• 한국구조물진단유지관리공학회 논문집
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• 제28권1호
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• pp.98-106
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• 2024

건설 기술과 해석 도구의 발전으로 인해 최근에는 점점 더 많은 사장교가 설계되고 건설되었다. 케이블은 사장교의 주요한 하중을 전달하는 부재이며 일반적으로 전체 교량 시스템의 상태를 반영하는 데 가장 중요한 역할을 한다. 이 연구에서는 원거리에 위치한 사장재 케이블의 장력을 추정하기 위하여 영상기반 방법을 적용하였다. 영상기반 방법을 이용하여 케이블의 응답을 측정하기 위해서는 케이블에 특이점 또는 타겟의 설치가 필요하다. 그러나 측정하고자 하는 지점의 위치에 따라 케이블에 특이점이 존재하지 않을 수 있으며 또한 케이블에 타겟의 설치가 어려울 수 있는 한계가 존재한다. 따라서 기존의 영상기반 방법의 한계를 극복하여 케이블 응답을 측정하는 방법이 필요하다. 이 연구에서는 케이블 형태의 특징을 이용하여 케이블 응답을 측정하는 방법을 제시하였다. 제시된 방법은 획득된 이미지에서 케이블 형태를 추출하였으며 추출된 케이블 형태의 중심을 산정하여 케이블 응답을 측정하였다. 측정된 응답을 이용하여 진동모드에 대한 고유진동수들을 추출하였으며 진동법에 적용하여 장력을 추정하였다. 영상기반 방법의 신뢰성을 확인하기 위해 공용 중인 화태대교에서 케이블 이미지를 상시진동 조건에서 획득하였다. 영상기반 방법을 이용하여 진동법에 적용하여 추정된 장력은 가속도 센서를 이용하여 추정된 장력과 1% 이내의 오차로 이 연구에서 제시된 방법의 신뢰성을 확인할 수 있었다.

• 한국강구조학회 논문집
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• 제29권1호
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• pp.49-60
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• 2017

부유식 구조물의 계류선의 설계는 강도뿐만 아니라 피로수명 측면에서도 검토가 반드시 요구된다. 일반적으로 계류선의 피로 설계에는 동적 응력을 야기하는 하중이 지배적인 영향을 미치게 된다. 즉, 파랑이 주요 설계 하중으로 고려가 된다. 본 연구에서는 불규칙 파랑에 대한 해중 터널 계류선의 피로 손상 특성에 대해 분석한다. 시간 이력 유체-구조 동역학 해석을 통해 특정 환경 하중에 대한 해중터널의 동적 운동 및 계류선에 발생하는 장력과 응력을 계산하고, Rainflow 집계법 및 Palmgren-Miner의 법칙 그리고 DNV 기준에서 제시하는 해양구조물 설계를 위한 S-N 곡선을 고려하여 단기 피로 손상을 추정한다. 해중 터널의 계류 형식과 유사한 계류 형식을 갖는 인장각 플랫폼의 텐던 설계를 참고하여 100년 재현 주기 파랑이 48시간 지속되는 조건을 가정하여 이 환경 하중에 의한 피로 손상도를 추정한다. 본 해석 절차를 따르며, 함체의 흘수와 계류선의 간격 및 초기 기울임 각도가 피로 손상도에 미치는 영향을 분석한다.

• 한국환경과학회지
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• 제21권3호
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• pp.289-296
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• 2012

