• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.1
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• pp.90-99
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• 2015

This study examined dynamic and characteristics and chloride penetration of concrete mixed with large amount of FA and BFS, which are considered for positive application to construction fields with purpose of long-tern durability of concrete structures. As a result of strength test on FA and BFS, FA concrete showed higher increase of strength compared to OPC, when FA4000 and FA5000 were mixed 30%, respectively. For BFS concrete, those mixed with 30% and 50% of BFS8000, respectively, showed higher or equivalent strength compare to OPC. As a result of test of chloride penetration on FA and BFS, diffusion coefficients of concrete mixed with 30% FA4000 and FA5000, respectively, showed to restrain average 6.5% of diffusion coefficient compared to OPC. And in case of BFS concrete, those mixed with BFS6000 and BFS8000, restrained diffusion of chloride ions 253% and 336%, respectively, compared to OPC. Therefore, Mixing 50% of BFS was most efficient in order to maximize restraint of chloride penetration according to metathesis of large amount. For relation between compression strength and diffusion coefficient of FA and BFS concrete, as strength increased, diffusion coefficient decreased. In this study, when mixing FA and BFS to concrete for long-run durability and restraint against chloride penetration, for FA, mixing it to concrete with less or equivalent 30% of replacement rate was most efficient. And for BFS, as fineness was higher and mixing it to concrete with less or equivalent 50% of replacement rate, there were results of higher strength compared to OPC and more efficient restraint of chloride ions.

• International Journal of Highway Engineering
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• v.8 no.4 s.30
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• pp.115-124
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• 2006

The objectives of this paper are to develop the structural condition evaluation technique using Falling Weight Deflectometer deflections and propose the structural condition criteria for asphalt pavements. To figure out correlation between surface deflections and critical pavement responses, the synthetic database has been established using the finite element pavement structural analysis program. A regression approach was adopted to develop the pavement response model that can be used to compute the stresses and strains within pavement structure using the FWD deflections. Based on the pavement response model, the procedure for assessing the structural condition of pavement layers was proposed in this study. To validate the condition evaluation procedure for asphalt pavements, the FWD test, dynamic cone penetrometer test, and repeated triaxial compression test were conducted on 11 sections of national highway and 8 sections of local road. Test results indicate that the tensile strain at the bottom of AC layer and AC elastic modulus were good indicators for estimating the stiffness characteristics of AC layer. For subbase layer, the BDI value and compressive strain on top of the subbase layer were appropriate to predict the structural capacity of subbase layer. The BCI value and compressive strain on top of the subgrade were found to be good indicators for evaluating the structural condition of the subgrade. The evaluation criteria for structural condition in asphalt pavements was also proposed in this paper.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.30 no.5
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• pp.389-396
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• 2017

Peridynamics has been widely used in the dynamic fracture analysis of brittle materials. Recently, various crack patterns(compact region, floret, Hertz-type crack, etc.) of multilayered glass structures in experiments(Bless et al. 2010) were implemented with a bond-based peridynamic simulation(Bobaru et al.. 2012). The actual glass layers are bound with thin elastic interlayer material while the interlayer is missing from the peridynamic model used in the previous numerical study. In this study, the peridynamic interlayer modeling for the multilayered structures is proposed. It requires enormous computational time and memory to explicitly model very thin interlayer materials. Instead of explicit modeling, fictitious peridynamic particles are introduced for modeling interlayer materials. The computational efficiency and accuracy of the proposed peridynamic interlayer model are verified through numerical tests. Furthermore, preventing penetration scheme based on short-range interaction force is employed for the multilayered structure under compression and verified through parametric tests.

