Browsing by Author "Hokelekli, E"

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    Collapse mechanism estimation of a historical slender minaret
    Nohutcu, H; Hokelekli, E; Ercan, E; Demir, A; Altintas, G
    The aim of this study is to accurately estimate seismic damage and the collapse mechanism of the historical stone masonry minaret Hafsa Sultan, which was built in 1522. Surveying measurements and material tests were conducted to obtain a 3D solid model and the mechanical properties of the components of the minaret. The initial Finite Element (FE) model is analyzed and numerical dynamic characteristics of the minaret are obtained. The Operational Modal Analysis (OMA) method is conducted to obtain the experimental dynamic characteristics of the minaret and the initial FE model is calibrated by using the experimental results. Then, linear time history (LTH) and nonlinear time history (NLTH) analyses are carried out on the calibrated FE model by using two different ground motions. Iron clamps which used as connection element between the stones of the minaret considerably increase the tensile strength of the masonry system. The Concrete Damage Plasticity (CDP) model is selected in the nonlinear analyses in ABAQUS. The analyses conducted indicate that the results of the linear analyses are not as realistic as the nonlinear analysis results when compared with existing damage.
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    Effect of model calibration on seismic behaviour of a historical mosque
    Demir, A; Nohutcu, H; Ercan, E; Hokelekli, E; Altintas, G
    The objective of the study is to investigate the effects of model calibration on seismic behaviour of a historical mosque which is one of the most significant Ottomon structures. Seismic analyses of calibrated and noncalibrated numeric models were carried out by using acceleration records of Kocaeli earthquake in 1999. In numerical analysis, existing crack zones on real structure was investigated in detail. As a result of analyses, maximum stresses and displacements of calibrated and noncalibrated numerical models were compared each other. Consequently, seismic behaviour and damage state of historical masonry Hafsa Sultan mosque was determined as more realistic in the event of a severe earthquake.
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    FINITE ELEMENT MODEL UPDATING OF A HISTORICAL MINARET VIA OPERATIONAL MODAL ANALYSIS
    Ercan, E; Hokelekli, E; Demir, A; Nohutçu, H
    Finite element method is commonly used for analysis of historical structures. However, since material properties of historical structures are evaluated from destructive tests using empirical formulas, this approach makes the results of finite element analysis questionable. In recent years Operational Modal Analysis of historical masonry structures have found great interest because by the help of Operational Modal Analysis, the material parameters and the boundary conditions can be verified and the finite element model can be updated. The updated model is a more realistic model of the historical structures and gives more accurate results. This study describes the results of a model updating study conducted on a historical minaret. For the purposes of developing a 3-D solid model of the minaret; the dimensions, defects and material degradations in the minaret were determined in detail by making a measurement survey. For evaluation of the material properties of the minaret, nondestructive and destructive testing methods were applied. The modal analysis of the structure was done by FEM. Then, Operational Modal Analysis was carried out and dynamic properties were extracted. The results obtained from ambient vibration measurements of the minaret were used to update the finite element model of the minaret. The natural frequencies and corresponding mode shapes were determined from both theoretical and experimental modal analyses and compared with each other. A good harmony was attained between mode shapes, but differences between natural frequencies were observed. Model updating was realized via changing material parameters and boundary conditions. Finally, the more realistic finite element model of the minaret was put forward and the results were discussed.
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    Investigation of a historic masonry structure by numerical and operational modal analyses
    Nohutcu, H; Demir, A; Ercan, E; Hokelekli, E; Altintas, G
    This paper presents the results of model calibration conducted on a historical mosque called Hafsa Sultan in Manisa, Turkey. The finite element model of the mosque was calibrated by the use of the results obtained from ambient vibration tests of the structure. In order to develop a solid model of the structure, the dimensions of the structure, defects such as cracks and material degradations in the structure, and the materials used in different parts were identified. For the evaluation of the material properties of the structure, nondestructive and destructive testing methods were used. The numerical and experimental modal parameters of the structure were obtained by finite element method (FEM) and Operational Modal Analysis (OMA), respectively. The natural frequencies and corresponding mode shapes were obtained from both FEM and OMA and compared with each other. While a good compatibility was achieved between mode shapes, some differences between natural frequencies occurred. It was thought that the differences resulted from variations in the Young's modulus of masonry, cracks in elements or boundary conditions. Therefore, the finite element model was calibrated by changing material parameters. Finally, a more realistic numerical model of the mosque was put forward and the results were discussed in detail. Copyright (c) 2015 John Wiley & Sons, Ltd.