• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.6
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• pp.14-22
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• 2022

In this study, a fire test was conducted to evaluate the fire performance of precast concrete (PC) slabs in an outdoor environment in response to the increase in fire incidents caused by the growth of warehouses. Prior to the field fire test, the tensile yield strength of the tendon at elevated temperatures was tested to analyze the mechanical properties. Also, by referring to previous studies, the thermal properties of tendon and the mechanical and thermal properties of concrete were investigated. A field fire test was conducted to analyze the structural and fire performance of two identical slabs with 50 and 150 mm bearing length. As the bearing length increased, deflection and horizontal displacement decreased. The fire test lasted for 200 minutes without the collapse of slabs, validating current codes. Based on the structural performance which maintained even with concrete spalling and rupture of some tendons, the bonded method is assumed to be practical in pre-tensioned PC slabs. The results of fire test are expected to be utilized in evaluating the fire performance of PC slabs in warehouses.

• Journal of Dental Rehabilitation and Applied Science
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• v.17 no.4
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• pp.245-256
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• 2001

The purpose of this study is to analyze the mechanical stress and displacement on the jaws during the simulated bilateral clenching task on the three-dimensional finite element model of the dentated skull with unilateral molar loss. For this study, the computed tomography(G.E.8800 Quick, USA) was used to scan the total length of human skull in the frontal plane at 2.0mm intervals. The fully assembled finite element model consists of the articular disc, maxilla, mandible, teeth, periodontal ligament and cranium. The FE model was used to simulate the bilateral clenching in intercuspal position. The loading condition was the force of the masseter muscle exerted on the mandible as reported by Korioth et al. degrees of freedom of the zygomatic region where the masseter muscle is attached were fixed as restraints. In order to reflect the actual action of the muscles force, the displacement of the region was attached where the muscle is connected to the temporal bone and restraint conditions were given values identical to values at the attachment region of the masticatory muscle but with the opposite direction of the reaction from when the muscle force is acted on the mandible. Although the mandible generally has higher displacement and von Mises stress than the maxilla, its mandibular corpus on the molar-loss side has a higher stress and displacement than the molar-presence side. Because the displacement and von Mises Stress was the highest on the lateral surface of mandibular corpus with molar loss, the stress level of the condyle on the molar-loss side is greater than that of the molar-presence side, which in turn caused the symphysis of the mandible to bend. In conclusion, the unilateral posterior bite collapse with molar loss under para-functional activities such as bruxism and clenching can affect the stress concentration on the condyle and mandibular corpus. It is therefore necessary to consider the biomechanical function of dento-skeleton under masticatory force while designing the occlusal scheme of restoration on alveolar bone with the posterior collapse.

• Journal of the Korean Society for Marine Environment & Energy
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• v.11 no.2
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• pp.86-91
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• 2008

Ships operating in littoral sea are likely to be subjected to accidental load such as stranding. Once she has damage on the hull structure, her ultimate strength will be reduced. This paper is to investigate the effect of the stranding damage on ultimate strength of ship structure by using a series of collapse tests. For the experiment, 720 mm $\times$720 mm in section and 900mm in length of five box-girder models with stiffeners were pre- pared. Of the five, one has no damage and faur have an diamond shaped damage which represents the shape of rock section in seabed. The damage size is different between models. Among the damaged models, the damages of 3 of them were made by cutting the plate and one by pressing to represent stranding damage. Experiments were carried out under pure bending load and the applied load and displacements were recorded. The ultimate strength is reduced as the damage size increases, as expected. The largest damaged model has the damage size of 30% of breadth and its ultimate strength is reduced by 21% than that of no damaged one. The pressed one has lower ultimate strength than cut one. This might be due to the fact that the plate around the pressed damage area effect negatively on the ultimate strength.

