• Smart Structures and Systems
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• v.24 no.4
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• pp.475-490
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• 2019

The detection of structural damage without a priori information on the healthy state is challenging. In order to address the issue, the study presents a baseline-free approach to detect damage in beam structures based on an actual influence line. In particular, a multi-segment function-fitting calculation is developed to extract the actual deflection influence line (DIL) of a damaged beam from bridge responses due to a passing vehicle. An intact basis function based on the measurement position is introduced. The damage index is defined as the difference between the actual DIL and a constructed function related to the intact basis, and the damage location is indicated based on the local peak value of the damage index curve. The damage basis function is formulated by using the detected damage location. Based on the intact and damage basis functions, damage severity is quantified by fitting the actual DIL using the least-square calculation. Both numerical and experimental examples are provided to investigate the feasibility of the proposed method. The results indicate that the present baseline-free approach is effective in detecting the damage of beam structures.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.43 no.4
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• pp.511-523
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• 2023

Research on the integration of unmanned aerial vehicles and deep learning for reinforced concrete damage detection is actively underway. Convolutional neural networks have a high impact on the performance of image classification, detection, and segmentation as backbones. The MobileNet, a pre-trained convolutional neural network, is efficient as a backbone for an unmanned aerial vehicle-based damage detection model because it can achieve sufficient accuracy with low computational complexity. Analyzing vanilla convolutional neural networks and MobileNet under various conditions, MobileNet was evaluated to have a verification accuracy 6.0~9.0% higher than vanilla convolutional neural networks with 15.9~22.9% lower computational complexity. MobileNetV2, MobileNetV3Large and MobileNetV3Small showed almost identical maximum verification accuracy, and the optimal conditions for MobileNet's reinforced concrete damage image feature extraction were analyzed to be the optimizer RMSprop, no dropout, and average pooling. The maximum validation accuracy of 75.49% for 7 types of damage detection based on MobilenetV2 derived in this study can be improved by image accumulation and continuous learning.

• Smart Structures and Systems
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• v.13 no.5
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• pp.775-796
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• 2014

This study presents a vibration-based health monitoring strategy for short span bridges utilizing an inspection vehicle. How to screen the health condition of short span bridges in terms of a drive-by bridge inspection is described. Feasibility of the drive-by bridge inspection is investigated through a scaled laboratory moving vehicle experiment. The feasibility of using an instrumented vehicle to detect the natural frequency and changes in structural damping of a model bridge was observed. Observations also demonstrated the possibility of diagnosis of bridges by comparing patterns of identified bridge dynamic parameters through periodical monitoring. It was confirmed that the moving vehicle method identifies the damage location and severity well.

• Earthquakes and Structures
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• v.11 no.5
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• pp.841-859
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• 2016

Bridge bearings are important connection elements between bridge superstructures and substructures, whose health states directly affect the performance of the bridges. This paper systematacially presents a new method to identify the bridge bearing damage based on the neural network theory. Firstly, based on the analysis of different damage types, a description of the bearing damage is introduced, and a uniform description for all the damage types is given. Then, the feasibility and sensitivity of identifying the bearing damage with bridge vibration modes are investigated. After that, a Radial Basis Function Neural Network (RBFNN) is built, whose input and output are the beam modal information and the damage information, respectively. Finally, trained by plenty of data samples formed by the numerical method, the network is employed to identify the bearing damage. Results show that the bridge bearing damage can be clearly reflected by the modal information of the bridge beam, which validates the effectiveness of the proposed method.

• Korean Journal of Computational Design and Engineering
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• v.20 no.3
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• pp.238-245
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• 2015

Vulnerability assessment is a process to calculate the damage degree of a combat vehicle when the combat vehicle is attacked by an enemy. When the vehicle is hit, it is necessary to analyze the shot line to calculate which components are damaged and judge whether the armor of the vehicle is penetrated by enemy's warhead. To analyze the shot line efficiently, this paper presents the target modeling and the shot line analysis system to assess vulnerability of the ground combat vehicle. This system is easily able to do several functions: 1) the program reads STL files converted from CAD model which is designed by commercial CAD software. 2) It calculates the intersection between triangle of STL mesh and the shot line, and check if the components of the model are penetrated. 3) This program can visualize the results using OpenGL. The vulnerability assessment using the shot line analysis can be used to model the armor of the combat vehicle and arrange the inner components effectively in the early stage of development of the combat vehicle.

