• Earthquakes and Structures
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• v.15 no.6
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• pp.595-603
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• 2018

Shake table testing has been regarded as one of the most effective experimental approaches to evaluate seismic response of structural systems subjected to earthquakes. However, reproducing a prescribed acceleration time history precisely over the frequency of interest is challenging because shake table test systems are eventually nonlinear by nature. In addition, interaction between the table and specimen could affect the control accuracy of shake table testing significantly. Various novel control algorithms have been proposed to improve the control accuracy of shake table testing; however, reference values for control performance assessment remain rare. In this study, reference values for control performance assessment of shake table testing are specified based on the statistical analyses of 1,209 experimental data provided by the Seismic Simulator Laboratory of National Center for Research on Earthquake Engineering in Taiwan. Three individual reference values are considered for the assessment including the root-mean-square error of the achieved acceleration time history; the percentage of the spectral acceleration that exceeds the determined tolerance range over the frequency of interest; and the error-ratio of the achieved peak ground acceleration. Quartiles of the real experimental data in terms of the three objective variables are obtained, providing users with solid and simple references to evaluate the control performance of shake table testing. Finally, a set of experimental data of a newly developed control framework implementation for uni-axial shake tables are used as an application example to demonstrate the significant improvement of control accuracy according to the reference values provided in this study.

• The Journal of Engineering Geology
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• v.33 no.2
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• pp.293-305
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• 2023

Three ground models are analyzed using a 1g shaking table and laminar shear box (LSB) to investigate the impact of the ground structure on seismic wave amplification during earthquakes. Multi-layer horizontal, embankment, and basin ground models are selected for this investigation, with each model being divided into dense and loose ground layers, Accelerometers are installed during the construction of each ground model to capture any seismic wave amplification owing th the propagation of an artificial seismic wave, sine wave sweep, and 10-Hz sine wave through a given ground model. The amplification of the tested seismic waves is analyzed using the observed peak ground acceleration and spectrum acceleration. The observed acceleration amplification in the multi-layer horizontal ground model is significantly higher the seismic waves that propagated across the dense ground-loose ground boundary compared with those that only propagated through the dense ground. Furthermore, the observed acceleration amplification gradually increases in the central part of the multi-layer embankment and basin models for the seismic waves that propagated across the dense ground-loose ground boundary.

• Advances in concrete construction
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• v.9 no.4
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• pp.423-435
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• 2020

Open ground story (OGS) reinforced concrete (RC) buildings are vulnerable to the complete collapse or severe damages under seismic actions. This study investigates the effectiveness of four different strengthening techniques representing the local and global modifications to improve the seismic performance of a non-ductile RC OGS frame. Steel caging and concrete jacketing methods of column strengthening are considered as the local modification techniques, whereas steel bracing and RC shear wall systems are selected as the global strengthening techniques in this study. Performance-based plastic design (PBPD) approach relying on energy-balance concept has been adopted to determine the required design force demand on the strengthening elements. Nonlinear static and dynamic analyses are carried out on the numerical models of study frames to assess the effectiveness of selected strengthening techniques in improving the seismic performance of OGS frame.. Strengthening techniques based on steel braces and RC shear wall significantly reduced the peak interstory drift response of the OGS frame. However, the peak floor acceleration of these strengthened frames is amplified by more than 2.5 times as compared to that of unstrengthened frame. Steel caging technique of column strengthening resulted in a reasonable reduction in the peak interstory drift response without substantial amplification in peak floor acceleration of the OSG frame.

• Journal of the Korean Geotechnical Society
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• v.36 no.11
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• pp.21-33
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• 2020

Ground response analysis has been conducted for each borehole data in Pohang area, using 1D equivalent linear method program, to investigate the applicability of amplification factor to estimate peak ground acceleration. Earthquake motions for ground response analysis were prepared by matching response spectrums for return period of 500, 1000, and 2400 years suggested by seismic design code (MOIS, 2017). Ground survey data were acquired from Geotechnical Information DB System. It has been confirmed that response spectrum obtained from ground response analysis showed good agreement with those from seismic design code irrespective of ground classification. However, PGA (Peak Ground Accelerations) of ground response analysis did not coincide with PGA calculated using amplification factor suggested by seismic design code.

• Journal of the Earthquake Engineering Society of Korea
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• v.8 no.6 s.40
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• pp.31-43
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• 2004

Seismic risk assessment of bridge is presented using fragility curves which represent the probability of damage of a structure virsus the peak ground acceleration. In theseismic fragility analysis, the structural damage is defined using the rotational ductility at the base of the bridge pier, which is obtained through nonlinear dynamic analysis for various input earthquakes. For the assessment of seismic risk of bridge, peak ground accelerations are obatined for various return periods from the seismic hazard map of Korea, which enables to calculate the probability density function of peak ground acceleration. Combining the probability density function of peak ground acceleration and the seismic fragility analysis, seismic risk assessment is performed. In this study, seismic fragility analysis is developed as a function of not the surface motion which the bridge actually suffers, but the rock outcrop motion which the aseismic design code is defined on, so that further analysis for the seismic hazard assessment may become available. Besides, the effects of the friction pot bearings and the friction pendulum bearings on the seismic fragility and risk analysis are examined. Lastly, three regions in Korea are considered and compared in the seismic risk assessment.