• Journal of Korean Neurosurgical Society
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• v.61 no.1
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• pp.81-88
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• 2018

Objective : Spondylitis is often chemotherapy resistant and requires long-term treatment. Without adequate chemotherapy, the outcome can be fatal or result in severe neurologic damage. Therefore, differentiating the etiology of spondylitis is very important, particularly in spontaneous cases. As the prevalence of tuberculosis in Korea has decreased in recent years, updated clinical research about spondylitis is warranted. Methods : From April 2010 to March 2016, data from spondylitis patients were collected retrospectively. In total, 69 patients (51 with pyogenic spondylitis and 18 with tuberculous spondylitis) were included. Clinical data, laboratory findings including erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) level, measurements of Cobb angles at the initial and final follow-up, and radiologic features on magnetic resonance imaging (MRI) scans were evaluated. To test differences between the pyogenic and tuberculous groups, numerical data were compared using the student's t-test and Mann-Whitney U test, and categorical data were compared using the chi-square test and Fisher's exact test. Results : The patients' mean age was 60.0 years. Male sex was slightly predominant (56.5%). There was no difference in mean age and sex between the two groups. The pyogenic group had a relatively higher proportion of immunocompromised patients. The peak CRP value was higher in the pyogenic group than in the tuberculous group (14.08 mg/dL and 8.50 mg/dL, respectively, p=0.009), whereas the ESR was not significantly different between the groups (81.5 mm/h and 75.6 mm/h, respectively, p=0.442). Radiologically, the presence of disc space sparing and vertebral body collapse differed between the groups. In the tuberculous group, the disc was more commonly preserved on contrast-enhanced MRI (50% and 23.5%, respectively, p=0.044), and vertebral body collapse was more common (66.6% and 15.7%, respectively, p<0.001). The mean length of hospitalization was longer in the pyogenic group (56.5 days and 41.2 days, respectively, p=0.001). Four mortality cases were observed only in the pyogenic group. The most commonly isolated microorganism in the pyogenic group was Staphylococcus aureus(S. aureus) (methicillin susceptible S. aureus and methicillin resistant S. aureus [MRSA] in 8 and 4 cases, respectively). Conclusion : The clinical and radiological manifestations of spontaneous spondylitis differ based on the causative organism. Pyogenic spondylitis patients tend to have a higher CRP level and a more severe clinical course, whereas tuberculous spondylitis patients present with destruction of the vertebral body with disc sparing more frequently. The presence of MRSA is increasing in community-acquired spondylitis cases.

• The Journal of the Petrological Society of Korea
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• v.18 no.3
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• pp.237-253
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• 2009

The lava flows forming the Manjanggul lava tube are commonly said to have a potential source from the Geomunoreum scoria cone. We inferred the source of lava flows with the Manjanggul lava tube, based on many studies about lava tubes within lava flows of active volcano in the world. We made a lava flow field map from lithofacies, features and latitude of lava surfaces in the northeastern part of Jeju Island, and then examined closely the distribution and mutual relation of lava tubes in each lava flow field. As result, the Geomunoreum lava tube system is divided into a series of master tubes(Utsanjeungul, Bukoreumgul, Daerimdonggul, Manjanggul, Gimnyeonggul, Yongcheondonggul and Dangcheomuldonggul lava tube), a complicated networks of small tubes(Bengdwigul lava tube), and a series of unitary tubes(Gimyeongbilemotgul~Gaeusaemgul lava tube) in Geomunoreum lava flows. Particularly a canyon, 2km in length to NNE direction from the Geomunoreum scoria cone, is interpreted to be collapse trench of lava tube roof that belongs to an upflow part of the master tube in the Geomunoreum lava tube system, according to the location and direction. Accordingly, the source of lava flows, forming the Manjanggul lava tube, is the Geomunoreum scoria cone.

• Journal of the Korean Society of Safety
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• v.30 no.1
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• pp.40-46
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• 2015

Many construction equipment or supporting structure should be installed in a field without appropriate anchorage to cause a collapse of those. Anchor length, anchor diameter, hooked or non hooked will be made and tested in the study. This one will be analyzed and compared with the previous study in order to find out some difference, strength by strength, based on this study. Embedded re-bar and the resistant capacity against pulled out force of re bar have been tested and analyzed by concrete design strength and rebar diameter in the study. 21Mpa and 24MPa compressive strength which are used in construction practice have been applied as variables. Those rebars are composed of D13, D16. D22 which are mostly used at construction sites. The followings are summarized as conclusions.1) ductility is not increased as rebar diameter becomes larger under the condition of non-hooked anchorage.2) those are two times of displacement difference between small diameter of rebar and large one with hooked anchorage of rebar while being 1/10 times difference with non-hooked condition but, only 10% difference of maximum load are shown, not conspicuously between hooked and non-hooked condition.3) displacement related to ductility can be three(3) times decreased if only concrete compressive strength and rebar diameter become larger with heavy support weight.

