• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.4
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• pp.353-362
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• 2007

Unlike large satellites, small satellites, such as nanosatellite and microsatellite, can provide a limited interior space for components mounting. In order to mitigate this issue, the compact Bus Electronic Unit(BEU) that integrates satellite electronic modules, combining most of bus subsystems and payload electronic modules into one unit, has been developed for HAUSAT-2 nanosatellite. This paper addresses the design and environmental test result analyses of BEU. The vibration and thermal vacuum tests were conducted at qualification level for the verification of design margin of newly developed BEU. The performance of individual electronic subsystem modules has been verified through performance tests before and after the qualification tests. It was confirmed that the natural frequency of BEU satisfies the design stiffness requirement without structural damage in the vibration test. Thermal analysis results were also almost consistent with test results through modified thermal analysis modeling.

• Journal of the Korea institute for structural maintenance and inspection
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• v.7 no.3
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• pp.183-191
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• 2003

A four-story reinforced concrete moment resisting frame damaged from an ultimate limit state earthquake is upgraded with prestressing cable bracing. The purpose of this study is to investigate the bracing configuration effects on the 3-D building response using thee different locations of the bracing systems for the retrofitted building. Since the previous work done by the author proved that static incremental loads to collapse analysis as a substitute to dynamic non-linear time history analysis was a valid alternative tool. Thus, static load to collapse analysis is solely applied to evaluate the seismic performance parameters of both the original and upgraded buildings in this study. In results, the exterior bracing system is effective in restraining torsional behavior of the structure under seismic loads, and no sudden failure occurs in this system that enhances the ductility of the building due to the gradual change of building stiffness as the lateral load increases.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.9
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• pp.1033-1039
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• 2012

Artificial joints are used when joints lose their function because of either the destruction or damage of the composing bones of the joints. To evaluate the primary stability of a femur-implant system, the relative displacement caused by a repeated load is measured immediately after the insertion of the artificial joint. For more accurate stability evaluation, the accurate measurement of the penetration displacement of the artificial joint to the bone and the rotation angle of the artificial joint is essential. In this study, to evaluate the primary stability of the femur-implant system, we propose a new relative displacement measurement method. By using this new method, we comparatively evaluate the primary stability for various surgical methods and the varying stiffness of the cadaver femur-implant itself.

• Advances in concrete construction
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• v.8 no.3
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• pp.173-185
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• 2019

This article presents a comparative study of the effect of steel layouts on the seismic behavior of transition steel-concrete composite connections, both experimental and analytical investigations of concrete filled steel tube-reinforced concrete (CFST-RC) and steel reinforecd concrete-reinforced concrete (SRC-RC) structures were conducted. The steel-concrete composite connections were subjected to combined constant axial load and lateral cyclic displacements. Tests were carried out on four full-scale connections extracted from a real project engineering with different levels of axial force. The effect of steel layouts on the mechanical behavior of the transition connections was evaluated by failure modes, hysteretic behavior, backbone curves, displacement ductility, energy dissipation capacity and stiffness degradation. Test results showed that different steel layouts led to significantly different failure modes. For CFST-RC transition specimens, the circular cracks of the concrete at the RC column base was followed by steel yielding at the bottom of the CFST column. While uncoordinated deformation could be observed between SRC and RC columns in SRC-RC transition specimens, the crushing and peeling damage of unconfined concrete at the SRC column base was more serious. The existences of I-shape steel and steel tube avoided the pinching phenomenon on the hysteresis curve, which was different from the hysteresis curve of the general reinforced concrete column. The hysteresis loops were spindle-shaped, indicating excellent seismic performance for these transition composite connections. The average values of equivalent viscous damping coefficients of the four specimens are 0.123, 0.186 and 0.304 corresponding to the yielding point, peak point and ultimate point, respectively. Those values demonstrate that the transition steel-concrete composite connections have great energy dissipating capacity. Based on the experimental research, a high-fidelity ABAQUS model was established to further study the influence of concrete strength, steel grade and longitudinal reinforcement ratio on the mechanical behavior of transition composite connections.

