FINITE ELEMENT MODEL UPDATING OF A HISTORICAL MINARET VIA OPERATIONAL MODAL ANALYSIS

Abstract

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.