• Journal of Korean Society of Steel Construction
• /
• v.24 no.6
• /
• pp.671-682
• /
• 2012

The use of sinusoidal corrugated web girder for the box-type girders and gable steel main frames has recently been increasing very much. The reasons are that the thin web of the girder affords a significant weight reduction compared with rolled beam and welded built-up girder, and that corrugation prevents the buckling failure of the web. Improvements of the automatic fabrication process makes mass production of the corrugated web and unit possible, and applications of this girder have been extended considerably. Thus, the research for the optimum design processer considering the production data is needed practically. For doing this research, we develope the discrete optimum structural design program in consideration of production list data for the research, and the program apply to the single girder under the uniform load and the concentrated load as numerical example. We consider objective function as minimum weight of the girder, and use slenderness ratio, stress of flanges and corrugated web, and the girder deflection as the constraint functions. And also the Genetic Algorithms is adopted to search the global minimum point by using the production list as a discrete design variable. Finally, to verify the optimality of the design, we conduct a comparison of the results of the discrete optimum design with those of the continuous one, and also analyze the characteristics of the optimum cross-section.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.21 no.3
• /
• pp.578-584
• /
• 2017

$SiO_2$ buffer layer (100 nm) has been deposited on PET substrate by electron beam evaporation. And then, IZTO (In-Zn-Sn-O) thin film has been deposited on $SiO_2$/PET substrate with different RF power of 30 to 60 W, working pressure, 1 to 7 mTorr, by RF magnetron sputtering. Structural, electrical and optical properties of IZTO thin film have been analyzed with various RF powers and working pressures. IZTO thin film deposited on the process condition of 50 W and 3 mTorr exhibited the best characteristics, where figure of merit was $4.53{\times}10^{-3}{\Omega}^{-1}$, resistivity, $4.42{\times}10^{-4}{\Omega}-cm$, sheet resistance, $27.63{\Omega}/sq.$, average transmittance (400-800 nm), 81.24%. As a result of AFM, all the IZTO thin film has no defects such as pinhole and crack, and RMS surface roughness was 1.147 nm. Due to these characteristics, IZTO thin film deposited on $SiO_2$/PET structure was found to be a very compatible material that can be applied to the next generation flexible display device.

• Journal of Aerospace System Engineering
• /
• v.14 no.1
• /
• pp.21-27
• /
• 2020

Aircraft should be equipped with various external stores for mission performance. Since these external stores may cause structural instability of aircraft, an evaluation of the effects between the aircraft and the external stores is required. For this purpose, an aircraft dynamic characteristics analysis reflecting an external store was performed, and the finite element model for the analysis of aircraft dynamic characteristics should simulate the dynamic characteristics of the component as accurately as possible while using a minimum of the nodes and elements. In this study, a stick model was constructed for dynamic characteristics analysis of the external fuel tank and installation pylon using MSC Patran/Nastran. For the calculation of the equivalent stiffness of the stick model, a simple beam theory was applied to construct the stick model of each part, and the validity of each stick models was confirmed by mode comparison with the fine model. Additionally, the model analysis of the stick model assembly, simulating a pylon equipped with an external fuel tank was performed to confirm that the basic modes required for the analysis of aircraft dynamic characteristics are well extracted. Finally, it was confirmed that the developed stick model assembly could be used for analysis of aircraft dynamic characteristics by comparing the errors in modes between the fine model assembly and the stick model assembly.

• Journal of Technology Innovation
• /
• v.22 no.4
• /
• pp.145-164
• /
• 2014

Nuclear fusion is one of the most promising options for generating large amounts of carbon-free energy in the future. Major countries such as China, EU, and Japan have established a national plan for DEMO construction and they are implementing it. Korea has started a nuclear fusion research and development by the KSTAR project started in 1995. There are matured needs for a full-scale research and development initiatives to ensure competition with the major countries for DEMO as well as achieve the final goal to commercialize fusion energy. In this paper, we apply the TRL and AHP methods in order to identify the key technologies to conduct DEMO R&D. We propose the priorities of future R&D on DEMO by deriving a core technology in the field. At first, we review the scientific theory of fusion and trend of progress of DEMO activities in major countries. For previous studies, we review TRL and AHP methods to examine the technology classification system of DEMO and identify key technologies. We apply TRL method to identify readiness level of DEMO technologies and AHP to compensate shortcoming of TRL. The key technologies of DEMO to be secured from a synthesis result of the TRL and AHP are burning plasma, plasma facing material, structural material, high frequency heating, neutral particle beam, safety, plasma diagnostic, and simulation technologies.

• Journal of Korean Society of Steel Construction
• /
• v.26 no.5
• /
• pp.407-418
• /
• 2014

As a continuing work of previously conducted standard tension tests, full-scale flexural tests were conducted in this study to assess the structural performance the CJP groove welded joints connecting thick HSA800 plates. Two welding electrodes were available at the time of this experimental research; one was GMAW-based electrode A and the other FCAW-based electrode B. Three full-scale box-type beam specimens with single bevel- and V-groove CJP welded joints were fabricated from 60mm and 25mm thick HSA800 plates according to the AWS-prequalified groove welded joint details. In designing the specimens, all possible limit states like local and lateral torsional buckling were carefully controlled in order to induce flexural plastic yielding or eventual joint fracture. All the CJP joints made by both welding electrodes showed satisfactory performance and were able to transfer the tensile flange forces higher than that corresponding to the measured tensile strength of HSA800 flange plates. However, it should be noted that, during fabrication, serious concerns about the welding efficiency and workability of the GMAW-based electrode were raised by a certified welder. The fracture occurred at the unbeveled (or vertical) interface between the weldment and the base metal when the GMAW-based electrode was used in the single-bevel joint, implying the possibility of insufficient melting. Thus, the FCAW-based electrode B is again recommended as the choice of welding electrode for HSA800 plates. The limited test data of this study implies that the V-groove CJP joint should be used in favor of the single bevel CJP joint, if possible.

