• Steel and Composite Structures
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• 제30권5호
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• pp.471-481
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• 2019

Beam-columns are structural members subjected to a combination of axial and bending forces. Lateral-torsional buckling is one of the main failure modes. Beam-columns that are bent about its strong axis may buckle out of the plane by deflecting laterally and twisting as the values of the applied loads reach a limiting state. Lateral-torsional buckling failure occurs suddenly in beam-column elements with a much greater in-plane bending stiffness than torsional or lateral bending stiffness. This study intends to establish a unique convenient closed-form equation that it can be used for calculating critical elastic lateral-torsional buckling load of beam-column in the presence of a known axial load. The presented equation includes first order bending distribution, the position of the loads acting transversely on the beam-column and mono-symmetry property of the section. Effects of axial loads, slenderness and load positions on lateral torsional buckling behavior of beam-columns are investigated. The proposed solutions are compared to finite element simulations where thin-walled shell elements including warping are used. Good agreement between the analytical and the numerical solutions is demonstrated. It is found out that the lateral-torsional buckling load of beam-columns with mono-symmetric sections can be determined by the presented equation and can be safely used in design procedures.

• 대한토목학회논문집
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• 제29권3A호
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• pp.227-234
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• 2009

최근 강박스거더교량 가로보와 박스거더 연결부에 니브레이스(Knee-brace) 설치가 일반화 되어있다. 니브레이스는 가로보-박스거더 연결부의 응력완화 및 횡변형 방지를 목적으로 설치되는 보강재나, 구조적 보강효과에 대해서는 아직 명확하지 않다. 본 연구에서는 유한요소해석을 통하여 니브레이스의 보강효과를 검토하였다. 가로보-박스거더 높이비와 니브레이스 유무를 변수로한 구조해석을 통하여 부재별 응력흐름, 응력수준과 가로보 처짐을 검토하였다. 그리고 수치해석결과의 비교를 통하여 니브레이스의 보강효과를 평가하였다. 유한요소해석 결과는 니브레이스가 박스거더-가로보 연결부의 보강재로서 응력완화 및 구조적 보강효과가 매우 낮음을 보이고 있다.

• 한국통신학회논문지
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• 제32권8A호
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• pp.827-835
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• 2007

본 논문은 ECMA(European Computer Manufacturers Association) 표준의 MB-OFDM(MultiBand-Orthogonal Frequency Division Multiplexing) UWB 시스템에 AAS(Adaptive Antenna Systems)를 적용함으로써 데이터 전송범위를 확장하는 방법을 제안하고, ECMA UWB 시스템의 다중 접속 방법으로 사용되는 CSMA/CA(Carrier Sense Multiple Access with Collision Avoidance) 환경에서 AAS를 적용할 때 발생하는 음영 빔 문제를 해결하기 위해 보완 빔 형성 방법을 제안한다. 제안된 보완 빔은 그람-슈미츠(Gram-Schmidt) 직교화 방법을 이용하여 주 빔에 간섭을 주지 않고 빔 음영 지역의 노드들이 채널의 사용 유무를 감지할 수 있도록 하였으며, 주 빔을 형성할 때 다양한 빔 형성 알고리즘의 적용이 가능한 장점이 있다. 전산 모의실험을 통하여 제안된 AAS 및 보완 빔 방법이 480Mbps 데이터 전송 속도의 데이터 전송 범위를 2m에서 3.95m로 증가시키고, 일반적인 ECMA UWB AAS 시스템에 비해 시스템 전송률을 약 20%정도 향상시키는 것을 확인하였다.

• Advances in concrete construction
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• 제13권1호
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• pp.45-69
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• 2022

This paper investigates the shear behavior of reinforced concrete haunched beams (RCHBs) without stirrups. The research objective is to study the effectiveness of the ideal steel fiber (SF) ratio, which is used to resist shear strength, besides the influence of main steel reinforcement, compressive strength, and inclination angles of the haunched beam. The modeling and analysis were carried out by Finite Element Method (FE) based on a software package, called Atena-GiD 3D. The program of this study comprises two-part. One of them consists of nine results of experimental SF RCHBs which are used to identify the accuracy of FE models. The other part comprises 81 FE models, which are divided into three groups. Each group differed from another group by the area of main steel reinforcement (A_s) which are 226, 339, and 509 mm². The other parameters which are considered in each group in the same quantities to study the effectiveness of them, were steel fiber volumetric ratios (0.0, 0.5, and 1.0)%, compressive strength (20.0, 40.0, 60.0) MPa, and the inclination angle of haunched beam (0.0°, 10.0°, and 15.0°). Moreover, the parametric analysis was carried out on SF RCHBs to clarify the effectiveness of each parameter on the mechanical behavior of SF RCHBs. The results show that the correlation coefficient (R²) between shear load capacities of FE proposed models and shear load capacities of experimental SF RCHBs is 0.9793, while the effective inclination angle of the haunched beam is 10° which contributes to resisting shear strength, besides the ideal ratio of steel fibers is 1% when the compressive strength of SF RCHBs is more than 20 MPa.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1999년도 학회창립 10주년 기념 1999년도 가을 학술발표회 논문집
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• pp.537-540
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• 1999

