• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2214-2219
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• 2008

The thermal contact resistance(TCR) of nanosized contact spots has been investigated through a multiscale analysis which considers the resolution of surface topography. A numerical simulation is performed on the finite element model of rough surfaces. Especially, as the contact size decreases below the phonon mean free path, the size dependent thermal conductivity is considered to calculate the TCR. In our earlier model which follows an elastic material, the TCR increases without limits as the number of nanosized contact spots increases in the process of scale variation. However, the elastoplastic contact induces a finite limit of TCR as the scale varies. The results are explained through the plastic behavior of the two contacting models. Furthermore, the effect of air conduction in nanoscale is also investigated.

• Journal of Korean Society of Steel Construction
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• v.20 no.3
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• pp.377-387
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• 2008

The post-buckling behavior of slender members, such as the chord of truss structures generally implies extreme strength degradation. The buckling strength is usually determined as the performance of the compressed steel members, so it is important to understand the exact buckling behavior of a member in order to design the entire structure. A target analytical model is usually divided by beam or shell element when we simulate the buckling behavior of a compressed steel member such as atruss member. In this case, it is possible to accurately obtain the behavior, but such would be expensive and would require experience inanalysis even in monotonic loading. In this paper, we propose a consistent and convenient method to analyze the post-buckling behavior of elastoplastic compression members. The present methods are formulated to satisfy the second law of thermodynamics. Three numerical examples were tested to determine the validity of the proposed model in cyclic loading with comparable F.E.M results.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.2
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• pp.41-49
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• 1993

This paper presents a geometrically non-linear and elastoplastic F.E. formulation using a total Lagrangian approach for the two dimensional isoparametric curved beam elements. The beam element is derived by using plane stress elements. The basic element geometry is constructed using the coordinates of the nodes on the element center line and the nodal point normals. The element displacement field is described using two translations of the node on the center line and a rotation about the axes normal to the plane containing the center line of the element. The layered approach is used for the elastoplastic analysis of the plane framed structure with the arbitrary cross section. The iterative load or displacement incremental method for non-linear finite element analysis of the frame structure is used. Numerical examples are presented to demonstrate the behavior and the accuracy of the proposed beam element for geometric and elastoplastic non-linear applications. Comparisons made with present theory and other published data show that tilt' beam element products accurate results with good convergence characteristics.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.10a
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• pp.181-184
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• 2009

The hot press farming process, which is the press hardening of steel parts using cold dies, can utilize both ease of shaping and high strength due to the hardening effect of rapid quenching during the pressing. In this study, a thermo-elastoplastic analysis of the hot press forming process using the finite element method was performed in order to investigate the deformation behavior and temperature history during the process and the mechanical properties of the pressed parts.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05a
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• pp.386-389
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• 2006

Prestressed composite girder bridges with concrete infilled steel tube at negative flexural moment region takes the advantages of enhancing local buckling and flexural resistances resulting from the lateral confining effect of concrete due to the interactive reaction in the interface layer of steel tube and concrete. The interface behavior in concrete infilled tube of the test composite girder is analyzed by 8-node zero thickness interface finite element combined with 3-D. elastoplastic concrete constitutive model and 3-D. elastoplastic Mindlin shell element. The interface effects between infillled concrete and steel tube are investigated through the comparision of the experimental and numerical results.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1996.10a
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• pp.173-179
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• 1996

A computer simulation has been performed for the application to the elastoplastic stress analysis in a discontinuous composite solid. To obtain the internal field quantities of composite the micromechanics analysis and finite element analysis (FEA) were implemented. As the procedure the reasonably optimized FE mesh generations the appropriate imposition of boundary condition and the relevant postprocessing such as elastoplastic thermomechanical analysis were taken into account. For the numerical illustration an aligned axisymmetric single fiber model has been employed to assess field quantities. It was found that the proposed simulation methodology for stress analysis is applicable to the complicated inhomogeneous solid for the investigation of micromechanical behavior.

