• Journal of the Korea Concrete Institute
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• v.11 no.6
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• pp.113-119
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• 1999

Fatigue failure is a phenomenon such that structures under cyclic service load is failed by sudden brittle manner. Therefore, in order to obtain structures safety against the fatigue failure during their service lifes, fatigue characteristics should be considered for design and analysis of the structures. As stress range of prestressed (PS) tendons, which governs fatigus characteristic of prestressed concrete (PSC) structures, increases with increased use of partial prestressig, it is more necessary to consider fatigue characteristics of PS tendons. In this paper, direct-tension fatigue experiments with special specimen-setting devices are carried out to obtain fatigue characteristics of domestic low relaxation PS strands having different diameters and PS strands connected with coupler. Then, allowable stress range of fatigue for PSC beams using low relaxation strands are presented for the fatigue examination of prestressed concrete beams applied cyclic loading.

• Journal of Biosystems Engineering
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• v.7 no.2
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• pp.8-17
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• 1983

특수(特殊)한 기능(機能)을 수행(遂行)하기 위한 4링크 기구(機構)의 설계(設計)에서는 링크의 연간궤적(連稈軌跡)이 중요(重要)한 설계조건(設計條件)이 된다. 이앙기(移秧機)의 이식기구(移植機構)나 바인던의 방출(放出)암은 모두 4링크 기구(機構)를 이용(利用)하여 작업수행(作業遂行)에 필요(必要)한 연간궤적(連稈軌跡)을 얻고 있는 것이다. 필요(必要)한 연간궤적(連稈軌跡)을 얻기위한 4링크 기구(機構)의 합성(合成)은 도해적(圖解的), 해석적(解析的) 방법(方法)을 통(通)하여 많은 연구(硏究)가 이루어져 왔으며 최근(最近)에는 콤퓨터를 이용(利用)한 기구합성(機構合成)에 대(對)한 연구(硏究)가 활발하게 이루어지고 있다. 본(本) 연구(硏究)에서는 연간궤적상(連稈軌跡上)의 점(點)들을 이용(利用)하여 주어진 연간궤적(連稈軌跡)을 얻기 위한 4링크 기구(機構)의 합성(合成)에 대(對)한 새로운 방법(方法)을 개발(開發)하고 이 방법(方法)을 콤퓨터 프로그래밍하여 주어진 연간궤적(連稈軌跡)과 콤퓨터로 합성(合成)한 4링크 기구(機構)의 연간궤적(連稈軌跡)을 비교(比較)검토 하였다.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.887-892
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• 2004

On curved rail, the speed of train must be reduced in order to keep riding comfort. So, the train has the speed limitation in conventional railway line. But if the train has the tilting mechanism, the speed of train is able to be increased while maintaining the riding comfort. Generally, the tilting train is faster than the non-tilting train about 30% in curve. The tilting train technology and reduction of travel time has been carefully investigated by KRRI (Korea Railroad Research Institute). Based on the primary research result from KRRI, tilting control system and tilting operation interlace are considered its core technology to apply tilting train to Korean conventional railway. In this paper application of non-tilting pantograph to tilting system will be introduced. New type of bogie frame and system modification of vehicle are invented to apply non-tilting pantograph to tilting train.

• Korean Journal of Optics and Photonics
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• v.20 no.5
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• pp.266-271
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• 2009

We designed a thermo-optic switch based on a directional coupler with not only a high extinction ratio but also significantly low power consumption. The switch operates by using the thermo-optic effect of the polymer which the refractive index changes by heating the electrode. If the electrode is not powered (OFF), the input light will be coupled completely to the other waveguide. When the electrode is powered at a certain level (ON), input light launched into the input waveguide will remain in that waveguide due to the lower index adjusted in the other waveguide. The switch based on the directional coupler was designed using the generalized extinction ratio curve and the lateral shift of the input waveguide. The coupling length is 1,610 ${\mu}m$ and the extinction ratios are -28 and -30 dB for ON and OFF states, respectively. The electrode structures were optimized by thermal analysis. The transported heat into the waveguide is increased, as the electrode width (w) is increased and the center distance between the electrode and the waveguide (d) is decreased. Also, because the heat generated in the electrode affects the other waveguide, the temperature difference between two waveguides is varied as the given w and d. There are specific conditions which have the maximum of the temperature difference. That of the temperature difference is increased as the width and the temperature of the electrode are increased. Especially, when the switch is designed using the condition with the maximum of the temperature difference for switching, the temperature of the electrode can be decreased. We expect this condition will be the novel method for the reduction of the power consumption in a thermo-optic switch.