The primary objective of this study is to make a contribution to the construction of 40~60 story R/C high rise building by developing the reinforcing details which can improve the seismic performance of high-strength (f'c=700kg/$\textrm{cm}^2$, fy=4000, 8000kg/$\textrm{cm}^2$) R/C beam-column joints. And the purpose of this study is to investigate experimentally the effect of load history on the total energy dissipation capacity of reinforced concrete flexural members. The reinforcing details which can make beam plastic hinging zones moved and spreaded from the column face is proposed to insure the ductile behavior of high-strength RC beam-column joints. The intermediate reinforcement which is horizontally anchored by interlinking each intermediate reinforcements is proposed and tested to examine the mechanical performance of proposed details. Main variables are the shape of the intermediate reinforcements and yield strength of rebars. From the test results, the newly proposed intermediate reinforcement details can move and spread the beam plastic hinging zone about 1.0d from the column face.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2004년도 추계학술대회 논문집
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• pp.1017-1020
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• 2004

It is not efficient and scarcely out of the question to use commercial expensive electron beam lithography system widely used for semiconductor fabrication process for the manufacturing application field of various devices in the small business scope. Then scanning electron microscope based electron beam machining system is maybe regarded as a powerful model can be used for it simply. To get a complete suite of thus proper system, column unit build up with several electo-magnetic lens is necessarily required more than anything else to modify scanning electron microscope. In this study, various components included several electro-magnetic lens and main body which are essentially constructed for column unit are designed and manufactured. And this established column unit will be used for next connected study in the development step of scanning electron microscope based electron beam machining system.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1999년도 봄 학술발표회 논문집(I)
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• pp.547-552
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• 1999

The purpose of this study is to make a contribution to the construction of 40∼60 story R/C high rise building by developing the reinforcing details which can improve the seismic performance of high-strength (f'c=700㎏/㎠, fy=4000, 8000㎏/㎠) R/C beam-column joints. The reinforcing details which can make beam plastic hinging zones moved and spreaded from the column face is proposed to insure the ductile behavior of high-strength RC beam-column joints. The intermediate reinforcement which is vertically anchored by interlinking each intermediate reinforcements is proposed and tested to examine the mechanical performance of proposed details. Main variables are the shape of the intermediate reinforcements and yield strength of rebars. From the test results, the newly proposed intermediate reinforcement details can move and spread the beam plastic hinging zone about 1.0d from the column face.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제52권11호
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• pp.516-520
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• 2003

A novel dual beam heterodyne Laser Doppler Vibrometer (LDV) in conjunction with FM demodulators, which utilizes a residual beam to eliminate the perturbationdue due to the vibrometer body vibration without any external reference surface, has been developed. Residual laser beam from the beam splitter is used to pick up the vibration of damper, which is mounted in the vibrometer, and combined with reference beam at the photodetector. The output signal of this detector and main signal are processed to extract the object vibration, using a least mean square adaptive algorithm. It is shown experimentally that the body vibration of 1-5 Hz can be effectively removed from the measured signal using DSP technology to extract unperturbed 100 Hz original signal.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 춘계학술대회논문집
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• pp.62-65
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• 2006

In this paper, nonlinear nonplanar vibration of a flexible rectangular cantilever beam is analyzed when one-to-one resonance occurs to the beam. The planar and nonplanar motions of the beam are analyzed in time and frequency domains. In frequency domain, FFT analyzer is used to perform autospectrum and cepstrum analyses for nonlinear response of the beam. In time domain, an oscilloscope is used to investigate the phase difference between the planar and nonplanar motions and to perform Torus analysis in the phase space. Through those analyzing process, the main frequencies of superharmonic, subharmonic, and super-subharmonic motions are investigated in the nonplanar motion due to one-to-one resonance. Analyzing the phase difference between the planar and nonplanar motions, it is observed that the phase difference varies in time.

• Journal of Welding and Joining
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• 제31권4호
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• pp.23-27
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• 2013

Laser heat source was used for automotive interior and exterior parts to reduce weights. Typically, 900's nm wavelength of laser has been widely used for polymer joining, however, the transmittance of the laser beam thorough clear polymers such as PMMA or PC has been an issue to overcome. To solve this issue, 1,940nm laser was applied on the clear polymer for the better absorption and 900nm laser beam was used for main laser for the joining. Conventional Gaussian or Elliptical heat source approximation has limitation in polymer which had deeper skin depth where major laser beam absorbs. To accurately simulate the physical laser beam absorption and joining optical properties were experimentally measured for the computer FEM simulation. The simulation results showed close correlation between theoretical and experimental results. The developed laser process is expected to increase productivity and gap closing which can cause failure of joining in laser material processing.