotometer). Electrical performance measured insulation resistance measurement, leakage current measurement, critical operation voltage measurement etc.. In addition to, the results were compared with those for the L.As deteriorated in the field. Thus, the accelerative deterioration degree of polymer materials by immersion treatment was evaluated, by which the structural defects of the polymer L.As could be inferred.

• 자연, 터널 그리고 지하공간
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• 제21권2호
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• pp.117-129
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• 2019

Tunnelling in urban environments is very common nowadays as large cities are expanding and transportation demands require the use of the underground space for creating extra capacity. Inevitably, any such new construction may have significant effects on existing nearby infrastructure and therefore relevant assessment of structural integrity and soil-structure interaction is required. Foundation piles can be rather sensitive to nearby tunnel construction and therefore their response needs to be evaluated carefully. Although detailed three-dimensional continuum finite element analysis can provide a wealth of information about this behaviour of piles, such analyses are generally very computationally demanding and may require a number of material and other model parameters to be properly calibrated. Therefore, relevant simplified approaches are used to provide a practical way for such an assessment. This paper presents a simple method where the pile is modelled with beam finite elements, pile-soil interaction is modelled with soil springs and tunnelling-induced displacements are introduced as an input boundary condition at the end of the soil springs. The performance of this approach is assessed through some examples of applications.

• Computers and Concrete
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• 제33권4호
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• pp.341-348
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• 2024

Ultra-high-performance concrete (UHPC) has received remarkable attentions in civil infrastructure due to its unique mechanical characteristics and durability. UHPC gains increasingly dominant in essential structural elements, while its unique properties pose challenges for traditional inspection methods, as damage may not always manifest visibly on the surface. As such, the need for robust inspection techniques for detecting cracks in UHPC members has become imperative as traditional methods often fall short in providing comprehensive and timely evaluations. In the era of artificial intelligence, computer vision has gained considerable interest as a powerful tool to enhance infrastructure condition assessment with image and video data collected from sensors, cameras, and unmanned aerial vehicles. This paper presents a computer vision-based approach employing deep learning to detect cracks in UHPC beams, with the aim of addressing the inherent limitations of traditional inspection methods. This work leverages computer vision to discern intricate patterns and anomalies. Particularly, a convolutional neural network architecture employing transfer learning is adopted to identify the presence of cracks in the beams. The proposed approach is evaluated with image data collected from full-scale experiments conducted on UHPC beams subjected to flexural and shear loadings. The results of this study indicate the applicability of computer vision and deep learning as intelligent methods to detect major and minor cracks and recognize various damage mechanisms in UHPC members with better efficiency compared to conventional monitoring methods. Findings from this work pave the way for the development of autonomous infrastructure health monitoring and condition assessment, ensuring early detection in response to evolving structural challenges. By leveraging computer vision, this paper contributes to usher in a new era of effectiveness in autonomous crack detection, enhancing the resilience and sustainability of UHPC civil infrastructure.

• Structural Engineering and Mechanics
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• 제90권6호
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• pp.591-600
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• 2024

This study investigated the acceleration response and shape change characteristics of a gravity quay wall according to the magnitude of the applied acceleration. The quay wall was defined as a port facility damaged by the Kobe earthquake. Four experimental scenarios were established based on the inclination condition grades, considered to be a significant defect factor in the quay wall. Then, the shaking table test was conducted using scaled-down quay wall models constructed per each scenario. The ground acceleration was gradually increased from the peak ground acceleration (PGA) of 0.1 g to 0.7 g. After each ground acceleration test, acceleration installed on the wall and backfill ground and inclination on the top of the wall were measured to assess the amplification of peak response acceleration and maximum response amplitude and the change in the inclination of the quay wall. This study also analyzed the separation of the quay wall from the backfill and the crack pattern of the backfill ground according to PGA values and inclination condition grades. The result of this study shows that response acceleration could provide a reasonable prediction for the changes in the inclination of the quay wall and the crack generation and propagation on the backfill from a current inclination condition grade.

• Steel and Composite Structures
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• 제49권4호
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• pp.407-417
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• 2023

After a disaster like the catastrophic earthquake, the government have to use rapid assessment of the condition (or damage) of bridges, buildings and other infrastructures is mandatory for rapid feedbacks, rescue and post-event management. Many domain schemes based on the measured vibration computations, including least squares estimation and neural fuzzy logic control, have been studied and found to be effective for online/offline monitoring of structural damage. Traditional strategies require all external stimulus data (input data) which have been measured available, but this may not be the generalized for all structures. In this article, a new method with unknown inputs (excitations) is provided to identify structural matrix such as stiffness, mass, damping and other nonlinear parts, unknown disturbances for example. An analytical solution is thus constructed and presented because the solution in the existing literature has not been available. The goals of this paper are towards access to adequate, safe and affordable housing and basic services, promotion of inclusive and sustainable urbanization and participation, implementation of sustainable and disaster-resilient buildings, sustainable human settlement planning and manage. Simulation results of linear and nonlinear structures show that the proposed method is able to identify structural parameters and their changes due to damage and unknown excitations. Therefore, the goal is believed to achieved in the near future by the ongoing development of AI and control theory.

