• Journal of Korean Society of Steel Construction
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• v.29 no.3
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• pp.205-215
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• 2017

This study presents an example of conceptual design for hollow circular section multi-column tower system subjected to 10MW level wind load by introducing a method based on member utilization that examine both structural stability and economical efficiency. The basic assumptions for the proto type of a multi-column tower that can replace a single-cylinder tower were suggested and structural models were constructed following the assumptions and analyzed for identifying member forces. Based on the calculated member strengths and acting loads, the member utilization of the proposed multi-column tower structures were calculated for axial force, shear, bending and torsion and evaluaed for suitability as a wind tower. Design parameters such as steel tube dimensions, slenderness ratio, and number of floors for braces was proposed in the acceptable range of member utilization for conceptual design of multi-column wind towers.

• Journal of the Korean Society of Safety
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• v.31 no.6
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• pp.1-5
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• 2016

A bicycle is one of the most popular sporting goods in view of a sport activity and a human health. Metallic materials such as steel, aluminum, etc. were mainly used to the bicycle fork in the past. Nowadays, the carbon fiber reinforced composite materials are widely used to the manufacturing of a bicycle fork to reduce the weight and to increase the efficiency. Safety is a most important design parameter of a bicycle fork even if the weight and cost reduction are important. Bicycle failure may happen at the critical spot of a bicycle fork and cause the accident. In this paper, the composite bicycle fork will be analyzed to secure the safety and detect a critical spot by using the finite element method with Tsai-Wu failure criterion. The stress data were obtained for the laminated composites with various number of plies and fiber orientation under the bending load. Thus, design concept of a bicycle fork was proposed to secure the safety of a bicycle. The finite element analysis results show that the connection area between a steer tube and a fork blade is critical spot, and 75 or more layers of 0 degree are needed to secure the safety of a bicycle fork.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.1
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• pp.55-60
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• 2002

For the development of a new creep test technique, the availability of SP-Creep test is discussed for 1Cr-0.5Mo boiler header material. And some results are also compared with those of 2.25Cr- 1Mo steel which widely uses as boiler superheater tube. The results can be summarized as follows. The load exponents(n) obtained by SP-Creep test for 1Cr-0.5Mo steel are decreased with increasing creep temperature and the values are 15.67, 13.89, and 17.13 at 550$^{circ}C$ ,575$^{circ}C$ and 600$^{circ}C$, respectively. The temperature dependence of the load exponent is given by n = 107.19 - 0.1108T. This reason that load exponents show the extensive range of 10∼16 is attributed to the fine carbide such as M$_{23}$C$_{6}$ in lath tempered martensitic structures. At the same creep condition, the secondary creep rate of 1Cr-0.5Mo steel is lower than the 2.25Cr-1Mo steel1 due to the strengthening microstructure composed by normalizing and tempering treatments. Through a SEM observation, it can be summarized that the primary, secondary, and tertiary creep regions of SP-Creep specimen are corresponding to plastic bending, plastic membrane stretching, and plastic instability regions among the deformation behavior of four steps in SP test, respectively.y.

• Journal of the Korean Ceramic Society
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• v.41 no.7
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• pp.560-566
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• 2004

To fabricate the continuously porous alumina bodies by multi-extrusion process, carbon powder and ethylene vinyl acetate were used as a pore forming agent and a binder, respectively. As the change of extrusion pass number, reduction ratio as well as the volume fraction of core and tube, the porous alumina bodies having various kind of pore size and porosity could be obtained. The porous bodies showed continuous pore shape, high specific surface as well as high bending strength, which were compared with those of commercial alumina bodies. In-vitro study was carried out using MG-63 osteoblast cells to investigate of their biocompatibility. As a result, the cells grew well on top and bottom as well as inside surface of pore. From the result of in-vivo study of 3-dimensional porous alumina bodies using rats, it was confirmed that any inflammatory response was not found in the subcutaneous tissue around porous body. Also the porous bodies removed from the rats were fully covered with well-developed fibrous tissues and showed the formation of new capillary blood vessels.

• Steel and Composite Structures
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• v.29 no.4
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• pp.451-464
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• 2018

This paper presents some quasi-static tests for 4 mixed columns composed of CFST column and RC column. The seismic performance and failure mode were studied under low-cyclic revised loading. The failure mode was observed under different axial compression ratios. The hysteretic curve and skeleton curve were obtained. The effects of axial compression ratio on yield mechanism, displacement ductility, energy dissipation, stiffness and strength attenuation were analyzed. The results indicate that the failure behavior of CFST-RC mixed column with archaized style is mainly caused by bending failure and accompanied by some shear failure. The axial compression ratio performs a control function on the yielding order of the upper and lower columns. The yielding mechanism has a great influence on the ductility and energy dissipation capacity of specimens. Based on the experiment, finite element analysis was made to further research the seismic performance by ABAQUS software. The variable parameters were stiffness ratio of upper and lower columns, axial compression ratio, yielding strength of steel tube, concrete strength and rebar ratio. The simulation results show that with the increase of stiffness ratio of the upper and lower columns, the bearing capacity and ductility of specimens can correspondingly increase. As the axial compression ratio increases, the ductility of the specimen decreases gradually. The other three parameters both have positive effect on the bearing capacity but have negative effect on the ductility. The results can provide reference for the design and engineering application of mixed column consisted of CFST-RC in Chinese archaized buildings.

