• Structural Monitoring and Maintenance
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• v.11 no.2
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• pp.87-100
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• 2024

Traffic-induced vibrations (TIVs) possess the potential to induce structural damage in both historical and critical edifices. Recent investigations have underscored the adverse impact of TIVs within buildings, manifesting as a deleterious influence on the quality of life and operational efficiency of occupants. Consequently, these studies have dichotomized TIVs into two primary limit categories: the threshold for vibrations capable of causing structural damage and the limit values associated with human comfort. In this current research endeavor, an exhaustive analysis of peak ground acceleration (PGA), peak ground velocity (PGV), peak ground displacement (PGD), and the frequency spectrum of ground motions originating from diverse traffic sources has been conducted. Furthermore, the detrimental repercussions of these vibrations on structures, gauged through the assessment of the peak particle velocity (PPV) parameter, have been systematically evaluated. The findings of this study elucidate that TIVs within the examined structures do not attain magnitudes conducive to structural compromise; however, the levels surpassing human comfort limits are evident, attributable to specific sources and distances. Moreover, this investigation sheds light on the absence of comprehensive criteria and guidelines pertaining to the assessment of TIVs in structures within the Turkish Building Seismic Design Code 2018. It seeks to raise awareness among building constructors about the critical importance of addressing this issue, emphasizing the imperative for guidelines in mitigating the impact of TIVs on both structural integrity and human well-being.

• Journal of Drive and Control
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• v.21 no.3
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• pp.9-19
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• 2024

Many modern hydraulic excavators now use EPPRVs (Electronic Proportional Pressure Reducing Valves) in their pilot systems to control the spool displacement of the main hydraulic system. However, the performance of these systems is often limited by factors such as magnetic hysteresis, mechanical wear, and transient responses influenced by operating conditions and component installation. This paper presents a pressure feedback controller for excavator pilot systems that utilize EPPRVs. This controller significantly reduces steady-state pressure control errors and mitigates the hysteresis effects commonly seen in traditional open-loop systems. To achieve this, we integrated EPPRVs with the main hydraulic valve and injected a chirp signal into the solenoid current. By doing so, we were able to measure the frequency response of the pilot system across different operating pressures and estimate the system dynamics model. Using these models, we designed a set of PI pressure feedback controllers that are guaranteed to be stable. These controllers were then integrated with a gain scheduler based on a lookup table. Experimental results demonstrate that when the developed pressure feedback controller is incorporated into the conventional open-loop controller, it effectively reduces steady-state pressure control errors and mitigates hysteresis.

• Journal of Korean Tunnelling and Underground Space Association
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• v.21 no.2
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• pp.279-299
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• 2019

Recently occurred earthquake Gyeongju and Pohang served as a momentum to remind that Korean peninsular is not a safety zone from earthquake anymore. The importance of seismic design, therefore, have been realized and researches regarding design response spectrum have been actively carried out by many researchers and engineers. Current tunnel seismic design method is conducted to check safety of tunnel structure by dynamic numerical analysis with condition of completed lining installation, so, it is impossible to consider safety of tunnel behavior under construction. In this study, therefore, dynamic numerical analysis considering seismic wave propagations has been performed after back analysis using results from field monitoring of tunnel under construction in fractured zone and 1st reinforcement (shotcrete, rockbolt) behaviour are analyzed. Waves are classified by period characteristic (short and long). As a result, the difference depending on period characteristic is minor, and increasements of displacement are obtained at crown displacement due to seismic wave is 28~31%, 14~16% at left side of tunnel in the fractured zone, 13~27% at right side of tunnel in the bed rock, respectively. In case of shotcrete axial force is increased 113~115% at tunnel crown, 102% at left side, 106~110% at right side, respectively. Displacement and axial force of rockbolts which are selected by type of anchored grounds (only fractured zone, fractured zone and bed rock, only bedrock) are analyzed, as a result, rockbolt which is anchored to fractured zone and bed rock at the same time are weaker than any other case.

• Korean Journal of Applied Biomechanics
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• v.32 no.3
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• pp.94-102
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• 2022

Objective: The purpose of this study was to investigate the effect of acute transcranial direct current stimulation (tDCS) on the isokinetic muscular endurance of the lower extremity for young adults. Method: Thirteen young adults performed isokinetic fatigue tasks for two experimental conditions including real tDCS and sham stimulation protocols. Before and after the task, the tensiomyography was used for evaluating muscle contraction characteristics of vastus medialis and semitendinosus. Paired t-test was performed to compare the fatigue index, changes in maximum radial displacement (∆Dm), delay time (∆Tc), and velocity of contraction (∆Vc) between tDCS conditions. Results: We found no significant differences in the fatigue index between real and sham conditions. In addition, the analyses identified no significant different values of ∆Dm, ∆Tc, and ∆Vc in the vastus medialis and semitendinosus between real and sham conditions. Conclusion: These findings suggest that the tDCS protocols may have no acute effect on lower limb muscle endurance for young adults. Future studies should consider the long-term effects of repetitive tDCS sessions, various stimulation positions, exercise tasks, and participant characteristics to more clearly understand the effect of tDCS on muscle endurance of lower extremities.

