• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.4
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• pp.94-103
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• 2016

For elevated railway station on which track is connected with superstructure of station, structural vibration level and structure-borne-noise level has exceeded the reference level due to structural characteristics which transmits vibration directly. Therefore, existing elevated railway station is in need of economical and effective vibration reduction method which enable train service without interruption. In this study, structural vibration non-transmissible system which is applied to vibroisolating material for column member is developed to reduce vibration. That system is cut covering material of the column section using water-jet method and is installed with vibroisolating material on cut section. To verify vibration reduction effect and structural performance for structural vibration non-transmissible system, impact hammer test and cyclic lateral load test are performed for 1/4 scale test specimens. It is observed that natural period which means vibration response characteristics is shifted, and damping ratio is increased about 15~30% which means that system is effective to reduce structural vibration through vibration test. Also load-displacement relation and stiffness change rate of the columns are examined, and it is shown that ductility and energy dissipation capacity is increased. From test results, it is found that vibration non-transmissible system which is applied to column member enable to maintains structural function.

• Journal of The Geomorphological Association of Korea
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• v.20 no.1
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• pp.45-56
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• 2013

Rock strength test on Dunduri cliff, Chungnam province, Korea, was performed using N-type Schmidt hammer and the depositional ages of the sediments overlying the cliff were derived using OSL dating method. The averaged R-values of the cliffs investigated here were lower than those observed from the shore platforms, but with larger scatter in the former. R-values were negatively correlated to cliff face retreat, implying that the irregularity of the coastal rock faces was closely related to lithology as the weaker rocks retreated much faster than the harder rocks. The overlying deposit of the cliff tends to be thicker at valleys and were poorly sorted with angular to subangular clasts in a matrix of silt. The OSL ages (ca. 70-77 ka) presented here were older than the previously reported exposure ages (ca. 7-30 ka) of the cliff face. Therefore, it is likely that the present sea cliff was developed by expansion of the platform which had been covered by slope deposits since the last interglacial and exposed again during the Holocene.

• The Journal of the Convergence on Culture Technology
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• v.5 no.4
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• pp.93-98
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• 2019

The purpose of this study was to identify and analyze the rate of change of air respirator consumption based on field fire fighting activities, The results of the experiment are as follows. The mean air consumption of the Five subjects was $15.56{\ell}/min$ when standing still, $32.43{\ell}/min$ when walking with normal pace, $43.07{\ell}/min$ when the fire hoses was expanded and arranged, $55.28{\ell}/min$ when climbing stairs, The situation of running up the stairs and hitting the hammer continuously increases to $127.14{\ell}/min$, which means that the consumption of air increases according to the energy consumption. Despite being the oldest, Experimental subject A was $13.23{\ell}/min$ when standing still, $29.33{\ell}/min$ when walking normally, and $41.08{\ell}/min$ when the fire hose was deployed and arranged. This is a result of familiarity with deep and slow breathing methods. The average respiratory use rate of subjects D was $63.58{\ell}/min$. The reason for this is that obesity seems to increase the air consumption, and it is considered that the physical strength is exhausted by the action of the hammer, which has a greater influence on the increase of air consumption. The subject E had significantly lower air respiratory use rate of $49.90{\ell}/min$. The reason for this is that the age of E is the youngest among the subjects, and it is presumed that it possesses strong physical strength.

• Journal of the Korean Geotechnical Society
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• v.37 no.11
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• pp.61-69
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• 2021

In this study, scale down model bridge piers were fabricated and non-destructive experiments conducted with an impact load to determine scours in the ground adjacent to the bridge piers using the natural frequency of the bridge piers. Three scale-model bridge piers with different heights were fabricated, and they penetrated the ground at a depth of 0.35 m. The scours around the bridge piers were simulated as a side scour and foundation scour. The experiments were conducted in 13 steps, in which scouring around the model bridge piers was performed in 0.05 m excavation units. To derive the natural frequency, the impact load was measured with three accelerometers attached to the model bridge piers. The impact load was applied with an impact hammer, and the top of the model bridge pier was struck perpendicularly to the bridge axis. The natural frequency according to the scour progress was calculated with a fast Fourier transform. The results demonstrated that the natural frequency of each bridge pier tended to decrease with scour progress. The natural frequency also decreased with increasing pier height. With scour progress, a side scour occurred at 70% or higher of the initial natural frequency, and a foundation scour occurred at less than 70%.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.6A
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• pp.535-542
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• 2010

Precise estimation of a structure's dynamic characteristics is indispensable for ensuring stable dynamic responses during lifetime especially for the structures which can experience resonance such as railway bridges. In this paper, the results of forced vibration tests of different excitation methods (vibration exciter and impact hammer) are compared to examine the differences and the cause of differences of extracted natural frequencies. Consequently a natural frequency modification method is suggested to eliminate effects of non-structural disturbance factors. Also, sequential forced vibration tests are performed before and after track construction according to the construction stage of a railway bridge, and the variation of natural frequencies are examined. Effect of added mass of vibration exciter and variation of support condition due to the level of excitation force are concluded as the major cause of natural frequency differences. Thus eliminating these effects can enhance the reliability of the extracted natural frequencies. Construction of track affects not only the mass of structure but also the stiffness of the structure. Also, the amount of increase in stiffness varies according to the level of structural deflection. Therefore, reasonable estimation of the level of structural response during operation is important for precise natural frequency calculation at design phase.

