• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.4
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• pp.415-422
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• 2016

When shock acceleration is applied to a mechanical system, it may cause malfunctioning and damage to the system. Hence, to prevent these problems when developing a gimbal structure system for observation reconnaissance, the MIL-STD-810G shock standard must be satisfied as a design specification. Rubber vibration isolators are generally assembled on the base of the system in order to reduce the shock transferred from the aircraft. It is difficult to analyze the transient behavior of the system accurately, because rubber has a nonlinear load-deformation curve. To treat the nonlinear characteristic of the rubber, bilinear approximation was introduced. Using this assumption, transient responses of the system under base shock acceleration were calculated by the finite element method. In addition, experiments with a true prototype were performed using the same conditions as the analytical model. Compared with experimental data, the proposed numerical method is useful for the transient analysis of gimbal structure systems, including rubber vibration isolators with nonlinear stiffness and damping.

• Journal of Korean Society of Steel Construction
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• v.13 no.5
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• pp.535-545
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• 2001

A refined method of analysis which is called the Advanced Analysis has been introduced This method is to consider the intial member imperfection residual stress and second-order effects so as to estimate the overall behavior of steel frame accurately Based on the refined plastic hinge method that is more suitable and practical in design practice. the program RPH-2DF is coded using the log model which represents the moment-rotation relationship of connection. The validity of this program is examined by frame test data. Finally to investigate the difference between behaviors of rigid and semi-rigid frame. the 10-story frame analysis results designed by MIDAS-GEN v4.2.2 are compared with the results by RPH-2DF.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.3
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• pp.58-65
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• 2016

Various passive energy dissipation systems have been proposed and widely applied to real building structures under seismic load due to their high energy-dissipation potential and low cost for installation and maintenance. This paper presents nonlinear dynamic analysis results of the effectiveness of exterior-installed Kagome damping system(EKDS) in passively reducing seismic response. Kagome damping system proposed by previous studies has isotropic and bi-linear hysteretic characteristics and the installation configuration is newly presented in this study. The 15 and 20 story RC framed apartment buildings are used for verifying the effectiveness of the EKDS. The stiffness ratio of the damper supporting column to the original building, the number of the dampers, and the installed stories were considered as design parameters. Numerical results demonstrated that the EKDS were very effective in reducing both the two horizontal directional seismic responses by just using smaller number of exterior-installed damping system when compared to the traditional one-directional inter-story installed damping systems.

• Journal of the Earthquake Engineering Society of Korea
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• v.9 no.6 s.46
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• pp.21-30
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• 2005

In this study, a seismic design methodology for friction dampers based on the story shear force distribution of an elastic building structure is proposed. First, using two normalization methods for the slip-load of a friction damper, numerical analyses of various single-degree-of-freedom systems are peformed. From those analyses, the effect of the slip-load and the brace stiffness was investigated and the optimal silliness ratio of the brace versus original structure was found. Second, from the numerical analysis for five multi-story building structures with different natural frequency and the number of story, reasonable decision method for the total number of installation floor, location of installation and distribution of the slip-loads are drawn. In addition, an empirical equation on the optimal number of installation floor is proposed. Finally, the superiority of the proposed method compared to the existing design method is verified from the numerical analysis using real earthquake data.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.6
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• pp.742-752
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• 2017

The bridge type of steel concrete composite rahmen or pre-flex has been applied where a lower depth girder is required due to vertical clearance restrictions caused by the crossing of rivers and roads. On the other hand, because these types are not only complicated to manufacture and construct, but also expensive, void slab bridges may be an alternative. In this study, prefabricated PSC-I shape girder was used to make a void slab and all procedures for bridge development, such as analysis, design, fabrication, and real-scale test, were included in the scope of research. The results of this study will provide sufficient background data to be applied to the field and the structural safety has been verified through experiments.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.5
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• pp.1363-1372
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• 2014

In the previous study, the structural performance of proposed precast concrete arch with reinforced joint was evaluated by structural experiment. In this paper, finite element analysis considering both material and contact nonlinearity was carried out on the specimens of the previous study. Based on the result of analysis and experiment, friction coefficient between concrete blocks was determined. To evaluate the strength of sectional member, elastic analysis was carried out on the arch using linear elastic analysis program. The section force was compared with the nominal strength of arch section. It was concluded that the maximum load of all the specimens exceed the nominal strength of arch section. Those results of the strength evaluation were similar to the results of structural experiments. Therefore, it is concluded that the elastic analysis and ultimate strength model can effectively evaluate the strength for the proposed precast concrete arch composed of concrete blocks and reinforced joint in design.

