• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.6
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• pp.3068-3073
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• 2013

Recently, studies of vibration control performance improvement of tall buildings connected by a sky-bridge have been conducted. In this study, the effect of difference of natural vibration periods of two buildings and install location of a sky-bridge on vibration control performance has been investigated. To this end, 40-story and 50-story building structures were selected as example structures. Analytical models were developed by varying the natural period difference ratio from 1.0 to 1.5. Artificial earthquake load based on KBC2009 was used as an excitation for time history analyses. Based on numerical simulation results, it has been shown that control performance for displacement and velocity of tall buildings connected by a sky-bridge is improved as the difference of natural periods of two buildings increases and the linked story becomes higher. However, in the case of acceleration response, it shows a counter trend compared to displacement and velocity responses.

• Journal of the Korean GEO-environmental Society
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• v.8 no.3
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• pp.67-75
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• 2007

This study was undertaken in order to investigate the load bearing capacity of raft in a piled raft through the laboratory model tests, the numerical and analytical analyses. The model tests were conducted about a piled raft, the free-standing pile group, a single pile, as well as a shallow foundation under equal conditions. The pile spacing and length, group type and soil conditions were varied in the laboratory model tests. The experimental results were compared with those by the commercial program, DEFPIG, conventional methods and Phung's method. According to this study, the behavior of piled raft was affected by pile spacing, length and soil conditions. Phung's method proved to be reliable for estimating the experimental results.

• Journal of the Korea Concrete Institute
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• v.25 no.2
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• pp.165-173
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• 2013

Splice sleeves for HD25 and HD32 rebars with yield strength 500 MPa were studied experimentally and analytically. The shapes of sleeve was examined with nonlinear finite element analyses. A total of 18 specimens were tested with test variables of rebar types, sleeve lengths, mortar compressive strengths, and rebar development lengths. Three identical specimens per each variable were tested in order to prevent any test errors. After tests, numerical studies with a nonlinear finite element method were conducted to evaluate the test results. Experimental studies with 18 specimens showed that the sleeves of this study satisfies the code requirement. It was found that the strength of mortar and the bar development length within the sleeves did not affect to the load-carrying capacity of sleeves.

• Advances in nano research
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• v.7 no.4
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• pp.249-263
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• 2019

In the current paper, an exact solution method is carried out for analyzing the thermo-mechanical vibration of curved FG nano-beams subjected to uniform thermal environmental conditions, by considering porosity distribution via nonlocal strain gradient beam theory for the first time. Nonlocal strain gradient elasticity theory is adopted to consider the size effects in which the stress for not only the nonlocal stress field but also the strain gradients stress field is considered. It is perceived that during manufacturing of functionally graded materials (FGMs) porosities and micro-voids can be occurred inside the material. Material properties of curved porous FG nanobeam are assumed to be temperature-dependent and are supposed to vary through the thickness direction of beam which modeled via modified power-law rule. Since variation of pores along the thickness direction influences the mechanical and physical properties, porosity play a key role in the mechanical response of curved FG nano-structures. The governing equations and related boundary condition of curved porous FG nanobeam under temperature field are derived via the energy method based on Timoshenko beam theory. An analytical Navier solution procedure is utilized to achieve the natural frequencies of porous FG curved nanobeam supposed to thermal loading. The results for simpler states are confirmed with known data in the literature. The effects of various parameters such as nonlocality parameter, porosity volume fractions, thermal effect, gradient index, opening angle and aspect ratio on the natural frequency of curved FG porous nanobeam are successfully discussed. It is concluded that these parameters play key roles on the dynamic behavior of porous FG curved nanobeam. Presented numerical results can serve as benchmarks for future analyses of curve FG nanobeam with porosity phases.

• Journal of the Earthquake Engineering Society of Korea
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• v.9 no.5 s.45
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• pp.1-10
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• 2005

This study proposes a fatigue reliability evaluation procedure for steel-composite high-speed railway bridge based on dynamic analysis and investigates the effectiveness of Tuned Mass Damper(TMD) in terms of the extension of fatigue life of the bridge. For the fatigue reliability evaluation, the limit state is determined using S-N curve and linear fatigue-damage accumulation. Dynamic analyses are peformed repeatedly to consider the uncertainties of train-velocity and damping ratio of the bridge. The distribution of random variables related to fatigue damage for the intended service life is then statistically estimated from analytical results. Finally, the fatigue reliability indices are obtained by means of the Advanced First-Order Second-Moment (AFOSM) method. Through numerical simulation of a steel-composite bridge of 40m span, the effectiveness of TMD on fatigue life of the bridge is examined and the results are presented.