• The Journal of Korean Physical Therapy
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• v.31 no.5
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• pp.266-272
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• 2019

Purpose: This study compared the effects of Static stretching and Mulligan's Two-leg rotation about the Hamstring flexibility, Hip range of motion, and pain. Methods: The subjects were allocated randomly into two groups: Static stretching group (n=13) and Mulligan's two leg rotation group (n=14). The study was designed with stretching protocols for four minutes and thirty seconds per day five times a week for three weeks in total. Measurements, including the Sit and reach test, Active/Passive Straight leg raise, and Visual analogue scale, were conducted before and after the intervention. The data were analyzed using a paired t-test and independent t-test. Results: The flexibility of the two leg rotation group was higher than the static stretching group after the intervention. The post-sit and reach test value of the two leg rotation group was significantly higher than the pre-sit and reach test value of the static stretching group. In addition, the variance of the sit and reach test of the two leg rotation group was significantly higher than that of the static stretching group. Conclusion: These results showed that two leg rotation techniques have a positive effect on the changes in the sit and reach test and active straight leg raise test. Two leg rotation techniques can be recommended as a self-stretching and easier way to stabilize the lumbopelvic rhythm, reduce the stiffness of the muscle and relieve pain. This is effective in preventing muscle damage, enabling muscle relaxation and reducing the risk of injury to the spine during daily lives and in sports activities.

• Smart Structures and Systems
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• v.15 no.1
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• pp.99-117
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• 2015

The Stonecutters Bridge (SCB) in Hong Kong is the third-longest cable-stayed bridge in the world with a main span stretching 1,018 m between two 298 m high single-leg tapering composite towers. A Wind and Structural Health Monitoring System (WASHMS) is being implemented on SCB by the Highways Department of The Hong Kong SAR Government, and the SCB-WASHMS is composed of more than 1,300 sensors in 15 types. In order to establish a linkage between structural health monitoring and maintenance management, a Structural Health Rating System (SHRS) with relevant rating tools and indices is devised. On the basis of a 3D space frame finite element model (FEM) of SCB and model updating, this paper presents the development of an SHR-oriented 3D multi-scale FEM for the purpose of load-resistance analysis and damage evaluation in structural element level, including modeling, refinement and validation of the multi-scale FEM. The refined 3D structural segments at deck and towers are established in critical segment positions corresponding to maximum cable forces. The components in the critical segment region are modeled as a full 3D FEM and fitted into the 3D space frame FEM. The boundary conditions between beam and shell elements are performed conforming to equivalent stiffness, effective mass and compatibility of deformation. The 3D multi-scale FEM is verified by the in-situ measured dynamic characteristics and static response. A good agreement between the FEM and measurement results indicates that the 3D multi-scale FEM is precise and efficient for WASHMS and SHRS of SCB. In addition, stress distribution and concentration of the critical segments in the 3D multi-scale FEM under temperature loads, static wind loads and equivalent seismic loads are investigated. Stress concentration elements under equivalent seismic loads exist in the anchor zone in steel/concrete beam and the anchor plate edge in steel anchor box of the towers.

• Earthquakes and Structures
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• v.20 no.2
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• pp.149-160
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• 2021

