• Explosives and Blasting
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• v.35 no.1
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• pp.34-42
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• 2017

It is very difficult to clearly define the damages caused by blasting-induced noise and vibration, because the damages depend on, besides the level of noise and vibration, the response of the object, environmental conditions, subjective feeling, and mental condition. Especially, it is more difficult when the fish is concerned, because that experimental approach is not easy and that we lack of the reasonable criterion for the acceptance level of noise and vibration. In Korea, the acceptance level for damage due to underwater noise is 140 dB re $1{\mu}Pa$, and the difference from the underwater background sound level is defined as more than 20 dB re $1{\mu}Pa$. It is however, appropriate for continuous noise not for transient sound. The authors compared the relationship between vibration velocity and underwater noise measured from the test blasting around Marphysa sanguinea farm. This paper presents the measurement results and suggestions the acceptance level for damage due to underwater noise from explosive blasting.

• Journal of the Korean Society for Railway
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• v.14 no.6
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• pp.545-554
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• 2011

In order to get dynamic serviceability of a train travelling on a railway bridge, comfort limits with the deflection of bridge and vertical acceleration on car body are proposed in Eurocode, Shinkansen design criteria, The design guideline of the Honam High-speed railway. The design guideline of the Honam High-speed railway has quoted Eurocode. Therefore it is expected that supplementation of comfort limit of railway bridge according to expansion of span length and the improvement traveling speed of trains in the future would relatively fall behind developed countries in railway. Therefore, in order to secure technological competitiveness in world market, the study was conducted to propose the deflection limit based on vibration serviceability of railway bridges that can consider bridge-train interaction and travelling speed increase. The parameter study and bridge-train dynamic interaction analysis was conducted to figure out the correlation of vertical acceleration on car body and bridge displacement according to the increase in travelling speed. Also, the trend of increasing vertical acceleration on car body according to the increase in travelling speed was confirmed, and the amplification coefficient of vertical acceleration on car body was suggested. And the deflection form and vibration of the bridge were assumed to be in harmonic motion, and transfer function and the amplification coefficient were used to develop the dynamic serviceability deflection limit of the high-speed railway bridge as a formula.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.1
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• pp.19-28
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• 2022

In this study, three types of combined isolator consisting of High Damping Rubber Bearing (HDRB) and wire isolator were developed for Uninterruptible Power Supply system (UPS). The dynamic characteristics of the combined isolator were investigated through one-axis shaking table test. The input acceleration were generated in accordance with ICC-ES AC156 code. Scale factors of the input acceleration were designed to be 0.5-2 times the required response spectrum defined in ICC-ES AC156. Based on the test results, damage and dynamic characteristics of the UPS were investigated: including natural frequency, damping ratio, acceleration time history response, dynamic amplification factor and relative displacement. Based on that, it was found that the combined isolator developed in this study could improve the seismic behavior of the UPS, in particular, the response acceleration.

• Journal of Korean Society of Steel Construction
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• v.22 no.5
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• pp.445-453
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• 2010

Recently, the remodeling projects of old low-rise buildings were launched in Korea. However, most of them were not satisfied with the value set forth by the KBC2005. Even though there are some research studies on how to improve the seismic performance of such buildings as newly constructed buildings, there is little research in measuring the actual vibrations on low old buildings to prove the effect of retrofit. There also has not been any in-depth research on the dynamic characteristics of full-scale structures using vibration measurements of the building that was damaged to failure. Using an actuator, the dynamic characteristics of reinforced three-storey concrete buildings were evaluated before and after they were damaged. After an 80-mm horizontal displacement by the actuator, frequency in the long and short directions were reduced to 20.85% and 5.77% respectively ; damping ratio was also reduced to 53.9% and 23.15% respectively.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2000.11a
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• pp.73.2-77
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• 2000

A possibility of the implementation of a quartz crystal sensor to the detennination of chemical oxygen demand is examined by checking the electrochemical behavior of the sensor in a glucose solution. Since the surface of a quartz crystal has to be oxidized, a relatively active metal is coated on the surface of a usual 9 MHz AT-cut crystal. The electrochemical behavior is investigated by measuring the changes of current, resonant frequency and resonant resistance while a constant potential is applied. The crystal is installed in a specially designed container, and a QUartz crystal analyzer is utilized to measure the frequency and resistance simultaneously. The variations of the measurements are examined at different concentrations of glucose solution and the effect of the concentration is analyzed to find a proper relation between the concentration and the measurements. It is fOlmd that a linear relation between the concentration of less than 900 Dpm and the peak current when a constant potential of -180 m V vs. Ag/ AgCI reference is applied.

• Computational Structural Engineering
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• v.4 no.1
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• pp.20-27
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• 1991

