• Steel and Composite Structures
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• v.13 no.6
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• pp.587-606
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• 2012

Concrete-filled-steel-tubular (CFST) columns have been well proven to improve effectively the strength, stiffness and ductility of concrete members. However, the central part of concrete in CFST columns is not fully utilised under uni-axial compression, bending and torsion. It has small contribution to both flexural and torsion strength, while it can be replaced effectively by steel with smaller area to give similar load-carrying capacity. Also, the confining pressure in CFST columns builds up slowly because the initial elastic dilation of concrete is small before micro-crackings of concrete are developed. From these observations, it is convinced that the central concrete can be effectively replaced by another hollow steel tube with smaller area to form double-skinned concrete-filled-steel-tubular (CFDST) columns. In this study, a series of uni-axial compression tests were carried out on CFDST and CFST columns with and without external steel rings. From the test results, it was observed that on average that the stiffness and elastic strength of CFDST columns are about 25.8% and 33.4% respectively larger than CFST columns with similar equivalent area. The averaged axial load-carrying capacity of CFDST columns is 7.8% higher than CFST columns. Lastly, a theoretical model that takes into account the confining effects of steel tube and external rings for predicting the uni-axial load-carrying capacity of CFDST columns is developed.

• Nuclear Engineering and Technology
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• v.52 no.5
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• pp.889-896
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• 2020

The vertically inverted U-tube steam generator (UTSG) is widely used in the pressurized water reactor (PWR). The reverse flow behavior generally exists in some U-tubes of a steam generator (SG) under both single- and two-phase natural circulations (NCs). The behavior increases the flow resistance in the primary loop and reduces the heat transfer in the SG. As a consequence, the NC ability as well as the inherent safety of nuclear reactors is faced with severe challenges. The theoretical models for calculating single- and two-phase flow pressure drops in U-tubes are developed and validated in this paper. The two-phase reverse flow characteristics in two types of SGs are investigated base on the theoretical models, and the effects of the U-tube height, bending radius, inlet steam quality and primary side pressure on the behavior are analyzed. The conclusions may provide some promising references for SG optimization to reduce the disadvantageous behavior. It is also of significance to improve the NC ability and ensure the PWR safety during some accidents.

• Steel and Composite Structures
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• v.30 no.2
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• pp.185-199
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• 2019

Modular construction is an emerging technology to accommodate the increasing restrictions in terms of construction period, energy efficiency and environmental impacts, since each structural module is prefabricated offsite beforehand and assembled onsite using industrialized techniques. However, some innate structural drawbacks of this innovative method are also distinct, such as connection tying inaccessibility, column instability and system robustness. This study aims to explore the theoretical and numerical stability analysis of a tenon-connected square hollow section (SHS) steel column to address the tying and stability issue in modular construction. Due to the excellent performance of composite structures in fire resistance and buckling prevention, concrete-filled steel tube (CFST) columns are also taken into account in the analysis to evaluate the feasibility of adopting composite sections in modular buildings. Characteristic equations with three variables, i.e., the length ratio, the bending stiffness ratio and the rotational stiffness ratio, are generated from the fourth-order governing differential equations. The rotational stiffness ratio is recognized as the most significant factor, with interval analysis conducted for its mechanical significance and domain. Numerical analysis using ABAQUS is conducted for validation of characteristic equations. Recommendations and instructions in predicting the buckling performance of both SHS and CFST columns are then proposed.

• Nuclear Engineering and Technology
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• v.54 no.5
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• pp.1874-1889
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• 2022

In this study, we evaluate the thermal-hydraulic performance and economics of Printed Circuit Heat Exchanger (PCHE) according to the channel types and associated shape variables for the design of recuperators with Sodium-cooled Fast Reactors (SFRs). To perform the evaluations with variables such as the Reynolds number, channel types, tube diameter, and shape variables, a code for the heat exchanger is developed and verified through a comparison with experimental results. Based on the code, the volume and pressure drop are calculated, and an economic assessment is conducted. The zigzag type, which has bending angle of 80° and a tube diameter of 1.9 mm, is the most economical channel type in a SFR using CO₂ as the working fluid. For a SFR using N₂, we recommend the airfoil type with vertical and horizontal numbers of 1.6 and 1.1, respectively. The airfoil type is superior when the mass flow rate is large because the operating cost changes significantly. When the mass flow rate is small, volume is a more important design parameter, therefore, the zigzag type is suitable. In addition, we conduct a sensitivity analysis based on the production cost of the PCHE to identify changes in optimal channel types.