• 한국해양공학회지
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• 제30권2호
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• pp.100-108
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• 2016

A high-pressure ball valve was developed, and both the structural strength and sealing performance were assessed based on a nonlinear finite element analysis. Different parts were modeled with solid elements and assembled, taking into account both contact and sliding effects. Three different loading scenarios were analyzed, including a high-pressure closure test and fire and shell test conditions. The structural safety of each part was checked under each loading condition, and the sealing performance was also investigated to validate the performance of the valve.

• Structural Monitoring and Maintenance
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• 제7권2호
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• pp.149-166
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• 2020

This paper presents the results of an experimental investigation on a vibration-based damage identification framework for a steel girder type and a truss bridge based on acceleration responses to operational loading. The method relies on sensor clustering-based time-series analysis of the operational acceleration response of the bridge to the passage of a moving vehicle. The results are presented in terms of Damage Features from each sensor, which are obtained by comparing the actual acceleration response from the sensors to the predicted response from the time-series model. The damage in the bridge is detected by observing the change in damage features of the bridge as structural changes occur in the bridge. The relative severity of the damage can also be quantitatively assessed by observing the magnitude of the changes in the damage features. The experimental results show the potential usefulness of the proposed method for future applications on condition assessment of real-life bridge infrastructures.

• 한국안전학회지
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• 제11권1호
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• pp.11-15
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• 1996

For the assessment of fracture behaviors of structural components, various fracture mechanics parameters have been applied to date. New approaches to analyze structural fracture performance under elastic-plastic condition have been proposed by the development of testing methods for characterization of material behavior which is defying to the analysis by conventional fracture parameters. In this study, on the assumption that, initiation of crack propagation of a piping materials occurs when the crack tip strain field reaches "the local fracture strain", following two major issues are discussed ; 1) The relationship between the critical value of J-integral($J_{IC}$) and the local fracture strain (${\varepsilon}_c$) in uniaxial tensile test in the region of maximum reduction area was described. 2) To proved the validity of above relations a series of tests were performed under various temperature and on the different piping materials.materials.

• Earthquakes and Structures
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• 제8권4호
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• pp.859-887
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• 2015

Structural health monitoring (SHM) has gained in popularity in recent years since it can assess the performance and condition of instrumented structures in real time and provide valuable information to the asset's manager and owner. Operational modal analysis plays an important role in SHM and it involves the determination of natural frequencies, damping ratios and mode shapes of a constructed structure based on measured dynamic data. This paper presents the operational modal analysis and seismic response characterization of the Tsing Ma Suspension Bridge of 2,160 m long subjected to different earthquake events. Three kinds of events, i.e., short-distance, middle-distance and long-distance earthquakes are taken into account. A fast Bayesian modal identification method is used to carry out the operational modal analysis. The modal properties of the bridge are identified and compared by use of the field monitoring data acquired before and after the earthquake for each type of the events. Research emphasis is given on identifying the predominant modes of the seismic responses in the deck during short-distance, middle-distance and long-distance earthquakes, respectively, and characterizing the response pattern of various structural portions (deck, towers, main cables, etc.) under different types of earthquakes. Since the bridge is over 2,000 m long, the seismic wave would arrive at the tower/anchorage basements of the two side spans at different time instants. The behaviors of structural dynamic responses on the Tsing Yi side span and on the Ma Wan side span under each type of the earthquake events are compared. The results obtained from this study would be beneficial to the seismic design of future long-span bridges to be built around Hong Kong (e.g., the Hong Kong-Zhuhai-Macau Bridge).

• Advances in concrete construction
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• 제10권6호
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• pp.499-507
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• 2020

In current study, utilizing the Kelvin's theory with polynomial, exponential and trigonometric volume fraction laws for functionally graded cylindrical shell vibrations. Effects of different parameters for ratios of length- and height-to-radius and angular speed versus fundamental natural frequencies been determined for two categories of cylindrical shells with clamped-free edge condition. By increasing different value of height-to-radius ratio, the resulting backward and forward frequencies increase and frequencies decrease on increasing length-to-radius ratio. Moreover, on increasing the rotating speed, the backward frequencies increases and forward frequencies decreases. The frequencies are same when the cylinder is stationary. The frequencies increases and decreases on changing the constituent materials. The frequency results are verified with the earlier literature for the applicability of present model.