Browsing by Author "Harmandar, Ebru."

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    Performance of higher order finite elements
    (Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2002., 2002.) Harmandar, Ebru.; Tezcan, Semih S.,
    This study is focused on the evaluation of the performance of the higher order finite elements for the solution of basic and complex problems. Performances of higher order finite elements are compared with those of the regular order elements. Results of this comparison revealed the efficiency and accuracy of higher order finite elements. Following a brief discussion of the finite element method; isoparametric elements, higher order elements, and shape functions are explained. For the purpose of illustration, four different case studies are investigated in a comparative fashion.Firstly, a cantilever deep beam under a concentrated force at the tip is selected as a plane stress problem and is analyzed using five different types of finite elements and in each case the mesh size is gradually decreased. Second problem consists of a circular plate, which is analyzed using two different types of regular and higher order finite elements. The third and the fourth plate bending problems are the fixed boundary square plates, under uniform and central point loads, modeled by the same four different types of finite elements. The analyses of all these four problems are handled by the LUSAS package program. The purpose of utilizing higher order finite elements is to obtain as accurate solutions as possible, with as little number of degrees of freedom as possible. It is demonstrated in all four case studies that the accuracies of higher order finite element were much superior than those of the regular finite elements.
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    Spatial variation of strong ground motion
    (Thesis (Ph.D.)-Bogazici University.Kandilli Observatory and Earthquake Research Institute, 2009., 2009.) Harmandar, Ebru.; Durukal, Eser.; Erdik, Mustafa.
    Earthquake ground accelerograms measured at different locations along a large engineered structure could be significantly different. This has led to considerable research in the last decade on the modeling of the spatially varying earthquake ground motion. The spatial variability of strong ground motion incorporates the effects of wave propagation, amplitude variability and phase variability, as well as the local site effects on the motion. This variation of ground motion could have the possibility to cause important effect on the response of linear lifelines such as long bridges, pipelines, communication systems, and should preferably be accounted for in their design. The objective is to evaluate and improve existing spatial variation quantification relationships by studying data available from different networks; investigate the possibility of employing functional forms for the characterization of spatial variation of ground motion in the assessment of strong ground motion distribution. This thesis focuses on studying on the spatial variability of ground motion using strong ground motion measurements. A rational and rigorous methodology for the interpolation of measured ground motion from discrete array stations to be used in the bias adjustment of the theoretical shake map assessments with the empirical ground motion measurements is developed. The generation of the estimated maps of shaking after an earthquake is often influenced by the limited number of sensors and/or difficulty of monitoring at inaccessible locations that impacts the collection of desired information. This gap in information can be filled through the estimation of missing information conditional upon the measured records. Methodology is presented for estimating properly-correlated earthquake ground motion parameters; herein peak ground acceleration (PGA), at an arbitrary set of closely-spaced points, compatible with known or prescribed ground motion parameters (PGA) at other locations. The variation of ground strain due to wave propagation, site response and loss of coherence is investigated. This study concentrates on the stochastic description of the spatial variation, and focuses on spatial coherency. The estimation of coherency from recorded data and its interpretation are presented. Coherency model for Istanbul for the assessment of simulation of spatially variable ground motion needed for the design of extended structures is derived. In addition to the realistic characterization of spatial variation, simulation of spatially variable earthquake ground motion is another essential part of the examination of the effects of spatial variation, especially for extended lifeline structures. This thesis concludes with the generation of earthquake ground motion compatible with prescribed target-response spectrum and their coherencies are consistent with a given spatial coherency function for a finite array of ground surface stations.