• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.6
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• pp.496-502
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• 2007

In the present paper, a new version of DYMORE, which is an analysis to solve a nonlinear multi-body dynamics problem, is used to simulate an Individual Blade Control (IBC) algorithm in order to reduce vibration in helicopter rotors. The Active Twist Rotor (ATR), in which Active Fiber Composites (AFC) are embedded, is utilized for IBC. The main purpose of the present investigation is to compare the analytical results with experiments and previous version of DYMORE. The experiments are performed at NASA Langley Transonic Dynamics Tunnel. According to the present result, it is observed that the correlation regarding the vibratory loads is improved.

• Journal of the Korean Society for Railway
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• v.11 no.1
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• pp.61-68
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• 2008

Resilient modulus has been used for characterizing the stress-strain behavior of subgrade soils subjected to traffic loadings. With the recent release of the M-E Design Guide, highway agencies are further encouraged to implement the resilient modulus test to improve subgrade design. The subgrade design for the trackbed, however, is primarily relying on the static test results such as $K_{30}$ and deformation modulus, Ev. Therefore applicability of the resilient modulus for the design of trackbed needs to be evaluated. In this study, physical property tests, unconfined compressive tests and resilient modulus tests were conducted to assess the resilient and permanent strain behavior of 14 cohesive subgrade soils. A predictive model for estimating the resilient modulus is proposed based on the results of unconfined compressive tests and tangent elastic modulus, unconfined compressive strength, failure strain, secant modulus at peak, and yield strain. The predicted resilient moduli using the predictive models compared satisfactorily with measured ones. Although the permanent strain occurs during the resilient modulus test, the permanent behavior of subgrade soils is currently not taken into consideration.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.24 no.2
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• pp.43-50
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• 1979

In order to determine the effect of mixtures of different barley genotypes, four barley varieties that were similar to the variety Kangbori for earliness, culm length, spike type and spike color were tested. The variety Kangbori was mixed with the 4 other barleys in ratios ranging from 20% to 80% of Kangbori. Tests were conducted at Suweon and Iri. It was difficult to distinguish differences in heading date, maturing date and culm length in the various mixtures. In the mixed populations the degree of lodging was decreased due to the superior straw strength of Kangbori. The mixtures of 20% Kangbori and 80% Bunong and 20% Kangbori and 80% Milyang #6 gave the highest yield increase among the combinations.

• Journal of the Korea Concrete Institute
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• v.23 no.6
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• pp.809-815
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• 2011

An experimental investigations on the bond-slip properties of the steel and Glass Fiber Reinforced Polymer(GFRP) bars in engineered cementitious composite (ECC) with Polyvinyl Alcohol (PVA) fibers are presented. Total of 8 beam specimens prepared according to the Rilem procedures with 2% of PVA and PE fiber volume percentage and steel and GFRP reinforcements significantly changed the failure mechanism and slightly improved bond strength. The main objective of the tests was to evaluate the load versus displacement and load versus slip behaviors and the bond strength for the following parameters: concrete type (normal and fiber concrete) and bar diameter (10 and 13 mm). The study results showed that ordinary concrete and ECC specimens showed similar behavior for steel reinforced specimen. However, GFRP reinforced specimen showed different behavior that the steel specimen. The code analytical results showed more accuracy compared to the experimental results as expected in conservative code provisions. Based on the obtained results, it is safe to conclude that the new parameters need to be adopted to ensure safe usage of ECC for construction applications.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.6
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• pp.18-28
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• 2015

The purpose of this study is to develop a new seismic resistant method by using precast concrete wall panels for existing low-rise, reinforced concrete beam-column buildings such as school buildings. Three quasi-static hysteresis loading tests were performed on one unreinforced beam-column specimen and two reinforced specimens with U-type precast wall panels. The results were analyzed to find that the specimen with anchored connection experienced shear failure, while the other specimen with steel plate connection principally manifested flexural failure. The ultimate strength of the specimens was determined to be the weaker of the shear strength of top connection and flexural strength at the critical section of precast panel. In this setup of U-type panel specimens, if a push loading is applied to the reinforced concrete column on one side and push the precast concrete panel, a pull loading from upper shear connection is to be applied to the other side of the top shear connection of precast panel. Since the composite flexural behavior of the two members govern the total behavior during the push loading process, the ultimate horizontal resistance of this specimen was not directly influenced by shear strength at the top connection of precast panel. However, the RC column and PC wall panel member mainly exhibited non-composite behavior during the pull loading process. The ultimate horizontal resistance was directly influenced by the shear strength of top connection because the pull loading from the beam applied directly to the upper shear connection. The analytical result for the internal shear resistance at the connection pursuant to the anchor shear design of ACI 318M-11 Appendix-D, agreed with the experimental result based on the elastic analysis of Midas-Zen by using the largest loading from experiment.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1995.10a
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• pp.111-121
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• 1995