• Structural Engineering and Mechanics
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• v.77 no.2
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• pp.179-196
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• 2021

Experimental investigations on the seismic behaviors of the PVC-FRP Confined Reinforced Concrete (PFCRC) columns under low cyclic loading are carried out and two variable parameters including CFRP strips spacing and axial compression ratio are considered. The PFCRC column finally fails by bending and is characterized by the crushing of concrete and yielding of the longitudinal reinforcement, and the column with a high axial compression ratio is also accompanied by the cracking of the PVC tube and the fracture of CFRP strips. The hysteretic curves and skeleton curves of the columns are obtained from the experimental data. With the increase of axial compression ratio, the stiffness degradation rate accelerates and the ductility decreases. With the decrease of CFRP strips spacing, the unloading sections of the skeleton curves become steep and the ductility reduces significantly. On the basis of fiber model method, a numerical analysis approach for predicting the skeleton curves of the PFCRC columns is developed. Additionally, a simplified skeleton curve including the elastic stage, strengthening stage and unloading stage is suggested depending on the geometric drawing method. Moreover, the loading and unloading rules of the PFCRC columns are revealed by analyzing the features of the skeleton curves. The quantitative expressions that are used to predict the unloading stiffness of the specimens in each stage are proposed. Eventually, an analytical model for the PFCRC columns under low cyclic loading is established and it agrees well with test data.

• Composites Research
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• v.22 no.6
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• pp.32-38
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• 2009

In this study, the energy absorption capabilities and failure modes of four different kinds of circular tubes made of carbon, Kevlar and carbon-Kevlar hybrid composites with epoxy resin have been evaluated. In order to achieve these goals, these tubes were fabricated with unidirectional prepregs and compressive tests were conducted for the tubes under 10mm/min loading speed. From the test results, carbon/epoxy tubes were collapsed by brittle fracturing mode and showed the best energy absorption capabilities, while Kevlar/epoxy tubes were crushed by local buckling mode and worst. The hybrid [$90_C/0_K$] tubes were failed in a local bucking mode and showed good post crushing integrity, whereas [$90_K/0_C$] tubes were failed in a lamina bending mode and bad post crushing integrity.

• Steel and Composite Structures
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• v.49 no.6
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• pp.615-631
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• 2023

To investigate the seismic behavior of steel slag self-stressing concrete-filled circular steel tubular (SSSCFCST) columns, 14 specimens were designed, namely, 10 SSSCFCST columns and four ordinary steel slag (SS) concrete (SSC)-filled circular steel tubular (SSCFCST) columns. Comparative tests were conducted under low reversed cyclic loading considering various parameters, such as the axial compression ratio, diameter-thickness ratio, shear-span ratio, and expansion ratio of SSC. The failure process of the specimens was observed, and hysteretic and skeleton curves were obtained. Next, the influence of these parameters on the hysteretic behavior of the SSSCFCST columns was analyzed. The self stress of SS considerably increased the bearing capacity and ductility of the specimens. Results indicated that specimens with a shear-span ratio of 1.83 exhibited compression bending failure, whereas those with shear-span ratios of 0.91 or 1.37 exhibited drum-shaped cracking failure. However, shear-bond failure occurred in the nonloading direction. The stiffness of the falling section of the specimens decreased with increasing shear-span ratio. The hysteretic curves exhibited a weak pinch phenomenon, and their shapes evolved from a full shuttle shape to a bow shape during loading. The skeleton curves of the specimens were nearly complete, progressing through elastic, elastoplastic, and plastic stages. Based on the experimental study and considering the effects of the SSC expansion rate, shear-span ratio, diameter-thickness ratio, and axial compression ratio on the seismic behavior, a peak displacement coefficient of 0.91 was introduced through regression analysis. A simplified method for calculating load-displacement skeleton curves was proposed and loading and unloading rules for SSSCFCST columns were provided. The load-displacement restorative force model of the specimens was established. These findings can serve as a guide for further research and practical application of SSSCFCST columns.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.3
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• pp.2242-2248
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• 2015

The damages from greenhouses collapsing due to heavy snowfall in winter are increasing, and the current frames of greenhouse are required to be improved. This study was conducted to seek solutions to improve intensities of greenhouse frame to bear heavy snows. We investigated a structural safety of greenhouses by calculating axial force, bending moment and combined stress when snow load was increased up to 30% of the current standard ground snow load of the conventional greenhouse types (07-single type 3, 07-single type 18) in the three regions (Gyeongju, Sokcho, and Gangneung) where were most damaged by recent heavy snows. In addition, we determined what structural type was most efficiently bear snow loads by measuring the differences between the load bearing strength according to the changes of tube diameter and thickness or the rafter spacing of greenhouses circular pipe. MIDAS GEN program was used in the analysis. As a result, with the snow load increase of 30%, greenhouse in Gyongju was still safe, but in Sokcho was at a risk, and in Gangneung was possible to be collapsed even in the current snow load. Increased pipe diameter than increased pipe thickness was more efficient in terms of improved performance of greenhouse structure. Accordingly, it is suggested to revise standards of greenhouse to increase pipe diameter of rafter for minimizing damages by heavy snow.

• Journal of the Mineralogical Society of Korea
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• v.22 no.4
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• pp.385-393
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• 2009

The spectroscopic characteristics of Madagascar tourmaline were investigated by UV-Vis and FTIR spectroscopy. Physical features were similar to other region's tourmalines. The green and blue samples showed strong absorption band in the 714~743 nm due to $Fe^{3+}$, pink samples showed strong absorption band in the 510~530 nm due to $Mn^{3+}$, brown samples showed strong absorption at 324 nm due to $Mn^{2+}-Ti^{4+}$ IVCT and the colorless samples only revealed weak absorption at 406~413 nm or no absorptions due to low quantity of Mn. Combination of the stretching and bending mode cationic hydroxyl units (metal-OH) are observed in the 4300~4500 $cm^{-1}$. The parallel tube-shaped inclusions which contain hematite were detected generally. This investigation revealed that Cu was not detected but Fe and Mn were detected in the Madagascar tourmalines, and the various colors appear according to the amount of those impurity elements.