Seismic damage detection in existing buildings by finite element model updating

Earthquake events of moderate size may induce damage in structures in urban areas. For buildings designed according to the capacity based philosophy, the damage resulting from an earthquake is distributed throughout the structure, in regions specifically designed to dissipate energy (plastic hinges). After occurrence of the earthquake, an ambient vibration test will reveal altered modal properties of the building, from which damage can be identified by inverse modeling techniques. The aim of this study is to develop vibration based damage assessment of buildings after a moderate earthquake for which the occurred damage is hardly detectable by visual inspection. A typical building from the region north of the Sea of Marmara in Turkey is selected and used subsequently for a numerical simulation. The building is analyzed with a finite element model and the damaged regions are selected as the elements adjacent to the beam-column joints. The stiffness values of these elements are decreased to simulate damage. The damage parameters are updated iteratively by minimizing the differences between the modal properties from the FE-model and those identified on the damaged building model. This paper deals with the sensitivity-based FE model updating method and its application to damage detection. The extent of the decrease in the stiffnesses of the elements will be a good indication for the severity and the location of the damage. The same procedure is repeated in the presence of noise in order to investigate the sensitivity of the updating procedure to the presence of noise.