Interpretation of Records From Temporary and Permanent Instrumentation to Identify the Dynamic Response of a Historical Building to Seismic Actions

Abstract eng:
The CEDRAV building in Cerreto di Spoleto, originally a monastery, was built in the 14th century on the top of a rock ridge. The two events occurred on September 26th, 1997, with magnitude Ms=5.4 and Ms=6, respectively, caused damages to it. Ambient vibration measurements were first performed by using fifteen SS-1 uniaxial velocity sensors (natural frequency 1.0 Hz) connected to five K-2 recorders and deployed in nine different configurations. Then the building was permanently instrumented by using 36 accelerometers. Results from analyses of representative seismic response data acquired from the building specific permanent deployment are also included and classified by means of cumulative normalized energy plots. The building is very complex and rigid. In fact, translational and torsional frequencies are close to one another, coupling occurs and damping ratio is low. Coupling of the frequencies and low damping are two factors that cause beating effect when shaking is strong enough. In the case of this study, the shaking levels are not large but yet the building is affected by beating effect. As stated the CEDRAV is an old buildings and has been altered repeatedly over time. This will cause dynamic interactions with other buildings or substructures during an earthquake.. On the base of recorded data a preliminary analysis in frequency domain, based on the determination of auto and cross power spectral density, has been carried out. Then the modal structure’s identification has been performed by means of Ibrahim technique, working in the time domain, and Frequency Domain Decomposition technique, working in the frequency domain.

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