• Steel and Composite Structures
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• v.50 no.5
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• pp.499-513
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• 2024

This paper describes the experimental and numerical investigations of octagonal Concrete-Filled Double Skinned Steel Tube (CFDST) short columns under the influence of various internal sizes of the circular and square steel tubes, with constant cross-sectional dimensions of the external octagonal steel tube under concentric loading. The non-linear finite element analysis of octagonal CFDST columns was executed using the ABAQUS to forecast and compare the axial compression behavior influenced by the various sizes of internal circular and square steel tubes. The study shows that the axial compressive strength and ductility of octagonal CFDST columns were significantly influenced by various internal dimensions of the circular and square steel tubes with the strengths of constituent materials.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.23 no.6 s.165
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• pp.1026-1038
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• 1999

Interlaminar fracture toughness of carbon/epoxy composite materials has been studied under tensile and flexural loading by the use of width tapered double cantilever beam(WTDCB) and end notched flexure(ENF) specimens. This study has significantly examined the effect of various interfacial ply orientation, ${\alpha}(0^{\circ},\;45^{\circ}\;and\;90^{\circ})$ and crack propagation direction, ${\theta}(0^{\circ},\;15^{\circ},\;30^{\circ}\;and\;45^{\circ})$ in terms of critical strain energy release rate through experiments. Twelve differently layered laminates were investigated. The data reduction for evaluating the fracture energy is based on compliance method and beam theory. Beam theory is used to analyze the effect of crack propagation direction. The geometry and lay-up sequence of specimens are considered various conditions such as skewness parameter, beam volume, and so on. The results show that the fiber bridging occurred due to the non-midplane crack propagation and causes the difference of fracture energy evaluated by both methods. For safer and more reliable composite structures, we obtain the optimal stacking sequence from initial fracture energy in each mode.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2012.06a
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• pp.388-389
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• 2012

Current offshore wind power towers are made of steel. As the capacity of wind power increases, the tower structures become higher. Steel structures have buckling problem and their increased slenderness ratios make them weak against buckling and vibration. In this study, double skinned composite tubular (DSCT) offshore wind power tower was proposed and its optimum design method was suggested. Fiber reinforced polymer (FRP) and steel were considered as material of the tubes. And both materials satisfied the required capacity.

• Wind and Structures
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• v.21 no.6
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• pp.727-753
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• 2015

A double-skinned composite tubular (DSCT) wind power tower was suggested and automatic section design software was developed. The developed software adopted the nonlinear material model and the nonlinear column model. If the outer diameter, material properties and design capacities of a DSCT wind power tower are given, the developed software performs axial force-bending moment interaction analyses for hundreds of sections of the tower and suggests ten optimized cross-sectional designs. In this study, 80 sections of DSCT wind power towers were designed for 3.6 MW and 5.0 MW turbines. Moreover, the performances of the 80 designed sections were analyzed with and without considerations of large displacement effect. In designing and analyzing them, the material nonlinearity and the confining effect of concrete were considered. The comparison of the analysis results showed the moment capacity loss of the wind power tower by the mass of the turbine is significant and the large displacement effect should be considered for the safe design of the wind power tower.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2018.05a
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• pp.247-248
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• 2018

In order to secure the variability of long-life housing, dry walls are used. The composite gypsum board panel is the most frequently used infill system for the wall, and it is an excellent construction method in terms of constructability and economic feasibility. However, there are also problems such as the destruction of Ondol pipes at the bottom floor and being unable to fix the light weight steel frame (M-bar) when a variable composite gypsum board panel is used. To solve such problems, a wall with a method of fixing only the top part without fixing the bottom floor is developed, but it is difficult to identify the durability of ceiling frame according to the tensile force of stud and the safety according to the Stiffness and impact resistance (soft body) of ceiling frame. Therefore, this study verified the effectiveness of infill system for the wall by conducting experiment on the stiffness and impact resistance of composite gypsum board panel according to the reinforcement of ceiling frame (wooden frame, double saw-toothed bracket, Cross M-bar). As a result, it was possible to secure the safety of wooden frame while the impact resistance and the Stiffness of double saw-toothed bracket and cross M-bar were not secured.

