Output-Only Modal Identification of Ancient L’Aquila City Hall and Civic Tower
Publication: Journal of Structural Engineering
Volume 138, Issue 4
Abstract
The ancient masonry city hall in L’Aquila, Italy (Margherita Palace) that was severely damaged during the L’Aquila earthquake in April 2009 has been subjected to ambient vibration tests to determine its dynamic characteristics such as the natural frequencies, mode shapes, and damping ratios. The processing of ambient vibration responses is performed with three output-only identification approaches: (1) the frequency-domain decomposition, (2) random decrement (RD) technique combined with the eigensystem realization algorithm (ERA), and (3) the natural excitation technique (NExT) combined with ERA. Measurements were made in the palace and in the civic tower using 15 sensors in three different configurations, and the ambient vibration tests involved the simultaneous measurements of longitudinal and lateral vibrations. Lateral vibration modes for the civic tower were identified clearly; a total of five modal shapes and frequencies were identified in the frequency range 0 to 7 Hz. The modal identification in the palace was more difficult because of the severe damage; however, the two bending modes in the perpendicular directions were identified. The comparison of the three experimental techniques shows good agreement, confirming the reliability of the three identification methods. The results of the modal identification have been used to update the finite-element model of the palace.
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Acknowledgments
The research leading to these results has received funding from the European Community’s Seventh Framework Programme—Marie Curie International Reintegration Actions—FP7/2007-2013 under Grant Agreement No. PIRG06-GA-2009-256316 of the project ICRED—Integrated European Disaster Community Resilience. This research was conducted in collaboration with the National Agency for the new technologies, the Energy and the Sustainable Economic Development (ENEA) headquartered in Rome. Special thanks go to the ENEA team that took part in the modal identification campaign, and in particular to the engineer Giacomo Buffarini that have coordinated the operations.
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Published In
Journal of Structural Engineering
Volume 138 • Issue 4 • April 2012
Pages: 481 - 491
Copyright
© 2012. American Society of Civil Engineers.
History
Received: Oct 30, 2010
Accepted: Aug 15, 2011
Published online: Aug 17, 2011
Published in print: Apr 1, 2012
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