• Magazine of the Korea Concrete Institute
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• v.7 no.2
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• pp.136-145
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• 1995

A method for lmprovlng strengths of recycled concrete was studied to make use of it in nolmal concrete structures. Recycled conc~ete was prepared by replacing 50% by weight of coarse aggregate with recycled aggregate. Mix design rnet hod for crushed aggregates was used and specirriens were cured by normal moisture curing method. A plastlciser and a fly ash were added to the mix to improve performance of recycled concrete. Compressive strength, flexural strength, tensile strength, elastic modulus, stress-strain relationship, long-term compressive strength and fracture toughness were evaluated and compared with those of rlormal concretes. Recycled concrete showed, in general, lower compressive strength than normal concreks. It also showed lower elastic modulus, lower tensile and flexural strengths, and higher strain under the same stress level. However, by reducing w /c ratio down to 35% using the plasticiser. average compressive strength(${\alpha}_{28}$) of recycled concrete was reached. with slump of $16{\pm}2$cm, to $225kg/cm^2$ or hlgher, which is an acceptable strmgth level for normal structural concrete. I-Iowevei., elastic modulus and strain should be improved further for practical use of recycled concrctc: in normal structure. Fly ash addition in both concretes showed an effect of irnprovilig long term compressive strength and reducing strengths.

• Journal of the Korean Geotechnical Society
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• v.31 no.9
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• pp.17-27
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• 2015

We perform a series of experimental tests to evaluate whether the shear strength of clean sands can be reliably predicted from shear wave velocity. Isotropic drained triaxial tests on clean sands reconstituted at different relative densities are performed to measure the shear strength and bender elements are used to measure the shear wave velocity. Laboratory tests reveal that a correlation between shear wave velocity, void ratio, and confining pressure can be made. The correlation can be used to determine the void ratio from measured shear wave velocity, from which the shear strength is predicted. We also show that a unique relationship exists between maximum shear modulus and effective axial stress at failure. The accuracy of the equation can be enhanced by including the normalized confining pressure in the equation. Comparisons between measured and predicted effective friction angle demonstrate that the proposed equation can accurately predict the internal friction angle of granular soils, accounting for the effect of the relative density, from shear wave velocity.

• Journal of the Society of Naval Architects of Korea
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• v.43 no.4 s.148
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• pp.512-520
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• 2006

The effects of flexibilities of supporting structures on shaft alignment are growing as ship sizes are Increasing mainly for container carrier and LNG carrier. But, most of classification societies not only do not suggest any quantitative guidelines about the flexibilities but also do not have shaft alignment design program considering the flexibility of supporting structures. A newly developed program, which is based on innovative shaft alignment technologies including nonlinear elastic multi-support bearing concept and hull deflection database approach, has S basic modules : 1)fully automated finite element generation module, 2) hull deflection database and it's mapping module on bearings, 3) squeezing and oil film pressure calculation module, 4) optimization module and 5) gap & sag calculation module. First module can generate finite element model including shafts, bearings, bearing seats, hull and engine housing without any misalignment of nodes. Hull deflection database module has built-in absolute deflection data for various ship types, sizes and loading conditions and imposes the transformed relative deflection data on shafting system. The squeezing of lining material and oil film pressures, which are relatively solved by Hertz contact theory and built-in hydrodynamic engine, can be calculated and visualized by pressure calculation module. One of the most representative capabilities is an optimization module based on both DOE and Hooke-Jeeves algorithm.

• Journal of the Korean Society of Hazard Mitigation
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• v.10 no.5
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• pp.27-33
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• 2010

In this study, a monotonic loading test to estimate structural capacity of 12 meter long full scale precast pre-stressed concrete beam specimen was performed with a 2,000 kN dynamic actuator. A couple of embedded steel plate was installed at the ends of the beam and specimens were connected to steel girder frame with high tension bolts. Nominal compressive strength of pre-stressed concrete beam and slab were 50 MPa and 24 MPa respectively. Two HD25 tensile steel reinforcements were welded on vertical plate of embedded steel plate. Pre-stressed concrete beam specimen was loaded by displacement control method with a certain loading pattern which was repeated loading and unloading with 10mm increment displacement. About 88.34%, 86.97% and 66.83% of displacement restoration ratios were evaluated at elastic, inelastic and plastic behavior region of specimen respectively.