• Earthquakes and Structures
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• v.8 no.3
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• pp.665-679
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• 2015

The strain rate of reinforced concrete (RC) structures stimulated by earthquake action has been generally recognized as in the range from $10^{-4}/s$ to $10^{-1}/s$. Because both concrete and steel reinforcement are rate-sensitive materials, the RC beam-column joints are bound to behave differently under different strain rates. This paper describes an investigation of seismic behavior of RC beam-column joints which are subjected to large cyclic displacements on the beam ends with three loading velocities, i.e., 0.4 mm/s, 4 mm/s and 40 mm/s respectively. The levels of strain rate on the joint core region are correspondingly estimated to be $10^{-5}/s$, $10^{-4}/s$, and $10^{-2}/s$. It is aimed to better understand the effect of strain rates on seismic behavior of beam-column joints, such as the carrying capacity and failure modes as well as the energy dissipation. From the experiments, it is observed that with the increase of loading velocity or strain rate, damage in the joint core region decreases but damage in the plastic hinge regions of adjacent beams increases. The energy absorbed in the hysteresis loops under higher loading velocity is larger than that under quasi-static loading. It is also found that the yielding load of the joint is almost independent of the loading velocity, and there is a marginal increase of the ultimate carrying capacity when the loading velocity is increased for the ranges studied in this work. However, under higher loading velocity the residual carrying capacity after peak load drops more rapidly. Additionally, the axial compression ratio has little effect on the shear carrying capacity of the beam-column joints, but with the increase of loading velocity, the crack width of concrete in the joint zone becomes narrower. The shear carrying capacity of the joint at higher loading velocity is higher than that calculated with the quasi-static method proposed by the design code. When the dynamic strengths of materials, i.e., concrete and reinforcement, are directly substituted into the design model of current code, it tends to be insufficiently safe.

• Journal of Adhesion and Interface
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• v.20 no.3
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• pp.87-95
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• 2019

In the present study, the effect of alkali treatment of rice straw on the flexural properties and impact strength of rice straw/recycled polyethylene composite was investigated. Alkali treatments were performed by means of two different methods at various sodium hydroxide (NaOH) concentrations. One is static soaking method and the other is dynamic shaking method. The composites were made by compression molding technique using rice straw/recycled polyethylene pellets produced by twin-screw extrusion process. The result strongly depends on the alkali treatment method and concentration. The shaking method done with a low concentration of 1 wt% NaOH exhibits the highest flexural and impact properties whereas the soaking method done with a high concentration of 10 wt% NaOH exhibits the highest properties, being supported qualitatively by the fiber-matrix interfacial bonding of the composites. The properties between the two highest property cases above-described are comparable each other. The study suggests that such a low concentration of 1 wt% NaOH may be used for alkali treatment of natural fibers to improve the flexural and impact properties of resulting composites, rather than using high concentrations of NaOH, 10 wt% or higher. Considering of environmental concerns of alkali treatment, the shaking method is preferable to use.

• Proceedings of the KSR Conference
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• 2008.11b
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• pp.993-999
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• 2008

A girder height limitation is the critical parameter for rapid construction of bridge deck and construction space limitation especially in urban area such as high population area and high density habitats. A standard post-tensioned I-shaped concrete girder usually demands relatively higher girder height in order to retain sufficient moment arm between compression force and tensile force. To elaborate this issue, a small U-shaped section with wide flanges can be used as a possible replacement of I-shaped standard girder. This prestressed concrete box girder allows more flexible girder height adjustment rather than standard I-shaped post-tensioned girder plus additional torsion resistance benefits of closed section. A 30m-long, 1.7m-high and 3.63m-wide actual small prestressed concrete box girder is designed and a laboratory test for its static behaviors by applying 6,200kN amount of load in the form of 4-point bending test was performed. The load-deflection curve and crack patterns at different loading stage are recorded. In addition, to extracting the dynamic characteristics such as natural frequency and damping ratio of this girder, several excitation tests with artificial mechanical exciter with un-symmetric mass are carried out using operational frequency sweep-up. Nonlinear finite element analysis of this 4 point bending test under monotonic static load is investigated and discussed with aids of concrete damaged plasticity formulation using ABAQUS program.

