• Journal of Korean Society of Steel Construction
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• v.27 no.5
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• pp.447-454
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• 2015

The researches on circular hollow section(CHS) connections have been conducted continuously because of development of material properties and complex local behavior of the connections. The purpose of this study is that the effects of material strength and chord wall slenderness on chord plastification and strength of CHS X-joint truss connection under compression on branch member were evaluated. To this end, finite element analyses were performed for various connections, using ANSYS Mechanical APDL program. Based on the analysis results, the design strength of the connections according to chord plastification limit state in KBC were examined. Finally, special considerations for CHS X-joint connection design were suggested.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.7
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• pp.1-8
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• 2005

For study on the unsteady wall interference effect, flows around a circular cylinder in closed test-section wind tunnels have been numerically investigated by solving compressible Navier-Stokes equations. The numerical scheme is based on a node-based finite-volume method with the Roe's flux-difference splitting and an implicit time-integration method coupled with dual time-step sub-iteration. The computed results showed that the unsteady pressure gradient over the cylinder is enhanced by the wall interference, and as a result the fluctuations of lift and drag are augmented. The drag is further increased because of the lower base pressure. The vortex shedding frequency is also increased by the wall interference. The pressure on the test section wall shows the harmonics having the shedding frequency contained in the wall effect.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.04a
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• pp.479-484
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• 2000

In this study, optimal design of reinforced concrete piers under seismic load is numerically investigated. Object function is the area of the concreate-section. Design variables are the total area of reinforcement and concrete-section dimension(Circular section diameter). Constraints of the design strength of the column, longitudinal reinforcement ratio and lower and upper bounds on the design variables are imposed. The reinforcement concrete column is analysed and designed by the Ultimated Strength Design method and load combination involving dead, live, wind and seismic load is used. For numerical optimization, ADS(Garret N, Vanderplaats_ routine is used. From the result of numerical examples, the concrete-section dimension was reduced, but longitudinal reinforcement was not changed. The results show that confinement reinforcement was reduced and confinement reinforcement spacing is increased. The higher strength of reinforcement used, the more concrete-section area was reduced.

• Journal of the Korean Society of Safety
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• v.16 no.3
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• pp.89-98
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• 2001

There have been a lot of studies about repair & strengthening of the concrete structure. But there has almost not been my study on section damage effect due to holes drilled out for installing additional facilities or equipment, such as rack on the wall of building or underground culvert system, plumbing system through the column or wall of it, after being occupied. This study is to find out how much the section loss due to holes will give loss of section strength. We cm determine if we repair or reinforce it completely or not, using strength loss from the hole. Hole size of diameter 3cm, 2cm, lcm, depth of 3cm, 5cm, 10cm, and position of each hole has been considered as variables of this study. It is concluded that section loss 30% results in 53% of strength damage.

• Journal of Korean Society of Steel Construction
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• v.24 no.2
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• pp.163-173
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• 2012

A connection composed of a circular hollow structural section (HSS) has complicated details, and exhibits a very complex local deformation when it reaches the yield stress. Given these circumstances, proposing a simple design equation considering local deformation is difficult. The design equations of the Korea Building Code (KBC 2009) for HSS joints are simple and are very similar to those of the AISC. These design equations limit the maximum yield stress up to 360MPa and yield ratio (yield strength/tensile strength) up to 0.8. This means that the material with yield strength exceeding 360MPa could be used after verification based on the test or rational analysis for the similar connection. This paper introduces an experimental program and finite element analysis (FEA) for the circular hollow section (CHS) with a transverse gusset plate made of high-strength steel (HSB600) or structural steel (SS400) when the joints are subjected to lateral force. Comparison of the design equations with the results of FEA and test may be used for the modification of the design equations.

