• Structural Engineering and Mechanics
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• v.83 no.1
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• pp.19-29
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• 2022

The angle steel frame confined concrete columns (ASFCs) are an emerging form of hybrid columns, which comprise an inner angle steel frame and a concrete column. The inner angle steel frame can provide axial bearing capacity and well confining effect for composite columns. This paper presents the experimental and theoretical studies on the seismic behaviour of ASFCs. The experimental study of the 6 test specimens is presented, based on the previous study of the authors. The theoretical study includes two parts. One part establishes the section analysis model, and it uses to analyze section axial force-moment-curvature. Another part establishes the section moment-curvature hysteresis model. The test and analysis results show that the axial compression ratio and the assembling of steel slabs influence the local buckling of the angle steel. The three factors (axial compression ratio, content of angle steel and confining effect) have important effects on the seismic behaviour of ASFCs. And the theoretical model can provide reasonably accurate predictions and apply in section analysis of ASFCs.

• Steel and Composite Structures
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• v.42 no.2
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• pp.221-241
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• 2022

Perfobond rib connectors are widely used in composite structures to achieve the composite action between the steel and the concrete, and empirical expressions for their strength and secant stiffness have been obtained by numerical simulations or push-out tests. Since perfobond connections are generally in an elastic state in the service process and the structural analysis are always based on the elastic properties of the members, the secant stiffness is not applicable for the normal structural analysis. However, the tangent stiffness of perfobond connections has not been introduced in previous studies. Moreover, the perfobond connections are bearing tension and shear force simultaneously when the composite beams subjected to torque or local loads, but the current studies fail to arrive at the elastic stiffness considering the combined effects. To resolve these discrepancies, this paper investigates the initial elastic stiffness of perfobond connections under combined forces. The calculation method for the elastic stiffness of perfobond connections is analyzed, and the contributions of the perfobond rib, the perforating rebar and the concrete dowel are investigated. A finite element method was verified with a high value of correlation for the test results. Afterwards, parametric studies are carried out using the reliable finite element analysis to explore the trends of several factors. Empirical equations for predicting the initial elastic stiffness of perfobond connections are proposed by the numerical regression of the data extracted by parametric studies. The equations agree well with finite element analysis and test results, which indicates that the proposed empirical equations reflect a high accuracy for predicting the initial elastic stiffness of perfobond connections.

• Journal of The Korean Astronomical Society
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• v.55 no.6
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• pp.215-220
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• 2022

To seek an atmospheric heating mechanism operating on the Sun we investigated a heating source generated by a downflow, both of which may arise in a magnetic loop dynamically formed on the Sun via flux emergence. Since an observation shows that the illumination of evolving magnetic loops under the dynamic formation occurs sporadically and intermittently, we performed a magnetohydrodynamic simulation of flux emergence to obtain a high-cadence simulated data, where temperature enhancement was identified at the footpoint of an evolving magnetic loop. Unlike a rigid magnetic loop with a confined flow in it, the evolving loop in a low plasma β atmosphere is subjected to local compression by the magnetic field surrounding the loop, which drives a strong supersonic downflow generating an effective footpoint heating source in it. This may introduce an energy conversion system to the magnetized atmosphere of the Sun, in which the free magnetic energy causing the compression via Lorentz force is converted to the flow energy, and eventually reduced to the thermal energy. Dynamic and thermodynamic states involved in the system are explained.

• Steel and Composite Structures
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• v.45 no.6
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• pp.819-830
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• 2022

This paper presented an experimental study of the bond-slip behavior of reactive powder concrete (RPC)-filled square steel tube. A total of 18 short composite specimens were designed forstatic push-out test, and information on their failure patterns, load-slip behavior and bond strength was presented. The effects of width-to-thickness ratio, height-to-width ratio and the compressive strength of RPC on the bond behavior were discussed. The experimental results show that:(1) the push-out specimens remain intact and no visible local buckling appears on the steel tube, and the interfacial scratches are even more pronounced at the internal steel tube of loading end; (2) the bond load-slip curves with different width-to-thickness ratios can be divided into two types, and the main difference is whether the curves have a drop in load with increasing slip; (3) the bond strength decreases with the increase of the width-to-thickness ratio and height-width ratio, while the influence of RPC strength is not consistent; (4) the slippage has no definite correlation with bond strength and the influence of designed parameters on slippage is not evident. On the basis of the above analysis, the expressions of interface friction stress and mechanical interaction stress are determined by neglecting chemical adhesive force, and the calculation model of bond strength for RPC filled in square steel tube specimens is proposed. The theoretical results agree well with the experimental data.

