• Structural Engineering and Mechanics
• /
• v.68 no.1
• /
• pp.67-80
• /
• 2018

Recently, U-section decks have been more and more used in metro and light rail bridges as an innovative concept in bridge deck design and a successful alternative to conventional box girders because of their potential advantages. U-section may be viewed as a single vent box girder eliminating the top slab connecting the webs, with the moving vehicles travelling on the lower deck. U-section bridges thus solve many problems like limited vertical clearance underneath the bridge lowest point, besides providing built-in noise barriers. Beam theory in mechanics assumes that plane section remains plane after bending, but it was found that shearing forces produce shear deformations and the plane section does not remain plane. This phenomenon leads to distortion of the cross section. For a box or a U section, this distortion makes the central part of the slab lagging behind those parts closer to the webs and this is known as shear lag effect. A sample real-world double-track U-section metro bridge is modelled in this paper using a commercial finite element analysis program and is analysed under various loading conditions and for different geometric variations. The three-dimensional finite element analysis is used to demonstrate variations in the transverse bending moments in the deck as well as variations in the longitudinal normal stresses induced in the cross section along the U-girder's span thus capturing warping and shear lag effects which are then compared to the stresses calculated using conventional beam theory. This comparison is performed not only to locate the distortion, warping and shear lag effects typically induced in U-section bridges but also to assess the main parameters influencing them the most.

• Wind and Structures
• /
• v.20 no.1
• /
• pp.15-36
• /
• 2015

Characterization of wind flows over a complex terrain, especially mountain-gorge terrain (referred to as the very complex terrain with rolling mountains and deep narrow gorges), is an important issue for design and operation of long-span bridges constructed in this area. In both wind tunnel testing and numerical simulation, a transition section is often used to connect the wind tunnel floor or computational domain bottom and the boundary top of the terrain model in order to generate a smooth flow transition over the edge of the terrain model. Although the transition section plays an important role in simulation of wind field over complex terrain, an appropriate shape needs investigation. In this study, two principles for selecting an appropriate shape of boundary transition section were proposed, and a theoretical curve serving for the mountain-gorge terrain model was derived based on potential flow theory around a circular cylinder. Then a two-dimensional (2-D) simulation was used to compare the flow transition performance between the proposed curved transition section and the traditional ramp transition section in a wind tunnel. Furthermore, the wind velocity field induced by the curved transition section with an equivalent slope of $30^{\circ}$ was investigated in detail, and a parameter called the 'velocity stability factor' was defined; an analytical model for predicting the velocity stability factor was also proposed. The results show that the proposed curved transition section has a better flow transition performance compared with the traditional ramp transition section. The proposed analytical model can also adequately predict the velocity stability factor of the wind field.

• Journal of Mechanical Science and Technology
• /
• v.16 no.1
• /
• pp.32-38
• /
• 2002

The purpose of this study is to analyze the collapse characteristics of widely used spot welded section members (hat and double hat section, nembers of vehicles) which possess the greatest energy absorbing capacity In an axial impact collapse. This study also suggests how the collapse load and deformation mode are obtained under impact. In the program system presented in this study, an explicit finite element code, LS-DY7A3D, is adopted for simulating complicated collapse behavior of the hat and double hat shaped section members with respect to section dimensions and spot weld pitches. Comparing the results with experiments, the simulation has been verified under a velocity of 7.19 m/sec (impact energy of 1034J)

• Geomechanics and Engineering
• /
• v.17 no.2
• /
• pp.133-143
• /
• 2019

An optimal hydraulic section is critical for irrigated water conservancy in seasonal frozen ground due to a large proportion of water leakage, as investigated by in-situ surveys. This is highly correlated with the frost heave of underlain soils in cold season. This paper firstly derived a practical model for frost heave of clayey soils, with temperature dependent thermal indexes incorporating phase change effect. A model test carried out on clay was used to verify the rationality of the model. A novel approach for optimizing the cross-section of irrigation canals in cold regions was suggested with live updated geometry characterized by three unique geometric constraints including slope of canal, ratio of practical flow section to the optimal and lining thickness. Allowable frost heave deformation and tensile stress in canal lining are utilized as standard in computation iterating with geometry updating while the construction cost per unit length is regarded as the eventual target in optimization. A typical section along the Jinghui irrigation canal was selected to be optimized with the above requirements satisfied. Results prove that the optimized hydraulic section exhibits smaller frost heave deformation, lower tensile stress and lower construction cost.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.62 no.10
• /
• pp.1470-1474
• /
• 2013

In this paper, proper length of neutral section and neutral section system configuration is proposed to minimize accidents if ATO urban railway vehicle stops maintaining the leading vehicles in air section at regular intervals. When considering the minimum voltage sensing of power conversion unit in the urban railway vehicle, the effective length of 14,280[mm] with neutral section can be minimized damage due to high current because the urban railway vehicle is very little present chance compare neutral section with pantograph interval installed on a unit vehicle. In addition, uplift of catenary line and contact wire consider to minimize damage. The result of theoretical review, as the proposed neutral section shorter, isolated neutral section is effective than the integrated neutral section.