• Journal of Korean Society of Forest Science
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• v.112 no.4
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• pp.451-458
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• 2023

As forest fires continue to increase in scale worldwide, the importance of forest roads in relation to forest fire prevention and suppression has become increasingly evident. To ensure effective functioning during a forest fire disaster, it is crucial to apply appropriate road planning and ensure roads' structural integrity. However, previous studies have predominantly focused on the impact of forest fires on firebreak efficacy and road placement, meaning that insufficient attention has been paid to ensuring the safety of these facilities. Therefore, this study sought to compare the strength of concrete facilities within areas damaged by forest fires over the past three years by using the rebound hammer test to identify signs of thermal degradation. The results revealed that concrete facilities damaged by forest fires exhibited significantly lower strength (15.6 MPa) when compared with undamaged facilities (18.0 MPa) (p<0.001), and this trend was consistent across all the target facilities. Consequently, it is recommended that safety assessment criteria for concrete forest road facilities be established to prevent secondary disasters following forest fire damage. Moreover, continuous monitoring and research involving indoor experiments are imperative in terms of enhancing the stability of forest road structures. It is expected that such research will lead to the development of more effective strategies for forest fire prevention and suppression.

• Journal of the Society of Disaster Information
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• v.20 no.2
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• pp.369-378
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• 2024

Purpose: This study aims to verify structural stability by manufacturing a 40m full-scale specimen composed of a segmental U-shaped PSC girder with integrated tensioning systems and a concrete slab, proceeding dynamic behavior tests, and compare the results of the tests with the results of numerical analysis. Method: Dynamic behavior tests were conducted on a full-scale, undamaged specimen using an impact hammer, and the natural frequency and damping ratio were measured and compared with numerical analysis techniques and the general damping ratio of the facilities. Result: The natural frequency of the numerical analysis model consisting of a girder and slab composite section was calculated to be 2.561Hz, the natural frequency of the full-scale specimen was measured to be 2.670Hz, and the damping ratio was calculated to be 0.42~0.68%. Conclusion: The natural frequency of the full-scale specimen was found to be 4.3% larger than that of the numerical analysis model. Since the masses of the full-scale specimen and the numerical analysis model are the same as 99.97%, it can be derived that the stiffness of the full-scale specimen has secured structural safety and stability. As a result, the dynamic behavior stability of the specimen was verified. The measured damping ratio of 0.42~0.68% was found to be a stable dynamic behavior compared to the PSC structures damping ratio of 0.5~1.0% in the elastic region.

• Journal of Chest Surgery
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• v.13 no.4
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• pp.455-461
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• 1980

This is one case report of surgically treated ventricular septal defect [VSD] with aortic insufficiency [AI] at department of thoracic and cardiovascular surgery, Hanyang university hospital. He had had progressive dyspnea on exertion and palpitation for 3 years prior to admission to our hospital. On examination, the blood pressure was 120/0 mmHg and the pulse rate 88 times/min. Bobbing motion of the head, Water hammer pulse, Corringan`s pulse, Quincke`s pulse and to and fro murmur were present. The heart murmur was consistent with .VSD and AI. Cardiomegaly was seen in chest X-ray. EKG, echocardiogram, aortogram and right heart catheterization was performed. On Sep. 9, 1980, open heart surgery was performed under the impression of VSD with AI. Infracrystal type VSD measuring 2 x 1.5 cm in diameter was closed with Teflon patch graft through the transverse ventriculotomy. AI was due to prolapsed, elongated right coronary and noncoronary cusp, especially noncoronary cusp. The prolapsed, elongated aortic leaflets were plicated by placing three 8-figure sutures between the free edge and the base of the leaflet [Frater`s method] through a transverse aortotomy. Postoperatively, he made an uneventful recovery, his blood pressure was 120/70 mmHg and showed no signs AI or residual shunt at discharge.

• Geotechnical Engineering
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• v.8 no.1
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• pp.59-66
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• 1992

The SPT If value has been known to be influenced by various factors, among which the actually delivered energy level of the falling ram has the most significant effect. If N values of different energy levels are to be applied in the general analysis which is based on N values of standard energy levee the safety of the foundation might be in danger or the design might be overestimated. In this study the actual falling velocity of the ram has been measured so that the energy level could be estimated. The results Indicated that the energy level should be considered in the analysis or the design in this country, since the measured values are different from the internationally accepted scandard value, N60

• Journal of Korean Neurosurgical Society
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• v.57 no.4
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• pp.298-302
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• 2015

This case report describes the symptoms and clinical course of a 35-year-old female patient who was diagnosed with a temporo-sphenoidal encephalocele. It is characterized by herniation of cerebral tissue of the temporal lobe through a defect of the skull base localized in the middle fossa. At the time of first presentation the patient complained about recurrent nasal discharge of clear fluid which had begun some weeks earlier. She also reported that three months earlier she had for the first time suffered from a generalized seizure. In a first therapeutic attempt an endoscopic endonasal approach to the sphenoid sinus was performed. An attempt to randomly seal the suspicious area failed. After frontotemporal craniotomy, it was possible to localize the encephalocele and the underlying bone defect. The herniated brain tissue was resected and the dural defect was closed with fascia of the temporalis muscle. In summary, the combination of recurrent rhinorrhea and a first-time seizure should alert specialists of otolaryngology, neurology and neurosurgery of a temporo-sphenoidal encephalocele as a possible cause. Treatment is likely to require a neurosurgical approach.