• Advances in nano research
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• v.12 no.2
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• pp.167-183
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• 2022

In this paper, the free and forced vibration analysis of rotating cantilever nanoscale cylindrical beams and tubes is investigated under the external dynamic load to examine the nonlocal effect. A couple of nonlocal strain gradient theories with different beams and tubes theories, involving the Euler-Bernoulli, Timoshenko, Reddy beam theory along with the higher-order tube theory, are assumed to the mathematic model of governing equations employing the Hamilton principle in order to derive the nonlocal governing equations related to the local and accurate nonlocal boundary conditions. The two-dimensional functional graded material (2D-FGM), made by the axially functionally graded (AFG) in conjunction with the porosity distribution in the radial direction, is considered material modeling. Finally, the derived Partial Differential Equations (PDE) are solved via a couple of the generalized differential quadrature element methods (GDQEM) with the Newmark-beta techniques for the time-dependent results. It is indicated that the boundary conditions equations play a crucial task in responding to nonlocal effects for the cantilever structures.

• Journal of the Korean institute of surface engineering
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• v.57 no.3
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• pp.192-200
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• 2024

Cu as a heat exchanger tube is an important component in thermal fluid transfer. However, Cu tubes are exposed to stress in certain environments, leading to stress corrosion cracking (SCC). In this study, the effect of Sn addition on microstructure and corrosion characteristics was examined. The microstructural examination revealed the presence of columnar crystal and a grain refinement due to the addition of Sn. Electrochemical measurements showed that the 5 wt.% NH₃ environment was the most vulnerable environment to Cu corrosion, and the corrosion current density increased as stress increased. The immersion test exhibited the formation of Cu2O and Cu(OH)₂ corrosion product in 3.5 wt.% NaCl and 5 wt.% NH₃ environments, respectively. Results indicated that Sn addition to Cu was an important factor in improving the mechanical strength.

• Journal of Korean Society of Steel Construction
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• v.25 no.1
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• pp.15-24
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• 2013

This paper presents the results from a systematic finite element study on the bending moment resisting capacity of double web-angle connection for a CFT(concrete filled tube) composite frame subjected to cyclic loading. The three-dimensional nonlinear finite element models are constructed to investigate the rotational stiffness, bending moment capacity, and failure modes of the partially restrained composite CFT connections. A wide scope of additional structural behaviors explain the different influences of the double web-angle connections parameters, such as the different thickness of connection angles and the gage distances of high strength steel connection bar. The moment-rotation angle relationships obtained statically from the finite element analysis are compared with those from Richard's theoretical equation.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.3
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• pp.313-318
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• 2012

In CANDU, feeder pipes supply heavy water to pressure tube and steam generator. Under service conditions, Flow-Accelerated Corrosion (FAC) produces local wall-thinning in the feeder pipes. The wall-thinning in these pipes affects the integrity of the piping system, as verified in previous research. This paper provides limit loads for wallthinned feeder pipes with $45^{\circ}$ and $60^{\circ}$ bend angles, and proposes an equation that predicts the limit loads for wallthinned feeder pipes with arbitrary bend angles. On the basis of finite element limit analyses, limit loads are obtained for wall-thinned feeder pipes under in-plane bending and internal pressure. There are two cases of in-plane bending: the in-plane closing direction and the in-plane opening direction. The material is considered the effect of the large deformation, so an elastic-perfectly-plastic material is assumed in the calculations.

• Journal of the Korea institute for structural maintenance and inspection
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• v.13 no.2 s.54
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• pp.223-230
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• 2009

In this study we deal with bending behaviors of a concrete filled tubular(CFT) with various diameter-thickness ratios and concrete strengths. In finite element analysis using a commercial package(LUSAS), the bonding effect between concrete and steel in CFT structures is modeled by applying a joint element for the bonding surface. In order to consider the nonlinearity of concrete and steel tubes, stress-strain curves of the concrete and steel are used for the increased stresses in a plastic domain. The numerical results obtained from the proposed method show good agreement with the experimental data from load-displacement curves of a steel tube under distributed loads. Several parametric studies are focused on structural characteristics of CFT under bending effects for different diameter-thickness ratios and concrete strengths.

• Journal of Korean Society of Steel Construction
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• v.27 no.3
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• pp.289-298
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• 2015

The steel tube of Concrete-Filled Tube(CFT) confines the concrete and the concrete restrains the buckling of the tube, The objective of this study is to investigate the influences of the opening shape of the through diaphragm in case of the rectangular CFT column-to-beam connection through the structural experiment. The experiment results are compared with analysis results obtained by using the FEM program. These results are shown that strength of the rectangular CFT column-to-beam connection have similar structural performance regardless of the opening shape if opening areas of the through diaphragm are same. Also in case the connection area/shape of the through diaphragm and the flange of H-beam are similar, it was ascertained that the bending stress occurred at the beam can be transferred to the column through the diaphragm.