• Land and Housing Review
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• v.2 no.3
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• pp.287-297
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• 2011

This paper presents the results of performance verification tests of the isolated flat plate apartment building with the laminated rubber bearings. The shaking table test is carried out in CABR(China Academy of Building Research) with two 1/10 scale isolation and non-isolation models under 4 excitation waves. The shaking table test is proceeding from x axis, y axis and x+y axis with different amplitude of acceleration values. The results show that, to non-isolated model, the natural vibration period is remarkably decreased and entered non-linear condition after moderate earthquake. Its accelerations become lager with increasing storey number and completely collapsed under large earthquake. The inter-storey shifts largely exceed the limit values of regulated displacement angles. But to isolated model, the natural vibration period of isolated modal is almost the same in all conditions and still in its elastic condition. The earthquake loading is greatly reduced and the accelerations of superstructure are greatly reduced. The inter-storey drifts are very small and can be neglected. The isolated model is in translational state and can be seen as a rigid whole. The displacements of isolation layer are in the allowable range. This experiment demonstrates that the seismic isolation is very effective to mitigate the influence of earthquake on structures and it is possible to increase the serviceability due to decrease the floor acceleration. facilities from their good states that is superior to non-isolated structure.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.12
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• pp.50-56
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• 2017

The perimeter structure in high-rise buildings, which plays a major role in resisting lateral forces, is generally formed by the orthogonal placement of the beam and column, but currently various grid patterns are implemented. In a previous study, the adaptability of the $IsoTruss^{(R)}$ grid (ITG) as a perimeter structure was examined. In this study, a method of estimating the required cross sectional area of a member in a preliminary design is proposed. The members of the perimeter structure are placed in three planes, perpendicular (PPR), parallel (PPL) and oblique (POQ) to the lateral loading, and the stiffness of the members in the POQ was taken into account by projecting them onto the PPL or PPR. Three models are established for member size zoning through the height of the building, in order to investigate the effect of the shear and moment in the calculation of the required cross sectional area. To examine the effectiveness of this study, a 64-story building is designed and analyzed. The effect of the member size zoning was examined by comparing the maximum lateral displacement, required steel amount, and axial strength ratio of the columns. Judging from the maximum lateral displacement, which was 97.3% of the allowable limit, the proposed formula seems to be implemental in sizing the members of an ITG structure at the initial stage of member selection.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.31 no.2
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• pp.97-104
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• 2018

In this study, a structure satisfying the fatigue constraint is designed by applying the topology optimization based on the phase field design method. In order to predict life based on the stress value, high cycle fatigue failure theory in which stress acts within the range of elastic limit is discussed and three fatigue theories of modified-Goodman, Smith-Watson-Topper and Gerber theory are applied. To calculate the global maximum stress, a modified P-norm stress correction method is used. As a result, it is possible to obtain topology optimization results that minimize the volume while satisfying the fatigue constraints. By applying the phase field design method, a simple shape with a minimized gray scale was obtained, and the maximum stress value acting on the optimization result became very close to the allowable stress value due to the modified P-norm stress method. While previous studies does not consider the stress correction factor, this study proposes the determination method regarding the stress correction factor considering loading effects related to axial stress components.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.2C
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• pp.192-199
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• 2008

In ultra-wideband (UWB) systems, conventionally, the synchronization is to align time phases of a locally generated template and any of multipath components to within an allowable range. However, the synchronization with a low-power multipath component could incur significant performance degradation in receiver operation (e.g., detection) after the synchronization. On the other hand, the synchronization with a high-power multipath component can improve the performance in receiver operation after the synchronization. Generally, the first one among multipath components has the largest power. Thus, the synchronization with the first path component can make better performance than that with low-power component in receiver operation after the synchronization, Based on which, we first propose an optimal decision rule based on a maximum likelihood (ML) approach, and then, develope a simpler suboptimal decision rule for selecting the first path component. Simulation results show that the system has good demodulation performance, which uses new synchronization definition and the proposed decision rules have better performance than that of the conventional decision rule in UWB multipath channels. Between macroblocks in the previous and the current frame. On video samples with high motion and scene change cases, experimental results show that (1) the proposed algorithm adapts the encoded bitstream to limited channel capacity, while existing algorithms abruptly excess the limit bit rate; (2) the proposed algorithm improves picture quality with $0.4{\sim}0.9$dB in average.

• Journal of the Korean Society for Railway
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• v.20 no.5
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• pp.569-576
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• 2017

The electromagnetic valve of pneumatic doors of EMUs has a high failure rate due to air leakage because it supplies air on and off to operate the doors repeatedly. The electromagnetic valve is a very important safety component for which a very high reliability is required because failure makes it impossible to operate the passenger cars. However, domestic urban railway operators maintain electronic valves of the EMU door under a fixed cycle with a spare period according to the full overhaul cycle of the EMU. An improvement of the current maintenance cycle was suggested based on the reliability function and mission reliability. Using the statistical program MINITAB for the operational data of EMU line 6, we analyzed the characteristics of the fault distribution and derived the shape and scale parameters of the reliability function. If we limit the specific reliability probability to under a certain failure rate and calculate its statistical parameters, we can calculate the allowable inspection period with mission reliability. Through this study, we suggested a maintenance period based on RCM (reliability centered-maintenance) to improve the reliability of electromagnetic valves from 68% to 95%.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.27 no.1
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• pp.9-16
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• 2014

Using a level set method and topological derivatives, a topological shape optimization method that is independent of an initial design is developed for linearly elastic structures. In the level set method, the initial domain is kept fixed and its boundary is represented by an implicit moving boundary embedded in the level set function, which facilitates to handle complicated topological shape changes. The "Hamilton-Jacobi(H-J)" equation and computationally robust numerical technique of "up-wind scheme" lead the initial implicit boundary to an optimal one according to the normal velocity field while minimizing the objective function of compliance and satisfying the constraint of allowable volume. Based on the asymptotic regularization concept, the topological derivative is considered as the limit of shape derivative as the radius of hole approaches to zero. The required velocity field to update the H-J equation is determined from the descent direction of Lagrangian derived from optimality conditions. It turns out that the initial holes are not required to get the optimal result since the developed method can create holes whenever and wherever necessary using indicators obtained from the topological derivatives. It is demonstrated that the proper choice of control parameters for nucleation is crucial for efficient optimization process.