• Steel and Composite Structures
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• v.21 no.5
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• pp.1017-1029
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• 2016

When a welded circular hollow section (CHS) tubular joint is subjected to brace axial loading, failure position is located usually at the weld toe on the chord surface due to the weak flexural stiffness of the thin-walled chord. The failure mode is local yielding or buckling in most cases for a tubular joint subjected to axial load at the brace end. Especially when a cyclic axial load is applied, fracture failure at the weld toe may occur because both high stress concentration and welding residual stress along the brace/chord intersection cause the material in this region to become brittle. To improve the ductility as well as to increase the static strength, a tubular joint can be reinforced by increasing the chord thickness locally near the brace/chord intersection. Both experimental investigation and finite element analysis have been carried out to study the hysteretic behaviour of the reinforced tubular joint. In the experimental study, the hysteretic performance of two full-scale circular tubular T-joints subjected to cyclic load in the axial direction of the brace was investigated. The two specimens include a reinforced specimen by increasing the wall thickness of the chord locally at the brace/chord intersection and a corresponding un-reinforced specimen. The hysteretic loops are obtained from the measured load-displacement curves. Based on the hysteretic curves, it is found that the reinforced specimen is more ductile than the un-reinforced one because no fracture failure is observed after experiencing similar loading cycles. The area enclosed by the hysteretic curves of the reinforced specimen is much bigger, which shows that more energy can be dissipated by the reinforced specimen to indicate the advantage of the reinforcing method in resisting seismic action. Additionally, finite element analysis is carried out to study the effect of the thickness and the length of the reinforced chord segment on the hysteretic behaviour of CHS tubular T-joints. The optimized reinforcing method is recommended for design purposes.

• Computers and Concrete
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• v.19 no.3
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• pp.233-241
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• 2017

During the last two decades, CFRP have been extensively used for repair and rehabilitation of existing structures as well as in new construction applications. For rehabilitation purposes CFRP are currently used to increase the load and the energy absorption capacities and also the shear strength of concrete columns. Thus, the effect of CFRP confinement on the strength and deformation capacity of concrete columns has been extensively studied. However, the majority of such studies consider empirical relationships based on correlation analysis due to the fact that until today there is no general law describing such a hugely complex phenomenon. Moreover, these studies have been focused on the performance of circular cross section columns and the data available for square or rectangular cross sections are still scarce. Therefore, the existing relationships may not be sufficiently accurate to provide satisfactory results. That is why intelligent models with the ability to learn from examples can and must be tested, trying to evaluate their accuracy for composite compressive strength prediction. In this study the forecasting of wrapped CFRP confined concrete strength was carried out using different Data Mining techniques to predict CFRP confined concrete compressive strength taking into account the specimens' cross section: circular or rectangular. Based on the results obtained, CFRP confined concrete compressive strength can be accurately predicted for circular cross sections using SVM with five and six input parameters without spending too much time. The results for rectangular sections were not as good as those obtained for circular sections. It seems that the prediction can only be obtained with reasonable accuracy for certain values of the lateral confinement coefficient due to less efficiency of lateral confinement for rectangular cross sections.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.5
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• pp.924-932
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• 1992

This paper presents the results of an experimental study on the characteristics of the vortex- induced vibration of an elastically supported circular cylinder in the cross air flow. For a range of velocities, power spectral densities of the signals from a hot-wire anemometer placed in the wake of an oscillating circular cylinder and gap sensors placed in the both ends of a circular cylinder were obtained to determine vortex-shedding frequencies, natural frequencies and vibrating frequencies of a cylinder. The effects of slots in the test section on vortex shedding and cylinder oscillation were investigated. The present study covered the reduced velocity range 1.0 .leg. Ur .leg. 64.6. The response characteristics of the cylinder has been shown to vary extensively, depending on the slots in the test section as well as on the reduced velocity. For an elastically supported cylinder, a purely translation mode oscillation was observed at a low velocity, however a rotation mode oscillation was often superposed for higher velocities. These two oscillating frequencies were equal to their natural frequencies irrespective of the changes of free stream velocities.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1999.04a
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• pp.34-41
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• 1999

This paper is focused on numerical analysis for perforated plate with irregular section based on Kirchhoff's fundamental equations of a circular plate. The dimensions of analysis model are as following; 1) radius:100cm, 2) hole in center:20cm, 3)thickness: l0cm and variable and have a simple support in boundary. The theoretical results are compared with data obtained by the F.2.M analysis. Both data have good agreement with each other.

• Proceedings of the IEEK Conference
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• 2002.06a
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• pp.215-218
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• 2002

Design methods are presented for a broadband corrugated horn antenna operating X/Ku band (7.25-14.5 CHz). The corrugated horn consists of a circular waveguide taper, a mode converter, a waveguide-to-horn transition, and a hem section. Methods of design are presented for each section. The designed antenna shows excellent characteristics over the entire operating frequency range.