• Journal of Korean Society of Steel Construction
• /
• v.28 no.6
• /
• pp.467-476
• /
• 2016

For the connections between modular units in modular buildings, the bolted joints with connector plates are used commonly. The strength of structure is determined by the weakest part of structure and the connections may be weaker than the members being joined. Therefore, to check the safety of modular building, the structural performance of connections between modular units as well as that of beam-to-column connections should be evaluated. In this study, the behavior of module to module connection with straight and cross shaped connector plates is investigated by lateral cyclic tests according to KBC2009 0722.2.4 which shall be conducted by controlling the story drift angle in the width and the longitudinal direction respectively. All of test results generally show the stable ductile behavior up to 0.04rad drift levels and the tests in longitudinal direction show a superior energy dissipation per cycle in each of the load steps. However, the straight shaped connector plates have the degradation of stiffness with cyclic loading and the larger drift angle of column than the cross shaped connector plates.

• Journal of the Korea Concrete Institute
• /
• v.14 no.6
• /
• pp.892-899
• /
• 2002

Among the methods for enhancement of load-carrying capacity on flexural concrete member, recently, a concept is being investigated which replaces the steel in a conventional reinforced concrete member with a fiber reinforced polymer(FRP) shell. This study focuses on modeling of the structural behavior of concrete surrounded with FRP shells in flexural bending members. A numerical model of fiber cross-sectional analysis is proposed to predict the stress and deformation state of the FRP shell and concrete. The stress-strain relationship of concrete confined by a FRP shell is formulated to be based on the constitutive law of concrete in multi-axial compressive stress state, in assuming that the compression response is dependent on the radial expansion of the concrete. To describe the FRP shell behavior, equivalent orthotropic properties of in-plane behavior from classical lamination theory are used. The present model is validated to compare with the experiments of 4-point bending tests of FRP shell concrete beam, and has well predicted the moment-curvature relationships of the members, axial and hoop strains in the section, and the enhancement of confinement effect in concrete surrounded by FRP shell.

• Magazine of the Korea Concrete Institute
• /
• v.8 no.4
• /
• pp.149-159
• /
• 1996

Recent advances in material technology has accelerated the development of higher strength concretes using lightweight manufactured aggregates.Concretes with these chnractcristics are designable since the reductiun of dead loads and the increase in load capacity can oflix substantial cost reductions. Alt,hough thesc rharackristics are very desirable, very little information is availablc to the structural rivic;~~,cher about the properties of highstrength lightweight concrete. In general, shear strength of reinforced concrete beams is dependent on the compressive strength of concrete. the longitudinal steel ratio, the shear span to the depth ratio and shear reinforcement. In this study. eight single reinforced high strength lightweight concrete beams were tested to investigate their behavior and to determine their ultimate shear strengths.The variables studied in this investigation are shear span to effective depth ratio a/d = 1.5. 2.5, 3.5 and 4.5 : vertical shear reinforcement ratio ${\rho}_8= 0%$ and 1.136%. Test results were analyzed and compared with strengths predicted by ACI code equation. Zsutty's equation. As the results, ACI Eq.(ll-3) and ACI Eq.(ll-6) are conservative for high strength lightweight concrete beam. Also Zsuttyrs Eq. is conservative for beams except short beams. (a/d= 1.5)

• Journal of the Korea Concrete Institute
• /
• v.21 no.6
• /
• pp.797-804
• /
• 2009

The structural designs of RC flat plates that have insufficient flexural stiffness due to lack of support from boundary beams may be governed by serviceability as well as a strength criteira. Specially, since over-loading and tensile cracking in early-aged slabs significantly increase the deflection of a flat plate system under construction, a construction sequence and its impact on the slab deflections may be decisive factors in designs of flat plate systems. In this study, the procedure of calculating slab deflections considering construction sequences and concrete cracking effects is proposed. The construction steps and the construction loads are defined by the simplified method, and then the slab moments, elastic deflections, and the effective moment of inertia are calculated in each construction step. The elastic deflections in column and middle strips are magnified to inelastic deflections by the effective moment of inertia, and the center deflection of slab are calculated by the crossing beam method. The proposed method is verified by comparisons with the existing test result and the nonlinear analysis result. Also, by applications of the proposed method, the effects of the slab construction cycle and the number of shored floors on the deflections of flat plates under construction are analyzed.

• Journal of the Korea Concrete Institute
• /
• v.28 no.2
• /
• pp.177-185
• /
• 2016

This paper concerns the flexural behavior of steel fiber-reinforced ultra-high-performance concrete (UHPC) beams with compressive strength of 150 MPa. It presents experimental research results of hybrid steel fiber-reinforced UHPC beams with steel fiber content of 1.5% by volume and steel reinforcement ratio of less than 0.02. This study aims at investigating of compressive and tensile behavior of UHPC to perform a reasonable prediction for flexural capacity of UHPC beams. Tensile behavior modeling was performed using load-crack mouth opening displacement relationship obtained from bending test. The experimental results show that steel fiber-reinforced UHPC is in favor of cracking resistance and ductility of beams. The ductility indices range from 1.6 to 3.0, which means high ductility of hybrid steel fiber-reinforced UHPC. Test results and numerical analysis results for the moment-curvature relationship are compared. Though the numerical analysis results for the bending capacity of the UHPC beam without rebar is larger than test result, the overall comparative results show that the bending capacity of steel fiber-reinforced UHPC beams with compressive strength of 150 MPa can be predicted by using the established method in this paper.