• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.6
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• pp.230-237
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• 2022

It is essential that service life of reinforced concrete structures in economic and safety aspects should be secured. It is well-known that chloride attack is a typical deterioration mechanism in field concrete structures. To prevent serious accidents like collapse, many studies have been conducted to increase resistance of chloride ingress using concrete mixed with GGBS. The usage of GGBS concrete is nowadays mandatory. Since most concretes in the field are unsaturated, study regarding chloride absorption is necessary, but many studies have focused on the chloride diffusion phenomenon. Methods for evaluating chloride absorption are cost and improper in the field. It is necessary to develop a simple method for evaluating chloride absorption in practice. This study evaluated resistance of chloride ingress in GGBS concretes with impedance measurement and absorption test. From the results, it was confirmed that the contents of absorbed chloride were linearly correlated with the measured electrical resistivities (or conductivities) in the concrete. At the end of the test, the electrical conductivities were 250.8 S/m (w/b=0.4) and 303.1 S/m (w/b=0.6) for PC concretes, and 2.6 S/m (w/b=0.4) and 64.4 S/m (w/b=0.6) for GGBS concretes, respectively. Considering influencing factors for chloride absorption and impedance measurement, chloride ingress into concrete is mainly affected by pore structures due to replacement of GGBS. Especially, formations of pore structure are different with binder, thereby binders should be considered in building reinforced concrete structures exposed to chloride environments.

• Tunnel and Underground Space
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• v.24 no.5
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• pp.335-343
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• 2014

Room-and-pillar mining method is one of the most popular underground mining method in the world. If the room-and-pillar mining method is able to be adopted in civil works, it would be highly probable to reduce underground construction costs and to expand a underground structure in use. Therefore, this study aims to analyze the design procedure of unsupported rock pillars which are indispensable to ensure the stability of a room-and-pillar underground structure. Parametric studies on their key design parameters are also carried out for 125 different kinds of design conditions. From the study, the width of a rock pillar is found to show a linear relationship with its corresponding safety factor. The safety factor of a unsupported rock pillar decreased drastically like a negative exponential function as the ratio of room width to pillar width increases in the same rock strength condition. Based on the parametric studies, a design chart to simply evaluate the geometric design parameters of a unsupported rock pillar satisfying a design safety factor is also proposed in this study.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.28 no.5
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• pp.1099-1112
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• 2018

The field of post-quantum cryptography (PQC) is an active area of research as cryptographers look for public-key cryptosystems that can resist quantum adversaries. Among those categories in PQC, code-based cryptosystem provides high security along with efficiency. Recent works on code-based cryptosystems focus on the side-channel resistant implementation since previous works have indicated the possible side-channel vulnerabilities on existing algorithms. In this paper, we recovered the secret key in HyMES(Hybrid McEliece Scheme) using a single power consumption trace. HyMES is a variant of McEliece cryptosystem that provides smaller keys and faster encryption and decryption speed. During the decryption, the algorithm computes the parity-check matrix which is required when computing the syndrome. We analyzed HyMES using the fact that the joint distributions of nonlinear functions used in this process depend on the secret key. To the best of our knowledge, we were the first to propose the side-channel analysis based on joint distributions of leakages on public-key cryptosystem.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.3
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• pp.622-628
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• 2016

As the suction pad-supporting bike carrier attached to a car may be subject to an excessive dynamic load due to random vibrations and centrifugal forces during driving, its structural safety is of great concern. To examine this, the finite-element method with a fluid-structure interaction should be used because the pressure on the pad bottom is changed in real time according to the fluctuations of the force or the moment applied on the pad. This method, however, has high computing costs in terms of modeling efforts and software expense. Moreover, the accuracy of computation is not easily guaranteed. Therefore, a new method combining the experiment and computation is proposed in this paper: the bottom pressure and contact area of the pad under varying loads was measured in real time and the acquired data are then used in the nonlinear elastic finite-element calculations. The computational and experimental results obtained with the product under development showed that the safety margin of the pad under the axial loading is relatively sufficient, whereas with an excessive rotational loading, the pad is vulnerable to separation or a local surface damage; hence, the safety margin may not be secured. The predicted contact behavior under the variation of the magnitude and type of the loading were in good agreement with the one from the experiment. The proposed analysis method in this study could be used in the design of similar vacuum pad systems.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.35 no.2
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• pp.417-426
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• 2015

The representative design elements of the road geometric structure are longitudinal slope, horizontal curve radius, super elevation, and transition curve. According to the function of a road, the design standards of these elements is applied by diverse combinations of them. This study divided expressway into homogeneous segments based on longitudinal slope and horizontal curve radius. And then, data required for analysis were matched to each segment, and the safety performance function was built by using the established data. crash modification factors which can explain traffic accident exposure rate were calculated. When the threshold value of horizontal curve radius R=1,000 m was set to 1.0, the crash modification factors at R=300 m was calculated as 1.33, which means that the accident exposure rate is increased by 33%. When the threshold value of the longitudinal slope 0% was set to 1.0, the crash modification factors demonstrated that the accident exposure rate decreases on the upward slope and the accident exposure rate increases on the downward slope. The results of this study can be used as basic information in the design of expressway geometries during the improvement or the construction of expressways.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.3
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• pp.23-30
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• 2003