본 논문에서는 유체-구조 상호작용해석의 일종의 3차원 접수구조물의 진동해석을 효과적으로 수행하기 위한 해석방법을 제시하기 위하여 동적재해석기법을 검토하였다. 접수구조물의 유한구조 상호작용해석 결과는 구조진동의 관심 주파수역에서는 3차원 연성 부가수질량으로 표현되는 관성력으로 나타난다. 따라서 구조질량행렬에 부가수질량 행렬이 더해져서 전체 관성력으로 표현된다. 이 부가수질량을 추가질량으로 보고 재해석기법을 응용하는 방법을 수치실험을 통해 검증하였다. 이 때 재해석기법이 갖추어야 할 조건은 원구조의 질량과 거의 같은 정도의 질량이 추가되고 또한 완전 연성질량이 추가된 경우에도 정확한 해를 주어야 한다는 것이다. 이를 검증하기 위해 직접재해석기법과 섭동법을 이용한 재해석기법으로 4질량 스프링지지구조에 대한 해석을 수행한 결과 직접재해석기법의 응용이 적합함을 쉽게 입증할 수 있었다. 접수구조물의 예로는 3차원 잠수주상체에 대해 접수진동해석을 수행하였으며 그 결과 선체진동해석에 전통적으로 이용되고 있는 2차원 부가수질량과 3차원 수정계수를 사용한 기준차수법에서는 수지모드와 수평-비틔 연성모드와 같이 서로 독립적인 모드에 대해서는 따로 진동해석을 수행해 주어야 하는 단점이 발견되었다. 이 단점을 보완한 각 모드의 3차원 수정계수행렬을 이용한 재해석기법을 도입하여 모드에 상관없이 동시에 해를 구할 수 있었다. 그러나, 이 방법은 3차원 수정계수가 구해져 있는 경우에 한해서만 적용가능하며 실제 선체진동의 경우에는 10Hz 미만의 저차 주선체 진동에 한해서만 적용가능한 방법이다. 고차의 진도옴드에는 3차원 수정계수를 구할 수 없기 때문에 유체-구조 상호작용 해석결과로부터 얻은 3차원 연성 부가수질량을 이용하게 되며 이 때 이 행렬이 접수구조 표면의 전 자유도와 연성되어 있기 때문에 방대한 방정식을 푸어야 하지만 직접재해석기법을 적용함으로써 정확한 해를 구할 수 있었다. 또한 3차원 부가수질량을 이용한 직접재해석기법은 종래의 2차원 부가수질량과 3차원 수정계수를 이용한 방법에 비해 해석시간 면에서도 전혀 불리한 점이 없는 경제적 방법임이 밝혀졌다. 앞으로 Slamming 혹은 수중폭파 등의 충격하중에 의한 천이 구조응답 해석을 위한 효과적인 방법에 대해서도 연구결과를 발표할 계획이다.

• Journal of Korean Society of Steel Construction
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• v.26 no.6
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• pp.511-522
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• 2014

In this study, an innovative steel stair system is presented which enables rapid erection and high quality control in both residential and office building construction. This system features two lightweight steel stringers of box shape, bolted connections easy to absorb construction tolerance, and stair steps movable transversely (or sliding steps) such that the work space needed for concrete stairway wall could be easily provided. In this type of stairway system, other than providing robust connecting details, ensuring vibration performance is especially important since this system may be vibration-sensitive due to lightweight nature and/or probable low damping. To tackle these issues, a series of full-scale mock-up tests were conducted by using box-shape stringer members with or without concrete-fill. The connection system was shown to be sufficiently stiff and strong, or it remained elastic even under the 160% of service load level. Among the seven stringer alternatives, five exhibited satisfactory vibration performance according to the related North American and European acceptance criteria.

• Tunnel and Underground Space
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• v.26 no.1
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• pp.1-11
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• 2016

This study deals with the case that was the field application of the microseismic monitoring techniques for the stability monitoring in a domestic mine. The usefulness and limitations of the microseismic techniques were examined through analyzing the microseismic monitored data. The target limestone mine adopted a hybrid room-and-pillar mining method to improve the extraction ratio. The accelerometers were installed in each vertical pillar within the test bed which has the horizontal cross-section $50m{\times}50m$. The measured signals were divided into 4 types; blasting induced signal, drilling induced signal, damage induced signal, and electric noise. The stability analysis was performed based on the measured damage induced signals. After the blasting in the mining section close to the test bed, the damage of the pillar was increased and rockfall near the test bed could be estimated from monitored microseismic data. It was possible to assess the pillar stability from the changes of daily monitored data and the proposed safety criteria from the accumulated monitored data. However, there was a difficulty to determine the 3D microseismic source positions due to the 2D local sensor arrays. Also, it was needed to use real-time monitoring methods in domestic mines. By complementing the problems encountered in the mine application and comparing microseismic monitored data with mining operations, the microseismic monitoring technique can be used as a better safety method.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.35 no.2
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• pp.255-264
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• 2015

Steel plate concrete (SC) structure has been developed as a new structural type. Rational damping value shall be determined for the seismic design of SC structure. This study evaluated damping ratio of SC structure through experiments. For the study, a SC shear wall specimen was constructed and dynamically tested on the shaking table. Acceleration time history responses measured from testing were converted to the transfer functions and analyzed by using experimental modal analysis technique. The structural damping ratio of the specimen was identified as 4% to critical. Considering the shaking table test was performed at the excitation level corresponding to the low stress level of the specimen, 4% could be suggested as a structural damping for design of SC structure for operating basis earthquake.

• Journal of the Earthquake Engineering Society of Korea
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• v.10 no.5 s.51
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• pp.107-115
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• 2006

The power supply system is one of the most important infrafacilities which should maintain their inherent function during and after earthquakes. This study was performed to analyze dynamic characteristics and seismic performance of Korean typical 154kV transformer porcelain bushing. For the purpose of this study, actual 154kV porcelain bushings were selected and tested on the shaking table. The vibration tests consist of modal identification tests, seismic performance tests, and fragility tests. The sine sweep waves, artificial earthquake waves, and continuous resonant sine waves were used as shaking table motions. This paper describes the test specimens, shaking facilities, and test methods. Natural frequencies and damping ratios of the bushing have been evaluated from the experimental data. The failure mode and the performance level of the Korean transformer bushing have been first identified in this study.