• Wind and Structures
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• v.35 no.6
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• pp.369-383
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• 2022

Wind tunnel experiment was carried out to study the cross-wind layer forces on a square cross-section building model using a synchronous multi-pressure sensing system. The stationarity of measured wind loadings are firstly examined, revealing the non-stationary feature of cross-wind forces. By converting the measured non-stationary wind forces into an energetically equivalent stationary process, the characteristics of local wind forces are studied, such as power spectrum density and spanwise coherence function. Mathematical models to describe properties of cross-wind forces at different layers are thus established. Then, a conditional simulation method, which is able to ex-tend pressure measurements starting from experimentally measured points, is proposed for the cross-wind loading. The method can reproduce the non-stationary cross-wind force by simulating a stationary process and the corresponding time varying amplitudes independently; in this way the non-stationary wind forces can finally be obtained by combining the two parts together. The feasibility and reliability of the proposed method is highlighted by an ex-ample of across wind loading simulation, based on the experimental results analyzed in the first part of the paper.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.11
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• pp.115-120
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• 2021

In this study, cigarettes, which are an essential element in the production of tobacco, are generally not cylindrical. The main materials used for cigarettes are generally hemp and pulp. For the production of cylindrical cigarettes, the cigarettes or cylinders are mounted via gluing. This adhesive is a vinyl acetate emulsion, a high-temperature melt adhesive, and is adhered in a cylindrical shape immediately after being linearly applied to the inner surface of the paper roll or a local part. These adhesives are greatly affected by the atmospheric temperature of the manufacturing space in summer and winter. In the summer, even if the adhesive is temporarily adhered, the coagulation time of the adhesive is long, and problems such as deterioration of the adhesive state occur. in the winter, there is a problem that the temperature of the manufacturing space is low and the adhesive force of the adhesive is poor, resulting in defective adhesive products. In order to solve these problems, another heat transfer device is utilized to cure the remaining adhesive to ensure higher adhesiveness.

• Structural Engineering and Mechanics
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• v.83 no.4
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• pp.563-576
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• 2022

This study aimed to evaluate the progressive collapse potential of buildings designed using conventional design codes for the merchant occupancy classification and subjected to a sudden column failure. For this purpose, three reinforced concrete buildings having different story numbers were designed according to the seismic design recommendations of TSCB-2019. Later on, the buildings were analyzed using the GSA-2016 and UFC 4-023-03 to observe their progressive collapse responses. Three columns were removed independently in the structures from different locations. Nonlinear dynamic analysis method for the alternate path direct design approach was implemented for the design evaluation. The plasticity of the structural members was simulated by using nonlinear fiber hinges. The moment, axial, and shear force interaction on the hinges was considered by the Modified Compression Field Theory. Moreover, an existing experimental study investigating the progressive collapse behavior of reinforced concrete structures was used to observe the validation of nonlinear fiber hinges and the applied analysis methodology. The study results deduce that a limited local collapse disproportionately more extensive than the initial failure was experienced on the buildings designed according to TSCB-2019. The mercantile structures designed according to current seismic codes require additional direct design considerations to improve their progressive collapse resistance against the risk of a sudden column loss.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.03b
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• pp.173-178
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• 1999

In this study MD simulations have been performed to observe the behavior of a grain boundary in an a-Fe plate under 2-dimensional loading. In MD simulation the acceleration of every molecule can be achieved from the potential energy and the force interacting between each molecule and the integration of the motion equation by using Verlet method gives the displacement of each molecule. Initially four a-Fe rectangular plates having different misorientation angles of grain boundary were modeled by using the Johnson potential and Morse potential We compared the potential energy of the grain boundary system with that of the perfect structure model. Also we could obtain the width of the grain boundary by investigating the local potential energy distribution. The tensile loading for each grain boundary models was applied and the behavior of grin boundary was studied. From this study it was clarified that in the case using Johnson potential the obvious fracture mechanism occurs along the grain boundary in the case of Morse potential the diffusion of the grain boundary appears instead of the grain boundary fracture.

• Composites Research
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• v.22 no.4
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• pp.1-12
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• 2009

In this paper, quasi-static crushing tests of composite circular tubes under axial compression load are conducted to investigate the energy absorption characteristics. Circular tubes used for this experiment are glass/epoxy (GFRP) composite tubes which are fabricated by the filament winding method. One edge of the composite tube is chamfered to reduce the initial peak load and to prevent catastrophic failure during crushing process. Energy absorption characteristics vary significantly according to the constituent materials, fabrication conditions, tube geometry and test condition. In tube geometry, according as inner diameter increase, unstable crush mode is caused by local buckling of delamination, but control of the fiber orientation should help composite tubes get stable crush mode.

• Structural Engineering and Mechanics
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• v.84 no.4
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• pp.517-530
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• 2022

In re-assessing the Jacket-type fixed steel structures, the current standards often allow the simplicity of corrosion sections using local buckling or equivalent section approach to applying empirical formulae of frame stress and resistance analyses. However, those approaches can lead to significant errors for non-uniform corroded frames in a specific area, including force distribution, stress, and allowable strength of the tubular section, compared to the actual cases. This paper investigates a suitable approach to determine the actual stress on non-uniform corroded tubular frames under compression through the non-linear ABAQUS model by considering the effect of large deformation on the frame axis and the frame section. There are 3 scenarios of interest. In the 1st and 2nd scenarios with simple corrosion cases, the stress ratios using the numerical model and theoretical formulae correspond to the calculation of allowable strength reduction ratios in standards. However, scenario 3, which describes non-uniform corroded sections based on survey data, provides considerable differences in results. Therefore, it proves the reliable and effective results when using this method to analyze the resistance of the actual corroded section in the Jacket platforms.