• Composites Research
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• v.28 no.4
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• pp.197-203
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• 2015

Tensile properties of polypropylene based self-reinforced composites were investigated as a function of process variables of the double-belt lamination equipment such as pressure, temperature and cooling conditions. Elastic modulus was enhanced approximately 6 times from 0.2 to 1.2 GPa. The improvement mechanism was studied by identification of crystalline structure changes using DSC and XRD analysis. In addition, morphology change of self-reinforced composites was also investigated by SEM analysis in order to reveal the degree of impregnation.

• Steel and Composite Structures
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• v.43 no.4
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• pp.431-445
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• 2022

A double-skinned composite tubular (DSCT) column, which is an internally confined concrete-filled tubular column with a hollow section, has been developed for efficient use of materials that reduce self-weight and enhance seismic performance. It exhibits excellent material behavior with ductility owing to the confinement induced by outer and inner steel tubes. This study conducted axial compression tests considering the effects of steel tube thickness and hollow diameter ratios of DSCT columns on the material behavior of confined concrete under pure axial compression on concrete cores. From the axial compression tests, various combinations of outer and inner tube thicknesses and two different hollow section ratios were considered. Additionally, confined concrete material behavior, axial strength, failure modes, and ductility of DSCT columns were evaluated. Based on this study, it was concluded that the tests show a good correlation with peak strength and shapes of nonlinear stress-strain curves presented in literature; however, the thinner outer and inner steel tubes may reduce the ductility of DSCT columns when using thinner outer and inner tubes and higher confined stress levels. Finally, the minimum thickness requirements of the steel tubes for DSCT columns were discussed in terms of strength and ductility of test specimens.

• Steel and Composite Structures
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• v.43 no.6
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• pp.759-772
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• 2022

Concrete-filled double skinned steel tubular (CFDST) columns have been used to construct modern structures such as tall buildings and bridges as well as infrastructures as they provide better, lesser weight, and greater stiffness in structural performance than conventional reinforced concrete or steel members. Different shapes of CFDST columns may be needed to satisfy the architectural and aesthetic criteria. In the study, three-dimensional FE simulations of circular and elliptical CFDST columns under axial compression were developed and verified through the experimental test data from the perspectives of full load-displacement histories, ultimate axial strengths, and failure modes. The verified FE models were used to investigate and compare the structural performance of CFDST columns with circular and elliptical cross-section shapes by evaluating the overall load-deformation curves, interaction stress-deformation responses, and composite actions of the column. At last, the accuracy of available design models in predicting the ultimate axial strengths of CFST columns were investigated. Research results showed that circular and elliptical CFDST column behaviors were generally similar. The overall structural performance of circular CFDST columns was relatively improved compared to the elliptical CFDST column.

• Journal of the Korean Society of Safety
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• v.38 no.2
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• pp.1-7
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• 2023

Fiber-metal laminates (FMLs) and polymer matrix composites (PMCs) are formed in various ways. In particular, FMLs in which aluminum is laminated as a reinforced layer are widely used. Also, glass fiber-reinforced plastics (GFRPs) are generally applied as fiber laminates. The bonding interface layer between the aluminum and fiber laminate exhibits low strength when subjected to hot press fabrication in the event of delamination fracture at the interface. This study presents a simple method for strengthening the interface bonding between the aluminum metal and GFRP layer of FML composites. The surfaces of the aluminum interface layer are engraved with three kinds of patterns by using the laser machine before the hot press works. Furthermore, the effect of the laser patterns on the interfacial toughness is investigated. The interfacial toughness was evaluated by the energy release rate (G) using an asymmetric double cantilever bending specimen (ADCB). From the experimental results, it was shown that the strip type pattern (STP) has the most proper pattern shape in GFRP/Al FML composites. Therefore, this will be considered a useful method for the safety assessment of FML composite structures.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.381-382
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• 2006

The mechanical behaviors of multi-layered foam core sandwich composite were investigated through a 3-point bending test. The sandwich specimens were obtained from sandwich panel consisting of aluminum faces and urethane foam core. Three types of sandwich specimens such as a single structure, a double structure and a triple structure were considered. The span of sandwich specimens were varied from 170mm to 350mm. According to the results, the flexural and shear properties of multi-layered sandwich composite were found to be higher than those of single-layered sandwich composite.