• Journal of Korea Water Resources Association
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• v.35 no.1
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• pp.77-90
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• 2002

The condition of initial movement for the river bed revetment using rip rap is a limit condition beyond which the lining is progressively destroyed as the separate elements are removed by the flow. In the case of the river bed revetment using mattress, however, after the initial movement the containment offered by the mesh remains. A new situation of equilibrium with a deformed river bed revetment using mattress is obtained, allowing it to withstand more severe conditions without compromising the resistance and without further bed deformation. Shield's coefficient for the river bed revetment using mattress is twice the value of that for the river bed revetment using rip rap. This means that with the same hydraulic behavior conditions, the average dimension of the rocks to be used in the river bed revetment using mattress is half that of the river bed revetment using rip rap rock. When the same size rocks are used the allowable velocity for the river bed revetment using mattress is more than twice, even as much as 3 or 4 times that for the river bed revetment using rip rap.

• Journal of the Korean Society of Safety
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• v.35 no.5
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• pp.49-58
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• 2020

In domestic construction sites, when installing steel pipe scaffolding and system scaffolding, the guardrails are installed after the installation of the work platforms. This conventional guardrail system (CGS) is always exposed to the risk of falls because the safety railing is installed later. In order to prevent fall disasters during erecting and dismantling scaffolds, it is necessary to introduce the advanced guardrail system (AGS) which installs railings in advance of climbing onto a work platform. For the introduction of the AGS, the structural performance of the system scaffolding applying the CGS and the AGS was compared and evaluated. The structural analysis of the system scaffold (height: 31 m and width: 27.4 m) with AGS confirmed that structural safety was ensured because the maximum stress of each element of the system scaffolding satisfies the allowable stress of each element. As a result of performance comparison of CGS and AGS for each element, the combined stress ratio of vertical posts in AGS was 6.4% lower than that of CGS. In addition, in the case of ledger and transom, the combined stress ratios of AGS and CGS were almost the same. The compression test of the assembled system scaffolding (three-storied, 1 bay) showed that the AGS had better performance than the CGS by 9.7% (8.91 kN). The cross bracing exceeds the limit on slenderness ratio of codes for structural steel design. But the safety factor for the compressive load of the cross bracing was evaluated as meeting the design criteria by securing 3 or more. In actual experiments, it was confirmed that brace buckling did not occur even though the overall scaffold was buckled. Therefore, in the case of temporary structures, it was proposed to revise the standards for limiting on slenderness ratio of secondary or auxiliary elements to recommendations. This study can be used as basic data for the introduction of AGS for installing guardrails in advance at domestic construction sites.

• Journal of the Korean GEO-environmental Society
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• v.20 no.7
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• pp.5-10
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• 2019

In recent Gyeongju and Pohang earthquakes, motions that exceed the design ground motion were recorded. This has led to adjustments to the design earthquake intensity in selected design guidelines. An increment in the design intensity requires reevaluation of all associated facilities, requiring extensive time and cost. Firstly, the seismic factor of safety of built concrete retaining walls are calculated. Secondly, the seismic margin of concrete retaining walls is evaluated. The design sections of concrete walls built at power plants and available site investigation reports are utilized. Widely used pseudo-static analysis method is used to evaluate the seismic performance. It is shown that all concrete walls are safe against the adjusted design ground motion. To determine the seismic margin of concrete walls, the critical accelerations, which is defined as the acceleration that causes the seismic factor of safety to exceed the allowable value, are calculated. The critical acceleration is calculated as 0.36g~0.8g. The limit accelerations are significantly higher than the design intensity and are demonstrated to have sufficient seismic margin. Therefore, it is concluded that the concrete retaining walls do not need to be reevaluated even if the design demand is increased up to 0.3g.

• Journal of Aerospace System Engineering
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• v.16 no.1
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• pp.104-109
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• 2022

The bomb rack unit (BRU) installed inside the pylon serves to fix external attachments such as external fuel tank or external weapon, and also serves to separate external attachments in case of emergency. In particular, the load generated when the external attachment is separated from the BRU is called the punching load. In this study, we present the results of a structural static test performed to verify the structural integrity of the pylon under the BRU punching condition acting on it. In the structural static test report, we present the implementation method for the separation load of the external attachment and the test profile for the BRU punching load condition, and compared the error between the load input signal and the feed-back signal to determine the appropriateness of load control in each test. Furthermore, we compared the strain results obtained in the numerical analysis and structural test at the main positions of the specimen. As a result, it was shown that the load of the actuators were properly controlled within the allowable error range in each test, and the numerical analysis effectively predicted the test result. Finally, through structural static tests conducted by design limit load and design ultimate load, we verified that the aircraft pylon dealt with in this study has sufficient structural strength for external attachment separation condition.