• Journal of Aerospace System Engineering
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• v.17 no.2
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• pp.86-93
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• 2023

Pyrotechnic separation devices have been widely used as holding and release mechanism for deployable appendage. However, pyro-shock can cause temporal or permanent damage on shock sensitive components such as electronics, mechanism, and brittle components. This study proposed a low-stiffness blade based passive shock absorber using a multi-layered stiffener laminated with viscoelastic acrylic tapes for reducing transmitted pyro-shock upon explosion of pyrotechnic separation devices. The multi-layered structure with viscoelastic tape has high-damping characteristics to effectively secure structural integrity of low-stiffness blades under the launch environment. The design effectiveness was verified through a shock test by dropping a pendulum. The structural integrity of the shock absorber under a launch environment was evaluated through structural analysis under load conditions with a deployable payload.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.1A
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• pp.15-26
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• 2010

Quasi-static tests were conducted to evaluate structural performance of precast piers prestressed by bonded prestressing steels. Combinations of prestressing bars and normal reinforcing bars, embedded steel tubes and prestressing strands were used as continuous steels crossing the joints of a precast pier. Main design parameters were steel ratio, magnitude of prestress force, and section details. Flexural strength and energy dissipation capacity of precast columns with higher steel ratio showed better performance due to continuous steels after opening of the joints. Precast piers with embedded members showed stable behavior after reaching maximum loads resulting in higher displacement ductility and energy dissipation capacity increased as the introduced prestress increased. Self-centering behavior at early stages and stress increase of confining reinforcements were observed from highly prestressed columns. Combination of prestressing steels and normal reinforcing bars should be used in design to prevent rapid strength degradation after reaching the maximum load.

• Journal of the Korean Geotechnical Society
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• v.26 no.7
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• pp.117-133
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• 2010

A hybrid system of soil-nailing and compression anchor is proposed in this paper; the system is composed of an anchor bar (installed at the tip) with two PC strands and a steel bar. After drilling a hole, installing proposed hybrid systems, and filling the hole with grouting material, prestress is applied to the anchor bar to restrict the deformation at the head and/or to prevent shallow slope failures. However, since the elongation rate of PC strand is much larger than that of steel bar, yield at the steel bar will occur much earlier than at the PC strand. It means that the yield load of the hybrid system will be overestimated if we simply add yield loads of the two - anchor bar and PC strands. It might be needed to try to match the yielding time of the two materials by applying the prestress to the anchor bar. It means that the main purpose of applying prestress to the anchor bar should be two-fold: to restrict the deformation at the nail head; and more importantly, to maximize the design load of the hybrid system by utilizing load transfer mechanism that transfers the prestress applied at the tip to the head through anchor bar. In order to study the load transfer mechanism in a systematic way, in-situ pullout tests were performed with the following conditions: soil-nailing only; hybrid system with the variation of prestress stresses from 0 kN to 196 kN. It was found that the prestress applied to the anchor system will induce the compressive stress to the steel bar; it will result in decrease in the slope of load-displacement curve of the steel bar. Then, the elongation at which the steel bar will reach yield stress might become similar to that of PC strands. By taking advantage of prestress to match elongations at yield, the pullout design load of the hybrid system can be increased up to twice that of the soil-nailing system.

• Journal of Navigation and Port Research
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• v.32 no.1
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• pp.23-27
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• 2008

This study was carried out to the effect of wind load on the structural stability of an articulated type container crane according to the wind direction assuming that 75m/s wind velocity is applied on a container crane using FSI(fluid-structural interaction). To consider fluid phenomenon around the container crane, the wind load was derived by the computation fluid dynamic, and it applied to the FSI which can guarantee an accuracy and a reliability in the design stage for wind resistant structural stability to minimize the damage due to high wind load applied in a container crane with a 'ㄱ' type articulated boom which used in the total height restriction region. Following from this, the reaction force on the each support of a container crane was suggested. ANSYS ICEM CFD 10.0 and ANSYS CFX 10.0 used for computation fluid dynamic, and the ANSYS Workbench 11.0 was used for the fluid-structural interaction.

• The Journal of the Acoustical Society of Korea
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• v.39 no.4
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• pp.351-363
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• 2020

Launch vehicles are subject to airborne acoustic loads during atmospheric flight and these effects become pronounced especially in transonic region. As the vibration due to the acoustic loads can cause malfunction of payloads, it is essential to predict and reduce the acoustic loads. In this study, a complete process has been developed for predicting airborne vibro-acoustic environment inside the payload pairing and subsequent noise reduction procedure employing acoustic blankets and Helmholtz resonators. Acoustic loads were predicted by Reynolds-Averaged Navier-Stokes (RANS) analysis and a semi-empirical model for pressure fluctuation inside turbulent boundary layer. Coupled vibro-acoustic analysis was performed using VA One SEA's Finite Element Statistical Energy Analysis (FE-SEA) hybrid module and ANSYS APDL. The process has been applied to a hammerhead launch vehicle to evaluate the effect of acoustic load reduction and accordingly to verify the effectiveness of the process. The presently developed process enables to obtain quick analysis result with reasonable accuracy and thus is expected to be useful in the initial design phase of a launch vehicle.

