• Imaging Science in Dentistry
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• v.37 no.4
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• pp.197-203
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• 2007

Purpose: To provide diagnostic information by evaluation of the positional relationship between the mandibular third molar and the mandibular canal. Materials and Methods: Eighty-nine mandibular third molars were classified as mesioangular, horizontal, vertical, distoangular groups. The distances between the mandibular third molar and the mandibular canal were measured in cone-beam computed tomographs. The height and width ratios of distances from the mandibular third molar and the mandibular canal to the mandibular inferior border and to the lingual cortical plate were calculated. Results: The vertical and buccolingual distances between the mandibular third molar and the mandibular canal were 0.03 mm, 2.96 mm in the mesioangular, 0.37 mm, 3.38 mm in the horizontal, -1.50 mm, 1.38 mm in the vertical, -1.10 mm, 4.20 mm in the distoangular group. There were significant differences in vertical (P < 0.05), but not in buccolingual (P>0.05). The height and width ratios of distances on the mandibular third molar were 47.1 %, 36.1 % in the mesioangular, 47.4%, 34.4% in the horizontal, 37.0%, 46.7% in the vertical, 40.9%, 37.4% in the distoangular group. There were significant differences between the mesioangular and the vertical group, and the horizontal and the vertical group in height ratio (P < 0.05), and also between the mesioangular and the vertical group in width ratio (P < 0.05). The height and width ratios of distances on the mandibular canal showed no significant differences between groups (P > 0.05). Conclusion : The mesioangular group showed the nearest distance between the mandibular third molar and the mandibular canal vertically. The root apex of the mandibular third molar was positioned more buccally in the vertical group than in the mesioangular group.

• Steel and Composite Structures
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• v.27 no.4
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• pp.417-426
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• 2018

This paper presents the seismic behaviors and restoring force model of ring beam joints of steel tube-reinforced concrete column structure under cyclic loading. First, the main failure mode, ultimate bearing capacity, stiffness degradation and energy dissipation capacity are studied. Then, the effects of concrete grade, steel grade, reinforcement ratio and radius-to-width ratios are discussed. Finally, the restoring force model is proposed. Results show that the ring beam joints of steel tube-reinforced concrete column structure performs good seismic performances. With concrete grade increasing, the ultimate bearing capacity and energy dissipation capacity increase, while the stiffness degradation rates increases slightly. When the radius-width ratio is 2, with reinforcement ratio increasing, the ultimate bearing capacity decreases. However, when the radius-to-width ratios are 3, with reinforcement ratio increasing, the ultimate bearing capacity increases. With radius-to-width ratios increasing, the ultimate bearing capacity decreases slightly and the stiffness degradation rate increases, but the energy dissipation capacity increases slightly.

• Imaging Science in Dentistry
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• v.51 no.4
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• pp.429-438
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• 2021

Purpose: This study investigated the accuracy of laser-scanned models and 3-dimensional(3D) rendered cone-beam computed tomography (CBCT) compared to the gold standard (plaster casts) for linear measurements on dental arches. Materials and Methods: CBCT scans and plaster models from 30 patients were retrieved. Plaster models were scanned by an Emerald laser scanner (Planmeca, Helsinki, Finland). Sixteen different measurements, encompassing the mesiodistal width of teeth and both arches' length and width, were calculated using various landmarks. Linear measurements were made on laser-scanned models using Autodesk Meshmixer software v. 3.0 (Autodesk, Mill Valley, CA, USA), on 3D-rendered CBCT models using OnDemand 3D v. 1.0 (Cybermed, Seoul, Korea) and on plaster casts by a digital caliper. Descriptive statistics, the paired t-test, and intra- and inter-class correlation coefficients were used to analyze the data. Results: There were statistically significant differences between some measurements on plaster casts and laser-scanned or 3D-rendered CBCT models (P<0.05). Molar mesiodistal width and mandibular anterior arch width deviated significantly different from the gold standard in both methods. The largest mean differences of laser-scanned and 3D-rendered CBCT models compared to the gold standard were 0.12±0.23 mm and 0.42±0.53 mm, respectively. Most of the mean differences were not clinically significant. The intra- and inter-class correlation results were acceptable for all measurements(>0.830) and between observers(>0.801). Conclusion: The 3D-rendered CBCT images and laser-scanned models were useful and accurate alternatives to conventional plaster models. They could be used for clinical purposes in orthodontics and prostheses.

• Computers and Concrete
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• v.19 no.6
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• pp.711-716
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• 2017

This paper presents a method using artificial neural networks (ANNs) to predict the residual moment capacity of thermally insulated reinforced concrete (RC) beams exposed to fire. The use of heat resistant insulation material protects concrete beams against the harmful effects of fire. If it is desired to calculate the residual moment capacity of the beams in this state, the determination of the moment capacity of thermally insulated beams exposed to fire involves several consecutive calculations, which is significantly easier when ANNs are used. Beam width, beam effective depth, fire duration, concrete compressive and steel tensile strength, steel area, thermal conductivity of insulation material can influence behavior of RC beams exposed to high temperatures. In this study, a finite difference method was used to calculate the temperature distribution in a cross section of the beam, and temperature distribution, reduction mechanical properties of concrete and reinforcing steel and moment capacity were calculated using existing relations in literature. Data was generated for 336 beams with different beam width ($b_w$), beam account height (h), fire duration (t), mechanical properties of concrete ($f_{cd}$) and reinforcing steel ($f_{yd}$), steel area ($A_s$), insulation material thermal conductivity (kinsulation). Five input parameters ($b_w$, h, $f_{cd}$, $f_{yd}$, $A_s$ and $k_{insulation}$) were used in the ANN to estimate the moment capacity ($M_r$). The trained model allowed the investigation of the effects on the moment capacity of the insulation material and the results indicated that the use of insulation materials with the smallest value of the thermal conductivities used in calculations is effective in protecting the RC beam against fire.