• Composites Research
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• v.32 no.2
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• pp.90-95
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• 2019

Sloshing impact loads on liquefied natural gas (LNG) carr iers are the main issue of damage to the insulation system in LNG cargo containment system (LNG CCS). The damage to the insulation system would be fatal in maintaining a temperature-savings environment in LNG CCS. The typical method is to enhance the insulation materials that can maintain a constant cryogenic temperature. Insulation materials consist of polyurethane foam and plywood, an adhesive for bonding these two materials. This study intends to improve the absorption energy of the material when the impact load is applied by creating a glass bubble/epoxy composite resin as part of the insulation. The experimental scenarios consider the effect of temperature ($20^{\circ}C$, $-163^{\circ}C$), glass bubble weight fraction in epoxy resin through free fall experiments. Experiments have shown that if the glass bubble additive reaches 20 wt.%, the cryogenic absorption energy is a maximum performance and that 0 wt.% has a maximum ambient absorption energy. However, the agglomeration has been occurred due to deterioration of the stirring performance if weight fraction was 20 wt.% and the result of 0 wt.% have been revealed that ambient absorption energy is significantly lower.

• Journal of Broadcast Engineering
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• v.24 no.3
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• pp.472-484
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• 2019

This paper proposes a time-domain sound event detection algorithm using DNN (Deep Neural Network). In this system, time domain sound waveform data which is not converted into the frequency domain is used as input to the DNN. The overall structure uses CRNN structure, and GLU, ResNet, and Squeeze-and-excitation blocks are applied. And proposed structure uses structure that considers features extracted from several layers together. In addition, under the assumption that it is practically difficult to obtain training data with strong labels, this study conducted training using a small number of weakly labeled training data and a large number of unlabeled training data. To efficiently use a small number of training data, the training data applied data augmentation methods such as time stretching, pitch change, DRC (dynamic range compression), and block mixing. Unlabeled data was supplemented with insufficient training data by attaching a pseudo-label. In the case of using the neural network and the data augmentation method proposed in this paper, the sound event detection performance is improved by about 6 %(based on the f-score), compared with the case where the neural network of the CRNN structure is used by training in the conventional method.

• Composites Research
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• v.35 no.4
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• pp.269-276
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• 2022

In this paper, a composite stiffened panel was fabricated using a three-dimensional weaving method that can reduce the risk of delamination, and mechanical properties such as buckling load and natural frequency were investigated. The preform of the stringer and skin of the stiffened panel were fabricated in one piece using T800 grade carbon fiber and then, resin (EP2400) was injected into the preform. The compression test and natural frequency measurement were performed for the stiffened panel, and the results were compared with the finite element analyses. In order to compare the performance of 3D weaving structures, the stiffened panels with the same configuration were fabricated using UD and 2D plain weave (fabric) prepregs. Compared to the tested buckling load of the 3D woven panel, the buckling loads of the stiffened panels of UD prepreg and 2D plain weave exhibited +20% and -3% differences, respectively. From this study, it was confirmed that the buckling load of the stiffened panel manufactured by 3D weaving method was lower than that of the UD prepreg panel, but showed a slightly higher value than that of the 2D plain weave panel.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.36 no.4
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• pp.213-220
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• 2023

This paper presents a model simulating the folding process and collision dynamics of "ddakji", a traditional Korean game played using paper tiles (which are also referred to as ddakji). The model uses two A4 sheets as the base materials for ddakji. The folding process involves a series of boundary conditions that transform the wing part of the paper structure into a twisted configuration. A rigid plate boundary condition is also adopted for squeezing, establishing the shape and stress state of the game-ready ddakji through dynamic relaxation analysis. The gaming process analysis involves a forced displacement of the striking ddakji to a predetermined collision position. Collision analysis then follows at a given speed, with the objective of overturning the struck ddakji--a winning condition. A genetic algorithm-based optimization analysis identifies the optimal collision conditions that result in the overturning of the struck ddakji. For efficiency, the collision analysis is divided into two stages, with the second stage carried out only if the first stage predicts a possible overturn. The fitness function for the genetic algorithm during the first stage is the direction cosine of the struck ddakji, whereas in the second stage, it is the inverse of the speed, thus targeting the lowest overall collision speed. Consequently, this analysis provides optimal collision conditions for various compression thicknesses.