• Structural Engineering and Mechanics
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• v.18 no.3
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• pp.287-301
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• 2004

Structural acceleration regulation is a means of managing structural response energy and enhancing the performance of civil structures undergoing large seismic events. A quadratic output regulator that minimizes a measure including the total structural acceleration energy is developed and tested on a realistic non-linear, semi-active structural control case study. Suites of large scaled earthquakes are used to statistically quantify the impact of this type of control in terms of changes in the statistical distribution of controlled structural response. This approach includes the impulses due to control inputs and is shown to be more effective than a typical displacement focused control approach, by providing equivalent or better performance in terms of displacement and hysteretic energy reductions, while also significantly reducing peak story accelerations and the associated damage and occupant injury. For earthquake engineers faced with the dilemma of balancing displacement and acceleration demands this control approach can significantly reduce that concern, reducing structural damage and improving occupant safety.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2008.04a
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• pp.410-415
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• 2008

This paper presents review on human comfort criteria in major codes and standards for tall buildings. In general, human comfort criteria of tall buildings have been used by magnitude of wind-induced acceleration response. Two different indexes in determination of the magnitude have been used: the peak value which occurs during a period of time and the rms value averaged over this same period. These distinctive acceleration indexes are discussed in detail and each criterion is reviewed and compared. The distinctions arisen because of the different wave forms, or acceleration signatures are addressed. It is described that which index of acceleration should be adopted in establishment of Korean human comfort criteria. In addition, some arguments from a technical standpoint that favor the use of each index are presented.

• Proceedings of the Korea Water Resources Association Conference
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• 2008.05a
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• pp.1111-1115
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• 2008

The relative magnitudes of the individual terms of the momentum equation are analyzed and compared by the analytical methods in open channel flow. The temporal variations of each term(local acceleration term, convective acceleration term, pressure force term, gravity force term, and friction force term) are analyzed for the influence factors to runoff expressed by the parameters of the momentum equation, stream slopes and roughness coefficients. The magnitudes of each term vary with the channel characteristics, especially when the roughness coefficients are dominant or for the mild stream slopes the pressure term can not be negligible. As a result of the characteristics of momentum equation in open channel flow, the acceleration terms are very small compared with the other terms. The magnitudes of local acceleration and convective acceleration offsets each other. The peak time of each term except the gravity term coincides with inflection point of the hydrograph rising limb each other.

• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.105-108
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• 2006

should be in This paper presents review on human comfort criteria in major codes and standards for tall buildings. In general, human comfort criteria of tall buildings have been used by magnitude of wind-induced acceleration response. Two different indexes in determination of the magnitude have been used: the peak value which occurs during a period of time and the rms value averaged over this same period. These distinctive acceleration indexes are discussed in detail and each criterium was reviewed and compared. The distinctions arisen because of the different wave forms, or acceleration signatures were addressed. It is described that which index of acceleration should be adopted in establishment of Korean human comfort criteria. In addition, some arguments from a technical standpoint that favor the use of each index are presented.

• Korean Journal of Applied Biomechanics
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• v.26 no.4
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• pp.433-441
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• 2016

Objective: The purpose of this study was to understand the injury mechanism and to provide quantitative data to use in prevention or posture correction training by conducting kinematic and kinetic analyses of risk factors of lower extremity joint injury depending on the change of direction at different angles after a landing motion. Method: This study included 11 men in their twenties (age: $24.6{\pm}1.7years$, height: $176.6{\pm}4.4cm$, weight: $71.3{\pm}8.0kg$) who were right-leg dominant. By using seven infrared cameras (Oqus 300, Qualisys, Sweden), one force platform (AMTI, USA), and an accelerometer (Noraxon, USA), single-leg drop landing was performed at a height of 30 cm. The joint range of motion (ROM) of the lower extremity, peak joint moment, peak joint power, peak vertical ground reaction force (GRF), and peak vertical acceleration were measured. For statistical analysis, one-way repeated-measures analysis of variance was conducted at a significance level of ${\alpha}$ <.05. Results: Ankle and knee joint ROM in the sagittal plane significantly differed, respectively (F = 3.145, p = .024; F = 14.183, p = .000), depending on the change of direction. However, no significant differences were observed in the ROM of ankle and knee joint in the transverse plane. Significant differences in peak joint moment were also observed but no statistically significant differences were found in negative joint power between the conditions. Peak vertical GRF was high in landing (LAD) and after landing, left $45^{\circ}$ cutting (LLC), with a significant difference (F = 9.363, p = .000). The peak vertical acceleration was relatively high in LAD and LLC compared with other conditions, but the difference was not significant. Conclusion: We conclude that moving in the left direction may expose athletes to greater injury risk in terms of joint kinetics than moving in the right direction. However, further investigation of joint injury mechanisms in sports would be required to confirm these findings.