• Journal of electromagnetic engineering and science
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• v.10 no.3
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• pp.86-91
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• 2010

In this paper, a double-layered frequency selective surface(FSS) superstrate was built and tested. The unit cell of the proposed FSS consists of a ring slot and a dipole-shaped structure and shows a complementary frequency response. Each unit cell is printed on two sides of a substrate. By using these double-layered structures, the first resonant frequency of the pass-band can be lowered. As a result, the size of the unit cell is minimized and the spacing between the other cells is reduced. The proposed FSS-dipole composite antenna is designed for the gain enhancement of wide-band code division multiple access(WCDMA) frequency bands(1.92~2.17 GHz) with a low quality factor(Q=0.17). To verify the gain enhancement performance of the FSS, an FSS-dipole composite antenna was created. Although the FSS layer enhances the gain of the primary radiation source of the dipole antenna, the FSS-dipole complex antenna cannot show a uniform gain over the entire desired frequency band. The experimental results show a gain enhancement of 3 dBi with an FSS superstrate in the WCDMA frequency band.

• Steel and Composite Structures
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• v.37 no.5
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• pp.533-549
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• 2020

Recently, Concrete-filled double skin steel tubular (CFDST) columns have proven an exceptional structural resistance in terms of strength, stiffness, and ductility. However, the resistance of these column members can be severely affected by the type of loading in which bending stresses increase in direct proportion with axial load and eccentricity value. This paper presents a non-linear finite element based modeling approach that studies the behavior of slender CFDST columns under biaxial loading. Finite element models were calibrated based on the outcomes of experimental work done by other researchers. Results from simulations of slender CFDST columns under axial loading eccentric in one direction showed good agreement with the experimental response. The calibrated models are expanded to a total of thirty models that studies the behavior of slender CFDST columns under combined compression and biaxial bending. The influences of parameters that are usually found in practice are taken into consideration in this paper, namely, eccentricity-to-diameter (e/D) ratios, slenderness ratios, diameter-to-thickness (D/t) ratios, and steel contribution ratios. Finally, an analytical study based on current code provisions is conducted. It is concluded that South African national standards (2011) provided the most accurate results contrasted with the Eurocode 4 (2004) and American Institute of Steel Construction (2016) that are found to be conservative. Accordingly, correction factors are proposed to the current design guidelines to provide more satisfactory results.

• Bulletin of the Korean Chemical Society
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• v.35 no.2
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• pp.392-396
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• 2014

New organic-inorganic composite of 2,4-dihydroxybenzophenone (BP-1) encapsulation into dodecylbenzenesulfonate (DBS) modified layered double hydroxide (LDH) was successfully prepared. The surface, structural, thermal and absorption properties of the BP-1/DBS-LDH nanohybrid was characterized by BET analysis, scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TG) and diffuse reflectance UV-Vis absorbance spectra (DRUV-vis). The interlayer configuration of composite and the adsorption mechanism of BP-1 on MgAl-DBS-LDH were discussed. It was suspected that DBS anions located in the form of monolayer arrangement with a $75^{\circ}$ anti parallel angle between dodecylbenzenesulfonate chain axis. The diffuse reflectance UV-Vis absorbance results revealed that the UV absorbing wavelength of BP-1/DBS-LDH evidently extends to about 400 nm, which shows that the BP-1/DBS-LDH has the potential application as a UV absorber.

• Steel and Composite Structures
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• v.20 no.3
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• pp.571-597
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• 2016

A new unified design formula for calculating the composite compressive strength of the axially loaded circular concrete filled double steel tubular (CFDST) short and slender columns is presented in this paper. The formula is obtained from the analytic solution by using the limit equilibrium theory, the cylinder theory and the "Unified theory" under axial compression. Furthermore, the stability factor of CFDST slender columns is derived on the basis of the Perry-Robertson formula. This paper also reports the results of experiments and finite element analysis carried out on concrete filled double steel tubular columns, where the tested specimens include short and slender columns with different steel ratio and yield strength of inner tube; a new constitutive model for the concrete confined by both the outer and inner steel tube is proposed and incorporated in the finite element model developed. The comparisons among the finite element results, experimental results, and theoretical predictions show a good agreement in predicting the behavior and strength of the concrete filled steel tubular (CFST) columns with or without inner steel tubes. An important characteristic of the new formulas is that they provide a unified formulation for both the plain CFST and CFDST columns relating to the compressive strength or the stability bearing capacity and a set of design parameters.