• Geomechanics and Engineering
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• v.28 no.1
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• pp.89-105
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• 2022

The behavior of the soil subgrade is complex and irregular against loads. When modeling, the soil is often replaced by a more straightforward system called a subgrade model. The Winkler method of linear elastic springs is a popular method of soil modeling in which the spring constant shows the modulus of subgrade reaction. In this research, the factors affecting the distribution of the modulus of subgrade reaction of elastoplastic subgrades are examined. For this purpose, critical theories about the modulus of subgrade reaction were examined. A square raft foundation on a sandy soil subgrade with was analyzed at different internal friction angles and Young's modulus values using ABAQUS software. To accurately model the actual soil behavior, the elastic, perfectly plastic constitutive model was applied to investigate a foundation on discrete springs. In order to increase the accuracy of soil modeling, equations have been proposed for the distribution of the subgrade reaction modulus. The constitutive model of the springs is elastic, perfectly plastic. It was observed that the modulus of subgrade reaction under an elastic load decreased when moving from the corner to the center of the foundation. For the ultimate load, the modulus of subgrade reaction increased as it moved from the corner to the center of the foundation.

• Advances in Computational Design
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• v.4 no.1
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• pp.53-72
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• 2019

Safety measures for tower cranes are extremely important among the seismic countermeasures at high-rise building construction sites. In particular, the collapse of a tower crane from a high position is a very serious catastrophe. An example of such an accident due to an earthquake is the case of the Taipei 101 Building (the author was the project director), which occurred on March 31, 2002. Failure of the bolted joints of the tower-crane mast was the direct cause of the collapse. Therefore, it is necessary to design for this eventuality and to take the necessary measures on construction sites. This can only be done by understanding the precise dynamic behavior of mast joints during an earthquake. Consequently, we created a new hybrid-element model (using beam, shell, and solid elements) that not only expressed the detailed behavior of the site joints of a tower-crane mast during an earthquake but also suppressed any increase in the total calculation time and revealed its behavior through computer simulations. Using the proposed structural model and simulation method, effective information for designing safe joints during earthquakes can be provided by considering workability (control of the bolt pretension axial force and other factors) and less construction cost. Notably, this analysis showed that the joint behavior of the initial pretension axial force of a bolt is considerably reduced after the axial force of the bolt exceeds the yield strength. A maximum decrease of 50% in the initial pretension axial force under the El Centro N-S Wave ($v_{max}=100cm/s$) was observed. Furthermore, this method can be applied to analyze the seismic responses of general temporary structures in construction sites.

• Transactions of Materials Processing
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• v.26 no.1
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• pp.41-47
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• 2017

Cyclic behavior of advanced high strength steel sheets was measured using an inverse-optimization approach with pre-straining and bending. First, tensile specimens were pre-strained, and three-point bending was conducted for the pre-strained specimens. By using the inverse finite element optimization, the combined isotropic-kinematic hardening parameters that minimize the error between the measured and predicted bending force-displacement curves. The measured cyclic behavior agreed well with the cyclic behavior measured by sheet tension-compression test, which confirms the validity of the measuring procedure based on inverse optimization.

• Steel and Composite Structures
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• v.31 no.1
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• pp.69-83
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• 2019

This paper investigates the structural behavior of very high strength concrete encased steel composite columns via combined experimental and analytical study. The experimental programme examines stub composite columns under pure compression and eccentric compression. The experimental results show that the high strength encased concrete composite column exhibits brittle post peak behavior and low ductility but has acceptable compressive resistance. The high strength concrete encased composite column subjected to early spalling and initial flexural cracking due to its brittle nature that may degrade the stiffness and ultimate resistance. The analytical study compares the current code methods (ACI 318, Eurocode 4, AISC 360 and Chinese JGJ 138) in predicting the compressive resistance of the high strength concrete encased composite columns to verify the accuracy. The plastic design resistance may not be fully achieved. A database including the concrete encased composite column under concentered and eccentric compression is established to verify the predictions using the proposed elastic, elastoplastic and plastic methods. Image-oriented intelligent recognition tool-based fiber element method is programmed to predict the load resistances. It is found that the plastic method can give an accurate prediction of the load resistance for the encased composite column using normal strength concrete (20-60 MPa) while the elastoplastic method provides reasonably conservative predictions for the encased composite column using high strength concrete (60-120 MPa).