The purpose of this study was to identify the irrigation intervals and the amount of suitable growing substrate needed to achieve the desired shallow-extensive green roof system during a dry summer in Korea. In terms of treatment, three types (SL, $P_6P_2L_2$, $P_4P_4L_2$) with varying soil mixture ratios and two types (15 cm, 25 cm) with varying soil depths were created. The results have been analyzed after measuring growth and soil water contents. The difference of growth by treatment was significant in terms of green coverage, height, leaf width and photosynthesis. In measurement of chlorophyll content, no difference was detected when measured against soil depth. According to the growth measurement of Zoysia japonica with respect to differing soil mixture ratios in the 15 cm-deep treatment, a statistical difference was detected at the 0.05 significance level in photosynthesis. In case of green coverage, height, chlorophyll content and leaf width, no statistical significance was observed. In case of the 25 cm-deep treatment, a statistical significance was observed in height and photosynthesis. In terms of green coverage, chlorophyll content and leaf width, no statistical significance was detected. In comparisons of soil moisture tension and soil water contents, the irrigation interval and amount were 8 days and 14.9 L in the SL (15 cm) treatment, respectively. The irrigation interval showed for 10 days a 1.3-fold increase, and the irrigation amount was 27.4 L 1.8-fold more than SL (25 cm), respectively. For $P_6P_2L_2$ (15 cm) treatment, the irrigation interval and amount were 12 days and 20.7 L, respectively. However, an irrigation interval under $P_6P_2L_2$ (25 cm) was for 15 days 1.3 times longer than $P_6P_2L_2$ (15 cm), and an irrigation amount of 40 L was 1.9 times more than that under $P_6P_2L_2$ (15 cm). In $P_4P_4L_2$ (15 cm) treatment, it was indicated that the irrigation interval was 15 days, and the irrigation amount was 19.2 L. It was not needed to irrigate for 16 days under $P_4P_4L_2$ (25 cm) treatment during the dry summer and the longest no-rain periods. The irrigation interval and amount under $P_4P_4L_2$ were 1.8-fold and 1.3-fold, respectively, more than SL treatment as affected by soil mixture ratio. Comparatively $P_4P_4L_2$ had more 1.3-fold and 0.9-fold in irrigation interval and amount more than $P_6P_2L_2$. Therefore, it can be noted that different soil depth and soil mixture ratios had a significant effect on the irrigation interval and amount.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1989년도 봄 학술발표회 논문집
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• pp.44-49
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• 1989

The primary purpose of using bracings is to improve tile lateral rigidity of main structural system, i.e., columns and beams, by reinforcing them with much smaller members. Conventional design methods consider bracings as tension-only mambers, since difficulties arise in the analysis to consider the P - effects and post-buckling behaviour of the bracing members. This is particulary true for X-bracings. Recently, however, both analytical and experimental studies have been conducted to investigate the more precise and real behaviour of bracing members, especially for the nonlinear un plastic behaviour under cyclic loads. In this study, an analytical model is proposed to investigate the nonlinear behavior of steel bracing members subjected to cyclic loads. Results of tile analysis were compared with previous experimental results, and good agreements were obtained between these results.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2005년도 학술발표회 논문집
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• pp.211-219
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• 2005

Nowadays, various grades of high-strength steels are available. The application of ultra-high grades of steels for building structures, however, is limited only to the elements stressed under tension. The highest grade of steels generally used has a tensile strength of around 600N/mm2. Most research is focused on lower yield ratios of high strength steel in the inelastic range to ensure the stability of structures. In this paper, however, the possibility of an effective application of high strength steel with high yield ratio to building structures is discussed. An efficient structural system and a design method based on earthquake response analysis and experimental results are proposed.

• 한국생산제조학회지
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• 제8권6호
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• pp.78-83
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• 1999

This study discusses a non-contact optical technique, electronic speckle pattern interformetry(ESPI), that is well suited for in-plane and out-of-plane deformation measurement. However, the existing ESPI methods that are based on dual-exposure, real-time and time-average method have difficulties for accurate measurement of structure, due to irregular intensity and shake of phase. Therefore, phase shifting method has been proposed in order to solve this problem. About the method, the path of reference light in interferometry is shifted and added to least square fitting method to make the improvement in distinction and precision. This proposed method is applied to measure in -plane displacement that is compared with the previous method. Also, Used as specimen AS4/PE따 [30/=30/90]s was analyzed by ESPI based on real-time to determine the characteristics of vibration under no-load and tension. These results are quantitatively compared with those of FEM analysis inmode shapes.

