• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.10a
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• pp.293-296
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• 2009

In roll forming process, a sheet metal is continuously progressively formed into a product with required cross-section and longitudinal shape, such as a circular tube with required diameter, wall-thickness and straightness, by passing through a series of forming rolls in arranged in tandem. In recent years, that process is often applied to the bumper rail in the automotive industries. In this study, a optimal front side member manufacturing technology, model deign and proper roll-pass sequences can be suggested by forming number of roll-pass and bending angle. And also effects of the process parameters on the final shape formed by roll forming defects were evaluated.

• Earthquakes and Structures
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• v.4 no.1
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• pp.41-62
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• 2013

A comprehensive experimental program of cyclic tests on 1:3-scale models of bridge piers is going to be carried out at the Laboratory of Structures and Materials of the University of Basilicata. The testing models include eight RC single shaft piers with hollow circular cross section. Four piers have been realised using corroded steel rebars. In this paper, the results of preliminary numerical simulation analyses of the cyclic behaviour of the piers, carried out with Opensees using fiber-based models, are presented. Pull-out and lap-splice effects of steel rebars have been taken into account in the numerical analyses. First, the experimental specimens and the test set up are presented. Next, the results of the numerical analyses are discussed. In the numerical analyses, different configurations and levels of corrosion have been considered. The effective stiffness and equivalent damping of the piers is reported as a function of pier ductility and pier drift.

• Structural Engineering and Mechanics
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• v.7 no.2
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• pp.127-145
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• 1999

This paper deals with the development of an approach for evaluating the squash load and rigidity of unprotected concrete filled steel columns at elevated temperatures. The current approach of evaluating these properties is reviewed. It is shown that with a non-uniform temperature distribution, over the composite cross-section, the calculations for the squash load and rigidity are tedious in the current method. A simplified approach is proposed to evaluate the temperature distribution, squash load, and rigidity of composite columns. This approach is based on the model in Eurocode 4 and can conveniently be used to calculate the resistance to axial compression of a concrete filled steel column for any fire resistance time. The accuracy of the proposed approach is assessed by comparing the predicted strengths against the results of fire tests on concrete filled circular and square steel columns. The applicability of the proposed approach to a design situation is illustrated through a numerical example.

• Steel and Composite Structures
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• v.21 no.2
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• pp.303-321
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• 2016

Tubular column members have been widely adopted in current construction due to its numerous advantages. However, the closed-section profile characteristics of tubular columns severely limit the connection possibilities. Welding type is acceptable but discouraged because of on-site issues. Blind-bolted connection is preferable because of its simplicity, economic benefit, and easy assembly. This paper presents a state-of-the-art review on bolted connections to tubular columns for bare steel tubes, including square and circular sections. Available studies on bolted connections at ambient and elevated temperatures are reviewed, but emphasis is given on the latter. Various methods of determining the connection performance through experimental, analytical, component based, and finite element approaches are examined. Future research areas are also identified.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.1
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• pp.83-91
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• 1994

An efficient method was developed to determine the ultimate strength for the segment subjected to cross-sectional distortion. Cumulative data based on the finite element analysis were used to perform the multi-regression analysis. A moment-thrust-curvature relationship of short segment was obtained with mathematical forms in the nonlinear range. The extensive parametric study was performed to generate the ultimate strength for the various segments. The result was compared with the experimental result which was not included in the database. The proposed method gives an essential tool for the nonlinear analysis of beam-column.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.3
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• pp.690-700
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• 1994

The effects of thermal stratification on the flow of a stratified fluid past a circular cylinder were examined in a wind tunnel. In order to produce strong thermal stratifications, a compact heat exchanger type variable electric heater is employed. Linear temperature gradient of up to $250^{\circ}C/m$ can be well sustained. The velocity and temperature profiles in the cylinder wake with a strong thermal gradient of $200^{\circ}C/m$ were measured and the smoke wire flow visualization method was used to investigate the wake characteristics. It is found that the temperature field effects as an active contaminant, so that the mean velocity and temperature profiles can not sustain their symmetricity about the wake centerline when such a strong thermal gradient is superimposed. It is evident that the turbulent mixing in the upper half section is stronger than that of the lower half of the wake in a stably stratified flow.

• Transactions of Materials Processing
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• v.19 no.1
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• pp.32-37
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• 2010

Hydroforming has attracted a great deal of attention in the manufacturing industries for vehicles and transportation systems. Hydroforming technology contributes to weight reduction, increased strength, improved quality and reduced tooling cost. Hydroformed automotive parts used as structure components in vehichle body frame often have to be structurally joined at some point. Therefore it is useful if the hydroformed automotive parts can be given a localized attachment flange. For a given flange shape, a parting plane for the dies is established relative to which the various surfaces of the flange shape, in cross section, have no significant reverse curvature. In this study, hydroforming process for flange forming was proposed. FE analysis to form flanged circular shape and flanged rectangular shape was preformed with Dynaform 5.5. To accomplish successful hydroforming process design, thorough investigation on proper combination of process parameters such as tool geometry and hydraulic pressure has been performed and optimized. The results show that flanged automotive parts can be successfully produced with tube hydroforming.

• Transactions of Materials Processing
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• v.17 no.7
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• pp.511-516
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• 2008

A drawbead die for the experimental determination of drawbead forces was newly introduced in this paper. While the conventional Nine's drawbead die inevitably includes effects of a blank holding force on the measured drawbead forces, the new drawbead die excludes it by removing the blank holder contact in the dieface. Therefore, the new drawbead die can provide more realistic drawbead forces without considering somewhat arbitrary effect of blank holder with the computational procedure of forming process. The drawbead opening force and restraining force obtained by adopting the two experimental dies were compared for the validation of accuracy in the FEM simulation of automotive fender forming process. The compared section strains and draw-ins confirmed that the present drawbead die provides better drawbead forces for an accurate FEM simulation of sheet metal forming process.

• 유체기계공업학회:학술대회논문집
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• 2002.12a
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• pp.370-377
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• 2002

Generally, the system of calculation for the multi-path ultrasonic flow meters can be divided into two methods by how to get the mean velocity, namely, weighting and direct method. Weighting-method derive the mean velocity through modeling in theoretical velocity profile. Direct-method derive the mean velocity though actual flow distribution. The system of calculation varies with maker's transducer configuration and integration method. Each system has merits and demerits. This paper describes the system of integration that calculates line velocity over cross-section of the circular pipe. Flow rate mr discussed in this paper is a difference between theoretical flow rate and integrated flow rate according to values of Reynolds number in symmetric flow field or theoretical flow rate and integrated flow rate according to rotated model in asymmetric flow field.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.2 no.3
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• pp.26-31
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• 1991

The scattering property of TMz illuminated a elliptic dielectric cylinders with arbitrary cross section are analyzed by the boundary element techniques. The boundary element equations are for- mulated via Maxwell's equations, weighted residual of Green's theorem, and the boundary conditions. The unknown surface fields on the boundaries are then calculated by the boundary element integral equations. Once the surface fields are found, the scattered fields in far-zone and scattering widths (SW) are readily determined. To show the validity and usefulness of this formulation, computations are compared with those obtained using analytical method and one layer circular cylinder. As exten- sion to arbitrary cross-sectioned cylinders, plane wave scattering from a elliptic dielectric cylinders are numerically analyzed. A general computer program has been developed using the quadratic ele- ments(Higher order borndary elements) and the Gaussian quadrature.