In Extracting the dynamic parameters for estimating the load carrying capacity and integrity of bridges, both the instrumentation and the processing the data plays important role . When the fixed point can not be secured, it is difficult and expensive to measure dynamic displacements. Even if the displacement is obtained through the integration of the acceleration data, the results can be quite different from the real behavior, because the main frequency contents can be leaked during discretized data processing. The instrumentation is used for measurements, and every measurement involves error and uncertainty, such as systematic, conformance, environmental, observational, sampling, and ranmom error. Systematic and conformance error can be remedied through the proper sellection and installation of the instruments, but sampling and random errors could not have been corrected properly and it becomes the limitation for using acceleration data. In this paper, the errors which can be occurred in numerical processing of dynamic data are referred, and the method to sellect proper sampling rate for the structural frequency range are proposed. Using the proposed method, the displacement response of the structures can be economically obtained from the measured acceleration record, and this procedure can be used properly to estimate the integrity of the bridges and infrastructures subjected to dynamic loads.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.5
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• pp.433-441
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• 2009

Generally, the events in nature have multi-disciplinary characteristics. To solve this problems, these days loosely coupled methods are widely applied because of advantage of solvers which are already developed and well proved. Those solvers use different mesh system, so transformation and mapping of data are vital in the field of fluid-structure interaction(FSI). In this paper, the interpolation of deformation which is used globally and compactly supported radial basis functions(RBF), and mapping of force which use principle of virtual work are examined for computing time and accuracy to compare ability with simple 3-D problem. As the results, interpolation scheme of compactly supported radial basis functions are useful to interpolation and mapping for large-scale airplane in FSI with a k-dimensional tree(kd-tree) which is a space-partitioning data structure for organizing points in a k-dimensional space.

• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.6
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• pp.439-447
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• 1999

One of the problems for practical use of fiber-reinforced plastics is the performance degradation by fatigue damage in the joints. The study is to develop a nondestructive technique for real-time evaluation of adhesively bonded composite-metal joints. From the prior study we confirmed that the bonding strength can be estimated from the correlation between the qualify of bonded parts and AUP's. We obtained a curve showing the correlation between the degree of fatigue damage and AUP's calculated from signals acquired during fatigue loading of single-lap and double-lap joints of CFRP and Al6061. The curve is an analogy to the one showing stiffness reduction ($E/E_o$) of polymer matrix composites by fatigue damage. From those facts, it is plausible to predict the degree of fatigue damage in real-time. Amplitude and AUP2 appeared to be optimal parameters to provide more reliable results for single-lap joints whereas Amplitude and AUP2 did for double-lap joints. It is recommended to select optimal parameters for different geometries in the application for real structures.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.4
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• pp.8-14
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• 2019

In Korean traditional wooden architecture, joint performance varies with the material characteristics of timber, the form of joint, the precision of timber-trimming and the like. Case studies prove that the beam-to-column joint type has large influence on the degrees of deformation and spacing. This is not only true of single-story buildings, but also of large-scale multi-story buildings more apparently. Therefore, this study followed the process of examining to joint types, producing their specimens and testing their structural performance. As a consequence of structural test, the dovetail joint specimen showed the best outcomes of the maximum load and rigidity. Synthesizing the structural performances by respective forms of joints, the Doraegeoji dovetail joint specimen showed the higher performance, followed in order by the Doraegeoji mortise joint specimen and the Tongneoko dovetail joint specimen. The structural performance of a building varies with the characteristics by the shouldering forms of penetrating beams and with the joint types within the columns. This should be considered for the new construction or restoration of multi-story buildings, and be continuously researched henceforth.

• Journal of the Korean Geotechnical Society
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• v.24 no.7
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• pp.61-73
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• 2008

Piles of a bridge pier are connected with the column through the pile cap (footing). Behavior of the pile foundation can be different according to the connection method between piles and the pile cap. Connection methods between pile heads and the pile cap are divided into two groups : rigid connections and hinge connections. Domestic design code has been specified to use rigid connection method for the highway bridge. In the rigid connection method, maximum bending moment of a pile occurs at the pile head and this helps the pile to prevent the excessive displacement. Rigid methods are also good to improve the seismic performance. However, some specifications prescribe that conservative results through investigations of both the fixed-head condition and the free-head condition should be reflected in the design. This statement may induce an over-estimated design for the bridge which has high-quality structures with casing covered drilled shafts and the PC-house contained pile cap. Because the assumption of free-head conditions (hinge connections) is unreal for the elevated pile cap system with multiple piles of the long span sea-crossing bridges. On the other hand, elastic displacement method to evaluate the pile reactions under the pile cap is not suitable for this type of bridges due to impractical assumptions. So, full modeling techniques which analyze the superstructure and the substructure simultaneously should be performed. Loads and stress state of the large diameter drilled shaft and the pile cap for Incheon Bridge which will be the longest bridge of Korea were investigated through the full modeling for rigid connection conditions.