• Journal of the Korean Ceramic Society
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• v.40 no.10
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• pp.981-984
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• 2003

A novel linear ultrasonic motor for precision position control was designed and fabricated. It was composed of two piezoelectric actuators with longitudinal ultrasonic fluctuations and shaking beam. When two AC electric fields (Usinwt, Ucoswt) were applied to piezoelectric actuators respectively, the middle part of shaking beam had an elliptical trajectory. According to experimental results, the generative force was proportional to pre-load force but the speed of slider was in inverse proportion. And the bar of shaking beam had a same trajectory with simulation result.

• Transactions on Electrical and Electronic Materials
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• v.5 no.2
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• pp.61-65
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• 2004

Bolt-tightened Langevin type vibrators using longitudinal mode of bar were designed and fabricated. In order to amplify the displacement of the tip of the vibrators, stacked ceramics were used and five different shapes of the horns were designed and jointed. Resonant frequencies and vibration characteristics of vibrators and horns were analyzed by ANSYS(finite element analysis computer program), and the displacements of tips of the horns were measured. As results, when the numbers of the stacked ceramics were increased, the displacements of the tips were increased and the driving voltages were decreased. Step l horn (BLT-St1) showed maximum displacement of 36.92 $\mu\textrm{m}$ at 36.7 ㎑ with 45 V$\sub$rms/ and 0.11 A. The displacement amplification ratio was about 5.2. But, the stress of step l horn was concentrated on intersection, where two diameters meet. To lessen the stress, step3 shaped hem is recommended.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.297-300
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• 2008

This study focuses on the evaluation of efficiency of the explicit FEM program LS-DYNA to predict the failure behavior of reinforced concrete. Analysis variables of reinforced concrete beams were longitudinal bar ratio, shear steel ratio and span-depth ratio. Failure behavior of reinforced concrete beams was approximately simulated by LS-DYNA.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2014.11a
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• pp.83-84
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• 2014

The whole wall system behaves as one section because single walls composing irregular wall are connected to each other. Although stress of a single wall is affected to the connected wall under lateral load, the stress is not transferred to whole sections and is concentrated on particular part of the wall as well. Therefore these walls can be divided into the effective and ineffective section. The purpose of this study is to compare design result of irregular wall using codes and previous studies on an effective width of the wall and to analyze reduction of the longitudinal bar of irregular wall.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.41-44
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• 2004

This experimental investigation was conducted to examine the behaviour of eight one-third scale columns made of high-strength concrete (HSC). The columns were subjected to a constant axial load corresponding to 30 per cent of the column axial load capacity and a cyclic horizontal load-inducing reversed bending moment. The variables studied in this research are the volumetric ratio of transverse reinforcement, tie configuration and tie yield strength. Columns with 42 per cent higher amounts of transverse reinforcement than that required by seismic provisions of ACI 318-02 showed ductile behaviour. Relationships between the calculated damage index and the observed damage such as initial crack, spalling of concrete, buckling of longitudinal bar, and crushing of concrete are propose.

• Journal of the Korean Society for Heat Treatment
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• v.32 no.1
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• pp.17-28
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• 2019

Jominy hardenability curves of low alloy steel containing less than 5 wt.% of alloying elements in total were calculated by applying Scheil's rule of additivity to pre-calculated isothermal transformation curve. Isothermal transformation curve for each phase in steel was approximated as a simple mathematical equation by using Kirkaldy's approach and all coefficients in the equation were estimated from experimental temperature-time-transformation (TTT) and/or continuous cooling transformation (CCT) data in the literature. Then jominy test with simple boundary conditions was performed in computer by applying the finite difference scheme. The resultant cooling curves at each location along a longitudinal direction of Jominy bar were applied to calculate phase fractions as well as mechanical properties such as micro Vickers hardness. The simulated results were compared with experimental CCT data and Jominy curves in the literature.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.6
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• pp.81-88
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• 2018