• Steel and Composite Structures
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• v.43 no.6
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• pp.689-706
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• 2022

Thin-walled square concrete-filled double steel tubular (CFDST) columns composed of the inner circular tube filled with concrete can be used to carry the large axial loads or strengthen existing CFST columns in composite constructions. This paper reports an experimental program carried out on short square CFDST columns loaded concentrically. The influences of important column parameters on the post-buckling performance of such columns are investigated. Test results exhibit that the inner circular tube significantly improves the ultimate loads and the ductility of such columns compared to conventional concrete-filled steel tubular (CFST) and double-skin CFST (DCFST) columns with an inner void. A mathematical model developed is used to simulate the ultimate strengths and load-strain curves of such columns loaded axially. Furthermore, the ultimate strengths of such columns are predicted using existing codified design models for conventional CFST columns as well as the formulas proposed by previous researchers and compared against a large database comprising 500 CFDST columns. Lastly, an accurate artificial neural network model is developed for the practical applications of such columns under axial loading.

• Advanced Composite Materials
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• v.17 no.3
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• pp.301-317
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• 2008

The energy release rate associated with crack growth in adhesive double cantilever beam (DCB) specimens, including the effect of residual stresses, was formulated using beam theory. Because of the rotation of the asymmetric arms in the adhesive DCB specimens due to temperature change, it is necessary to correct the evaluated fracture toughness of the DCB specimens, specifically in the case of a large temperature change. This study shows that the difference between the true toughness and an apparent toughness due to the consequence of ignoring residual stresses can be calculated for a given specimen geometry and thermo-mechanical properties (e.g. coefficient of thermal expansion). The calculated difference in the energy release rates based on the present correction method is compared with that from FEM in order to verify the present correction method. The residual stress effects on the evaluation of the adhesive fracture toughness are discussed.

• Journal of the Korean Society for Railway
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• v.3 no.2
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• pp.92-99
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• 2000

Composites are very useful material for light train carbody due to its high specific strength and lightweight characteristics. The composites, called 3-D board, are developed with a special stitching method. In this process, the glass fiber fabrics of skin material and foam core material are stitched together with glass fiber thread. The glass thread in Z-axis turns into FRP form. The conventional delamination problem can be solved with 3-D sandwich structure. In addition, with the lower density of foam, the weight of the panel and the operation expenses can be highly reduced. To evaluate the usefulness of the 3-D board, the double-deck light train carbody is studied. The stress analyses are carried out under various loads and boundary conditions with FEM Code, ANSYS. On comparing with the aluminum carbody, 3-D board carbody can be reduced by about 2 ton for the total weight of carbody.

• Journal of Industrial Technology
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• v.31 no.A
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• pp.33-38
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• 2011

In an express tilting train, side wall insulating the noise from the exterior sound source consists of two parts. One is the layered composite panel including aluminum honeycomb, glass wool and nomex honeycomb. The other is the double glazed window. In this study, sound insulation performance of the two parts is investigated by mass law and experiment. Based on ASTM E2249-02, the intensity sound transmission loss (TL) is measured on the specimens of the two parts. Mass law deviation (MLD) is considered in order to compare the sound insulation performance in respect of weight. Contribution of each part to the sound insulation is analyzed and the sound insulation strategy for the interior noise reduction is investigated.

• 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.

• Steel and Composite Structures
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• v.29 no.1
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• pp.1-22
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• 2018

Multi-storey precast concrete skeletal structures are assembled from individual prefabricated components which are erected on-site using various types of connections. In the current design of these structures, beam-to-column connections are assumed to be pin jointed. Welded plate beam to-column connections have been used in the precast concrete industry for many years. They have many advantages over other jointing methods in component production, quality control, transportation and assembly. However, there is at present limited information concerning their detailed structural behaviour under bending and shear loadings. The experimental work has involved the determination of moment-rotation relationships for semi-rigid precast concrete connections in full scale connection tests. The study reported in this paper was undertaken to clarify the behaviour of such connections under symmetrical vertical loadings. A series of full-scale tests was performed on sample column for which the column geometry and weld arrangements conformed with successful commercial practice. Proprietary hollow core slabs were tied to the beams by tensile reinforcing bars, which also provide the in-plane continuity across the connections. The strength of the connections in the double sided tests was at least 0.84 times the predicted moment of resistance of the composite beam and slab. The secant stiffness of the connections ranged from 0.7 to 3.9 times the flexural stiffness of the attached beam. When the connections were tested without the floor slabs and tie steel, the reduced strength and stiffness were approximately a third and half respectively. This remarkable contribution of the floor strength and stiffness to the flexural capacity of the joint is currently neglected in the design process for precast concrete frames. In general, the double sided connections were found to be more suited to a semi-rigid design approach than the single sided ones. The behaviour of double sided welded plate connection test results are presented in this paper. The behaviour of single sided welded plate connection test results is the subject of another paper.