Buildings made using the locally available clay materials are amongst the least expensive forms of construction in many developing countries, and therefore, widely popular in remote areas. It is despite the fact that these low-strength masonry structures are vulnerable to seismic forces. Since transporting imported materials like cement and steel in areas inaccessible by motorable roads is challenging and financially unviable. This paper presents, and experimentally investigates, adobe masonry structures that utilize the abundantly available local clay materials with moderate use of imported materials like cement, aggregates, and steel. Shake-table tests were performed on two 1:3 reduce-scaled adobe masonry models for experimental seismic testing and verification. The model AM1 was confined with vertical lightly reinforced concrete columns provided at all corners and reinforced concrete horizontal bands (i.e., tie beams) provided at sill, lintel, and eave levels. The model AM2 was confined only with the horizontal bands provided at sill, lintel, and eave levels. The models were subjected to sinusoidal base motions for studying the damage evolution and response of the model under dynamic lateral loading. The lateral forcedeformation capacity curves for both models were developed and bi-linearized to compute the seismic response parameters: stiffness, strength, ductility, and response modification factor R. Seismic performance levels, story-drift, base shear coefficient, and the expected structural damages, were defined for both the models. Seismic performance assessment of the selected models was carried out using the lateral seismic force procedure to evaluate their safety in different seismic zones. The use of vertical columns in AM1 has shown a considerable increase in the lateral strength of the model in comparison to AM2. Although an R factor equal to 2.0 is recommended for both the models, AM1 has exhibited better seismic performance in all seismic zones due to its relatively high lateral strength in comparison to AM2.

• Journal of the Korean Geotechnical Society
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• v.37 no.6
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• pp.39-50
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• 2021

Recently, as the occurrence of earthquakes with a magnitude of 5.0 or higher in Korea increases, many studies and interests in seismic design are increasing. A lot of damage was caused by the Pohang earthquake in 2017, and port facilities such as a breakwater were also damaged. This study analyzed the dynamic behavior of the upright breakwater, an external facility, based on a centrifugal model experiment. A series of centrifugal model test was conducted by three different seismic waves such as Pohang Earthquake Wave, Artificial Wave I, and II. As a result, the dynamic behavior of upright breakwater was analyzed. The review showed that acceleration amplification tends to be suppressed as breakwater foundation ground increases support and stiffness through DCM reinforcement and riprap replacement.

• Smart Structures and Systems
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• v.30 no.6
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• pp.687-701
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• 2022

Inevitable response loss under complex operational conditions significantly affects the integrity and quality of measured data, leading the structural health monitoring (SHM) ineffective. To remedy the impact of data loss, a common way is to transfer the recorded response of available measure point to where the data loss occurred by establishing the response mapping from measured data. However, the current research has yet addressed the structural condition changes afterward and response mapping learning from a small sample. So, this paper proposes a novel data driven structural response reconstruction method based on a sophisticated designed generating adversarial network (UAGAN). Advanced deep learning techniques including U-shaped dense blocks, self-attention and a customized loss function are specialized and embedded in UAGAN to improve the universal and representative features extraction and generalized responses mapping establishment. In numerical validation, UAGAN efficiently and accurately captures the distinguished features of structural response from only 40 training samples of the intact structure. Besides, the established response mapping is universal, which effectively reconstructs responses of the structure suffered up to 10% random stiffness reduction or structural damage. In the experimental validation, UAGAN is trained with ambient response and applied to reconstruct response measured under earthquake. The reconstruction losses of response in the time and frequency domains reached 16% and 17%, that is better than the previous research, demonstrating the leading performance of the sophisticated designed network. In addition, the identified modal parameters from reconstructed and the corresponding true responses are highly consistent indicates that the proposed UAGAN is very potential to be applied to practical civil engineering.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.42 no.6
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• pp.775-786
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• 2022

In the plant structures including nuclear power plants, penetrations are frequently installed in walls and slabs to reinforce facilities during operation, and reinforcing bars are sometimes cut off during concrete coring. Since these penetrations are not considered at the design or construction stage, cutting of reinforcing bar during opening installation is actually damage to the structure, structural integrity evaluation considering the stress transition range or effective width around the new penetration is necessary. In this study, various nonlinear analyses and static loading experiments are performed to evaluate the effect of reinforcing bar cutting that occurs when a penetration is newly installed in the shear wall of wall-type building of operating nuclear power plant. In addition, the decrease in wall stiffness due to the installed new penetration and cutting of reinforcing bars is evaluated and the stress and strain distributions of rebars around penetration are also measured.