• Research in Community and Public Health Nursing
• /
• v.11 no.2
• /
• pp.499-512
• /
• 2000

The number of deliveries by cesarean section has increased internationally. However, The cesarean section rate is different by country to country. It is because each country has different social and cultural background and. practices its unique delivery policies. Hence, it is very important to understand the uniqueness that one country faces related with the cesarean section. In Korea, there have been many researches on the clinical. maternal. hospital and community factors and so on. However, few studies have attempted to reveal the physician factors in Korea because it is difficult to approach hospital records. So, in this study, the physician factors that influence the increase of cesarean section rate in Korea was investigated, and preliminary research agenda for policy establishment to keep the cesarean section rate from excessive increase was provided. In this study, all 2744 cesarean section deliveries performed by 36 physicians at the hospital was considered. and detailed delivery records of 12 months selected randomly from January 1996 to August 1998 was reviewed retrospectively. Chi-square analysis is used to examine the homogeneity of distribution of maternal, fetal, and clinical factors. In addition, multiple regression analysis is used to examine the effect of physician characteristics on the cesarean section rate. Physician characteristics as independent variable and the cesarean section rate as dependent variable was put in this analysis. Follows are the results of this study. 1) Total cesarean section rate is 34.8%. primary cesarean section rate is 12.5 % and repeated cesarean section rate is 22.3 %. Among the indications for the primary cesarean section, 15.6 % is for breech presentation. 40.2 % is for dystocia. 7.6 % is for fetal distress. and 36.6 % is for others. 2) There is positive correlation between physician's age and the cesarean section rate (p<0.001). And statistically significant correlation is found between the physician's educational attainment and the cesarean section rate (p<0.001). A physician with Ph.D degree has lower cesarean section rate than a physician with B.A only and M.A. degree (p<0.001). However. physician's gender, location of graduated university. position at the hospital, and the religious belief were not shown statistically significant relations with the cesarean section rate. 3) Among all cesarean sections in this study, only 15.4 % is performed during weekend. While 18.2 % is performed on monday only. This suggests that physicians may not prefer weekend operation of cesarean section. In addition, 86.1 % among all cesarean section operations is performed from 6 a.m. to 6 p.m. So the cesarean section rate could be related with a day of the week and a time of the day. From this results. there is a possibility that the physicians' personal comfort may influence the cesarean section rate.

• Proceedings of the Korean Society of Medical Physics Conference
• /
• 2002.09a
• /
• pp.457-460
• /
• 2002

The image quality of three-dimensional (3D) images has been widely investigated by the qualitative analysis method. A need remains for an objective and quantitative method to assess the image quality of 3D volume-rendered images. The purpose of this study was to evaluate the quantitative accuracy of distance measurements on 3D volume-rendered images of a dry human skull by using multi-detector computed tomography (MDCT). A radiologist measured five times the twenty-one direct measurement line items composed among twelve reference points on the skull surface with a digital vernier caliper. The water filled skull specimen was scanned with a MDCT according to the section thicknesses of 1.25, 2.50, 3.75, and 5.00 mm for helical (high quality; pitch 3:1) scan mode. MDCT data were reconstructed with its acquisition section thickness and with 1.25 mm section thickness for all scans. An observer also measured seven times the corresponding items on 3D volume-rendered images with measuring tools provided by volumetric analysis software. The quantitative accuracy of distance measurements on the 3D volume-rendered images was statistically evaluated (p-value < 0.05) by comparatively analyzing these measurements with the direct distance measurements. The accuracy of distance measurements on the 3D volume-rendered MDCT images acquired with 1.25, 2.50, 3,75 and 5.00 mm section thickness and reconstructed with its section thickness were 48%, 33%, 23%, and 14%, respectively. Meanwhile, there were insignificant statistical differences in accuracy of distance measurements among 3D volume-rendered images reconstructed with 1.25 mm section thickness for the each acquisition section thickness. MDCT images acquired with thick section thickness and reconstructed with thin section thickness in helical scan mode should be effectively used in medical planning of 3D volume-rendered images. The quantitative analysis of distance measurement may be a useful tool for evaluating the quantitative accuracy and the defining optimal parameters of 3D volume-rendered CT images.

• Proceedings of the Korean Society of Veterinary Clinics Conference
• /
• 2007.05a
• /
• pp.101-101
• /
• 2007

• Proceedings of the Korean Society of Veterinary Clinics Conference
• /
• 2008.05a
• /
• pp.72-72
• /
• 2008

• Proceedings of the Korean Society of Veterinary Clinics Conference
• /
• 2008.05a
• /
• pp.73-73
• /
• 2008