• Journal of the Korean Society of Safety
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• v.29 no.5
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• pp.40-46
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• 2014

This paper deal with due to the additional equipment established on the vehicle fire accident cases. Recently, vehicle was recognized as other living spaces and it was increasing installation of additional devices such as a black box, multivision, additional battery and so on. However, these additional devices were established on the vehicle by non-specialists such as the general public user or manufacturing and distributors of additional devices since the vehicle factory. Resulting from the additional equipments due to installation errors in these additional equipments connected to the electrical wiring insulation damage or electrical breakdown occurs, and finally leading to a fire caused by the additional equipments. Therefore, additional equipment established on the vehicle due to a fire in order to prevent accidents during the manufacturing process of these devices are installed. If not installed unless the manufacturing process, the installation of additional equipments established by professional who knows the vehicle structure that will be able to prevent the fire.

• Structural Engineering and Mechanics
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• v.49 no.2
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• pp.203-223
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• 2014

The extensive use of prestressed reinforced concrete (PSC) highway bridges in marine environment drastically increases the sensitivity to both fatigue-and corrosion-induced damage of their critical structural components during their service lives. Within this scenario, an integrated method that is capable of evaluating the fatigue reliability, identifying a condition-based maintenance, and predicting the remaining service life of its critical components is therefore needed. To accomplish this goal, a procedure for fatigue reliability prediction of PSC highway bridges is proposed in the present study. Vehicle-bridge coupling vibration analysis is performed for obtaining the equivalent moment ranges of critical section of bridges under typical fatigue truck models. Three-dimensional nonlinear mathematical models of fatigue trucks are simplified as an eleven-degree-of-freedom system. Road surface roughness is simulated as zero-mean stationary Gaussian random processes using the trigonometric series method. The time-dependent stress-concentration factors of reinforcing bars and prestressing tendons are accounted for more accurate stress ranges determination. The limit state functions are constructed according to the Miner's linear damage rule, the time-dependent S-N curves of prestressing tendons and the site-specific stress cycle prediction. The effectiveness of the methodology framework is demonstrated to a T-type simple supported multi-girder bridge for fatigue reliability evaluation.

• Transactions of the Korean Society of Automotive Engineers
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• v.25 no.3
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• pp.389-396
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• 2017

Restorations of automotive parts have been done ever since the first vehicle was produced. Because the most expensive parts of a vehicle are in the engine system, there have been various restoration methods developed for engine parts. In the case of commercial diesel engines, the fuel injection device is a key and expensive component. It also has a significant effect on vehicle performance. In particular, reduced engine power and increased exhaust gas emissions may result from mechanical damage due to abrasion of the spill valve in the fuel injection system of a diesel engine. In this paper, restoration techniques for damaged parts are applied to restore the abrasion of a spill valve of fuel injection, also called as the "unit injector", of commercial diesel engines. In order to recover the damage, optimized polishing techniques using hard-metal and coating processes are applied. To evaluate restoration techniques for the spill valve, performance and durability tests are performed on a test bench.

• Journal of Power System Engineering
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• v.12 no.4
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• pp.64-71
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• 2008

This study is on pedestrian protection device using pneumatic cylinder and simple link mechanism when vehicle collide with pedestrian. This study ensured the safety space between engine and hood after it applies to simple link mechanism and pneumatic cylinder. It can absorb the damage which measure the specific device if vehicle collide with pedestrian. Combination of simple link mechanism and pneumatic cylinder was more superior than the present pedestrian protection device. Simple link mechanism could confirm superior height and survival probability than when only cylinder operated. It also ensured enough space between engine and hood. And if a cylinder is not working because of old cylinder, poor repair or damage of accident vertical cylinder would be difficult to execute because there exists the irregular space between engine and hood. If simple link mechanism operates with only one cylinder it could ensure the regular space because simple link mechanism set up at the middle of hood. So this device could confirm high safety for pedestrian.

• The Korean Journal of Physiology and Pharmacology
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• v.4 no.1
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• pp.73-79
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• 2000

This study investigated whether propofol, an intravenous, non-barbiturate anesthetic, could reduce brain damage following global forebrain ischemia. Transient global ischemia was induced in gerbils by occlusion of bilateral carotid arteries for 3 min. Propofol (50 mg/kg) was administered intraperitoneally 30 min before, immediately after, and at 1 h, 2 h, 6 h after occlusion. Thereafter, propofol was administered twice daily for three days. Treated animals were processed in parallel with ischemic animals receiving 10% intralipid as a vehicle or with sham-operated controls. In histologic findings, counts of viable neurons were made in the pyramidal cell layer of the hippocampal CA1 area 4 days after ischemia. The number of viable neurons in the pyramidal cell layer of CA1 area was similar in animals treated with a vehicle or a subanesthetic dose of propofol. In terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end-labeling (TUNEL) assay, semiquantitative analysis of dark-brown neuronal cells was made in the hippocampal CA1 area. There was no significant difference in the degree of TUNEL staining in the hippocampal CA1 area between vehicle-treated and propofol-treated animals. These results show that subanesthetic dose of propofol does not reduce delayed neuronal cell death following transient global ischemia in Mongolian gerbils.