• Journal of the Korean Society for Precision Engineering
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• v.24 no.9
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• pp.130-139
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• 2007

The disaster from functional gastrointestinal disorders (FGID) has detrimental impact on the quality of life of the affected population. There are, however, rare diagnostic methods for FGID. Our research group identified recently that the gastrointestinal tract well of the patients with FGID became more rigid than that of healthy people when palpating the abdominal regions overlaying the gastrointestinal tract. The objective of the current study is, therefore, to identify feasibility of a diagnostic system for FGID based on ultrasound technique, which can quantify the characteristics above. Two-dimensional finite difference (FD) models (one normal and two rigid models) were developed to analyze the reflective characteristic (displacement) on each soft-tissue layer responded after application of ultrasound signals. Based on the results from FD analysis, the ultrasound system for diagnosis of the FGID was developed and clinically tested via application of it to 40 human subjects with/without FGID who were assigned to Normal and Patient Groups. The results from FD analysis showed that the maximum displacement amplitude in the rigid models (0.12 and 0.16) at the interface between the fat and muscle layers was explicitly less than that in the normal model (0.29). The results from actual specimens showed that the maximum amplitude of the ultrasound reflective signal in the rigid models $(0.2{\pm}0.1Vp-p)$ at the interface between the fat and muscle layers was explicitly higher than that in the normal model $(0.1{\pm}0.0Vp-p)$. Clinical tests using our customized ultrasound system showed that the maximum amplitudes of the ultrasound reflective signals near to the gastrointestinal tract well for the patient group $(2.6{\pm}0.3Vp-p)$ were generally higher than those in normal group $(0.1{\pm}0.2Vp-p)$. These findings suggest that our customized ultrasound system using the ultrasound reflective signal may be helpful to the diagnosis of the FGID.

• Geophysics and Geophysical Exploration
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• v.14 no.2
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• pp.127-132
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• 2011

We acquired and interpreted more than 650 km of high-resolution seismic reflection profiles in the Hupo Basin, offshore east coast of Korea at $37^{\circ}N$ in the East Sea (Japan Sea) to image shallow and basement deformation. The seismic profiles reveal that the main depocenter of the Hupo Basin in the study area is bounded by the large offset Hupo Fault on the east and an antithetic fault on the west; however, the antithetic fault is much smaller both in horizontal extension and in vertical displacement than the Hupo Fault. Sediment infill in the Hupo Basin consists of syn-rift (late Oligocene. early Miocene) and post-rift (middle Miocene.Holocene) units. The Hupo Fault and other faults newly defined in the Hupo Basin strike dominantly north and show a sense of normal displacement. Considering that the East Sea has been subjected to compression since the middle Miocene, we interpret that these normal faults were created during continental rifting in late Oligocene to early Miocene times. We suggest that the current ENE direction of maximum principal compressive stress observed in and around the Korean peninsula associated with the motion of the Amurian Plate induces the faults in the Hupo Basin to have reverse and right-lateral, strike-slip motion, when reactivated. A recent earthquake positioned on the Hupo Fault indicates that in the study area and possibly further in the eastern Korean margin, earthquakes would occur on the faults created during continental rifting in the Tertiary.

• Journal of the Korea Concrete Institute
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• v.16 no.2 s.80
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• pp.249-260
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• 2004

The longitudinal steel connection of reinforced concrete bridge column is sometimes practically unavoidable, however the current Korean bridge design specifications have no special provisions about lap-splices of longitudinal steel. This paper reports experimental results of a research program investigating the seismic performance of circular RC bridge columns with respect to longitudinal steel connection detailing. Twenty-one circular column specimens were tested under quasi-static test. The columns with the entire longitudinal steel lap-spliced within plastic hinge region show relatively sudden strength degradation and low ductility than the columns with continuous longitudinal steel and the columns with half of longitudinal steel lap-spliced. However, the seismic performance of the column with mechanically connected longitudinal steel is similar to that of the column with continuous longitudinal steel. The final objectives of this study are to suggest appropriate longitudinal reinforcement connection details for the limited ductility design concept and to provide quantitative reference data and tendency for performance or damage assessment based on the performance levels such as cracking, yielding, collapse, etc. Ultimate displacement/drift ratio, displacement ductility, response modification factor, equivalent viscous damping ratio, residual deformation index, and effective stiffness are investigated and discussed in this paper.