• 산업기술연구
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• 제27권A호
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• pp.47-53
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• 2007

A theoretical model based on Rayleigh-Ritz method is proposed to predict the resonance frequency of a W/T(Wind Turbine) tower structure supported by guy cables. In order to verify the validity of the theoretical model, a reduced W/T tower system is manufactured and tested. Frequency response and mode data are determined by modal testing and finite element analysis is performed to calculate the natural frequency of the tower model. Numerical and experimental results are compared with those by the theoretical analysis. Parametric study by the theoretical model shows how the cable tension and cable elasticity influence the resonance frequency of the W/T tower structure. Finally, vibration response under various rotating speed is investigated to examine the possibility of severe resonance.

• Earthquakes and Structures
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• 제15권3호
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• pp.243-251
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• 2018

The dynamic responses of a rocking wall-moment frame (RWMF) with a post-tensioned cable are investigated. The nonlinear equations of motions are developed, which can be categorized as a single-degree-of-freedom (SDOF) model. The model is validated through comparison of the rocking response of the rigid rocking wall (RRW) and displacement of the moment frame (MF) against that obtained from Finite Element analysis when subjected ground motion excitation. A comprehensive parametric analysis is carried out to determine the seismic performance factors of the RWMF systems under near-fault trigonometric pulse excitation. The horizontal displacement of the RWMF system is compared with that of MF structures without RRW, revealing the damping effect of the RRW. Frame displacement spectra excited by trigonometric pulses and recorded earthquake ground motions are constructed. The effects of pulse type, mass ratio, frame stiffness, and wall slenderness variations on the displacement spectra are presented. The paper shows that the coupling with a RRW has mixed results on suppressing the maximum displacement response of the frame.

• Ocean Systems Engineering
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• 제7권4호
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• pp.413-433
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• 2017

The dynamic and structural responses of a 1000-m long circular submerged floating tunnel (SFT) with both ends fixed under survival irregular-wave excitations are investigated. The floater-mooring nonlinear and elastic coupled dynamics are modeled by a time-domain numerical simulation program, OrcaFlex. Two configurations of mooring lines i.e., vertical mooring (VM) and inclined mooring (IM), and four different buoyancy-weight ratios (BWRs) are selected to compare their global performances. The result of modal analysis is included to investigate the role of the respective natural frequencies and elastic modes. The effects of various submergence depths are also checked. The envelopes of the maximum/minimum horizontal and vertical responses, accelerations, mooring tensions, and shear forces/bending moments of the entire SFT along the longitudinal direction are obtained. In addition, at the mid-section, the time series and the corresponding spectra of those parameters are also presented and analyzed. The pros and cons of the two mooring shapes and high or low BWR values are systematically analyzed and discussed. It is demonstrated that the time-domain numerical simulation of the real system including nonlinear hydro-elastic dynamics coupled with nonlinear mooring dynamics is a good method to determine various design parameters.

• International Journal of Advanced Culture Technology
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• 제7권1호
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• pp.209-215
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• 2019

In order to provide a safe free-weight-training environment to people without workout trainers, we suggest a smart bench press machine with an automatic weight control system sensitive to user tiredness. Physical weight plates on the machine are replaced with a hydraulic cylinder as a press load and the cylinder knob is coupled with a step motor to change its tensile force automatically in-between lifting exercises. Three subjects participated to verify the usability of the smart bench press machine. They were asked to lift a 6-RM press load 10 times with 3 different lifting conditions: 1) no assistance, 2) a human assistance, and 3) the automatic weight control. All subjects were not able to complete the 10 sets without assistance due to tiredness, but they finished the full sets under the two assistive conditions. Average lifting speeds under the automatic weight control condition showed the most consistent level. Normalized quasi-tension data based on surface electromyogram signals of both Pectoralis Majors revealed that the subjects maintained the target muscle activation level above 50% but not more than 80% throughout the 10 sets. Therefore, the smart bench press machine is expected to both keep pace with the lifting exercise and reduce risk of injuries due to excessive muscle tensions.