• Journal of Wind Energy
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• v.14 no.3
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• pp.91-99
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• 2023

In research conducted on a southwestern Korean offshore meteorological tower, acceleration datasets were gathered over half a year with time-history sensors. To enhance data credibility, a parallel measurement system was used for verification. A model of the tower was configured using beam elements, and with modifications accounting for added stiffness from auxiliary structures. Ground interactions were considered as calibrated springs based on soil layer properties. The tower's dynamic attributes and mass sensitivity were discerned using eigenvalue analysis. The structural natural frequency was consistent, with variations primarily due to new equipment adding approximately 1400 kgs. With free vibration damping assumptions, a damping ratio of roughly 1 % was derived.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.30 no.1
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• pp.7-15
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• 2017

This paper presents the results of the parametric study to investigate the effects of several analysis modeling parameters such as support conditions, member connectivities and cable member stiffness on the main mode shapes and natural frequencies of a representative disaster resilient greenhouse structure. In addition, an ambient vibration test was performed on the representative greenhouse structure and its main mode shapes and natural frequencies were obtained. By comparing the experimental and analysis results, a proper analysis modeling method of the representative greenhouse structure was proposed.

• Journal of the Korean Geotechnical Society
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• v.34 no.11
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• pp.81-92
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• 2018

For a marine bridge foundation construction, a large-circular-steel-pipe has been proposed for supporting vertical load and preventing water infiltration. However, a ship collision can adversely affect the structural stability. This paper presents a fundamental study on dynamic responses of the large-circular-steel-pipe by an impact load. In laboratory experiments, small-scaled steel pipe is installed in a soil tank. The soil height and water level are set to 23 cm and 25~70 cm, respectively. The upper part of the steel pipe is impacted using a hammer to simulate the ship collision. The dynamic responses are measured using accelerometers and strain gauges. Experimental results show that the strain decreases as the measured location is lowered. The higher frequency components appear in the impact load condition compared to the microtremor condition. However, the higher frequency components measured at the strain gauge located below the water level do not appear. For the accelerometer signal, the maximum frequency under the impact load is higher than that of the microtremor. The maximum frequency decreases as water level increases but it is larger than the maximum frequency of the microtremor. This study shows that strain gauge and accelerometer can be useful for evaluating the dynamic responses of large-circular-steel-pipes.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.1
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• pp.71-80
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• 2013

According to design specifications for structural safety, a bridge in initial design step has been modelled to have larger self-weight, external loads and less stiffness than those of real one in service. Thereby measured buffeting responses of existing bridge show different distributions from those of the design model in design step. In order to obtain accurate buffeting responses of the in-site bridge, the analysis model needs to be modified by considering the measured natural frequencies. Until now, a Manual Tuning Method (MTM) has been widely used to obtain the Measurement-based Model(MBM) that has equal natural frequencies to the real bridge. However, since state variables can be selected randomly and its result is not apt to converge exact rapidly, MTM takes a lot of effort and elapsed time. This study presents Buffeting Response Correction Method (BRCM) to obtain more exact buffeting response above MTM. The BRCM is based on the idea the commonly used frequency domain buffeting analysis does not need all structural properties except mode shapes, natural frequencies and damping ratio. BRCM is used to improve each modal buffeting responses of the design model by substituting measured natural frequencies. The measured natural frequencies are determined from acceleration time-history in ordinary vibration of the real bridge. As illustrated examples, simple beam is applied to compare the results of BRCM with those of a assumed MBM by numerical simulation. Buffeting responses of BRCM are shown to be appropriate for those of in-site bridge and the difference is less than 3% between the responses of BRCM and MTM. Therefore, BRCM can calculate easily and conveniently the buffeting responses and improve effectively maintenance and management of in-site bridge than MTM.

• Journal of the Korea institute for structural maintenance and inspection
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• v.28 no.1
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• pp.98-106
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• 2024

Due to advancements in construction technology and analytical tools, an increasing number of cable-stayed bridges have been designed and constructed in recent years. A cable is a structural element that primarily transmits the main load of a cable-stayed bridge and plays the most crucial role in reflecting the overall condition of the entire bridge system. In this study, a vision-based method was applied to estimate the tension of the stay cables located at a long distance. To measure the response of a cable using a vision-based method, it is necessary to install feature points or targets on the cable. However, depending on the location of the point to be measured, there may be no feature points in the cable, and there may also be limitations in installing the target on the cable. Hence, it is necessary to find a way to measure cable response that overcomes the limitations of existing vision-based methods. This study proposes a method for measuring cable responses by utilizing the characteristics of cable shape. The proposed method involved extracting the cable shape from the acquired image and determining the center of the extracted cable shape to measure the cable response. The extracted natural frequencies of the vibration mode were obtained using the measured responses, and the tension was estimated by applying them to the vibration method. To verify the reliability of the vision-based method, cable images were obtained from the Hwatae Bridge in service under ambient vibration conditions. The reliability of the method proposed in this study was confirmed by applying it to the vibration method using a vision-based approach, resulting in estimated tensions with an error of less than 1% compared to tensions estimated using an accelerometer.