The present study evaluated the effective arrangement approach of transverse reinforcement in the jacket section for seismic strengthening of reinforced concrete columns. To simulate the full-scale columns, the section dimensions were determined as $450{\times}450mm$ for non-seismic existing columns and $750{\times}750mm$ for section enlargement strengthening columns. Over-lapped channel-shape bars and prefabricated bar units were proposed for closed-hoops in the jacket section, and conventional cross-ties anchored into existing columns and V-ties were considered for the supplementary ties. Test results showed that the axial capacity of the existing column and section enlargement columns with over-lapped channel-shape hoops was similar to the nominal strength calculated using ACI 318-14 procedure whereas the section enlargement column with prefabricated bar units possessed 1.25 times higher axial capacity than the nominal prediction. Furthermore, the axial ductility ratio of the section enlargement column with prefabricated bar unit was 139% higher than that of the existing column despite the potential size effect on ductility of concrete. Thus, it can be concluded that the developed prefabricated bar unit technique is practically useful for preventing the premature buckling of longitudinal reinforcement and confining core concrete in the section enlargement strengthening columns.

• Journal of the Korea Concrete Institute
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• v.24 no.6
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• pp.705-714
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• 2012

Precast reinforced concrete bridge columns with hollow rectangular section were tested under cyclic lateral load with constant axial force to investigate its seismic performance. After all the precast column segments were erected, longitudinal reinforcement was inserted in the sheath prefabricated in the segments, which were then mortar grouted. Main variables of the test series were column aspect ratio, longitudinal reinforcement ratio, amount of lateral reinforcement, and location of segment joints. The aspect ratios were 4.5 and 2.5, and the longitudinal steel ratios were 1.15% and 3.07%. The amount of lateral reinforcement were 95%, 55%, 50%, and 27% of the minimum amount for full ductility design requirements in the Korean Bridge Design Code. The locations of segment joints in plastic hinge region were 0.5 and 1.0 times of the section depth from the bottom column end. The test results of cracking and failure mode, axial-flexural strength, lateral load-displacement relationship, and displacement ductility are presented. Then, safety of the ductility demand based seismic design in the Korean Bridge Design Code is discussed. The column specimens showed larger ductility than expected, because buckling of longitudinal reinforcing bar was prevented due to confinement developed not only by transverse steel but also by sheath and infilling mortar.

• Journal of the Korean Society of Marine Environment & Safety
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• v.18 no.2
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• pp.153-159
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• 2012

This study gives the vertical motion analysis in multi-directional irregular waves using a commercial code(MAXSURF v.16) based on linear strip theory for a training ship. To verify the commercial code prior to the analysis, we guarantees the reliability of this paper's results using the commercial code by comparing with the results(Flokstra, 1974) of same hull and experimental conditions on a Panamax container. The analysis conditions are Beaufort wind scale No. 5($\bar{T}=5.46$, $H_{1/3}=2m$) based on ITTC wave spectrum, encounter angle Head & bow seas($150^{\circ}$) and Froude number Fn=0.257. Finally, we calculates heave RAO, pitch RAO and obtains the result of ship's response spectra for heave and pitch motions. In the motion response spectrum under the multi-directional irregular waves, heave motion reacts slightly high in short-crested waves and pitch motion reacts high in long-crested waves.

• Steel and Composite Structures
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• v.20 no.5
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• pp.1067-1085
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• 2016

Recent research on steel moment-resisting connection between steel beams and concrete filled steel tubes has shown that there are considerable advantages to be obtained by anchoring the connection to the concrete infill within the tube using anchors in blind bolts. In the research reported here, extensive experimental tests and numerical analyses have been performed to study the anchorage behaviour of cogged deformed reinforcing bars within concrete filled circular steel tubes. This data in essential knowledge for the design of the steel connections that use anchored blind bolts, both for strength and stiffness. A series of pull-out tests were conducted using steel tubes with different diameter to thickness ratios under monotonic and cyclic loading. Both hoop strains and longitudinal strains in the tubes were measured together with applied load and slip. Various lead-in lengths before the bend and length of tailed extension after the bend were examined. These dimensions were limited by the dimensions of the steel tube and did not meet the requirements for "standard" cogs as specified in concrete standards such as AS 3600 and ACI 318. Nevertheless, all of the tested specimens failed by bar fracture outside the steel tubes. A comprehensive 3D Finite Element model was developed to simulate the pull-out tests. The FE model took into account material nonlinearities, deformations in reinforcing bars and interactions between different surfaces. The FE results were found to be in good agreement with experimental results. This model was then used to conduct parametric studies to investigate the influence of the confinement provided by the steel tube on the infilled concrete.