• Journal of the Korean Geotechnical Society
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• v.34 no.12
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• pp.93-103
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• 2018

Behaviors of splices between bolts and welding spliced PHC piles using the tensile strength test were analyzed. The bolts spliced PHC piles, which were tightened over $200N{\cdot}m$ tightening torque, showed straight V shaped line at splices at the lowest 20 N load. Both sides of PHC piles stayed straight, so the full section of bolts spliced piles did not show the unifying behavior, which was the most important performance requirement as pile. Other bolts spliced PHC piles, tightened with $20N{\cdot}m$ loosening torque, also showed the same straight V shaped line at splices for each step of loading. The full section of bolts spliced piles did not return to the initial position after each step of unloading and did not show the elastic material behavior. The splices quality of bolts spliced piles is much lower than that of welding spliced piles with respect to displacement of splices during each step of loadings, residual displacements during each step of unloadings, and failure loads. Results showed that bolts spliced PHC piles, tightened with both over $200N{\cdot}m$ and as low as $20N{\cdot}m$ torque, fell short of performance requirements of spliced PHC pile.

• Journal of the Korean Geotechnical Society
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• v.39 no.3
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• pp.29-40
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• 2023

In this study, we investigated the reinforcing effects of waveform micropiles in a stratigraphic setting comprising buried soil, weathered soil, and weathered rock. We conducted a series of field load tests and determined that waveform micropiles exhibited sufficient bearing capacity through frictional resistance in the soil layer and demonstrated favorable constructability in conditions with deep bedrock layers. Moreover, the vertical stiffness of waveform micropiles was approximately 2.2 times higher than that of conventional micropiles when subjected to the same design load. Pile group load tests comprising conventional and waveform micropiles showed that micropiles with higher stiffness carried a greater proportion of the load. Although there was no significant difference in the bearing capacity between conventional and waveform micropiles under the same design load, waveform micropiles with higher stiffness showed a load-carrying capacity 1.7 to 3.2 times greater than that of conventional micropiles. These findings suggest that waveform micropiles can be effectively used for foundation reinforcement and reduce the risk of foundation failure when increased loads due to modifications such as expansion remodeling are expected.

• Journal of the Korean Geotechnical Society
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• v.25 no.9
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• pp.29-43
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• 2009

As computational technologies have been developed, the load transfer analysis method using load transfer curves is widely performed. Now the load transfer analysis methods are widely used in our country. But most of the curves using in the analysis have been developed in foreign countries. In this study we gathered the data of in situ pile load tests on domestic nine sites in order to derive load transfer curves of driven steel pipe piles. Then we derived average lines of $f/f_{max}$-w/D curves for sandy and clayey soils respectively, which are expressed by hyperbolic function. And the results using these curves and the results using TZPile 2.0 (Analysis program of pile) were compared and analyzed with the results of pile load tests on domestic 3 sites in order to ascertain the applicability of the curves. The results show that the load-settlement relations using the curves in this study are more similar to the measured data and more conservative than those using TZPile 2.0.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.3D
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• pp.499-509
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• 2006

Precast concrete deck has many advantages comparing with the in-situ concrete deck, and has been successfully applied to replacement of the deteriorated decks and to the newly constructed highway bridges in domestic region. In order to apply the precast decks into the railway bridges, however, differences of the load characteristics between the highway and the railway should be properly taken into account including the train load, longitudinal force of the continuous welded rail, acceleration or braking force, temperature change and shrinkage. Proper level of the longitudinal prestress of the tendons that can ensure integrity of the transverse joints in the deck system is of a primary importance. To this aim, the longitudinal tensile stresses induced by the design loads are derived using three-dimensional finite element analyses for the frequently adopted PSC composite girder railway bridge. The effect of the temperature change is also investigated considering the design codes and theoretical equations in an in-depth manner. The estimated proper prestress level to counteract those tensile stresses is above 2.4 MPa, which is similar to the case of the highway bridges.

• Journal of the Korean GEO-environmental Society
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• v.7 no.3
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• pp.77-83
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• 2006

The purpose of this study is to analyze lateral displacement behavior of clay layers in case of the banking in soft ground through model tests. Seven model tests varying with thickness of soft clay and loading velocity are performed to correlate between ground heaving and loading velocity. In case of low loading velocity, vertical settlement below loading plate and small ground heaving are obviously observed. In case of the high loading velocity, it is shown that both soil displacement at the end of a loading plate and surface heaving are large. In addition, the calculated displacements show good agreement with three cases of field measurements in clay with high moisture contents so that we can predict the range of heaving area and the amount of heaving.