• Computers and Concrete
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• 제2권6호
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• pp.455-479
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• 2005

This paper describes a 2D nonlinear finite element analysis (NLFEA) platform that combines heat flow analysis with realistic analysis of cracked reinforced concrete structures. The behavior models included in the structural analysis are mainly based on the Modified Compression Field Theory and the Distributed Stress Field Model. The heat flow analysis takes into account time-varying thermal loads and temperature-dependent material properties. The capability of 2D nonlinear transient thermal analysis is then implemented into a nonlinear finite element analysis program VecTor2(C) for 2D reinforced concrete membranes. Analyses of four numerical examples are performed using VecTor2, and results obtained indicate that the suggested nonlinear finite element analysis procedure is capable of modeling the complete response of a concrete structure to thermal and mechanical loads.

• 한국전산구조공학회논문집
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• 제23권6호
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• pp.659-665
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• 2010

The finite element method(FEM) is proven to be an effective approximate method of structural analysis if proper element types and meshes are chosen, and recently, the method is often applied to solve complex dynamic and nonlinear problems. A properly chosen element type and mesh yields reliable results for dynamic finite element structural analysis. However, dynamic behavior of a structure may include unpredictably large strains in some parts of the structure, and using the initial mesh throughout the duration of a dynamic analysis may include some elements to go through strains beyond the elements' reliable limits. Thus, the finite element mesh for a dynamic analysis must be dynamically adaptive, and considering the rapid process of analysis in real time, the dynamically adaptive finite element mesh generating schemes must be computationally efficient. In this paper, a computationally efficient dynamically adaptive finite element mesh generation scheme for dynamic analyses of structures is described. The concept of representative strain value is used for error estimates and the refinements of meshes use combinations of the h-method(node movement) and the r-method(element division). The shape coefficient for element mesh is used to correct overly distorted elements. The validity of the scheme is shown through a cantilever beam example under a concentrated load with varying values. The example shows reasonable accuracy and efficient computing time. Furthermore, the study shows the potential for the scheme's effective use in complex structural dynamic problems such as those under seismic or erratic wind loads.

• Computers and Concrete
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• 제3권6호
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• pp.423-437
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• 2006

Stress wave propagation through concrete is simulated by finite element analysis. The concrete medium is modeled as a homogeneous material with smeared properties to investigate and establish the suitable finite element analysis method (explicit versus implicit) and analysis parameters (element size, and solution time increment) also suitable for rigorous investigation. In the next step, finite element analysis model of the medium is developed using a digital image processing technique, which distinguishes the mortar and aggregate phases of concrete. The mortar and aggregate phase topologies are, then, directly mapped to the finite element mesh to form a heterogeneous concrete model. The heterogeneous concrete model is then used to simulate wave propagation. The veracity of the model is demonstrated by evaluating the intrinsic parameters of nondestructive ultrasonic pulse velocity testing of concrete. Quantitative relationships between aggregate size and testing frequency for nondestructive testing are presented.

• 한국해양공학회지
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• 제13권2호통권32호
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• pp.1-10
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• 1999

This study is concerned with the application of new criterion for membrane/shell mixed element in the rigid-plastic finite element analysis and elastic-plastic finite element analysis. The membrane/shell mixed element can be selctively adapted to the pure stretching condition by using membrane or a shell element in the bending effect areas. Thus, membrane/shell mixed element requires a efficient criterion for a distinction between membrane and shell element. In the present study introduce the criterion using the angle of between two element and confirm a generality of criterion from appling the theory to a rigid-plastic and elastic-plastic problems.

• 소성∙가공
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• 제16권8호
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• pp.590-595
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• 2007

This paper introduces a new approach to take account of bending history in finite element inverse analysis during sheet metal forming process. A modified membrane element was adopted for finite element inverse analysis so that bending-unbending energy was additionally imposed in the total plastic energy, predicting bending-unbending regions using the geometry of the final shape and tools. An algorithm was applied to a cylindrical cup deep drawing process. The blank shape and the distribution of the thickness strain were compared with those obtained from the incremental finite element analysis in order to evaluate the effect of the bending history. The algorithm reduced the difference between the results of the inverse analysis from those of the incremental analysis due to bending history. The analysis was also carried out with the variation of the thickness of the initial blank to investigate the effect of bending deformation. The results showed that the difference was remarkably reduced as the thickness of the initial blank increased. This indicates that the finite element inverse analysis cooperated with the suggested scheme is useful to obtain more accurate results, especially when bending effects are significant.