• Journal of the Korean Society for Precision Engineering
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• v.33 no.11
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• pp.911-918
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• 2016

A conical roll-shaping process was proposed for fabrication of a metallic spiral blade applied to a small-scale wind turbine system. A spiral blade has continuously different curvatures, with a range of 100 to 350 mm radius. To fabricate this complex shape, we developed a conical roll-shaping process having two main conical rollers for feeding a blank sheet, and two cylindrical side rollers for control of local bending. For clear understanding of the process parameters, numerical analyses were conducted using a commercial code, Pam-Stamp. This study optimized the effects of process parameters, such as gap and angle between the main rollers and side rollers, and also the movement of side rollers. In order to increase the forming efficiency, a central rotation point was also calculated by the analytical approach. This developed rolling process can thus be utilized in a sheet metal forming process for obtaining spirally curved sheet metal shapes.

• Journal of Korean Society of Steel Construction
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• v.9 no.4 s.33
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• pp.649-658
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• 1997

When steel tube as a column is filled with concrete, it is common that the load-bearing capacities of CFST(Concrete Filled Steel Tube) column are increased substantially, And the CFST column can obtain a capacity of fire resistance without any additional detail on the surface of the steel tube for fire protection. In order to clarify the behavior of CFST column during fire occurrence, a theoretical study is performed, that is, a thermal analysis is used to find temperature gradient dependent on the time on the steel tube and the infilled concrete. N-M (axial force-moment) interaction curves are summarized under the consideration for time dependent variation. The material properties of concrete and steel in accordance with a temperature variation are referred to the existing general data. Thermal transient analyses are performed by finite element method through ANSYS and then these results are verified by comparing with the existing test results. On the basis of analytical results, load-carrying capacities (N-M interaction curves) are calculated by numerical analysis method.

• Journal of Korean Society of Steel Construction
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• v.14 no.5 s.60
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• pp.603-612
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• 2002

Numerical analyses have been carried out in order to check the applicability of high-strength steel to a medium-sized steel bridge. Using the yield strength of steel, Average Daily Truck Traffic (ADTT), and fatigue grade of structural detail as analytical parameters, the minimum weight sections that satisfy the limit states of the AASHTO LRFD design specification were determined through an optimization scheme. Likewise, the effects of the number of girders and span length on the applicability of high-strength steel were evaluated. Results show that high-strength steel may be employed in the steel bridge, since steel weight decreases with increasing yield strength regardless of the fatigue effect. Nonetheless, appropriate countermeasures against fatigue should be determined since it is a major factor in the effective use of high-strength steel in steel bridges.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.10
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• pp.985-993
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• 2015

Free-piston Stirling engines (FPSEs) have attracted much attention in the renewable energy field as a key device in the conversion from thermal to mechanical energy, and in the recycling of waste energy. Traditional Stirling engines consist of two pistons that are connected by a mechanical link, while FPSEs are formed as a vibration system by connecting each piston to a spring without a physical link. To ensure the correct design and control of operations, this requires elaborate dynamic-performance predictions. In this paper, we present the performance-prediction methodology using a linear and nonlinear dynamic analytical model considering the external load of FPSEs. We perform linear analyses to predict the operating point of the engine using the root locus technique. Using nonlinear analysis, we also predict the amplitude of pistons by performing numerical integration considering both the linear and nonlinear damping terms of the external load. We utilize the predicted dynamic behavior to predict the engine performance. In addition, we compare the experiment results and existing model predictions for RE-1000 to verify the reliability of the analytical model.

• Proceedings of the KWS Conference
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• 2009.11a
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• pp.100-100
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• 2009

This paper is concerned with numerical analyses of residual stresses in welds and material's susceptibility to stress corrosion cracking (SCC) for the primary piping system in nuclear power plants: Both the dissimilar metal weld (DMW) for stainless steel to low alloy steel joints and the similar metal weld (SMW) for forged stainless steel to cast stainless steel joints are considered. Thermal elasto-plastic analyses using the finite element method (FEM) are performed to predict residual stresses generated in fabrication welding and its related processes for both the DMW and SMW, including effects of quenching for cast stainless steel piping, machining of the DMW root, and grinding of the SMW root. As a result, the effect of quenching should be included in the evaluation of residual stresses in the SMW for the cast stainless steel piping. It is deemed that residual stresses in both the DMW and SMW would not affect the SCC susceptibility of the welds providing that the welding processes are completed without any weld repair on the inside wall of the joint. However, the grinding process if performed on the safe-end to piping weld, would produce a high level of residual stresses in the inner surface region and thus a stress improvement process (e.g. buffing) should be considered to reduce susceptibilities to SCC.