• Journal of the Korean Geosynthetics Society
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• v.23 no.2
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• pp.29-42
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• 2024

The 2017 Pohang earthquake caused damage to quay structures due to liquefaction. Liquefaction occurs when effective stress is lost due to an increase in excess pore water pressure during an earthquake. As a result, the damage caused to the pier-type quay wall was identified and the damage caused by liquefaction was analyzed. In addition, in the case of improved ground, damage occurred due to liquefaction of the lower sand layer due to the difference in stiffness from the soft rock layer, so additional numerical analysis was performed assuming non-liquefaction ground. There are several factors that affect the increase in excess pore water pressure ratio, such as the relative density of the ground and the magnitude of the input seismic acceleration. Therefore, this study performed numerical analysis for Cases 1 to 3 by increasing the magnitude of the input acceleration, and in the case of improved ground, damage occurred due to liquefaction of the lower sand layer, so the analysis was performed assuming non-liquefaction ground. As a result, the improved ground requires additional reinforcement when there is liquefied ground below, and the horizontal displacement of the pier-type quay piles was reduced by about two times.

• Journal of Ocean Engineering and Technology
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• v.30 no.4
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• pp.287-293
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• 2016

This paper presents an effective damage detection method for offshore jackets using natural frequency change ratios. Two parameters, cosine similarity and magnitude index, are considered to estimate the location and severity of the damage in the structure. A numerical jacket structure model is considered to verify the performance of the proposed method. As observed through analysis, the damages in the structure are detected accurately.

• Journal of the Korean Professional Engineers Association
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• v.38 no.1
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• pp.59-63
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• 2005

A Tsunami was generated by the magnitude 9.0 earthquake which occurred near Indonesia. An energetic Tsunami will display vertical water displacement of the order of ten meters and lateral scales of the order of tens of kilometers. The Tsunami destroyed many coastal villages in Asia. So, there are many victims in southeastern part Asia by Tsunami. Therefore, the construction of Tsunami prediction and warning system is needed for minimize the damage by seismic sea waves.

• Smart Structures and Systems
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• v.22 no.2
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• pp.239-247
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• 2018

A magnetic flux leakage (MFL) method was applied to detect and quantify defects in a steel bar. A multi-channel MFL sensor head was fabricated using Hall sensors and magnetization yokes with permanent magnets. The MFL sensor head scanned a damaged specimen with five levels of defects to measure the magnetic flux density. A series of signal processing procedures, including an enveloping process based on the Hilbert transform, was performed to clarify the flux leakage signal. The objective damage detection of the enveloped signals was then analyzed by comparing them to a threshold value. To quantitatively analyze the MFL signal according to the damage level, five kinds of damage indices based on the relationship between the enveloped MFL signal and the threshold value were applied. Using the proposed damage indices and the general damage index for the MFL method, the detected MFL signals were quantified and analyzed relative to the magnitude of the damage increase.

• Structural Engineering and Mechanics
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• v.9 no.2
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• pp.195-208
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• 2000

To confirm the theory and static defect energy (SDE) equations proposed in the first part, extensive numerical simulation studies are performed in this portion. Stiffness method is applied to calculate the components of the stresses and strains from which the energy components and finally, the SDE are obtained. Examples are designed to cover almost all kinds of possibilities. Variables include structural type, material, cross-section, support constraint, loading type, magnitude and position. The SDE diagram is unique in the way of presenting damage information: two different energy constants are separated by a sharp vertical drop right at the damage location. Simulation results are successfully implemented for both methods in all the cases.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.969-974
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• 2004

Although guided-waves are very efficient for long-range nondestructive damage inspection, it is not easy to extract meaningful pulses of small magnitude out of noisy signals. The ultimate goal of this research is to develop an efficient signal processing technique for the current guided-wave technology. The specific contribution of this investigation towards achieving this goal, a two-stage Gabor pulse-based matching pursuit algorithm is proposed : rough approximations with a set for predetermined parameters characterizing the Gabor pulse and fine adjustments of the parameters by optimization. The parameters estimated from the measured signal are then used to assess not only the location but also the size of a crack existing in a rod. To validate the effectiveness of the proposed method, the longitudinal wave-based damage detection in rods is considered. To estimate the crack size, Love's theory for the dispersion of longitudinal waves is employed.

• Journal of the Korea institute for structural maintenance and inspection
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• v.8 no.4
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• pp.247-256
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• 2004

The damage curves for the 2-story shear building to the impulsive rectangular loads were established with the peak load and Impulse ratio producing the critical displacement. The convolution integrations with the Impulse response matrix and the loads were used to find the responses of the building. The impulse response matrix required in the calculations of the convolution integration were found with the mode superposition method It is shown from the established damage curves that the responses of the top and bottom floor are sensitive to the magnitude and the impulse of the loads respectively.

• Nuclear Engineering and Technology
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• v.45 no.4
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• pp.553-564
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• 2013

This study evaluates the local damage of a turbine in an auxiliary building of a nuclear power plant due to an external impact by using the LS-DYNA finite element program. The wall of the auxiliary building is SC structure and the material of the SC wall plate is high manganese steel, which has superior ductility and energy absorbance compared to the ordinary steel used for other SC wall plates. The effects of the material of the wall, collision speed, and angle on the magnitude of the local damage were evaluated by local collision analysis. The analysis revealed that the SC wall made of manganese steel had significantly less damage than the SC wall made of ordinary steel. In conclusion, an SC wall made of manganese steel can have higher effective resistance than an SC wall made of ordinary steel against the local collision of an airplane engine or against a turbine impact.

• Earthquakes and Structures
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• v.22 no.3
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• pp.305-318
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• 2022

This paper presents a comparative study of the damage potentials for the 2016 Gyeongju and 2017 Pohang earthquakes in Korea. Plausible technical explanations are provided for the more severe damage observed in the 2017 Pohang earthquake in spite of its relatively weaker magnitude and intensity measures based on the response analysis of elastic and inelastic single-degree-of-freedom systems for the recorded ground motions. In addition, a detailed case study was conducted for a fatally damaged piloti building with an eccentric shear wall core based on nonlinear dynamic analysis using the input ground motions modified for the building site.

• Smart Structures and Systems
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• v.2 no.2
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• pp.127-140
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• 2006

In this study, a wavelet-based covariance-driven system identification technique is proposed for damage assessment of structures under ambient excitation. Assuming the ambient excitation to be a white-noise process, the covariance computation is shown to be able to separate the effect of random excitation from the response measurement. Wavelet transform (WT) is then used to convert the covariance response in the time domain to the WT magnitude plot in the time-scale plane. The wavelet coefficients along the curves where energy concentrated are extracted and used to estimate the modal properties of the structure. These modal property estimations lead to the calculation of the stiffness matrix when either the spectral density of the random loading or the mass matrix is given. The predicted stiffness matrix hence provides a direct assessment on the possible location and severity of damage which results in stiffness alteration. To demonstrate the proposed wavelet-based damage assessment technique, a numerical example on a 3 degree-of-freedom (DOF) system and an experimental study on a three-story building model, which are all under a broad-band excitation, are presented. Both numerical and experimental results illustrate that the proposed technique can provide an accurate assessment on the damage location. It is however noted that the assessment of damage severity is not as accurate, which might be due to the errors associated with the mode shape estimations as well as the assumption of proportional damping adopted in the formulation.