• Journal of Korean Society of Steel Construction
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• v.17 no.2 s.75
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• pp.207-216
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• 2005

The maximum strength of the stainless steel square and the circular hollow section columns, which are cold-formed and TIG welded, is experimented on and analyzed. The paper presents centrally compressed experiments, including stub column tests and coupon tests, on stainless steel pipe columns. A total of 24 stainless steel pipe column experiments are conducted, using the slenderness ratios ($L_k/r$ = 20, 30, 40, 50, 60, 70) as parameters. The experimental results were compared with the design standard curves, AIK-LSD and AISC-LRFD, AIJ-LSD, SIJ-ASD curves, and multiple column curves.

• Journal of Korean Society of Steel Construction
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• v.25 no.3
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• pp.299-305
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• 2013

This paper presents the experimental results of behacior of slender square hollow section columns strengthened with carbon fiber reinforced polymers (CFRP) sheets subjected to concentrated axial loading. Three long specimens were fabricated and one stub column were fabricated. The main parameters were the number of CFRP layers. From the tests, it was observed that global buckling were occurred at the center of specimen for unretrofitting slender column. However, CFRP retrofitting could prevent the global buckling of slender column. Maximum increase of 22% was also achieved in axial-load capacity with three longitudinal layered CFRP applied on four sides of steel tubes.

• Steel and Composite Structures
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• v.29 no.1
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• pp.91-106
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• 2018

This paper investigates the deflection of the steel-concrete composite truss beam (SCCTB) at the serviceability limit state. A precise solution for the distributed uplift force of the SCCTB, considering five different loading types, is first derived based on the differential and equilibrium equations. Furthermore, its approximate solution is proposed for practical applications. Subsequently, the shear slip effect corresponding to the shear stiffness of the stub connectors, uplift effect corresponding to the axial stiffness of the stub connectors and shear effect corresponding to the brace deformation of the steel truss are considered in the derivation of deflection. Formulae for estimating the SCCTB deflection are proposed. Moreover, based on the proposed formulae, a practical design method is developed to provide an effective and convenient tool for designers to estimate the SCCTB deflection. Flexure tests are carried out on three SCCTBs. It is observed that the SCCTB stiffness and ultimate load increase with an increase in the shear interaction factor. Finally, the reliability of the practical design method is accurately verified based on the available experimental results.

• Journal of Korean Society of Steel Construction
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• v.13 no.2
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• pp.123-131
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• 2001

The objective of this study is to investigate the criteria of the width-to-thickness ratio and to evaluate the buckling strength of high strength steel beam-columns and to compare their buckling strength with design codes, which are the Limit State Design code and the Allowable Stress Desogn code(drift). SM520TMC and SM570Q class steels are used for high strength steels. The coupon test and the stub column test were carried out to investigate the properties of high strength steels and the stress-strain curves of stub columns. The buckling strength of high strength steel beam-columns are assessed by numerical analysis used axial force, moment and curvature relationships.

• ETRI Journal
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• v.31 no.3
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• pp.271-281
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• 2009

This paper presents a novel multiband microstrip-fed right angle slot antenna design technique for multiple independent frequency bands. The new technique uses various slot sizes at various appropriate positions. We first propose a tri-band slot antenna consisting of three right angle slots. Then, a quad-band slot antenna is developed with four right angle slots which achieves slant ${\pm}45^{\circ}$ linear polarization, omnidirectional pattern coverage, good antenna gain, and acceptable impedance bandwidths over all the operating frequency range. Moreover, an open-circuited tuning stub is introduced to achieve good impedance matching. Both proposed antennas are designed on a ground plane of RT/duroid 5880 substrate with a thickness of 1.575 mm. The real measurable results show that the desired frequencies used in wireless communication systems, namely, WLAN and WiMax, are efficiently achieved.

• Steel and Composite Structures
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• v.16 no.5
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• pp.455-480
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• 2014

Sixteen concrete filled square CFRP-steel tubular (S-CFRP-CFST) stub columns under axial compression were experimentally investigated. The experimental results showed that the failure mode of the specimens is strength loss of the materials, and the confined concrete has good plasticity due to confinement of the CFRP-steel composite tube. The steel tube and CFRP can work concurrently. The load versus longitudinal strain curves of the specimens can be divided into 3 stages, i.e., elastic stage, elasto-plastic stage and softening stage. Analysis based on finite element method showed that the longitudinal stress of the steel tube keeps almost constant along axial direction, and the transverse stress at the corner of the concrete is the maximum. The confinement effect of the outer tube to the concrete is mainly focused on the corner. The confinements along the side of the cross-section and the height of the specimen are both non-uniform. The adhesive strength has little effect both on the load versus longitudinal strain curves and on the confinement force versus longitudinal strain curves. With the increasing of the initial stress in the steel tube, the load carrying capacity, the stiffness and the peak value of the average confinement force are all reduced. Equation for calculating the load carrying capacity of the composite stub columns is presented, and the estimated results agree well with the experimental results.