• Proceedings of the KWS Conference
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• 2009.11a
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• pp.97-97
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• 2009

The use of thin plate increases due to the need for light weight in large ship. Thin plate is easily distorted and has residual stress by welding heat. Therefore, the thin plate should be carefully joined to minimize the welding deformation which costs time and money for repair. For one effort to reduce welding deformation, it is very useful to predict welding deformation before welding execution. There are two methods to analyze welding deformation. One is simple linear analysis. The other is nonlinear analysis. The simple linear analysis is elastic analysis using the equivalent load method or inherent strain method from welding experiments. The nonlinear analysis is thermo-elastic analysis which gives consideration to the nonlinearity of material dependent on temperature and time, welding current, voltage, speed, sequence and constraint. In this study, the welding deformation is analyzed by using thermo-elastic method for PCTC(Pure Car and Truck Carrier) which carries cars and trucks. PCTC uses thin plates of 6mm thickness which is susceptible to welding heat. The analysis dimension is 19,200mm(length) * 13,825mm(width) * 376mm(height). MARC and MENTAT are used as pre and post processor and solver. The boundary conditions are based on the real situation in shipyard. The simulations contain convection and gravity. The material of the thin block is mild steel with $235N/mm^2$ yield strength. Its nonlinearity of conductivity, specific heat, Young's modulus and yield strength is applied in simulations. Welding is done in two pass. First pass lasts 2,100 second, then it rests for 900 second, then second pass lasts 2,100 second and then it rests for 20,000 second. The displacement at 0 sec is caused by its own weight. It is maximum 19mm at the free side. The welding line expands, shrinks during welding and finally experiences shrinkage. It results in angular distortion of thin block. Final maximum displacement, 17mm occurs around welding line. The maximum residual stress happens at the welding line, where the stress is above the yield strength. Also, the maximum equivalent plastic strain occurs at the welding line. The plastic strain of first pass is more than that of second pass. The flatness of plate in longitudinal direction is calculated in parallel with the direction of girder and compared with deformation standard of ${\pm}15mm$. Calculated value is within the standard range. The flatness of plate in transverse direction is calculated in perpendicular to the direction of girder and compared with deformation standard of ${\pm}6mm$. It satisfies the standard. Buckle of plate is calculated between each longitudinal and compared with the deformation standard. All buckle value is within the standard range of ${\pm}6mm$.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.1
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• pp.1-8
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• 2017

Three small scale hollow circular reinforced concrete columns with aspect ratio 4.5 were tested under cyclic lateral load with constant axial load. Diameter of section is 400 mm, hollow diameter is 200 mm. The selected test variable is transverse steel ratio. Volumetric ratios of spirals of all the columns are 0.302~0.604% in the plastic hinge region. It corresponds to 45.9~91.8% of the minimum requirement of confining steel by Korean Bridge Design Specifications, which represent existing columns not designed by the current seismic design specifications or designed by seismic concept. The longitudinal steel ratio is 2.017%. The axial load ratio is 7%. This paper describes mainly crack behavior, load-displacement hysteresis loop, seismic performance such as equivalent damping ratio, residual displacement and effective stiffness and flexural over-strength of circular reinforced concrete bridge columns with respect to test variable. The regulation of flexural over-strength is adopted by Korea Bridge Design Specifications (Limited state design, 2012). The test results are compared with nominal strength, result of nonlinear moment-curvature analysis and the design specifications such as AASHTO LRFD and Korea Bridge Design Specifications(Limited state design).

• Journal of Sensor Science and Technology
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• v.19 no.5
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• pp.361-368
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• 2010

ACROSS device, which is composed of an implantable microphone, a signal processor, and a vibrating transducer, is a fullyimplantable middle ear hearing device(F-IMEHD) for the recovery of patients with hearing loss. And since a microphone is implanted under skin and tissue at the temporal bones, the amplitude of the sound wave is attenuated by absorption and scattering. And the vibrating transducer attached to the ossicular chain caused also the different displacement from characteristic of the stapes. For the gain control of auditory signals, most of implantable hearing devices with the digital audio signal processor still apply to fitting rules of conventional hearing aid without regard to the effect of the implanted microphone and the vibrating transducer. So it should be taken into account the effect of the implantable microphone and the vibrating transducer to use the conventional audio fitting rule. The aim of this study was to measure gain characteristics caused by the implanted microphone and the vibrating transducer attached to the ossicle chains for the gain compensation of ACROSS device. Differential floating mass transducers (DFMT) of ACROSS device were clipped on four cadaver temporal bones. And after placing the DFMT on them, displacements of the ossicle chain with the DFMT operated by 1 $mA_{peak}$ current was measured using laser Doppler vibrometer. And the sensitivity of microphones under the sampled pig skin and the skin of 3 rat back were measured by stimulus of pure tones in frequency from 0.1 to 8.9 kHz. And we confirmed that the microphone implanted under skin showed poorer frequency response in the acoustic high-frequency band than it in the low- to mid- frequency band, and the resonant frequency of the stapes vibration was changed by attaching the DFMT on the incus, the displacement of the DFMT driven with 1 $mA_{rms}$ was higher by the amount of about 20 dB than that of cadaver's stapes driven by the sound presssure of 94 dB SPL in resonance frequency range.