33 Comparative Study on Modal Identification of a 10 Story RC Structure Using Free, Ambient and Forced Vibration Data 269 Fig. 33.3 Wall removal and damage states. (a) Structure initial condition and damage states. (b) Wall removal using jack hammer Fig. 33.4 Example of the time history responses for different excitation types recorded at 10th floor. (a) Ambient vibration. (b) Forced vibration (sine sweep). (c) Wall demolition in 2nd story (DS1) resulted from the removal of two walls in the western exterior frame on the third story. The third state of damage (DS2) occurred from the removal of two walls in the northern exterior frame on the third story. The fourth and final damage state (DS3) occurred after the demolition of walls in the north-west corner of the second story. The wall removal was achieved using a jack hammer installed on an excavator as shown in Fig. 33.3b. 33.3.2 Testing Method and Sequence A series of dynamic tests were performed on the building using a mobile shaker bolted to the second floor slab in a location eccentric along the Y axis as shown in Fig. 33.2. The harmonic excitations induced by the shaker were sine sweeps, sine steps, and sine dwells around the identified natural frequencies. More details about the dynamic tests are available in [19]. This study focuses on the sine sweeps and the excitations due to the jack hammer impacts to the exterior RC walls of the structure during the demolition process. Figure 33.4 shows the sample response of the structure recorded at the 10th floor. It can be seen that accelerations induced during the demolition were significantly larger compared to those induced during the forced vibrations using the shaker.
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