• Journal of the Korean Institute of Intelligent Systems
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• v.24 no.4
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• pp.437-442
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• 2014

Recently, the needs for the development and application of the micro marine robot (MMR) which has the advantages in terms of size and cost are increasing. However, the basis is very short in the domestic. While the obstacle avoidance sonar (OAS) which was optimized in terms of size and performance and has the ability of 4-directional detection was developed for the obstacle avoidance of the micro surface robot (MSR) fortunately, the problem that the detection performance is degraded according to the shape of the obstacle because of using the fixed sonar-beam with the limited beam width and detection range exists. To solve this problem, the MSR mechanism that implements the rotating sonar-beam using the spur gear and the servo motor is proposed in this paper. To verify the performance of the proposed mechanism, the wall-tracking of the MSR is considered and the comparison and analysis in term of detection performance and actuation command is performed with conventional fixed sonar-beam. The test results show the validity of the proposed mechanism.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.4
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• pp.431-440
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• 2012

In this paper, new beam-forming array antenna is proposed. The proposed beam-forming array antenna has control ability for beam-direction/width by employing low loss reconfigurable power divide and three-dimensional array structure. The reconfigurable power divider is key idea in the proposed antenna, because it has reconfigurable RF power distribution ability to each antenna. And, for research and verification of the proposed antenna, 3-dimensional beam-forming array antenna is implemented, and the experimental results show that the proposed antenna has various radiation modes from 1:1 to 1:N by adjusting RF power distribution.

• Journal of the Korea Concrete Institute
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• v.14 no.3
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• pp.392-401
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• 2002

The results of analysis of simply supported reinforced concrete slab by special orthotropic plate theory have been reported. This method, however, may be too difficult for some practising engineers. In this paper, the result of analysis of such a plate by means of the beam theory with unit width is reported. By using the "correction factor", the accurate solution for the plate can be obtained by the beam theory. The plate aspect ratio considered is from 1 : 1 to 1 ：6

• Journal of the Computational Structural Engineering Institute of Korea
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• v.29 no.3
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• pp.269-275
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• 2016

In this paper, shear performance of concrete wide beams was evaluated through shear failure tests. The specimens were designed to have two continuous spans with a column at the center of the wide beam. Also the specimens were reinforced with plates with openings as shear reinforcements. For the test, total eight specimens, including five specimens were reinforced with steel plates and the other three specimens were reinforced with GFRP plates were manufactured. And the shear strengths obtained from the tests were compared with ones from the equation provided by ACI 318. Support width of wide beam, support section of wide beam and shear reinforcement material were considered as variables. The results showed that the support width was proportional to the increase of shear strength. Also, regardless of material type of shear reinforcement, the shear reinforcing effect was similar when the amount of shear reinforcement was the same.

• Journal of Korean Society of Steel Construction
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• v.19 no.5
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• pp.493-501
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• 2007

Recently, in the domestic amount of materials,curtailment and economic efficiency security by purpose, tapered beam application is achieved, but the architectural design technology of today based on the material non-linear method does not consider solutions to problems such as brittle fracture. So, geometric non-linear evaluation thatincludes initial deformation, width-thickness ratio, web stiffener and unbraced length is required. Therefore, in this study, we used ANSYS, a proven finite elementanalysis program,and material and geometric non-linear analysis to study existing and completed tapered H-section as deep beam's analysis model. Main parameters include the width-thickness ratio of web, stiffener, and flange brace, with the experimental result obtained by main variable buckling and limit strength evaluation. We made certain that a large width-thickness ratio of the web decreases the buckling strength and short unbraced web significantly improves ductility.

• Structural Engineering and Mechanics
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• v.84 no.3
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• pp.311-321
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• 2022

In the buildings with long spans and high floors, such as logistics warehouses and semiconductor factories, it is difficult to install supporting posts under beams during construction. Therefore, the size of structural members becomes larger inevitably, resulting in a significant increase in construction costs. Accordingly, a prestressed hybrid wide flange (PHWF) beam with hollowed steel webs was developed, which can reduce construction costs by making multiple openings in the web of the steel member embedded in concrete. However, since multiple openings exist and prestress is introduced only into the bottom flange concrete, it is necessary to identify the shear resistance mechanism of the PHWF beam. This study presents experimental shear tests of PHWF beams with hollowed steel webs. Four PHWF beams with cast-in-place (CIP) concrete were fabricated, with key variables being the width and spacing of the steel webs embedded in the concrete and the presence of shear reinforcing bars, and web-shear tests were conducted. The shear behavior of the PHWF beam, including crack patterns, strain behavior of steel webs, and composite action between the prestressed bottom flange and CIP concrete, were measured and analyzed comprehensively. The test results showed that the steel web resists external shear forces through shear deformation when its width is sufficiently large, but as its width decreased, it exerted its shear contribution through normal deformation in a manner similar to that of shear reinforcing bars. In addition, it was found that stirrups placed on the cross section where the steel web does not exist contribute to improving the shear strength and deformation capacity of the member. Based on the shear behavior of the specimens, a straightforward calculation method was proposed to estimate the web-shear strength of PHWF beams with CIP concrete, and it provided a good estimation of the shear strength of PHWF beams, more accurate than the existing code equations.