• Journal of Electrical Engineering and Technology
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• v.9 no.1
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• pp.301-306
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• 2014

We proposed a new PCB-type 'common-mode current($I_c$) and differential-mode current($I_d$) detector' working for fast detection of $I_c$ and $I_d$ from the differential-mode signaling, with miniaturization effect and possibility of cheaper fabrication. In order to realize this device, we suggest a branch-line-coupler balun having a composite right- and left-handed(CRLH) one-layer microstrip phase-shifting line as compact as roughly ${\lambda}_g/14$. The presented balun obviously is different from the conventional bent-&-folded delay lines or slits on the ground for coupling the lines on the top and bottom dielectrics. As we connect the suggested balun output ports of the differential-mode signal lines via the through-port named U and coupled-port named L, $I_c$ and $I_d$ will appear at port ${\Delta}$ and port ${\Sigma}$ of the present device, in order. The validity of the design scheme is verified by the circuit-and numerical electromagnetic analyses, and the dispersion curve proving the metamaterial characteristics of the geometry. Besides, the examples of the $I_c$ and $I_d$ indicator are observed as the even and odd modes in differential-mode signal feeding. Also, the proposed device is shown to be very compact, compared with the conventional structure.

• Journal of the Earthquake Engineering Society of Korea
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• v.27 no.3
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• pp.129-137
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• 2023

This study presents a dry precast concrete (PC) beam-column connection, and its target seismic performance level is set to be emulative to the reinforced concrete (RC) intermediate moment resisting frame system specified in ACI 318 and ASCE 7. The key features include self-sustaining ability during construction with the dry mechanical splicing method, enabling emulative connection performances and better constructability. Test specimens with code-compliant seismic details were fabricated and tested under reversed cyclic loading, which included a PC beam-column connection specimen with dry connections and an RC control specimen. The test results showed that all the specimens failed in a similar failure mode due to plastic deformations in beam members, while the hysteretic response curve of the PC specimen showed comparable and emulative performances compared to the RC specimen. Seismic performance evaluation was quantitatively addressed, and on this basis, it confirmed that the presented system can fully satisfy all the required performance for the intermediate RC moment resisting frame.

• The Journal of Engineering Geology
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• v.14 no.4 s.41
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• pp.361-369
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• 2004

The authors designed a new technique to measure dielectric constant of a soil media by Frequency Domain Reflectometry (FDR) system and its measurement sensor probe with different length such as 7m, 10cm and 15cm for estimating the variations of dielectric constant. Measurement of dielectric constant of soil material is possible to measure an interference wave generated by between incidence wave and reflection wave which are detected to electro-magnetic wave through the directional coupler at the high frequency range,0.1 to 1.7GHz, by FDR system. The obtained experimental results verified that the technique is very promising for non-destructive and continuous soil volumetric water content measurement monitoring in a laboratory. The relationship between the soil volumetric water content and the dielectric constant of soil media (standard sand) was expressed by a single regression ewe independent of soil texture at a small experimental error. Also the derived regression curve coincided well with that obtained by Topp curve.

• Journal of the Korea Concrete Institute
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• v.27 no.4
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• pp.363-375
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• 2015

This research investigated the effects of diameter and material of energy frame on the impact velocity or strain rate of Strain Energy Frame Impact Machine (SEFIM). The impact speed of SEFIM have been clearly affected by changing the diameter and material of the energy frame. The reduced diameter of the energy frame clearly increased the impact velocity owing to the higher strain at the moment of coupler breakage. And, titanium alloy energy frame produced the fastest speed of impact among three materials including steel, aluminum and titanium alloys because titanium alloy has faster wave velocity than steel. But, aluminium energy frame was broken during impact tests. In addition, the tensile stress versus strain response of high performance fiber reinforced cementitious composites at higher and wider strain rates between 10 and 72 /sec was successfully obtained by using four different energy frames.