In this study, the various load cases by specified by the IEC61400-1 international specification and GL Regulations for the wind energy conversion system were considered, and a specific composite structure configuration which can effectively endure various loads was proposed. In order to evaluate the structure, the structural analysis for the composite wind turbine blade was performed using the finite element method(FEM). In the structural design, the acceptable configuration of blade structure was determined through the parametric studies, and the most dominant design parameters were confirmed. In the stress analysis using the FEM, it was confirmed that the blade structure was safe and stable for all the considerd load cases. Moreover the safety of the blade root joint with insert bolts, newly devised in this study, was checked against the design loads and also the fatigue loads. The fatigue life for operating more than 20 years was estimated by using the well-known S-N linear damage rule, the load spectrum and Spera's empirical equations. The full-scale static test was performed under the simulated aerodynamic loads. from the experimental results, it was found that the designed blade had the structural integrity. Furthermore the measured results were agreed with the analytical results such as deflections, strains, the mass and the radial center of gravity. The studied blade was successfully certified by an international institute, GL, of Germany.

• Journal of the Korean Society for Railway
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• v.14 no.5
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• pp.433-441
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• 2011

It is a fact that the straightening of track alignment is one of the undoubted ways to improve the train speed on conventional lines, while that requires huge investment resources. Therefore, the operation of a tilting train as well as the minimum improvement of track is suggested as an effective and economical alternative way for the speed-up of conventional lines. Since a driving mechanism of tilting train is different from those of existing trains, in order to make sure its operation safety and stability on conventional line, the performance of track and roadbed must be preferentially evaluated on the conventional line. Furthermore, it is necessary to estimate the tilting-train-induced roadbed response in detail since the roadbed settlement can lead to the track deformation and even derailment. In this research, the patterns of wheel load and lateral force were monitored and analyzed through the field tests, and the derailment coefficient and degree of wheel off-loading were calculated in order to evaluate the tilting train running safety depending on the running speeds (120km~180km) on the conventional line. Moreover, roadbed pressure, settlement and acceleration were also observed as tilting-train-induced roadbed responses in order to estimate the roadbed stability depending on the running speeds. Consequently, the measured derailment coefficient and degree of wheel off-loading were satisfied with their own required limits, and all of the roadbed responses were less than those of existing high-speed train (KTX) over an entire running speed range considered in this study. As a result of this study, the tilting train which will be operated in combination with existing trains is expected to give no adverse impact on the conventional line even with its improved running speed.

• Korean Journal of Remote Sensing
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• v.38 no.6_3
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• pp.1777-1788
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• 2022

The reservoir is a major water supply source in the domestic agricultural environment, and the monitoring of water storage of reservoirs is important for the utilization and management of agricultural water resource. Remote sensing via satellite imagery can be an effective method for regular monitoring of widely distributed objects such as reservoirs, and in this study, image classification and image segmentation algorithms are applied to Sentinel-1 Synthetic Aperture Radar (SAR) imagery for water body detection in 53 reservoirs in South Korea. Six algorithms are used: Neural Network (NN), Support Vector Machine (SVM), Random Forest (RF), Otsu, Watershed (WS), and Chan-Vese (CV), and the results of water body detection are evaluated with in-situ images taken by drones. The correlations between the in-situ water surface area and detected water surface area from each algorithm are NN 0.9941, SVM 0.9942, RF 0.9940, Otsu 0.9922, WS 0.9709, and CV 0.9736, and the larger the scale of reservoir, the higher the linear correlation was. WS showed low recall due to the undetected water bodies, and NN, SVM, and RF showed low precision due to over-detection. For water body detection through SAR imagery, we found that aquatic plants and artificial structures can be the error factors causing undetection of water body.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.23 no.1
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• pp.37-43
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• 2010

In this paper, a reliability-based design optimization is developed for the topology design of linear structures using a performance measure approach. Spatial domain is discretized using three dimensional Reissner-Mindlin plate elements and design variable is taken as the material property of each element. A continuum based adjoint variable method is employed for the efficient computation of sensitivity with respect to the design and random variables. The performance measure approach of RBDO is employed to evaluate the probabilistic constraints. The topology optimizationproblem is formulated to have probabilistic displacement constraints. The uncertainties such as material property and external loads are considered. Numerical examples show that the developed topology optimization method could effectively yield a reliable design, comparing with the other methods such as deterministic, safety factor, and worst case approaches.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.4
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• pp.1515-1522
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• 2011

This paper proposed the finite element analysis technique for improving the correleration accuracy between FEA and test on a pedestrian lower legform impact. Europe has been evaluating the bumper pedestrian impact by Euro-NCAP, and it will also be applied in a domestic area by K-NCAP in 2013. By using the compression test result of bending resisting stiffener, a pedestrian bumper modeling guide was presented by analayzing the force-displacement curve of stiffener. And by using the sensor measurement results in car pedestrian test, pedestrian impact behavior was analyzed between test and finite element analysis result. Finally, the finite element analysis guide for a pedestrian bumper impact was presented to improve the correleration accuracy.