Abstract In this study, the dynamic behavior of a model building for different damage cases is studied based on the changes in the natural frequencies and mode shapes. The damage is assumed to occur on the walls and at the column-ends of the first story, because they are generally affected by earthquakes, explosions, etc. A ½-scale three-story reinforced-concrete (RC) building model is constructed in the laboratory. Different damage cases are applied to the model gradually by using mechanical cutting equipment. The wall damage is assumed to reach the interior of the walls and the column-end damage is created by removing the cover of columns. The ambient vibration tests are performed by using the operational modal analysis method under unknown random impact loads. The accelerometers are placed on the columns in the transverse and longitudinal directions to get the responses of the model in these directions. It is observed that the natural frequencies, corresponding mode shapes, and modal damping ratios of the building model vary depending on the damage location and damage extent. The natural frequencies show a decreasing trend with damage, and for the last damage case the natural frequencies are 60 % lower than for the undamaged case. In addition, the mode shapes are affected considerably by wall damage.
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