• 한국농공학회논문집
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• 제48권6호
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• pp.45-56
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• 2006

The finite element method is a practical tool to compute the response of the irregularly layered soil deposit to the base-rock motions. The method is useful not only in estimating the interaction between the structure and the surrounding soil as a whole and the local behavior of the contacting area in detail, but also in predicting the resulting behavior of the superstructure affected by such soil-structure interactions. However, the computation of finite element analysis is marched in the time domain (TD), while the site response analysis has been carried out mostly in the frequency domain (FD) with equivalent linear analysis. This study is intended to compare the results of the TD and FD analysis with focus on the peak response accelerations and the predominant frequencies, and thus to evaluate the applicability and the validity of the finite element analysis in the site response analysis. The comparison shows that one can obtain the results very close to that of FD analysis, from the finite element analysis by including sufficiently large width of foundation in the model and further by applying partial mode superposition. The finite element analysis turned out to be well agreeing with FD analysis in their computed results of the peak acceleration and the acceleration response spectra, especially at the surface layer.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 춘계학술대회 논문집
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• pp.481-484
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• 2005

The AutoForm previously used the membrane element and it accomplished sheet metal forming analysis. The membrane analysis has been widely applied to various sheet metal forming processes because of its time effectiveness. However, it's well known that the membrane analysis can not provide correct information for the processes which have considerable bending effects. In this research it tried to compare the analysis results which use the shell element which is applied newly in the AutoForm commercial software with actual experimental results. The shell element is compromise element between continuum element and membrane element. The Finite element method by using shell element is the most efficient numerical method. From this research, it is known that FEA by using shell element can predict accurately the problems happened in actual experimental auto-body panel.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2001년도 춘계학술대회 논문집
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• pp.115-119
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• 2001

This paper presents development of a Finite Element Analysis program. The program was developed on the based of second-dimensional plane strain rigid plasticity finite element analysis and an implicit program is coded. The program was tested by being applied to the axisymetric hydrostatic bulge forming processes using the circle dies. By the Finite Element Analysis at the fluid in chamber and at the blank material, we could know that the hydrostatic bulge forming processes can be influenced of material, the diameter of product and the forming velocity The developed Finite Element Analysis program was approved by the analysis results about forming variables.

• Structural Engineering and Mechanics
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• 제5권1호
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• pp.33-49
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• 1997

A method of analysis is proposed for curved multicell box girder grillages. The method can be used to analyze box girder grillages comprising straight and/or curved segments. Each segment can be modelled by a number of beam elements. Each element has three nodes and the nodal degrees of freedom (DOF) consist of the six DOF for a conventional beam plus DOF to account for torsional warping, distortion, distortional warping, and shear lag. This element is an extension of a straight element that was developed earlier. For a more realistic analysis of the intersection regions of non-colinear box girder segments, the concept of a rigid connector is introduced, and the compatibility requirements between adjoining elements in those regions are discussed. The results of the analysis showed good agreement with the shell finite element results, but the proposed method of analysis needs a fraction of the time and effort compared to the shell finite element analysis.

• Structural Engineering and Mechanics
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• 제51권1호
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• pp.89-110
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• 2014

In this study, two beam-column elements based on the Elasto-Fiber element theory for reinforced concrete (RC) element have been developed and compared with each other. The first element is based on Elasto Fiber Approach (EFA) was initially developed for steel structures and this theory was applied for RC element in there and the second element is called as Fiber & Bernoulli-Euler element approach (FBEA). In this element, Cubic Hermitian polynomials are used for obtaining stiffness matrix. The beams or columns element in both approaches are divided into a sub-element called the segment for obtaining element stiffness matrix. The internal freedoms of this segment are dynamically condensed to the external freedoms at the ends of the element by using a dynamic substructure technique. Thus, nonlinear dynamic analysis of high RC building can be obtained within short times. In addition to, external loads of the segment are assumed to be distributed along to element. Therefore, damages can be taken account of along to element and redistributions of the loading for solutions. Bossak-${\alpha}$ integration with predicted-corrected method is used for the nonlinear seismic analysis of RC frames. For numerical application, seismic damage analyses for a 4-story frame and an 8-story RC frame with soft-story are obtained to comparisons of RC element according to both approaches. Damages evaluation and propagation in the frame elements are studied and response quantities from obtained both approaches are investigated in the detail.