• Steel and Composite Structures
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• v.8 no.2
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• pp.115-128
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• 2008

A method is proposed to estimate the ultimate strength of rectangular concrete-filled steel tubular (CFT) stub columns under axial compression. The ultimate strength of concrete core is determined by using the conception of the effective lateral confining pressure and a failure criterion of concrete under true triaxial compression, which takes into account the difference between the lateral confining pressure provided by the broad faces of the steel tube and that provided by the narrow faces of the steel tube. The longitudinal steel strength of broad faces and that of the narrow faces of the steel tube are calculated respectively due to that buckling tends to occur earlier and more extensively on the broader faces. Finally, the proposed method is verified with experimental results. Corresponding values of ultimate strength calculated by ACI (2005), AISC (1999) and GJB4142-2000 are given respectively for comparison. It is found from comparison that the proposed method shows a good agreement with the experimental results.

• Computers and Concrete
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• v.19 no.3
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• pp.263-273
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• 2017

In this paper, a finite element model (FEM) in ATENA-3D software was constructed to investigate the behavior of circular ultra high performance concrete (UHPC) filled steel tube stub columns (UHPC-FSTCs) under concentric loading on concrete core. The "CC3DNonLinCementitious2User" material type for concrete in ATENA-3D software with some modifications of material laws, was adopted to model for UHPC core with consideration the confinement effect. The experimental results obtained from Schneider (2006) were then employed to verify the accuracy of FEM. Extensive parametric analysis was also conducted to examine the influence of concrete compressive strength, steel tube thickness and steel yield strength on the compressive behavior of short circular UHPC-FSTCs. It can be observed that the columns with thicker steel tube show better strength and ductility, the sudden drop of load after initial peak load can be prevented. Based on the regression analysis of the results from parametric study, simplified formulae for predicting ultimate loads and strains were proposed and verified by comparing with previous analytical models, design codes and experimental results.

• ETRI Journal
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• v.34 no.5
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• pp.674-683
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• 2012

We propose a slot antenna consisting of a rectangular slot on the ground plane, fed by a microstrip line with a rectangular-ring-shaped tuning stub that can be deployed in ultra-wideband (UWB) communication systems to avoid interference with wireless local area network (WLAN) communication. Our antenna can achieve a single band-notched property from the 5 GHz frequency to the 6 GHz frequency owing to a controllable band notch that uses L- and J-shaped parasitic elements. The antenna characteristics can be modified to tune the band-notched property (4 GHz to 5 GHz or 6 GHz to 7 GHz) and the bandwidth of the band notch (1 GHz to 2 GHz). Furthermore, the shifted notch with enhanced width of the band notch from 1 GHz to 1.5 GHz is described in this paper. The UWB slot antenna and L- and J-shaped parasitic elements also provide the band-rejection function for reference in the WiMAX (3.5 GHz) and WLAN (5 GHz to 6 GHz) regions of the spectrum. Experiment results evidence the return loss performance, radiation patterns, and antenna gains at different operational frequencies.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.12
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• pp.2462-2467
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• 2009

This paper proposes a dual band branch line coupler (BLC) using a composite right/left handed (CRLH) transmission line. The existing dual band BLCs with open stubs require hundreds of line impedance for the open stub as the frequency bands approach to each other, so it has been almost impossible to realize them. However in the proposed BLC, a CRLH transmission line replaces the open stub with an extremely high line impedance so that the BLC circuit may be realized even two frequencies are close to each other. As an example, a dual band BLC operating at 1800MHz and 2300MHz (the frequency ratio is 1:1.28) is designed and measured. Open stubs with $560\Omega$ line impedance are replaced by CRLH transmission lines for realizing the dual band BLC. The measured performances prove that the dual band operation is well acceptable and the proposed design method is successful even the ratio between two frequencies is not around two nor more.