Finite Element Model Updating and Damage Identification of a School Building in Sankhu, Nepal

Abstract eng:
In this paper, a finite element model of a school building is calibrated in its linear range using the identified modal parameters from recordings of its ambient vibration. The structure, located in Sankhu, Nepal, is a four-story masonryinfilled reinforced concrete frame which experienced severe damage during the Gorkha earthquake on April 25th, 2015. The authors visited the country, in June 2015, to conduct a post-earthquake assessment for certain structures including the case study building. To achieve this purpose, post-earthquake ambient vibration data were collected to be used for performance assessment of the building. The ambient acceleration response of the structure was recorded using 12 uniaxial accelerometers at two setups. The modal properties of the building (i.e., natural frequencies, mode shapes, and damping ratios) are identified using an operational modal analysis method, namely the Natural Excitation Technique combined with the Eigen-system Realization Algorithm. An initial finite element model of the structure is created based on the gathered design information as well as site inspections. To account for the effects of earthquake induced damage on the effective stiffness of the model, severely damaged structural elements are removed from the model. The initial model is then updated through a finite element model updating approach by minimizing an objective function. The objective function is defined as the difference between identified and model estimated modal parameters and a regularization term. To achieve this goal, different structural elements are grouped together and their equivalent stiffness parameters (i.e., effective elasticity moduli) are updated through a global optimization approach. Performance of the updating approach is studied when considering different regularization terms in the objective function. Finally, the obtained changes in the updating parameters are compared to the observed damage in the building.

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