The paper illustrates how different dynamic identification techniques can be used to justify the significant vibration phenomena observed in modern bell tower during the swinging motion of the bells. First, the modal model of the tower is extracted from the structure ambient vibration. The results obtained by two output-only identification techniques, working in the frequency (EFDD) and the time domain (SSI), are compared. Then the bell excitation is characterized from the steady-state of the tower forced response to the bell swinging motion. The resonance between the fundamental tower frequency and the third harmonic of the horizontal dynamic force applied to the structure by the swinging bells is clearly recognized as the source of large oscillations. A finite element model is developed and updated to properly reproduce the tower spectral properties. Aiming to mitigate the identified phenomenon, the model allows the design of a stiffening intervention to properly shift the tower resonant frequency. The effectiveness of the designed solution is successfully verified by a post-intervention dynamic test campaign

"Resonance identification in a modern bell tower exhibiting high amplitude oscillations"

LEPIDI, MARCO;
2008

Abstract

The paper illustrates how different dynamic identification techniques can be used to justify the significant vibration phenomena observed in modern bell tower during the swinging motion of the bells. First, the modal model of the tower is extracted from the structure ambient vibration. The results obtained by two output-only identification techniques, working in the frequency (EFDD) and the time domain (SSI), are compared. Then the bell excitation is characterized from the steady-state of the tower forced response to the bell swinging motion. The resonance between the fundamental tower frequency and the third harmonic of the horizontal dynamic force applied to the structure by the swinging bells is clearly recognized as the source of large oscillations. A finite element model is developed and updated to properly reproduce the tower spectral properties. Aiming to mitigate the identified phenomenon, the model allows the design of a stiffening intervention to properly shift the tower resonant frequency. The effectiveness of the designed solution is successfully verified by a post-intervention dynamic test campaign
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11567/504003
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