• Journal of Korean Society of Steel Construction
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• v.14 no.6
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• pp.721-728
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• 2002

Modern structrues are being built using high-strength and light-weight construction materials resulting in decreased structural mass and damping properties. Rhythmic activities such as jumping, dancing and clapping during lively concerts can produce excessive vibration of steel structures. In this study, dynamic load factors that occur during lively concerts were presented through vibration test and real-time monitoring of an existing concert hall. The vibration test included modal analysis and jumping test according to the forcing frequencies and the number of participants. Dynamic load foactors were acquired directly from peak acceleration responses of each harmonics. Comparing NBCC 1995, the 3rd harmonic must be included in the design of concert halls. Dynamic load factors must be increased as a result of the vibration test.

• Journal of Korean Association for Spatial Structures
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• v.9 no.3
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• pp.59-66
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• 2009

Dynamic characteristics such as frequency and damping ratio in the ambient state of building has been progressed in domestic and foreign. However, there has not been any deep research of dynamic characteristics of full-scale structure using vibration measurement of the building damaged up to failure. Dynamic characteristics of three-story reinforced concrete building was evaluated before and after it was damaged by using a actuator. Dynamic characteristics is reviewed and compared with previous study. Ambient vibration and human excitation test were applied. After 120mm horizontal displacement by actuator, frequency of long and short direction is reduced to 34.3%, 33.7% and damping ratio is reduced to 36.5%, 19.5% respectively.

• Journal of Korean Association for Spatial Structures
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• v.15 no.3
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• pp.77-83
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• 2015

The cases of conducting the vibration measurement using the mobile phone with regard to the building's horizontal vibration are very rare in Korea and foreign countries. Therefore, this study analyzed the horizontal vibration nature of the building using the mobile phone targeting 5 tall buildings, and reviewed about the applicability of the mobile phone vibration measuring instrument through the comparison/verification with the data of the existing vibration measuring instrument. The peak of the measured time series waveform was measured clearly and it showed a similar value to the existing natural frequency.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2011.04a
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• pp.516-520
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• 2011

본 논문에서는 먼저 흥인지문에 대해 상시진동실험을 수행하고, 그 데이터를 분석하여 흥인지문의 고유진동수, 모드, 감쇠비의 특성을 분석하였다. 그 결과로부터 흥인지문의 병진모드를 파악하였고, 병진모드에서 측정한 여러 기둥의 모드 상대크기와 위상이 동일함을 확인하였다. 저차 병진모드에서 모든 기둥이 같은 방향으로 강성을 발휘하기 때문에 각층의 강성을 합한 등가의 층강성을 가지는 2자유도의 동적강체해석모델을 제시하였다. 이 해석모델은 선형 범위 내에서 거동한다는 것으로 가정하여 층강성을 산정하였다. 실제 흥인지문의 접합부에는 부재간의 이음과 맞춤에 의한 마찰력이 작용한다. 접합부를 누르는 무거운 지붕하중에 의해 이 마찰력은 증가하게 되고, 이로써 횡하중에 저항하게 된다. 이러한 접합부에 강한 횡하중이 작용하게 되면, 접합부의 이완 및 마찰력의 저하 등으로 인하여 횡강성의 저하가 급격히 일어나는 비선형 특성을 갖게 된다. 이러한 흥인지문의 비선형적인 특성을 파악하기 위해 흥인지문 해석모델에 쿨롱 마찰력을 도입하여 비선형적인 해석모델을 제시하였다.

• Journal of the Korea institute for structural maintenance and inspection
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• v.10 no.1
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• pp.139-148
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• 2006

The dynamic characteristics of a bridge deduced by using the modeling techniques depend on its stiffness and mass calculated from its geometric model. This research develops the FE modeling techniques for a steel plate girder bridge with composite section. and proves their validity by comparing the results with those from actual measurement. The FE modeling techniques are divided into two categories--a simplified one and two-dimensional model and a detailed three-dimensional model. In the meantime, the dynamic responses of the bridge tested for this research were measured by the ambient vibration some of accelerometers were been attached to its upper slab girder under normal traffic load. The Cross Power Spectrum obtained from the measurement was used to analyze the dynamic characteristics by natural excitation techniques. The analytic results are compared to those of each FE modeling, and thereby the modeling techniques were proved to be valid.