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Peak Factors for Bridges Subjected to Asynchronous Multiple Earthquake Support Excitations
윤종열,박준석 한국방재학회 2011 한국방재학회논문집 Vol.11 No.1
Accurate response analysis of long span bridges subjected to seismic excitation is important for earthquake hazard mitigation. In this paper, the performance of a typical four span continuous reinforced concrete bridge model subjected to asynchronous multiple seismic excitations at the supports is investigated in both the time and frequency domains and the results are compared with that from a relevant uniform support excitations. In the time domain analysis, a linear modal superposition approach is used to compute the peak response values. In the frequency domain analysis, linear random vibration theory is used to determine the root mean square response values where the cross correlation effects between the modal and the support excitations on the seismic response of the bridge model are included. From the two sets of results, a practical range of peak factors which are defined to be the ratio of peak and the root mean square responses are suggested for displacements and forces in members. With reliable practical values of peak factors, the frequency domain analysis is preferred for the performance based design of bridges because of the computational advantage and the generality of the results as the time domain analysis only yields results for the specific excitation input.
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윤종열 한국방재학회 2009 한국방재학회논문집 Vol.9 No.1
A simple outline for teaching adaptive scheme based finite element method for planar problems as a part of computer aided teaching of structural engineering curriculum is presented. Displacement based finite element formulation for planar problems and representative strain value based adaptive scheme for mesh generation are considered. As examples, a cantilever beam with a concentrated load treated as a planar problem and stretching of a plate with a circular hole are analyzed with displacement based finite element method with adaptive meshes. The examples and outlines show how adaptive based finite element method may become an essential part of computer aided teaching of structural engineering.
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An Adaptive Mesh Generation Scheme for the Finite Element Method
윤종열 한국방재학회 2014 한국방재학회논문집 Vol.14 No.4
Ideal structures in hazard mitigation systems must have automated state identification capabilities in order to function acceptably incase of a severe hazard. This capability must be efficient in terms of real time computations. The finite element method has becomethe most widely used method of structural analysis and in an automated finite element structural analysis, an adaptive mesh generationscheme has become an essential component. Without an adaptive scheme, the same mesh is used throughout the analysis andthis causes computational inefficiency due to fine mesh where they are not needed and inaccuracy due to overly distorted elementsformed during the analysis that may proceed undetected as only the initial and the final element shapes are generally checked in practice. This is especially true for dynamic and nonlinear problems in structural analyses. Thus, the finite element mesh for these types ofanalyses must be dynamically adaptive and computationally efficient. In this paper, an efficient adaptive finite element mesh generationscheme for dynamic analyses of planar problems is described. Representative strain values are used for error estimates andrefinements of meshes use combinations of the h-method (node movement) and the r-method (element division) based on a dispersionparameter. A coefficient that depends on the shape of element is used to correct overly distorted elements. A case study shows thevalidity and computational efficiency of the scheme. The study also demonstrates the potential applicability of the scheme's effectiveuse in complex structural problems such as those under severe environmental hazards such as seismic loads, erratic wind loads, andgeneral nonlinear problems.
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Adaptive Finite Element Mesh Generation for Dynamic Planar Problems
윤종열 한국방재학회 2012 한국방재학회논문집 Vol.12 No.6
In structural design and analysis used for hazard mitigation systems, automation is becoming an essential feature. For analysis,the finite element method has proven to be an effective approximate method if proper element types and meshes are chosen. Recently, the method has been successfully applied to solve complex dynamic and nonlinear problems; and with a properly chosen element type and mesh, reliable results have been obtained. However, in automation and in complex analyses of a structures,using the initial mesh throughout the analysis may involve some elements to go through strains beyond the elements' reliable limits. Thus, the finite element mesh for these types of analyses 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 planar problems 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). A coefficient that depends on shape of elements is used to correct overly distorted elements. The validity of the scheme is shown by a deep cantilever beam example under a dynamic concentrated load. The example shows reasonable accuracy and efficient computing time. Furthermore, the study shows the potential for the scheme's effective use in complex structural problems such as those under severe environmental hazards such as seismic or erratic wind loads.
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