• Journal of the Korea Concrete Institute
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• v.27 no.4
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• pp.377-385
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• 2015

The span-lengthening of PSC I girder has increased the risk of lateral instability of the girder with the increases in the aspect ratio and self-weight of the girder. Recently, collapses of PSC I girder during construction raise the necessity of evaluating the lateral instability of the girder. Thus, the present study evaluated the lateral behavior and instability of PSC I girders under wind load, regarded as one of the main causes of the roll-over collapse during construction. Lateral instability of the girder is mainly dependent on the length of the girder and the stiffness of the support. The analysis results of this study showed the decrease in the critical wind load and the increase in the critical deformation and angle of the girder, leading to the lateral instability of the girder. Finally, this study proposed analytical equations that can predict the critical amount of wind load and lateral deformation of the girder, which would provide quantitative management values to maintain lateral stability of PSC I girder during construction.

• Journal of the Korea Concrete Institute
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• v.26 no.2
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• pp.109-116
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• 2014

The flexural behavior test of UHPC segmental box girder which has 160 MPa compressive strength and 15.4 m length was carried out. The effect of steel fibers in combination with reinforcing bars on improving the ductile performance of UHPC box girder was evaluated by comparing the flexural behavior of the UHPC segmental box girders made by the two kinds of mixing portion. The test variables are volume fraction of steel fibers and the arrangement of reinforcing bars. The behavior of UHPC box girder BF2 composed of 1% volume fraction of steel fibers and longitudinal reinforcing bars in web and upper flange with stirrup showed the similar ductile behavior with the girder BF1 composed of 2% volume fraction without stirrup in elastic stress region. But BF1 had the better stiffness and showed the more ductile behavior in inelastic stress region. Segmental interfaces of UHPC box girder have not any crack and slide until the final flexural collapse load.

• Journal of Korean Society of Forest Science
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• v.105 no.4
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• pp.435-440
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• 2016

This study was carried out to examine of soil physical property and crack shape by collapse process on landslide area (by land creeping) in Hadong, Gyeongnam. We investigated morphological characteristics (length, depth, cut slope) between main crack and local crack, soil physical properties change between undisturbed section and disturbed section. As a result, morphological characteristics of crack showed no significant difference main crack between local crack. In case of soil physical property variation, soil liquid phase was significantly higher at 31-40 cm of soil depth in disturbed section. And this result is likely to be due to site factors.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.1196-1200
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• 2004

Micropump is very useful component in micro/nano fluidics and bioMEMS applications. In this study, a bubble-powered micropump was fabricated and tested. The micropump consists of two-parallel micro line heaters, a pair of nozzle-diffuser flow controller and a 1 mm in diameter, 400 ${\mu}m$ in depth pumping chamber. The two-parallel micro line heaters with 20 ${\mu}m-width$ and 200 ${\mu}m-length$ were fabricated to be embedded in the silicon dioxide layer of a wafer which serves as a base plate for the micropump. The pumping chamber, the pair of nozzle-diffuser unit and microchannels including the liquid inlet and outlet port were fabricated by etching through another silicon wafer. A glass wafer (thickness of $525{\pm}15$ ${\mu}m$) having two holes of inlet and outlet ports of liquid serve as upper plate of the pump. Finally the silicon wafer of the base plate, the silicon wafer of pumping chamber and the glass wafer were aligned and bonded (Si-Si bonding and anodic bonding). A sequential photograph of bubble nucleation, growth and collapse was visualized by CCD camera. Clearly liquid flow through the nozzle during the period of bubble growth and slight back flow of liquid at the end of collapsing period can be seen. The mass flow rate was found to be dependent on the duty ratio and the operation frequency. As duty ratio increases, flow rate decreases gradually when the duty ratio exceeds 60%. Also as the operation frequency increases, the flow rate of the micropump decreases slightly.